<SEC-DOCUMENT>0001193125-13-429667.txt : 20131106
<SEC-HEADER>0001193125-13-429667.hdr.sgml : 20131106
<ACCEPTANCE-DATETIME>20131106131910
ACCESSION NUMBER:		0001193125-13-429667
CONFORMED SUBMISSION TYPE:	424B3
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20131106
DATE AS OF CHANGE:		20131106

FILER:

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ARROWHEAD RESEARCH CORP
		CENTRAL INDEX KEY:			0000879407
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-COMMERCIAL PHYSICAL & BIOLOGICAL RESEARCH [8731]
		IRS NUMBER:				460408024
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0930

	FILING VALUES:
		FORM TYPE:		424B3
		SEC ACT:		1933 Act
		SEC FILE NUMBER:	333-191922
		FILM NUMBER:		131195653

	BUSINESS ADDRESS:	
		STREET 1:		225 SOUTH LAKE AVENUE
		STREET 2:		SUITE 1050
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91101
		BUSINESS PHONE:		626-304-3400

	MAIL ADDRESS:	
		STREET 1:		225 SOUTH LAKE AVENUE
		STREET 2:		SUITE 1050
		CITY:			PASADENA
		STATE:			CA
		ZIP:			91101

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	INTERACTIVE GROUP INC
		DATE OF NAME CHANGE:	20020509

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	INTERACTIVE INC
		DATE OF NAME CHANGE:	19940224
</SEC-HEADER>
<DOCUMENT>
<TYPE>424B3
<SEQUENCE>1
<FILENAME>d617597d424b3.htm
<DESCRIPTION>PROSPECTUS
<TEXT>
<HTML><HEAD>
<TITLE>Prospectus</TITLE>
</HEAD>
 <BODY BGCOLOR="WHITE">
<h5 align="left"><a href="#toc">Table of Contents</a></h5>

 <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>Filed Pursuant to Rule 424(b)(3)<BR> Registration No. 333-191922 </B></FONT></P>
<P STYLE="font-size:12px;margin-top:0px;margin-bottom:0px">&nbsp;</P> <P STYLE="line-height:1px;margin-top:0px;margin-bottom:2px;border-bottom:1pt solid #000000">&nbsp;</P> <P STYLE="margin-top:12px;margin-bottom:0px"><FONT
STYLE="font-family:Times New Roman" SIZE="2"><B>Prospectus </B></FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="3"><B>Arrowhead Research Corporation </B></FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>10,921,501 shares of Common Stock </B></FONT></P> <P STYLE="font-size:12px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<P STYLE="line-height:1px;margin-top:0px;margin-bottom:2px;border-bottom:1pt solid #000000">&nbsp;</P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">This prospectus covers the sale of
an aggregate of 10,921,501 shares of our Common Stock, $0.001 par value per share (the &#147;Shares&#148;), by the selling security holders identified in this prospectus (collectively with any holder&#146;s transferee, pledgee, donee or successor,
the &#147;Selling Stockholders&#148;). Of the Shares covered by this prospectus, i) 3,071,672 were issued in a private offering of our Common Stock and ii) 7,849,829 are issuable upon conversion of the Company&#146;s currently outstanding Series C
Preferred Stock issued in a private offering. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">The Company will not receive any proceeds from the sale by the Selling
Stockholders of the Shares. We are paying the cost of registering the Shares covered by this prospectus as well as various related expenses. The selling stockholders are responsible for all selling commissions, transfer taxes and other costs related
to the offer and sale of their shares. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">Sales of the Shares by the Selling Stockholders may occur at fixed prices, at market
prices prevailing at the time of sale, at prices related to prevailing market prices, or at negotiated prices. The selling stockholders may sell shares to or through underwriters, broker-dealers or agents, who may receive compensation in the form of
discounts, concessions or commissions from the selling stockholders, the purchasers of the shares, or both. If required, the number of shares to be sold, the public offering price of those shares, the names of any underwriters, broker-dealers or
agents and any applicable commission or discount will be included in a supplement to this prospectus, called a prospectus supplement. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">The Company&#146;s Common Stock is traded on The NASDAQ Capital Market under the symbol &#147;ARWR.&#148; On November&nbsp;4, 2013, the closing sale price of our Common Stock on The NASDAQ Capital Market
was $7.36 per share. Our principal executive offices are located at 225&nbsp;South Lake Avenue, Suite&nbsp;1050, Pasadena, California 91101, and our telephone number is (626)&nbsp;304-3400. </FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><I>Investing in our securities involves a high degree of risk. You should carefully consider the <A HREF="#toc617597_4">Risk
Factors</A> beginning on page 2 before you invest in our securities. </I></B> </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>Neither the Securities and Exchange
Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense. </B></FONT></P>
<P STYLE="margin-top:18px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>The date of this prospectus is November 5, 2013 </B></FONT></P>

<p Style='page-break-before:always'>
<HR  SIZE="3" style="COLOR:#999999" WIDTH="100%" ALIGN="CENTER">
<h5 align="left"><a href="#toc">Table of Contents</a></h5>

 <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc"></A>Table of Contents </B></FONT></P>
<P STYLE="font-size:12px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE CELLSPACING="0" CELLPADDING="0" WIDTH="100%" BORDER="0" STYLE="BORDER-COLLAPSE:COLLAPSE" ALIGN="center">


<TR>
<TD WIDTH="97%"></TD>
<TD VALIGN="bottom" WIDTH="3%"></TD>
<TD></TD>
<TD></TD>
<TD></TD></TR>


<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><A HREF="#toc617597_1">ABOUT THIS PROSPECTUS</A></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">1</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><A HREF="#toc617597_2">SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS</A></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">1</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><A HREF="#toc617597_3">ABOUT THE COMPANY</A></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">2</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><A HREF="#toc617597_4">RISK FACTORS</A></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">2</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><A HREF="#toc617597_5">USE OF PROCEEDS</A></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">2</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><A HREF="#toc617597_6">SELLING SECURITYHOLDERS</A></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">3</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><A HREF="#toc617597_7">PLAN OF DISTRIBUTION</A></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">5</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><A HREF="#toc617597_8">EXPERTS</A></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">7</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><A HREF="#toc617597_9">LEGAL MATTERS</A></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">7</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><A HREF="#toc617597_10">WHERE YOU CAN FIND MORE INFORMATION</A></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">7</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><A HREF="#toc617597_11">INCORPORATION OF CERTAIN INFORMATION BY REFERENCE</A></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">7</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD></TR>
</TABLE>
 <p STYLE="margin-top:0px;margin-bottom:0px"><FONT SIZE="1">&nbsp;</FONT></P> <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2">i </FONT></P>


<p Style='page-break-before:always'>
<HR  SIZE="3" style="COLOR:#999999" WIDTH="100%" ALIGN="CENTER">
<h5 align="left"><a href="#toc">Table of Contents</a></h5>

 <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc617597_1"></A>ABOUT THIS PROSPECTUS </B></FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">You should read this prospectus, any applicable prospectus supplement and the information incorporated by reference in this prospectus
before making an investment in the securities of Arrowhead Research Corporation. See &#147;Where You Can Find Additional Information&#148; for more information, page 7. You should rely only on the information contained in or incorporated by
reference in this prospectus or a prospectus supplement. The Company has not authorized anyone to provide you with different information. This document may be used only in jurisdictions where offers and sales of these securities are permitted. You
should assume that information contained in this prospectus, or in any document incorporated by reference, is accurate only as of any date on the front cover of the applicable document. Our business, financial condition, results of operations and
prospects may have changed since that date. </FONT></P> <P STYLE="margin-top:24px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc617597_2"></A>SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS
</B></FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">This prospectus contains forward-looking statements within the meaning of the federal securities laws. You can identify
forward-looking statements by the use of the words &#147;believe,&#148; &#147;expect,&#148; &#147;anticipate,&#148; &#147;intend,&#148; &#147;estimate,&#148; &#147;project,&#148; &#147;will,&#148; &#147;should,&#148; &#147;may,&#148;
&#147;plan,&#148; &#147;intend,&#148; &#147;assume&#148; and other expressions which predict or indicate future events and trends and which do not relate to historical matters. You should not rely on forward-looking statements, because they involve
known and unknown risks, uncertainties and other factors, some of which are beyond the control of the Company. These risks, uncertainties and other factors may cause the actual results, performance or achievements of the Company to be materially
different from the anticipated future results, performance or achievements expressed or implied by the forward-looking statements. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">Factors that might cause these differences include the following: </FONT></P> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the integration of multiple technologies and programs; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the ability to successfully complete development and commercialization of products and the Company&#146;s expectations regarding market growth;
</FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the cost, timing, scope and results of ongoing safety and efficacy trials of preclinical and clinical testing; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the ability to successfully complete product research and further development; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the volume and profitability of product sales of future products; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">changes in existing and potential relationships with corporate collaborators and partners; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the availability, cost, delivery and quality of materials supplied by contract manufacturers; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the timing, cost and uncertainty of obtaining regulatory approvals of our products; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the ability to obtain substantial additional funding; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the ability to develop and commercialize products before competitors that are superior to the alternatives developed by competitors;
</FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the ability to retain certain members of management; </FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>

<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the Company&#146;s expectations regarding research and development expenses and general and administrative expenses; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">the Company&#146;s expectations regarding cash balances, capital requirements, anticipated revenue and expenses, including infrastructure expenses;
</FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">our belief regarding the validity of our patents and potential litigation; and </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">other factors detailed from time to time in filings with the Securities and Exchange Commission. </FONT></P></TD></TR></TABLE>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">In addition, the factors described under the section captioned &#147;Risk Factors&#148; in this prospectus, as may be updated from time
to time by our future filings under the Securities Exchange Act, and elsewhere in the documents </FONT></P>
 <p STYLE="margin-top:0px;margin-bottom:0px"><FONT SIZE="1">&nbsp;</FONT></P> <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2">1 </FONT></P>


<p Style='page-break-before:always'>
<HR  SIZE="3" style="COLOR:#999999" WIDTH="100%" ALIGN="CENTER">
<h5 align="left"><a href="#toc">Table of Contents</a></h5>

 <P STYLE="margin-top:0px;margin-bottom:0px"><FONT STYLE="font-family:Times New Roman" SIZE="2">
incorporated by reference in this prospectus, may result in these differences. You should carefully review all of these factors. These forward-looking statements were based on information, plans
and estimates at the date of this prospectus, and we assume no obligation to update any forward-looking statements to reflect changes in underlying assumptions or factors, new information, future events or other changes. </FONT></P>
<P STYLE="margin-top:24px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc617597_3"></A>ABOUT THE COMPANY </B></FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2"><I>Unless otherwise noted, (1)&nbsp;the term &#147;Arrowhead&#148; refers to Arrowhead Research Corporation, a Delaware corporation, (2)&nbsp;the terms the &#147;Company,&#148; &#147;we,&#148;
&#147;us,&#148; and &#147;our,&#148; refer to the ongoing business operations of Arrowhead and its subsidiaries, whether conducted through Arrowhead or a subsidiary of the company, (3)&nbsp;the term &#147;Common Stock&#148; refers to
Arrowhead&#146;s Common Stock and (4)&nbsp;the term &#147;stockholder(s)&#148; refers to the holders of Common Stock or securities exercisable for Common Stock. </I></FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">Arrowhead Research Corporation is a biopharmaceutical company developing targeted RNAi therapeutics. The Company is leveraging its proprietary drug delivery technologies to develop targeted drugs based on
the RNA interference (RNAi) mechanism that efficiently and specifically silence target genes. Arrowhead technologies also enable partners to create peptide-drug conjugates (PDCs) that specifically home to cell types of interest while sparing
off-target tissues. Arrowhead&#146;s pipeline includes programs in chronic hepatitis B virus, obesity, and cancer. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">Arrowhead
is leveraging its in-house R&amp;D expertise and capabilities, as well as a broad intellectual property portfolio for RNAi therapeutics, and RNAi and peptide delivery vehicles and targeting methods to seek development partnerships with other
pharmaceutical and biotech companies committed to bringing RNAi therapeutics to market, as well as continuing the preclinical and clinical development of its own clinical candidates. </FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">Our stock is listed on the Nasdaq Capital Market under the symbol &#147;ARWR&#148;. </FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">Our executive offices are located at 225 South Lake Avenue, Suite 1050, Pasadena CA 91101 and our telephone number is
(626)&nbsp;304-3400. Additional information regarding our company, including our audited financial statements and descriptions of our business, is contained in the documents incorporated by reference in this prospectus. See &#147;Where You Can Find
More Information&#148; on page&nbsp;7 and &#147;Incorporation of Certain Information by Reference&#148; on page&nbsp;
7. </FONT></P> <P STYLE="margin-top:24px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc617597_4"></A>RISK FACTORS </B></FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">We are a development-stage company and we have not yet generated significant revenues. Before making an investment decision, you should carefully consider the risks described in the sections entitled
&#147;Risk Factors&#148; in our most recent Annual Report on Form 10-K and subsequent Quarterly Reports on form 10-Q, as filed with the SEC, which are incorporated herein by reference in their entirety, as well any amendment or updates to our risk
factors reflected in subsequent filings with the SEC, including the applicable prospectus supplement. Our business, financial condition or results of operations could be materially adversely affected by any of these risks. The trading price of our
securities could decline due to any of these risks, and you may lose all or part of your investment. This prospectus and the incorporated documents also contain forward-looking statements that involve risks and uncertainties. Our actual results
could differ materially from those anticipated in these forward-looking statements as a result of certain factors, including the risks mentioned elsewhere in this prospectus. </FONT></P> <P STYLE="margin-top:24px;margin-bottom:0px" ALIGN="center"><FONT
STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc617597_5"></A>USE OF PROCEEDS </B></FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">The proceeds from the resale of
the Shares under this prospectus are solely for the account of the Selling Stockholders. We will not receive any proceeds from the sale of Shares under this prospectus. </FONT></P>
 <p STYLE="margin-top:0px;margin-bottom:0px"><FONT SIZE="1">&nbsp;</FONT></P> <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2">2 </FONT></P>


<p Style='page-break-before:always'>
<HR  SIZE="3" style="COLOR:#999999" WIDTH="100%" ALIGN="CENTER">
<h5 align="left"><a href="#toc">Table of Contents</a></h5>

 <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc617597_6"></A>SELLING SECURITYHOLDERS </B></FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">The Company has included in this prospectus 10,921,501 shares of Common Stock, which includes the following: </FONT></P>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">3,071,672 shares of Common Stock issued in a private offering; and </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">7,849,829 shares of Common Stock issuable upon conversion of Company Series C Preferred Stock issued in a private offering.
</FONT></P></TD></TR></TABLE> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">In connection with the private offering, we agreed to file a registration statement with the Securities and
Exchange Commission covering the resale of the shares of Common Stock included herein. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">The following table sets forth certain
information regarding the Selling Stockholders and the shares of Common Stock beneficially owned by them, which is based on information that is available to us as of October&nbsp;24, 2013, including information provided by the Selling Stockholders
regarding the number of shares held before the offering. Selling Stockholders may offer shares under this prospectus from time to time and may elect to sell none, some or all of the shares set forth next to their name. As a result, we cannot
estimate the number of shares of Common Stock that a Selling Stockholder will beneficially own after termination of sales under this prospectus. In addition, a Selling Stockholder may have sold, transferred or otherwise disposed of all or a portion
of that holder&#146;s shares of Common Stock since the date on which they provided information for this table. We have not made independent inquiries about this. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">All percentages of beneficial ownership are based on 38,537,199 shares of Common Stock issued and outstanding as of October&nbsp;24, 2013 and assumes the conversion of all the outstanding shares of the
Company&#146;s Series C Preferred Stock. Beneficial ownership is determined in accordance with the rules and regulations of the SEC and includes voting or investment power with respect to our Common Stock. Shares of our Common Stock subject to
options, warrants or convertible preferred stock that are currently exercisable or exercisable within 60&nbsp;days of October&nbsp;24, 2013 are considered outstanding and beneficially owned by the person holding the options, warrants or convertible
preferred stock for the purpose of calculating the percentage ownership of that person but not for the purpose of calculating the percentage ownership of any other person. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">We are relying on written commitments from the Selling Stockholders to notify us of any changes in their beneficial ownership after the date they originally provided this information. See &#147;Plan of
Distribution&#148; beginning on page 5. </FONT></P> <P STYLE="font-size:12px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE CELLSPACING="0" CELLPADDING="0" WIDTH="100%" BORDER="0" STYLE="BORDER-COLLAPSE:COLLAPSE" ALIGN="center">


<TR>
<TD WIDTH="62%"></TD>
<TD VALIGN="bottom" WIDTH="4%"></TD>
<TD></TD>
<TD></TD>
<TD></TD>
<TD VALIGN="bottom" WIDTH="4%"></TD>
<TD></TD>
<TD></TD>
<TD></TD>
<TD VALIGN="bottom" WIDTH="4%"></TD>
<TD></TD>
<TD></TD>
<TD></TD>
<TD VALIGN="bottom" WIDTH="4%"></TD>
<TD></TD>
<TD></TD>
<TD></TD></TR>
<TR>
<TD VALIGN="bottom" NOWRAP> <P STYLE="border-bottom:1px solid #000000;width:79pt"><FONT STYLE="font-family:Times New Roman" SIZE="1"><B>Selling Security Holder</B></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom" COLSPAN="2" ALIGN="center" STYLE="border-bottom:1px solid #000000"><FONT STYLE="font-family:Times New Roman" SIZE="1"><B>No. of<BR>Shares Held<BR>Before<BR>Offering</B></FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom" COLSPAN="2" ALIGN="center" STYLE="border-bottom:1px solid #000000"><FONT STYLE="font-family:Times New Roman" SIZE="1"><B>No.
of<BR>Shares</B></FONT><br><FONT STYLE="font-family:Times New Roman" SIZE="1"><B>Being<BR>Offered</B></FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom" COLSPAN="2" ALIGN="center" STYLE="border-bottom:1px solid #000000"><FONT STYLE="font-family:Times New Roman" SIZE="1"><B>No
of<BR>Shares<BR>Held</B></FONT><br><FONT STYLE="font-family:Times New Roman" SIZE="1"><B>After<BR>Offering&nbsp;(1)</B></FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom" COLSPAN="2" ALIGN="center" STYLE="border-bottom:1px solid #000000"><FONT STYLE="font-family:Times New Roman" SIZE="1"><B>Percentage<BR>of
Shares<BR>Held</B></FONT><br><FONT STYLE="font-family:Times New Roman" SIZE="1"><B>After<BR>Offering&nbsp;(2)</B></FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD></TR>


<TR BGCOLOR="#cceeff">
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2">14159, L.P.(3)</FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">127,680</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">59,385</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">(4)&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">68,295</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">*</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2">667, L.P.(3)</FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">643,084</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">304,778</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">(5)&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">338,306</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">*</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD></TR>
<TR BGCOLOR="#cceeff">
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2">Baker Brothers Life Sciences L.P.(3)</FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">5,099,611</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">2,366,212</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">(6)&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">2,733,399</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">5.89</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">%&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2">Blackwell Partners LLC(7)</FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">1,712,415</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">1,023,891</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">(8)&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">688,524</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">1.47</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">%&nbsp;</FONT></TD></TR>
<TR BGCOLOR="#cceeff">
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2">New Leaf Ventures II, L.P.(9)</FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">511,945</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">511,945</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#151;&nbsp;&nbsp;</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#151;&nbsp;&nbsp;</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2">QVT Fund V LP(10)</FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">1,587,031</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">1,587,031</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#151;&nbsp;&nbsp;</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#151;&nbsp;&nbsp;</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD></TR>
<TR BGCOLOR="#cceeff">
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2">QVT Fund IV LP(10)</FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">247,782</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">247,782</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#151;&nbsp;&nbsp;</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#151;&nbsp;&nbsp;</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2">Quintessence Fund L.P.(10)</FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">212,969</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">212,969</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#151;&nbsp;&nbsp;</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#151;&nbsp;&nbsp;</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD></TR>
<TR BGCOLOR="#cceeff">
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2">Ridgeback Capital Mgmt LP(11)</FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">1,817,717</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">511,945</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">1,305,772</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">2.81</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">%&nbsp;</FONT></TD></TR>
<TR>
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2">RA Capital Healthcare Fund, LP(12)</FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">6,849,661</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">4,095,563</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">(13)&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">2,754,098</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">&nbsp;</FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2">5.77</FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2">%&nbsp;</FONT></TD></TR>
<TR STYLE="font-size:1px">
<TD VALIGN="bottom"></TD>
<TD VALIGN="bottom">&nbsp;&nbsp;</TD>
<TD VALIGN="bottom"> <P STYLE="border-top:1px solid #000000">&nbsp;</P></TD>
<TD VALIGN="bottom"> <P STYLE="border-top:1px solid #000000">&nbsp;</P></TD>
<TD>&nbsp;</TD>
<TD VALIGN="bottom">&nbsp;&nbsp;</TD>
<TD VALIGN="bottom"> <P STYLE="border-top:1px solid #000000">&nbsp;</P></TD>
<TD VALIGN="bottom"> <P STYLE="border-top:1px solid #000000">&nbsp;</P></TD>
<TD>&nbsp;</TD>
<TD VALIGN="bottom">&nbsp;</TD>
<TD VALIGN="bottom"> <P STYLE="border-top:1px solid #000000">&nbsp;</P></TD>
<TD VALIGN="bottom"> <P STYLE="border-top:1px solid #000000">&nbsp;</P></TD>
<TD>&nbsp;</TD>
<TD VALIGN="bottom">&nbsp;&nbsp;</TD>
<TD VALIGN="bottom"></TD>
<TD VALIGN="bottom"></TD>
<TD VALIGN="bottom"></TD></TR>
<TR BGCOLOR="#cceeff">
<TD VALIGN="top"> <P STYLE="margin-left:1.00em; text-indent:-1.00em"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>Total</B></FONT></P></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>&nbsp;</B></FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>18,809,895</B></FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>&nbsp;&nbsp;</B></FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>&nbsp;</B></FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>10,921,501</B></FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>&nbsp;&nbsp;</B></FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>&nbsp;</B></FONT></TD>
<TD VALIGN="bottom" ALIGN="right"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>7,888,394</B></FONT></TD>
<TD NOWRAP VALIGN="bottom"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B>&nbsp;&nbsp;</B></FONT></TD>
<TD VALIGN="bottom"><FONT SIZE="1">&nbsp;&nbsp;</FONT></TD>
<TD VALIGN="bottom"></TD>
<TD VALIGN="bottom"></TD>
<TD VALIGN="bottom"></TD></TR>
</TABLE> <P STYLE="font-size:12px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">*</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Less than 1%. </FONT></TD></TR></TABLE>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(1)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Assumes all shares offered by the Selling Stockholders hereby are sold and that the Selling Stockholders buy or sell no additional shares of Common Stock prior to the
completion of this offering. </FONT></TD></TR></TABLE>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(2)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Percentage of shares held after the offering is based on 38,537,199 shares outstanding as of October&nbsp;24, 2013 plus the number of shares issued upon conversion of
all shares of Series C Preferred Stock and sold in the offering. </FONT></TD></TR></TABLE>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(3)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Julian C. Baker and Felix J. Baker hold investment and voting control with respect to the shares owned by 14159, L.P., 667 L.P., and Baker Brothers Life Sciences, L.P.
As Managing Members of Baker Bros Advisors (GP), LLC, the Sole General Partner of Baker Bros. Advisors L.P., Julian C. Baker and Felix J. Baker disclaim beneficial ownership of all shares except to the extent of their pecuniary interest.
</FONT></TD></TR></TABLE>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(4)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Includes 59,385 shares issuable upon the conversion of the Company&#146;s Series C Preferred Stock. </FONT></TD></TR></TABLE>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(5)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Includes 304,778 shares issuable upon the conversion of the Company&#146;s Series C Preferred Stock. </FONT></TD></TR></TABLE>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(6)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Includes 2,366,212 shares issuable upon the conversion of the Company&#146;s Series C Preferred Stock. </FONT></TD></TR></TABLE>
 <p STYLE="margin-top:0px;margin-bottom:0px"><FONT SIZE="1">&nbsp;</FONT></P> <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2">3 </FONT></P>


<p Style='page-break-before:always'>
<HR  SIZE="3" style="COLOR:#999999" WIDTH="100%" ALIGN="CENTER">
<h5 align="left"><a href="#toc">Table of Contents</a></h5>


<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(7)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Peter Kolchinsky, sole manager of RA Capital, holds investment and voting control with respect to the shares owned by Blackwell Partners, L.C. </FONT></TD></TR></TABLE>

<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(8)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Includes 1,023,891 shares issuable upon the conversion of the Company&#146;s Series C Preferred Stock. </FONT></TD></TR></TABLE>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(9)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Philippe O. Cambon, Jeani Delagardelle, Ronald Hunt, Vijay Lathi, James Niedel and Liam T. Ratcliffee, the members of the Investment Committee of New Leaf Venture
Management II, L.P., general partner of the general partner of New Leaf Ventures II, L.P, hold investment and voting control with respect to the shares owned by New Leaf Ventures II, L.P. </FONT></TD></TR></TABLE>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(10)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Management of Quintessence Fund L.P., QVT Fund IV LP and QVT Fund V LP is vested in their general partner, QVT Associates GP LLC, which may be deemed to beneficially
own the securities held by Quintessence Fund L.P., QVT Fund IV LP and QVT Fund V LP.&nbsp;QVT Financial LP is the investment manager of Quintessence Fund L.P., QVT Fund IV LP and QVT Fund V LP and shares voting and investment control over the
securities held by Quintessence Fund L.P., QVT Fund IV LP and QVT Fund V LP. QVT Financial GP LLC is the general partner of QVT Financial LP and as such has complete discretion in the management and control of the business affairs of QVT Financial
LP.&nbsp;The managing members of QVT Financial GP LLC are Daniel Gold, Nicholas Brumm, Arthur Chu and Tracy Fu.&nbsp;Each of QVT Financial LP, QVT Financial GP LLC, Daniel Gold, Nicholas Brumm, Arthur Chu and Tracy Fu disclaims beneficial ownership
of the securities held by Quintessence Fund L.P., QVT Fund IV LP and QVT Fund V LP. </FONT></TD></TR></TABLE>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(11)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Wayne Holman holds investment and voting control with respect to the shares owned by Ridgeback Capital Partners, L.P. </FONT></TD></TR></TABLE>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(12)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Peter Kolchinsky, sole manager of RA Capital, holds investment and voting control with respect to the shares owned by RA Capital Healthcare Fund, L.P.
</FONT></TD></TR></TABLE>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="4%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">(13)</FONT></TD>
<TD ALIGN="left" VALIGN="top"><FONT STYLE="font-family:Times New Roman" SIZE="2">Includes 4,095,563 shares issuable upon conversion of the Company&#146;s Series C Preferred Stock. </FONT></TD></TR></TABLE>
 <p STYLE="margin-top:0px;margin-bottom:0px"><FONT SIZE="1">&nbsp;</FONT></P> <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2">4 </FONT></P>


<p Style='page-break-before:always'>
<HR  SIZE="3" style="COLOR:#999999" WIDTH="100%" ALIGN="CENTER">
<h5 align="left"><a href="#toc">Table of Contents</a></h5>

 <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc617597_7"></A>PLAN OF DISTRIBUTION </B></FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">The selling stockholders, which as used herein includes donees, pledgees, transferees or other successors-in-interest selling shares of
Common Stock or interests in shares of Common Stock received after the date of this prospectus from a selling stockholder as a gift, pledge, partnership distribution or other transfer, may, from time to time, sell, transfer or otherwise dispose of
any or all of their shares of Common Stock or interests in shares of Common Stock on any stock exchange, market or trading facility on which the shares are traded or in private transactions. These dispositions may be at fixed prices, at prevailing
market prices at the time of sale, at prices related to the prevailing market price, at varying prices determined at the time of sale, or at negotiated prices. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">The selling stockholders may use any one or more of the following methods when disposing of shares or interests therein: </FONT></P> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">ordinary brokerage transactions and transactions in which the broker-dealer solicits purchasers; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">block trades in which the broker-dealer will attempt to sell the shares as agent, but may position and resell a portion of the block as principal to
facilitate the transaction; </FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">purchases by a broker-dealer as principal and resale by the broker-dealer for its account; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">an exchange distribution in accordance with the rules of the applicable exchange; </FONT></P></TD></TR></TABLE>
<P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">privately negotiated transactions; </FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">short sales effected after the date the registration statement of which this Prospectus is a part is declared effective by the SEC;
</FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
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<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">through the writing or settlement of options or other hedging transactions, whether through an options exchange or otherwise;
</FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
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<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">broker-dealers may agree with the selling stockholders to sell a specified number of such shares at a stipulated price per share;
</FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
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<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">a combination of any such methods of sale; and </FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
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<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">any other method permitted by applicable law. </FONT></P></TD></TR></TABLE> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">The selling stockholders may, from time to time, pledge or grant a security interest in some or all of the shares of Common Stock owned by them and, if they default in the performance of their secured
obligations, the pledgees or secured parties may offer and sell the shares of Common Stock, from time to time, under this prospectus, or under an amendment to this prospectus under Rule 424(b)(3) or other applicable provision of the Securities Act
amending the list of selling stockholders to include the pledgee, transferee or other successors in interest as selling stockholders under this prospectus. The selling stockholders also may transfer the shares of Common Stock in other circumstances,
in which case the transferees, pledgees or other successors in interest will be the selling beneficial owners for purposes of this prospectus. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">In connection with the sale of our Common Stock or interests therein, the selling stockholders may enter into hedging transactions with broker-dealers or other financial institutions, which may in turn
engage in short sales of the Common Stock in the course of hedging the positions they assume. The selling stockholders may also sell shares of our Common Stock short and deliver these securities to close out their short positions, or loan or pledge
the Common Stock to broker-dealers that in turn may sell these securities. The selling stockholders may also enter into option or other transactions with broker-dealers or other financial institutions or the creation of one or more derivative
securities which require the delivery to such broker-dealer or other financial institution of shares offered by this prospectus, which shares such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented
or amended to reflect such transaction). </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">The aggregate proceeds to the selling stockholders from the sale of the Common Stock
offered by them will be the purchase price of the Common Stock less discounts or commissions, if any. Each of the selling stockholders reserves the right to accept and, together with their agents from time to time, to reject, in whole or in part,
any proposed purchase of Common Stock to be made directly or through agents. We will not receive any of the proceeds from this offering. </FONT></P>
 <p STYLE="margin-top:0px;margin-bottom:0px"><FONT SIZE="1">&nbsp;</FONT></P> <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2">5 </FONT></P>


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 <P STYLE="margin-top:0px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">The selling stockholders also may resell all or a portion of the shares in open market
transactions in reliance upon Rule 144 under the Securities Act of 1933, provided that they meet the criteria and conform to the requirements of that rule. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">The selling stockholders and any underwriters, broker-dealers or agents that participate in the sale of the Common Stock or interests therein may be &#147;underwriters&#148; within the meaning of
Section&nbsp;2(11) of the Securities Act. Any discounts, commissions, concessions or profit they earn on any resale of the shares may be underwriting discounts and commissions under the Securities Act. Selling stockholders who are
&#147;underwriters&#148; within the meaning of Section&nbsp;2(11) of the Securities Act will be subject to the prospectus delivery requirements of the Securities Act. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">To the extent required, the shares of our Common Stock to be sold, the names of the selling stockholders, the respective purchase prices and public offering prices, the names of any agents, dealer or
underwriter, any applicable commissions or discounts with respect to a particular offer will be set forth in an accompanying prospectus supplement or, if appropriate, a post-effective amendment to the registration statement that includes this
prospectus. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">In order to comply with the securities laws of some states, if applicable, the Common Stock may be sold in these
jurisdictions only through registered or licensed brokers or dealers. In addition, in some states the Common Stock may not be sold unless it has been registered or qualified for sale or an exemption from registration or qualification requirements is
available and is complied with. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">We have advised the selling stockholders that the anti-manipulation rules of Regulation M
under the Exchange Act may apply to sales of shares in the market and to the activities of the selling stockholders and their affiliates. In addition, to the extent applicable we will make copies of this prospectus (as it may be supplemented or
amended from time to time) available to the selling stockholders for the purpose of satisfying the prospectus delivery requirements of the Securities Act. The selling stockholders may indemnify any broker-dealer that participates in transactions
involving the sale of the shares against certain liabilities, including liabilities arising under the Securities Act. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">We have
agreed to indemnify the selling stockholders against liabilities, including liabilities under the Securities Act and state securities laws, relating to the registration of the shares offered by this prospectus. </FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">We have agreed with the selling stockholders to keep the registration statement of which this prospectus constitutes a part effective
until the earlier of (1)&nbsp;such time as all of the shares covered by this prospectus have been disposed of pursuant to and in accordance with the registration statement or (2)&nbsp;the date on which all of the shares may be sold without
restriction pursuant to Rule 144 of the Securities Act. </FONT></P>
 <p STYLE="margin-top:0px;margin-bottom:0px"><FONT SIZE="1">&nbsp;</FONT></P> <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2">6 </FONT></P>


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 <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc617597_8"></A>EXPERTS </B></FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">The financial statements of the Company incorporated in this prospectus by reference from the Company&#146;s Annual Report on Form 10-K
for the year ended September&nbsp;30, 2012, have been audited by Rose, Snyder&nbsp;&amp; Jacobs LLP, as stated in their report incorporated by reference, and given upon the authority of said firm as experts in auditing and accounting. </FONT></P>
<P STYLE="margin-top:24px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc617597_9"></A>LEGAL MATTERS </B></FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT
STYLE="font-family:Times New Roman" SIZE="2">Certain legal matters, including the validity of the securities offered pursuant to this registration statement, will be passed upon for us by Ropes&nbsp;&amp; Gray LLP, San Francisco, California.
</FONT></P> <P STYLE="margin-top:24px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc617597_10"></A>WHERE YOU CAN FIND MORE INFORMATION </B></FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">We must comply with the informational requirements of the Securities Exchange Act of 1934, as amended, and we are required to file
reports and proxy statements and other information with the Securities and Exchange Commission. You may read and copy these reports, proxy statements and other information at the Public Reference Room maintained by the Securities and Exchange
Commission at 100 F Street, N.E., Washington, D.C. 20549. You may also obtain copies at the prescribed rates from the Public Reference Section of the Securities and Exchange Commission at its principal office in Washington, D.C. You may call the
Securities and Exchange Commission at 1-800-SEC-0330 for further information about the public reference room. The Securities and Exchange Commission also maintains a website that contains reports, proxy and information statements and other
information regarding issuers like us that file electronically with the Securities and Exchange Commission. You may access the Securities and Exchange Commission&#146;s web site at http://www.sec.gov. We maintain a website at
www.arrowheadresearch.com. The information contained in, or that can be accessed through, our website is not incorporated by reference herein and is not part of this prospectus. </FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">Statements contained in this prospectus as to the contents of any contract or other document are not necessarily complete, and in each
instance we refer you to the copy of the contract or document filed as an exhibit to the registration statement, each such statement being qualified in all respects by such reference. </FONT></P>
<P STYLE="margin-top:24px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2"><B><A NAME="toc617597_11"></A>INCORPORATION OF CERTAIN INFORMATION BY REFERENCE </B></FONT></P>
<P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">The Securities and Exchange Commission allows us to incorporate by reference in this prospectus the information that we file with them.
Incorporation by reference means that we can disclose important information to you by referring you to other documents that are legally considered to be part of this prospectus. Later information that we file with the Securities and Exchange
Commission will automatically update and supersede the information in this prospectus, any supplement and the documents listed below. Our SEC file number is 0-21898. We incorporate by reference the specific documents listed below and any filings
made with the Securities and Exchange Commission under Section&nbsp;13(a), 13(c), 14, or 15(d) of the Securities Exchange Act of 1934, as amended, (i)&nbsp;after the initial filing date of the registration statement of which this prospectus is a
part and prior to effectiveness of such registration statement and (ii)&nbsp;after the date of this prospectus; provided that all documents &#147;furnished&#148; by the Company to the SEC and not &#147;filed&#148; are not deemed incorporated by
reference herein: </FONT></P> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
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<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">The Company&#146;s Annual Report on Form 10-K for the fiscal year ended September&nbsp;30, 2012, filed on December&nbsp;28, 2012;
</FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
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<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD WIDTH="2%" VALIGN="top" ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">&#149;</FONT></TD>
<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">The Company&#146;s Quarterly Reports on Form 10-Q for the quarter ended December&nbsp;31, 2012, filed on February&nbsp;13, 2013, the quarter ended
March&nbsp;31, 2013, filed on May&nbsp;9, 2013 and the quarter ended June&nbsp;30, 2013, filed on August&nbsp;7, 2013; </FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
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<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">The Company&#146;s Current Reports on Form 8-K filed on December&nbsp;12, 2012,&nbsp;January&nbsp;30, 2013,&nbsp;March&nbsp;25, 2013,&nbsp;May&nbsp;1,
2013 and October&nbsp;10, 2013; and </FONT></P></TD></TR></TABLE> <P STYLE="font-size:6px;margin-top:0px;margin-bottom:0px">&nbsp;</P>
<TABLE STYLE="BORDER-COLLAPSE:COLLAPSE" BORDER="0" CELLPADDING="0" CELLSPACING="0" WIDTH="100%">
<TR>
<TD WIDTH="5%"><FONT SIZE="1">&nbsp;</FONT></TD>
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<TD WIDTH="1%" VALIGN="top"><FONT SIZE="1">&nbsp;</FONT></TD>
<TD ALIGN="left" VALIGN="top"> <P ALIGN="left"><FONT STYLE="font-family:Times New Roman" SIZE="2">The description of the Company&#146;s Common Stock contained in its registration statement on Form 8-A/A (Registration No. 000-21898), filed on
November&nbsp;1, 2010, including any amendments or reports filed for the purpose of updating such description. </FONT></P></TD></TR></TABLE>
 <p STYLE="margin-top:0px;margin-bottom:0px"><FONT SIZE="1">&nbsp;</FONT></P> <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2">7 </FONT></P>


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 <P STYLE="margin-top:0px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">We will furnish without charge to each person, including any beneficial owner, to whom this
prospectus is delivered, upon written or oral request, a copy of any document incorporated by reference. Requests should be addressed to Corporate Secretary, 225 South Lake Street, Suite 1050, Pasadena, CA 91101 or may be made telephonically at
(626)&nbsp;304-3400. </FONT></P> <P STYLE="margin-top:12px;margin-bottom:0px; text-indent:4%"><FONT STYLE="font-family:Times New Roman" SIZE="2">You should rely only on the information incorporated by reference or provided in this prospectus or any
prospectus supplement. We have not authorized anyone to provide you with different information. You should not assume that the information contained in this prospectus or the accompanying prospectus supplement is accurate on any date subsequent to
the date set forth on the front of the document or that any information we have incorporated by reference is correct on any date subsequent to the date of the document incorporated by reference, even though this prospectus and any accompanying
prospectus supplement is delivered or securities are sold on a later date. </FONT></P>
 <p STYLE="margin-top:0px;margin-bottom:0px"><FONT SIZE="1">&nbsp;</FONT></P> <P STYLE="margin-top:0px;margin-bottom:0px" ALIGN="center"><FONT STYLE="font-family:Times New Roman" SIZE="2">8 </FONT></P>

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