<SEC-DOCUMENT>0001144204-13-027506.txt : 20130509
<SEC-HEADER>0001144204-13-027506.hdr.sgml : 20130509
<ACCEPTANCE-DATETIME>20130509171806
ACCESSION NUMBER:		0001144204-13-027506
CONFORMED SUBMISSION TYPE:	SC 13G
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20130509
DATE AS OF CHANGE:		20130509
GROUP MEMBERS:		PETER KOLCHINSKY
GROUP MEMBERS:		RA CAPITAL HEALTHCARE FUND, L.P.

SUBJECT COMPANY:	

	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:		SC 13G
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	005-48710
		FILM NUMBER:		13830024

	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

FILED BY:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			RA CAPITAL MANAGEMENT, LLC
		CENTRAL INDEX KEY:			0001346824
		IRS NUMBER:				830406777
		STATE OF INCORPORATION:			MA
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SC 13G

	BUSINESS ADDRESS:	
		STREET 1:		20 PARK PLAZA, SUITE 1200
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
		BUSINESS PHONE:		617-778-2500

	MAIL ADDRESS:	
		STREET 1:		20 PARK PLAZA, SUITE 1200
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
</SEC-HEADER>
<DOCUMENT>
<TYPE>SC 13G
<SEQUENCE>1
<FILENAME>v344536_sc13g.htm
<DESCRIPTION>SC 13G
<TEXT>
<HTML>
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     <TITLE></TITLE>
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<BODY STYLE="font: 10pt Times New Roman, Times, Serif">

<P STYLE="margin: 0"></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">UNITED STATES<BR>
SECURITIES AND EXCHANGE COMMISSION<BR>
Washington, D.C. 20549</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>SCHEDULE 13G</B></P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">Under the Securities Exchange Act of
1934</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center; text-indent: 0in"><B>(Amendment No.__)*</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center; text-indent: 0in">&nbsp;</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><BR>
Arrowhead Research Corporation</P>

<P STYLE="font: bold 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">(Name of Issuer)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>Common Stock, $0.001 par value</B></P>

<HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 640px; width: 480.25pt; color: gray">

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">(Title of Class of Securities)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>042797209</B></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">(CUSIP Number)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><B>April 29, 2013</B></P>

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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">(Date of Event Which Requires Filing of
this Statement)</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Check the appropriate box to designate the rule pursuant to
which this Schedule is filed:</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="width: 100%; font: 10pt Times New Roman, Times, Serif">
<TR>
    <TD STYLE="padding: 3pt">[ &nbsp; ]</TD>
    <TD STYLE="padding: 3pt">Rule 13d-1(b)</TD></TR>
<TR>
    <TD STYLE="padding: 3pt">[<B>X</B>]</TD>
    <TD STYLE="padding: 3pt">Rule 13d-1(c)</TD></TR>
<TR>
    <TD STYLE="padding: 3pt">[ &nbsp; ]</TD>
    <TD STYLE="padding: 3pt">Rule 13d-1(d)</TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">*The remainder of this cover page shall be filled out for a
reporting person&rsquo;s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment
containing information which would alter the disclosures provided in a prior cover page.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">The information required in the remainder of this cover page
shall not be deemed to be &ldquo;filed&rdquo; for the purpose of Section 18 of the Securities Exchange Act of 1934 (&ldquo;<B><I>Act</I></B>&rdquo;)
or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however,
see the Notes).</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>


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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%">
<TR>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">CUSIP No. <B>042797209</B></FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 12pt; text-align: center"><FONT STYLE="font-size: 12pt"><B>13G</B></FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Page <U>&nbsp;&nbsp;&nbsp;<B>2</B>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</U>&nbsp;of <U>&nbsp;&nbsp;&nbsp;<B>7</B>&nbsp;&nbsp;&nbsp;</U>&nbsp;Pages</FONT></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
<HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="vertical-align: top; padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">1.</FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Names of Reporting Persons.<BR>
        I.R.S. Identification Nos. of above persons (entities only).</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>RA Capital Management, LLC&#9;</B></P></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="vertical-align: top; padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">2. </FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Check the Appropriate Box if a Member of a Group (See Instructions)</FONT></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">(a)</FONT></TD>
    <TD COLSPAN="3" STYLE="padding-bottom: 6pt; font-size: 10pt">[_]</TD></TR>
<TR>
    <TD STYLE="padding-bottom: 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding-bottom: 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">(b)</FONT></TD>
    <TD COLSPAN="3" STYLE="padding-bottom: 6pt; font-size: 10pt">[_]</TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt auto; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">3.</FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">SEC Use Only </FONT></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">4.</FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Citizenship or Place of Organization&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT>&nbsp;<FONT STYLE="font-size: 10pt"><B>Massachusetts</B></FONT></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="width: 4%">&nbsp;</TD>
    <TD STYLE="width: 7%">&nbsp;</TD>
    <TD STYLE="width: 6%">&nbsp;</TD>
    <TD STYLE="width: 26%">&nbsp;</TD>
    <TD STYLE="width: 22%">&nbsp;</TD>
    <TD STYLE="width: 35%">&nbsp;</TD></TR>
</TABLE>
<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%">
<TR>
    <TD ROWSPAN="7" STYLE="width: 18%; padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">Number of</FONT><BR>
<FONT STYLE="font-size: 10pt">Shares</FONT><BR>
<FONT STYLE="font-size: 10pt">Beneficially</FONT><BR>
<FONT STYLE="font-size: 10pt">Owned by</FONT><BR>
<FONT STYLE="font-size: 10pt">Each Reporting</FONT><BR>
<FONT STYLE="font-size: 10pt">Person With</FONT></TD>
    <TD STYLE="width: 3%; padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">5.</FONT></TD>
    <TD STYLE="width: 79%; font-size: 10pt"><FONT STYLE="font-size: 10pt">Sole Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>0</B></FONT></TD></TR>
<TR>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">6.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Shared Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>3,127,401<SUP>1</SUP></B></FONT></TD></TR>
<TR>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">7.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Sole Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>0</B></FONT></TD></TR>
<TR>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">8.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Shared Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>3,127,401<SUP>1</SUP></B></FONT></TD></TR>
</TABLE>
<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%">
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="width: 4%; padding: 1.45pt 3pt auto; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="width: 7%; padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">9.</FONT></TD>
    <TD STYLE="width: 89%; padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Aggregate Amount Beneficially Owned by Each Reporting Person</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>3,127,401<SUP>1</SUP></B></P></TD></TR>
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">10.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><FONT STYLE="font-size: 10pt">Check if the Aggregate Amount
        in Row (9) Excludes </FONT>[_]</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Certain Shares (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></TD></TR>
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">11.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Percent of Class Represented by Amount in Row (9)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>9.9%<SUP>1</SUP></B></P></TD></TR>
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">12.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Type of Reporting Person (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>IA</B></P></TD></TR>
</TABLE>
<HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray">

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>_______________________________</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><SUP>1</SUP> <FONT STYLE="font-size: 10pt">The Reporting Persons
own 3,114,755 shares of Common Stock and also 6,300 shares of Series B Preferred Stock that are convertible into 3,442,623 shares
of Common Stock. The Series B Preferred Shares may not be converted such that the number of shares of common stock held by them
and their affiliates after such conversion exceeds 9.99% of the outstanding shares of Common Stock. See Item 4 below.</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>


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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>&nbsp;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>












<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%">
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    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">CUSIP No. <B>042797209</B></FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 12pt; text-align: center"><FONT STYLE="font-size: 12pt"><B>13G</B></FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Page <U>&nbsp;&nbsp;&nbsp;<B>3</B>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</U>&nbsp;of <U>&nbsp;&nbsp;&nbsp;<B>7</B>&nbsp;&nbsp;</U>&nbsp;Pages</FONT></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="vertical-align: top; padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">1.</FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Names of Reporting Persons.<BR>
        I.R.S. Identification Nos. of above persons (entities only).</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>Peter Kolchinsky&#9;</B></P></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="vertical-align: top; padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">2. </FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Check the Appropriate Box if a Member of a Group (See Instructions)</FONT></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">(a)</FONT></TD>
    <TD COLSPAN="3" STYLE="padding-bottom: 6pt; font-size: 10pt">[_]</TD></TR>
<TR>
    <TD STYLE="padding-bottom: 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding-bottom: 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">(b)</FONT></TD>
    <TD COLSPAN="3" STYLE="padding-bottom: 6pt; font-size: 10pt">[_]</TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt auto; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">3.</FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">SEC Use Only </FONT></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">4.</FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Citizenship or Place of Organization&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT>&nbsp;<B>United States</B></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="width: 4%">&nbsp;</TD>
    <TD STYLE="width: 7%">&nbsp;</TD>
    <TD STYLE="width: 6%">&nbsp;</TD>
    <TD STYLE="width: 26%">&nbsp;</TD>
    <TD STYLE="width: 22%">&nbsp;</TD>
    <TD STYLE="width: 35%">&nbsp;</TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>








<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%">
<TR>
    <TD ROWSPAN="7" STYLE="width: 18%; padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">Number of</FONT><BR>
<FONT STYLE="font-size: 10pt">Shares</FONT><BR>
<FONT STYLE="font-size: 10pt">Beneficially</FONT><BR>
<FONT STYLE="font-size: 10pt">Owned by</FONT><BR>
<FONT STYLE="font-size: 10pt">Each Reporting</FONT><BR>
<FONT STYLE="font-size: 10pt">Person With</FONT></TD>
    <TD STYLE="width: 3%; padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">5.</FONT></TD>
    <TD STYLE="width: 79%; font-size: 10pt"><FONT STYLE="font-size: 10pt">Sole Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>0</B></FONT></TD></TR>
<TR>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">6.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Shared Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>3,127,401<SUP>1</SUP></B></FONT></TD></TR>
<TR>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">7.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Sole Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>0</B></FONT></TD></TR>
<TR>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">8.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Shared Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>3,127,401<SUP>1</SUP></B></FONT></TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>












<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%">
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="width: 4%; padding: 1.45pt 3pt auto; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="width: 7%; padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">9.</FONT></TD>
    <TD STYLE="width: 89%; padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Aggregate Amount Beneficially Owned by Each Reporting Person</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>3,127,401<SUP>1</SUP></B></P></TD></TR>
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">10.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><FONT STYLE="font-size: 10pt">Check if the Aggregate Amount
        in Row (9) Excludes </FONT>[_]</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Certain Shares (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></TD></TR>
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">11.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Percent of Class Represented by Amount in Row (9)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>9.9%<SUP>1</SUP></B></P></TD></TR>
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">12.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Type of Reporting Person (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>IN</B></P></TD></TR>
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>&nbsp;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>_______________________________</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><SUP>1</SUP> <FONT STYLE="font-size: 10pt">The Reporting Persons
own 3,114,755 shares of Common Stock and also 6,300 shares of Series B Preferred Stock that are convertible into 3,442,623 shares
of Common Stock. The Series B Preferred Shares may not be converted such that the number of shares of common stock held by them
and their affiliates after such conversion exceeds 9.99% of the outstanding shares of Common Stock. See Item 4 below.</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>&nbsp;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>


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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>&nbsp;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>












<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%">
<TR>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">CUSIP No. <B>042797209</B></FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 12pt; text-align: center"><FONT STYLE="font-size: 12pt"><B>13G</B></FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Page <U>&nbsp;&nbsp;&nbsp;<B>4</B>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</U>&nbsp;of <U>&nbsp;&nbsp;&nbsp;<B>7</B>&nbsp;&nbsp;&nbsp;</U>&nbsp;Pages</FONT></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="vertical-align: top; padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">1.</FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Names of Reporting Persons.<BR>
        I.R.S. Identification Nos. of above persons (entities only).</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>RA Capital Healthcare Fund, L.P.&#9;</B></P></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="vertical-align: top; padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">2. </FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Check the Appropriate Box if a Member of a Group (See Instructions)</FONT></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">(a)</FONT></TD>
    <TD COLSPAN="3" STYLE="padding-bottom: 6pt; font-size: 10pt">[_]</TD></TR>
<TR>
    <TD STYLE="padding-bottom: 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding-bottom: 6pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt 6pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">(b)</FONT></TD>
    <TD COLSPAN="3" STYLE="padding-bottom: 6pt; font-size: 10pt">[_]</TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt auto; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">3.</FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">SEC Use Only </FONT></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">4.</FONT></TD>
    <TD COLSPAN="4" STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Citizenship or Place of Organization&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</FONT>&nbsp;<FONT STYLE="font-size: 10pt"><B>Delaware</B></FONT></TD></TR>
<TR>
    <TD COLSPAN="6" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="width: 4%">&nbsp;</TD>
    <TD STYLE="width: 7%">&nbsp;</TD>
    <TD STYLE="width: 6%">&nbsp;</TD>
    <TD STYLE="width: 26%">&nbsp;</TD>
    <TD STYLE="width: 22%">&nbsp;</TD>
    <TD STYLE="width: 35%">&nbsp;</TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>








<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%">
<TR>
    <TD ROWSPAN="7" STYLE="width: 18%; padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">Number of</FONT><BR>
<FONT STYLE="font-size: 10pt">Shares</FONT><BR>
<FONT STYLE="font-size: 10pt">Beneficially</FONT><BR>
<FONT STYLE="font-size: 10pt">Owned by</FONT><BR>
<FONT STYLE="font-size: 10pt">Each Reporting</FONT><BR>
<FONT STYLE="font-size: 10pt">Person With</FONT></TD>
    <TD STYLE="width: 3%; padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">5.</FONT></TD>
    <TD STYLE="width: 79%; font-size: 10pt"><FONT STYLE="font-size: 10pt">Sole Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;0</B></FONT></TD></TR>
<TR>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">6.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Shared Voting Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>2,501,921<SUP>2</SUP></B></FONT></TD></TR>
<TR>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">7.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Sole Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;0</B></FONT></TD></TR>
<TR>
    <TD COLSPAN="2" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">8.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">Shared Dispositive Power&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<B>2,501,921<SUP>2</SUP></B></FONT></TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>












<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%">
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="width: 4%; padding: 1.45pt 3pt auto; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="width: 7%; padding: 1.45pt 3pt auto; font-size: 10pt"><FONT STYLE="font-size: 10pt">9.</FONT></TD>
    <TD STYLE="width: 89%; padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Aggregate Amount Beneficially Owned by Each Reporting Person</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>2,501,921<SUP>2</SUP></B></P></TD></TR>
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">10.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><FONT STYLE="font-size: 10pt">Check if the Aggregate Amount
        in Row (9) Excludes </FONT>[_]</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Certain Shares (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P></TD></TR>
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">11.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Percent of Class Represented by Amount in Row (9)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>8.0%<SUP>2</SUP></B></P></TD></TR>
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
<TR>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt">&nbsp;</TD>
    <TD STYLE="padding: 1.45pt 3pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">12.</FONT></TD>
    <TD STYLE="padding: 1.45pt 3pt">
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Type of Reporting Person (See Instructions)</P>
        <P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in"><B>PN</B></P></TD></TR>
<TR>
    <TD COLSPAN="3" STYLE="padding: 1.45pt 3pt">
        <HR SIZE="2" NOSHADE ALIGN="CENTER" STYLE="width: 100%; color: gray"></TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>&nbsp;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;<B>_______________________________</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><SUP>2</SUP> <FONT STYLE="font-size: 10pt">The Reporting Person
owns 2,491,804 shares of Common Stock and also 5,040 shares of Series B Preferred Stock that are convertible into 2,754,098 shares
of Common Stock. The Series B Preferred Shares may not be converted such that the number of shares of common stock held by them
and their affiliates after such conversion exceeds 9.99% of the outstanding shares of Common Stock. See Item 4 below.</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;&nbsp;</P>


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<TR STYLE="vertical-align: top">
    <TD STYLE="width: 52%; padding-right: 5.4pt; padding-left: 5.4pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">CUSIP No. <B>042797209</B></FONT></TD>
    <TD STYLE="width: 48%; padding-right: 5.4pt; padding-left: 5.4pt; font-size: 10pt; text-align: right">Page 5 of 7</TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>&nbsp;&nbsp;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 1.</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">(a)&#9;<B>Name of Issuer:</B> Arrowhead Research Corporation
(the &ldquo;Issuer&rdquo;).</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">(b)&#9;<B>Address of the Issuer&rsquo;s Principal Executive
Offices:</B> 225 South Lake Avenue, Suite 1050, Pasadena, CA 91101.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 2.&#9;</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">(a)&#9;<B>Name of Person Filing: </B> This
joint statement on Schedule 13G is being filed by Peter Kolchinsky, RA Capital Management, LLC, and RA Capital Healthcare Fund,
L.P., who are collectively referred to herein as the &ldquo;Reporting Persons.&rdquo; Mr. Kolchinsky (the &ldquo;Manager&rdquo;)
is the manager of RA Capital Management, LLC (&ldquo;Capital&rdquo;), which is the investment adviser and sole general partner
of RA Capital Healthcare Fund, L.P. (&ldquo;Fund&rdquo;) and serves as the investment adviser to a separate discretionary account.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">(b)&#9;<B>Address of Principal Business Office:</B>
The principal business office of the Reporting Persons is c/o RA Capital Management, LLC, 20 Park Plaza, Suite 1200,
Boston, MA 02116.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">(c) &#9;<B>Citizenship:</B> Capital is a Massachusetts
limited liability company. The Fund is a Delaware limited partnership. The Manager is a United States citizen.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">(d)&#9;<B>Title and Class of Securities: </B>Common
stock (&ldquo;Common Stock&rdquo;).</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">(e)&#9;<B>CUSIP Number:</B> 042797209.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 3.&#9;If this statement is filed pursuant to &sect;&sect;240.13d-1(b)
or 240.13d-2(b) or (c), check whether the person filing is a:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 4. &#9;Ownership:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">As of the date of this filing, the Reporting Persons, in the
aggregate, beneficially own 3,114,755 shares of the Common Stock of the Issuer, representing approximately 9.9% of such class
of securities. The Reporting Persons also own 6,300 shares of Series B Preferred Stock that are convertible into 3,442,623 shares
of Common Stock. The beneficial ownership of each Reporting Person is as follows: (i) Fund beneficially owns 2,491,804 shares
of Common Stock representing approximately 8.0% of the class and also 5,040 shares of Series B Preferred Stock that are convertible
into 2,754,098 shares of Common Stock and (ii) Capital, as the investment adviser and sole general partner of the Fund and&nbsp;investment
adviser to an account owned by a separate investment vehicle which holds shares of the Issuer's Common Stock,<I> </I>and<I> </I>Mr.
Kolchinsky as the manager of Capital, each beneficially own 3,114,755 shares of Common Stock of the Issuer representing approximately
9.9% of the class and also 6,300 shares of Series B Preferred Stock that are convertible into 3,442,623 shares of Common Stock.
The Series B Preferred Stock referred to above may not be converted such that the number of shares of common stock held by the
Reporting Persons after such conversion exceeds 9.99% of the outstanding shares of common stock (&quot;Beneficial Ownership
Limitation&quot;). The Preferred Shares are eligible to vote with the common stock of the Company on an as-converted basis,
but only to the extent that the Preferred Shares are eligible for conversion without exceeding the Beneficial Ownership Limitation.</P>



<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>


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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%; border-collapse: collapse">
<TR STYLE="vertical-align: top">
    <TD STYLE="width: 52%; padding-right: 5.4pt; padding-left: 5.4pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">CUSIP No. <B>042797209</B></FONT></TD>
    <TD STYLE="width: 48%; padding-right: 5.4pt; padding-left: 5.4pt; font-size: 10pt; text-align: right">Page 6 of 7</TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">The Fund has the power to vote and dispose of the shares of
Common Stock beneficially owned by such entity (as described above). Capital, as the investment adviser and sole general partner
of the Fund and as the investment adviser&nbsp;to&nbsp;an account owned by a separate investment vehicle which holds<FONT STYLE="color: blue"><B><I>
</I></B></FONT>shares of the Issuer&rsquo;s Common Stock, has the authority to vote and dispose of all of the shares of Common
Stock reported in this Schedule 13G. The Manager, by virtue of his position as manager of Capital, has the authority to vote
and dispose of all of the shares of Common Stock reported in this Schedule 13G.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 5.&#9;Ownership of Five Percent or Less of a Class:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 1in; text-indent: -1in"><B>Item 6.&#9;Ownership of More than
Five Percent on Behalf of Another Person:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 1in; text-indent: -1in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 7. &#9;Identification and Classification of the Subsidiary
Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 8.&#9;Identification and Classification of Members of
the Group:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 9.&#9;Notice of Dissolution of Group:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">Not applicable.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0"><B>Item 10.&#9;Certification:</B></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">By signing below I hereby certify that, to the best of my knowledge
and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing
or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant
in any transaction having that purpose or effect.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><I>&nbsp;</I></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>


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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>
<TABLE CELLSPACING="0" CELLPADDING="0" STYLE="font: 10pt Times New Roman, Times, Serif; width: 100%; border-collapse: collapse">
<TR STYLE="vertical-align: top">
    <TD STYLE="width: 52%; padding-right: 5.4pt; padding-left: 5.4pt; font-size: 10pt"><FONT STYLE="font-size: 10pt">CUSIP No. <B>042797209</B></FONT></TD>
    <TD STYLE="width: 48%; padding-right: 5.4pt; padding-left: 5.4pt; font-size: 10pt; text-align: right">Page 7 of 7</TD></TR>
</TABLE>
<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><I>&nbsp;</I></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><I>Signature</I></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">After reasonable inquiry and to the best
of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><FONT STYLE="text-transform: uppercase">Date: may
09, 2013</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">RA CAPITAL HEALTHCARE FUND, L.P.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: RA Capital Management, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in; text-indent: 0.5in">General Partner</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: /s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Manager</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><BR>
RA CAPITAL MANAGEMENT, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: /s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Manager</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">PETER KOLCHINSKY</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">/s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>


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<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><U>Exhibit 1</U></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center"><U>JOINT FILING AGREEMENT</U></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-align: center">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0; text-indent: 0.5in">Pursuant to Rule 13d-1(k)(1) under the Securities
Exchange Act of 1934, as amended, the undersigned hereby agrees, that only one statement containing the information
required by Schedule 13G, and each amendment thereto, need be filed with respect to the ownership by each of the undersigned of
shares of Common Stock of Arrowhead Research Corporation and such statement to which this Joint Filing Agreement is attached as
<U>Exhibit 1</U> is filed on behalf of each of the undersigned.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><FONT STYLE="text-transform: uppercase">&nbsp;</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><FONT STYLE="text-transform: uppercase">Date: may
09, 2013</FONT></P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">RA CAPITAL HEALTHCARE FUND, L.P.</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: RA Capital Management, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in; text-indent: 0.5in">General Partner</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: /s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Manager</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in"><BR>
RA CAPITAL MANAGEMENT, LLC</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">By: /s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">Manager</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">PETER KOLCHINSKY</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">/s/ Peter Kolchinsky</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">-------------------------------------------------</P>

<P STYLE="font: 10pt Times New Roman, Times, Serif; margin: 0pt 0 0pt 3.5in">&nbsp;</P>



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