<SEC-DOCUMENT>0001415889-25-004277.txt : 20250214
<SEC-HEADER>0001415889-25-004277.hdr.sgml : 20250214
<ACCEPTANCE-DATETIME>20250214183142
ACCESSION NUMBER:		0001415889-25-004277
CONFORMED SUBMISSION TYPE:	SCHEDULE 13G/A
PUBLIC DOCUMENT COUNT:		2
FILED AS OF DATE:		20250214
DATE AS OF CHANGE:		20250214

SUBJECT COMPANY:	

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Day One Biopharmaceuticals, Inc.
		CENTRAL INDEX KEY:			0001845337
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		ORGANIZATION NAME:           	03 Life Sciences
		IRS NUMBER:				832415215
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SCHEDULE 13G/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	005-92582
		FILM NUMBER:		25631691

	BUSINESS ADDRESS:	
		STREET 1:		2000 SIERRA POINT PARKWAY, SUITE 501
		CITY:			BRISBANE
		STATE:			CA
		ZIP:			94005
		BUSINESS PHONE:		650 484-0899

	MAIL ADDRESS:	
		STREET 1:		2000 SIERRA POINT PARKWAY, SUITE 501
		CITY:			BRISBANE
		STATE:			CA
		ZIP:			94005

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	Day One Biopharmaceuticals Holding Co LLC
		DATE OF NAME CHANGE:	20210209

FILED BY:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			RA CAPITAL MANAGEMENT, L.P.
		CENTRAL INDEX KEY:			0001346824
		ORGANIZATION NAME:           	
		IRS NUMBER:				830406777
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		SCHEDULE 13G/A

	BUSINESS ADDRESS:	
		STREET 1:		200 BERKELEY STREET, 18TH FLOOR
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116
		BUSINESS PHONE:		617-778-2500

	MAIL ADDRESS:	
		STREET 1:		200 BERKELEY STREET, 18TH FLOOR
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02116

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	RA CAPITAL MANAGEMENT, LLC
		DATE OF NAME CHANGE:	20051213
</SEC-HEADER>
<DOCUMENT>
<TYPE>SCHEDULE 13G/A
<SEQUENCE>1
<FILENAME>primary_doc.xml
<TEXT>
<XML>
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  <headerData>
    <submissionType>SCHEDULE 13G/A</submissionType>
		<previousAccessionNumber>0001104659-21-077732</previousAccessionNumber>
	    <filerInfo>
      <filer>
        <filerCredentials>
          <cik>0001346824</cik>
          <ccc>XXXXXXXX</ccc>
        </filerCredentials>
      </filer>
      <liveTestFlag>LIVE</liveTestFlag>





    </filerInfo>
  </headerData>

  <formData>
    <coverPageHeader>
		<amendmentNo>3</amendmentNo>
	      <securitiesClassTitle>Common Stock, par value $0.0001 per share</securitiesClassTitle>
      <eventDateRequiresFilingThisStatement>12/31/2024</eventDateRequiresFilingThisStatement>
      <issuerInfo>
        <issuerCik>0001845337</issuerCik>        <issuerName>DAY ONE BIOPHARMACEUTICALS, INC.</issuerName>        <issuerCusip>23954D109</issuerCusip>
        <issuerPrincipalExecutiveOfficeAddress>
          <com:street1>2000 SIERRA POINT PARKWAY, SUITE 501</com:street1>
                    <com:city>BRISBANE</com:city>
          <com:stateOrCountry>CA</com:stateOrCountry>
          <com:zipCode>94005</com:zipCode>
        </issuerPrincipalExecutiveOfficeAddress>
      </issuerInfo>

	        <designateRulesPursuantThisScheduleFiled>
	   				        <designateRulePursuantThisScheduleFiled>Rule 13d-1(c)</designateRulePursuantThisScheduleFiled>
		      </designateRulesPursuantThisScheduleFiled>

    </coverPageHeader>

	    <coverPageHeaderReportingPersonDetails>




    <reportingPersonName>RA Capital Management, L.P.</reportingPersonName>



		 <citizenshipOrOrganization>DE</citizenshipOrOrganization>

      <reportingPersonBeneficiallyOwnedNumberOfShares>
                <soleVotingPower>0.00</soleVotingPower>
                          <sharedVotingPower>5755577.00</sharedVotingPower>
                          <soleDispositivePower>0.00</soleDispositivePower>
                         <sharedDispositivePower>5755577.00</sharedDispositivePower>
             </reportingPersonBeneficiallyOwnedNumberOfShares>

              <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>5755577.00</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>


     	    <classPercent>5.7</classPercent>




	  	  	  	  <typeOfReportingPerson>IA</typeOfReportingPerson>

	        <typeOfReportingPerson>PN</typeOfReportingPerson>









    </coverPageHeaderReportingPersonDetails>
	    <coverPageHeaderReportingPersonDetails>




    <reportingPersonName>Peter Kolchinsky </reportingPersonName>



		 <citizenshipOrOrganization>X1</citizenshipOrOrganization>

      <reportingPersonBeneficiallyOwnedNumberOfShares>
                <soleVotingPower>0.00</soleVotingPower>
                          <sharedVotingPower>5755577.00</sharedVotingPower>
                          <soleDispositivePower>0.00</soleDispositivePower>
                         <sharedDispositivePower>5755577.00</sharedDispositivePower>
             </reportingPersonBeneficiallyOwnedNumberOfShares>

              <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>5755577.00</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>


     	    <classPercent>5.7</classPercent>







	        <typeOfReportingPerson>HC</typeOfReportingPerson>



	        <typeOfReportingPerson>IN</typeOfReportingPerson>




    </coverPageHeaderReportingPersonDetails>
	    <coverPageHeaderReportingPersonDetails>




    <reportingPersonName>Rajeev Shah</reportingPersonName>



		 <citizenshipOrOrganization>X1</citizenshipOrOrganization>

      <reportingPersonBeneficiallyOwnedNumberOfShares>
                <soleVotingPower>0.00</soleVotingPower>
                          <sharedVotingPower>5755577.00</sharedVotingPower>
                          <soleDispositivePower>0.00</soleDispositivePower>
                         <sharedDispositivePower>5755577.00</sharedDispositivePower>
             </reportingPersonBeneficiallyOwnedNumberOfShares>

              <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>5755577.00</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>


     	    <classPercent>5.7</classPercent>







	        <typeOfReportingPerson>HC</typeOfReportingPerson>



	        <typeOfReportingPerson>IN</typeOfReportingPerson>




    </coverPageHeaderReportingPersonDetails>
	    <coverPageHeaderReportingPersonDetails>




    <reportingPersonName>RA Capital Healthcare Fund, L.P.</reportingPersonName>



		 <citizenshipOrOrganization>DE</citizenshipOrOrganization>

      <reportingPersonBeneficiallyOwnedNumberOfShares>
                <soleVotingPower>0.00</soleVotingPower>
                          <sharedVotingPower>5307848.00</sharedVotingPower>
                          <soleDispositivePower>0.00</soleDispositivePower>
                         <sharedDispositivePower>5307848.00</sharedDispositivePower>
             </reportingPersonBeneficiallyOwnedNumberOfShares>

              <reportingPersonBeneficiallyOwnedAggregateNumberOfShares>5307848.00</reportingPersonBeneficiallyOwnedAggregateNumberOfShares>


     	    <classPercent>5.3</classPercent>





	        <typeOfReportingPerson>PN</typeOfReportingPerson>









    </coverPageHeaderReportingPersonDetails>

    <items>
      <item1>
        <issuerName>DAY ONE BIOPHARMACEUTICALS, INC.</issuerName>
        <issuerPrincipalExecutiveOfficeAddress>2000 SIERRA POINT PARKWAY, SUITE 501, BRISBANE, CA, 94005.</issuerPrincipalExecutiveOfficeAddress>
      </item1>

      <item2>
        <filingPersonName>The names of the persons filing this report (collectively, the "Reporting Persons") are:

RA Capital Management, L.P. ("RA Capital")
Peter Kolchinsky
Rajeev Shah
RA Capital Healthcare Fund, L.P. (the "Fund")

The Reporting Persons expressly disclaim status as a "group" for purposes of this Schedule 13G.</filingPersonName>        <principalBusinessOfficeOrResidenceAddress>The address of the principal business office of each of the Reporting Persons is:

c/o RA Capital Management, L.P., 200 Berkeley Street, 18th Floor, Boston MA 02116</principalBusinessOfficeOrResidenceAddress>        <citizenship>RA Capital and the Fund are Delaware limited partnerships.
Dr. Kolchinsky and Mr. Shah are United States citizens.
</citizenship>      </item2>

        <item3>
		        <notApplicableFlag>Y</notApplicableFlag>

      </item3>



    <item4>
    <amountBeneficiallyOwned>Row 9 of each Reporting Person's cover page to this Schedule 13G sets forth the aggregate number of securities of the Issuer beneficially owned by such Reporting Person as of December 31, 2024 and is incorporated by reference.

The Reporting Persons' ownership of the Issuer's securities includes (i) 5,307,848 shares of Common Stock directly held by the Fund, and (ii) 447,729 shares of Common Stock directly held by RA Capital Nexus Fund II, L.P. (the "Nexus Fund II").

RA Capital Healthcare Fund GP, LLC is the general partner of the Fund and RA Capital Nexus Fund II GP, LLC is the general partner of the Nexus Fund II. The general partner of RA Capital is RA Capital Management GP, LLC, of which Dr. Kolchinsky and Mr. Shah are the controlling persons. RA Capital serves as investment adviser for each of the Fund and the Nexus Fund II and may be deemed a beneficial owner, for purposes of Section 13(d) of the Act, of any securities of the Issuer held by the Fund or the Nexus Fund II. Each of the Fund and the Nexus Fund II has delegated to RA Capital the sole power to vote and the sole power to dispose of all securities held in its portfolio, including the shares of the Issuer's Common Stock reported herein. Because each of the Fund and the Nexus Fund II has divested itself of voting and investment power over the reported securities it holds and may not revoke that delegation on less than 61 days' notice, each of the Fund and the Nexus Fund II disclaims beneficial ownership of the securities it holds for purposes of Section 13(d) of the Act and therefore disclaims any obligation to report ownership of the reported securities under Section 13(d) of the Act. As managers of RA Capital, Dr. Kolchinsky and Mr. Shah may be deemed beneficial owners, for purposes of Section 13(d) of the Act, of any securities of the Issuer beneficially owned by RA Capital. RA Capital, Dr. Kolchinsky, and Mr. Shah disclaim beneficial ownership of the securities reported in this Schedule 13G other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of this Schedule 13G shall not be deemed an admission that either RA Capital, Dr. Kolchinsky, or Mr. Shah is the beneficial owner of such securities for any other purpose.</amountBeneficiallyOwned>    <classPercent>Row 11 of each Reporting Person's cover page to this Schedule 13G sets forth the percentages of the securities of the Issuer beneficially owned by such Reporting Person as of December 31, 2024 and is incorporated by reference. The percentage set forth in Row 11 of each Reporting Person's cover page is based upon 100,846,294 shares of the Issuer's Common Stock outstanding as of October 24, 2024, as reported in the Issuer's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (the "SEC") on October 30, 2024.</classPercent>
      <numberOfSharesPersonHas>
        <solePowerOrDirectToVote>Row 5 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person as of December 31, 2024 and is incorporated by reference.</solePowerOrDirectToVote>
        <sharedPowerOrDirectToVote>Row 6 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person as of December 31, 2024 and is incorporated by reference.</sharedPowerOrDirectToVote>
        <solePowerOrDirectToDispose>Row 7 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person as of December 31, 2024 and is incorporated by reference.</solePowerOrDirectToDispose>
        <sharedPowerOrDirectToDispose>Row 8 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person as of December 31, 2024 and is incorporated by reference.</sharedPowerOrDirectToDispose>
      </numberOfSharesPersonHas>
    </item4>


        <item5>
	          <notApplicableFlag>Y</notApplicableFlag>


    </item5>


        <item6>
	  	  <notApplicableFlag>Y</notApplicableFlag>
		        </item6>


        <item7>
	  	  <notApplicableFlag>Y</notApplicableFlag>


    </item7>


          <item8>
                <notApplicableFlag>Y</notApplicableFlag>

              </item8>


            <item9>
                <notApplicableFlag>Y</notApplicableFlag>
                      </item9>


      <item10>
                <notApplicableFlag>N</notApplicableFlag>
        <certifications>By signing below I 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, other than activities solely in connection with a nomination under ?? 240.14a-11.</certifications>

      </item10>
    </items>

		<exhibitInfo>Exhibit 99.1	Joint Filing Agreement</exhibitInfo>

	    <signatureInformation>
      <reportingPersonName>RA Capital Management, L.P.</reportingPersonName>

      <signatureDetails>
        <signature>/s/ Peter Kolchinsky</signature>
        <title>By Peter Kolchinsky, Authorized Signatory</title>
        <date>02/14/2025</date>
      </signatureDetails>

    </signatureInformation>
	     <signatureInformation>
      <reportingPersonName>Peter Kolchinsky </reportingPersonName>

      <signatureDetails>
        <signature>/s/ Peter Kolchinsky</signature>
        <title>Peter Kolchinsky</title>
        <date>02/14/2025</date>
      </signatureDetails>

    </signatureInformation>
	     <signatureInformation>
      <reportingPersonName>Rajeev Shah</reportingPersonName>

      <signatureDetails>
        <signature>/s/ Rajeev Shah</signature>
        <title>Rajeev Shah</title>
        <date>02/14/2025</date>
      </signatureDetails>

    </signatureInformation>
	     <signatureInformation>
      <reportingPersonName>RA Capital Healthcare Fund, L.P.</reportingPersonName>

      <signatureDetails>
        <signature>/s/ Peter Kolchinsky</signature>
        <title>By RA Capital Healthcare Fund GP, LLC, its General Partner, By Peter Kolchinsky, Manager</title>
        <date>02/14/2025</date>
      </signatureDetails>

    </signatureInformation>



  </formData>


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<DOCUMENT>
<TYPE>EX-99.1
<SEQUENCE>2
<FILENAME>ex-99-02142025_110242.htm
<DESCRIPTION>JOINT FILING AGREEMENT
<TEXT>
<!DOCTYPE html PUBLIC "-//IETF//DTD HTML//EN">
<html><head><title>ex-99-02142025_110242.htm</title></head><body style="margin-top:0;font-family:Times New Roman; font-size:10pt; color:#000000">
<p style="margin:0px" align="right">EXHIBIT 99.1</p>
<p style="margin:0px" align="right"><br></p>
<p style="margin:0px" align="center"><b>JOINT FILING AGREEMENT</b></p>
<p style="margin:0px"><br></p>
<p style="margin:0px" align="justify">This Joint Filing Agreement, dated as of February 14, 2025, is by and among RA Capital Management, L.P., Peter Kolchinsky, Rajeev Shah, and RA Capital Healthcare Fund, L.P. (the foregoing are collectively referred to herein as the <font style="font-family:Arial Unicode MS,Times New Roman">&ldquo;</font>Filers<font style="font-family:Arial Unicode MS,Times New Roman">&rdquo;</font>). </p>
<p style="margin:0px" align="justify"><br></p>
<p style="margin:0px" align="justify">Each of the Filers may be required to file with the United States Securities and Exchange Commission a statement on Schedule 13G and/or 13D with respect to the Common Stock, $0.0001 par value per share of Day One Biopharmaceuticals, Inc. beneficially owned by them from time to time.</p>
<p style="margin:0px" align="justify"><br></p>
<p style="margin:0px" align="justify">Pursuant to and in accordance with Rule 13(d)(1)(k) promulgated under the Securities Exchange Act of 1934, as amended, the Filers hereby agree to file a single statement on Schedule 13G and/or 13D (and any amendments thereto) on behalf of each of such parties, and hereby further agree to file this Joint Filing Agreement as an exhibit to such statement, as required by such rule.</p>
<p style="margin:0px" align="justify"><br></p>
<p style="margin:0px" align="justify">This Joint Filing Agreement may be terminated by any of the Filers upon one week<font style="font-family:Arial Unicode MS,Times New Roman">&rsquo;</font>s prior written notice or such lesser period of notice as the Filers may mutually agree.</p>
<p style="margin:0px"><br></p>
<p style="margin:0px">Executed and delivered as of the date first above written.</p>
<p style="margin:0px"><br></p>
<p style="margin:0px"><br></p>
<p style="margin:0px"><b>RA CAPITAL MANAGEMENT, L.P.</b></p>
<p style="margin:0px"><br></p>
<p style="margin-top:0px; margin-bottom:-2px; width:48px; float:left">By:</p>
<p style="margin:0px; text-indent:-2px"><u>/s/ Peter Kolchinsky</u></p>
<p style="margin-top:0px; margin-bottom:-2px; text-indent:48px; width:96px; clear:left; float:left">Name:</p>
<p style="margin:0px; padding-left:48px; text-indent:-2px">Peter Kolchinsky</p>
<p style="margin-top:0px; margin-bottom:-2px; text-indent:48px; width:96px; clear:left; float:left">Title:</p>
<p style="margin:0px; padding-left:48px; text-indent:-2px">Authorized Signatory</p>
<p style="margin:0px; clear:left"><br></p>
<p style="margin:0px"><br></p>
<p style="margin:0px"><b>PETER KOLCHINSKY</b></p>
<p style="margin:0px"><br></p>
<p style="margin:0px"><u>/s/ Peter Kolchinsky</u></p>
<p style="margin:0px"><br></p>
<p style="margin:0px"><br></p>
<p style="margin:0px"><b>RAJEEV SHAH</b></p>
<p style="margin:0px"><br></p>
<p style="margin:0px"><u>/s/ Rajeev Shah</u></p>
<p style="margin:0px"><br></p>
<p style="margin:0px"><br></p>
<p style="margin:0px"><b>RA CAPITAL HEALTHCARE FUND, L.P.</b></p>
<p style="margin:0px"><br></p>
<p style="margin-top:0px; margin-bottom:-2px; width:48px; float:left">By:</p>
<p style="margin:0px; text-indent:-2px">RA Capital Healthcare Fund GP, LLC</p>
<p style="margin-top:0px; margin-bottom:-2px; width:48px; clear:left; float:left">Its:</p>
<p style="margin:0px; text-indent:-2px">General Partner</p>
<p style="margin:0px; clear:left"><br></p>
<p style="margin-top:0px; margin-bottom:-2px; width:48px; float:left">By:</p>
<p style="margin:0px; text-indent:-2px"><u>/s/ Peter Kolchinsky</u></p>
<p style="margin-top:0px; margin-bottom:-2px; text-indent:48px; width:96px; clear:left; float:left">Name:</p>
<p style="margin:0px; padding-left:48px; text-indent:-2px">Peter Kolchinsky</p>
<p style="margin-top:0px; margin-bottom:-2px; text-indent:48px; width:96px; clear:left; float:left">Title:</p>
<p style="margin:0px; padding-left:48px; text-indent:-2px">Manager</p>
<p style="margin:0px; clear:left"><br></p>
<p style="margin:0px"><br></p>
<p style="margin:0px"><br></p>
</body></html>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
