# EDGAR Filing Document

**Accession Number:** 0001580111
**File Stem:** 0001415889-25-015620
**Filing Date:** 2025-6
**Character Count:** 7382
**Document Hash:** fbfe6e55ffeb0825dc97ab54047b9a81
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001415889-25-015620.hdr.sgml**: 20250604

**ACCESSION NUMBER**: 0001415889-25-015620

**CONFORMED SUBMISSION TYPE**: 4

**PUBLIC DOCUMENT COUNT**: 1

**CONFORMED PERIOD OF REPORT**: 20250602

**FILED AS OF DATE**: 20250604

**DATE AS OF CHANGE**: 20250604

**REPORTING-OWNER**: 

**OWNER DATA:**
- **COMPANY CONFORMED NAME:** Holles Natalie C.
- **CENTRAL INDEX KEY:** 0001580111

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** 4
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-40431
- **FILM NUMBER:** 251024299

**MAIL ADDRESS:**
- **STREET 1:** C/O HYPERION THERAPEUTICS, INC.
- **STREET 2:** 2000 SIERRA POINT PARKWAY, SUITE 400
- **CITY:** BRISBANE
- **STATE:** CA
- **ZIP:** 94005
**ISSUER**: 

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

**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

### UNITED STATES SECURITIES AND EXCHANGE COMMISSION
**Washington, D.C. 20549**

## FORM 4

### STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

[ ] Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

---

| | | |
|:---|:---|:---|
| **1. Name and Address of Reporting Person**<sup>*</sup><br>Holles Natalie C.<br><sub>(Last) (First) (Middle)</sub><br>1800 SIERRA POINT PARKWAY, SUITE 200<br><sub>(Street)</sub><br>BRISBANE, CA 94005<br><sub>(City) (State) (Zip)</sub> | **3. Date of Earliest Transaction (Month/Day/Year)**<br>2025-06-02 | **5. Relationship of Reporting Person(s) to Issuer**<br>(Check all applicable)<br>[X] Director [ ] 10% Owner<br>[ ] Officer (give title below) [ ] Other (specify below)<br>_ _ |
| **2. Issuer Name and Ticker or Trading Symbol**<br>Day One Biopharmaceuticals, Inc. [ DAWN ] | **4. If Amendment, Date of Original Filed (Month/Day/Year)**<br>  | **6. Individual or Joint/Group Filing (Check Applicable Line)**<br>[X] Form filed by One Reporting Person<br>[ ] Form filed by More than One Reporting Person |

---

## Table I - Non-Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | 3. Transaction Code (V) | 3. Transaction Code (V) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | Code | V | Amount | (A) or (D) | Price | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
|  |  |  |  |  |  |  |  |  |  |  |

---

## Table II - Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | 4. Transaction Code (V) | 4. Transaction Code (V) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 6. Date Exercisable and Expiration Date | 6. Date Exercisable and Expiration Date | 7. Title and Amount of Underlying Securities | 7. Title and Amount of Underlying Securities | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | Code | V | (A) | (D) | Date Exercisable | Expiration Date | Title | Amount or Number of Shares | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| Stock Option (right to buy Common Stock) | $7.01 | 2025-06-02 |  | A |  | 22500 |  | <sup>(1)</sup> | 2035-06-01 | Common Stock | 22500 | $0 | 22500 | D |  |
| Deferred Restricted Stock Unit (RSU) | 0<sup>(2)</sup> | 2025-06-02 |  | A |  | 15000 |  | <sup>(3)</sup> | <sup>(4)</sup> | Common Stock | 15000 | $0 | 15000 | D |  |

---

### Footnotes:

(1) The option vests as to 1/12th of the total grant on each monthly anniversary, beginning on July 2, 2025, subject to the Reporting Person's provision of service to the Issuer on each option vesting date.

(2) Each restricted stock unit ("RSU") represents a contingent right to receive one share of the Issuer's Common Stock upon settlement for no consideration.

(3) The RSUs will vest as to 100% of the award on the earlier of (i) June 2, 2026 and (ii) the date of the Issuer's 2026 annual meeting of stockholders (in each case, the "RSU Vesting Date"), subject to the Reporting Person's provision of services to the Issuer on each vesting date. On the RSU Vesting Date, pursuant to the Reporting Person's election, the RSUs will automatically convert into an equal number of deferred stock units, which will be settled for an equal number of shares of the Issuer's Common Stock on the earlier of the calendar year 2030 or the Reporting Person's separation with the Issuer. Notwithstanding the aforementioned deferral period, from and after the RSU Vesting Date, the deferred stock units may settle earlier upon the Reporting Person's death, disability, or separation from service with the Issuer, or upon the occurrence of an "unforeseeable emergency," as that term is defined under the Issuer's deferred compensation plan.

(4) RSUs do not expire; they either vest or are canceled prior to the RSU Vesting Date.

**Signature:** /s/ Charles N. York II, as Attorney-in-Fact  
**Date:** 2025-06-04

### Remarks:

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.

**Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.**