Company: DAWN
Filing Date: 2025-11-13
Form Type: SC TO-C
Source: 0001104659-25-110815
Chunk: 1

Company: Day One Biopharmaceuticals, Inc.
Filing Date: 2025-11-13
Form: SC TO-C
Chunk 1
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b-2 of the Securities Exchange
Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ¨

If an emerging growth company, indicate by check mark if the registrant
has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant
to Section 13(a) of the Exchange Act. ¨

| Item 1.01 | Entry into a Material Definitive Agreement. |

Agreement and Plan of Merger

On November 12, 2025, Day One Biopharmaceuticals, Inc., a Delaware
corporation (“Parent”), Emerald Merger Sub, Inc., a Delaware corporation and a direct wholly owned subsidiary of Parent (“Merger
Sub”) and Mersana Therapeutics, Inc., a Delaware corporation (the “Target”), entered into an Agreement and Plan of Merger
(the “Merger Agreement”).

Pursuant to the Merger Agreement, and upon the terms and subject to
the conditions therein, Merger Sub will commence a tender offer (the “Offer”) to acquire all of the issued and outstanding
shares (the “Target Shares”) of common stock, par value $0.0001 per share, of the Target (the “Target Common Stock”),
for (i) $25.00 net per Target Share, payable in cash, without interest (such amount, or any different amount per share paid pursuant to
the Offer, the “Upfront Consideration”), plus (ii) one contingent value right per Target Share (each, a “CVR”),
which represents the right to receive milestone payments of up to an aggregate of $30.25 per share in cash upon the achievement of certain
specified milestones in accordance with the terms and subject to the conditions of a contingent value rights agreement (the “CVR
Agreement”) to be entered into with a rights agent (the “Rights Agent”) mutually agreeable to Parent and the Target
(the Upfront Consideration plus one CVR, together, the “Offer Price”). The Offer will remain open for 20 business days, subject
to extension under certain circumstances.

Following the consummation of the Offer, subject to the terms and conditions of the Merger Agreement, and in accordance with the General Corporation Law of the State of Delaware (the “DGCL”), Merger Sub will merge with and into the Target as provided in the Merger Agreement, with the Target continuing as the surviving