SUPPLEMENT
TO
PROXY STATEMENT
FOR THE 2022 ANNUAL MEETING OF STOCKHOLDERS
TO BE HELD ON JUNE 1, 2022
On April 20, 2022, Calithera Biosciences, Inc. filed with the Securities and Exchange Commission a definitive proxy statement, or the
Proxy Statement, relating to its 2022 annual meeting of stockholders, or the Annual Meeting, to be held virtually, via live webcast at www.virtualshareholdermeeting.com/CALA2022 originating from South San Francisco,
California on Wednesday, June 1, 2022 at 10:00 a.m. local time. This supplement to the Proxy Statement, or this Supplement, is being furnished to the holders of common stock as of the record date, in connection with the solicitation of proxies
by our board of directors for the Annual Meeting, and at any adjournments and postponements of the Annual Meeting.
Proposal 5 in the
Proxy Statement includes a proposal to approve the issuance of more than 20% of our issued and outstanding common stock. After making the Proxy Statement available to stockholders, on May 23, 2022, we filed a Certificate of Amendment to the
Certificate of Designations filed with the Secretary of State of the State of Delaware, or the Certificate of Amendment, which limits the aggregate number of shares of common stock to be issued upon conversion of the Series A Convertible Preferred
Stock to a maximum of 132,880,282 shares of common stock (subject to adjustment in the event of a stock split, stock dividend, combination or other proportionate adjustment).
This Supplement to the Proxy Statement is being released on or about May 23, 2022 and should be read in conjunction with the Proxy
Statement. The information contained in this Supplement to the Proxy Statement modifies or supersedes any inconsistent information contained in the Proxy Statement. The information provided above may be deemed additional soliciting
materials within the meaning of the Securities Exchange Act of 1934, as amended.
Calithera encourages stockholders to vote and
submit their proxy in advance of the Annual Meeting by one of the methods described in the proxy materials for the Annual Meeting.
PROPOSAL 5
APPROVAL OF THE ISSUANCE OF MORE THAN 20% OF OUR ISSUED AND OUTSTANDING COMMON STOCK
Proposal 5 of the Proxy Statement seeks the
approval of our stockholders for the issuance of shares of common stock in excess of the Share Cap (as defined in the Certificate of Designations), specifically the conversion of the Series A preferred stock into common stock with such
full-ratchet, anti-dilution price protections as in effect pursuant to the Certificate of Designations.
On May 23, 2022,
we filed the Certificate of Amendment to the Certificate of Designations to limit the aggregate number of shares of common stock to be issued upon conversion of the Series A Convertible Preferred Stock to a maximum of 132,880,282 shares of common
stock (subject to adjustment in the event of a stock split, stock dividend, combination or other proportionate adjustment).
Accordingly,
the following shall replace the entirety of the Dilutive Effect of Issuances of Common Stock section for Proposal No. 5 of the Proxy Statement:
Dilutive Effect of Issuances of Common Stock
The Series A preferred stock may be converted into common stock at the election of Millennium, resulting in a potential issuance of at least
17,156,863 shares of common stock. If the price-based anti-dilution adjustments are triggered the conversion of the Series A preferred stock would result in the issuance of additional shares of common stock at the time of conversion. If the
price-based full ratchet anti-dilution occurs, it would result in significant dilution in ownership interests and voting rights to our stockholders. Pursuant to the Certificate of Amendment to the Certificate of Designations that we
filed on May 23, 2022, the maximum number of shares of common stock to be issued upon the conversion of the Series A Preferred Stock shall not exceed 132,880,282 shares (subject to adjustment in the event of a stock split, stock dividend,
combination or other proportionate adjustment).