UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d)

of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): March 11, 2020

Calithera Biosciences, Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (650) 870-1000

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-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.  ☐

In this report, “Calithera,” “we,” “us” and “our” refer to Calithera Biosciences, Inc.

On March 11, 2020, Calithera issued a press release announcing its financial results for the quarter ended December 31, 2019. A copy of this press release is attached hereto as Exhibit 99.1.

In accordance with General Instruction B.2 of Form 8-K, the information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liability of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, whether made before or after the date hereof, except as expressly set forth by specific reference in such filing to this Current Report on Form 8-K.

Sales Agreement

On March 11, 2020, Calithera entered into an Open Market Sale Agreement (the “Sales Agreement”) with Jefferies LLC, as agent (“Jefferies”), pursuant to which we may offer and sell, from time to time through Jefferies, shares of our common stock, par value $0.0001 per share (the “Common Stock”), having an aggregate offering price of up to $50.0 million (the “Shares”). The Shares will be sold pursuant to our effective registration statement on Form S-3 (Registration Statement No. 333-219791), as previously filed with the Securities and Exchange Commission. We filed a prospectus supplement, dated March 11, 2020, with the Securities and Exchange Commission in connection with the offer and sale of the Shares.

Under the Sales Agreement, Jefferies may sell the Shares by any method permitted by law and deemed to be an “at the market offering” as defined in Rule 415 promulgated under the Securities Act of 1933, as amended (the “Securities Act”), including sales made directly on the Nasdaq Global Select Market, on any other existing trading market for the Common Stock or to or through a market maker. In addition, under the Sales Agreement, Jefferies may sell the Shares by any other method permitted by law, including in privately negotiated transactions. We may instruct Jefferies not to sell the Shares if the sales cannot be effected at or above the price designated by us from time to time.

We are not obligated to make any sales of the Shares under the Sales Agreement. The offering of the Shares pursuant to the Sales Agreement will terminate upon the earlier of (a) the sale of all of the Shares subject to the Sales Agreement or (b) the termination of the Sales Agreement by Jefferies or us, as permitted therein.

The Sales Agreement contains customary representations, warranties and agreements by us, and customary indemnification and contribution rights and obligations of the parties. We will pay Jefferies a commission rate of up to 3.0% of the aggregate gross proceeds from each sale of the Shares. We will also reimburse Jefferies for certain specified expenses in connection with entering into the Sales Agreement.

The Sales Agreement is filed as Exhibit 1.1 to this report, and the description of the terms of the Sales Agreement is qualified in its entirety by reference to such exhibit. A copy of the opinion of Cooley LLP relating to the legality of the issuance and sale of the Shares is attached as Exhibit 5.1 hereto.

(d) Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.