UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-K/A

(Amendment No. 1)

(Mark One)

For the fiscal year ended December 31, 2019

OR

For the transition period from                 to                

Commission File Number 001-38662

SUTRO BIOPHARMA, INC.

(Exact Name of Registrant as Specified in Its Charter)

(650) 392-8412

(Registrant’s telephone number, including area code)

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

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

None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    Yes   ☐     No   ☒

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.    Yes   ☐     No   ☒

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  ☒    No  ☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).    Yes  ☒    No  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

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. ☐

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    Yes  ☐    No  ☒

The aggregate market value of the voting and non-voting common equity held by non-affiliates of the Registrant on June 28, 2019 (the last business day of the Registrant’s second fiscal quarter), based upon the closing price of $11.38 of the Registrant’s common stock as reported on The Nasdaq Global Market, was approximately $235.6 million.

The number of shares of the registrant’s common stock outstanding as of March 9, 2020, was 23,098,969.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s definitive proxy statement filed for its 2020 Annual Meeting of Stockholders are incorporated by reference into Part III hereof. Such proxy statement was filed with the Securities and Exchange Commission within 120 days of the end of the fiscal year covered by this Annual Report on Form 10-K.

EXPLANATORY NOTE

We are filing this Amendment No. 1 to Annual Report on Form 10-K/A (this “Amendment”) to amend our Annual Report on Form 10-K for the fiscal year ended December 31, 2019, as filed with the Securities and Exchange Commission (the “SEC”) on March 16, 2020 (the “10-K”). This Amendment is being filed solely to refile the certifications of our principal executive officer and principal financial officer as exhibits to this Amendment as required pursuant to Rules 13a-14(a) and 15d-14(a) under the Securities and Exchange Act of 1934.

No attempt has been made in this Amendment to otherwise modify or update the other disclosures presented in the 10-K. This Amendment does not reflect events occurring after the filing of the original 10-K (i.e., those events occurring after March 16, 2020) or modify of update those disclosures that may be affected by subsequent events. Such subsequent matters are addressed in subsequent reports filed with the SEC. Accordingly, this Amendment should be read in conjunction with the 10-K and our other filings with the SEC.

PART IV

(1)Financial Statements:

The financial statements required by Item 15(a) are filed as part of this Annual Report on Form 10-K under Item 8 “Financial Statements and Supplementary Data.”

(2)Financial Statement Schedules

The financial statement schedules required by Item 15(a) are omitted because they are not applicable, not required or the required information is included in the financial statements or notes thereto as filed in Item 8 of this Annual Report on Form 10-K.

(3)Exhibits.

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) the Securities Exchange Act of 1934, the registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized.

Pursuant to the requirements of the Securities Exchange Act of 1934, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.