UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-K/A

(Amendment No. 1)

For the fiscal year ended: December 31, 2012

For the transition period from             to             

Commission File Number 000-52228

SORRENTO THERAPEUTICS, INC.

(Exact Name of Registrant as Specified in Its Charter)

(858) 210-3700

(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:    None

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

Common Stock, par value $0.0001 per share

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

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Exchange Act.    ¨ Yes    x 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 the filing requirements for at least the past 90 days.    x Yes    ¨ No

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (Section 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    x Yes    ¨ No

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§229.405 of this chapter) is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.    x

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

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

The aggregate market value of voting stock held by non-affiliates of the registrant is calculated based upon the closing sale price of the common stock on June 30, 2012 (the last trading day of the registrant’s second fiscal quarter of 2012), as reported on the Over-the-Counter Bulletin Board, and such aggregate market value was approximately $33,667,189.

At March 22, 2013, the registrant had 336,075,440 shares of common stock outstanding.

EXPLANATORY NOTE

This Amendment No. 1 (this “Amendment”) to the Annual Report on Form 10-K for the period ended December 31, 2012 (the “Form 10-K”) of Sorrento Therapeutics, Inc. is being filed for the purpose of furnishing Exhibit 101 to the Form 10-K in accordance with Rule 405 of Regulation S-T. Exhibit 101 to this report provides the consolidated financial statements and related notes from the Form 10-K formatted in eXtensible Business Reporting Language (“XBRL”). The Interactive Data File Exhibits were incomplete in the earlier filing.

Pursuant to Rule 406T of Regulation S-T, the interactive data files on Exhibit 101 hereto are deemed not filed or part of a registration statement or prospectus for purposes of Sections 11 or 12 of the Securities Act of 1933, as amended, are deemed not filed for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, and otherwise are not subject to liability under those sections.

No attempt has been made in this Amendment to modify or update the other disclosures presented in the Form 10-K. This Amendment does not reflect events occurring after the filing of the Form 10-K (i.e., occurring after March 25, 2013) or modify or update those disclosures that may be affected by subsequent events. Such subsequent matters are addressed in subsequent reports filed by the registrant with the SEC. Accordingly, this Amendment should be read in conjunction with the Form 10-K and the registrant’s other filings with the SEC.

(a)(3) Exhibits

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this Amendment No. 1 to its Annual Report on Form 10-K to be signed on its behalf by the undersigned, thereunto duly authorized.

Pursuant to the requirements of the Securities Exchange Act of 1934, this Amendment No. 1 to the Annual Report on Form 10-K has been signed below by the following persons on behalf of the Registrant and in the capacities and on the dates indicated.