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): September 26, 2017

SORRENTO THERAPEUTICS, INC.

(Exact Name of Registrant as Specified in its Charter)

4955 Directors Place

San Diego, CA 92121

(Address of Principal Executive Offices) (Zip Code)

Registrant’s telephone number, including area code: (858) 203-4100

N/A

(Former Name, or Former Address, if Changed Since Last Report)

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:

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. ¨

Item 5.02. Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

Effective September 26, 2017, the Board of Directors (the “Board”) of Sorrento Therapeutics, Inc. (the “Company”) appointed each of Dorman Followwill and David Lemus as directors of the Company. Mr. Followwill will serve as a member of the Compensation Committee of the Board and Mr. Lemus will serve as a member of the Audit Committee of the Board.

Dorman Followwill, age 54, has been Senior Partner, Transformational Health at Frost & Sullivan, a business consulting firm involved in market research and analysis, growth strategy consulting and corporate training across multiple industries, since 2016. Prior to that time, he served in various roles at Frost & Sullivan, including Partner on the Executive Committee managing the P&L of the business in Europe, Israel and Africa, and Partner overseeing the Healthcare and Life Sciences business in North America, since initially joining Frost & Sullivan to help found the Consulting practice in January 1988. Mr. Followwill has more than 30 years of organizational leadership and management consulting experience, having worked on hundreds of consulting projects across all major regions and across multiple industry sectors, each project focused around the strategic imperative of growth. He obtained his BA from Stanford University in The Management of Organizations in 1985.

David Lemus, age 54, currently serves as a non-executive board member of BioHealth Innovation, Inc., The MIT Club of Washington DC and Proteros BioScience GmbH. From January 2016 to May 2017, he served as Interim Chief Financial Officer and Chief Operating Officer of Medigene AG, a publicly-listed German biotechnology company focused on the research and development of T-Cell-Receptor based immunotherapies. Prior to that time, at Sigma Tau Pharmaceuticals, Inc., he served as Chief Executive Officer from January 2013 to July 2015, as Chief Operating Officer from March 2012 to December 2012, and as V.P. Finance from July 2011 to February 2012. Previous to this, Mr. Lemus served as Chief Financial Officer and Executive V.P. of MorphoSys AG from January 1998 to May 2011. Prior to his role at MorphoSys AG, he held various positions, including Operations Manager and Controller (Pharma International Division) and Global IT Project Manager (Pharma Division) at Hoffman La Roche, Group Treasurer of Lindt & Spruengli AG and Treasury Consultant for Electrolux AB. Mr. Lemus received an M.S. from the Massachusetts Institute of Technology Sloan School of Management in 1988 and a B.S. in Accounting from the University of Maryland in 1984. Mr. Lemus is also a certified public accountant licensed in the State of Maryland.

On the third trading day following the date of public disclosure of the Company’s financial results for the quarter ending September 30, 2017, each of Mr. Followwill and Mr. Lemus will be granted an option to purchase 35,000 shares of the Company’s common stock that will vest on monthly basis commencing on September 26, 2017. Each option will have an exercise price that is equal to the closing price of the Company’s common stock on the date of grant. As non-employee directors, each of Mr. Followwill and Mr. Lemus will also be entitled to receive the Company’s standard cash retainers for membership on the Board and the committees of the Board, as disclosed under “New Outside Director Compensation Policy” in the Company’s definitive proxy statement for its 2017 Annual Meeting of Stockholders on Schedule 14A filed with the Securities and Exchange Commission on June 26, 2017.

The Company also entered into an indemnification agreement with each of Mr. Followwill and Mr. Lemus in the same form as its standard form of indemnity agreement with its other directors.

There are no family relationships between Mr. Followwill or Mr. Lemus and any director or executive officer of the Company and neither of them was selected by the Board to serve as a director pursuant to any arrangement or understanding with any person. Neither Mr. Followwill nor Mr. Lemus has engaged in any transaction that would be reportable as a related party transaction under Item 404(a) of Regulation S-K.

On October 2, 2017, the Company issued a press release announcing the appointments of Mr. Followwill and Mr. Lemus to the Board. A copy of the press release is filed herewith as Exhibit 99.1.

Item 9.01. Financial Statements and Exhibits.

(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.