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

Mast Therapeutics, Inc.
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(Exact name of registrant as specified in its charter)

Not Applicable
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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:

[  ]  Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)
[  ]  Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)
[  ]  Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))
[  ]  Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

On June 19, 2013, the stockholders of Mast Therapeutics, Inc. (the “Company”) approved the Mast Therapeutics, Inc. 2013 Omnibus Incentive Plan (the “2013 Plan”) at the Company’s 2013 Annual Meeting of Stockholders (the “Annual Meeting”) and it became effective as of that date. The Company’s board of directors (the “Board”) approved the 2013 Plan on March 21, 2013, subject to stockholder approval at the Annual Meeting. The Company’s directors and employees, including its principal executive officer, president and principal operating officer, chief medical officer (who is a named executive officer), and principal financial and accounting officer, are eligible to participate in the 2013 Plan.

On June 19, 2013, after the Annual Meeting, the independent members of the Board granted stock option awards under the 2013 Plan to all of the Company’s employees and non-employee directors. The option awards have a 10-year term and an exercise price of $0.50 per share, which is a greater than 10% premium to the fair market value of the Company’s common stock on the grant date based on the closing sale price of $0.45 per share on the NYSE MKT on June 19, 2013. The employee option awards vest and become exercisable over a minimum of a 48-month period from the grant date and the director option awards vest and become exercisable over a 12-month period from the grant date. In December 2012, the Board’s compensation committee had determined to change its general practice of granting employee options once a year at the beginning of the year to a twice-yearly schedule, with one grant generally occurring around the beginning of the year and the other generally occurring around the time of the Company’s annual meeting of stockholders. The sizes of the option awards granted to employees were determined based on what the Company refers to as a “carried interest” framework and a target carried interest percentage for each employee, as described in the Company’s definitive proxy statement for the for the Annual Meeting filed with the Securities and Exchange Commission (“SEC”) on April 29, 2013 (the “Proxy Statement”). The size of the option awards granted to non-employee directors was determined based on the Company’s Director Compensation Policy, adopted on March 21, 2013, as described in the Proxy Statement.

On June 19, 2013, the independent members of the Board also approved the following stock option grant agreement forms, for use under the 2013 Plan for awards to the Company’s non-employee directors and employees, including its executive officers: (a) form of Non-Statutory Stock Option Grant Agreement — Director (for grants to non-employee directors); (b) form of Incentive Stock Option Grant Agreement (for grants to employees); (c) form of Senior Executive Incentive Stock Option Grant Agreement (for grants to the registrant’s chief executive officer and president and chief operating officer); and (d) form of CMO Incentive Stock Option Grant Agreement (for grants to the registrant’s chief medical officer). Copies of the forms described in (a) through (d) in the preceding sentence are attached as Exhibits 10.2, 10.3, 10.4 and 10.5, respectively.

The 2013 Plan amends, restates and renames the Amended and Restated 2008 Omnibus Incentive Plan, which the Company’s stockholders approved at its 2011 annual meeting of stockholders (the “Amended and Restated 2008 Plan”), and, accordingly, no new awards may be granted under the Amended and Restated 2008 Plan, which was the Company’s sole active plan for providing equity compensation to eligible employees, non-employee directors and consultants prior to June 19, 2013. All outstanding awards under the Amended and Restated 2008 Plan and the Company’s 2008 Omnibus Incentive Plan and 2005 Equity Incentive Plan (collectively, the “Prior Plans”) will continue to be governed by under the terms of those plans.

The principal differences between the 2013 Plan and the Amended and Restated 2008 Plan are as follows:

A more detailed summary of the 2013 Plan is set forth in “Proposal 3 — Approval of the Mast Therapeutics, Inc. 2013 Omnibus Incentive Plan” in the Proxy Statement. The summary in this report of the principal differences between the 2013 Plan and the Amended and Restated 2008 Plan, and the more detailed summary of the 2013 Plan set forth in the Proxy Statement, are qualified in their entirety by reference to the 2013 Plan, a copy of which is filed as Exhibit 10.1 to this report.

Item 5.07. Submission of Matters to a Vote of Security Holders.

On June 19, 2013, the Company held the Annual Meeting. The following is a brief description of each matter voted upon at the Annual Meeting and final voting results showing the number of votes cast for and against (or, with respect to Proposal 5, the number of votes cast for 1 Year, 2 Years and 3 Years), as well as the number of abstentions and broker non-votes as to each such matter, as applicable.

Proposal 1 – To elect five directors to hold office until the next annual meeting of stockholders and until their respective successors are elected and qualified or until their earlier resignation or removal:

In accordance with the above results, each nominee was elected to serve as director.

Proposal 2 — To ratify the appointment of PricewaterhouseCoopers LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2013:

In accordance with the above results, the appointment of PricewaterhouseCoopers LLP was ratified.

Proposal 3 — To approve the Mast Therapeutics, Inc. 2013 Omnibus Incentive Plan:

In accordance with the above results, the Mast Therapeutics, Inc. 2013 Omnibus Incentive Plan was approved.

Proposal 4 – To approve, on an advisory basis, the compensation of the Company’s named executive officers, as disclosed in the Proxy Statement:

In accordance with the above results, the compensation of the Company’s named executive officers, as disclosed in the Proxy Statement, was approved on an advisory basis.

Proposal 5 – To indicate, on an advisory basis, the preferred frequency of stockholder advisory votes on the compensation of the Company’s named executive officers:

In accordance with the above results, the stockholders indicated, on an advisory basis, that the preferred frequency of stockholder advisory votes on the compensation of the Company’s named executive officers is once every three years.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

The list of exhibits called for by this Item is incorporated by reference to the Exhibit Index filed with this report.

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.

Exhibit Index