Edgar Filing: Mast Therapeutics, Inc.

Mast Therapeutics, Inc.

August 9, 2013

/s/ Patrick L. Keran

Name: Patrick L. Keran

Title: President and Chief Operating Officer

424B3

Filed Pursuant to Rule 424(b)(3)
Registration No. 333-188870

Prospectus Supplement No. 3

(To prospectus dated June 14, 2013)

LOGO

Warrants to Purchase up to 28,097,500 Shares of Common Stock

This Prospectus Supplement No. 3 (the “Prospectus Supplement”) supplements our Prospectus dated June 14, 2013 and Prospectus Supplements No. 1 and 2 dated June 26, 2013 and August 5, 2013, respectively (together, the “Prospectus”), relating to the issuance of up to 28,097,500 shares of our common stock issuable upon exercise of outstanding warrants issued in connection with our registered offering which closed on June 19, 2013. We cannot predict when or if the warrants will be exercised, and it is possible that the warrants may expire and never be exercised.

Recent Developments

This Prospectus Supplement is being filed to update and supplement the information in the Prospectus with the information contained in our Current Report on Form 8-K filed with the Securities and Exchange Commission on August 9, 2013 (the “Current Report”). Accordingly, we have attached the Current Report to this Prospectus Supplement. Any statement contained in the Prospectus shall be deemed to be modified or superseded to the extent that information in this Prospectus Supplement modifies or supersedes such statement. Any statement that is modified or superseded shall not be deemed to constitute a part of the Prospectus except as modified or superseded by this Prospectus Supplement.

This Prospectus Supplement should be read in conjunction with, and may not be delivered or utilized without, the Prospectus.

In reviewing this Prospectus Supplement, you should carefully consider the matters described under the caption “Risk Factors” beginning on page 4 of the Prospectus.

Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved these securities or determined if this Prospectus Supplement is truthful or complete. Any representation to the contrary is a criminal offense.

This Prospectus Supplement does not constitute an offer to sell or the solicitation of an offer to buy any securities.

The date of this Prospectus Supplement is August 9, 2013

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): August 6, 2013

Mast Therapeutics, Inc.

(Exact name of registrant as specified in its charter)


Delaware	001-32157	84-1318182
(State or other jurisdiction	(Commission	(I.R.S. Employer
of incorporation)	File Number)	Identification No.)

12390 El Camino Real, Suite 150,

San Diego, California

92130

(Address of principal executive offices)

(Zip Code)

Registrant’s telephone number, including area code: 858-552-0866

Not Applicable

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.

Following discussions with management and members of the board of directors of Mast Therapeutics, Inc. (the “Company”) regarding his current and planned commitments outside of his duties as a member of the Company’s board of directors, on August 6, 2013, Ted W. Love delivered notice to the Company of his resignation from the Company’s board of directors and from all committees of the board, which was effective the following day. Dr. Love resigned due to other commitments and not due to any disagreement with the Company known to any of its executive officers on any matter relating to the Company’s operations, policies or practices.

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.