SAN DIEGO, June 14, 2013 /PRNewswire/ -- Mast Therapeutics, Inc. (NYSE MKT: MSTX) today announced the pricing of an underwritten public offering of 50,000,000 units, each unit consisting of a fixed combination of one share of common stock and one warrant to purchase 0.5 of a share of common stock, at a public offering price of $0.50 per unit. The units will not be issued or certificated and the shares of common stock and the warrants are immediately separable and will be issued separately, but purchased together. Each warrant will have an exercise price of $0.65 per share and will expire five years from the date of issuance. The Company has granted the underwriters a 30-day option to purchase up to an additional 7,500,000 units to cover over-allotments, if any. The offering is expected to close on June 19, 2013, subject to customary closing conditions. All of the shares in the offering are being sold by the Company. The Company expects to receive net proceeds from the offering of approximately $22.9 million, after deducting underwriting discounts and commissions and estimated offering expenses. The Company intends to use the net proceeds primarily to fund EPIC, the Company's phase 3 clinical study of MST-188 in sickle cell disease, and for working capital and general corporate purposes. Piper Jaffray & Co. is acting as the sole book-running manager of the offering and Canaccord Genuity Inc. is acting as lead manager of the offering. JMP Securities LLC and Brinson Patrick Securities Corporation are acting as financial advisors in connection with the offering. A registration statement relating to the public offering of the securities described above has been filed with the Securities and Exchange Commission and was declared effective June 14, 2013. The offering may be made only by means of a prospectus. A copy of the final prospectus may be obtained by contacting: Piper Jaffray & Co., 800 Nicollet Mall, J12S03, Minneapolis, Minnesota 55402, or by telephone at (800) 747-3924, or by e-mail at firstname.lastname@example.org. This press release shall not constitute an offer to sell or the solicitation of an offer to buy these securities, nor shall there be any sale of these securities in any state or other jurisdiction in which such offer, solicitation, or sale would be unlawful prior to the registration or qualification under the securities laws of any such state or other jurisdiction.