Proteostasis Therapeutics Prices Public Offering of Common Stock

BOSTON, Oct. 23, 2018 /PRNewswire/ -- Proteostasis Therapeutics, Inc. (Nasdaq: PTI), a clinical stage biopharmaceutical company dedicated to the discovery and development of groundbreaking therapies to treat cystic fibrosis (CF) and other diseases caused by dysfunctional protein processing, announced today that it has priced an underwritten public offering of 11,000,000 shares of its common stock at a price to the public of $6.75 per share. The gross proceeds to Proteostasis from the offering, before underwriting discounts and commissions and offering costs, are expected to be approximately $74.3 million.  Proteostasis has granted the underwriters a 30-day option to purchase up to an additional 1,650,000 shares of common stock. All of the shares to be sold in the offering are being sold by Proteostasis. The offering is expected to close on or about October 26, 2018, subject to satisfaction of customary closing conditions. Proteostasis intends to use the net proceeds from the proposed offering to fund critical path activities for PTI-428 as an add on to standard of care and continue the advancement of PTI-proprietary combination therapies, for drug substance (API) for Phase 3 for PTI-428, PTI-801 and PTI-808, including starting material that can be used in registrational studies and for working capital and other general corporate purposes.

Leerink Partners, Piper Jaffray & Co. and Cantor Fitzgerald & Co. are acting as joint book-running managers for the offering. H.C. Wainwright & Co. is acting as lead manager for the offering.

The securities described above are being offered by Proteostasis pursuant to a shelf registration statement (File No. 333-224180), which was declared effective by the Securities and Exchange Commission (SEC) on April 26, 2018.

The securities may be offered only by means of a prospectus. A preliminary prospectus supplement related to the offering was filed with the SEC on October 23, 2018 and is available on the SEC's website  final prospectus supplement related to the offering will be filed with the SEC and will be available on the SEC's website Copies of the final prospectus supplement and the accompanying prospectus for the securities being offered may also be obtained, when available, from Leerink Partners LLC, Attention: Syndicate Department, One Federal Street, 37th Floor, Boston, MA 02110, by telephone at 800-808-7525, ext. Piper Jaffray & Co., 800 Nicollet Mall, J12S03, Minneapolis, MN, 55402, Attention: Prospectus Department, by telephone at (800) 747-3924 or by email and Cantor Fitzgerald & Co., Attention: Capital Markets, 499 Park Ave., 6th Floor, New York, New York 10022, or by e-mail at 

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 jurisdiction in which such offer, solicitation or sale would be unlawful prior to the registration or qualification under the securities laws of any such jurisdiction.

About Proteostasis Therapeutics, Inc.

Proteostasis Therapeutics, Inc. is a clinical stage biopharmaceutical company developing small molecule therapeutics to treat cystic fibrosis and other diseases caused by dysfunctional protein processing. Headquartered in Boston, MA, the Proteostasis Therapeutics team focuses on identifying therapies that restore protein function. In addition to its multiple programs in cystic fibrosis, Proteostasis Therapeutics has formed a collaboration with Astellas Pharma, Inc. to research and identify therapies targeting the Unfolded Protein Response (UPR) pathway.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of Section 21E of the Securities Exchange Act of 1934, as amended. All statements other than statements of historical facts contained in this press release are forward-looking statements, including statements regarding Proteostasis' expectations of market conditions and the satisfaction of customary closing conditions related to the public offering and the anticipated use of proceeds therefrom including the timing of our clinical trials. In some cases, you can identify forward-looking statements by terms such as "may," "will," "should," "expect," "plan," "anticipate," "could," "intend," "target," "project," "contemplates," "believes," "estimates," "predicts," "potential" or "continue" or the negative of these terms or other similar expressions. These forward-looking statements speak only as of the date of this press release and are subject to a number of risks, uncertainties and assumptions, including the risks and uncertainties associated with market conditions and the satisfaction of customary closing conditions related to the public offering, as well as risks and uncertainties inherent in Proteostasis' business, including those described in the company's periodic filings with the SEC. The events and circumstances reflected in the company's forward-looking statements may not be achieved or occur and actual results could differ materially from those projected in the forward-looking statements. Additional information on risks facing Proteostasis can be found under the heading "Risk Factors" in Proteostasis' periodic reports, including its annual report on Form 10-K for the year ended December 31, 2017, its quarterly report on Form 10-Q for the quarter ended June 30, 2018 and in the preliminary prospectus supplement related to the proposed offering filed with the SEC on October 23, 2018, each available on the SEC's web site at  Except as required by applicable law, the company does not plan to publicly update or revise any forward-looking statements contained herein, whether as a result of any new information, future events, changed circumstances or otherwise.

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