PhaseRx Receives Positive Opinion for Orphan Drug Designation for PRX-OTC from European Medicines Agency

SEATTLE, April 25, 2017 /PRNewswire/ -- PhaseRx, Inc. (NASDAQ: PZRX), a biopharmaceutical company developing mRNA treatments for life-threatening inherited liver diseases in children, today announced that the European Medicines Agency's (EMA) Committee for Orphan Medicinal Products (COMP) has issued a positive opinion recommending orphan medicinal product (orphan drug) designation for PRX-OTC for the treatment of ornithine transcarbamylase deficiency (OTCD). OTCD is a rare genetic disorder characterized by a complete or partial lack of the enzyme ornithine transcarbamylase, an essential urea cycle enzyme that facilitates the break down and removal of ammonia from the body.

"This positive opinion recommending orphan drug designation for PRX-OTC in the European Union represents another important step forward towards potentially bringing this novel therapy to patients that suffer from the devastating effects of OTCD," said Robert W. Overell, Ph.D., president and chief executive officer of PhaseRx. "We believe that PRX-OTC, with its first-in-class mechanism of action that can replace the missing protein in these patients, may address this significant unmet medical need."

Applications for orphan designation are initially reviewed by the COMP. Positive opinions are then forwarded to the European Commission, which is responsible for formally granting the orphan designation. Orphan medicinal product designation in the European Union is given to products that are intended for the treatment, prevention or diagnosis of a disease that is life-threatening or chronically debilitating; where prevalence of the condition in the EU is less than 5 in 10,000; and where the product represents a significant benefit over existing treatments.

About PRX-OTC for Ornithine Transcarbamylase Deficiency

Ornithine Transcarbamylase (OTC) is an enzyme in the urea cycle, the body's pathway for metabolizing ammonia which results from protein breakdown. Ornithine Transcarbamylase Deficiency (OTCD), a rare liver disorder caused by an inherited single-gene deficiency, results in hyperammonemia (elevated ammonia in the blood), often leading to irreversible neurological impairment, coma and death. PRX-OTC is an intracellular enzyme replacement therapy (i-ERT) designed to replace the missing or defective enzyme inside the cells of patients with OTCD. PRX-OTC has shown therapeutic potential in a preclinical model of OTCD, including lowering of blood ammonia and survival of 100% of treated mice. PRX-OTC has received Orphan Drug Designation by the U.S. Food and Drug Administration.

About PhaseRx

PhaseRx is a biopharmaceutical company developing a portfolio of mRNA products to correct life-threatening inherited liver diseases in children. PhaseRx's initial product development focus is on urea cycle disorders, a group of rare genetic diseases that generally present before the age of 12 and are characterized by the body's inability to remove ammonia from the blood. The company's i-ERT approach is enabled by its proprietary Hybrid mRNA Technology^TM platform and is applicable to a significant number of inherited liver diseases. PhaseRx is headquartered in Seattle. For more information, please visit www.phaserx.com.

Safe Harbor Statement

This press release contains "forward-looking statements." Such statements may be preceded by the words "intends," "may," "will," "plans," "expects," "anticipates," "projects," "predicts," "estimates," "aims," "believes," "hopes," "potential" or similar words. Forward-looking statements are not guarantees of future performance, are based on certain assumptions and are subject to various known and unknown risks and uncertainties, many of which are beyond the company's control, and cannot be predicted or quantified and consequently, actual results may differ materially from those expressed or implied by such forward-looking statements. Such risks and uncertainties include, without limitation, risks and uncertainties associated with (i) the fact that the company has incurred significant losses since its inception and anticipates that it will continue to incur significant losses for the foreseeable future, (ii) the company being dependent on technologies it has licensed and that it may need to license in the future, (iii) the fact that the company will need to raise substantial additional funding to develop its planned products, (iv) the fact that the company's Hybrid mRNA Technology has not previously been tested beyond company preclinical studies, and that mRNA-based drug development is unproven, (v) the fact that all of the company's programs are in preclinical studies or early stage research and it is uncertain that any company product candidates will receive regulatory approval or be commercialized, (vi) the fact that development of the company's product candidates will be expensive, time-consuming and subject to regulatory approval, (vii) the company expecting to continue to incur significant research and development expenses, (viii) the company becoming dependent on collaborative arrangements for the development and commercialization of its products, (ix) the company's ability to adequately protect its proprietary technology from legal challenges, infringement or alternative technologies and (x) the biotechnology and pharmaceutical industries being intensely competitive. More detailed information about the company and the risk factors that may affect the realization of forward looking statements is set forth in the company's filings with the Securities and Exchange Commission (SEC), including the most recent annual report on Form 10-K and its quarterly reports on Form 10-Q. Investors and security holders are urged to read these documents free of charge on the SEC's web site at http://www.sec.gov. The company assumes no obligation to publicly update or revise its forward-looking statements as a result of new information, future events or otherwise.

Contacts:

Company Contact:
Erin Cox
PhaseRx, Inc.
Director of Investor Relations
erin@phaserx.com
206.805.6306

Corporate Communications Contact:
Jason Spark
Canale Communications
Senior Vice President
jason@canalecomm.com
619.849.6005

Investor Contact:
Robert H. Uhl
Westwicke Partners, LLC
Managing Director
robert.uhl@westwicke.com
858.356.5932

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