Metabasis Announces European Commission Grants Orphan Medicinal Product Designation to MB07133, Its Product Candidate for the Treatment of Primary Liver Cancer.

SAN DIEGO -- Metabasis Therapeutics (Nasdaq:MBRX) announced today that MB07133 has been granted orphan medicinal product status for the treatment of hepatocellular carcinoma (HCC), or primary liver cancer, by the European Commission (EC). This designation is based on a recommendation from the Committee for Orphan Medicinal Products (COMP) of the European Agency for the Evaluation of Medicinal Products (EMEA).

MB07133 is a novel HepDirect([R]) prodrug of cytarabine monophosphate (araCMP) designed to produce the oncolytically active form, cytarabine triphosphate (araCTP), in the liver tumor where it acts to inhibit cell proliferation and cause DNA damage resulting in cell death. Preliminary results from a Phase 1/2 clinical trial for MB07133, which was completed in the second quarter of this year, were presented at the Annual Meeting of the American Association for Cancer Research (AACR) in April 2007. This first dose escalation trial showed that MB07133 was well tolerated at doses up to 2400 mg/m2/day when administered as a 7 day continuous IV infusion to patients with unresectable HCC. No clinically significant dose-limiting toxicities associated with the therapy and few treatment-related hepatic adverse events were observed. Additionally, the trial revealed encouraging signs of drug activity evidenced by intra-hepatic tumor shrinkage and prolonged disease stabilization in some patients. Intra-hepatic tumor reduction was observed in eight patients (29% of those studied), and increased median overall survival was seen in these patients relative to the other patients in the study.

Primary liver cancer represents the fifth most common and third most deadly cancer worldwide and is reported to claim as many as one million lives a year1,2. In addition, up to one million new cases of primary liver cancer occur worldwide each year3-10. In Europe and the U.S., incidence of HCC has tripled in the last 15 years and is increasing at 6-8% per year. In 2006, there were 15,000-20,000 cases of HCC reported in the U.S. and 35,000-40,000 in Europe, while there were almost 500,000 in parts of Asia2.

"HCC is a devastating disease in Africa and Eastern Asia and is on the rise in the developed world, including Europe and the U.S.," commented Dr. Paul Laikind, president and chief executive officer. "Patients with primary liver cancer often die within months of diagnosis and at this time, they face this disease without any approved drug therapy. This orphan medicinal product designation in the EU builds upon our previous success of obtaining orphan drug designation for MB07133 in the US. Both will help in the development of this product candidate and bring hope of a new treatment option to liver cancer patients in Europe and the U.S."

"The granting of orphan medicinal product designation to MB07133 by the EC is an important piece of the global regulatory strategy for the development of this product candidate in the European Union," stated Dr. Wayne Frost, vice president, regulatory affairs. "This designation provides protocol assistance in which the EMEA will provide advice on the development of MB07133, which should improve the chance of success at the time of marketing authorization to commercialize this much needed therapy."

Orphan Medicinal Product Designation in the European Union

The EU orphan medicinal product designation aims to encourage the development of drugs involved in the diagnosis, prevention or treatment of a life-threatening or chronically debilitating condition that affects no more than five in 10,000 persons in the European Union. Orphan medicinal product designation for MB07133 would entitle Metabasis Therapeutics to ten years of market exclusivity for MB07133 in the event it is approved for the treatment of hepatocelluar carcinoma. Additional incentives include protocol assistance to advise on the development of orphan medicinal products, fee reductions for marketing authorization and eligibility for grants.

About Metabasis (www.mbasis.com):

Metabasis Therapeutics is a biopharmaceutical company focused on the discovery, development and commercialization of novel drugs to address some of the world's most widespread and costly chronic diseases involving pathways in the liver. The Company has established a pipeline that includes clinical stage and preclinical product candidates targeting major diseases with significant unmet medical needs. Targeted diseases include major metabolic diseases such as diabetes, hyperlipidemia and obesity as well as liver diseases such as hepatitis and primary liver cancer. Metabasis has developed several proprietary technologies for use in discovering and optimizing drugs, including the NuMimetic([TM]) and HepDirect([R]) technologies. Metabasis is continuing to identify and develop new product candidates using its proprietary technologies and expertise.

Forward-Looking Statements:

Statements in this press release that are not strictly historical in nature constitute "forward-looking statements." Such statements include, but are not limited to, references to the potential efficacy of MB07133 as well as the potential advantages of orphan medicinal product designation for MB07133. Forward-looking statements involve known and unknown risks, uncertainties and other factors which may cause Metabasis' actual results to be materially different from historical results or from any results expressed or implied by such forward-looking statements. These factors include, but are not limited to, the progress and timing of clinical trials for Metabasis' product candidates; the fact that positive results from clinical trials does not necessarily mean later clinical trials will succeed; serious adverse side effects of, or serious adverse events related to, Metabasis' product candidates or proprietary technologies; difficulties or delays in development, testing, obtaining regulatory approval, producing and marketing Metabasis' product candidates; the potential and progress of preclinical compounds and programs; and other factors discussed in the "Risk Factors" section of Metabasis' Quarterly Report on Form 10-Q for the quarter ended June 30, 2007. All forward-looking statements are qualified in their entirety by this cautionary statement. Metabasis is providing this information as of this date of this release and does not undertake any obligation to update any forward-looking statements contained in this release as a result of new information, future events or otherwise.

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