Allos Therapeutics, Inc. announced that the US Food and Drug Administration (FDA) has awarded orphan drug designation to the company's novel, next-generation antifolate PDX (pralatrexate) for the treatment of patients with T-cell lymphoma. The company currently plans to initiate a phase 2 study of PDX in patients with relapsed or refractory peripheral T-cell lymphoma (PTCL) in the third quarter of 2006.

"This designation underscores the acute need for new therapies to treat T-cell lymphoma and provides Allos with potential market exclusivity and other benefits to support the development of PDX in this important clinical setting," said Paul L. Berns, president and chief executive officer.

Interim results from a phase 1/2 study of PDX in patients with relapsed or refractory non-Hodgkin's lymphoma (NHL) and Hodgkin's disease currently on-going at Memorial Sloan-Kettering Cancer Center demonstrated preliminary evidence of activity in patients with various subtypes of aggressive and chemotherapy resistant T-cell lymphoma. As reported at the 2005 American Society of Haematology Annual Meeting, four of seven evaluable patients with T-cell lymphoma achieved a complete response following treatment with PDX, despite having failed multiple prior chemotherapies. The addition of vitamins to the treatment regimen appeared to successfully mitigate the previously established dose-limiting toxicity of stomatitis.

The US Orphan Drug Act is intended to assist and encourage companies to develop safe and effective therapies for the treatment of rare diseases and disorders. Under the Orphan Drug Act, the FDA will not accept or approve other applications from other sponsors to market the identical medicinal products for the same therapeutic indication for a seven-year period once a designated orphan drug is approved for marketing. In addition to potential market exclusivity, orphan drug designation provides potential protocol assistance, advice on the conduct of clinical trials, tax credits for clinical research expenses, grant funding for research of rare disease treatments and waiver of the Prescription Drug User Fee Act (PDUFA) filing fee for the drug's sponsor.

PDX is a novel, next-generation small molecule chemotherapeutic agent that inhibits dihdrofolate reductase, or DHFR, a folic acid (folate) dependent enzyme involved in the building of DNA and other processes. PDX was rationally designed for improved transport into tumour cells via the reduced folate carrier (RFC-1), and greater intracellular drug retention. These biochemical features, together with preclinical data in a variety of tumours, suggest that PDX has an enhanced potency and toxicity profile relative to methotrexate and other related DHFR inhibitors.

Peripheral T-cell lymphomas, or PTCLs, are a biologically diverse group of blood cancers that account for approximately 10 per cent to 15 per cent of all cases of NHL, or about 6,700 patients. The average five year survival rate for PTCL patients is approximately 25 per cent. There are currently no pharmaceutical agents approved for the treatment of relapsed or refractory PTCLs.