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May 2, 2006 — The US Food and Drug Administration (FDA) has approved orphan drug indications for thymalfasin injection in the treatment of stage 2b through stage 4 malignant melanoma, and sorafenib tosylate tablets in the treatment of hepatocellular carcinoma.

Orphan Drug Thymalfasin Injection (Zadaxin) for Malignant Melanoma

On March 13, the FDA approved orphan drug status for thymalfasin injection (Zadaxin, made by SciClone Pharmaceuticals, Inc) in the treatment of stage 2b through stage 4 malignant melanoma.

The synthetic version of thymosin alpha 1 belongs to a class of drugs known as biologic response modifiers. Although its mechanism of action remains unclear, the compound is thought to play a role in the eradication of virally infected cells and cancer cells by promoting T-cell maturation and increasing immune system response.

The approval was based in part on interim results from an ongoing open-label, multicenter, 4-group, phase 2 trial of 320 patients with stage 4 malignant melanoma. Patients were randomized to receive thymalfasin (1.6 mg and 3.2 mg), low-dose interferon-alfa, or both in addition to dacarbazine (DTIC) chemotherapy for six 1-month cycles and then followed for 1 year posttherapy.

Preliminary results in 270 patients have revealed that the addition of 3.2 mg of thymalfasin to DTIC chemotherapy is associated with a significant increase in overall tumor response compared with DTIC alone (12.9% vs 3.9%).

Furthermore, the efficacy of thymalfasin for achieving overall tumor response when added to DTIC chemotherapy plus low-dose interferon-alfa appears to be dose-related. In the study, doubling the dose of thymalfasin from 1.6 g to 3.2 g was linked to a significant increase in overall tumor response (7.4% vs 10.9%). A fifth treatment group has recently been added to evaluate the potential incremental benefit of a 6.4-mg dose in combination with DTIC and interferon-alfa.

According to the news release, adverse events observed to date in the trial have been consistent with those expected for this group of patients treated with DTIC and interferon-alfa. In other clinical trials of thymalfasin, the drug was generally well tolerated and no significant adverse reactions were reported.

Thymalfasin was previously granted traditional approval by the FDA for use alone or in combination with interferon therapy in the treatment of hepatitis B and hepatitis C. It is also being investigated for use in non-small cell lung cancer, hepatocellular carcinoma, and AIDS.

Orphan Drug Sorafenib Tosylate (Nexavar) for Hepatocellular Carcinoma

On April 26, the FDA approved orphan drug status for sorafenib tosylate (Nexavar tablets, made by Onyx Pharmaceuticals, Inc, and Bayer Pharmaceuticals Corporation; marketed by Bayer) in the treatment of hepatocellular carcinoma (HCC).

Sorafenib is an oral multikinase inhibitor that targets serine/threonine and receptor tyrosine kinases to decrease tumor growth and angiogenesis. Preclinical models demonstrated the drug's activity against RAF kinase, VEGFR-2, VEGFR-3, PDGFR-B, KIT, and FLT-3.

The approval was based in part on data from a phase 2, single-agent study showing that 43% of patients receiving sorafenib experienced stable disease for at least 4 months; an additional 9% of patients experienced tumor shrinkage.

Fatigue (9.5%), diarrhea (8%), and hand-foot skin reaction (5%) were most commonly reported in patients receiving sorafenib.

According to a company news release, the drug's toxicity profile was similar to that previously reported in studies of patients with renal cell carcinoma. In those studies, sorafenib was linked to an increased incidence of cardiac ischemia/infarction (2.9% vs 0.4%) and bleeding (15% vs 8%) compared with placebo. Because of the risk for hypertension early in the course of therapy, weekly monitoring of blood pressure is recommended during the first 6 weeks of treatment.

Further studies of sorafenib in HCC are ongoing, including a phase 3 trial designed to measure its benefit vs placebo with respect to overall survival, time to symptom progression, and time to tumor progression. A phase 2 trial is also being conducted to evaluate its use in combination with doxorubicin.

Sorafenib was previously granted orphan drug status for this indication by the European Commission on April 18. In the United States and Switzerland, it has also been granted traditional approval for the treatment of adults with advanced renal cell carcinoma after nephrectomy and prior palliative or adjuvant therapy with cytokines (such as interleukin 2 and interferon).

According to the news release, other potential indications for sorafenib include advanced HCC, metastatic melanoma, and non-small cell lung cancer.

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