Fanny Chan, Erika E. Samlowski and Wolfram E. Samlowski

From the Section of Melanoma, Renal Cancer and Immunotherapy of the Nevada Cancer Institute, Las Vegas, NV, USA

Abstract

The mTOR (mammalian target of rapamycin) signaling pathway was discovered during studies of the immunosuppressive agent rapamycin. This pathway regulates cell growth, protein synthesis and angiogenesis in response to environmental factors. The mTOR complex-1 inhibitor temsirolimus was derived from rapamycin to have less immuno-suppressive and improved solubility characteristics. The safety, tolerability and efficacy of temsirolimus have been well established in clinical trials. Drug related toxicity included rash, mucositis, asthenia, nausea, hyperglycemia, hypophospha- temia, anemia, and hypertriglyceridemia. An active and well-tolerated single agent dose is 25 mg i.v. weekly. A large Phase III trial in poor-prognosis patients with metastatic renal cancer compared i.v weekly temsirolimus administration to subcutaneous interferon alpha (IFNα), or a combination of temsirolimus plus IFNα. This study established that median overall survival was improved to 10.9 months in the temsirolimus group compared to 7.3 months in IFNα-treated group (0.73 hazard ratio for death; 95% confidence interval [CI], 0.58 to 0.92; P = 0.008). A modest objective response rate of 8.6%, 4.8%, and 8.1%, respectively was observed in the three groups, associated with a median time to treatment failure of 3.8 months for temsirolimus alone, 1.9 months for IFNα, and 2.5 months for the combination. These results led to approval of temsirolimus for the treatment of renal cancer in the United States. Temsirolimus is clearly indicated for first-line therapy of Motzer “poor risk” renal cancer and aggressive non-clear cell renal cancer. Temsirolimus may be useful after failure of VEGF tyrosine kinase inhibitors. Clinical activity in other tumor types, such as endometrial cancer has been observed. Temsirolimus is therefore an important new agent for cancer treatment.