The biology behind mTOR inhibition in sarcoma

Dysregulation of the mammalian target of rapamycin (mTOR) pathway has been found in many human tumors and implicated in the promotion of cancer cell growth and survival. Hence, the mTOR pathway is considered an important target for anticancer drug development. Currently, the mTOR inhibitor rapamycin and its derivatives CCI-779, RAD001, and AP23573 are being evaluated in cancer clinical trials. To date, clinical results have shown good tolerability of treatment with mTOR inhibitors in most reports and varying effectiveness of mTOR inhibitors in a variety of tumors in a subset of patients. For the targeted treatment of sarcomas, AP23573 has shown promising clinical efficacy and low toxicity profiles in patients. Further studies should define the optimal dose/schedule, patient selection, and combination strategies with other biological agents, especially those targeting signaling pathways crucial for cell survival. Disclosure of potential conflicts of interest is found at the end of this article.

Intracellular signal transduction pathway proteins as targets for cancer therapy

Circulating cytokines, hormones, and growth factors control all aspects of cell proliferation, differentiation, angiogenesis, apoptosis, and senescence. These chemical signals are propagated from the cell surface to intracellular processes via sequential kinase signaling, arranged in modules that exhibit redundancy and cross talk. This signal transduction system comprising growth factors, transmembrane receptor proteins, and cytoplasmic secondary messengers is often exploited to optimize tumor growth and metastasis in malignancies. Thus, it represents an attractive target for cancer therapy. This review will summarize current knowledge of selected intracellular signaling networks and their role in cancer therapy. The focus will be on pathways for which inhibitory agents are currently undergoing clinical testing. Original data for inclusion in this review were identified through a MEDLINE search of the literature. All papers from 1966 through March 2005 were identified by the following search terms: "signal transduction," "intracellular signaling," "kinases," "proliferation," "growth factors," and "cancer therapy." All original research and review papers related to the role of intracellular signaling in oncogenesis and therapeutic interventions relating to abnormal cell signaling were identified. This search was supplemented by a manual search of the Proceedings of the Annual Meetings of the American Association for Cancer Research, American Society of Clinical Oncology, and the American Association for Cancer Research (AARC)--European Organisation for Research and Treatment of Cancer (EORTC)--National Cancer Institute (NCI) Symposium on New Anticancer Drugs.