Mammalian target of rapamycin: Biological function and target for novel anticancer agents

Purpose. The biological function of the mammalian target of rapamycin (mTOR) and mechanisms of action of mTOR inhibitors currently available for clinical use are described. Summary. mTOR is a target for anticancer agents due to its role in cancer development, progression, and resistance to other antineoplastic agents. Currently, two mTOR inhibitors, temsirolimus and everolimus, are approved for the treatment of patients with advanced renal cell carcinoma (RCC). Clinical trials comparing single-agent temsirolimus with interferon alfa-2a demonstrated an improvement in overall survival and progression-free survival (PFS) in patients with metastatic RCC. Clinical studies comparing everolimus with placebo indicated improved PFS in advanced RCC patients whose disease had progressed on or after vascular endothelial growth factor (VEGF) inhibitor therapy. Due to its role in the phosphatidylinositol 3-kinase (PI3K) signaling pathway, mTOR is a rational target for inhibition in combination with other agents, including traditional chemotherapy and agents that are affected by or target the PI3K pathway. Data from these studies review the use of mTOR inhibitors in non-Hodgkin's lymphoma and endometrial, breast, and neuroendocrine tumors. Common toxicities of mTOR inhibitors include mucositis, stomatitis, rash, asthenia, fatigue, and myelosuppression. Additional toxicities requiring monitoring include hyperglycemia, hyperlipidemia, and pneumonitis. Conclusion. The mTOR signaling pathway is upregulated in a variety of solid and hematologic tumors. Two inhibitors of this pathway, temsirolimus and everolimus, have been approved for use in metastatic RCC. Although relatively safe, these drugs are associated with some unique adverse effects, such as hyperlipidemia, hyperglycemia, and pneumonitis, that require monitoring and may require clinical intervention.