mTOR signaling pathway and mTOR inhibitors in cancer therapy.

Mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase. It is ubiquitously expressed in cells and is a therapeutic target for the cancer treatment arsenal. Despite the great responses obtained in tumors addicted to specific mutations or overactivation of key members of the mTOR pathway (HiF1α in RCC, cyclin D1 in MCL, or TSC in SEGA), mTOR inhibitors as single agents have modest activity. Dual PI3K/mTOR kinase inhibitors have been developed with the idea of overcoming resistance to the mTOR inhibition through preventing the activation of PI3K/Akt as a result of release negative feedback loops.