Molecular mechanisms of tumor resistance to PI3K-mTOR-targeted therapy

Deregulation of the phosphatidylinositide 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) signaling pathway occurs frequently in a wide range of human cancers and is a major driving force in tumorigenesis. Thus, small molecules targeting this pathway are under active development as anticancer therapeutics. Although small-molecule inhibitors of the PI3K-mTOR pathway have shown promising clinical efficacy against human cancers, the emergence of drug resistance may limit their success in the clinic. To date, several resistance mechanisms, including both PI3K-dependent and -independent mechanisms, have been described. Here, we summarize the current understanding of resistance mechanisms to PI3K-mTOR inhibitors and discuss potential strategies for overcoming resistance for potential clinical application.