Toward rapamycin analog (rapalog)-based precision cancer therapy

Rapamycin and its analogs (rapalogs) are the first generation of mTOR inhibitors, which have the same molecular scaffold, but different physiochemical properties. Rapalogs are being tested in a wide spectrum of human tumors as both monotherapy and a component of combination therapy. Among them, temsirolimus and everolimus have been approved for the treatment of breast and renal cancer. However, objective response rates with rapalogs in clinical trials are modest and variable. Identification of biomarkers predicting response to rapalogs, and discovery of drug combinations with improved efficacy and tolerated toxicity are critical to moving this class of targeted therapeutics forward. This review focuses on the aberrations in the PI3K/mTOR pathway in human tumor cells or tissues as predictive biomarkers for rapalog efficacy. Recent results of combinational therapy using rapalogs and other anticancer drugs are documented. With the rapid development of next-generation genomic sequencing and precision medicine, rapalogs will provide greater benefits to cancer patients.