MTOR and cancer: The first generation of mTOR inhibitors, rapamycin and its analogs (known as rapalogs) such as everolimus (RAD001), temsirolimus (CCI-779) and ridaforolimus (AP23573) have entered clinical trials but, unfortunately, shown limited clinic benefits against many types of cancers [24,25], even though temsirolimus has been approved for clinical treatment of renal cell carcinoma in United States [26].