Temsirolimus, a rapamycin (sirolimus) derivative, also known as CCI-779, is an mTOR inhibitor with anti-cancer activity. Temsirolimus down-regulated the mTOR signaling intermediate phospho-S6 in xenografted human ALL. Temsirolimus has been shown to reverse cisplatin resistance in small cell lung cancer cell lines selected for cisplatin resistance and in cell lines derived from patients who failed cisplatin therapy.