Exploring mammalian target of rapamycin (mTOR) inhibition for treatment of mantle cell lymphoma and other hematologic malignancies.

The mammalian target of rapamycin (mTOR) pathway regulates translation of key proteins that contribute to the pathogenesis of advanced hematologic malignancies. Inhibitors of mTOR (temsirolimus, everolimus, and deforolimus) constitute a new class of antitumor agents, with potential for treatment of relapsed and/or refractory hematologic malignancies. Mantle cell lymphoma (MCL) was the first hematologic malignancy in which mTOR inhibition was explored as a treatment strategy, owing to its characteristic overexpression of cyclin D1, a G1 cyclin regulated by mTOR signaling. Temsirolimus and everolimus exhibited antitumor activity against relapsed, refractory disease in phase II studies. In a randomized phase III trial, once-weekly intravenous temsirolimus 175 mg for 3 weeks followed by 75 mg once weekly was recently shown to improve progression-free survival (p=0.0009) and objective response rate (p=0.0019) versus investigator's choice of therapy in relapsed or refractory MCL. Evidence of antitumor activity seen in early clinical trials for other non-Hodgkin lymphoma subtypes, multiple myeloma, and myeloid leukemias supports further studies of mTOR inhibitors, alone or in combination strategies, in these diseases. Overall, the clinical findings to date strengthen mTOR inhibition as a novel and promising strategy for the treatment of certain hematologic malignancies, particularly for MCL.