The Mammalian Target of Rapamycin (mTOR) is a serine/threonine kinase which regulates cell growth, proliferation and metabolism and plays those roles by forming two functionally distinct complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Deregulation of mTOR pathway is common in different cancers including multiple myeloma (MM). Moreover, recent studies on the role of Deptor and Grb10 in myeloma cells emphasize the importance of mTOR pathway in MM. However, a clear identification of the role of mTORC1 and mTORC2 in myeloma cells has not been achieved due to the lack of inhibitors specifically targeting these two branches. In this study, we show that both mTORC1 and mTORC2 are constitutively active in a panel of MM cell lines. Moreover, we analyzed the basal status of both branches in a cohort of MM patients (n=40) by means of multiple parameter flow cytometry using phospho-S6 and phospho-Akt as readouts for activation of mTORC1 and mTORC2, respectively. To explore the contribution of mTORC1 or mTORC2 route to the proliferation of MM cells, we employed the RNA interference of Raptor and Rictor through infection of OPM2 and MM1S with shRNA expressing lentivirus, and found that downregulation of Raptor substantially decreased cell proliferation to a higher extent than Rictor and knockdown of mTOR fully prevented cell proliferation. These data suggested a major role of mTOR pathway in the regulation of myeloma cell proliferation and support the idea of mTOR as a target for anti-myeloma therapy. For this reason, we evaluated the novel mTOR inhibitor CC214. This drug inhibited cell growth in all the cell lines tested, induced cell cycle arrest at G0/G1 by altering cell cycle related proteins, and provoked apoptosis evident by the cleavage of caspases and PARP. Besides, CC214 induced cell death in plasma cells in ex vivo culture of freshly isolated cells from bone marrow of MM patients. These results suggest that mTOR inhibitors may be of help in the future treatment of myeloma patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C66.