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Antimyeloma Activity of the Orally Bioavailable Dual Phosphatidylinositol 3-Kinase/Mammalian Target of Rapamycin Inhibitor NVP-BEZ235

¹ Jerome Lipper Multiple Myeloma Center, Department of Medical Oncology, Dana-Farber Cancer Institute; ² Department of Medicine, Harvard Medical School, Boston, Massachusetts and ³ Novartis Institutes for Biomedical Research, Basel, Switzerland

Requests for reprints: Constantine S. Mitsiades, Jerome Lipper Multiple Myeloma Center, Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, 44 Binney Street, Boston, MA 02115. Phone: 617-632-1962; Fax: 617-812-7701; E-mail: Constantine_Mitsiades{at}dfci.harvard.edu.

Key Words: mTOR • myeloma • PI3K

The phosphatidylinositol 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) pathway mediates proliferation, survival, and drug resistance in multiple myeloma (MM) cells. Here, we tested the anti-MM activity of NVP-BEZ235 (BEZ235), which inhibits PI3K/Akt/mTOR signaling at the levels of PI3K and mTOR. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric survival assays showed that MM cell lines exhibited dose- and time-dependent decreased viability after exposure to BEZ235 (IC₅₀, 25–800 nmol/L for 48 hours). MM cells highly sensitive (IC₅₀, <25 nmol/L) to BEZ235 (e.g., MM.1S, MM.1R, Dox40, and KMS-12-PE) included both lines sensitive and resistant to conventional (dexamethasone, cytotoxic chemotherapeutics) agents. Pharmacologically relevant BEZ235 concentrations (25–400 nmol/L) induced rapid commitment to and induction of MM.1S and OPM-2 cell death. Furthermore, normal donor peripheral blood mononuclear cells were less sensitive (IC₅₀, >800 nmol/L) than the majority of MM cell lines tested, suggesting a favorable therapeutic index. In addition, BEZ235 was able to target MM cells in the presence of exogenous interleukin-6, insulin-like growth factor-1, stromal cells, or osteoclasts, which are known to protect against various anti-MM agents. Molecular profiling revealed that BEZ235 treatment decreased the amplitude of transcriptional signatures previously associated with myc, ribosome, and proteasome function, as well as high-risk MM and undifferentiated human embryonic stem cells. In vivo xenograft studies revealed significant reduction in tumor burden (P = 0.011) and survival (P = 0.028) in BEZ235-treated human MM tumor-bearing mice. Combinations of BEZ235 with conventional (e.g., dexamethasone and doxorubicin) or novel (e.g., bortezomib) anti-MM agents showed lack of antagonism. These results indicate that BEZ235 merits clinical testing, alone and in combination with other agents, in MM. [Cancer Res 2009;69(14):5835–42]