Anti-Myeloma Activity of the Small-Molecule Aurora Kinase Inhibitor VE465.

Multiple Myeloma (MM) remains an incurable plasma cell neoplasia, despite recent additions in the therapeutic arsenal for its management. Aurora kinases play integral roles in the orchestration of chromosomes and cytoskeletal mobility during the process of cell division. Aurora kinase activity has been implicated in several tumor types, including ovarian, colon, and prostate cancers. To determine whether inhibition of Aurora kinase activity could attenuate myeloma cell survival, we performed studies of the Aurora kinase inhibitor VE465 (Vertex Pharmaceuticals / Merck & Co., Inc.). VE465 inhibits all 3 Aurora isoforms (Aur A, B and C) with approximate Ki values of 1, 26, and 8.7 nM respectively. MTT colormetric survival assays (72–96hrs exposure) showed that VE465 is active against a wide panel of human MM cell lines: 26 of 38 MM cell lines had IC₅₀ values at or < 100 nM, which are significantly lower than IC₅₀ values for normal hematopoietic cells, e.g. unstimulated or PHA-stimatuled PBMCs. Importantly, VE465 was active in vitro against MM cell lines and/or primary MM tumor cells resistant to various anti-MM therapeutics, including dexamethasone, alkylating agents, anthracyclines, the proteasome inhibitor bortezomib, and/or immunomodulatory thalidomide derivatives (IMiDs). Moreover, VE465 maintained its activity despite the presence of protective bone marrow-derived cytokines (e.g. IL-6). PI cell cycle analyses showed that VE465 causes (even within 8 hrs of treatment) caused pronounced G2 arrest, followed by significant shift of MM cells to sub-G1 gate, consistent with cell death. Immunoblotting analyses confirmed that VE465 treatment induces cleavage of PARP, as well as cleavage of caspases-8 and -9, without significant changes in the expression levels of several key molecular effectors (e.g. Mcl-1, Bax, p53, hsp70, hsp90, hs27) which have been previously implicated in the mechanism of anti-MM activity of diverse other therapeutics. Screening of VE465-based combination regimens with other anti-MM agents showed additive effects of VE465 with the histone deacetylase inhibitor Vorinostat (SAHA) (Merck & Co., Inc). Ongoing studies in our Center are addressing the identification of specific molecular markers correlating with the degree of sensitivity of MM cells to VE465. Our in vitro evidence for induction of MM cell death and therapeutic window for the anti-MM effect of VE465, its ability to overcome protective effect of BM-derived cytokines, and the clearly distinct pattern of molecular sequelae of VE465 compared to several other agents in our current anti-MM therapeutic armamentarium, all suggest that Aurora kinase inhibition represents an intriguing novel targeted treatment strategy in MM. Importantly, these studies, particularly the identification of a sizeable subset of MM cell lines with higher sensitivity to VE465 than normal cells, provide the framework for in vivo VE465 studies in progress, alone and in combination with other anti-MM agents, to inform the design of potential clinical trials of this class of agents for MM.