Multiple myeloma (MM) is a malignancy characterized by clonal expansion and accumulation of long-lived plasma cells within the bone marrow. Phosphatidylinositol 3\#8217; kinase (PI3K) -mediated signaling is frequently dysregulated in cancer and controls fundamental cellular functions such as cell migration, growth, survival and development of drug resistance in many cancers, including MM, and therefore represents an attractive therapeutic target. Here, we demonstrate in vitro, that a potent and selective pan-isoform PI3K-inhibitor, GDC-0941, modulates the expected pharmacodynamic markers, inhibits cell-cycle progression and induces apoptosis; overcomes resistance to apoptosis in MM cells conferred by IGF-1 and IL-6; and is additive or synergistic with current standard of care drugs including dexamethasone, melphalan, revlimid and velcade. In a limited number of cell lines we find sensitivity to GDC-0941 is correlated with the activation status of AKT as determined by phospho-AKT-specific flow-cytometry and Western-blot analysis. Preliminary results indicate apoptosis of MM cells is correlated with increased expression of the proapoptotic BH3-only protein BIM; mechanisms of increased apoptosis in MM will be further explored and an update presented. We further extend these in vitro findings to show that GDC-0941 has activity as a single agent in vivo and combines well with standard of care agents in several murine xenograft models to delay tumor progression and prolong survival. Our results suggest that GDC-0941 may combine well with existing therapies, providing a framework for the clinical use of this agent, and a rational approach to improving the efficacy of myeloma treatment.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 3704.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO