Abstract 4492: BEZ235, a dual PI3K/mTOR inhibitor, enhances the activity of the multikinase inhibitor sorafenib in acute myeloid leukemia (AML)

Abstract

Abstract The PI3K/Akt/mTOR and RAS/RAF/MEK/ERK signaling pathways are activated in 50 to 75% of primary AML cases, which have been associated with poor long-term outcome. The class I PI3K isoforms α, β, δ are expressed in nearly all primary childhood AML blast samples (Ross, Blood 2004), providing a potential target to circumvent aberrant signaling in this pathway. However, because of cross-talk and redundancy of signal transduction pathways, rational combinations of inhibitors may represent an advantageous treatment strategy for AML. We have previously shown that sorafenib, a multikinase inhibitor in development for the treatment of AML, effectively inhibits phosho-ERK in AML cells, with limited inhibition of AKT signaling (Hu, Mol Cancer Ther, 2008). Here we evaluated the anti-leukemic activity of the dual PI3K/mTOR inhibitor BEZ235 as a single agent and in combination with sorafenib at in vivo relevant concentrations (≤ 1 µM BEZ235 and ≤ 10 µM sorafenib) in four AML cell lines (HL60, U937, THP-1, and OCI-AML3), and 9 primary childhood AML blast samples (7 with wild-type FLT3 and 2 with FLT3 internal tandem duplication mutations). We first evaluated the single-agent activity of BEZ235 in AML cells in suspension culture. After exposure to increasing concentrations of BEZ235 for 72h, IC50 values in a MTT assay ranged from 0.125 to 0.5 µM, but maximal growth inhibition did not exceed 40% of untreated controls. After exposure to BEZ235 1 µM for 72 h, an increase in apoptosis (Annexin V positive cells) to 30% was observed in U937 and OCI-AML3 cells, and inhibition of proliferation (EdU incorporation) was observed in U937 and THP-1 cells; no change in cell cycle distribution was observed. Phospho-Akt was inhibited by 50% to 80% of untreated controls in 3 cell lines (U937, THP-1, and HL-60) treated with BEZ235 1 µM for 1 h. We next examined the anti-leukemic activity of the combination of BEZ235 and sorafenib (simultaneous exposure for 72 h) in AML cell lines and primary blast samples that were co-cultured in direct contact with bone-marrow-derived mesenchymal stromal cells. In AML cell lines, sorafenib 10 µM induced apoptosis in twice as many cells (39% to 54%) than BEZ235 1.0 µM (17% to 23%); however, the combination increased apoptosis to 50 to 68% in all cell lines. Enhanced apoptosis was also observed in all primary childhood AML blasts samples treated with the drug combination compared to single agent treatment. In conclusion, BEZ235 has limited single-agent activity but enhances the activity of sorafenib in vitro in AML cell lines and primary blast samples. Studies are ongoing to evaluate the drug combination in a xenograft model of AML. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4492.