Abstract 4708: Short-term romidepsin treatment combined with mitogen-activated protein kinase and phosphatidylinositol 3-kinase inhibition causes increased Bim expression and cell death in KRAS mutant cell lines

Abstract Romidepsin (FK228) is a histone deacetylase inhibitor (HDI) that modulates chromatin and activates apoptotic pathways in vitro. Clinical efficacy observed in peripheral and cutaneous T-cell lymphoma has not been replicated in solid tumors, as for other HDIs. We thus sought drug combinations that might improve the activity of romidepsin in solid tumors. Mutations in KRAS induce the mitogen activated protein kinase pathway (MAPK) and the phosphatidylinositol 3-kinase (PI3K) pathway. Laboratory data have suggested that activated MEK or AKT can confer resistance to HDIs. To determine if mitogen-activated protein kinase kinase (MEK) or AKT inhibitors could increase sensitivity to romidepsin, we measured cell death by annexin assay in a panel of 20 cell lines, nine KRAS mutants and eleven KRAS wild-type (WT). Cells were exposed to 25 ng/ml romidepsin for 6 h in the presence of 250 nM MEK inhibitor PD0325901 and/or 1 µM AKT inhibitor MK2206, after which romidepsin was removed and cells were incubated with the inhibitors alone for an additional 42 h. Among the 20 solid tumor cell lines examined, those harboring a KRAS mutation had a higher percentage of cell death than lines with WT KRAS when treated with the PD0325901/romidepsin combination (46.1±18% vs. 21.6±7.6% respectively, p-value .0057), the MK2206/romidepsin combination (43.8±15.8% vs. 28.6±13.6%, respectively, p-value .0470), or the PD0325901/MK2206/romidepsin combination (66.5±14.8% vs. 35.0±18.8%, respectively, p-value .0008). There was no statistically significant difference (p-value > .05) in cell death between KRAS and WT cell lines treated with any of the compounds alone. As expression of the pro-apoptotic protein Bim has been associated with romidepsin-mediated cell death, and as the MAPK pathway has been shown to phosphorylate and inactivate Bim, we examined Bim expression in cell lines sensitive to combined treatment with romidepsin and inhibitors. In the OVCAR5 cell line, which harbors a G12V KRAS mutation, we noted that romidepsin induced Bim expression and that combined treatment with PD0325901 led to higher expression by western blot. The high levels of Bim expression were associated with increased poly ADP ribose polymerase cleavage. These data demonstrate the benefit of combining an HDI with MEK and AKT inhibitors in KRAS mutant cell lines. Romidepsin and MAPK pathway inhibitor combinations should be further evaluated in patients with mutant KRAS cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4708. doi:1538-7445.AM2012-4708