Abstract 1919: Pharmacological characterization of BI 847325, a dual inhibitor of MEK and Aurora kinases

Abstract

Abstract The RAS-dependent MAP kinase signaling pathway plays an important role in the regulation of cell proliferation and survival. RAS genes are frequently mutated in human cancer; however, it has not been possible to date to design direct inhibitors of RAS proteins. Inhibitors of the downstream kinase MEK are active against a subset of KRAS-mutant cancers in preclinical studies, but have shown limited success to date in clinical trials. We have identified a compound that potently inhibits MEK as well as Aurora kinases, a family of serine/threonine kinases involved in the regulation of mitosis. In enzymatic assays, BI 847325 inhibited the activity of Aurora A, B and C with IC50 values of 3, 25 and 15 nM, respectively; IC50 values of 25 and 4 nM were determined for MEK1 and MEK2, respectively. To determine whether the enzyme profile translates into cellular activity we used Western blot and FACE-ELISA assays of phospho-histone H3 (pHH3) and phospho-ERK (pERK) levels in cells treated with BI 847325 and observed EC50 values of 44 nM (NCI-H460 cells, KRAS and PI3Kα mutant) and 37 nM (A375 cells, BRAF mutant), respectively. In vitro profiling in a panel of 240 cell lines with diverse tissue origin and genetic background demonstrated that BI 847325 is a potent inhibitor of cell proliferation (gm GI50 = 28 nM) and induces cell death in a subset of cell lines. In vitro potency significantly correlated with mutations in RAS or BRAF. For comparison, a significant correlation of mutation status and sensitivity was also observed for a selective MEK inhibitor, AZD6244, but not for a selective Aurora inhibitor, BI 811283. In vivo efficacy was studied in nude mouse xenograft models of NSCLC (Calu-6, mutant KRAS) and cutaneous melanoma (A375, mutant BRAF). A daily oral dose of 10 mg/kg resulted in complete inhibition of tumor growth in the Calu-6 model (TGI = 102%, regression in 4/7 animals) and the A375 model (TGI = 116%, regression in 7/7 animals). Inhibition of Aurora B and MEK was monitored ex vivo by determining the phosphorylation state of histone H3 and ERK1/2 in tumor tissue. Immunohistochemical analyses confirmed a significant reduction of both pERK and pHH3 levels in the A375 tumors of treated animals compared to controls. To further profile the mode of action of the compound, the efficacy of BI 847325 in the MIAPaCa2-pancreatic adenocarcinoma model (mutant KRAS) was directly compared with that of the MEK inhibitor GSK 1120212. BI 847325 effectively induced tumor regression (TGI on day 22 = 126%) that was maintained in all animals on day 43. In contrast, treatment with GSK 112021 resulted in initial tumor regression, followed by re-growth after 3-4 weeks (TGI on day 22 = 129%; regrowth on day 43 in 5/7 animals). Inhibition of Aurora kinase in addition to MEK blockade thus may prevent/delay onset of resistance. Additional xenograft models with diverse genetic background are currently under investigation. Clinical development of BI 847325 has been initiated. 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 1919. doi:1538-7445.AM2012-1919