Abstract 1822: Novel potent inhibitor of Bcr-Abl mutated imatinib resistant chronic myeloid leukemia cell lines

Abstract

Abstract The hallmark of chronic myeloid leukemia (CML) is the presence of Bcr-Abl oncoprotein that is essential for leukemogenesis and accumulation of neoplastic cells. The Abl tyrosine kinase inhibitor imatinib mesylate (Gleevec) represents the standard treatment for CML. However, a number of CML patients develop imatinib resistance and several mechanisms of resistance have been described. While most mutant forms are sensitive to second-generation tyrosine kinase inhibitors, the T315I mutation remains completely refractory to imatinib, as well as to these agents. Treatment of CML patients harboring T315I mutation is still an unmet medical need in the imatinib and post-imatinib era. We have identified P2745, a novel orally bioavailable small molecule that is effective in imatinib resistant mutations and particularly T315I mutation form to address this unmet medical need. In vitro P2745 showed potent cytotoxicity (IC50 0.8-5 μM) in twelve Bcr-Abl mutated imatinib resistant cell lines including T315I compared to wild type Bcr-Abl cell lines. P2745 did not show cytotoxicity upto 30 μM in normal fibroblasts (MRC-5 and WI-38) and normal human peripheral blood mononuclear cells thus indicating specificity towards cancerous cells. P2745 inhibited pCrkLTyr207 in imatinib-resistant CML cell lines accompanied with down regulation of Bcr-Abl protein levels. Additionally, it up regulated tumor suppressor protein SMAR-1 which resulted in negative regulation TGF-β/SMAD-dependent pathway as demonstrated by low phosphorylated levels of SMAD2 and SMAD3, two key players implicated in the preservation of the malignant progenitor population, and partly responsible for the resistance to treatments targeting Bcr-Abl. P2745 also induced significant apoptosis in imatinib resistant cell lines (Y253F, T315I and E255V) but not in normal MRC-5 cell line. In addition, like imatinib it induced 80-90 % apoptosis in cells derived from CML patients. In vivo studies demonstrated significant (p<0.001), dose dependent efficacy in imatinib resistant T315I cells xenograft in SCID mice. It also demonstrated significant in vivo efficacy in Bcr-Abl wild type imatinib sensitive K-562 (p<0.05) and Ba/F3 (p<0.001) xenografts in SCID mice. PK-PD evaluation in imatinib resistant xenograft experiments indicated that at the efficacious dose, P2745 modulated proteins responsible for CML pathogenesis (60-80 %), which correlates with the levels of P2745 in the tumors. This unique mechanism of action makes P2745 a promising clinical candidate for CML patients harboring T315I mutation. 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 1822. doi:1538-7445.AM2012-1822