Abstract 2671: Structural analysis of the inhibitory mechanism of AP24534, a pan-BCR-ABL inhibitor overriding the T315I gatekeeper mutation

Abstract

Abstract Although durable response in many chronic myeloid leukemia (CML) patients can be achieved by imatinib treatment, point mutations in the kinase domain of the BCR-ABL fusion protein can lead to drug resistance and relapse. Nilotinib and dasatinib, the two second generation Abl kinase inhibitors, are active against most imatinib resistant mutants with a few exceptions, particularly the T315I gatekeeper residue mutation. Using a structure-based approach we have identified AP24534, a molecule that potently inhibits the T315I mutant and all other mutants tested, thus acting as a pan-BCR-ABL inhibitor. To elucidate the basis for this unique profile of AP24534, we have used a combination of X-ray crystallographic and structure-activity relationship analysis on AP24534 and its analogs. The crystal structure of the T315I mutant Abl in complex with the inhibitor clearly demonstrates that AP24534 binds to Abl in a DFG-out binding mode with the ethynyl chemical moiety skirting the mutated gate-keeper residue avoiding steric clashes. The X-ray co-structures of both the wild type and the T315I mutant Abl, in conjunction with the SAR analysis, further reveal that AP24534 retains potency against the T315I and other imatinib-resistant ABL mutants through optimized multiple points of contact, balancing and distributing the overall binding affinity so that mutation-based disruption of one facet of the binding network results in only a slight reduction in binding affinity. Our structural analysis enables us to predict and rationalize the different degree of sensitivity of ABL point mutants to AP24534, and to understand how AP24534 can completely abrogate resistance in cell-based mutagenesis screens at relatively low concentrations. AP24534 is currently being investigated in a Phase I clinical trial in patients with refractory and resistant CML and other hematological malignancies. 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 2671.