Mutation in the ABL kinase domain is the principal mechanism of imatinib resistance in patients with BCR-ABL-positive leukemia. The need for alternative or additional treatment in imatinib-resistant patients has guided the way to design a second generation of targeted therapies, resulting mainly development of novel ABL kinase inhibitors like nilotinib and dasatinib. Despite promising results from clinical studies, a challenging problem that remains is T315I mutation against which neither nilotinib nor dasatinib showed significant activity. In the present study, we investigated the activity of a novel aurora kinase inhibitor, VE-465, which is a related compound to VX-680 (
) against wild-type BCR-ABL or T315I mutant form of BCR-ABL-expressing leukemia cells. Wild-type BCR-ABL or T315I mutant-expressing BaF3 cells were incubated in the presence of VE-465 for 24 hrs, and then immunoprecipitated with anti-ABL mAb. We observed a dose-dependent reduction in the level of BCR-ABL kinase activity as judged by autophosphorylation and CrkL phosphorylation in VE-465-treated cells. The IC50 values for VE-465 are comparable for wild-type BCR-ABL (2.0 μM) and T315I mutant (3.5 μM). We also observed a dose-dependent cleavage of PARP and caspase-3 in wild-type BCR-ABL or T315I mutant-expressing BaF3 cells. Next, we determined the effect of co-treatment with VE-465 and imatinib in K562 cells. Combined treatment with VE-465 and imatinib caused more attenuation of the levels of phospho-CrkL, phospho-AKT, and c-Myc. Following co-treatment with VE-465 and imatinib was also associated with more PARP cleavage, which is due to increased activation of caspase-3 and caspase-7 during apoptosis. Co-treatment with VE-465 and imatinib also caused significantly more inhibition of colony growth than treatment with either compound alone. Further, exposure to the combination of VE-465 and imatinib exerted enhanced apoptotic effect in K562 cells determined by APO2.7 mAb. To assess the in vivo efficacy of VE-465, athymic nude mice were injected i.v. with BaF3 cells expressing T315I mutant form of BCR-ABL. 24 hrs after injection, the mice were divided three groups (5 mice per group), with each group receiving either vehicle, VE-465 (75mg/kg b.i.d.; ip for 14 days), imatinib (50mg/kg b.i.d.; ip for 14 days). The vehicle or imatinib-treated mice died of a condition resembling acute leukemia by 28 days, however, nearly all mice treated with VE-465 survived for more than 56 days. All VE-465-treated mice demonstrated modest weight loss (less than 10% initial body weight). Histopathologic analysis of vehicle or imatinib-treated mice revealed infiltration of the spleen and bone marrow with leukemic blasts. In contrast, histopathologic analysis of organs from VE-465-treated mice demonstrated normal tissue architecture and no evidence of residual leukemia. Taken together, the present study shows that VE-465 exhibits a desirable therapeutic index that can reduce the in vivo growth of T315I mutant form of BCR-ABL-expressing cells in an efficacious manner.
Disclosure: No relevant conflicts of interest to declare.
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