Abstract 2275: A novel heat shock protein 90 inhibitor, NVP-AUY922, enhances the antitumor effect of imatinib via autophagy on imatinib-resistant CML cells

Abstract

Abstract The BCR-ABL tyrosine kinase inhibitor (TKI), imatinib mesylate, has revolutionized the treatment of CML, however, the development of TKI-resistance caused in approximately 10-25% of cases by mutation in the BCR-ABL kinase domain. Therefore, novel therapeutic strategies are needed to address the emerging problem of imatinib-resistant CML. Recently, the heat shock proteins of 90 kDa (Hsp90) have emerged as targets of interest in cancer therapy. NVP-AUY922 (Novartis) is a novel 4, 5-diaryloxazole ATP-binding site heat shock protein 90 (HSP90) inhibitor, which has been shown to inhibit the chaperone function of HSP90 and delete the levels of HSP90 client protein including BCR-ABL. We have recently reported that combined treatment of NVP-AUY922 and BCR-ABL TKI exhibits a desirable therapeutic index that can reduce the in vivo growth of mutant form of BCR-ABL-expressing cells (Oncogene 30, 2789-97, 2011). However, the mechanism of programmed cell death (PCD) is not yet completely understood. In the present study, we examined the mechanism of PCD induction by the combined treatment of NVP-AUY922 and imatinib on wild-type (WT) and mutant forms of BCR-ABL Baf-3 cells (E255K and T315I). Imatinib-mediated inhibitory effect was observed on WT cells, however, E255K and T315I cells were less sensitive to imatinib than WT cells. BCR-ABL mutant T315I cells were the most resistant to imatinib. On the other hands, NVP-AUY922 was synergistically sensitized tumor cells to imatinib on both WT and imatinib-resistant Baf-3 cells. Activity of caspase-3/7 was increased by combined treatment with imatinib and/or NVP-AUY922 on WT cells, indicating induction of apoptosis. In contrast, apoptosis induced by combined treatment with imatinib and/or NVP-AUY922 was significantly suppressed, although the inhibition of cell growth was still detectable on E255K and T315I cells. May-Giemsa staining revealed that many vacuoles were detected in the cytoplasm by combined treatment with imatinib and NVP-AUY922 on E255K and T315I cells, indicating the morphologic features of autophagy. We are currently conducting autophagy-detection assay and determining autophagic signaling pathways. Our findings indicate that NVP-AUY922 enhances the antitumor effect of imatinib, through activation of autophagy on imatinib-resistant CML cells. These data strongly suggest that combined treatment of imatinib and NVP-AUY922 is a novel approach for the treatment of patients with imatinib-resistant CML. 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 2275. doi:1538-7445.AM2012-2275