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Abstract 4524: Targeting Bcl-2 family proteins in adult T-cell leukemia/lymphoma: in vitro and in vivo effects of a novel Bcl-2 family inhibitor, ABT-737

Adult T-cell lymphoma/leukemia (ATLL) is a T-cell malignancy caused by the human T-lymphotrophic virus type I (HTLV-I), and its therapeutic outcome still remains extremely poor. Therefore, novel therapeutic strategies are needed to improve treatment outcomes. In this study, we elucidated the therapeutic potential of targeting the anti-apoptotic Bcl-2 family proteins for the treatment of ATLL using ABT-737 (Abbott Laboratories, Abbott Park, IL, USA), a small molecule inhibitor of Bcl-2, Bcl-X L and Bcl-w. We first validated the rationale of this study by immunohistochemically assessing the expression of Bcl-2 family proteins in 25 lymph-node specimens derived from ATLL patients. The Bcl-2 and/or Bcl-X L proteins were expressed in 80% of specimens. We next examined the cytotoxicity of ABT-737 against three ATLL cell lines by the Colorimetric method. ABT-737 significantly inhibited growth of MT-1, MT-2 and HuT 102 cells with concentrations of 50 percent inhibition of 2.4, 0.23 and 0.008μM at 72 h, respectively. We then tried to clarify the mechanism of growth inhibition induced with ABT-737 using MT-1 and MT-2 cells. ABT-737 induced apoptosis in both cells with cleavage of caspases 9 and 3, and PARP. ABT-737 also induced apoptosis in fresh tumor cells derived from patients with ATLL. We also tested if ABT-737 enhances the cytotoxicity induced by conventional chemotherapeutic agents or novel agents. The interactions between them were evaluated using the Chou-Talalay method. ABT-737 synergistically enhanced the cytotoxicity and apoptosis induced by doxorubicin, vincristine or etoposide and bortezomib or suberolyanilide hydroxamic acid, which are current key drugs and promising candidates for the treatment of ATLL, respectively. Finally, we investigated the growth inhibition of ABT-737 in ATLL-xenografted mice. The mean tumor volume and weight, and mean serum level of soluble interleukin-2 receptor α at day 21 of the treated mice with ABT-737 (100mg/kg/day) were significantly lower than those of vehicle-treated mice. Moreover, massive induction of apoptosis was observed in tumors treated with ABT-737 by the TUNEL assay. These results suggest that the use of ABT-737, either alone, or in combination with other conventional cytotoxic and novel drugs, represents a promising novel targeted approach to overcome drug resistance and to improve patient outcome in ATLL. 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 4524.