Abstract 5115: The Bcl-2 Homology Domain-3 Mimetic, Obatoclax, chemosensitizes muscle invasive bladder cancer cell lines to cisplatin treatment

Abstract

Abstract The primary objective of this study was to determine whether inhibition of anti-apoptotic Bcl-2 family protein activity causes decreased clonogenicity and/or increased apoptosis of muscle invasive bladder cancer (MI-BC) cell lines when used in combination with cisplatin, the standard of care treatment for MI-BC, and/or pre-miR-34a, a miRNA that targets several components of pathways know to promote tumor progression and chemoresistance. Obatoclax, a Bcl-2 homology domain-3 mimetic that has been demonstrated to prevent Bcl-2, Bcl-xL, and Mcl-1 from interacting with and inhibiting Bax and Bak, was used for this study. The impact of Obatoclax, in combination with cisplatin and/or pre-miR-34a, on clonogenic potential and apoptosis was assessed in three MI-BC cell lines (T24, TCCSuP, 5637) using clonogenic assay and annexin V flow cytometry respectively. The ability of Obatoclax to prevent interaction between Bcl-2, Bcl-xL, and Mcl-1, with Bax and Bak was assessed via immunoprecipitation and western blot. The impact of treatments on apoptosis/survival pathways was assessed via western blot. Obatoclax mediated a dose-dependent increase in apoptosis in all three MI-BC cell lines. Obatoclax was able to decrease binding of Bak to Bcl-xL, and cause decreased expression of Bcl-2 and Bcl-xL. Unexpectedly, Obatoclax also mediated a dose-dependent decrease in cdk4, cdk6, and cyclin D1. Combining Obatoclax with cisplatin or/and pre-miR-34a caused further inhibition of clonogenic potential of all three cell lines compared to treatment with single agents. Of the combination treatments, Obatoclax combined with cisplatin mediated the biggest increase in apoptosis levels. Treatment with Obatoclax, cisplatin, and pre-miR-34a actually decreased apoptosis levels. Western blot revealed that treatment with Obatoclax was unable to overcome the effect of pre-miR-34a on causing increased Bcl-2 and Bcl-xL expression. Our data demonstrate that Obatoclax chemosensitizes MI-BC cell lines to cisplatin and indicate that in vivo testing of this combination treatment is warranted. The data do not support further testing of pre-miR-34a in this setting. With the current 5-year survival rate for MI-BC being only 35%, clearly new and improved treatment options are needed for this disease. Citation Format: Thomas Steele, Dan Pham, Kathy Phan, Paramita Ghosh, Ralph deVere White, Ruth L. Vinall. The Bcl-2 Homology Domain-3 Mimetic, Obatoclax, chemosensitizes muscle invasive bladder cancer cell lines to cisplatin treatment. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5115. doi:10.1158/1538-7445.AM2014-5115