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Blood, 26 February 2009, Vol. 113, No. 9, pp. 1982-1991. Prepublished online as a Blood First Edition Paper on December 5, 2008; DOI 10.1182/blood-2008-05-156851.
LYMPHOID NEOPLASIA Defining the target specificity of ABT-737 and synergistic antitumor activities in combination with histone deacetylase inhibitors1 Cancer Immunology Program, The Peter MacCallum Cancer Centre, Trescowthick Research Laboratories, East Melbourne, Australia; 2 Department of Biological Sciences, Columbia University, New York, NY; 3 Department of Translational Oncology, National Center for Tumor Diseases and German Cancer Research Center, Heidelberg, Germany; and 4 University of Melbourne, Melbourne, Australia
The apoptotic and therapeutic activities of the histone deacetylase inhibitor (HDACi) vorinostat are blocked by overexpresssion of Bcl-2 or Bcl-XL. Herein, we used the small molecule inhibitor ABT-737 to restore sensitivity of Eµ-myc lymphomas overexpressing Bcl-2 or Bcl-XL to vorinostat and valproic acid (VPA). Combining low-dose ABT-737 with vorinostat or VPA resulted in synergistic apoptosis of these cells. ABT-737 was ineffective against Eµ-myc/Mcl-1 and Eµ-myc/A1 cells either as a single agent or in combination with HDACi. However, in contrast to the reported binding specificity data, Eµ-myc/Bcl-w lymphomas were insensitive to ABT-737 used alone or in combination with HDACi, indicating that the regulatory activity of ABT-737 is restricted to Bcl-2 and Bcl-XL. Eµ-myc lymphomas that expressed Bcl-2 throughout the tumorigenesis process were especially sensitive to ABT-737, while those forced to overexpress Mcl-1 were not. This supports the notion that tumor cells "addicted" to ABT-737 target proteins (ie, Bcl-2 or Bcl-XL) are likely to be the most sensitive target cell population. Our studies provide important preclinical data on the binding specificity of ABT-737 and its usefulness against primary hematologic malignancies when used as a single agent and in combination with HDACi.
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