Abstract
<div>Abstract<p><b>Purpose:</b> Mantle cell lymphoma (MCL) is considered to be incurable. ABT-737 is a BH3 mimetic that targets Bcl-2, which is overexpressed in MCL and implicated in drug resistance. The present work investigated the antitumor effect of ABT-737.</p><p><b>Experimental Design:</b> Six MCL cell lines and primary MCL cells (<i>n</i> = 13) were used. Sensitivity to ABT-737 was assessed, and expression levels of Bcl-2 and Mcl-1 were analyzed. Finally, ABT-737 was combined with other cytotoxic agents to promote tailored therapy.</p><p><b>Results:</b> MINO and GRANTA-519 cell lines were highly sensitive to ABT-737 [the median lethal dose (LD<sub>50</sub>) = 20 and 80 nmol/L, respectively], whereas other cell lines were resistant. In primary MCL cells, 46% of patients' samples were sensitive to ABT-737. The analysis of protein expression levels revealed that both sensitive cell lines and primary MCL cells could be characterized by a Bcl-2<i><sup>high</sup></i>/Mcl-1<i><sup>low</sup></i> profile, whereas resistant MCL cells contained high levels of Mcl-1. ABT-737 induced a rapid disruption of both Bcl-2/Bax and Bcl-2/Bik complexes. In addition, silencing of Mcl-1 by siRNA sensitized MCL cell lines to ABT-737. Similarly, flavopiridol, which induces Mcl-1 downregulation, in combination with ABT-737 led to a synergistic anti-MCL effect in ABT-737–resistant cell lines. This synergy was also observed when ABT-737 was combined with either bortezomib or cytarabine.</p><p><b>Conclusions:</b> The present work shows that ABT-737 induces strong apoptosis in MCL cells expressing a Bcl-2<i><sup>high</sup></i>/Mcl-1<i><sup>low</sup></i> profile. In ABT-737–resistant MCL cells, downregulation of Mcl-1 overcomes Mcl-1–induced resistance and synergizes ABT-737 effects. Our results strongly support the use of ABT-737 according to the Bcl-2/Mcl-1 tumor cell profiles in the treatment of MCL. <i>Clin Cancer Res; 17(18); 5973–81. ©2011 AACR</i>.</p></div>
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