Data from Quercetin Induces Tumor-Selective Apoptosis through Downregulation of Mcl-1 and Activation of Bax

Abstract

<div>Abstract<p><b>Purpose:</b> To investigate the <i>in vivo</i> antitumor efficacy of quercetin in U937 xenografts and the functional roles of Mcl-1 and Bax in quercetin-induced apoptosis in human leukemia.</p><p><b>Experimental Design:</b> Leukemia cells were treated with quercetin, after which apoptosis, Mcl-1 expression, and Bax activation and translocation were evaluated. The efficacy of quercetin as well as Mcl-1 expression and Bax activation were investigated in xenografts of U937 cells.</p><p><b>Results:</b> Administration of quercetin caused pronounced apoptosis in both transformed and primary leukemia cells but not in normal blood peripheral mononuclear cells. Quercetin-induced apoptosis was accompanied by Mcl-1 downregulation and Bax conformational change and mitochondrial translocation that triggered cytochrome <i>c</i> release. Knockdown of Bax by siRNA reversed quercetin-induced apoptosis and abrogated the activation of caspase and apoptosis. Ectopic expression of Mcl-1 attenuated quercetin-mediated Bax activation, translocation, and cell death. Conversely, interruption of Mcl-1 by siRNA enhanced Bax activation and translocation, as well as lethality induced by quercetin. However, the absence of Bax had no effect on quercetin-mediated Mcl-1 downregulation. Furthermore, <i>in vivo</i> administration of quercetin attenuated tumor growth in U937 xenografts. The TUNEL-positive apoptotic cells in tumor sections increased in quercetin-treated mice as compared with controls. Mcl-1 downregulation and Bax activation were also observed in xenografts.</p><p><b>Conclusions:</b> These data suggest that quercetin may be useful for the treatment of leukemia by preferentially inducing apoptosis in leukemia versus normal hematopoietic cells through a process involving Mcl-1 downregulation, which, in turn, potentiates Bax activation and mitochondrial translocation, culminating in apoptosis. <i>Clin Cancer Res; 16(23); 5679–91. ©2010 AACR.</i></p></div>