Trastuzumab Down-Regulates Bcl-2 Expression and Potentiates Apoptosis Induction by Bcl-2/Bcl-XL Bispecific Antisense Oligonucleotides in HER-2 Gene–Amplified Breast Cancer Cells

Abstract

Purpose: To investigate the possible existence of an antiapoptotic cross-talk between HER-2 and antiapoptotic Bcl-2 family members.Experimental Design: Bcl-2 and Bcl-X L expression and apoptosis induction were analyzed in HER-2 gene-amplified (BT474) and nonamplified (ZR 75-1) breast cancer cell lines exposed to trastuzumab, alone or in combination with either Bcl-2/Bcl-X L bispecific antisense oligonucleotides (AS-4625) or the small-molecule Bcl-2 antagonist HA14-1.Results: In addition to HER-2 and epidermal growth factor receptor, trastuzumab down-regulated Bcl-2, but not Bcl-X L , protein, and mRNA expression in BT474 cells. Interestingly, trastuzumab-induced down-regulation of HER-2 and Bcl-2 was also observed in three of five and two of three breast cancer patients undergoing trastuzumab treatment, respectively. Despite Bcl-2 down-regulation, however, trastuzumab only marginally increased the rate of apoptosis (7.3 ؎ 3.5%). We therefore investigated whether a combination of AS-4625 and trastuzumab might increase proapoptotic efficiency. AS-4625 treatment of BT474 cells decreased both Bcl-2 and Bcl-X L expression, resulting in a 21 ؎ 7% net apoptosis induction; the combination of AS-4625 followed by trastuzumab resulted in a significantly stronger induction of apoptosis (37 ؎ 6%, P < 0.01) that was not observed with the reverse treatment sequence (trastuzumab followed by AS-4625). Similar results were obtained with the Bcl-2 antagonist HA14-1; indeed, exposure of BT474 cells to HA14-1 followed by trastuzumab resulted in a striking proapoptotic synergism (combination index ‫؍‬ 0.58 ؎ 0.18), as assessed by isobologram analysis.Conclusions: Altogether our findings suggest that combined targeting of HER-2 and Bcl-2 may represent a novel, rational approach to more effective breast cancer therapy.

Trastuzumab signaling in ErbB2-overexpressing inflammatory breast cancer correlates with X-linked inhibitor of apoptosis protein expression

“…The ErbB2-overexpressing IBC cell line (SUM190PT) described in this study mimics this phenomenon, because it has low phosphatase and tensin homologue expression (data not shown), activated AKT, and relatively high expression of XIAP, all of which were observed to correlate with resistance. In addition, a previous report has shown the ability of trastuzumab to decrease Bcl-2 protein levels in trastuzumab-sensitive non-IBC cells (26), further supporting the role of antiapoptotic proteins in sensitivity to trastuzumab.…”

Bcl2/bcl-xl inhibitor engenders apoptosis and increases chemo-sensitivity in mesothelioma

“…Bcl2 or bcl-x L antisense have been reported to sensitize a variety types of tumors to different chemotherapeutic drugs. 17,18 In this study, we validate the relationship between highly expressed bcl-x L expression and chemoresistance by combining a bcl2/bcl-x L inhibitor and cisplatin. Our in vitro and in vivo studies also demonstrate the capability of chemo-sensitization by inhibiting bcl2/bcl-x L .…”

Extrinsic versus intrinsic apoptosis pathways in anticancer chemotherapy

“…To optimize antisense-based therapy, bispecific antisense oligonucleotides directed against a sequence, which is highly homologous in Bcl-2 and Bcl-xL, but missing in Bcl-xS mRNA, were subsequently designed (Zangemeister-Wittke et al, 2000). Simultaneous downregulation of both Bcl-2 and Bcl-xL induced apoptosis and enhanced chemosensitivity in various cancer cells (Gautschi et al, 2001;Tortora et al, 2003;Milella et al, 2004;Yamanaka et al, 2005).…”