Data from TRAIL-Induced Apoptosis Is Preferentially Mediated via TRAIL Receptor 1 in Pancreatic Carcinoma Cells and Profoundly Enhanced by XIAP Inhibitors

Abstract

<div>Abstract<p><b>Purpose:</b> We previously reported that small molecule X-linked inhibitor of apoptosis (XIAP) inhibitors synergize with soluble TRAIL to trigger apoptosis in pancreatic carcinoma cells. Because cancers may preferentially signal via 1 of the 2 agonistic TRAIL receptors, we investigated these receptors as a therapeutic target in pancreatic cancer in the present study.</p><p><b>Experimental Design:</b> We examined TRAIL receptor expression and cytotoxicity of specific monoclonal antibodies to TRAIL-R1 (HGS-ETR1, mapatumumab) or TRAIL-R2 (HGS-ETR2, lexatumumab) and of TRAIL receptor selective mutants alone and in combination with small molecule XIAP inhibitors in pancreatic cancer cell lines, in primary specimens, and in a xenotransplant model <i>in vivo</i>.</p><p><b>Results:</b> The majority of primary pancreatic carcinoma samples and all cell lines express one or both agonistic TRAIL receptors. Nine of 13 cell lines are more sensitive to mapatumumab-induced apoptosis, whereas lexatumumab requires cross-linking for maximal activity. Similarly, TRAIL-R1 selective mutants display higher cytotoxicity than TRAIL-R2 selective mutants. Small molecule XIAP inhibitors preferentially act in concert with mapatumumab to trigger caspase activation, caspase-dependent apoptosis, and suppress clonogenic survival. Also, primary cultured pancreatic carcinoma cells are more susceptible to mapatumumab than lexatumumab, which is significantly enhanced by a XIAP inhibitor. Importantly, combined treatment with mapatumumab and a XIAP inhibitor cooperates to suppress tumor growth <i>in vivo</i>.</p><p><b>Conclusions:</b> Mapatumumab exerts antitumor activity, especially in combination with XIAP inhibitors against most pancreatic carcinoma cell lines, whereas lexatumumab requires cross-linking for optimal cytotoxicity. These findings have important implications for the design of TRAIL-based protocols for pancreatic cancer. <i>Clin Cancer Res; 16(23); 5734–49. ©2010 AACR.</i></p></div>