Abstract 2424: Synergistic induction of apoptosis in human solid cancer cells by Lexatumumab and cisplatin in a caspase-dependent manner

Abstract Introduction and Objectives: Mapatumumab and Lexatumumab are human agonistic antibodies against TNF-related apoptosis-inducing ligand (TRAIL)-receptor 1 (TRAIL-R1) and TRAIL-R2, respectively, which induce apoptosis specifically in cancer cells. Here, we investigated whether chemotherapeutic agents enhance Mapatumumab- or Lexatumumab-mediated apoptosis against various solid cancer cells. Methods: Cytotoxicity and synergy was assessed by MTT and isobolograpic analyses, respectively. TRAIL-R2 expression was detected by real-time RT-PCR, flow cytometry, and Western blotting. Apoptosis was assessed by DNA Ladder and caspase assays. Results: Treatment of ACHN human renal cell carcinoma (RCC) cells with cisplatin combined with Mapatumumab did not overcome resistance to these agents. However, treatment with cisplatin in combination with Lexatumumab had a synergistic cytotoxicity. Synergy was also achieved in six primary RCC cell cultures. Lexatumumab and cisplatin also synergistically enhanced apoptosis. Pretreatment with cisplatin followed by Lexatumumab resulted in high cytotoxicity compare with the reverse sequence. Cisplatin significantly increased TRAIL-R2 expression at both mRNA and protein levels. Furthermore, the combination of Lexatumumab and cisplatin significantly enhanced caspase-8 activity, Bid cleavage, up-regulation of Bax, cytochrome c release, and caspase-9, caspase-6, and caspase-3 activities. Importantly, the activation of capase-8 was significantly abrogated by the specific inhibitors of caspase-9, caspase-6, and caspase-3. Furthermore, combination-induced cytotoxicity was significantly suppressed by DR5: Fc chimeric protein and the specific inhibitors of caspase-8, caspase-9, caspase-6, and caspase-3. Similar effect was observed in prostate cancer, bladder cancer, lung cancer, and cervical cancer cells. Conclusions: Cisplatin sensitizes solid cancer cells to Lexatumumab-induced apoptosis by potentiation of the extrinsic and intrinsic apoptotic pathways that lead to enhancement of caspase activation, particularly caspase-8. These results suggest that combination of cisplatin plus Lexatumumab is promising against solid cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2424.