title: Enhancement of lexatumumab-induced apoptosis in human solid cancer cells by Cisplatin in caspase-dependent manner.
abstract: OBJECTIVE
  This study was designed to evaluate the apoptotic effect of mapatumumab or lexatumumab, human agonistic antibodies that target the tumor necrosis factor-related apoptosis-inducing ligand receptor 1 (TRAIL-R1) and receptor 2 (TRAIL-R2), in combination with chemotherapeutic agents, against human solid cancer cells.
  
  
  METHODS
  Cytotoxicity was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Synergy was assessed by isobolographic analysis.
  
  
  RESULTS
  Treatment of ACHN human renal cell carcinoma 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 renal cell carcinoma cell cultures. Lexatumumab and cisplatin also synergistically enhanced apoptosis. Pretreatment with cisplatin followed by lexatumumab resulted in high cytotoxicity compared with the reverse sequence. Cisplatin significantly increased TRAIL-R2 expression at both the mRNA and the 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 caspase-8 was significantly abrogated by the specific inhibitors of caspase-9, caspase-6, and caspase-3. Furthermore, combination-induced cytotoxicity was significantly suppressed by the DR5:Fc chimeric protein and the specific inhibitors of caspase-8, caspase-9, caspase-6, and caspase-3. A 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 amplification of caspase activation, particularly caspase-8, suggesting the combination treatment of solid cancers with cisplatin and lexatumumab might overcome their resistance.
authors.affiliation: Authors' Affiliations: Department of Urology, Faculty of Medicine, Kagawa University, Kagawa, Japan; and Qiqiha Medical College, Heilongjiang, China.
authors.forename: Xiu-Xian
authors.initials: XX
authors.lastname: Wu
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Kakehi
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D002292:Carcinoma, Renal Cell / Q000188:drug therapy / Q000473:pathology; D020169:Caspases / Q000502:physiology*; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology*; D004357:Drug Synergism; D006801:Humans; D007680:Kidney Neoplasms / Q000188:drug therapy / Q000473:pathology; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000502:physiology
chemical_list: D000911:Antibodies, Monoclonal; D000970:Antineoplastic Agents; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; C510234:lexatumumab; D020169:Caspases; D002945:Cisplatin