title: Killing of resistant cancer cells with low Bak by a combination of an antimesothelin immunotoxin and a TRAIL Receptor 2 agonist antibody.
abstract: OBJECTIVE
  Many solid tumors express cell surface mesothelin making them attractive targets for antibody-based therapies of cancer. SS1P [antimesothelin(Fv)PE38] is a recombinant immunotoxin (RIT) that has potent cytotoxic activity on several cancer cell lines and clinical activity in mesothelioma patients. Pancreatic cancers express mesothelin and are known to be resistant to most chemotherapeutic agents. The goal of this study is to treat pancreatic cancer with RIT by targeting mesothelin.
  
  
  METHODS
  We measured the cytotoxic activity of an antimesothelin immunotoxin on pancreatic cancer cells. We also measured the levels of several pro- and antiapoptotic proteins, as well as the ability of TNF-related apoptosis-inducing ligand (TRAIL) or the anti-TRAIL receptor 2 agonist antibody (HGS-ETR2) to kill pancreatic cells, and the cytotoxic activity of the two agents together in cell culture and against tumors in mice.
  
  
  RESULTS
  In two pancreatic cancer cell lines, immunotoxin treatment inhibited protein synthesis but did not produce significant cell death. The resistant lines had low levels of the proapoptotic protein Bak. Increasing Bak expression enhanced the sensitivity to immunotoxins, whereas Bak knockdown diminished it. We also found that combining immunotoxin with TRAIL or HGS-ETR2 caused synergistic cell death, and together triggered caspase-8 recruitment and activation, Bid cleavage and Bax activation. Combining SS1P with HGS-ETR2 also acted synergistically to decrease tumor burden in a mouse model.
  
  
  CONCLUSIONS
  Our data show that low Bak can cause cancer cells to be resistant to immunotoxin treatment and that combining immunotoxin with TRAIL or a TRAIL agonist antibody can overcome resistance.
authors.affiliation: Laboratory of Molecular Biology, Center for Cancer Research, and Pediatric Oncology Branch, National Cancer Institute, NIH, Bethesda, Maryland, USA.
authors.forename: Xing
authors.initials: X
authors.lastname: Du
authors.forename: Laiman
authors.initials: L
authors.lastname: Xiang
authors.forename: Crystal
authors.initials: C
authors.lastname: Mackall
authors.forename: Ira
authors.initials: I
authors.lastname: Pastan
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004357:Drug Synergism; D058851:GPI-Linked Proteins / Q000037:antagonists & inhibitors*; D045325:HCT116 Cells; D006367:HeLa Cells; D006801:Humans; D000922:Immunotoxins / Q000627:therapeutic use; D000090204:Mesothelin; D051379:Mice; D008819:Mice, Nude; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000819:agonists*; D023041:Xenograft Model Antitumor Assays; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D058851:GPI-Linked Proteins; D000922:Immunotoxins; C000715528:Msln protein, mouse; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; C474515:SS1(dsFv)PE38; D050998:bcl-2 Homologous Antagonist-Killer Protein; C510234:lexatumumab; D000090204:Mesothelin