title: Inhibition of GSK3B bypass drug resistance of p53-null colon carcinomas by enabling necroptosis in response to chemotherapy.
abstract: OBJECTIVE
  Evasion from chemotherapy-induced apoptosis due to p53 loss strongly contributes to drug resistance. Identification of specific targets for the treatment of drug-resistant p53-null tumors would therefore increase the effectiveness of cancer therapy.
  
  
  METHODS
  By using a kinase-directed short hairpin RNA library and HCT116p53KO drug-resistant colon carcinoma cells, glycogen synthase kinase 3 beta (GSK3B) was identified as a target whose silencing bypasses drug resistance due to loss of p53. p53-null colon cancer cell lines with different sets of mutations were used to validate the role of GSK3B in sustaining resistance and to characterize cell death mechanisms triggered by chemotherapy when GSK3B is silenced. In vivo xenograft studies were conducted to confirm resensitization of drug-resistant cells to chemotherapy upon GSK3 inhibition. Colon cancer samples from a cohort of 50 chemotherapy-treated stage II patients were analyzed for active GSK3B expression.
  
  
  RESULTS
  Downregulation of GSK3B in various drug-resistant p53-null colon cancer cell lines abolished cell viability and colony growth after drug addition without affecting cell proliferation or cell cycle in untreated cells. Cell death of 5-fluorouracil (5FU)-treated p53-null GSK3B-silenced colon carcinoma cells occurred via PARP1-dependent and AIF-mediated but RIP1-independent necroptosis. In vivo studies showed that drug-resistant xenograft tumor mass was significantly reduced only when 5FU was given after GSK3B inhibition. Tissue microarray analysis of colon carcinoma samples from 5FU-treated patients revealed that GSK3B is significantly more activated in drug-resistant versus responsive patients.
  
  
  CONCLUSIONS
  Targeting GSK3B, in combination with chemotherapy, may represent a novel strategy for the treatment of chemotherapy-resistant tumors.
authors.affiliation: Department of Surgery and Interdisciplinary Medicine, University of Milano-Bicocca, Milano, Italy. emanuela.grassilli@unimib.it
authors.forename: Emanuela
authors.initials: E
authors.lastname: Grassilli
authors.forename: Robert
authors.initials: R
authors.lastname: Narloch
authors.forename: Elena
authors.initials: E
authors.lastname: Federzoni
authors.forename: Leonarda
authors.initials: L
authors.lastname: Ianzano
authors.forename: Fabio
authors.initials: F
authors.lastname: Pisano
authors.forename: Roberto
authors.initials: R
authors.lastname: Giovannoni
authors.forename: Gabriele
authors.initials: G
authors.lastname: Romano
authors.forename: Laura
authors.initials: L
authors.lastname: Masiero
authors.forename: Biagio Eugenio
authors.initials: BE
authors.lastname: Leone
authors.forename: Serena
authors.initials: S
authors.lastname: Bonin
authors.forename: Marisa
authors.initials: M
authors.lastname: Donada
authors.forename: Giorgio
authors.initials: G
authors.lastname: Stanta
authors.forename: Kristian
authors.initials: K
authors.lastname: Helin
authors.forename: Marialuisa
authors.initials: M
authors.lastname: Lavitrano
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000401:mortality; D004249:DNA Damage; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D004789:Enzyme Activation; D005260:Female; D005472:Fluorouracil / Q000494:pharmacology* / Q000627:therapeutic use; D055785:Gene Knockdown Techniques; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D045325:HCT116 Cells; D006801:Humans; D053208:Kaplan-Meier Estimate; D018021:Lithium Chloride / Q000494:pharmacology / Q000627:therapeutic use; D051379:Mice; D008819:Mice, Nude; D009336:Necrosis; D034741:RNA, Small Interfering / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: D000964:Antimetabolites, Antineoplastic; D034741:RNA, Small Interfering; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D018021:Lithium Chloride; D005472:Fluorouracil