title: Reversal of Mutant KRAS-Mediated Apoptosis Resistance by Concurrent Noxa/Bik Induction and Bcl-2/Bcl-xL Antagonism in Colon Cancer Cells.
abstract: KRAS mutations are frequently detected in human colorectal cancer and contribute to de novo apoptosis resistance and ultimately therapeutic failure. To overcome KRAS-mediated apoptosis resistance, the irreversible proteasome inhibitor, carfilzomib, was evaluated and found to potently induce Noxa, which was dependent upon c-Myc, and Bik. Isogenic mutant versus wild-type KRAS carcinoma cells showed elevated Bcl-xL, confirmed by KRAS siRNA or ectopic expression. Upregulated Bcl-xL by mutant KRAS was mediated by ERK as indicated by ERK knockdown. Bcl-xL expression was regulated at the level of mRNA and protein as shown using actinomycin D and cyclohexamide, respectively. Suppression of Bcl-xL by shRNA sensitized mutant KRAS cells to carfilzomib. Concurrent Bcl-xL antagonism by the BH3 mimetic ABT-263 combined with carfilzomib synergistically enhanced apoptosis that was dependent on Bax or p53, and was attenuated by Noxa or Bik shRNA. In support of this strategy, ectopically expressed Noxa enhanced apoptosis by ABT-263. Carfilzomib-induced Noxa and Bik sequestered Mcl-1 and ABT-263 released Bik and Bak from Bcl-xL, suggesting a mechanism for drug synergy. These preclinical findings establish mutant KRAS-mediated Bcl-xL upregulation as a key mechanism of apoptosis resistance in KRAS-mutant colorectal cancer. Furthermore, antagonizing Bcl-xL enabled carfilzomib-induced Noxa and Bik to induce synergistic apoptosis that reversed KRAS-mediated resistance.
  
  
  CONCLUSIONS
  This novel study reveals a promising treatment strategy to overcome apoptosis resistance in KRAS-mutant colorectal cancer by concurrent upregulation of Noxa/Bik and antagonism of Bcl-xL.
authors.affiliation: Department of Medicine, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota. Department of Oncology, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota.
authors.forename: Koichi
authors.initials: K
authors.lastname: Okamoto
authors.affiliation: Department of Medicine, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota. Department of Oncology, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota.
authors.forename: Aziz
authors.initials: A
authors.lastname: Zaanan
authors.affiliation: Department of Medicine, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota. Department of Oncology, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota.
authors.forename: Hisato
authors.initials: H
authors.lastname: Kawakami
authors.affiliation: Department of Medicine, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota. Department of Oncology, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota.
authors.forename: Shengbing
authors.initials: S
authors.lastname: Huang
authors.affiliation: Department of Medicine, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota. Department of Oncology, GI Research Unit, Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota. sinicrope.frank@mayo.edu.
authors.forename: Frank A
authors.initials: FA
authors.lastname: Sinicrope
mesh_terms: D000814:Aniline Compounds / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004357:Drug Synergism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D024101:Mitochondrial Proteins; D009154:Mutation; D009842:Oligopeptides / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras); D013449:Sulfonamides / Q000494:pharmacology*; D051020:bcl-X Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics*
chemical_list: D000814:Aniline Compounds; D051017:Apoptosis Regulatory Proteins; C000595707:BCL2 protein, human; C494811:BCL2L1 protein, human; C096820:BIK protein, human; C117307:KRAS protein, human; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D009842:Oligopeptides; C498702:PMAIP1 protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D013449:Sulfonamides; D051020:bcl-X Protein; C524865:carfilzomib; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins; C528561:navitoclax