title: Down-regulation of DNA mismatch repair proteins in human and murine tumor spheroids: implications for multicellular resistance to alkylating agents.
abstract: Similar to other anticancer agents, intrinsic or acquired resistance to DNA-damaging chemotherapeutics is a major obstacle for cancer therapy. Current strategies aimed at overcoming this problem are mostly based on the premise that tumor cells acquire heritable genetic mutations that contribute to drug resistance. Here, we present evidence for an epigenetic, tumor cell adhesion-mediated, and reversible form of drug resistance that is associated with a reduction of DNA mismatch repair proteins PMS2 and/or MLH1 as well as other members of this DNA repair process. Growth of human breast cancer, human melanoma, and murine EMT-6 breast cancer cell lines as multicellular spheroids in vitro, which is associated with increased resistance to many chemotherapeutic drugs, including alkylating agents, is shown to lead to a reproducible down-regulation of PMS2, MLH1, or, in some cases, both as well as MHS6, MSH3, and MSH2. The observed down-regulation is in part reversible by treatment of tumor spheroids with the DNA-demethylating agent, 5-azacytidine. Thus, treatment of EMT-6 mouse mammary carcinoma spheroids with 5-azacytidine resulted in reduced and/or disrupted cell-cell adhesion, which in turn sensitized tumor spheroids to cisplatin-mediated killing in vitro. Our results suggest that antiadhesive agents might sensitize tumor spheroids to alkylating agents in part by reversing or preventing reduced DNA mismatch repair activity and that the chemosensitization properties of 5-azacytidine may conceivably reflect its role as a potential antiadhesive agent as well as reversal agent for MLH1 gene silencing in human tumors.
authors.affiliation: Molecular and Cellular Biology Research, Sunnybrook and Women's College Health Sciences Centre, University of Toronto, S-217 Research Building, 2075 Bayview Avenue, Toronto, Ontario, Canada M4N 3M5.
authors.forename: Giulio
authors.initials: G
authors.lastname: Francia
authors.forename: Shane K
authors.initials: SK
authors.lastname: Green
authors.forename: Guido
authors.initials: G
authors.lastname: Bocci
authors.forename: Shan
authors.initials: S
authors.lastname: Man
authors.forename: Urban
authors.initials: U
authors.lastname: Emmenegger
authors.forename: John M L
authors.initials: JM
authors.lastname: Ebos
authors.forename: Adina
authors.initials: A
authors.lastname: Weinerman
authors.forename: Yuval
authors.initials: Y
authors.lastname: Shaked
authors.forename: Robert S
authors.initials: RS
authors.lastname: Kerbel
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D001374:Azacitidine / Q000494:pharmacology; D020137:Base Pair Mismatch; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology; D019175:DNA Methylation; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D008325:Mammary Neoplasms, Experimental / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D018874:Spheroids, Cellular; D014407:Tumor Cells, Cultured
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018906:Antineoplastic Agents, Alkylating; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D006877:Hydroxamic Acids; C501486:MLH1 protein, human; C501485:Mlh1 protein, mouse; D009687:Nuclear Proteins; C012589:trichostatin A; D000251:Adenosine Triphosphatases; C094934:PMS2 protein, human; C499533:Pms2 protein, mouse; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D045643:DNA Repair Enzymes; D001374:Azacitidine; D002945:Cisplatin