title: Gene expression analysis of tumor spheroids reveals a role for suppressed DNA mismatch repair in multicellular resistance to alkylating agents.
abstract: Drug resistance is a major obstacle in the successful treatment of cancer. Thus, elucidation of the mechanisms responsible is a critical first step in trying to prevent or delay such manifestations of resistance. In this regard, three-dimensional multicellular tumor cell spheroids are intrinsically more resistant to virtually all anticancer cytotoxic drugs than conventional monolayer cultures. We have employed the EMT-6 subline PC5T, which forms highly compact spheroids, and differential display to identify candidate genes whose expression differs between monolayer and spheroids. Approximately 5,000 bands were analyzed, revealing 26 to be differentially expressed. Analysis of EMT-6 tumor variants selected in vivo for acquired resistance to alkylating agents identified eight genes whose expression correlated with drug resistance in tumor spheroids. Four genes (encoding Nop56, the NADH SDAP subunit, and two novel sequences) were found to be down-regulated in EMT-6 spheroids and four (encoding 2-oxoglutarate carrier protein, JTV-1, and two novel sequences) were up-regulated. Analysis of the DNA mismatch repair-associated PMS2 gene, which overlaps at the genomic level with the JTV-1 gene, revealed PMS2 mRNA to be down-regulated in tumor spheroids, which was confirmed at the protein level. Analysis of PMS2(-/-) mouse embryo fibroblasts confirmed a role for PMS2 in sensitivity to cisplatin, and DNA mismatch repair activity was found to be reduced in EMT-6 spheroids compared to monolayers. Dominant negative PMS2 transfection caused increased resistance to cisplatin in EMT-6 and CHO cells. Our results implicate reduced DNA mismatch repair as a determinant factor of reversible multicellular resistance of tumor cells to alkylating agents.
authors.affiliation: Molecular and Cellular Biology Research, Sunnybrook and Women's College Health Sciences Centre, S-217 Research Building, 2075 Bayview Ave., Toronto, Ontario, Canada M4N 3M5.
authors.forename: Giulio
authors.initials: G
authors.lastname: Francia
authors.forename: Shan
authors.initials: S
authors.lastname: Man
authors.forename: Beverly
authors.initials: B
authors.lastname: Teicher
authors.forename: Luigi
authors.initials: L
authors.lastname: Grasso
authors.forename: Robert S
authors.initials: RS
authors.lastname: Kerbel
mesh_terms: D000477:Alkylating Agents / Q000494:pharmacology*; D000818:Animals; D020137:Base Pair Mismatch; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D016466:CHO Cells; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology; D006224:Cricetinae; D004260:DNA Repair; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D005260:Female; D020869:Gene Expression Profiling; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008957:Models, Genetic; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D018874:Spheroids, Cellular / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
chemical_list: D000477:Alkylating Agents; D012313:RNA; D002945:Cisplatin