title: MLH1 deficiency enhances tumor cell sensitivity to ganciclovir.
abstract: Suicide gene therapy with herpes simplex virus thymidine kinase (HSV-TK) and ganciclovir (GCV) is notable for producing multi-log cytotoxicity in a unique pattern of delayed cytotoxicity in S-phase. As hydroxyurea, a ribonucleotide reductase inhibitor that activates mismatch repair, can increase sensitivity to GCV, we evaluated the role of MLH1, an essential mismatch repair protein, in GCV cytotoxicity. Using HCT116TK (HSV-TK-expressing) colon carcinoma cells that express or lack MLH1, cell-survival studies demonstrated greater GCV sensitivity in the MLH1-deficient cells, primarily at high concentrations. This could not be explained by differences in GCV metabolism, as the less sensitive MLH1-expresssing cells accumulated more GCV triphosphate and incorporated more of the analog into DNA. SiRNA suppression of MLH1 in U251 glioblastoma or SW480 colon carcinoma cells also enhanced sensitivity to high concentrations of GCV. Studies in a pa nel of yeast deletion mutants confirmed the results with MLH1, and further suggested a role for homologous recombination repair and several cell-cycle checkpoint proteins in GCV cytotoxicity. These data suggest that MLH1 can prevent cytotoxicity with GCV. Targeting mismatch repair-deficient tumors may increase efficacy of this suicide gene therapy approach to cancer treatment.
authors.affiliation: Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, MI 48109-5633, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: O'Konek
authors.forename: P D
authors.initials: PD
authors.lastname: Boucher
authors.forename: A A
authors.initials: AA
authors.lastname: Iacco
authors.forename: T E
authors.initials: TE
authors.lastname: Wilson
authors.forename: D S
authors.initials: DS
authors.lastname: Shewach
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology* / Q000628:therapy; D004249:DNA Damage; D053843:DNA Mismatch Repair; D015774:Ganciclovir / Q000494:pharmacology*; D015316:Genetic Therapy; D005909:Glioblastoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology* / Q000628:therapy; D006801:Humans; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000254:growth & development
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D000070957:MutL Protein Homolog 1; D015774:Ganciclovir