title: Differential chemosensitivity of breast cancer cells to ganciclovir treatment following adenovirus-mediated herpes simplex virus thymidine kinase gene transfer.
abstract: The development of resistance to radiation and chemotherapeutic agents that cause DNA damage is a major problem for the treatment of breast and other cancers. The p53 tumor suppressor gene plays a direct role in the signaling of cell cycle arrest and apoptosis in response to DNA damage, and p53 gene mutations have been correlated with increased resistance to DNA-damaging agents. Herpes simplex virus thymidine kinase (HSV-tk) gene transfer followed by ganciclovir (GCV) treatment is a novel tumor ablation strategy that has shown good success in a variety of experimental tumor models. However, GCV cytotoxicity is believed to be mediated by DNA damage-induced apoptosis, and the relationship between p53 gene status, p53-mediated apoptosis, and the sensitivity of human tumors to HSV-tk/GCV treatment has not been firmly established. To address this issue, we compared the therapeutic efficacy of adenovirus-mediated HSV-tk gene transfer and GCV treatment in two human breast cancer cell lines: MCF-7 cells, which express wild-type p53, and MDA-MB-468 cells, which express high levels of a mutant p53 (273 Arg-His). Treating MCF-7 cells with AdHSV-tk/GCV led to the predicted increase in endogenous p53 and p21WAF1/CIP1 protein levels, and apoptosis was observed in a significant proportion of the target cell population. However, treating MDA-MB-468 cells under the same conditions resulted in a much stronger apoptotic response in the absence of induction in p21WAF1/CIP1 protein levels. This latter result suggested that HSV-tk/GCV treatment can activate a strong p53-independent apoptotic response in tumor cells that lack functional p53. To confirm this observation, four additional human breast cancer cell lines expressing mutant p53 were examined. Although a significant degree of variability in GCV chemosensitivity was observed in these cell lines, all displayed a greater reduction in cell viability than MCF-7 or normal mammary cells treated under the same conditions. These results suggest that endogenous p53 status does not correlate with chemosensitivity to HSV-tk/GCV treatment. Furthermore, evidence for a p53-independent apoptotic response serves to extend the potential of this therapeutic strategy to tumors that express mutant p53 and that may have developed resistance to conventional genotoxic agents.
authors: Ontario Cancer Institute, Princess Margaret Hospital, and Department of Medical Biophysics, University of Toronto, Canada.
authors: P X
authors: PX
authors: Li
authors: D
authors: D
authors: Ngo
authors: A M
authors: AM
authors: Brade
authors: H J
authors: HJ
authors: Klamut
mesh_terms: D000165:Acridine Orange / Q000378:metabolism; D000256:Adenoviridae / Q000378:metabolism; D017209:Apoptosis; D015152:Blotting, Northern; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000628:therapy*; D002470:Cell Survival; D053938:DNA Fragmentation; D004996:Ethidium / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D015774:Ganciclovir / Q000627:therapeutic use*; D015316:Genetic Therapy; D006801:Humans; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D012680:Sensitivity and Specificity; D018139:Simplexvirus / Q000235:genetics*; D013937:Thymidine Kinase / Q000008:administration & dosage / Q000235:genetics*; D013997:Time Factors; D014161:Transduction, Genetic; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects / Q000378:metabolism
chemical_list: D005456:Fluorescent Dyes; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D013937:Thymidine Kinase; D004996:Ethidium; D000165:Acridine Orange; D015774:Ganciclovir