title: Mechanisms for ganciclovir resistance in gastrointestinal tumor cells transduced with a retroviral vector containing the herpes simplex virus thymidine kinase gene.
abstract: Transfer of the herpes simplex thymidine kinase (HSV-TK) gene into tumor cells confers sensitivity to the cells to the viral drug ganciclovir (GCV). Although the efficacy of the HSV-TK/GCV approach is well studied, the mechanisms for the resistance of HSV-TK-transduced tumor cells to GCV are poorly understood. Here, we examined the mechanisms for GCV resistance in HSV-TK-transduced gastrointestinal (GI) cell lines. Our results show that GCV sensitivities vary in vitro and in vivo among the different HSV-TK-transduced GI tumor cell lines. GCV-resistant colonies were isolated from several different HSV-TK-transduced GI tumor cell lines after 14 days of GCV treatment. Characterization of GCV-resistant colonies demonstrated that the HSV-TK gene was either partially or completely deleted from the resistant HSV-TK-transduced cells. In the HT-29 RM and MIAPACA-2 RM cells, a 220-bp deletion of the gene was found, whereas in the HT-29 R1-R5-resistant cells, the whole TK gene was found to be absent. Immunocytochemical studies using a polyclonal antibody to the TK protein demonstrated that the HSV-TK protein was absent in the GCV-resistant, HSV-TK-transduced cells. Transfection of the resistant cells with an adenoviral vector containing a HSV-TK gene restored sensitivity to GCV. The presence of GCV-resistant cells was only demonstrable in GI tumor cell lines that also demonstrated a poor bystander effect. Our results suggest that GCV resistance found in tumor cells transduced with a retroviral HSV-TK gene is due to the lack of a functional TK protein in the tumor cells rather than any intrinsic resistance of the cells to GCV. In tumor cells with a good bystander effect, the small percentage of TK-transduced cells that do not express the TK protein are probably killed by the bystander effect because GCV-resistant tumor cells were not found in these cell lines. GCV-resistant tumor cells were found only in tumor cell lines with a poor bystander effect, by which, presumably, the transduced tumor cells lacking a functional TK gene were not killed by the bystander killing effect.
authors.affiliation: Gene Therapy Laboratories, Los Angeles, California, USA.
authors.forename: L
authors.initials: L
authors.lastname: Yang
authors.forename: R
authors.initials: R
authors.lastname: Hwang
authors.forename: Y
authors.initials: Y
authors.lastname: Chiang
authors.forename: E M
authors.initials: EM
authors.lastname: Gordon
authors.forename: W F
authors.initials: WF
authors.lastname: Anderson
authors.forename: D
authors.initials: D
authors.lastname: Parekh
mesh_terms: D000998:Antiviral Agents / Q000633:toxicity; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D003110:Colonic Neoplasms; D019008:Drug Resistance, Neoplasm; D015774:Ganciclovir / Q000633:toxicity*; D018014:Gene Transfer Techniques; D015316:Genetic Therapy; D005822:Genetic Vectors; D006801:Humans; D007700:Kinetics; D010190:Pancreatic Neoplasms; D012190:Retroviridae; D018139:Simplexvirus / Q000201:enzymology / Q000235:genetics*; D013274:Stomach Neoplasms; D013937:Thymidine Kinase / Q000096:biosynthesis / Q000235:genetics*; D014407:Tumor Cells, Cultured
chemical_list: D000998:Antiviral Agents; D013937:Thymidine Kinase; D015774:Ganciclovir