THE EXTENT OF HETEROCELLULAR COMMUNICATION MEDIATED BY GAP-JUNCTIONS IS PREDICTIVE OF BYSTANDER TUMOR-CYTOTOXICITY IN-VITRO

Herpes simplex virus thymidine kinase (HSV-tk)/ganciclovir (GCV) viral -directed enzyme prodrug gene therapy causes potent, tumor-selective c ytotoxicity in animal models in which HSV-tk gene transduction is limi ted to a minority of tumor cells. The passage of toxic molecules from HSV-tk(+) cells to neighboring HSV-tk(-) cells during GCV therapy is o ne mechanism that may account for this ''bystander'' cytotoxicity. To investigate whether gap junction-mediated intercellular coupling could mediate this bystander effect, we used a flow cytometry assay to quan titate the extent of heterocellular coupling between HSV-tk(+) murine fibroblasts and both rodent and human tumor cell lines. Bystander tumo r cytotoxicity during GCV treatment in a coculture assay was highly co rrelated (P < 0.001) with the extent of gap junction-mediated coupling . These findings show that gap junction-mediated intercellular couplin g contributes to the in vitro bystander effect during HSV-tk/GCV thera py and that retroviral transduction of tumor cells is not required for bystander cytotoxicity.