NONVIRAL VECTOR-MEDIATED THYMIDINE KINASE GENE-TRANSFER AND GANCICLOVIR TREATMENT IN LEIOMYOMA CELLS

Objective: To test the hypotheses that ganciclovir is cytotoxic to lei omyoma cells transfected with herpes simplex virus thymidine kinase an d that estrogen modulates the responsiveness of tumor cells to this ge ne therapy approach. Methods: Human and rat cultured uterine leiomyoma cells were transfected with plasmids encoding the beta-galactosidase gene, thymidine kinase gene, or a control plasmid. Transfection effici ency was monitored by measuring beta-galactosidase enzyme activity. Ga nciclovir cytotoxicity in thymidine kinase-transfected cells was asses sed by monitoring cell viability using trypan blue exclusion. The ''by stander effect,'' a phenomenon in which thymidine kinase-expressing ce lls exposed to ganciclovir are toxic to adjacent thymidine kinase-none xpressing cells, was assessed when thymidine kinase vector-transfected cells were cocultured with control plasmid-transfected cells at Vario us percentages before exposure to ganciclovir. The effect of estradiol on ganciclovir-thymidine kinase-mediated cytotoxicity was assessed in estrogen-responsive rat leiomyoma cells. Results: A thymidine kinase- ganciclovir-mediated ''bystander effect'' was demonstrated, with 48.6% (human) and 65.6% (rat) cell death when 5% of the leiomyoma cells wer e transfected with the pNGVL1-tk vector, with 0.84% and 1.9% of the ce lls expected to express thymidine kinase as based on the 16.7% and 39. 8% transfection efficiency determined by the reporter gene assay in hu man and rat leiomyoma cells, respectively. Estradiol promoted cell gro wth and enhanced the ''bystander effect'' in rat leiomyoma cells. Conc lusion: These Endings demonstrate the feasibility of using thymidine k inase gene therapy as a novel treatment for uterine leiomyomas. The ef fect of estrogen may provide a mechanism to enhance the tumor-suppress ive effect of this approach. (C) 1998 by The American College of Obste tricians and Gynecologists.