Transduction of a Drug-Sensitive Toxic Gene into Human Leukemia Cell Lines with a Novel Retroviral Vector

Abstract

Abstract

To investigate the possibility of killing tumor cells by the expression of an exogenously introduced toxic gene, we have constructed a novel retroviral vector (LTRNL) which has the polyA signal deleted herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene. The vector becomes toxic by treating cells expressing <HSV1-tk with the antiherpetic drugs acyclovir or ganciclovir (GCV). Cells of the human leukemia lines (K562, MEG-01) were infected with this vector and two transduced cell lines (K562/LTRNL, MEG-01/LTRNL) were established. Southern blot analysis confirmed the integration of the <HSV1-tk transgene in these cells and Northern blot analysis exhibited the expression of 4.8-kb viral mRNA containing the <HSV1-tk gene. The MTT (3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay for the <in vitro cytotoxic effects of GCV to these cells demonstrated that concentrations of about 2.5 μM for K562/LTRNL and 1.25μM for MEG-01/LTRNL cells resulted in 50% inhibition of cell growth after 72 hr. Subcutaneous tumors of MEG-01/LTRNL in KSN nude mice, but not those of uninfected MEG-01 cells, showed durable regressions after exposure of the mice to 40 mg/kg of GCV given subcutaneously once a day for 15 days. This study indicates that the LTRNL-infected human leukemia cells exhibit inducible susceptibility to GCV.