TRANSDUCTION OF A DRUG-SENSITIVE TOXIC GENE INTO HUMAN LEUKEMIA-CELL LINES WITH A NOVEL RETROVIRAL VECTOR

To investigate the possibility of killing tumor cells by the expressio n of an exogenously introduced toxic gene, we have constructed a novel retroviral vector (LTRNL) which has the polyA signal deleted herpes s implex virus type 1 thymidine kinase (HSV1-tk) gene. The vector become s toxic by treating cells expressing HSV1-tk with the antiherpetic dru gs acyclovir or ganciclovir (GCV). Cells of the human leukemia lines ( K562, MEG-01) were infected with this vector and two transduced cell l ines (K562/LTRNL, MEG-01/LTRNL) were established. Southern blot analys is confirmed the integration of the HSV1-tk transgene in these cells a nd Northern blot analysis exhibited the expression of 4.8-kb viral mRN A containing the HSV1-tk gene. The MTT (3-(4,5-dimethylthiazol-2-yl)-2 ,5-diphenyl tetrazolium bromide) assay for the in vitro cytotoxic effe cts of GCV to these cells demonstrated that concentrations of about 2. 5 muM for K562/LTRNL and 1.25 muM for MEG-01/LTRNL cells resulted in 5 0% inhibition of cell growth after 72 hr. Subcutaneous tumors of MEG-0 1/LTRNL in KSN nude mice, but not hose of uninfected MEG-01 cells, sho wed durable regressions after exposure of the ice to 40 mg/kg of GCV g iven subcutaneously once a day for 15 days. This study indicates that the LTRNL-infected human leukemia cells exhibit inducible susceptibili ty to GCV.