Ectopic expression of herpes simplex virus‐thymidine kinase gene in human non‐small cell lung cancer cells conferred caspase‐activated apoptosis sensitized by ganciclovir

Abstract Human non‐small cell lung cancer (NSCLC) cells were transfected with recombinant prodrug herpes simplex virus type I thymidine kinase (HSV‐ tk ) cDNA, and the selected clones underwent apoptosis in response to induction by antiviral ganciclovir (GCV). The efficiency of GCV‐induced growth inhibition and the extent of the bystander effect were associated with the expression level of HSV‐TK in stable transfectants. Development in the HSV‐ tk /GCV system toward cell death was initiated with cell‐cycle accumulation at S and G 2 /M phases, immediately followed by the appearance of sub‐G 0 /G 1 cells after drug exposure. To investigate the regulation of cell‐cycle modulators during drug treatment, we analyzed release of the apoptosis initiator cytochrome c and activation of the downstream effectors caspase‐9, caspase‐3 and poly(ADP‐ribose)polymerase 16 hr after GCV sensitization, followed by transient escalation of tumor‐suppressor p53 and cell‐cycle modulators cyclin A and B 1 before committing to programmed cell death. Furthermore, tumor regression was proportional to the degree of ectopic expression of the transferred HSV‐ tk gene. Our results demonstrate that the HSV‐ tk /GCV system effectively inhibits the proliferation of NSCLC cells in vitro and in vivo through potent induction of apoptosis, thus providing a rationale for further development. © 2002 Wiley‐Liss, Inc.