The antitumor effects of herpes simplex virus thymidine kinase(HSV-tk) and ganciclovir(GCV) strategies for cancer gene therapy have a the following advantages:1) a direct cytotoxicity to HSV-tk modified cancer cells by GCV 2) a cell death by the local transfer of toxic metabolites from the HSV-tk modified cells to nearby unmodified tumor cells(bystander effect), and 3) in vivo bystander effect such as antitumor-immunity. Retroviral and adenoviral sequences can silence transgene expression in cells and mice. In this study, we investigated the above described advantages of HXV-tk/GCV strategy in Lewis lung cell and mouse lung cancer model using retroviral vector and adenoviral vector. Also, we observed whether the expression of a silenced gene can be reactivated by treating cell with butyrate.

Retrovirus-HSV-tk and adenovirus-HSV-tk vectors were used for the transduction of Lewis lung carcinoma(LLC) cells. The change of HSV-tk expression by butyrate was measured by Western blot.The antitumor activities containing bystander effect were observed in vivo(by MTT assay) and in vivo tumor models of various combinations of LLC and LLC-tk.

1. Butyrate induced the enhancement of HSV-tk expression from adenovirally transduced cells but not from retrovirally transduced cells. 2. Both retrovirus-HSV-tk and adenovirus-HSV-tk vectors with GCV treatment were effective for killing of tumor cell in vitro and suppression of LLC tumorigenicity. Bystander effect was responsible for killing of mixture of LLC-tk and LLC in vitro and in vivo-tumorigenicity model.

Butyrate could augment adenoviral vector seems to be an effective approach for lung cancer therapy.