Adenovirus-mediated suicide-gene therapy using the herpes simplex virus thymidine kinase gene in cell and animal models of human prostate cancer: changes in tumour cell proliferative activity

Objectives To determine the feasibility and efficacy of suicide-gene therap y using adenovirus (Ad)-mediated herpes simplex virus thymidine kinase (HSV -TK) and the prodrug acyclovir, and to evaluate changes in the biological p henotype for tumour cell proliferative activity after suicide-gene therapy in animal models of human prostate cancer. Materials and methods Using a replication-defective adenoviral vector (cyto megalovirus, CMV) containing the beta-galactosidase gene (Ad-CMV-beta-gal) as a control and Ad-CMV-TK as the therapeutic vector under the transcriptio nal control of the CMV promoter, transduction efficiency was assessed in vi tro by infecting LNCaP and PC-3 androgen-dependent and independent human pr ostate cancer cells with Ad-CMV-beta-gal, and using X-gal staining. The TK activity in prostate cancer cells infected with Ad-CMV-TK was determined by measuring TK-mediated [H-3]-gancyclovir phosphorylation. The sensitivity o f LNCaP and PC-3 cells to Ad-CMV-TK in vitro was determined after infection with the therapeutic vector with or without acyclovir. The inhibition of P C-3 tumour growth in vivo induced by the Ad-CMV-TK/acyclovir suicide-gene s ystem was assessed in separate and controlled experiments using human prost ate cancer mouse models. Ki-67 proliferative antigen and proliferating cell nuclear antigen (PCNA), both useful proliferative indices, were evaluated using immunohistochemical staining (MIB-1 monoclonal antibody and monoclona l anti-PCNA antibody) in formalin-fixed, paraffin-embedded tissues from gen e therapy-treated and control animals. Results The mean TK activity was significantly higher in LNCaP and PC-3 cel ls infected with Ad-CMV-TK than in cells infected with Ad-CMV-beta-gal, use d as a control (P<0.05). The growth of human prostate cancer cells with Ad- CMV-TK was significantly inhibited by adding acyclovir in vitro (P<0.05). I n the in vivo experiments using the PC-3 human prostate cancer mouse model, tumour volume and growth was lower in mice treated with Ad-CMV-TK/acyclovi r than in those treated with Ad-CMV-TK only, acyclovir only or untreated (c ontrols) (P<0.05). Histochemical staining of tumour tissues showed that Ad- CMV-TK/ acyclovir destroyed PC-3 tumours through tumour cell death and apop tosis, with local lymphatic infiltration. The mean PCNA labelling index in prostate cancer cells of mice treated with Ad-CMV-TK/acyclovir was signific antly lower than that in untreated controls (P<0.05, Mann-Whitney U-test). The Ki-67 labelling index in prostate cancer cells of mice treated with Ad- CMV-TK/acyclovir was also lower than that in untreated controls (P<0.05, St udent's t-test). Adenovirus-mediated suicide-gene therapy using the HSV-TK gene decreased the proliferative activity of PC-3 human prostatic cancer ce lls in vivo. Conclusions Adenovirus-mediated suicide-gene therapy using an HSV-TK/acyclo vir system provided effective therapy in an experimental human prostate can cer mouse model, by significantly inhibiting tumour growth and decreasing t he proliferative activity of human prostate cancer cells. Such therapy coul d be developed as a novel method for treating patients with androgen-indepe ndent prostate cancer.