Cooperative therapeutic effects of androgen ablation and adenovirus-mediated herpes simplex virus thymidine kinase gene and ganciclovir therapy in experimental prostate cancer

Abstract

Adenovirus-mediated transduction of the herpes simplex thymidine kinase gene (HSV-tk) in conjunction with ganciclovir (GCV) has been shown to result in significant growth suppression and to enhance survival in a model of mouse prostate cancer. However, this therapeutic activity is not sustained, because in most cases tumors eventually regrow and ultimately cause the death of the host. Androgen ablation, an inducer of apoptosis in prostate cells which is used widely as palliative therapy in patients with prostate cancer, was combined with HSV-tk plus GCV using an androgen-sensitive mouse prostate cancer cell line. The combination of castration and HSV-tk plus GCV led to markedly enhanced tumor growth suppression in both subcutaneous and orthotopic models compared with either treatment alone and resulted in an enhanced survival in which combination-treated animals lived twice as long as controls in the subcutaneous model and over 50% longer than controls in the orthotopic model. Further analysis of apoptotic activity demonstrated high levels of apoptosis only in combined androgen ablation and HSV-tk plus GCV-treated tumors after 14 days of growth in an androgen-depleted environment and 8 days after HSV-tk plus GCV therapy. At this time, the apoptotic index, but not the percent of necrotic tissue, was significantly higher for combination therapy-treated tumors relative to control-treated tumors or either treatment alone. These data indicate that the therapeutic effects of androgen ablation and HSV-tk plus GCV are cooperative and that increased apoptosis may, in part, underlie these activities.

Combination gene therapy with adenoviral vector-mediated HSV-tk+GCV and IL-12 in an orthotopic mouse model for prostate cancer

“…To determine an optimal concentration of AdmIL-12 for use with AdHSV-tk GCV in regard to tumor growth suppression, we performed a dose escalation study with a ®xed optimal concentration of AdHSV-tk (5610 8 ) PFU and increasing concentrations of AdmIL-12 beginning with 1610 7 PFU/mL. The results indicated that a dose of 1610 8 PFU of AdmIL-12, which we previously demonstrated to be the maximally effective, nontoxic dose in this system, 4 was also able to generate co-operative activities (Figure 1a), although a dose of 5610 7 PFU of AdmIL-12 was nearly as effective when combined with AdHSV-tk.…”

“…Animals with pre-existing metastases were killed on the eighth day after vector injection at which time the lungs were weighed, ®xed in Bouin's ®xative, and visible lung metastases counted with the aid of a dissecting microscope at 106 magni®cation as previously described. 4,8 To block NK activity mice were injected with 5000 RM-9 cells orthotopically and 100 000 cells via the tail vein. Five days later one group received an intraperitoneal injection of 100 mg of anti-asialo-GM1 serum in 0.15 ml.…”

“…13 The extent of apoptosis was assessed quantitatively via computer assisted image analysis as previously described. 8 The extent of necrosis was also assessed quantitatively on H&E stained slides via computer-assisted range image analysis. 8 For immunohistochemical analyses tissues were snap frozen with liquid nitrogen in Tissue-Tec OCT compound.…”

“…8 The extent of necrosis was also assessed quantitatively on H&E stained slides via computer-assisted range image analysis. 8 For immunohistochemical analyses tissues were snap frozen with liquid nitrogen in Tissue-Tec OCT compound. They were then sectioned and 6 mm slices ®xed on polylysine-coated slides with cold acetone.…”

“…The activities of AdHSV-tk GCV could not only generate signi®cant cytotoxic activities locally and, thereby, contribute to a therapeutic response, but also potentially maximize tumor antigen presentation through its necrotic and apoptotic effects. 1,8,9 The addition of adenoviral vector-delivered locally active IL-12 could potentially maximize the in®ltration of speci®c immune cells and cause them to be activated and mature into active effectors and thus effectively co-operate with AdHSVtk GCV gene therapy. In this study we evaluated the speci®c in®ltration of immune cells within orthotopic mouse prostate cancer under single AdHSV-tk GCV or AdmIL-12 in situ gene therapy and combined treatment conditions.…”