Bifidobacterium infantis-mediated HSV-TK/GCV suicide gene therapy induces both extrinsic and intrinsic apoptosis in a rat model of bladder cancer

Bladder cancer is the most common cancer in the urological tract. Here, we investigated the molecular pathways involved in the apoptosis of rodent bladder cancer, which was treated with Bifidobacterium infantis (BI)-mediated herpes simplex virus thymidine kinase (HSV-TK)/ganciclovir (GCV) suicide gene therapy. We engineered the BI-TK system, which consists of BI with the recombinant plasmid PGEX-1λT carrying HSV-TK (that is, TK) gene. Tumor-bearing rats were randomly divided into three groups and tail vein injected with normal saline (group A), BI/PGEX-1λT (group B) or BI-TK (group C), followed by intraperitoneal injection of GCV. The BI-TK/GCV system (group C) was shown to inhibit tumor growth and caused the apoptosis of tumor cells as assessed by in situ terminal transferase dUTP nick-end labeling assay. While varied extents of apoptosis were detected in tumor cells from all groups, tumor cells treated with BI-TK/GCV system (group C) exhibited the highest level of apoptosis (P<0.05), consistent with our previous studies. Furthermore, we found that the expression levels of Fas, FasL, Cyt-C and caspase-9 in tumor tissues derived from group C were significantly higher than the other two groups (P<0.001). Therefore, our results have demonstrated that the BI-TK/GCV therapy system exhibits a sustainable antitumor growth activity in the rodent model of bladder cancer. Mechanistically, both extrinsic and intrinsic apoptosis pathways are involved in the BI-TK/GCV antitumor functionality.