Currently animal models of bladder tumors are mostly limited to the use of xenograft tumor models with subcutaneous or planting bladder tumor cells. Subcutaneous tumor model is most commonly used because of its easy manipulation, tumor growth consistency, and easy observation. However, the subcutaneous xenograft models ignore the anatomic and physiological characteristics of the organ. The method of MNU induce tumor have many good quality: easy, little used, induce way agility, it can be filling into bladder or injection by vein. Steinberg  evaluate the drug treatment therapeutic efficacy in MNU induced rat bladder tumor model, the result showed that the occurrence and biological behaviour is similar between MNU induced rat bladder tumor model and human TCCB, so MNU induced rat bladder tumor model can be used to research the treatment of bladder tumor.
In this study, we demonstrated that MNU reperfusion - induced rat bladder tumor have a high rate of success (nearly 100%) with morphological and pathological features similar to that of human bladder cancer. At the endpoint of this study, we also examined other organs, including liver, kidney, heart and lungs, and did not found any tumor formation, which is consistent with earlier reports [7, 13–15]. Tumor-bearing rat was put to death l2 weeks after filling with MNU, cut open the bladder, we fond that the wall of bladder is thickening, pale and cauliflower like neoplasia, most of the bladder have many neoplasia, the serious one is full of neoplasia in the bladder. After 12 weeks, HE stain showed the typical TCCB (transitional cell carcinoma of the bladder) change appearance and focal under membrana mucosa, muscular layer infiltrate of tumor. It seems that the MNU bladder perfusion induced-cancer has organ specificity; and we did not find any adenocarcinoma or squamous cell carcinoma of the bladder histological changes. Therefore, MNU perfusion may represent an ideal approach for the establishment of animal models of bladder cancer for evaluating novel anti-cancer treatments.
Targeted cancer gene therapy is an ideal treatment for eradicating and/or limiting cancer growth and improving quality of life and survival rate of cancer patients. HSV-TK/GCV system is one of the most commonly used suicide gene therapy systems. However, most studies have used viral expression vectors, such as adenoviral or retroviral vectors to achieve the TK gene expression. Although efficient, these viral delivery systems have their own limitations, such as host immune response, low titer, the limited host range, serum complement inactivation, and detrimental mutations caused by random integrations into the host genome [3, 16–19].
In this study, we explored the possible use of Bifidobacterium infantis as a tumor-targeting gene delivery vehicle in bladd cancer gene therapy. Bifidobacterium infantis are gram-positive bacteria which are non-pathogenic and strictly anaerobic without internal and external toxin production. It has been reported that Bifidobacterium can inhibit tumor growth [9, 15, 20]. Yazawa et al confirmed that when mammary tumors induced in rats were injected with Bifidobacterium via the tail vein, Bifidobacterium could propagate specifically in tumor tissuesproliferation, resulting in tumor tissue atrophy and extending the survival of tumor-bearing rats [9, 15, 20]. It has also been reported that when Bifidobacterium expressing human endostatin were injected to tumor-bearing mice via the tail vein, the antitumor effect was improved than the prototype Bifidobacterium [5, 17, 19]. These reports indicate that Bifidobacterium can be used as a tumor-targeting vector for cancer gene therapy [2–5, 21]).
We have demonstrated the successful use of a novel Bifidobacterium infantis-mediated tumor-targeting suicide gene therapy system in inhibiting bladder tumor growth. Our results also indicate that induced apoptosis may at least in part account for the anticancer activity of the BI-TK system. Apoptosis, also known as programmed cell death, refers to certain physiological or pathological conditions in which the end of active life is regulated by the activation of a set of apoptotic factors. In normal cells, apoptosis and proliferation coexist and maintain a dynamic equilibrium. When the BI-TK/GCV suicide gene targeting system was delivered into tumor-bearing rats, we found that the system can significantly inhibit rat bladder tumor growth, induce apoptosis in tumor cells, and increase Caspase 3 protein. Therefore, our findings strongly suggest that Bifidobacterium infantis-mediated tumor-targeting suicide gene therapy system may represent a novel therapy for bladder cancer.