Effects of intravesical instillation of antitumor chemotherapeutic and immunotherapeutic agents on bladder lesion development in rats pretreated with N-butyl-N-(4-hydroxybutyl)nitrosamine

Promoting the effects of intravesical instillation of saline on bladder lesion development in rats pre-treated with BBN

BACKGROUND

At present, immunotherapeutic agents such as bacillus Calmette-Guerin (BCG) and anti-tumor chemotherapeutic agents in saline are used intravesically in patients with bladder carcinoma. However, of greater significance is the possibility that the saline vehicle may itself promote carcinoma development in the bladder.

METHODS

The potential promoting effects of intravesical instillation of saline were assessed in female F344 rats. The animals were divided into 3 groups, all of which received 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in their drinking water for the first 10 weeks. They were then maintained without further treatment (group 1) or received intravesical instillations of 0.3 mL of saline or distilled water once a week for 6 weeks, 15 weeks after the end of the BBN treatment (groups 2 and 3). At 32 weeks, all the animals were killed and examined immunohistochemically with proliferating cell nuclear antigen (PCNA) antibody, as well as by routine histopathologic examination.

RESULTS

Both the incidence and the number of bladder carcinomas were higher in the animals that received instillations of saline than in those who did not receive the instillations. Significant increases in tumor size were also noted for the saline-treated groups, although this was not linked with the PCNA labeling index.

CONCLUSIONS

The results indicate that saline is a promoter of urinary bladder carcinogenesis either because of the catheterization or the fluid itself.

Promoting effects of intravesical instillation of saline on bladder lesion development in rats pretreated with N-butyl-N-(4-hydroxybutyl) nitrosamine are inhibited by bacillus Calmette-Guerin

The promoting effects of intravesical instillation of saline and the efficacy of bacillus Calmette-Guerin (BCG) for prophylaxis of bladder carcinogenesis were assessed. Rats were given 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) for 10 weeks; they were then given 6 weekly intravesical instillations of BCG, saline or distilled water starting 1 week or 15 weeks after the BBN treatment. At 32 weeks, both the incidences and numbers of bladder cancers were elevated in animals receiving the saline. An exception was the early phase BCG group. Significant increases in tumor size were also noted for the saline, but not the distilled water group. The results indicate that intravesical instillation of saline promotes urinary bladder carcinogenesis. However, the inhibitory influence of BCG was suggested if administered at the early, but not the late phase, of carcinogenesis.

Strategy of research for cancer—chemoprevention

It has been reported that environmental chemicals are important factors in terms of both development and prevention of human cancer. For the latter, detection of early stages is an essential first step followed by clinical trials for surveying populations at risk. Thus a great deal of attention has been focused on these areas. However, investigations of possibilities for active prevention of cancer development itself form another major project. Chemoprevention of carcinogenesis, which means prevention of carcinogenesis by exogenous chemical compounds, has been investigated extensively in a variety of organs in animal models. Usually attention is concentrated on only one organ. However, antioxidants, such as BHA, exert very different effects on different organs, suggesting the necessity of whole body approaches to the question of chemoprevention. Furthermore, the mechanisms of chemoprevention, including the step of carcinogenesis, i.e., initiation, promotion, progression or whole carcinogenesis steps, in which exogenous compounds exert their protective effects, should be considered. A medium-term bioassay system and a multi-organ carcinogenesis system, which can be used for investigation of potential for cancer chemoprevention, have been developed in our laboratory. Dose dependent inhibitory effects were established for both BHA and alpha-tocopherol in the medium-term bioassay system, and inhibition of small intestinal carcinogenesis by catechins in green tea has also been investigated in our multi-organ carcinogenesis protocol. It is extremely important for prevention of human cancer that we find new candidates for chemopreventive agents using animal studies. This paper reviews published reports on chemoprevention, taking into account effective stages, and proposes suitable experimental animal models for future investigations in this increasingly important area.