Lack of an antitumoral effect of immunomodulatory galactoside-specific mistletoe lectin on N-methyl-N-nitrosourea-induced urinary bladder carcinogenesis in rats

The aim of the present animal experiment was to study the effect of galactoside-specific lectin or agglutinin (VAA) from mistletoe (Viscum album L.) on chemically induced tumor development in the urinary bladder of rats. Since VAA has been shown to exert a remarkable immunomodulating effect, any change in tumor formation would indicate a lectin-triggered immune control of urothelial carcinogenesis in the used model. To produce vesical neoplasms the direct-acting urothelial carcinogen N-methyl-N-nitrosourea (MNU) was administered at a single intravesical dose (7.5 mg/kg body weight). Highly purified VAA was given subcutaneously twice a week at the immunomodulatory dose of 1 ng/kg body weight over a period of 6 months during the critical phases of tumor development. After a total experimental time of 15 months the incidence of epithelial bladder tumors was 29.3 % in controls versus 27.9 % in rats additionally receiving the lectin and thus not significantly different in both experimental groups. There were, moreover, no substantial differences in the histopathologic spectrum of epithelial tumors induced, their patterns of growth, grades of cellular malignancy and local extension. The frequency and histopathology of mesenchymal bladder tumors as well as the incidence and morphology of carcinomas of the ureters and renal pelves also proved to be similar in controls and in rats treated with VAA. In conclusion, the present data provide no evidence for a modifying or even inhibitory effect of the immunomodulatory galactoside-specific mistletoe lectin on experimental urothelial carcinogenesis.