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 ga lactoside-specific lectin or agglutinin (VAA) from mistletoe (Viscum a lbum L.) on chemically induced tumor development in the urinary bladde r of rats. Since VAA has been shown to exert a remarkable immunomodula ting effect, any change in tumor formation would indicate a lectin-tri ggered 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 subcutaneo usly 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 developm ent. After a total experimental time of 15 months the incidence of epi thelial bladder tumors was 29.3 % in controls versus 27.9 % in rats ad ditionally receiving the lectin and thus not significantly different i n both experimental groups. There were, moreover, no substantial diffe rences in the histopathologic spectrum of epithelial tumors induced, t heir patterns of growth, grades of cellular malignancy and local exten sion. The frequency and histopathology of mesenchymal bladder tumors a s well as the incidence and morphology of carcinomas of the ureters an d renal pelves also proved to be similar in controls and in rats treat ed with VAA. In conclusion, the present data provide no evidence for a modifying or even inhibitory effect of the immunomodulatory galactosi de-specific mistletoe lectin on experimental urothelial carcinogenesis .