The tumor-inhibiting effect of diethylstilbestrol and its diphosphate on the Nb-H and Nb-R prostatic carcinomas of the rat.

For many years, diethylstilbestrol (DES) and its diphosphate (DESPP; Honvan) have been standard therapies for prostatic carcinoma. The effects of DES, its monophosphate (DESP) and of DESPP on the weights of accessory sex organs of mice and rats, and on the experimental Noble Nb-H and Nb-R prostatic carcinomas of the rat were, therefore, compared. In intact mature mice, all three compounds led to a strong and dose-dependent inhibition of seminal vesicle weights and testosterone levels, whereas only a slight antiandrogenic activity in castrated mice was found. In intact rats, DES, DESP and DESPP strongly inhibited accessory sex organ weights and testosterone levels. In castrated rats, however, no antiandrogenic activity was determinable. The prostate carcinoma-inhibiting effects of DES and DESPP were tested in comparison with castration in the transplantable hormone-sensitive Nb-H and Nb-R prostatic carcinoma in rats. Whereas castration caused only a retardation of tumor growth, DES and DESPP (3 x 0.1 mg/kg and 1.0 mg/kg weekly s.c.) led to an almost complete inhibition, which was significantly (P less than 0.01) better than the effect of castration. As the weights of accessory sex organs were identically reduced by either castration or the estrogens, a direct tumor-inhibiting effect of DES and DESPP in addition to their testosterone-lowering activity is obvious. This was proved in an experiment with castrated rats. The only slightly inhibitory activity of castration was strongly potentiated by concomitant administration of DES. Moreover, histological examinations revealed that Nb-H and Nb-R tumors were much more damaged by treatment with DES or DESPP than after castration. Morphometry of the tumors showed that tumor reduction is associated with a decrease in the ratio of the epithelial to the stromal density, i.e. there was an even more pronounced decrease in epithelial cells than that found by merely measuring tumor area. These studies show that the prostate carcinoma-inhibiting effect of DES and DESPP in the Nb model is superior to the effect of castration and that they act directly on the tumor cells used, even in castrated rats.