In vivo selection of androgen-insensitive cells in R3327-G rat prostate tumors: diethylstilbestrol diphosphate treatment versus orchiectomy.

Tumors grown in diethylstilbestrol diphosphate (DES)-treated rats grew significantly more slowly than tumors grown in orchiectomized animals, and tumors grown in orchiectomized animals grew significantly more slowly than tumors grown in controls (intact male rats). When these tumors (phase I) were dispersed and reimplanted into DES-treated, orchiectomized, or control rats in all possible combinations (phase II), a partial selection of androgen-insensitive cells was observed in tumors grown in DES-treated animals. Tumors grown in DES-treated phase I animals responded significantly less to DES treatment or orchiectomy in phase II. In contrast, tumors from phase I orchiectomized animals showed the same responses to orchiectomy in phase II. Since the administration of exogenous testosterone propionate prevented the growth rate inhibitory effects of both DES treatment and orchiectomy, the added effect of DES seemed to be antiandrogenic.