The effects of dihydrotestosterone (17β-hydroxy-5α-androstan-3-one) and testosterone on the growth of the androgen-dependent Shionogi SC-115 tumour in mice have been compared and the metabolites in the tumour arising from each steroid have been identified. After the transfer of SC-115 tumour cells to castrated male mice, treatment of the recipients with dihydrotestosterone produced a striking proliferative response that enabled earlier tumour detection and led to a higher tumour incidence than obtained with testosterone. At short intervals after the intravenous injection of 200μCi of [1,2-3H]testosterone the amounts of radioactivity in tumour, muscle and seminal vesicles were almost equal. The metabolism of [1,2-3H]testosterone in tumour and muscle was slight in comparison with the extensive metabolism in seminal vesciles. Whereas up to 7% of the total neutral steroid recovered from whole tumour tissue and isolated nuclei was in the form of [1,2-3H]dihydrotestosterone, the amount of this compound in the corresponding preparations from seminal vesciles was several times greater. When the metabolism of [1,2-3H]dihydrotestosterone in tumour tissue was studied, it was found that more than 60% of the total neutral steroid in both cytoplasm and nuclei consisted of [1,2-3H]dihydrotestosterone. Thus much higher intracellular concentrations of dihydrotestosterone occurred with the administration of this steroid than with testosterone. Tumour cell proliferation was suppressed by oestradiol and the amount of androgen in nuclei was significantly decreased by high doses of this hormone.
