To evaluate a possible direct cytotoxic effect of diethylstilbestrol diphosphate (DESDP) in the treatment of prostate cancer we exposed three prostatic carcinoma cell lines (LNCaP, DU 145, and PC-3), 2 nonprostatic neoplastic cell lines (KB and EJ), and one nontransformed cell line (MRC-5) to diethylstilbestrol (DES), diethylstilbestrol monophosphate, and DESDP at levels occurring in patients' sera during p.o. DES therapy (2 to 5 ng/ml) or DESDP infusions (1 to 20 µg/ml), respectively. With 5 ng/ml of DES no effect was seen in LNCaP cells, even after 14 days of exposure. In contrast, drug levels attained during DESDP infusions showed marked, dose-dependent cytotoxicity towards all cell lines under study. Prostatic cells were not exceptionally sensitive. High-dose DES slightly stimulated the synthesis of prostatic acid phosphatase in LNCaP cells. Formation of foci of polygonal cells was induced by 5 µg/ml of DES in cultures of MRC-5 fibroblasts. We conclude that, at high doses, DES liberated from DESDP acts upon a regulatory or metabolic mechanism common to many if not all human cells. Preferential sensitivity of prostate cancer cells in vivo may be due to high local phosphatase activity and/or DES accumulation in prostatic tissue.

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This work was supported by Asta-Werke AG, Degussa Pharma Gruppe, Bielefeld (Federal Republic of Germany), Deutsche Forschungsgemeinschaft, and Fonds der Chemischen Industrie.

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