11α-Hydroxyprogesterone, a potent 11β-hydroxysteroid dehydrogenase inhibitor, is metabolised by steroid-5α-reductase and cytochrome P450 17α-hydroxylase/17,20-lyase to produce C11α-derivatives of 21-deoxycortisol and 11-hydroxyandrostenedione in vitro.

11α-Hydroxyprogesterone (11αOHP4) and 11β-hydroxyprogesterone (11βOHP4) have been reported to be inhibitors of 11β-hydroxysteroid dehydrogenase (11βHSD) type 2, together with 11β-hydroxytestosterone and 11β-hydroxyandrostenedione, and their C11-keto derivatives being inhibitors of 11βHSD1. Our in vitro assays in transiently transfected HEK293 cells, however, show that 11αOHP4 is a potent inhibitor of 11βHSD2 and while this steroid does not serve as a substrate for the enzyme, the aforementioned C11-oxy steroids are indeed substrates for both 11βHSD isozymes. 11βOHP4 is metabolised by 11βHSD2 yielding 11-ketoprogesterone with 11βHSD1 catalysing the reverse reaction, similar to the reduction of the other C11-oxy steroids. In the same model system, novel 11αOHP4 metabolites were detected in its conversion by steroid-5α-reductase (SRD5A) types 1 and 2 yielding 11α-hydroxydihydroprogesterone and its conversion by cytochrome P450 17A1 (CYP17A1) yielding the hydroxylase product, 11α,17α-dihydroxyprogesterone, and the 17,20 lyase product, 11α-hydroxyandrostenedione. We also detected both 11αOHP4 and 11βOHP4 in prostate cancer tissue- ∼23 and ∼32 ng/g respectively with 11KP4 levels >300 ng/g. In vitro assays in PC3 and LNCaP prostate cancer cell models, showed that the metabolism of 11αOHP4 and 11βOHP4 was comparable. In LNCaP cells expressing CYP17A1, 11αOHP4 and 11βOHP4 were metabolised with negligible substrate, 4%, remaining after 48 h, while the steroid substrate 11β,17α-dihydroxyprogesterone (21dF) was metabolised to C11-keto C₁₉ steroids yielding 11-ketotestosterone. Despite the fact that 11αOHP4 is not metabolised by 11βHSD2, it is a substrate for SRD5A and CYP17A1, yielding C11α-hydroxy C₁₉ steroids as well as the C11α-hydroxy derivative of 21dF-the latter associated with clinical conditions characterised by androgen excess. With our data showing that 11αOHP4 is present at high levels in prostate cancer tissue, the steroid may serve as a precursor to unique C11α-hydroxy C₁₉ steroids. The potential impact of 11αOHP4 and its metabolites on human pathophysiology can however only be fully assessed once C11α-hydroxyl metabolite levels are comprehensively analysed.

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