Role of human 3α-hydroxysteroid dehydrogenase isoforms (AKR1C1-AKR1C3) in the extrahepatic metabolism of the steroidal aromatase inactivator Formestane.

The clinical use of the steroidal aromatase inhibitor Formestane (4-hydroxandrostenedione, 4-OHA) in the treatment of advanced ER+ breast cancer has been discontinued, and therefore, interest in this remarkable drug has vanished. As a C-19 sterol, 4-OHA can undergo extensive intracellular metabolism depending on the expression of specific enzymes in the corresponding cells. We used the metabolites 4ß-hydroxyandrosterone, 4ß-hydroxyepiandrosterone and its 17ß-reduced derivative as standards for the proof of catalytic activity present in the cell culture medium and expressed by the isolated enzymes. All of the aldo-keto reductases AKR1C1, AKR1C2, AKR1C3 and AKR1C4 catalysed the reduction of the 3-keto-group and the Δ4,5 double bond of 4-OHA at the same time. Molecular docking experiments using microscale thermophoresis and the examination of the kinetic behaviour of the isolated enzymes with the substrate 4-OHA proved that AKR1C3 had the highest affinity for the substrate, whereas AKR1C1 was the most efficient enzyme. Both enzymes (AKR1C1and AKR1C3) are highly expressed in adipose tissue and lungs, exhibiting 3ß-HSD activity. The possibility that 4-OHA generates biologically active derivatives such as the androgen 4-hydroxytestosterone or some 17ß-hydroxy derivatives of the 5α-reduced metabolites may reawaken interest in Formestane, provided that a suitable method of administration can be developed, avoiding oral or intramuscular depot-injection administration.

Testosterone's metabolism in the hippocampus may mediate its anti-anxiety effects in male rats.

Androgens may mediate anxiety behaviors; however, these effects and mechanisms of androgens are not well understood. The following experiments investigated whether testosterone (T)'s effects on anxiety behavior are mediated by its 5alpha-reduced, nonaromatizable metabolite dihydrotestosterone (DHT) and/or its 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) reduced metabolite 3alpha-androstanediol (3alpha-diol). In Experiment 1, gonadally-intact adult male rats and gonadectomized (GDX), DHT-replaced rats had similar low levels of anxiety behavior in the open field and elevated plus maze and fear behavior in the defensive freezing task compared with GDX control rats. In Experiment 2, intact or DHT-replaced rats that received blank inserts to the hippocampus demonstrated less anxiety behavior than did rats administered an implant of indomethacin, a 3alpha-HSD inhibitor, to the dorsal hippocampus. These data indicate that T's 5alpha-reduced metabolite, DHT, can reduce anxiety behavior and that blocking metabolism to 3alpha-diol in the hippocampus can attenuate these effects.