Reduction of photoswitched, nitrogen bridged N-acetyl diazocines limits inhibition of 17βHSD3 activity in transfected human embryonic kidney 293 cells

Testosterone depletion is a common aim in the treatment of hormone-dependent prostate cancer, since the steroid boosts the tumor's proliferation. Therefore, inhibition of 17β-hydroxysteroid dehydrogenase type 3 (17βHSD3), which catalyzes the carbonyl reduction of androstenedione to testosterone, represents an expedient therapeutic drug target. Among the compounds targeting 17βHSD3, tetrahydrodibenzazocines have been reported to be highly potent inhibitors. Thus, we hypothesized that structural analogs to the tetrahydrodibenzazocine scaffold, namely diazocines, which contain an azo group instead of the ethylene moiety, are also able to inhibit 17βHSD3. Diazocines consist of a photoresponsive core and can be isomerized from Z into E configuration by irradiation with a specific wavelength. In the present study, 17βHSD3 inhibition by diazocine photoisomers was examined in transfected human embryonic kidney 293 cells (HEK-293) and isolated microsomes. For this purpose, cells or microsomes were treated with androstenedione and incubated for 2 or 24 h in the presence or absence of irradiated and non-irradiated diazocines. Testosterone formation was determined by uHPLC. We report a weak inhibition of 17βHSD3 activity by diazocines in HEK-293 cells and microsomes. Furthermore, we found no significant difference between samples treated with irradiated and non-irradiated diazocines in terms of inhibition. However, we detected a new compound by HPLC analysis, which only appeared in light-treated samples, indicating a chemical modification of the photoswitched diazocines, presumably rendering them ineffective. Further investigations revealed that this modification occurs in the presence of reducing agents like dithiothreitol and glutathione. A preliminary mass-spectrometric analysis suggests that the N–N double bond is reduced, resulting in a dianiline derivative. Nevertheless, optimized photoswitchable diazocine derivatives, which are stable in a cellular environment, might serve as potent 17βHSD3 inhibitors, effective only in irradiated tissue. •Highlights (3–5 bullet points, max. 85 characters each, including spaces):•The aim was to decrease testosterone synthesis by inhibition of 17βHSD3.•Inhibition of irradiated and non-irradiated diazocines does not differ significantly.•After photoisomerization diazocines become susceptible to reduction.•Reduction may contribute to the limited inhibition of photoswitched diazocines.