[Lotus]

Greetings, 


Steroidal lactones as inhibitors of 17beta-hydroxysteroid dehydrogenase type 5: chemical synthesis, enzyme inhibitory activity, and assessment of estrogenic and androgenic activities.
Bydal P1, Luu-The V, Labrie F, Poirier D.
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* 1Medicinal Chemistry Division, Oncology and Molecular Endocrinology Research Center, CHUL Research Center and University Laval, 2705 Laurier Boulevard, Québec, Québec G1V 4G2, Canada.
Abstract
Androgens are well known to play a predominant role in prostate cancer and other androgen-dependent diseases. To decrease the level of androgen testosterone in the prostate, we are interested in developing inhibitors of 17beta-hydroxysteroid dehydrogenase type 5 (17beta-HSD5). This enzyme expressed in the prostate is one of the two enzymes able to convert 4-androstene-3,17-dione into testosterone. From a screening study, it was found that a series of steroid derivatives bearing a lactone on D-ring demonstrated potent inhibition of 17beta-HSD5 over-expressed in HEK-293 cells. The results of enzymatic assays using intact cells indicated that a C18-steroid (estradiol or 3-deoxyestradiol) backbone and a spiro-delta-lactone (six-member ring) are important for a strong inhibitory activity. Moreover, the presence of a dimethyl group at the alpha-position of the lactone carbonyl increases the selectivity of the inhibitor toward 17beta-HSD5. Compound 26, a 3-deoxyestradiol derivative with a dimethylated spiro-delta-lactone at position 17, possesses the most potent inhibitory activity for 17beta-HSD5 (IC(50)=2.9 nM). It showed no binding affinity for estrogen, androgen, progestin and glucocorticoid receptors (ER, AR, PR and GR). A weak proliferative effect was, however, observed on ZR-75-1 (ER+) cells in culture at high concentration (1 microM), but not at 0.03 microM. Interestingly, no significant proliferative effect was detected on Shionogi (AR+) cells in culture in the presence of 0.1 and 1 microM of lactone 26.


So check this out:

C18-steroid (estradiol or 3-deoxyestradiol) backbone and a spiro-delta-lactone (six-member ring) are important for a strong inhibitory activity.

My translation?, estradiol with spiro demonstrated a potent inhibition of 17beta-HSD5 in the prostate ( inhibiting DHT). Now when a dimethyl group (e.g. MSM) was added it had the strongest inhibiting effect. 

even more loosely translated    E2 + spiro + MSM has an effective inhibiting effect over DHT, and thus boosting spiro's ability (or bioavailability).