ANTIANDROGENIC PROPERTIES OF NOMEGESTROL ACETATE

Nomegestrol acetate (NOM-Ac; TX 066, 17 cetoxy-6-methyl-19-nor-4,6-pre gnadiene-3,20-dione, CAS 58652-20-3), a 19-nor-progesterone derivative showed a significant antiandrogenic effect on ventral prostate and se minal vesicles weights of immature castrated rats treated with testost erone. However, this effect was 20 times less potent than that of cypr oterone acetate (CYP-Ac). In contrast to norethindrone acetate, a 19-n or-testosterone derivative. NOM-Ac was totally devoid of androgenic ef fect on male accessory sex organs. Relative binding affinity against H -3-testosterone for androgen receptor of rat ventral prostate showed a nd IC50 of 22.6 +/- 4.0 and 21.1 +/- 5.3 nmol/l for NOM-Ac and CYP-Ac, respectively, while Dixon analysis disclosed a K-i of 7.58 +/- 0.94 a nd 4.30 +/- 0.17 nmol/l. Then, Scatchard plot analysis of H-3-NOM-Ac b inding revealed a K-D of 20.9 +/- 3.1 nmol/l and a B-max of 217 +/- 27 fmol/mg protein.