Comparative effects of chlormadinone acetate and its 3alpha- and 3beta-hydroxy metabolites on progesterone, androgen and glucocorticoid receptors.

AIM/METHODS: In vitro binding tests to human receptors and in vivo functional activities in animals were used to compare the effects of the progestin chlormadinone acetate (CMA) and its 3alpha- and 3beta-hydroxy metabolites (3alpha-OH-CMA and 3beta-OH-CMA) on progesterone, androgen and glucocorticoid receptors.

RESULTS

CMA, 3alpha-OH-CMA, 3beta-OH-CMA and the reference progestin R5020 bound to human progesterone receptor with Ki values of 2.5 nm, 13 nm, 6.0 nm and 4.3 nm, respectively. Binding affinities to the human androgen receptor were characterized by Ki values of 3.8 nM for CMA, 83 nM for 3alpha-OH-CMA, 20 nM for 3beta-OH-CMA and 2.9 nM for the reference androgen methyltrienolone. The Ki values for binding to the human glucocorticoid receptor were 16 nM for CMA, 69 nM for 3alpha-OH-CMA, 21 nM for 3beta-OH-CMA and 1.2 nM for the glucocorticoid dexamethasone. In the rabbit endometrial proliferation test CMA, 3alpha-OH-CMA and 3beta-OH-CMA (5 and 45 microg/kg p.o. for 5 days) had similar progestomimetic activities. CMA, 3alpha-OH-CMA and, to a lesser extent, 3beta-OH-CMA (4.64 and 21.5 mg/kg p.o. for 7 days) inhibited testosterone-stimulated growth of prostate and seminal vesicles in castrated rats showing antiandrogenic activities. Glucocorticoid properties were demonstrated for CMA and 3alpha-OH-CMA (21.5 and 100 mg/kg p.o. for 6 days) but not for 3beta-OH-CMA as reduction in thymus and adrenal gland weights in immature rats.

CONCLUSION

Binding assays at human receptors showed similarly high affinities of CMA with the progesterone and androgen receptors and a 5 times lower affinity with the glucocorticoid receptor. At all receptor types, CMA had the highest, 3alpha-OH-CMA the lowest and 3beta-OH-CMA an intermediate affinity. Animal studies revealed progestomimetic and antiandrogenic activities of CMA, 3alpha-OH-CMA and 3beta-OH-CMA and glucocorticoid activities of CMA and 3alpha-OH-CMA.