The Translational Pharmacology of a Novel, Potent, and Selective Nonsteroidal Progesterone Receptor Antagonist, 2-[4-(4-Cyano-phenoxy)-3,5-dicyclopropyl-1H-pyrazol-1-yl]-N-methylacetamide (PF-02367982)

Abstract

The progesterone receptor (PR) is an important regulator of endometrial function. Blockade of PR function has been recognized as the potential basis for preventing gynecological conditions such as endometriosis and uterine fibroids. In this study, we examine the in vitro and in vivo properties of a nonsteroidal PR antagonist, 2-[4-(4-cyano-phenoxy)-3,5-dicyclopropyl-1H-pyrazol-1-yl]-N-methylacetamide (PF-02367982) in comparison with the nonselective steroidal antagonist RU-486 (mifepristone). PF-02367982 was found to be a potent PR antagonist with far greater selectivity over the glucocorticoid receptor than RU-486. Both PF-02367982 and RU-486 blocked progesterone-induced arborization of the rabbit endometrium in a dose-dependent manner at unbound drug exposures that were commensurate with their potencies as PR antagonists in vitro. Translation of this pharmacology to a clinically relevant system was required to bridge the pharmacological gap between nonmenstruating rabbits and humans. Thus, the pharmacokinetic (PK) and pharmacodynamic (PD) data from the rabbit were combined to predict pharmacological effects on the naturally cycling cynomolgus macaque endometrium. PF-02367982 blocked the effect of progesterone on the cynomolgus macaque endometrium to the same degree as RU-486 and at exposures predicted by the rabbit PK-PD model. With such an efficacious and superior selectivity profile to the nonselective RU-486, PF-02367982 may have significant therapeutic value in the treatment of gynecological conditions such as endometriosis.The discovery of synthetic progesterone receptor (PR) modulators has underscored the important role that progesterone plays in reproductive physiology, including the menstrual cycle, endometrial growth, breast development and maintenance of pregnancy (Chabbert-Buffet et al., 2005;Spitz, 2006). RU-38486 (RU-486, mifepristone) is the founding member of steroidal PR antagonists and is approved clinically for pregnancy termination and emergency contraception. Studies with RU-486 and other PR antagonists, such as onapristone, ZK-137316 (Zelinski-Wooten et al., 1998), and ZK-230211, have revealed that these agents, as well as directly antagonizing progesterone function, can block ovarian function and also arrest the effect of estrogen on the endometrium in women and nonhuman primates (NHP) (Wolf et al., 1989;Baird et al., 2003;Brenner et al., 2005; ChabbertBuffet et al., 2005;Slayden et al., 2006).The potential usefulness of RU-486 and other PR antagonists in the treatment of pathological conditions such as endometriosis, uterine fibroids, and cancer is supported by a number of preclinical observations and clinical findings (Grow et al., 1996;Kettel et al., 1996;Baird et al., 2003;Fiscella et al., 2006). Although RU-486 has potent antiprogestagenic activity, it is also an equipotent antagonist at the glucocorticoid receptor (GR) (Heikinheimo et al., 1987). As a consequence, RU-486 suppresses the inhibition of corticotropin secretion induced by corticosteroids, limiting its wider usefu...

The Translational Efficacy of a Nonsteroidal Progesterone Receptor Antagonist, 4-[3-Cyclopropyl-1-(mesylmethyl)-5-methyl-1H-pyrazol-4-yl]oxy,-2,6-dimethylbenzonitrile (PF-02413873), on Endometrial Growth in Macaque and Human

“…In contrast to RU-486, at high doses of PF-02413873 there was an apparent increase in the basal response, indicative of the agonism of PF-02413873 observed at high concentrations in the absence of progesterone. Similar data were generated in a recombinant ␤-lactamase reporter cell line where the effects PF-02413873 on the progesterone-induced response on PR are coupled to a mouse mammary tumor virus promoter (de Giorgio-Miller et al, 2008), suggesting the observed pharmacological response was not caused by the T47D cell line (data not shown). When the effect of RU-486 and PF-02413873 was assessed in an enzyme complementation assay that measures PR nuclear translocation, RU-486 induced nuclear translocation consistent with its functional antagonist potency (Fig.…”

“…PF-02413873 was identified from a drug discovery campaign for agents that could block PR signaling function. PF-02413873 was assessed for its ability to block an in vitro native progesterone response in a human T47D mammary carcinoma cellbased functional reporter gene assay (de Giorgio-Miller et al, 2008) and block binding to PR. PF-02413873 blocked radioligand binding to PR in a CEREP MCF-7 cytosol binding assay with a K i value of 2.6 nM (Table 1).…”

“…Plasma protein binding of PF-02413873 was determined by equilibrium dialysis, and unbound plasma concentrations were then calculated using values for "free fractions" of 0.046 and 0.031 for cynomolgus macaque and human, respectively. The free fraction value for RU-486 was 0.028 for cynomolgus macaque (de Giorgio-Miller et al, 2008).…”

“…The in-life phase of the study was performed at Covance (Mü nster, Germany) in cynomolgus macaques (weight range 3.7-5.7 kg and ages 5-6 years) previously used to assess the effects of PF-02367982 (de Giorgio- Giorgio-Miller et al, 2008) with the objective of targeting 0.5 and 2 nmol ⅐ h/ml PF-02413873 exposures. Animals were dosed for 10 days and 1 h before euthanasia, and approximately 4 h after the final drug dose, the animals were treated with bromodeoxyuridine (BrdU; 100 mg/animal i.v.).…”

“…RU-486/mifepristone was purchased from Sigma-Aldrich (St. Louis, MO). The in vitro functional pharmacological properties of PF-02413873 for PR, androgen receptor (AR), GR, and mineralocorticoid receptor (MR) was determined as described previously (de Giorgio-Miller et al, 2008). CEREP (Poitiers, France) was used for supplemental wide receptor-profiling assay data and additional binding assays as described.…”