Progesterone receptor (PR) agonists have several important applications in women's health, such as in oral contraception and post-menopausal hormone therapy. Currently, all PR agonists used clinically are steroids. Because of their interactions with other steroid receptors, steroid-metabolizing enzymes, or other steroid-signaling pathways, these drugs can pose significant side effects in some women. Efforts to discover novel nonsteroidal PR agonists with improved biological properties led to the discovery of tanaproget (TNPR). TNPR binds to the PR from various species with a higher relative affinity than reference steroidal progestins. In T47D cells, TNPR induces alkaline phosphatase activity with an EC 50 value of 0.1 nM, comparable with potent steroidal progestins such as medroxyprogesterone acetate (MPA) and trimegestone (TMG), albeit with a reduced efficacy (ϳ60%). In a mammalian two-hybrid assay to measure PR agonist-induced interaction between steroid receptor co-activator-1 and PR, TNPR showed similar potency (EC 50 value of 0.02 nM) and efficacy to MPA and TMG. Importantly, in key animal models such as the rat ovulation inhibition assay, TNPR demonstrates full efficacy and an enhanced progestational potency (30-fold) when compared with MPA and TMG. Furthermore, TNPR has relatively weak interactions with other steroid receptors and binding proteins and little effect on cytochrome P450 metabolic pathways. Finally, the three-dimensional crystal structure of the PR ligand binding domain with TNPR has been delineated to demonstrate how this nonsteroidal ligand achieves its high binding affinity. Therefore, TNPR is a structurally novel and very selective PR agonist with an improved preclinical pharmacological profile.

ABSTRACT:The study was initiated as an observation of incomplete extraction recovery of N-(4- (

ABSTRACT:Bazedoxifene is a selective estrogen receptor modulator under development for the prevention and treatment of osteoporosis. The disposition of [ 14 C]bazedoxifene was determined in six healthy postmenopausal women after administration of a single oral dose of 20 mg (200 Ci). After dosing, blood was collected at frequent intervals, and urine and fecal samples were collected for up to 10 days. Aliquots of plasma, blood, urine, and fecal homogenates were analyzed for concentrations of radioactivity. Bazedoxifene metabolite profiles in plasma and feces were determined by highperformance liquid chromatography with radioactivity flow detection; metabolite structures were confirmed by liquid chromatography-mass spectrometry. Bazedoxifene was rapidly absorbed, exhibiting a mean peak plasma concentration of 3.43 ng/ml at 1.2 h postdose. The total mean recovery of the radioactive dose in excreta was 85.6%, with the majority recovered in feces (84.7%) and only a small fraction (0.81%) in urine. Radiochromatograms of plasma revealed that glucuronidation was the major metabolic pathway; little or no cytochrome P450-mediated metabolism was evident. The majority of circulating radioactivity was constituted by metabolites, with bazedoxifene-5-glucuronide being the predominant metabolite (up to 95%). Bazedoxifene-4-glucuronide was a minor metabolite (up to 20%), and unchanged bazedoxifene represented 0 to 13% of the radioactivity in most plasma samples. Unchanged bazedoxifene was the major radioactive component in feces, however, reflecting unabsorbed drug and/or glucuronides that were hydrolyzed by intestinal bacterial enzymes. [ 14 C]Bazedoxifene was generally well tolerated. These findings demonstrated that, after oral administration in healthy postmenopausal women, bazedoxifene was rapidly absorbed, metabolized via glucuronidation, and excreted predominantly in feces.

Neratinib (HKI-272), an irreversible inhibitor of Her 2 tyrosine kinase, is currently in development as an alternative for first and second line therapy in metastatic breast cancer patients who overexpress Her 2. Following incubation of [(14)C]neratinib in control human plasma at 37°C for 6 hours, about 60% to 70% of the radioactivity was not extractable, due to covalent binding to albumin. In this study, factors that could potentially affect the covalent binding of neratinib to plasma proteins, specifically to albumin were investigated. When [(14)C]neratinib was incubated at 10 μg/mL in human serum albumin (HSA) or control human plasma, the percent binding increased with time; the highest percentages of binding (46 and 67%, respectively) were observed at 6 hours, the longest duration of incubation examined. Binding increased with increasing temperature; the highest percentages of binding to HSA or human plasma (59 and 78%) were observed at 45°C, the highest temperature tested. The binding also increased with increasing pH of incubation; the highest percentages of binding (56 and 65%) were observed at pH 8.5, the highest pH value tested. The percentages of binding were similar (53% to 57%) when a wide range of concentrations of [(14)C]neratinib (50 ng/mL to 10 μg/mL) were incubated with human plasma at 37°C for 6 hours, indicating that the binding was independent of the substrate concentration, especially in the therapeutic range (50 to 200 ng/mL). When human plasma proteins containing covalently bound [(14)C]neratinb were suspended in a 10 fold volume of phosphate buffer at pH 4.0, 6.0, 7.4, and 8.5, and further incubated at 37°C for ~ 16 hours, about 45%, 44%, 32%, and 12% of the total radioactivity, respectively, was released as unchanged [(14)C]neratinib, indicating that the binding is reversible in nature, with more released at pH 7.4 and below. In conclusion, the covalent binding of neratinib to serum albumin is pH, time and temperature dependent, but not substrate concentration dependent, especially in the therapeutic range. Acidification and incubation of human plasma proteins that contained covalently bound [(14)C]neratinib leads to the release of the drug, indicating that the binding is reversible in nature. It is reasonable to speculate that the release of neratinib from human serum albumin provides a transport system leading to release of neratinib in the more acidic environment of the tumor.

The effect of 17 alpha-dihydroequilin sulfate (DHES), a water-soluble estrogen of conjugated estrogens (Premarin), and ethynylestradiol (EE), a commonly used estrogen found in many oral contraceptives, on the development of atherosclerosis was studied in rabbits fed an atherogenic diet (0.2% cholesterol) for 24 weeks. Ten animals were given 15 micrograms. kg-1.d-1 EE, 10 received 3.8 mg.kg-1.d-1 of DHES, and the remaining 10 sham-ovariectomized and 10 ovariectomized animals served as cholesterol-fed controls. These doses were chosen to have similar estrogenic potency. Plasma cholesterol concentrations increased to about 900 mg/dL and did not differ among the experimental groups. After 24 weeks, plasma beta-VLDL and HDL cholesterol concentrations were the same for all cholesterol-fed groups, while LDL cholesterol was significantly higher in the two estrogen-treated groups. In spite of this, both EE and DHES significantly reduced atherosclerosis by 35% in the aortic arch and 75% to 80% in the thoracic and abdominal aorta. The reduction in atherosclerosis was seen in animals with a wide range (400 to 1400 mg/dL) of plasma cholesterol concentrations and was independent of lipoprotein profile. beta-VLDL isolated from estrogen-treated animals was not significantly different from control beta-VLDL in its ability to stimulate cholesterol accumulation in THP-1 macrophages in culture. This suggests that the protective effect of estrogens on the development of atherosclerosis is not mediated by qualitative differences in beta-VLDL that affect uptake by macrophages. The results of this study extend our knowledge of the range of estrogens that reduce atherosclerosis. Given the lack of effect on plasma lipid and lipoprotein concentrations, these data are consistent with the conclusion that estrogens exert some of this beneficial effect directly at the level of the arterial wall by influencing certain key components in the pathogenesis of atherosclerosis.