Gerard M. McGeehan

INHIBITORS OF 11BETA-HYDROXYSTEROID DEHYDROGENASE TYPE 1

Carcinogenesis of hormone-related cancers involves hormone-stimulated cell proliferation, which increases the number of cell divisions and the opportunity for random genetic errors. In target tissues, steroid hormones are interconverted between their potent, high affinity forms for their respective receptors and their inactive, low affinity forms. One group of enzymes responsible for these interconversions are the hydroxysteroid dehydrogenases, which regulate ligand access to steroid receptors and thus act at a pre-receptor level. As part of this group, the 17β-hydroxysteroid dehydrogenases catalyze either oxidation of hydroxyl groups or reduction of keto groups at steroid position C17. The thoroughly characterized 17β-hydroxysteroid dehydrogenase type 1 activates the less active estrone to estradiol, a potent ligand for estrogen receptors. This isoform is expressed in gonads, where it affects circulating levels of estradiol, and in peripheral tissue, where it regulates ligand occupancy of estrogen receptors. Inhibitors of 17β-hydroxysteroid dehydrogenase type 1 are thus highly interesting potential therapeutic agents for the control of estrogen-dependent diseases such as endometriosis, as well as breast and ovarian cancers. Here, we present the review on the recent development of inhibitors of 17β-hydroxysteroid dehydrogenase type 1 published and patented since the previous review of 17β-hydroxysteroid dehydrogenase inhibitors of Poirier (Curr. Med. Chem., 2003, 10, 453). These inhibitors are divided into two separate groups according to their chemical structures: steroidal and non-steroidal 17β- hydroxysteroid dehydrogenase type 1 inhibitors. Their estrogenic/ proliferative activities and selectivities over other 17β-hydroxysteroid dehydrogenases that are involved in local regulation of estrogen action (types 2, 7 and 12) are also presented.

Discovery of VTP-27999, an Alkyl Amine Renin Inhibitor with Potential for Clinical Utility.

Structure guided optimization of a series of nonpeptidic alkyl amine renin inhibitors allowed the rational incorporation of additional polar functionality. Replacement of the cyclohexylmethyl group occupying the S1 pocket with a (R)-(tetrahydropyran-3-yl)methyl group and utilization of a different attachment point led to the identification of clinical candidate 9. This compound demonstrated excellent selectivity over related and unrelated off-targets, >15% oral bioavailability in three species, oral efficacy in a double transgenic rat model of hypertension, and good exposure in humans.

Development of Inhibitors of the Aspartyl Protease Renin for the Treatment of Hypertension

Renin is the rate-limiting enzyme in the renin-angiotensin-aldosterone system (RAS) which controls blood pressure and volume. The biological function of renin is to cleave the N-terminus of angiotensinogen releasing the decapeptide, angiotensin I (ANGI). Subsequently, angiotensin I is further processed by the angiotensin converting enzyme (ACE) to produce angiotensin II (ANGII). The RAS cascade is a major target for the clinical management of hypertension. Current clinical treatments include angiotensin converting enzyme inhibitors (ACEi) and ANGII receptor blockers (ARBs). As the rate-limiting enzyme in ANGII production, renin inhibitors have been pursued as an additional class of anti-hypertensives. Clinical studies conducted with renin inhibitors have shown them to be as effective as ACE inhibitors in lowering blood pressure. Most importantly, inhibitors of renin may have a number of potential advantages over ACEi and ARBs. Renin is specific for angiotensinogen and will not carry the ancillary pharmacology associated with ACEi or ARBs. To date, no renin inhibitors have made it to market. The development of these inhibitors has been hindered by poor bioavailability and complex synthesis. However, despite the pharmacokinetic challenges of designing renin inhibitors, the enzyme remains a promising target for the development of novel treatments for hypertension. This review will consist of an overview of renin biology, the pharmacology of renin and RAS and focus in on renin as a target for blood pressure regulation. We also cover the evaluation of renin inhibitors in animal models and clinical studies. Presently a number of new generation inhibitors of renin are in development with at least one in the clinic and these will be discussed. Finally we will discuss what might distinguish renin inhibitors from current therapeutic options and discuss other therapeutic indications renin inhibitors might have.

Structure-based design and synthesis of 1,3-oxazinan-2-one inhibitors of 11β-hydroxysteroid dehydrogenase type 1.

Structure based design led directly to 1,3-oxazinan-2-one 9a with an IC(50) of 42 nM against 11β-HSD1 in vitro. Optimization of 9a for improved in vitro enzymatic and cellular potency afforded 25f with IC(50) values of 0.8 nM for the enzyme and 2.5 nM in adipocytes. In addition, 25f has 94% oral bioavailability in rat and >1000× selectivity over 11β-HSD2. In mice, 25f was distributed to the target tissues, liver, and adipose, and in cynomolgus monkeys a 10 mg/kg oral dose reduced cortisol production by 85% following a cortisone challenge.

Multiple Ascending Dose Study With the New Renin Inhibitor VTP-27999 Nephrocentric Consequences of Too Much Renin Inhibition

This study compared the pharmacodynamic/pharmacokinetic profile of the new renin inhibitor VTP-27999 in salt-depleted healthy volunteers, administered once daily (75, 150, 300, and 600 mg) for 10 days, versus placebo and 300 mg aliskiren. VTP-27999 was well tolerated with no significant safety issues. It was rapidly absorbed, attaining maximum plasma concentrations at 1 to 4 hours after dosing, with a terminal half-life of 24 to 30 hours. Plasma renin activity remained suppressed during the 24-hour dosing interval at all doses. VTP-27999 administration resulted in a dose-dependent induction of renin, increasing the concentration of plasma renin maximally 350-fold. This induction was greater than with aliskiren, indicating greater intrarenal renin inhibition. VTP-27999 decreased plasma angiotensin II and aldosterone. At 24 hours and later time points after dosing on day 10 in the 600-mg group, angiotensin II and aldosterone levels were increased, and plasma renin activity was also increased at 48 and 72 hours, compared with baseline. VTP-27999 decreased urinary aldosterone excretion versus placebo on day 1. On day 10, urinary aldosterone excretion was higher in the 300- and 600-mg VTP-27999 dose groups compared with baseline. VTP-27999 decreased blood pressure to the same degree as aliskiren. In conclusion, excessive intrarenal renin inhibition, obtained at VTP-27999 doses of 300 mg and higher, is accompanied by plasma renin rises, that after stopping drug intake, exceed the capacity of extrarenal VTP-27999 to block fully the enzymatic reaction. This results in significant rises of angiotensin II and aldosterone. Therefore, renin inhibition has an upper limit. # Novelty and Significance {#article-title-16}This study compared the pharmacodynamic/pharmacokinetic profile of the new renin inhibitor VTP-27999 in salt-depleted healthy volunteers, administered once daily (75, 150, 300, and 600 mg) for 10 days, versus placebo and 300 mg aliskiren. VTP-27999 was well tolerated with no significant safety issues. It was rapidly absorbed, attaining maximum plasma concentrations at 1 to 4 hours after dosing, with a terminal half-life of 24 to 30 hours. Plasma renin activity remained suppressed during the 24-hour dosing interval at all doses. VTP-27999 administration resulted in a dose-dependent induction of renin, increasing the concentration of plasma renin maximally 350-fold. This induction was greater than with aliskiren, indicating greater intrarenal renin inhibition. VTP-27999 decreased plasma angiotensin II and aldosterone. At 24 hours and later time points after dosing on day 10 in the 600-mg group, angiotensin II and aldosterone levels were increased, and plasma renin activity was also increased at 48 and 72 hours, compared with baseline. VTP-27999 decreased urinary aldosterone excretion versus placebo on day 1. On day 10, urinary aldosterone excretion was higher in the 300- and 600-mg VTP-27999 dose groups compared with baseline. VTP-27999 decreased blood pressure to the same degree as aliskiren. In conclusion, excessive intrarenal renin inhibition, obtained at VTP-27999 doses of 300 mg and higher, is accompanied by plasma renin rises, that after stopping drug intake, exceed the capacity of extrarenal VTP-27999 to block fully the enzymatic reaction. This results in significant rises of angiotensin II and aldosterone. Therefore, renin inhibition has an upper limit.

Spirocyclic ureas: Orally bioavailable 11β-HSD1 inhibitors identified by computer-aided drug design

Structure-guided drug design led to the identification of a class of spirocyclic ureas which potently inhibit human 11beta-HSD1 in vitro. Lead compound 10j was shown to be orally bioavailable in three species, distributed into adipose tissue in the mouse, and its (R) isomer 10j2 was efficacious in a primate pharmacodynamic model.

Design and Optimization of Renin Inhibitors: Orally Bioavailable Alkyl Amines

Structure-based drug design led to the identification of a novel class of potent, low MW alkylamine renin inhibitors. Oral administration of lead compound 21l, with MW of 508 and IC(50) of 0.47nM, caused a sustained reduction in mean arterial blood pressure in a double transgenic rat model of hypertension.

Optimization of orally bioavailable alkyl amine renin inhibitors.

Structure-guided drug design led to new alkylamine renin inhibitors with improved in vitro and in vivo potency. Lead compound 21a, has an IC(50) of 0.83nM for the inhibition of human renin in plasma (PRA). Oral administration of 21a at 10mg/kg resulted in >20h reduction of blood pressure in a double transgenic rat model of hypertension.

Pharmacological characterization of the selective 11β-hydroxysteroid dehydrogenase 1 inhibitor, BI 135585, a clinical candidate for the treatment of type 2 diabetes.

To combat the increased morbidity and mortality associated with the developing diabetes epidemic new therapeutic interventions are desirable. Inhibition of intracellular cortisol generation from cortisone by blocking 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) has been shown to ameliorate the risk factors associated with the metabolic syndrome. A challenge in developing 11β-HSD1 inhibitors has been the species selectivity of small molecules, as many compounds are primate specific. Here we describe our strategy to identify potent selective 11β-HSD1 inhibitors while ensuring target engagement in key metabolic tissues, liver and fat. This strategy enabled the identification of the clinical candidate, BI 135585.

Regulation of Sphingomyelin Phosphodiesterase Acid-Like 3A Gene (SMPDL3A) by Liver X Receptors

Liver X receptor (LXR) α and LXRβ function as physiological sensors of cholesterol metabolites (oxysterols), regulating key genes involved in cholesterol and lipid metabolism. LXRs have been extensively studied in both human and rodent cell systems, revealing their potential therapeutic value in the contexts of atherosclerosis and inflammatory diseases. The LXR genome landscape has been investigated in murine macrophages but not in human THP-1 cells, which represent one of the frequently used monocyte/macrophage cell systems to study immune responses. We used a whole-genome screen to detect direct LXR target genes in THP-1 cells treated with two widely used LXR ligands [N-(2,2,2-trifluoroethyl)-N-[4-[2,2,2-trifluoro-1-hydroxy-1-(trifluoromethyl)-ethyl]phenyl]-benzenesulfonamide (T0901317) and 3-[3-[N-(2-chloro-3-trifluoromethylbenzyl)-(2,2-diphenylethyl)amino]propyloxy] phenylacetic acid hydrochloride (GW3965)]. This screen identified the sphingomyelin phosphodiesterase acid-like 3A (SMPDL3A) gene as a novel LXR-regulated gene, with an LXR response element within its promoter. We investigated the regulation of SMPDL3A gene expression by LXRs across several human and mouse cell types. These studies indicate that the induction of SMPDL3A is LXR-dependent and is restricted to human blood cells with no induction observed in mouse cellular systems.