The measurement of receptor occupancy (RO) using positron emission tomography (PET) has been instrumental in guiding discovery and development of CNS directed therapeutics. We and others have investigated muscarinic acetylcholine receptor 4 (M4) positive allosteric modulators (PAMs) for the treatment of symptoms associated with neuropsychiatric disorders. In this article, we describe the synthesis, in vitro, and in vivo characterization of a series of central pyridinerelated M4 PAMs that can be conveniently radiolabeled with carbon-11 as PET tracers for the in vivo imaging of an allosteric binding site of the M4 receptor. We first demonstrated its feasibility by mapping the receptor distribution in mouse brain and confirming that a lead molecule 1 binds selectively to the receptor only in the presence of the orthosteric agonist carbachol. Through a competitive binding affinity assay and a number of physiochemical properties filters, several related compounds were identified as candidates for in vivo evaluation. These candidates were then radiolabeled with 11 C and studied in vivo in rhesus monkeys. This research eventually led to the discovery of the clinical radiotracer candidate [ 11 C]MK-6884.

Pathologically, high levels of aldosterone are associated with severe cardiovascular diseases such as congestive heart failure, hypertension, and myocardial fibrosis. The inhibition of aldosterone synthase (CYP11B2) to reduce aldosterone levels has been proposed as a promising treatment for diseases related to CYP11B2 because it is the crucial enzyme in the biosynthesis of aldosterone. A series of novel pyridyl- or isoquinolinyl-substituted indolines and indoles was designed via a ligand-based approach. The synthesized compounds were tested and found to be strong CYP11B2 inhibitors. The most potent ones showed IC50 values of less than 3 nM, being similarly potent as fadrozole and LCI699. Among them, compounds 14 and 23 showed good selectivity over the highly homologous CYP11B1, with selectivity factors (SF = IC50 CYP11B1/IC50 CYP11B2) around 170; thus, they are superior to fadrozole and LCI699 (SFs < 15). These potent CYP11B2 inhibitors exhibited no inhibition (IC50 > 50 μM) of a panel of hepatic CYP enzymes including CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 and the crucial steroidogenic enzymes, CYP17 and CYP19. Because of these advantageous profiles, compounds 14 and 23 are considered to be candidates for further in vivo evaluation.

CYP11B2 inhibition is a promising treatment for diseases caused by excessive aldosterone. To improve the metabolic stability in human liver miscrosomes of previously reported CYP11B2 inhibitors, modifications were performed via a combination of ligand- and structure-based drug design approaches, leading to pyridyl 4,5-dihydro-[1,2,4]triazolo[4,3-a]quinolones. Compound 26 not only exhibited a much longer half-life (t1/2 ≫ 120 min), but also sustained inhibitory potency (IC50 = 4.2 nM) and selectivity over CYP11B1 (SF = 422), CYP17, CYP19, and a panel of hepatic CYP enzymes.

BackgroundNitric oxide donors are widely used to treat cardiovascular disease, but their major limitation is the development of tolerance, a multifactorial process to which the in vivo release of nitric oxide is thought to contribute. Here we describe the preclinical and clinical results of a translational drug development effort to create a next‐generation nitric oxide donor with improved pharmacokinetic properties and a unique mechanism of nitric oxide release through CYP3A4 metabolism that was designed to circumvent the development of tolerance.Methods and ResultsSingle‐ and multiple‐dose studies in telemetered dogs showed that MK‐8150 induced robust blood‐pressure lowering that was sustained over 14 days. The molecule was safe and well tolerated in humans, and single doses reduced systolic blood pressure by 5 to 20 mm Hg in hypertensive patients. Multiple‐dose studies in hypertensive patients showed that the blood‐pressure–lowering effect diminished after 10 days, and 28‐day studies showed that the hemodynamic effects were completely lost by day 28, even when the dose of MK‐8150 was increased during the dosing period.ConclusionsThe novel nitric oxide donor MK‐8150 induced significant blood‐pressure lowering in dogs and humans for up to 14 days. However, despite a unique mechanism of nitric oxide release mediated by CYP3A4 metabolism, tolerance developed over 28 days, suggesting that tolerance to nitric oxide donors is multifactorial and cannot be overcome solely through altered in vivo release of nitric oxide.Clinical Trial Registration URL: http://www.clinicaltrials.gov. Unique identifiers: NCT01590810 and NCT01656408.

The therapeutic application of nitric oxide, an endogenous cellular signaling molecule, has been limited due to the difficulty of developing stable pro-drugs with slow kinetics of NO release. Diazeniumdiolates are valuable NO donors; however, synthetic challenges have hampered their use. O 2 -alkylation or arylation of diazeniumdiolates form stable pro-drugs which have found application in hypertension, cancer, and as antimicrobial agents. The synthesis of sodium diazeniumdiolates has proven to be challenging due to hazardous reaction conditions (high N 2 O concentrations, and flammable solvents), which can lead to detonation and suffered from limited scope. We have previously disclosed that synthesis of calcium diazeniumdiolate salts are a safer and more scalable alternative. Herein, we report the expanded scope of calcium diazeniumdiolates from benzylic amines, amides, and sterically bulky amines hitherto inaccessible and a comparison of their reactivity in comparison to sodium diazeniumdiolate.