Clinical human genetic studies have recently identified the tetrodotoxin (TTX) sensitive neuronal voltage gated sodium channel Nav1.7 (SCN9A) as a critical mediator of pain sensitization. Herein, we report structure-activity relationships for a novel series of 2,4-diaminotriazines that inhibit hNav1.7. Optimization efforts culminated in compound 52, which demonstrated pharmacokinetic properties appropriate for in vivo testing in rats. The binding site of compound 52 on Nav1.7 was determined to be distinct from that of local anesthetics. Compound 52 inhibited tetrodotoxin-sensitive sodium channels recorded from rat sensory neurons and exhibited modest selectivity against the hERG potassium channel and against cloned and native tetrodotoxin-resistant sodium channels. Upon oral administration to rats, compound 52 produced dose- and exposure-dependent efficacy in the formalin model of pain.

Human genetic evidence has identified the voltage-gated sodium channel Na V 1.7 as an attractive target for the treatment of pain. We initially identified naphthalene sulfonamide 3 as a potent and selective inhibitor of Na V 1.7. Optimization to reduce biliary clearance by balancing hydrophilicity and hydrophobicity (Log D) while maintaining Na V 1.7 potency led to the identification of quinazoline 16 (AM-2099). Compound 16 demonstrated a favorable pharmacokinetic profile in rat and dog and demonstrated dose-dependent reduction of histamine-induced scratching bouts in a mouse behavioral model following oral dosing. KEYWORDS: Sodium channel, Na V 1.7, Na V 1.5, pain, histamine scratching model H uman genetics has implicated the voltage-gated sodium channel Na V 1.7, which is expressed in nociceptive sensory neurons in dorsal root ganglia (DRG), 1 as a compelling target for pain.2−4 The primary challenge associated with the development of Na V 1.7 inhibitors has historically been achieving selectivity over the other eight Na V isoforms. These isoforms are differentially expressed throughout the body, but inhibition of Na V 1.5, which is expressed in cardiac tissue, is of particular concern as it has been shown to prolong the cardiac QRS wave in humans. 5,6 Previous efforts, including our own, have met with limited success. 4 Here we report the characterization, structure−activity relationship (SAR) and optimization of a series of sulfonamide-derived Na V 1.7 inhibitors. These efforts delivered an isoform-selective compound that was effective in a histamine-induced scratching model that is representative of Na V 1.7 target engagement. Recently Pfizer and Icagen described a series of heteroarylsulfonamide Na V 1.7 inhibitors with high levels of selectivity over Na V 1.5. 7−9 These results were reproduced by our group and are exemplified by compound 1 (Figure 1A). The lack of Na V 1.5 activity was noteworthy, and we envisioned this as a good starting point for our own lead optimization efforts, which would initially be aimed at addressing some of the liabilities and shortcomings associated with this class of compounds. Namely, this series suffered from low passive permeability and high clearance in rodents. We believed constraining the linker within a bicyclic core such as indole 2 or naphthalene 3 would afford a similar conformation and potentially help address the pharmacokinetic liabilities of this class of compounds. An overlay of global minima conformations of compounds 1, 2, and 3 supported this hypothesis ( Figure 1B), 10 and we were pleased to find that 2 and 3 were potent Na V 1.7 inhibitors and showed greater than 200-fold selectivity over Na V 1.5 ( Figure 1C). 11 In general, analogues in the naphthalene series demonstrated superior Na V 1.7 inhibition compared to the corresponding indole analogues, thus the naphthalene scaffold was chosen for further optimization. Additional profiling showed 3 also suffered from high clearance; however, we believed that 3 represented a promising starting poin...

No abstract

Herein we describe a general three-step synthesis of 4-substituted chlorophthalazines in good overall yields. In the key step, N,N-dimethylaminophthalimide (8a) directs the selective monoaddition of alkyl, aryl, and heteroaryl organometallic reagents to afford 3-substituted 3-hydroxyisoindolinones 9b, 9i-9am. Many of these hydroxyisoindolinones are converted to chlorophthalazines 1b-1v via reaction with hydrazine, followed by chlorination with POCl(3). We have also discovered two novel transformations of 3-vinyl- and 3-alkynyl-3-hydroxyisoindolinones. Addition of vinyl organometallic reagents to N,N-dimethylaminophthalimide (8a) provided dihydrobenzoazepinediones 15a-15c via the proposed ring expansion of 3-vinyl-3-hydroxyisoindolinone intermediates. 3-Alkynyl-3-hydroxyisoindolinones react with hydrazine and substituted hydrazines to afford 2-pyrazolyl benzoic acids 16a-16d and 2-pyrazolyl benzohydrazides 17a-17g rather than the expected alkynyl phthalazinones.

No abstract

Efforts to improve upon the physical properties and metabolic stability of Aurora kinase inhibitor 14a revealed that potency against multidrug-resistant cell lines was compromised by increased polarity. Despite its high in vitro metabolic intrinsic clearance, 23r (AMG 900) showed acceptable pharmacokinetic properties and robust pharmacodynamic activity. Projecting from in vitro data to in vivo target coverage was not practical due to disjunctions between enzyme and cell data, complex and apparently contradictory indicators of binding kinetics, and unmeasurable free fraction in plasma. In contrast, it was straightforward to relate pharmacokinetics to pharmacodynamics and efficacy by following the time above a threshold concentration. On the basis of its oral route of administration, a selectivity profile that favors Aurora-driven pharmacology and its activity against multidrug-resistant cell lines, 23r was identified as a potential best-in-class Aurora kinase inhibitor. In phase 1 dose expansion studies with G-CSF support, 23r has shown promising single agent activity.

No abstract

No abstract