The discovery and optimization of a novel series of aminoisoquinolines as potent, selective, and efficacious inhibitors of the mutant B-Raf pathway is presented. The N-linked pyridylpyrimidine benzamide 2 was identified as a potent, modestly selective inhibitor of the B-Raf enzyme. Replacement of the benzamide with an aminoisoquinoline core significantly improved kinase selectivity and imparted favorable pharmacokinetic properties, leading to the identification of 1 as a potent antitumor agent in xenograft models.

Fragment based drug discovery (FBDD) is a widely used tool for discovering novel therapeutics. NMR is a powerful means for implementing FBDD, and several approaches have been proposed utilizing (1)H-(15)N heteronuclear single quantum coherence (HSQC) as well as one-dimensional (1)H and (19)F NMR to screen compound mixtures against a target of interest. While proton-based NMR methods of fragment screening (FBS) have been well documented and are widely used, the use of (19)F detection in FBS has been only recently introduced (Vulpetti et al. J. Am. Chem. Soc.2009, 131 (36), 12949-12959) with the aim of targeting "fluorophilic" sites in proteins. Here, we demonstrate a more general use of (19)F NMR-based fragment screening in several areas: as a key tool for rapid and sensitive detection of fragment hits, as a method for the rapid development of structure-activity relationship (SAR) on the hit-to-lead path using in-house libraries and/or commercially available compounds, and as a quick and efficient means of assessing target druggability.

Using fragment-based screening of a focused fragment library, 2-aminoquinoline 1 was identified as an initial hit for BACE1. Further SAR development was supported by X-ray structures of BACE1 cocrystallized with various ligands and molecular modeling studies to expedite the discovery of potent compounds. These strategies enabled us to integrate the C-3 side chain on 2-aminoquinoline 1 extending deep into the P2' binding pocket of BACE1 and enhancing the ligand's potency. We were able to improve the BACE1 potency to subnanomolar range, over 10(6)-fold more potent than the initial hit (900 μM). Further elaboration of the physical properties of the lead compounds to those more consistent with good blood-brain barrier permeability led to inhibitors with greatly improved cellular activity and permeability. Compound 59 showed an IC(50) value of 11 nM on BACE1 and cellular activity of 80 nM. This compound was advanced into rat pharmacokinetic and pharmacodynamic studies and demonstrated significant reduction of Aβ levels in cerebrospinal fluid (CSF).

A series of novel 4-oxopyrimidine TRPV1 antagonists was evaluated in assays measuring the blockade of capsaicin or acid-induced influx of calcium into CHO cells expressing TRPV1. The investigation of the structure-activity relationships in the heterocyclic A-region revealed the optimum pharmacophoric elements required for activity in this series and resulted in the identification of subnanomolar TRPV1 antagonists. The most potent of these antagonists were thoroughly profiled in pharmacokinetic assays. Optimization of the heterocyclic A-region led to the design and synthesis of 23, a compound that potently blocked multiple modes of TRPV1 activation. Compound 23 was shown to be effective in a rodent "on-target" biochemical challenge model (capsaicin-induced flinch, ED50 = 0.33 mg/kg p.o.) and was antihyperalgesic in a model of inflammatory pain (CFA-induced thermal hyperalgesia, MED = 0.83 mg/kg, p.o.). Based on its in vivo efficacy and pharmacokinetic profile, compound 23 (N-{4-[6-(4-trifluoromethyl-phenyl)-pyrimidin-4-yloxy]-benzothiazol-2-yl}-acetamide; AMG 517) was selected for further evaluation in human clinical trials.

The voltage-gated sodium channel Na1.7 is a genetically validated pain target under investigation for the development of analgesics. A therapeutic with a less frequent dosing regimen would be of value for treating chronic pain; however functional Na1.7 targeting antibodies are not known. In this report, we describe Na1.7 inhibitory peptide-antibody conjugates as an alternate construct for potential prolonged channel blockade through chemical derivatization of engineered antibodies. We previously identified Na1.7 inhibitory peptide GpTx-1 from tarantula venom and optimized its potency and selectivity. Tethering GpTx-1 peptides to antibodies bifunctionally couples FcRn-based antibody recycling attributes to the Na1.7 targeting function of the peptide warhead. Herein, we conjugated a GpTx-1 peptide to specific engineered cysteines in a carrier anti-2,4-dinitrophenol monoclonal antibody using polyethylene glycol linkers. The reactivity of 13 potential cysteine conjugation sites in the antibody scaffold was tuned using a model alkylating agent. Subsequent reactions with the peptide identified cysteine locations with the highest conversion to desired conjugates, which blocked Na1.7 currents in whole cell electrophysiology. Variations in attachment site, linker, and peptide loading established design parameters for potency optimization. Antibody conjugation led to in vivo half-life extension by 130-fold relative to a nonconjugated GpTx-1 peptide and differential biodistribution to nerve fibers in wild-type but not Na1.7 knockout mice. This study describes the optimization and application of antibody derivatization technology to functionally inhibit Na1.7 in engineered and neuronal cells.