Discovery of potent and selective inhibitors of calmodulin-dependent kinase II (CaMKII).

We hereby disclose the discovery of inhibitors of CaMKII (7h and 7i) that are highly potent in rat ventricular myocytes, selective against hERG and other off-target kinases, while possessing good CaMKII tissue isoform selectivity (cardiac γ/δ vs. neuronal α/ß). In vitro and in vivo ADME/PK studies demonstrated the suitability of these CaMKII inhibitors for PO (7h rat F = 73%) and IV pharmacological studies.

Discovery of triazolopyridinone GS-462808, a late sodium current inhibitor (Late INai) of the cardiac Nav1.5 channel with improved efficacy and potency relative to ranolazine.

Previously we disclosed the discovery of potent Late INa current inhibitor 2 (GS-458967, IC50 of 333nM) that has a good separation of late versus peak Nav1.5 current, but did not have a favorable CNS safety window due to high brain penetration (3-fold higher partitioning into brain vs plasma) coupled with potent inhibition of brain sodium channel isoforms (Nav1.1, 1.2, 1.3). We increased the polar surface area from 50 to 84Å(2) by adding a carbonyl to the core and an oxadiazole ring resulting in 3 GS-462808 that had lower brain penetration and serendipitously lower activity at the brain isoforms. Compound 3 has an improved CNS window (>20 rat and dog) relative to 2, and improved anti-ischemic potency relative to ranolazine. The development of 3 was not pursued due to liver lesions in 7day rat toxicology studies.

Discovery of triazolopyridine GS-458967, a late sodium current inhibitor (Late INai) of the cardiac NaV 1.5 channel with improved efficacy and potency relative to ranolazine.

We started with a medium throughput screen of heterocyclic compounds without basic amine groups to avoid hERG and ß-blocker activity and identified [1,2,4]triazolo[4,3-a]pyridine as an early lead. Optimization of substituents for Late INa current inhibition and lack of Peak INa inhibition led to the discovery of 4h (GS-458967) with improved anti-arrhythmic activity relative to ranolazine. Unfortunately, 4h demonstrated use dependent block across the sodium isoforms including the central and peripheral nervous system isoforms that is consistent with its low therapeutic index (approximately 5-fold in rat, 3-fold in dog). Compound 4h represents our initial foray into a 2nd generation Late INa inhibitor program and is an important proof-of-concept compound. We will provide additional reports on addressing the CNS challenge in a follow-up communication.

Discovery of Dihydrobenzoxazepinone (GS-6615) Late Sodium Current Inhibitor (Late INai), a Phase II Agent with Demonstrated Preclinical Anti-Ischemic and Antiarrhythmic Properties.

Late sodium current (late INa) is enhanced during ischemia by reactive oxygen species (ROS) modifying the Nav 1.5 channel, resulting in incomplete inactivation. Compound 4 (GS-6615, eleclazine) a novel, potent, and selective inhibitor of late INa, is currently in clinical development for treatment of long QT-3 syndrome (LQT-3), hypertrophic cardiomyopathy (HCM), and ventricular tachycardia-ventricular fibrillation (VT-VF). We will describe structure-activity relationship (SAR) leading to the discovery of 4 that is vastly improved from the first generation late INa inhibitor 1 (ranolazine). Compound 4 was 42 times more potent than 1 in reducing ischemic burden in vivo (S-T segment elevation, 15 min left anteriorior descending, LAD, occlusion in rabbits) with EC50 values of 190 and 8000 nM, respectively. Compound 4 represents a new class of potent late INa inhibitors that will be useful in delineating the role of inhibitors of this current in the treatment of patients.

Partial A(1) adenosine receptor agonists from a molecular perspective and their potential use as chronic ventricular rate control agents during atrial fibrillation (AF).

This review provides a molecular perspective of partial agonism at the A(1) adenosine receptor. The structure-activity relationships (SAR) for affinity and intrinsic efficacy of analogues of the full agonist N6-cyclopentyladenosine (CPA) are emphasized. Both general models of activation of G protein-coupled receptors and specific molecular models of the A(1)-adenosine receptor are used to interpret the results of efforts to synthesize and assay effects of partial agonists. The SAR of affinity and intrinsic efficacy of the 2', 3', and especially the 5'-deoxy derivatives of CPA is presented. From this analysis, the nature of the interactions of specific atoms and substituents of the CPA molecule with the A(1)-adenosine receptor are deduced and presented pictorially. As an example of the therapeutic potential of partial agonists, the design and testing of analogues of CPA to provide chronic ventricular rate control during atrial fibrillation is described. The challenges associated with designing a partial A(1)-adenosine receptor agonist for providing chronic ventricular rate control during atrial fibrillation are many. To meet these challenges, further medicinal chemistry efforts in the area of partial A(1)-adenosine receptor agonism are still needed.

Structure-affinity relationships of the affinity of 2-pyrazolyl adenosine analogues for the adenosine A2A receptor.

The structure-affinity relationships of two novel 2-substituted adenosine series containing a substituted pyrazole attached at the N-1 or C-4 position for the adenosine (ADO) A2A receptor are described. Compounds in the 2-(N-1-pyrazolyl) adenosine series IV provided the highest affinity for the ADO A2A receptor as compared to the 2-(C-4-pyrazolyl) series V. The main structural differences between the two series point to the N-1 nitrogen of series IV imparting more favorable binding interactions with the receptor than those of series V.

Affinity and intrinsic efficacy (IE) of 5'-carbamoyl adenosine analogues for the A1 adenosine receptor--efforts towards the discovery of a chronic ventricular rate control agent for the treatment of atrial fibrillation (AF).

The SAR for the affinity to the A(1) adenosine receptor and relative intrinsic efficacy (IE, [(35)S]-GTPgammaS binding) of a series of 5'-carbamate and 5'-thionocarbamate derivatives of tecadenoson is described. Based on this SAR, selected compounds were evaluated in guinea pig isolated hearts to determine whether they were partial or full agonists with respect to their negative dromotropism, an A(1) AdoR mediated effect. Progress towards obtaining a partial A(1) AdoR agonist to potentially control ventricular rate during atrial fibrillation has been made with the discovery of several potent partial A(1) AdoR agonists (compounds 13, 14, and 17).

Structure-affinity relationships of 5'-aromatic ethers and 5'-aromatic sulfides as partial A1 adenosine agonists, potential supraventricular anti-arrhythmic agents.

Atrial fibrillation (AF) is the most commonly encountered sustained clinical arrhythmia with an estimated 2.3 million cases in the US (2001). A(1) adenosine receptor agonists can slow the electrical impulse propagation through the atrioventricular (AV) node (i.e., negative dromotropic effect) resulting in prolongation of the stimulus-to-His bundle (S-H) interval to potentially reduce ventricular rate. Compounds that are full agonists of the A(1) adenosine receptor can cause high grade AV block. Therefore, it is envisioned that a compound that is a partial agonist of the A(1) adenosine receptor could avoid this deleterious effect. 5(') Phenyl sulfides (e.g., 17, EC(50)=1.26 microM) and phenyl ethers (e.g., 28, EC(50)=0.2 microM) are partial agonists with respect to their AV nodal effects in guinea pig isolated hearts. Additional affinity, GTPgammaS binding data suggesting partial activity of the A(1) adenosine receptor, and PK results for 5(') modified adenosine derivatives are shown.

CVT-4325: a potent fatty acid oxidation inhibitor with favorable oral bioavailability.

New inhibitors of palmitoyl-CoA oxidation are based on the introduction of nitrogen heterocycles in the 'Western Portion' of the molecule. SAR studies led to the discovery of CVT-4325 (shown), a potent FOXi (IC50=380 nM rat mitochondria) with favorable PK properties (F=93%, t(1/2)=13.6h, dog).