Structural insights into selective small molecule activation of PKG1α.

cGMP-dependent protein kinase I-α (PKG1α) is a target for pulmonary arterial hypertension due to its role in the regulation of smooth muscle function. While most work has focused on regulation of cGMP turnover, we recently described several small molecule tool compounds which were capable of activating PKG1α via a cGMP independent pathway. Selected molecules were crystallized in the presence of PKG1α and were found to bind to an allosteric site proximal to the low-affinity nucleotide binding domain. These molecules act to displace the switch helix and cause activation of PKG1α representing a new mechanism for the activation and control of this critical therapeutic path. The described structures are vital to understanding the function and control of this key regulatory pathway.

Diversifying Amino Acids and Peptides via Deaminative Reductive Cross-Couplings Leveraging High-Throughput Experimentation.

A deaminative reductive coupling of amino acid pyridinium salts with aryl bromides has been developed to enable efficient synthesis of noncanonical amino acids and diversification of peptides. This method transforms natural, commercially available lysine, ornithine, diaminobutanoic acid, and diaminopropanoic acid to aryl alanines and homologated derivatives with varying chain lengths. Attractive features include ability to transverse scales, tolerance of pharma-relevant (hetero)aryls and biorthogonal functional groups, and the applicability beyond monomeric amino acids to short and macrocyclic peptide substrates. The success of this work relied on high-throughput experimentation to identify complementary reaction conditions that proved critical for achieving the coupling of a broad scope of aryl bromides with a range of amino acid and peptide substrates including macrocyclic peptides.

Mechanistic insights on novel small molecule allosteric activators of cGMP-dependent protein kinase PKG1α.

cGMP-dependent protein kinase (PKG) represents a compelling drug target for treatment of cardiovascular diseases. PKG1 is the major effector of beneficial cGMP signaling which is involved in smooth muscle relaxation and vascular tone, inhibition of platelet aggregation and signaling that leads to cardioprotection. In this study, a novel piperidine series of activators previously identified from an ultrahigh-throughput screen were validated to directly bind partially activated PKG1α and subsequently enhance its kinase activity in a concentration-dependent manner. Compounds from initial optimization efforts showed an ability to activate PKG1α independent of the endogenous activator, cGMP. We demonstrate these small molecule activators mimic the effect of cGMP on the kinetic parameters of PKG1α by positively modulating the KM of the peptide substrate and negatively modulating the apparent KM for ATP with increase in catalytic efficiency, kcat. In addition, these compounds also allosterically modulate the binding affinity of cGMP for PKG1α by increasing the affinity of cGMP for the high-affinity binding site (CNB-A) and decreasing the affinity of cGMP for the low-affinity binding site (CNB-B). We show the mode of action of these activators involves binding to an allosteric site within the regulatory domain, near the CNB-B binding site. To the best of our knowledge, these are the first reported non-cGMP mimetic small molecules shown to directly activate PKG1α. Insights into the mechanism of action of these compounds will enable future development of cardioprotective compounds that function through novel modes of action for the treatment of cardiovascular diseases.

Optimization and Mechanistic Investigations of Novel Allosteric Activators of PKG1α.

Activation of PKG1α is a compelling strategy for the treatment of cardiovascular diseases. As the main effector of cyclic guanosine monophosphate (cGMP), activation of PKG1α induces smooth muscle relaxation in blood vessels, lowers pulmonary blood pressure, prevents platelet aggregation, and protects against cardiac stress. The development of activators has been mostly limited to cGMP mimetics and synthetic peptides. Described herein is the optimization of a piperidine series of small molecules to yield activators that demonstrate in vitro phosphorylation of vasodilator-stimulated phosphoprotein as well as antiproliferative effects in human pulmonary arterial smooth muscle cells. Hydrogen/deuterium exchange mass spectrometry experiments with the small molecule activators revealed a mechanism of action consistent with cGMP-induced activation, and an X-ray co-crystal structure with a construct encompassing the regulatory domains illustrated a binding mode in an allosteric pocket proximal to the low-affinity cyclic nucleotide-binding domain.

Discovery of the First Non-cGMP Mimetic Small Molecule Activators of cGMP-Dependent Protein Kinase 1 α (PKG1α).

PKG1α is a central node in cGMP signaling. Current therapeutics that look to activate this pathway rely on elevation of cGMP levels and subsequent activation of PKG1α. Direct activation of PKG1α could potentially drive additional efficacy without associated side effects of blanket cGMP elevation. We undertook a high-throughput screen to identify novel activators. After triaging through numerous false positive hits, attributed to compound mediated oxidation and activation of PKG1α, a piperidine series of compounds was validated. The hit 1 was a weak activator with EC50 = 47 µM. The activity could be improved to single digit micromolar, as seen in compounds 21 and 25 (7.0 and 3.7 µM, respectively). Several compounds were tested in a pVASP cell-based assay, and for compounds with moderate permeability, good agreement was observed between the biochemical and functional assays. These compounds will function as efficient tools to further interrogate PKG1α biology.

Efforts towards the optimization of a bi-aryl class of potent IRAK4 inhibitors.

IRAK4 has been identified as potential therapeutic target for inflammatory and autoimmune diseases. Herein we report the identification and initial SAR studies of a new class of pyrazole containing IRAK4 inhibitors designed to expand chemical diversity and improve off target activity of a previously identified series. These compounds maintain potent IRAK4 activity and desirable ligand efficiency. Rat clearance and a variety of off target activities were also examined, resulting in encouraging data with tractable SAR.

Bioavailable pyrrolo-benzo-1,4-diazines as Na(v)1.7 sodium channel blockers for the treatment of pain.

A series of pyrrolo-benzo-1,4-diazine analogs have been synthesized to improve the profile of the previous lead compound 1. The syntheses, structure-activity relationships, and selected pharmacokinetic data of these analogs are described. The optimization efforts allowed the identification of 33, a quinoline amide exhibiting potent Na(v)1.7 inhibitory activity and moderate selectivity over Na(v)1.5. Compound 33 displayed anti-nociceptive oral efficacy in a rat CFA inflammatory pain model at 100 mpk and in a rat spinal nerve ligation neuropathic pain model with an EC50 75 µM.

Discovery of pyrrolo-benzo-1,4-diazines as potent Na(v)1.7 sodium channel blockers.

A series of pyrrolo-benzo-1,4-diazine analogs have been synthesized and displayed potent Nav1.7 inhibitory activity and moderate selectivity over Nav1.5. The syntheses, structure-activity relationships, and selected pharmacokinetic data of these analogs are described. Compound 41 displayed anti-nociceptive efficacy in the rat CFA pain model at 100 mpk oral dosing.