Defining the structure-activity relationship for a novel class of allosteric MKP5 inhibitors.

Mitogen-activated protein kinase (MAPK) phosphatase 5 (MKP5) is responsible for regulating the activity of the stress-responsive MAPKs and has been put forth as a potential therapeutic target for a number of diseases, including dystrophic muscle disease a fatal rare disease which has neither a treatment nor cure. In previous work, we identified Compound 1 (3,3-dimethyl-1-((9-(methylthio)-5,6-dihydrothieno[3,4-h]quinazolin-2-yl)thio)butan-2-one) as the lead compound of a novel class of MKP5 inhibitors. In this work, we explore the structure-activity relationship for inhibition of MKP5 through modifications to the scaffold and functional groups present in 1. A series of derivative compounds was designed, synthesized, and evaluated for inhibition of MKP5. In addition, the X-ray crystal structures of six enzyme-inhibitor complexes were solved, further elucidating the necessary requirements for MKP5 inhibition. We found that the parallel-displaced π-π interaction between the inhibitor three-ring core and Tyr435 is critical for modulating potency, and that modifications to the core and functionalization at the C-9 position are essential for ensuring proper positioning of the core for this interaction. These results lay the foundation from which more potent MKP5 allosteric inhibitors can be developed for potential therapeutics towards the treatment of dystrophic muscle disease.

Racial Disparity in Oxygen Saturation Measurements by Pulse Oximetry: Evidence and Implications.

The pulse oximeter is a ubiquitous clinical tool used to estimate blood oxygen concentrations. However, decreased accuracy of pulse oximetry in patients with dark skin tones has been demonstrated since as early as 1985. Most commonly, pulse oximeters may overestimate the true oxygen saturation in individuals with dark skin tones, leading to higher rates of occult hypoxemia (i.e., clinically unrecognized low blood oxygen saturation). Overestimation of oxygen saturation in patients with dark skin tones has serious clinical implications, as these patients may receive insufficiently rigorous medical care when pulse oximeter measurements suggest that their oxygen saturation is higher than the true value. Recent studies have linked pulse oximeter inaccuracy to worse clinical outcomes, suggesting that pulse oximeter inaccuracy contributes to known racial health disparities. The magnitude of device inaccuracy varies by pulse oximeter manufacturer, sensor type, and arterial oxygen saturation. The underlying reasons for decreased pulse oximeter accuracy for individuals with dark skin tones may be related to failure to control for increased absorption of red light by melanin during device development and insufficient inclusion of individuals with dark skin tones during device calibration. Inadequate regulatory standards for device approval may also play a role in decreased accuracy. Awareness of potential pulse oximeter limitations is an important step for providers and may encourage the consideration of additional clinical information for management decisions. Ultimately, stricter regulatory requirements for oximeter approval and increased manufacturer transparency regarding device performance are required to mitigate this racial bias.

An allosteric site on MKP5 reveals a strategy for small-molecule inhibition.

The mitogen-activated protein kinase (MAPK) phosphatases (MKPs) have been considered "undruggable," but their position as regulators of the MAPKs makes them promising therapeutic targets. MKP5 has been suggested as a potential target for the treatment of dystrophic muscle disease. Here, we identified an inhibitor of MKP5 using a p38α MAPK-derived, phosphopeptide-based small-molecule screen. We solved the structure of MKP5 in complex with this inhibitor, which revealed a previously undescribed allosteric binding pocket. Binding of the inhibitor to this pocket collapsed the MKP5 active site and was predicted to limit MAPK binding. Treatment with the inhibitor recapitulated the phenotype of MKP5 deficiency, resulting in activation of p38 MAPK and JNK. We demonstrated that MKP5 was required for TGF-ß1 signaling in muscle and that the inhibitor blocked TGF-ß1-mediated Smad2 phosphorylation. TGF-ß1 pathway antagonism has been proposed for the treatment of dystrophic muscle disease. Thus, allosteric inhibition of MKP5 represents a therapeutic strategy against dystrophic muscle disease.

Synthesis and Biological Evaluation of an Indazole-Based Selective Protein Arginine Deiminase 4 (PAD4) Inhibitor.

Protein arginine deiminase 4 (PAD4) is a calcium-dependent enzyme that catalyzes the conversion of arginine to citrulline within target proteins. Dysregulation of PAD4 has been implicated in a number of human diseases, including rheumatoid arthritis and other inflammatory diseases as well as cancer. In this study, we report on the design, synthesis, and evaluation of a new class of haloacetamidine-based compounds as potential PAD4 inhibitors. Specifically, we describe the identification of 4,5,6-trichloroindazole 24 as a highly potent PAD4 inhibitor that displays >10-fold selectivity for PAD4 over PAD3 and >50-fold over PAD1 and PAD2. The efficacy of this compound in cells was determined by measuring the inhibition of PAD4-mediated H4 citrullination in HL-60 granulocytes.

Cellular Activity of New Small Molecule Protein Arginine Deiminase 3 (PAD3) Inhibitors.

The protein arginine deiminases (PADs) catalyze the post-translational deimination of arginine side chains. Multiple PAD isozymes have been characterized, and abnormal PAD activity has been associated with several human disease states. PAD3 has been characterized as a modulator of cell growth via apoptosis inducing factor and has been implicated in the neurodegenerative response to spinal cord injury. Here, we describe the design, synthesis, and evaluation of conformationally constrained versions of the potent and selective PAD3 inhibitor 2. The cell activity of representative inhibitors in this series was also demonstrated for the first time by rescue of thapsigargin-induced cell death in PAD3-expressing HEK293T cells.

Synthesis and Evaluation of Macrocyclic Peptide Aldehydes as Potent and Selective Inhibitors of the 20S Proteasome.

This research explores the first design and synthesis of macrocyclic peptide aldehydes as potent inhibitors of the 20S proteasome. Two novel macrocyclic peptide aldehydes based on the ring-size of the macrocyclic natural product TMC-95 were prepared and evaluated as inhibitors of the 20S proteasome. Both compounds inhibited in the low nanomolar range and proved to be selective for the proteasome over other serine and cysteine proteases, particularly when compared to linear analogues with similar amino acid sequences. In HeLa cells, both macrocycles efficiently inhibited activation of nuclear factor-κB (NF-κB) transcription factor by blocking proteasomal degradation of the inhibitor protein IκBα after cytokine stimulation. Due to their covalent mechanism of binding these compounds represent a 1000-fold increase in inhibitory potency over previously reported noncovalently binding TMC-95 analogues. Molecular modeling of the macrocyclic peptides confirms the preference of the large S3 pocket for large, hydrophobic residues and the ability to exploit this to improve selectivity of proteasome inhibitors.

Identification of multiple structurally distinct, nonpeptidic small molecule inhibitors of protein arginine deiminase 3 using a substrate-based fragment method.

The protein arginine deiminases (PADs) are a family of enzymes that catalyze the post-translational hydrolytic deimination of arginine residues. Four different enzymologically active PAD subtypes have been characterized and exhibit tissue-specific expression and association with a number of different diseases. In this Article we describe the development of an approach for the reliable discovery of low molecular weight, nonpeptidic fragment substrates of the PADs that then can be optimized and converted to mechanism-based irreversible PAD inhibitors. The approach is demonstrated by the development of potent and selective inhibitors of PAD3, a PAD subtype implicated in the neurodegenerative response to spinal cord injury. Multiple structurally distinct inhibitors were identified with the most potent inhibitors having >10,000 min(-1) M(-1) k(inact)/K(I) values and ≥10-fold selectivity for PAD3 over PADs 1, 2, and 4.