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Abstract In this work, the impact of physicochemical modifications on pharmacokinetics and in vivo targeting of a small molecule fibroblast activation protein inhibitor (FAPI) imaging ligand in a murine model of rheumatoid arthritis was evaluated. While similar ligands have been well-reported in oncology for molecular imaging and radiotherapy, there are limited reports of FAPI derivatives in targeted applications in immunology. As inflammation may increase both specific and non-specific delivery of targeted agents in general, we sought to identify the optimal targeted molecular imaging probe characteristics for efficient cell surface engagement. A series of FAPI derivatives were synthesized and their physicochemical properties modified via conjugation of fluorescent dyes and/or an albumin-binding small molecule. The impact of these modifications on cell surface binding affinity was assessed using an overexpressing cell line. Additionally, a thorough mechanistic characterization of fibroblast activation protein (FAP) cell surface internalization was evaluated in both overexpressing and endogenously expressing cells. Lastly, the pharmacokinetics and in vivo uptake in inflamed arthritic paws were characterized via near-infrared (NIR) imaging. All targeted molecular imaging agents tested maintained strong nanomolar binding affinity to cell surface FAP independent of chemical modification. The murine fibroblast-like synoviocytes expressed lower absolute cell-surface FAP compared to a transfected line, and the net internalization half-life measured for the transfected cells via flow cytometry was 7.2 h. The unmodified FAPI ligand exhibited the poorest in vivo targeting, likely resulting from its large apparent volume of distribution (62.7 ml) and rapid systemic clearance (t 1/2 = 0.5 h). Conjugation of a charged, hydrophilic AF647 fluorophore decreased systemic clearance (t 1/2 = 2.1 h) and demonstrated a 2-fold improvement in blocking FAPI-800CW engagement of FAP in vivo when compared to blocking of FAPI-800CW with FAPI with up to 2.8-fold improvements noted for the equivalent albumin binding construct comparison.

Abstract Anti-IL17A therapies have proven effective for numerous inflammatory diseases including psoriasis, axial spondylitis and psoriatic arthritis. Modulating and/or antagonizing protein–protein interactions of IL17A cytokine binding to its cell surface receptors with oral therapies offers the promise to bring forward biologics-like efficacy in a pill to patients. We used an NMR-based fragment screen of recombinant IL17A to uncover starting points for small molecule IL17A antagonist discovery. By examining chemical shift perturbations in 2D [1H, 13C-HSQC] spectra of isotopically labeled IL17A, we discovered fragments binding the cytokine at a previously undescribed site near the IL17A C-terminal region, albeit with weak affinity (> 250 µM). Importantly this binding location was distinct from previously known chemical matter modulating cytokine responses. Subsequently through analog screening, we identified related compounds that bound symmetrically in this novel site with two copies. From this observation we employed a linking strategy via structure-based drug design and obtained compounds with increased binding affinity (

Protein methyltransferases (PMTs) are epigenetic regulatory enzymes with significant therapeutic relevance. Here the authors describe a collection of chemical inhibitors and antagonists to modulate most of the key methylation marks on histones H3 and H4, and use the collection to study of the role of PMTs in mouse and human T cell differentiation.

A novel and innovative high-throughput screening assay was developed to identify both activators and inhibitors of AMP-activated protein kinase (AMPK) using microarrayed compound screening (μARCS) technology. Test compounds were arrayed at a density of 8640 on a polystyrene sheet, and the enzyme and peptide substrate were introduced into the assay by incorporating them into an agarose gel followed by placement of the gels onto the compound sheet. Adenosine triphosphate (ATP) was delivered via a membrane, and the phosphorylated biotinylated substrate was captured onto a streptavidin affinity membrane (SAM™). For detection, the SAM™ was removed, washed, and imaged on a phosphor screen overnight. A library of more than 700,000 compounds was screened using this format to identify novel activators and inhibitors of AMPK. [ABSTRACT FROM AUTHOR]

The SARS-CoV-2 main protease (Mpro) is essential for viral replication because it is responsible for the processing of most of the non-structural proteins encoded by the virus. Inhibition of Mpro prevents viral replication and therefore constitutes an attractive antiviral strategy. We set out to develop a high-throughput Mpro enzymatic activity assay using fluorescently labeled peptide substrates. A library of fluorogenic substrates of various lengths, sequences and dye/quencher positions was prepared and tested against full length SARS-CoV-2 Mpro enzyme for optimal activity. The addition of buffers containing strongly hydrated kosmotropic anion salts, such as citrate, from the Hofmeister series significantly boosted the enzyme activity and enhanced the assay detection limit, enabling the ranking of sub-nanomolar inhibitors without relying on the low-throughput Morrison equation method. By comparing cooperativity in citrate or non-citrate buffer while titrating the Mpro enzyme concentration, we found full positive cooperativity of Mpro with citrate buffer at less than one nanomolar (nM), but at a much higher enzyme concentration (∼320 nM) with non-citrate buffer. In addition, using a tight binding Mpro inhibitor, we confirmed there was only one active catalytical site in each Mpro monomer. Since cooperativity requires at least two binding sites, we hypothesized that citrate facilitates dimerization of Mpro at sub-nanomolar concentration as one of the mechanisms enhances Mpro catalytic efficiency. This assay has been used in high-throughput screening and structure activity relationship (SAR) studies to support medicinal chemistry efforts. IC50 values determined in this assay correlates well with EC50 values generated by a SARS-CoV-2 antiviral assay after adjusted for cell penetration.