Mercapto-pyrimidines are reversible covalent inhibitors of the papain-like protease (PLpro) and inhibit SARS-CoV-2 (SCoV-2) replication.

The papain-like protease (PLpro) plays a critical role in SARS-CoV-2 (SCoV-2) pathogenesis and is essential for viral replication and for allowing the virus to evade the host immune response. Inhibitors of PLpro have great therapeutic potential, however, developing them has been challenging due to PLpro's restricted substrate binding pocket. In this report, we screened a 115 000-compound library for PLpro inhibitors and identified a new pharmacophore, based on a mercapto-pyrimidine fragment that is a reversible covalent inhibitor (RCI) of PLpro and inhibits viral replication in cells. Compound 5 had an IC50 of 5.1 µM for PLpro inhibition and hit optimization yielded a derivative with increased potency (IC50 0.85 µM, 6-fold higher). Activity based profiling of compound 5 demonstrated that it reacts with PLpro cysteines. We show here that compound 5 represents a new class of RCIs, which undergo an addition elimination reaction with cysteines in their target proteins. We further show that their reversibility is catalyzed by exogenous thiols and is dependent on the size of the incoming thiol. In contrast, traditional RCIs are all based upon the Michael addition reaction mechanism and their reversibility is base-catalyzed. We identify a new class of RCIs that introduces a more reactive warhead with a pronounced selectivity profile based on thiol ligand size. This could allow the expansion of RCI modality use towards a larger group of proteins important for human disease.

A covalent inhibitor targeting the papain-like protease from SARS-CoV-2 inhibits viral replication.

Covalent inhibitors of the papain-like protease (PLpro) from SARS-CoV-2 have great potential as antivirals, but their non-specific reactivity with thiols has limited their development. In this report, we performed an 8000 molecule electrophile screen against PLpro and identified an α-chloro amide fragment, termed compound 1, which inhibited SARS-CoV-2 replication in cells, and also had low non-specific reactivity with thiols. Compound 1 covalently reacts with the active site cysteine of PLpro, and had an IC50 of 18 µM for PLpro inhibition. Compound 1 also had low non-specific reactivity with thiols and reacted with glutathione 1-2 orders of magnitude slower than other commonly used electrophilic warheads. Finally, compound 1 had low toxicity in cells and mice and has a molecular weight of only 247 daltons and consequently has great potential for further optimization. Collectively, these results demonstrate that compound 1 is a promising lead fragment for future PLpro drug discovery campaigns.

Facile Fabrication of Multilayer Stretchable Electronics via a Two-mode Mechanical Cutting Process.

A time- and cost-effective fabrication methodology via a two-mode mechanical cutting process for multilayer stretchable electronics has been developed without using the conventional photolithography-based processes. A commercially available vinyl cutter is used for defining complex patterns on designated material layers by adjusting the applied force and the depth of the cutting blade. Two distinct modes of mechanical cutting can be achieved and employed to establish the basic fabrication procedures for common features in stretchable electronics, such as the metal interconnects, contact pads, and openings by the "tunnel cut" mode, and the flexible overall structure by the "through cut" mode. Three robust and resilient stretchable systems have been demonstrated, including a water-resistant, omnidirectionally stretchable supercapacitor array, a stretchable mesh applicable in sweat extraction and sensing, and a skin-mountable human breathing monitoring patch. Results show excellent electronic performances of these devices made of multilayer functional materials after repetitive large deformations.

Acid-Sensitive Surfactants Enhance the Delivery of Nucleic Acids.

The development of endosomal disruptive agents is a major challenge in the field of drug delivery and pharmaceutical chemistry. Current endosomal disruptive agents are composed of polymers, peptides, and nanoparticles and have had limited clinical impact. Alternatives to traditional endosomal disruptive agents are therefore greatly needed. In this report, we introduce a new class of low molecular weight endosomal disruptive agents, termed caged surfactants, that selectively disrupt endosomes via reversible PEGylation under acidic endosomal conditions. The caged surfactants have the potential to address several of the limitations hindering the development of current endosomal disruptive agents, such as high toxicity and low excretion, and are amenable to traditional medicinal chemistry approaches for optimization. In this report, we synthesized three generations of caged surfactants and demonstrated that they can enhance the ability of cationic lipids to deliver mRNA into primary cells. We also show that caged surfactants can deliver siRNA into cells when modified with the RNA-binding dye thiazole orange. We anticipate that the caged surfactants will have numerous applications in pharmaceutical chemistry and drug delivery given their versatility.

Gold nanoparticle based plasmonic sensing for the detection of SARS-CoV-2 nucleocapsid proteins.

An inexpensive virus detection scheme with high sensitivity and specificity is desirable for broad applications such as the COVID-19 virus. In this article, we introduce the localized surface plasmon resonance (LSPR) principle on the aggregation of antigen-coated gold nanoparticles (GNPs) to detect SARS-CoV-2 Nucleocapsid (N) proteins. Experiments show this technique can produce results observable by the naked eye in 5 min with a LOD (Limits of Detection) of 150 ng/ml for the N proteins. A comprehensive numerical model of the LSPR effect on the aggregation of GNPs has been developed to identify the key parameters in the reaction processes. The color-changing behaviors can be readily utilized to detect the existence of the virus while the quantitative concentration value is characterized with the assistance of an optical spectrometer. A parameter defined as the ratio of the light absorption intensity at the upper visible band region of 700 nm to the light absorption intensity at the peak optical absorption spectrum of the GNPs at 530 nm is found to have a linear relationship with respect to the N protein concentrations. As such, this scheme could be utilized as an inexpensive testing methodology for applications in POC (Point-of-Care) diagnostics to combat current and future virus-induced pandemics.