Low-Toxicity Sulfonium-Based Probes for Cysteine-Specific Profiling in Live Cells

Oxidation Analysis of l-Cysteine with a Chiral Sensor Based on Quantum Weak Measurement

l-Cysteine, distinguished by its possession of reactive sulfhydryl groups within its molecular structure, plays a significant role in both biological systems and the pharmaceutical industry. It stands not only as a natural component integral to the constitution of glutathione but also as the principal precursor for the synthesis of l-cystine through an oxidation reaction. This study endeavors to introduce a novel approach to l-cysteine analysis, capitalizing on its optical activity, whereby an optical rotation detection system grounded in the principles of quantum weak measurement is proffered. The optical rotation angle corresponding to the concentration of chiral solutions can be accurately ascertained through spectral analysis. In practical implementation, a chiral sensing system, boasting a sensitivity of 372 nm/rad, was meticulously constructed, leveraging the concept of weak value amplification. Then, the real-time monitoring of chemical reactions involving l-cysteine and dimethyl sulfoxide was performed. Under the specific experimental conditions outlined in this investigation, it was observed that the oxidation process culminated within approximately 12 h. The application of weak measurement-based chiral sensors holds immense potential, providing robust technical support for real-time monitoring in fields such as chiral analysis and the synthesis of chiral pharmaceutical compounds.

Identification of sulfhydryl-containing proteins and further evaluation of the selenium-tagged redox homeostasis-regulating proteins

Chemoproteomic profiling of sulfhydryl-containing proteins has consistently been an attractive research hotspot. However, there remains a dearth of probes that are specifically designed for sulfhydryl-containing proteins, possessing sufficient reactivity, specificity, distinctive isotopic signature, as well as efficient labeling and evaluation capabilities for proteins implicated in the regulation of redox homeostasis. Here, the specific selenium-containing probes (Se-probes) in this work displayed high specificity and reactivity toward cysteine thiols on small molecules, peptides and purified proteins and showed very good competitive effect of proteins labeling in gel-ABPP. We identified more than 6000 candidate proteins. In TOP-ABPP, we investigated the peptide labeled by Se-probes, which revealed a distinct isotopic envelope pattern of selenium in both the primary and secondary mass spectra. This unique pattern can provide compelling evidence for identifying redox regulatory proteins and other target peptides. Furthermore, our examiation of post-translational modification (PTMs) of the cysteine site residues showed that oxidation PTMs was predominantly observed. We anticipate that Se-probes will enable broader and deeper proteome-wide profiling of sulfhydryl-containing proteins, provide an ideal tool for focusing on proteins that regulate redox homeostasis and advance the development of innovative selenium-based pharmaceuticals.

The expanding repertoire of covalent warheads for drug discovery

The reactive functionalities of drugs that engage in covalent interactions with the enzyme/receptor residue in either a reversible or an irreversible manner are called 'warheads'. Covalent warheads that were previously neglected because of safety concerns have recently gained center stage as a result of their various advantages over noncovalent drugs, including increased selectivity, increased residence time, and higher potency. With the approval of several covalent inhibitors over the past decade, research in this area has accelerated. Various strategies are being continuously developed to tune the characteristics of warheads to improve their potency and mitigate toxicity. Here, we review research progress in warhead discovery over the past 5 years to provide valuable insights for future drug discovery.

Pyridinium-Based Strategy for a Bioorthogonal Conjugation-Assisted Purification Method for Profiling Cell Surface Proteome

Cell surface proteins (CSPs) are valuable targets for therapeutic agents, but achieving highly selective CSP enrichment in cellular physiology remains a technical challenge. To address this challenge, we propose a newly developed sulfo-pyridinium ester (SPE) cross-linking probe, followed by two-step imaging and enrichment. The SPE probe showed higher efficiency in labeling proteins than similar NHS esters at the level of cell lysates and demonstrated specificity for Lys in competitive experiments. More importantly, this probe could selectively label the cell membranes in cell imaging with only negligible labeling of the intracellular compartment. Moreover, we successfully performed this strategy on MCF-7 live cells to label 425 unique CSPs from 1162 labeled proteins. Finally, we employed our probe to label the CSPs of insulin-cultured MCF-7, revealing several cell surface targets of key functional biomarkers and insulin-associated pathogenesis. The above results demonstrate that the SPE method provides a promising tool for the selective labeling of cell surface proteins and monitoring transient cell surface events.

Self-Luminescent Drug Delivery Vehicle: Synthesis, Self-Assembly Behavior, Cysteine-Responsive Property, and Application in the Visualization of Drug Release

Targeted drug delivery systems have gained great attention from the chemistry and biomedical fields in recent years due to the minimized harm to normal cells. When designing targeted drug delivery systems, the property of harmlessness to normal cells and the tracking ability of the whole process are quite crucial. These two characters can be brought into the related systems by applying a drug carrier that is self-luminescent and its drug release can be induced by the microenvironment of cancer cells. Therefore, the design and synthesis of drug delivery vehicles are significant for the fabrication of target drug delivery systems. Herein, we have synthesized a cysteine-responsive and fluorescent molecule, maleic acid-modified tetraphenylethylene derivative (MATPE), by a facile method. In addition, a drug delivery system with self-luminescence and cysteine-responsiveness based on the self-assembly of MATPE was fabricated. In this system, MATPE and cysteine both played dual roles as cysteine probe/drug carrier and emission-enhanced inducement/drug-release stimulus. The drug-release process was successfully realized in cancer cells and can be visualized, exhibiting great potential in the field of theranostics.

Cyclopropenone, Cyclopropeniminium Ion, and Cyclopropenethione as Novel Electrophilic Warheads for Potential Target Discovery of Triple-Negative Breast Cancer

Because very few targets are currently available for drug development, triple-negative breast cancer (TNBC) has been defined as one of the most difficult diseases for chemotherapy. Herein, we describe a suite of novel electrophilic warheads, which we have used in chemical proteomics studies in a search for potential targets for TNBC. Binding site analysis revealed that these warheads can modify not only highly nucleophilic residues, including cysteine and lysine, but also weakly nucleophilic residues. Cys12 of Kirsten rat sarcoma (KRAS^G12C) was successfully labeled by cyclopropenone and the cyclopropeniminium ions. Moderate inhibitory activity against TNBC cells was achieved with these novel electrophile-based probes. Activity-based protein profiling reveals that these electrophiles can covalently label a series of essential protein targets, including ALDH2, LRPPRC, and FABP5 from MDA-MB-231 cells. Further functional validation experiments demonstrated that FABP5 might be a potential target for TNBC.

Chemical modification of proteins - challenges and trends at the start of the 2020s

Ribosomally expressed proteins perform multiple, versatile, and specialized tasks throughout Nature. In modern times, chemically modified proteins, including improved hormones, enzymes, and antibody-drug-conjugates have become available and have found advanced industrial and pharmaceutical applications. Chemical modification of proteins is used to introduce new functionalities, improve stability or drugability. Undertaking chemical reactions with proteins without compromising their native function is still a core challenge as proteins are large conformation dependent multifunctional molecules. Methods for functionalization ideally should be chemo-selective, site-selective, and undertaken under biocompatible conditions in aqueous buffer to prevent denaturation of the protein. Here the present challenges in the field are discussed and methods for modification of the 20 encoded amino acids as well as the N-/C-termini and protein backbone are presented. For each amino acid, common and traditional modification methods are presented first, followed by more recent ones.