Design of Benzoxathiazin-3-one 1,1-Dioxides as a New Class of Irreversible Serine Hydrolase Inhibitors: Discovery of a Uniquely Selective PNPLA4 Inhibitor

Development of a Dual-Factor Activatable Covalent Targeted Photoacoustic Imaging Probe for Tumor Imaging

Photoacoustic imaging (PAI) is an emerging modality in biomedical imaging with superior imaging depth and specificity. However, PAI still has significant limitations, such as the background noise from endogenous chromophores. To overcome these limitations, we developed a covalent activity-based PAI probe, NOx-JS013, targeting NCEH1. NCEH1, a highly expressed and activated serine hydrolase in aggressive cancers, has the potential to be employed for the diagnosis of cancers. We show that NOx-JS013 labels active NCEH1 in live cells with high selectivity relative to other serine hydrolases. NOx-JS013 also presents its efficacy as a hypoxia-responsive imaging probe in live cells. Finally, NOx-JS013 successfully visualizes aggressive prostate cancer tumors in mouse models of PC3, while being negligibly detected in tumors of non-aggressive LNCaP mouse models. These findings show that NOx-JS013 has the potential to be used to develop precision PAI reagents for detecting metastatic progression in various cancers.

Complexity-Building ESIPT-Assisted Synthesis of Fused Polyheterocyclic Sulfonamides

Excited State Intramolecular Proton Transfer (ESIPT), originally discovered and explored in depth in a number of extensive photophysical studies, is more recently rediscovered as a powerful synthetic tool, offering rapid access to complex polyheterocycles. In our prior work we have employed ESIPT in aromatic o-keto amines and amides, leading to diverse primary photoproducts-complex quinolinols or azacanes possessing a fused lactam moiety-which could additionally be modified in short, high-yielding postphotochemical reactions to further grow complexity of the heterocyclic core scaffold and/or to decorate it with additional functional groups. Given that sulfonamides are generally known as privileged substructures, in this study we pursued two goals: (i) To explore whether sulfonamides could behave as proton donors in the context of ESIPT-initiated photoinduced reactions; (ii) To assess the scope of subsequent complexity-building photochemical and postphotochemical steps, which give access to polyheterocyclic molecular cores with fused cyclic sulfonamide moieties. In this work we show that this is indeed the case. Simple sulfonamide-containing photoprecursors produced the sought-after heterocyclic products in experimentally simple photochemical reactions accompanied by significant step-normalized complexity increases as corroborated by the Böttcher complexity scores.

Electrochemical Migratory Cyclization of N-Acylsulfonamides

Benzoxathiazine dioxide, as a bioisostere of the clinically widely used diazoxide, exhibits interesting biological activity. However, limited success has been achieved in terms of its concise and direct synthesis. We report herein a facile electrochemical migratory cyclization of N-acylsulfonamides to access a diverse array of benzoxathiazine dioxides. The inclusion of electrochemistry is crucial for realizing such a novel transformation, which is substantiated both by the experiments and density-functional-theory calculations.

Discovery of Potent and Selective Inhibitors against Protein-Derived Electrophilic Cofactors

Electrophilic cofactors are widely distributed in nature and play important roles in many physiological and disease processes, yet they have remained blind spots in traditional activity-based protein profiling (ABPP) approaches that target nucleophiles. More recently, reverse-polarity (RP)-ABPP using hydrazine probes identified an electrophilic N-terminal glyoxylyl (Glox) group for the first time in secernin-3 (SCRN3). The biological function(s) of both the protein and Glox as a cofactor has not yet been pharmacologically validated because of the lack of selective inhibitors that could disrupt and therefore identify its activity. Here, we present the first platform for analyzing the reactivity and selectivity of an expanded nucleophilic probe library toward main-chain carbonyl cofactors such as Glox and pyruvoyl (Pyvl) groups. We first applied the library proteome-wide to profile and confirm engagement with various electrophilic protein targets, including secernin-2 (SCRN2), shown here also to possess a Glox group. A broadly reactive indole ethylhydrazine probe was used for a competitive in vitro RP-ABPP assay to screen for selective inhibitors against such cofactors from a set of commercially available nucleophilic fragments. Using Glox-containing SCRN proteins as a case study, naphthyl hydrazine was identified as a potent and selective SCRN3 inhibitor, showing complete inhibition in cell lysates with no significant cross-reactivity detected for other enzymes. Moving forward, this platform provides the fundamental basis for the development of selective Glox inhibitors and represents a starting point to advance small molecules that modulate electrophile-dependent function.

Lipolysis: cellular mechanisms for lipid mobilization from fat stores

The perception that intracellular lipolysis is a straightforward process that releases fatty acids from fat stores in adipose tissue to generate energy has experienced major revisions over the last two decades. The discovery of new lipolytic enzymes and coregulators, the demonstration that lipophagy and lysosomal lipolysis contribute to the degradation of cellular lipid stores and the characterization of numerous factors and signalling pathways that regulate lipid hydrolysis on transcriptional and post-transcriptional levels have revolutionized our understanding of lipolysis. In this review, we focus on the mechanisms that facilitate intracellular fatty-acid mobilization, drawing on canonical and noncanonical enzymatic pathways. We summarize how intracellular lipolysis affects lipid-mediated signalling, metabolic regulation and energy homeostasis in multiple organs. Finally, we examine how these processes affect pathogenesis and how lipolysis may be targeted to potentially prevent or treat various diseases.

Development and application of novel electrophilic warheads in target identification and drug discovery

Nucleophilic amino acids play important roles in maintenance of protein structure and function, covalent modification of such amino acid residues by therapeutic agents is an efficient way to treat human diseases. Most of current clinical drugs are structurally limited to α,β-unsaturated amide as an electrophilic warhead. To alleviate this issue, many novel electrophiles have been developed in recent years that can covalently bind to different amino acid residues and provides a unique way to interrogate proteins, including "undruggable" targets. With an activity-based protein profiling (ABPP) approach, the activity and functionality of a protein and its binding sites can be assessed. This facilitates an understanding of protein function, and contributes to the discovery of new druggable targets and lead compounds. Meanwhile, many novel inhibitors bearing new reactive warhead were developed and displayed remarkable pharmaceutical properties. In this perspective, we have reviewed the recent remarkable progress of novel electrophiles and their applications in target identification and drug discovery.

Improved Stabilities of Labeling Probes for the Selective Modification of Endogenous Proteins in Living Cells and In Vivo

To date, various affinity-based protein labeling probes have been developed and applied in biological research to modify endogenous proteins in cell lysates and on the cell surface. However, the reactive groups on the labeling probes are also the cause of probe instability and nonselective labeling in a more complex environment, e. g., intracellular and in vivo. Here, we show that labeling probes composed of a sterically stabilized difluorophenyl pivalate can achieve efficient and selective labeling of endogenous proteins on the cell surface, inside living cells and in vivo. As compared with the existing protein labeling probes, probes with the difluorophenyl pivalate exhibit several advantages, including long-term stability in stock solutions, resistance to enzymatic hydrolysis and can be customized easily with diverse fluorophores and protein ligands. With this probe design, endogenous hypoxia biomarker in living cells and nude mice were successfully labeled and validated by in vivo, ex vivo, and immunohistochemistry imaging.

Fluorophosphonates on-Demand: A General and Simplified Approach toward Fluorophosphonate Synthesis

Herein, we report a general and simplified synthesis of fluorophosphonates directly from p-nitrophenylphosphonates. This FP on-demand reaction is mediated by a commercially available polymer-supported fluoride reagent that produces a variety (25 examples) of fluorophosphonates in high yields while only requiring reagent filtration for pure fluorophosphonate isolation. This reaction protocol facilitates the rapid profiling of serine hydrolases with diverse and novel sets of activated phosphonates with differential proteome reactivity. Moreover, slight modification of the procedure into a reaction-to-assay format has enabled additional screening efficiency.

Rapid and Selective Labeling of Endogenous Transmembrane Proteins in Living Cells with a Difluorophenyl Ester Affinity-Based Probe

The long-term stability of affinity-based protein labeling probes is crucial to obtain reproducible protein labeling results. However, highly stable probes generally suffer from low protein labeling efficiency and pose significant challenges when labeling low abundance native proteins in living cells. In this paper, we report that protein labeling probes based on an ortho-difluorophenyl ester reactive module exhibit long-term stability in DMSO stock solution and aqueous buffer, yet they can undergo rapid and selective labeling of native proteins. This novel electrophile can be customized with a wide range of different protein ligands and is particularly well-suited for the labeling and imaging of transmembrane proteins. With this probe design, the identity and relative levels of basal and hypoxia-induced transmembrane carbonic anhydrases were revealed by live cell imaging and in-gel fluorescence analysis. We believe that the extension of this difluorophenyl ester reactive module would allow for the specific labeling of various endogenous membrane proteins, facilitating in-depth studies of their distribution and functions in biological processes.

Hit-to-lead optimization of a benzene sulfonamide series for potential antileishmanial agents

A series of benzene sulphonamides with good potency and selectivity against Leishmania spp. intracellular amastigotes was identified by high-throughput screening. Approximately 200 compounds were synthesized as part of a hit-to-lead optimization program. The potency of the series appears to be strongly dependent on lipophilicity, making the identification of suitable orally available candidates challenging due to poor pharmacokinetics. Despite not identifying a clinical candidate, a likely solvent exposed area was found, best exemplified in compound 29. Ongoing detailed mode-of-action studies may provide an opportunity to use target-based medicinal chemistry to overcome the issues with the current series.

Strategies for Tuning the Selectivity of Chemical Probes that Target Serine Hydrolases

Serine hydrolases comprise a large family of enzymes that have diverse roles in key cellular processes, such as lipid metabolism, cell signaling, and regulation of post-translation modifications of proteins. They are also therapeutic targets for multiple human pathologies, including viral infection, diabetes, hypertension, and Alzheimer disease; however, few have well-defined substrates and biological functions. Activity-based probes (ABPs) have been used as effective tools to both profile activity and screen for selective inhibitors of serine hydrolases. One broad-spectrum ABP containing a fluorophosphonate electrophile has been used extensively to advance our understanding of diverse serine hydrolases. Due to the success of this single reagent, several robust chemistries have been developed to further diversify and tune the selectivity of ABPs used to target serine hydrolases. In this review, we highlight approaches to identify selective serine hydrolase ABPs and suggest new synthetic methodologies that could be applied to further advance probe development.

Blockade of the Lysophosphatidylserine Lipase ABHD12 Potentiates Ferroptosis in Cancer Cells

Ferroptosis is a type of cell death caused by the pathogenic accumulation of lipid hydroperoxides. Pharmacological mechanisms to induce ferroptosis may provide a way to kill cancer cells that are resistant to other forms of cell death like apoptosis. Nonetheless, the proteins that regulate ferroptotic sensitivity in cancer cells remain incompletely understood. Here, we screened a panel of inhibitors of serine hydrolases-an enzyme class important for regulating lipid metabolism-for potentiation of ferroptosis in HT1080 fibrosarcoma cells. We found that DO264, a selective inhibitor of the lyso- and ox-phosphatidylserine (PS) lipase ABHD12, enhances ferroptotic death caused by RSL3, an inhibitor of the lipid peroxidase GPX4. RSL3-induced ferroptosis was also potentiated by genetic disruption of ABHD12. Metabolomic experiments revealed that, in addition to elevated lyso-PS, ABHD12-inactivated cells show higher quantities of arachidonate (C20:4)-containing PS and 2-arachidonoyl glycerol, pointing to potential oxidation-sensitive lipid mediators of ferroptosis regulated by ABHD12.

"A Sweet Combination": Developing Saccharin and Acesulfame K Structures for Selectively Targeting the Tumor-Associated Carbonic Anhydrases IX and XII

The sweeteners saccharin (SAC) and acesulfame K (ACE) recently entered the topic of anticancer human carbonic anhydrase (CA, EC 4.2.1.1) inhibitors, as they showed to selectively inhibit the tumor-associated CAs IX/XII over ubiquitous CAs. A drug design strategy is here reported, which took SAC and ACE as leads and produced a series of 2H-benzo[e][1,2,4]thiadiazin-3(4H)-one-1,1-dioxides (BTD). Many derivatives showed greater potency (K_Is-CA IX 19.1-408.5 nM) and selectivity (II/IX SI 2-76) than the leads (K_Is-CA IX 103, 2400 nM; II/IX-SI 56, >4) against CA IX/XII over off-target isoforms. A thorough X-ray crystallographic study depicted their binding mode to both CA II and IX-mimic. The most representative BTDs were characterized in vitro for their antitumor activity against A549, PC-3, and HCT-116 cancer cell lines both in normoxia and hypoxia. The two most effective compounds were assayed for their effect on several apoptosis markers, identifying promising leads for the development of new anticancer drugs.

In-flow photooxygenation of aminothienopyridinones generates iminopyridinedione PTP4A3 phosphatase inhibitors

A continuous flow photooxygenation of 7-aminothieno[3,2-c]pyridin-4(5H)-ones to produce 7-iminothieno[3,2-c]pyridine-4,6(5H,7H)-diones has been developed, utilizing ambient air as the sole reactant. N-H Imines are formed as the major products, and excellent functional group tolerance and conversion on gram-scale without the need for chromatographic purification allow for facile late-stage diversification of the aminothienopyridinone scaffold. Several analogs exhibit potent in vitro inhibition of the cancer-associated protein tyrosine phosphatase PTP4A3, and the SAR supports an exploratory docking model.