New ε-N-thioglutaryl-lysine derivatives as SIRT5 inhibitors: Chemical synthesis, kinetic and crystallographic studies.

SIRT5 has been implicated in various physiological processes and human diseases, including cancer. Development of new highly potent, selective SIRT5 inhibitors is still needed to investigate disease-related mechanisms and therapeutic potentials. We here report new ε-N-thioglutaryllysine derivatives, which were designed according to SIRT5-catalysed deacylation reactions. These ε-N-thioglutaryllysine derivatives displayed potent SIRT5 inhibition, of which the potential photo-crosslinking derivative 8 manifested most potent inhibition with an IC50 value of 120 nM to SIRT5, and low inhibition to SIRT1-3 and SIRT6. The enzyme kinetic assays revealed that the ε-N-thioglutaryllysine derivatives inhibit SIRT5 by lysine-substrate competitive manner. Co-crystallographic analyses demonstrated that 8 binds to occupy the lysine-substate binding site by making hydrogen-bonding and electrostatic interactions with SIRT5-specific residues, and is likely positioned to react with NAD+ and form stable thio-intermediates. Compound 8 was observed to have low photo-crosslinking probability to SIRT5, possibly due to inappropriate position of the diazirine group as observed in SIRT5:8 crystal structure. This study provides useful information for developing drug-like inhibitors and cross-linking chemical probes for SIRT5-related studies.

Sensitive fluorogenic substrates for sirtuin deacylase inhibitor discovery.

Sirtuins (SIRTs) are NAD+-dependent lysine deacylases, regulating many important biological processes such as metabolism and stress responses. SIRT inhibitors may provide potential benefits against SIRT-driven human diseases. Development of efficient assay platforms based on fluorogenic substrates will facilitate the discovery of high-quality SIRT inhibitors. We here report 16 new fluorogenic peptide substrates (P1-P16) designed with structurally diverse tetrapeptides and acyl modifications. Tests of P1-P16 against SIRT isoforms identified several sensitive substrates for SIRT1, SIRT2, SIRT3 and SIRT5, which manifested lower KM values and higher catalytic efficiency, and particularly had less signal interference in inhibitor screening compared with our previously reported internally quenched fluorescent substrates. Co-crystallization of sensitive substrates P13 and P15 with SIRT5 revealed an unexpected binding mode, involving interactions with residues from active site bordering surfaces, different from that observed for other peptides derived from natural protein substrates. By using SIRT5 sensitive substrates, we found that TW-37, a Bcl-2 inhibitor, displayed low micromolar inhibition to SIRT5, which was further validated by isothermal titration calorimetry analyses, offering a new point to develop dual-action SIRT5/Bcl-2 inhibitors against cancers. This work provides assay platform and structural basis for developing new substrates and inhibitors targeting human SIRTs.

Discovery of mercaptopropanamide-substituted aryl tetrazoles as new broad-spectrum metallo-ß-lactamase inhibitors.

ß-Lactam antibiotic resistance mediated by metallo-ß-lactamases (MBL) has threatened global public health. There are currently no available inhibitors of MBLs for clinical use. We previously reported the ruthenium-catalyzed meta-selective C-H nitration synthesis method, leading to some meta-mercaptopropanamide substituted aryl tetrazoles as new potent MBL inhibitors. Here, we described the structure-activity relationship of meta- and ortho-mercaptopropanamide substituted aryl tetrazoles with clinically relevant MBLs. The resulting most potent compound 13a showed IC50 values of 0.044 µM, 0.396 µM and 0.71 µM against VIM-2, NDM-1 and IMP-1 MBL, respectively. Crystallographic analysis revealed that 13a chelated to active site zinc ions via the thiol group and interacted with the catalytically important residues Asn233 and Tyr67, providing further structural information for the development of thiol based MBL inhibitors.

Structure-Based Development of (1-(3'-Mercaptopropanamido)methyl)boronic Acid Derived Broad-Spectrum, Dual-Action Inhibitors of Metallo- and Serine-ß-lactamases.

The emergence and spread of bacterial pathogens acquired metallo-ß-lactamase (MBL) and serine-ß-lactamase (SBL) medicated ß-lactam resistance gives rise to an urgent need for the development of new dual-action MBL/SBL inhibitors. Application of a pharmacophore fusion strategy led to the identification of (2'S)-(1-(3'-mercapto-2'-methylpropanamido)methyl)boronic acid (MS01) as a new dual-action inhibitor, which manifests broad-spectrum inhibition to representative MBL/SBL enzymes, including the widespread VIM-2 and KPC-2. Guided by the VIM-2:MS01 and KPC-2:MS01 complex structures, further structural optimization yielded new, more potent dual-action inhibitors. Selectivity studies indicated that the inhibitors had no apparent inhibition to human angiotensin-converting enzyme-2 and showed selectivity across serine hydrolyases in E. coli and human HEK293T cells labeled by the activity-based probe TAMRA-FP. Moreover, the inhibitors displayed potentiation of meropenem efficacy against MBL- or SBL-positive clinical isolates without apparent cytotoxicity. This work will aid efforts to develop new types of clinically useful dual-action inhibitors targeting MBL/SBL enzymes.

Crystallographic and SAR analyses reveal the high requirements needed to selectively and potently inhibit SIRT2 deacetylase and decanoylase.

A high-quality X-ray crystal structure reveals the mechanism of compound 1a inhibiting SIRT2 deacetylase and decanoylase. Structure-activity relationship (SAR) analysis of the synthesized derivatives of 1a reveals the high requirements needed for selective inhibitors to bind with the induced hydrophobic pocket and potently inhibit sirtuin 2 deacetylase.

X-ray crystal structure guided discovery of new selective, substrate-mimicking sirtuin 2 inhibitors that exhibit activities against non-small cell lung cancer cells.

Human sirtuin 2 (SIRT2) is a nicotinamide adenine dinucleotide (NAD+)-dependent deacylase, and is implicated in human diseases including cancer. Selective small-molecule inhibitors for SIRT2 are sought as chemical tools and potential therapeutics. Here we report the X-ray crystal structure guided structure-activity relationship studies of new N-(3-(phenoxymethyl)phenyl)acetamide derivatives with SIRT2, which led to the identification of potent, selective SIRT2 inhibitors. Crystallographic analyses reveal that the new inhibitors act via inducing the formation of an enlarged hydrophobic pocket and particularly mimicking the interactions made by myristoylated-lysine substrates. The most potent inhibitor 24a could dose-dependently elevate the acetylation level of α-tubulin in the non-small cell lung cancer H441 cells, which have a high expression level of SIRT2 as determinated by Western blotting analyses. Further cellular assays reveal that 24a restrains cell growth mainly through inhibiting cellular proliferation rather than inducing apoptosis. Moreover, 24a could suppress the migration and invasion of H441 cells. These results provide an excellent basis for further development of new potent, selective, and cell active SIRT2 inhibitors as chemical tools and potential therapeutics for SIRT2-driven non-small cell lung cancers.

Virtual target screening reveals rosmarinic acid and salvianolic acid A inhibiting metallo- and serine-ß-lactamases.

Rosmarinic acid (RA), a polyphenolic phytochemical, has broad-spectrum biological and pharmacological activity. A virtual target screening method termed IFPTarget combined with enzyme inhibition assays led to the identification of the clinically relevant metallo-ß-lactamase (MBL) VIM-2 as one of unexploited targets of RA. The enzyme kinetic studies indicated that RA is a fully reversible, substrate-competitive VIM-2 inhibitor. The isothermal titration calorimetry (ITC) analyses revealed that the initial binding of RA to VIM-2 is mainly due to enthalpy contribution. Further inhibition assays with RA related compounds revealed that salvianolic acid A, a derivative of RA, manifests potent inhibition to VIM-2, more interestingly, which shows inhibitory activity against the NDM-1, another clinically relevant MBL subtype, and the serine-ß-lactamase TEM-1 that is structurally and mechanistically distinct from the VIM-2 and NDM-1.

((S)-3-Mercapto-2-methylpropanamido)acetic acid derivatives as metallo-ß-lactamase inhibitors: Synthesis, kinetic and crystallographic studies.

The emergence and global spread of metallo-ß-lactamase (MBL) mediated resistance to almost all ß-lactam antibacterials poses a serious threat to public health. Since no clinically useful MBL inhibitors have been reported, there is an urgent need to develop new potent broad-spectrum MBL inhibitors effective against antibacterial resistance. Herein, we synthesized a set of 2-substituted ((S)-3-mercapto-2-methylpropanamido) acetic acid derivatives, some of which displayed potent inhibition with high ligand efficiency to the clinically relevant MBL subtypes, Verona Integron-encoded MBL (VIM)-2 and New Delhi MBL (NDM)-1. Kinetic studies revealed that the inhibitors are not strong zinc chelators in solution, and they bind reversibly to VIM-2 but dissociate very slowly. Crystallographic analyses revealed that they inhibit VIM-2 via chelating the active site zinc ions and interacting with catalytically important residues. Further cell- and zebrafish-based assays revealed that the inhibitors slightly increase susceptibility of E. coli cells expressing VIM-2 to meropenem, and they have no apparent toxicity to the viability of HEK293T cells and the zebrafish embryogenesis.

Structure-based discovery of new selective small-molecule sirtuin 5 inhibitors.

Human sirtuin 5 (SIRT5) is a protein deacylase regulating metabolic pathways and stress responses and is implicated in metabolism-related diseases. Small-molecule inhibitors for SIRT5 are sought as chemical tools and potential therapeutics. Herein, we proposed a customized virtual screening approach targeting catalytically important and unique residues Tyr102 and Arg105 of SIRT5. Of the 20 tested virtual screening hits, six compounds displayed marked inhibitory activities against SIRT5. For the hit compound 19, a series of newly synthesized (E)-2-cyano-N-phenyl-3-(5-phenylfuran-2-yl)acrylamide derivatives/analogues were carried out structure-activity relationship analyses, resulting in new more potent inhibitors, among which 37 displayed the most potent inhibition to SIRT5 with an IC50 value of 5.59 ± 0.75 µM. The biochemical studies revealed that 37 likely acts via competitive inhibition with the succinyl-lysine substrate, rather than the NAD+ cofactor, and it manifested substantial selectivity for SIRT5 over SIRT2 and SIRT6. This study will aid further efforts to develop new selective SIRT5 inhibitors as tools and therapeutics.

IFPTarget: A Customized Virtual Target Identification Method Based on Protein-Ligand Interaction Fingerprinting Analyses.

Small-molecule target identification is an important and challenging task for chemical biology and drug discovery. Structure-based virtual target identification has been widely used, which infers and prioritizes potential protein targets for the molecule of interest (MOI) principally via a scoring function. However, current "universal" scoring functions may not always accurately identify targets to which the MOI binds from the retrieved target database, in part due to a lack of consideration of the important binding features for an individual target. Here, we present IFPTarget, a customized virtual target identification method, which uses an interaction fingerprinting (IFP) method for target-specific interaction analyses and a comprehensive index (Cvalue) for target ranking. Evaluation results indicate that the IFP method enables substantially improved binding pose prediction, and Cvalue has an excellent performance in target ranking for the test set. When applied to screen against our established target library that contains 11,863 protein structures covering 2842 unique targets, IFPTarget could retrieve known targets within the top-ranked list and identified new potential targets for chemically diverse drugs. IFPTarget prediction led to the identification of the metallo-ß-lactamase VIM-2 as a target for quercetin as validated by enzymatic inhibition assays. This study provides a new in silico target identification tool and will aid future efforts to develop new target-customized methods for target identification.