Send Orders for Reprints to reprints@benthamscience.ae

Current Topics in Medicinal Chemistry, 2018, 18, 1-10 1

REVIEW ARTICLE

1568-0266/18 $58.00+.00 © 2018 Bentham Science Publishers

The Development of New Small-Molecule Inhibitors Targeting Bacterial Metallo-β-lactamases

Ping Wang+,a,b, Jing Cheng+,a,b, Cong-Cong Liua,b, Kai Tanga,b, Feng Xua,b, Zhiqiang Yud, Bin Yu*,a,b,c,d, and Junbiao Chang*,a,c

aCo-Innovation Center of Henan Province for New Drug R & D and Preclinical Safety, Zhengzhou 450001, China; bSchool of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou 450001, China; cCollege of Chemistry and Mo-lecular Engineering, Zhengzhou University, Zhengzhou 450001, China; dGuangdong Provincial Key Laboratory of New Drug Screening, Guangzhou 510033, China

A R T I C L E H I S T O R Y

Received: January 02, 2018 Revised: March 08, 2018 Accepted: May 13, 2018 DOI: 10.2174/1568026618666180518101028

Abstract: Metallo-β-lactamases (MBLs) are a family of Zn(II)-dependent enzymes that can hydrolyze almost all β-lactam antibiotics. Horizontal transfer of the genes encoding MBLs among Gram-negative bacteria pathogens has led to the emergence of extensively drug-resistant pathogens, which now repre-sent a major threat to human health. As there is not to date yet a clinically available MBL inhibitor, the discovery of new MBL inhibitors has great urgency. This review highlights the recent developments in the discovery of small-molecule MBL inhibitors.

Keywords: Metallo-β-lactamases, Thiol derivatives, Dicarboxylic acid derivatives, Cyclic Boronates, Triazoles, Natural prod-ucts, Peptide inhibitors.

1. INTRODUCTION

β-Lactam antibiotics have a broad antibacterial spectrum and play an important role in the treatment of bacterial infec-tions. However, an increasing number of bacteria have be-come resistant to β-lactam antibiotics as a result of their producingβ-lactamases, including Extended-Spectrum β-Lactamases (ESBLs), the AmpCβ-lactamases, and the carbapenemaseβ-lactamases. These bacteria pose a great threat to global healthcare. Carbapenemases are β-lactamases that can hydrolyze nearly all β-lactam antibiotics including carbapenems, the last-resort antibiotics against drug-resistant Gram-negative bacteria. Carbapenemasesare members of the Ambler-class A, B, and D β-lactamasesub-families. Classes A and D are serine-β-lactamases that catalyze hydrolysis using an active-site serine, while class B β-lactamases(also called metallo-β-lactamases, MBLs)are metallo-enzymes that use one or two zinc ions for their activity [1]. MBLs are di-vided according to their sequence homology into three sub-classes (B1, B2, and B3) [2]. Among the reported MBLs, the NDM-type MBL is identified as the most widespread MBL responsible for the emergence of Gram-negative superbugs. The NDM-type MBL hydrolyzes all of the clinically effica-

*Address correspondence to these authors at the School of Pharmaceutical Sciences, Zhengzhou University, Zhengzhou 450001, China; E-mail: zzu-yubin@hotmail.com and Co-Innovation Center of Henan Province for New Drug R & D and Preclinical Safety, Zhengzhou 450001, China; E-mail: changjunbiao@zzu.edu.cn +The two authors contribute equally to this work.

cious β-lactams with the exception of themonobactams. As the NDM-encoding genes are always associated with trans-posable elements and conjugative plasmids, this MBL is now disseminated worldwide [3]. Accordingly, the development of inhibitors of MBLs is an essential strategy for maintaining the future usefulness of existing β-lactam antibiotics. While there are effective serine-β-lactamases inhibitors such as clavulanic acid, tazobactam, sulbactam, and avibactam—all of which are widely approved in combination with appropri-ate β-lactam antibiotics for clinical treatment [4, 5] —there are no reports of clinically useful MBL inhibitors. Accord-ingly, the development of new inhibitors targeting bacterial MBLs is needed urgently.

A number of recent articles provide excellent perspec-tives on the role of lipidation [6, 7], biology [8, 9], evolution [10-12], and protein chemistry [13-15] of the metallo-β-lactamases. Additional reviews discuss the structure [16-19], mechanism [19-21], and history [3] of metallo-β-lactamases, and summarize the various approaches [22], including criti-cal analysis [23], toward the discovery of a clinically useful MBL inhibitor (and especially, NDM-1) [24]. Various MBL inhibitors have been reported. The key structural feature of these inhibitors includethetrifluoromethyl alcohol and ketone [25], dicarboxylic acids [26, 27], thiols [28], sulfates [29], hydroxamates [30], tetrazoles [31], and sulfonamides [32]. This review focuses on the new inhibitors against MBLs, covering the literature from 2007 till now. The review is organized based on the chemotypes of these small-molecule inhibitors.

2 Current Topics in Medicinal Chemistry, 2018, Vol. 18, No. 00 Wang et al.

2. THE DEVELOPMENT OF NEW MBL INHIBITORS

2.1. Thiol Derivatives

Compounds with a thiol group, such as the D- and L-captoprildiastereomers (compounds 1 and 2, Fig. 1), inhib-ited MBLs as a result of their tight interaction with zinc within the active site.The captopril diastereomers were used originally to treat hypertension clinically, and were reported as New Delhi metallo-β-lactamase-1 (NDM-1) inhibitors [33]. D-Captopril was moreeffective inhibitor thanL-captopril [34]. Rydzik et al. demonstrated that L-and D-captopril had different modes of binding, using a 19F NMR method for monitoring conformational changes and specific ligand bind-ing to NDM-1 [35]. D-Captopril showed certain selectivity-toward the monozinc enzymes as represented by the metallo-β-lactamase subclasses B1 and B2fromBacillus cereus (BcII) and Aeromonashydrophila (CphA) [36]. Li et al. also used NMR filtering, combined with the structure-based virtual screening approach,to identify inhibitors of the clinical-lyrelevant Verona Integron-encoded MBL (VIM-2) MBL [37]. From the synthesis of a series of simplified captopril analogs, Li et al. identified the N-benzyl amide of (R)-3-mercapto-2-methylpropanoic acid 3, which showed moderate inhibition against NDM-1 (IC50 = 1µM). Compound 4, an inhibitor used in clinical practice, also showedmoderate anti-NDM-1 activity(IC50 =10.4µM) and low toxicity [38]. Crys-tallographic analyses ofthe VIM-5 metallo-β-lactamase (MBL) with isoquinoline inhibitors revealed non-zinc ion binding modes [39]. Compared with other MBL-inhibitor structures with a zinc-binding thiol,thecompounds potentiat-edmeropenem activity againstclinical isolates harboring MBLs.Yusof et al. [40] recently revealed that the potency of these inhibitors could be improved by shortening the length of the mercaptoalkanoyl sidechain, as exemplified by com-pounds5(Ki = 2.3 ± 1.5 µM) and 6 (Ki = 2.9 ± 0.9 µM). When the prolinering was replaced by the pipecolic acid, the inhibi-tory activity was maintained (7, Ki = 3.4 ± 1.3 µM) while the inhibitory activity wascompletely lost when the thiol group was substituted by a carboxylic acid.Klingler et al. devel-oped a fluorescence-based, functional assay for β-lactamase inhibitor testing [41] and applied the assay to the evaluation of several approved drugs with sulfhydryl moieties. DL-Thiorphan(8) and Tiopronin (9) exhibited moderate inhibi-tory activitywith theIC50value of 1.8 and 5.9 µM for NDM-1 and imipenemase-7 (IMP-7)respectively.

Faridoon et al. [42] reported analogs of compound10 (Fig. 1) through the fragment-based screening. Structure–activity studies of these analogs against the metallo-β-lactamase IMP-1 were undertaken. Although 1,2,4-triazole-3-thiols showed strong binding, the improvements in potency (from 1: Ki ~1 mM to 4i: Ki ~70 µM) were modest. Aninter-esting discovery was that the optimized product 11 of acylat-edthiosemicarbazides possessed moderate potencyagainst the IMP-1 MBL(Ki= 11 µM). In addition, several thiol deriva-tives ofL-amino acids (such as compound 12) also exhibited good activity against IMP-1 MBLs [43].

Skagseth et al. [44] replaced the carboxylate group of mercaptocarboxylic acids with bioisosteric groups like phos-phonate esters, phosphonic acids, and NH-tetrazoles. Com-pounds 13, 14 and 15 inhibited the three MBLs (VIM-2, German imipenemase-1 (GIM-1), and NDM-1).Chang et al.

[45] constructed a new scaffold, the N-substituted carbamyl-methyl mercaptoacetatethioether,which inhibited MBLs from all three subclasses, but preferentially L1 from subclass B3.

Martin et al. [46] demonstrated thatthiomandelic acid 16 and 2-mercapto-3-phenylpropionic acid 17 in combination with meropenem and cefoperazone showedthe improvement-sin activity against some Gram-negative carbapenem-resistant isolates, especially an imipenemase (IMP) produc-ing strain of Klebsiella pneumoniae.

The inhibitory effects of mercaptophosphonate deriva-tives against the three subclasses of MBLs (B1, B2, and B3) were investigated by Lassaux et al. Compound18, bearing two chloro atoms on the phenylring,wasa broad spectrum MBL inhibitor. Compound 19, the phosphonateanalog of thiomandelic acid, displayed an inhibitory activity against B1 (Ki = 1 µM), B2 (Ki = 5 µM) and B3 (Ki = 0.4 µM).The study also showed that the phosphonategroup of 18 inter-acted with the Zn2+ ion [47].

Nevertheless, there are many challenges of developing thiol-based MBL inhibitors.Newapproachesare needed for the further development of thiol-based MBL inhibi-tors.Recently, Büttner et al. [48] found that the piperidine and piperazinesubstructure provided selectivity and an in-creased activity on IMP-7, which is a promising result.

2.2. Dicarboxylic Acid Derivatives

2.2.1. Dipicolinic Acid Derivatives

2-Picolinic acid (20, Fig. 2) and its derivative pyridine-2,4-dicarboxylic acid (2,4-PDCA) (21) were reported as ef-fective inhibitors againstCphA, a subclass B2 enzyme [49]. Subsequently compound 22, derived from 2,6-dipicolinic acid (DPA), was reported to be a broad-spectrum andpo-tentinhibitor against NDM-1, IMP-1, and VIM-2 by usingthe fragment-based drug discovery (FBDD). This compound synergized with imipenem, thereby reducing the minimal inhibitory concentrations (measured by microdilution broth MICs) of imipenem to a susceptible range for clinical strains of Escherichia coli and Klebsiellapneumoniaestrains harbor-ing theblaNDM-1gene [50]. Shin et al.identified 1-hydroxypyridine-2(1H)-thione-6-carboxylic acid as a first-in-class metallo-β-lactamase inhibitor against VIM-2(Ki = 13 nM, ligand efficiency = 0.99), making it a promising lead candidate for antibacterial combined therapy [51]. 2.2.2. Phthalic Acid Derivatives

A series of 3-substituted phthalic acid derivatives were evaluated as the IMP-1 inhibitors. These compounds—and especially the p-hydroxyphenyl derivative 23—potentiated the inhibitory activity of biapenem against Pseudomonas aeruginosaproducing IMP-1 [52]. Moreover, 3-alkyloxy and 3-amino-substituted phthalic acid derivatives (compounds 24 and 25) were identified as moderatelyactive IMP-1 inhibitors, among which 3-aminophthalic acid deriva-tives displayed strong combination effect with biapenem as well. The study demonstrated that the 4'-hydroxypiperidine derivative (compound 26) could inhibit IMP-1and synergize the effect of various antibiotics [53].

The Development of New Small-Molecule Inhibitors Current Topics in Medicinal Chemistry, 2018, Vol. 18, No. 00 3

Fig. (1). Thiol compounds as MBL inhibitors.

According to Hiraiwa et al. [27],3-(4-hydroxypiperidin-1-yl) phthalic acid 27was another moderately active inhibitor with an IC50 of 2.7 µM. The crystal structure of IMP-1 in-complex with the 3-aminophthalic acid derivative suggested thatsubstitution at the 6-position of the phenylringofcom-pound 27 could improve potency. As a result, a series of3,6-disubstituted phthalic acid derivatives were synthesizedand then evaluated for their IMP-1 inhibitory activity and syner-gistic effect with the carbapenembiapenem (BIPM). The 3,6-bis-(4-hydroxypiperidin-1-yl) derivative 28 was the mostef-fective IMP-1 inhibitor (IC50 = 0.27 µM), having 10-fold higher inhibitory activity than 3-(4-hydroxypiperidin-1-yl) phthalic acid. 2.2.3. Succinic Acids

ME1071 (compound 29) [54],derived frommaleic acid, was agood MBL inhibitor andpotentiated the activity of cef-tazidime andcarbapenems (especially biapenem) against MBL-producing P.aeruginosa, achieving the reduction of the MICs of carbapenemsincluding VIM-2 and IMP-1. ME1071 was later reported to have a synergistic effect against strains ofEnterobacteriaceae and Acinetobacter spp. that express the NDM-1 enzyme, despite of the fact that the synergistic effect was weaker than for bacteria with IMP and VIM metallo-enzymes due to the weaker affinity of ME1071 for NDM-1 than IMP-1 and VIM-2 [55].

2.2.4. Thiophene-carboxylic Acid Derivatives

Thiophene-carboxylic acid derivatives were NDM-1 in-hibitors and exertedsynergistic antibacterial activity in com-bination with meropenem against E. coli BL21 (DE3)/pET30a-NDM-1 [56]. Compounds 30 and 31 might be used as potential compounds to discover antibacterial agents,in spite of their high IC50 values. As revealed by flexible dockingand quantum mechanics (QM) evaluation, the side chain of thiophene-carboxylic acid displayed weak interaction with theside chain group ofonly one amino acid residue (His189), while the active site of full-length NDM-1 was composed of two zinc ions, a water-bridge molecule, and six amino acids (His189, His120, His122, Asp124, Cys208, and His250).

2.3. Cyclic Boronates

Brem et al. [57] reported that cyclic boronates acted on both serine- and metallo-β-lactamases by mimicking the common tetrahedral intermediate. Accordingly, boronate-based inhibitors could serve as the templates for the devel-opment of broad-spectrum inhibitors. The in vitro screening of cyclic boronates demonstrated that compounds32 and 33 (Fig. 3) were potentinhibitors ofVIM-2 and NDM-1. Com-pound 34 displayed moderate inhibitory activity against CphA (IC50 = 4.4µM) and OXA-10 (IC50 = 0.33 µM).Cahill et al. [58] recently showed that cyclic boronatesinhibited

4 Current Topics in Medicinal Chemistry, 2018, Vol. 18, No. 00 Wang et al.

both serine- and metallo-β-lactamases. Their cyclic boro-nates inhibited all four classes of theβ-lactamases, as repre-sented by the class A extended spectrum β-lactamase CTX-M-15, the class C enzymeAmpC from P. aeruginosa, and the class D OXA enzymes. TheIC50values ranged from low mi-cromolar to low nanomolar.

2.4. Triazoles Inhibitors

2.4.1. Azolylthioacetamide

The azolylthioacetamides, and especially compound 35 (Ki= 1.2µM), inhibitedthe metallo-β-lactamasesand espe-cially forthe ImiSMBL (Fig. 4). Structure−activity relation-ships indicated that the aromatic carboxyl acid attached to the triazole ring improved inhibitory activity of the inhibitors against ImiS, while an aliphatic carboxyl acid group failed to enhance the activity, indicating that the aromatic carboxylic

acid-substituted azolylthioacetamide was a promising scaf-fold for the development ofnewinhibitors targeting the ImiS (and potentially other B2 subclass enzymes) MBLs [59].

Within another series of triazolylthioacetamidescom-pound 36 (Ki = 0.49 µM) and its derivatives inhibited NDM-1 with an IC50 values of 0.15-1.90 µM, while compound 36 was inactive (even at 10 µM) against the CcrA, ImiSand L1 MBLs. Structure−activity relationship studies revealed that the activity of triazolylthioacetamides was influenced by the replacement of hydrogen on the aromatic ring by chlorine, heteroatoms, or alkyl groups while leaving the aromatic ring of the triazolylthiols unmodified [60]. Sevaille et al. [61] showed a series of active compounds mainly featured either halogen or bulky bicyclic aryl substituents, having IC50 val-ues in the µM range towards at least four enzymes including NDM-1, VIM-2 and IMP-1.

Fig. (2). Dicarboxylic acid derivatives

Fig. (3). Cyclic Boronates.

The Development of New Small-Molecule Inhibitors Current Topics in Medicinal Chemistry, 2018, Vol. 18, No. 00 5

A family of 4,5-disubstituted 1,2,3-triazoles were identi-fied as selective VIM-2 inhibitors by Weide et al. through biochemical screening [62]. Their study revealed that the amino substitution on the C-4 methyl of the triazole was im-portant to achieve the high inhibitory activity against the VIM-2MBL, and thus to potentiate the antibacterial activity of imipenem. Compound37showedgood inhibitory activity against VIM-2 with an IC50 values of 0.07 ± 0.003µM.

2.5. Natural Products

The fungal natural product Aspergillomarasmine A (known as AMA) (compound38, Fig. 5) was found to be a promising inhibitor of NDM-1 and VIM-2 bothin vitro and in vivo [63]. Amongthese AMA derivatives, the lead com-pound39exhibited a synergistic effect in combination with meropenem against K. pneumoniae (BAA-2146) harboring NDM-1. AMA analogs 40 and 41, substituted by proline showed comparable activities [64]. Isomargololone (com-pound 42) and Nimbolide (compound 43) [65] showed ap-preciable binding affinity to NDM-1.Piperine (compound 44)and Norwedelic acid (compound 45)were also reported to have better inhibitory activity than L-captoprilagainst NDM-1 [66]. Recently，Bergstrom et al. [67] revealed that AMA inhibited NDM-1, VIM-2, andIMP-7 via a metal ion seques-tration mechanism.AMA could remove metal ion within the

active site that is required for catalyzing the hydrolysis ofβ-lactam.

2.6. Peptide Inhibitors

Arginine-containing peptides were highly potent inhibi-torsagainst VIM-2 as shown by kinetic assays in combina-tion with fluorescence spectroscopy. The length of the argin-ine core and the composition of the N-terminal segment of these peptides were crucial to achieveVIM-2 inhibitors with sub-micromolaraffinity [68].

2.7. Other MBLs Inhibitors

2.7.1. Pyrroles and Related Heterocycles

A series of novel pyrrole and pyrrolo [2,3-d] pyrimidine derivatives were synthesized as potential MBL inhibitors by Mohamed et al.Among these new pyrrole derivatives com-pounds 46, 47and 48 (Fig. 6) showed weak inhibitory effect (Kivaluesranging from approximately 10 to 30 µM) against the IMP-1 MBL from P. aeruginosa and K. pneumoniae [28]. SAR results showed that the introduction of a chloro group to compounds 49 and 50enhanced the inhibitory activ-ity of the pyrrolopyrimidine analogs.McGeary et al.revealed that the 3-carbonitrile group, vicinal 4,5-diphenyl and N-

Fig. (4). Triazole-based MBL inhibitors.

Fig. (5). Natural productsand structural analogs as MBL inhibitors.

6 Current Topics in Medicinal Chemistry, 2018, Vol. 18, No. 00 Wang et al.

benzyl side chains of the pyrrole were important for the in-hibitory potencies of these compounds against members rep-resenting the three main subclasses of MBLs, i.e. IMP-1(representing the B1 subgroup), CphA (B2), and AIM-1 (B3) [69].

N-Heterocyclic dicarboxylic acids 51 and 52, and pyridylmercaptothiadiazoles 53 and 54,were also reported as good scaffolds for inhibitors of MBLs. Feng et al.assessed their inhibition effect on the subclass B1-B3 MBLs CcrA, ImiS, and L1. The results showed that compounds 51 and 52 were CcrA and L1 inhibitors with Ki ≤ 2 µM [70]. 2.7.2. Hydroxamates

2,5-Substituted benzophenonehydroxamic acid 55 (Fig. 7) was identified as a potent andselective inhibitor of FEZ-1 MBL.Subsequently, thenovelhydroxamicacid-containing compoundN-hydroxy-3- [(6-(hydroxyamino)-6-oxohexyl) oxy] benzamide56 displayed reversible, competitive inhibi-tion with Ki =0.18 ± 0.06 µM against the Bla2 MBL. This result suggested that acid-containing compounds might bepromising Bla2 inhibitors [71]. 2.7.3. NOTA

1,4,7-Triazacyclononane-1,4,7-triacetic acid (NOTA) (compound57)and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) (compound58)restored the activities of carbapenems against three classes (VIM, IMP, and NDM)of MBL-producing bacteria at concentrations of 0.06 mg/L,a value which issuperior to the results obtained with-AMA.Cytotoxicity studies results showed NOTA and DOTA werenon-haemolytic at the applied concentration. Thus, the two compounds were potential inhibitors of MBLs [72]. 2.7.4. Bisthiazolidines

Both theL-and D-bisthiazolidine (BTZ) enantiomers were reported to be micromolar competitive inhibitors of two B1 sub-class MBLs (IMP-1 and NDM-1). Remarkably, BTZs

and especially L-CS319 (59), potentiated β-lactam activity against MBL-producing pathogens according to the cell-based time-kill assays [73]. González MM et al.presented the bisthiazolidine (BTZ) scaffold of β-lactam substrates, which could be modified with metal-binding groups to target the MBL active site. NMR spectroscopy demonstrated that they inhibited hydrolysis of imipenem in NDM-1-producing E. coli [74]. 2.7.5. DNA Aptamer

Single-stranded DNAs targeting the B. cereus 5/B/6 met-allo-beta-lactamase were rapid, reversible, non-competitive inhibitors screened by SELEX(Systematic Evolution of Ligands by EXpotential Enrichment). Byspecifically inter-fering with the actives itemetal ions of the enzyme, they acted on MBLs of both Gram-positive and Gram-negative antibiotic-resistant bacteria with Ki values in the nanomolar range, such as 30 residue ssDNA (Ki = 0.92 nM) and 10 resi-due ssDNA (Ki = 0.31 nM ) [75]. 2.7.6. Sulfonamide

VNI-41 (compound 60) was identified as a weakinhibi-tionagainst NDM-1 (IC50 = 29.6 ± 1.3 µM) by virtual screen-ing methodologies. The sulfonamide group of VNI-41 di-rectly interacted with Zn2+ within the activesite, which was critical for its activity. The study supported the conclu-sionthatthe sulfonamide was a valid functional group for the rational design of NDM-1 inhibitors [76]. 2.7.7. Chromone Inhibitors

A novel reversible covalent inhibitor of the clinically relevant MBL NDM-1 (compound 61) was reported for the first time, suggesting a new way of finding potent MBLs inhibitors in spite that compound 61has to be further opti-mized for a therapeutic use.Electrospray ionization-mass spectrometry (ESI-MS) and single site-directed mutagenesis demonstrated that the inhibitor formed a covalent bond with Lys224 in the active site of NDM-1 [77].

Fig. (6). Other MBLs inhibitors.

The Development of New Small-Molecule Inhibitors Current Topics in Medicinal Chemistry, 2018, Vol. 18, No. 00 7

Likewise, the chromone-containing compound 62 was a promising scaffold for the design of a broad-spectrum MBL inhibitor and showed high ligand efficiencies (LE) for NDM-1 with 0.39 kcal/mol per heavy atomand the LE for VIM-2 with 0.31 kcal/mol per heavy atomby using an orthogonal screening strategy combining a SPR-based assay and an en-zyme inhibition assay. However, it acted less effectively on VIM-2 than NDM-1 due to a higher affinity for NDM-1 [78]. 2.7.8. Phenylformic Acid Derivatives

Based on the FBDD strategy, compound 63(IC50 = 8 µM) was considered to be a new scaffold for designingpotent VIM-2inhibitors. The carboxyl group and the carbonyl group were assumed to beimportant for the activity.Furthermore, theSPR-based biosensor assay wasused to studythe kinetics of NDM-1 inhibitors [77]. This methodology may have gen-eral value for the discovery of other MBLs inhibitors. 2.7.9. Quinoline Inhibitors

Compounds 64 and 65 were broad-spectrum inhibitors against three clinically relevant MBLs (IMP-1, NDM-1 and VIM-2). Compound 65 interacted with the metal ion of NDM-1. Moreover, it potentiated the activity of cefoxitin on a VIM-2-producing E. colistrain in vitro [79].

The intensity of the effort to discover effective MBL in-hibitors is underscored by the diversity of publications that have occurred since the editorial acceptance of this review. These new efforts include complementary review [80, 81] ;experimental studies on the structure and mechanism of the MBLs [82-86] ; computational study of the MBL mechanism [87, 88] ; ITC as a screening method for inhibitor discovery [89] ; new inhibitor structures [90-95] ; thiol-modified NOTA inhibitor structures [96] ; and computational screen-ing in support of new inhibitor discovery [97-99].

CONCLUSION

The emergence of antibiotic resistance of Gram-negative pathogens represents a major threat to human health. It is urgent to develop new antibiotic agents to fight against anti-biotic resistance. Metallo-β-lactamases (MBLs) are an im-portant class of Zn(II)-dependent enzymes that can hydro-lyze almost all of β-lactams and render bacteria resistant to antibiotics in clinic. To date, there are no clinically available MBL inhibitors although a large number of MBL inhibitors have been identified. In this review, we highlight recent de-velopment of small-molecule MBL inhibitors developed in the past decade.

CONSENT FOR PUBLICATION

Not applicable.

CONFLICT OF INTEREST

The authors declare no conflict of interest, financial or otherwise.

ACKNOWLEDGEMENT

This work was supported by the National Natural Science Foundation of China (No. 81703326), Scientific Program of Henan Province (No. 182102310123), China Postdoctoral Science Foundation (No. 2018M630840), the Open Project of Guangdong Provincial Key Laboratory of New Drug Screening (No. GDKLNDS-2018OF006), Key Scientific Research Project for Higher Education by Department of Education of Henan Educational Committee (No. 18B350009), and the Starting Grant of Zhengzhou Univer-sity (No. 32210533).

Fig. (7). Other MBLs inhibitors.

8 Current Topics in Medicinal Chemistry, 2018, Vol. 18, No. 00 Wang et al.

REFERENCES [1] Bebrone, C. Metallo-β-lactamases (classification, activity, genetic

organization, structure, zinc coordination) and their superfamily. Biochem.Pharmacol.2007, 74, 1686-1701.

[2] Phelan, E.K.; Miraula, M.; Selleck, C.; Ollis, D.L.; Schenk, G.; Mitić, N. Metallo-β-Lactamases: A Major Threat to Human Health. Am.J. Mol. Biol.2014, 04, 89-104.

[3] Bonomo, R.A. β-Lactamases: A Focus on Current Challenges. Cold Spring Harb. Perspect. Med.2017, 7, a025239.

[4] Bebrone, C.; Lassaux, P.; Vercheval, L.; Sohier, J.S.; Jehaes, A.; Sauvage, E.; Galleni, M. Current challenges in antimicrobial chemotherapy: focus on β-lactamase inhibition. Drugs2010, 70, 651-679.

[5] Ehmann, D.E.; Jahic, H.; Ross, P.L.; Gu, R.F.; Hu, J.; Durand-Reville, T.F.; Lahiri, S.; Thresher, J.; Livchak, S.; Gao, N.; Palmer, T.; Walkup, G.K.; Fisher, S.L. Kinetics of avibactam inhibition against Class A, C, and D β-lactamases. J. Biol. Chem.2013, 288, 27960-27971.

[6] Gonzalez, L.J.; Bahr, G.; Nakashige, T.G.; Nolan, E.M.; Bonomo, R.A.; Vila, A.J. Membrane anchoring stabilizes and favors secretion of New Delhi metallo-β-lactamase. Nat. Chem. Biol.2016, 12, 516-522.

[7] Gonzalez, L.J.; Bahr, G.; Vila, A.J. Lipidated β-lactamases: from bench to bedside. Future. Microbiol.2016, 11, 1495-1498.

[8] Marshall, S.; Hujer, A.M.; Rojas, L.J.; Papp-Wallace, K.M.; Humphries, R.M.; Spellberg, B.; Hujer, K.M.; Marshall, E.K.; Rudin, S.D.; Perez, F.; Wilson, B.M.; Wasserman, R.B.; Chikowski, L.; Paterson, D.L.; Vila, A.J.; van Duin, D.; Kreiswirth, B.N.; Chambers, H.F.; Fowler, V.G., Jr.; Jacobs, M.R.; Pulse, M.E.; Weiss, W.J.; Bonomo, R.A. Can Ceftazidime-Avibactam and Aztreonam Overcome beta-Lactam Resistance Conferred by Metallo-β-Lactamases in Enterobacteriaceae? Antimicrob. Agents Chemother.2017, 61, e02243–16.

[9] Gottig, S.; Riedel-Christ, S.; Saleh, A.; Kempf, V.A.; Hamprecht, A. Impact of blaNDM-1 on fitness and pathogenicity of Escherichia coli and Klebsiella pneumoniae. Int. J. Antimicrob. Agents.2016, 47, 430-435.

[10] Bahr, G.; Vitor-Horen, L.; Bethel, C.R.; Bonomo, R.A.; Gonzalez, L.J.; Vila, A.J. Clinical Evolution of New Delhi Metallo-β-Lactamase (NDM) Optimizes Resistance under Zn(II) Deprivation. Antimicrob. Agents Chemother.2018, 62, e01849–17.

[11] Dortet, L.; Girlich, D.; Virlouvet, A.L.; Poirel, L.; Nordmann, P.; Iorga, B.I.; Naas, T. Characterization of BRPMBL, the Bleomycin Resistance Protein Associated with the Carbapenemase NDM. An-timicrob. Agents Chemother.2017, 61, e02413–16.

[12] Meini, M.-R.; Llarrull, L.; Vila, A. Evolution of Metallo-β-lactamases: Trends Revealed by Natural Diversity and in vitro Evolution. Antibiotics2014, 3, 285-316.

[13] Gao, K.; Zhao, Y. A Network of Conformational Transitions in the Apo Form of NDM-1 Enzyme Revealed by MD Simulation and a Markov State Model. J. Phys. Chem. B. 2017, 121, 2952-2960.

[14] Mojica, M.F.; Mahler, S.G.; Bethel, C.R.; Taracila, M.A.; Kosmopoulou, M.; Papp-Wallace, K.M.; Llarrull, L.I.; Wilson, B.M.; Marshall, S.H.; Wallace, C.J.; Villegas, M.V.; Harris, M.E.; Vila, A.J.; Spencer, J.; Bonomo, R.A. Exploring the Role of Residue 228 in Substrate and Inhibitor Recognition by VIM Metallo-β-lactamases. Biochemistry2015, 54, 3183-3196.

[15] Skagseth, S.; Carlsen, T.J.; Bjerga, G.E.; Spencer, J.; Samuelsen, O.; Leiros, H.K. Role of Residues W228 and Y233 in the Structure and Activity of Metallo-β-Lactamase GIM-1. Antimicrob. Agents Chemother.2016, 60, 990-1002.

[16] Stewart, A.C.; Bethel, C.R.; VanPelt, J.; Bergstrom, A.; Cheng, Z.; Miller, C.G.; Williams, C.; Poth, R.; Morris, M.; Lahey, O.; Nix, J.C.; Tierney, D.L.; Page, R.C.; Crowder, M.W.; Bonomo, R.A.; Fast, W. Clinical Variants of New Delhi Metallo-β-Lactamase Are Evolving To Overcome Zinc Scarcity. ACS. infect. Dis.2017, 3, 927-940.

[17] Moran-Barrio, J.; Lisa, M.N.; Larrieux, N.; Drusin, S.I.; Viale, A.M.; Moreno, D.M.; Buschiazzo, A.; Vila, A.J. Crystal Structure of the Metallo-β-Lactamase GOB in the Periplasmic Dizinc Form Reveals an Unusual Metal Site. Antimicrob. Agents Chemother.2016, 60, 6013-6022.

[18] Rodriguez, M.M.; Herman, R.; Ghiglione, B.; Kerff, F.; D'Amico Gonzalez, G.; Bouillenne, F.; Galleni, M.; Handelsman, J.; Charlier, P.; Gutkind, G.; Sauvage, E.; Power, P. Crystal structure

and kinetic analysis of the class B3 di-zinc metallo-β-lactamase LRA-12 from an Alaskan soil metagenome. PloS One2017, 12, e0182043.

[19] Parveen, S.; Amit, K.; Asad, U.K. Structure, Function of Serine and Metallo-β-lactamases and their Inhibitors. Curr. Protein Pept. Sci.2018, 19, 130-144.

[20] Lisa, M.N.; Palacios, A.R.; Aitha, M.; Gonzalez, M.M.; Moreno, D.M.; Crowder, M.W.; Bonomo, R.A.; Spencer, J.; Tierney, D.L.; Llarrull, L.I.; Vila, A.J. A general reaction mechanism for carbapenem hydrolysis by mononuclear and binuclear metallo-β-lactamases. Nat. Commun.2017, 8, 538.

[21] Meini, M.R.; Llarrull, L.I.; Vila, A.J. Overcoming differences: The catalytic mechanism of metallo-β-lactamases. FEBS. Lett.2015, 589, 3419-3432.

[22] McGeary, R.P.; Tan, D.T.; Schenk, G. Progress toward inhibitors of metallo-β-lactamases. Future. Med. Chem.2017, 9, 673-691.

[23] González, M.M.; Vila, A.J. An Elusive Task: A Clinically Useful Inhibitor of Metallo-β-Lactamases. Top. Med. Chem.2016, 22, 1–34.

[24] Groundwater, P.W.; Xu, S.; Lai, F.; Varadi, L.; Tan, J.; Perry, J.D.; Hibbs, D.E. New Delhi metallo-β-lactamase-1: structure, inhibitors and detection of producers.Future. Med. Chem.2016, 8, 993-1012.

[25] Walter, M.W.; Felici, A.; Galleni, M.; Soto, R.P.; Adlington, R.M.; Baldwin, J.E.; Frère, J.-M.; Gololobov, M.; Schofield, C.J. Trifluoromethyl alcohol and ketone inhibitors of metallo-β-lactamases. Bioorg. Med. Chem. Lett.1996, 6, 2455-2458.

[26] Toney, J.H.; Hammond, G.G.; Fitzgerald, P.M.; Sharma, N.; Balkovec, J.M.; Rouen, G.P.; Olson, S.H.; Hammond, M.L.; Greenlee, M.L.; Gao, Y.D. Succinic acids as potent inhibitors of plasmid-borne IMP-1 metallo-β-lactamase. J. Biol. Chem.2001, 276, 31913-31918.

[27] Hiraiwa, Y.; Saito, J.; Watanabe, T.; Yamada, M.; Morinaka, A.; Fukushima, T.; Kudo, T. X-ray crystallographic analysis of IMP-1 metallo-β-lactamase complexed with a 3-aminophthalic acid derivative, structure-based drug design, and synthesis of 3,6-disubstituted phthalic acid derivative inhibitors. Bioorg. Med. Chem. Lett.2014, 24, 4891-4894.

[28] Mohamed, M.S.; Hussein, W.M.; McGeary, R.P.; Vella, P.; Schenk, G.; Abd El-Hameed, R.H. Synthesis and kinetic testing of new inhibitors for a metallo-β-lactamase from Klebsiella pneumonia and Pseudomonas aeruginosa. Eur. J. Med. Chem.2011, 46, 6075-6082.

[29] Simm, A.M.; Loveridge, E.J.; Crosby, J.; Avison, M.B.; Walsh, T.R.; Bennett, P.M. Bulgecin A: a novel inhibitor of binuclear metallo-β-lactamases. Biochem. J.2005, 387, 585-590.

[30] Walter, M.W. Hydroxamate Inhibitors of Aeromonas hydrophila AE036Metallo-β-lactamase. Bioorg. Chem. 1999,27, 35-40.

[31] Toney, J.H.; Fitzgerald Pm Fau - Grover-Sharma, N.; Grover-Sharma N Fau - Olson, S.H.; Olson Sh Fau - May, W.J.; May Wj Fau - Sundelof, J.G.; Sundelof Jg Fau - Vanderwall, D.E.; Vanderwall De Fau - Cleary, K.A.; Cleary Ka Fau - Grant, S.K.; Grant Sk Fau - Wu, J.K.; Wu Jk Fau - Kozarich, J.W.; Kozarich Jw Fau - Pompliano, D.L.; Pompliano Dl Fau - Hammond, G.G.; Hammond, G.G. Antibiotic sensitization using biphenyl tetrazoles as potent inhibitors of Bacteroides fragilis metallo-β-lactamase. Chem. Biol. 1998, 5, 185-196.

[32] Dandia, A.; Khan, S.; Soni, P.; Indora, A.; Mahawar, D.K.; Pandya, P.; Chauhan, C.S. Diversity-oriented sustainable synthesis of antimicrobial spiropyrrolidine/thiapyrrolizidine oxindole derivatives: New ligands for a metallo-β-lactamase from Klebsiella pneumonia. Bioorg. Med. Chem. Lett.2017, 27, 2873-2880.

[33] Guo, Y.; Wang, J.; Niu, G.; Shui, W.; Sun, Y.; Zhou, H.; Zhang, Y.; Yang, C.; Lou, Z.; Rao, Z. A structural view of the antibiotic degradation enzyme NDM-1 from a superbug. Protein cell.2011, 2, 384-394.

[34] Brem, J.; van Berkel, S.S.; Zollman, D.; Lee, S.Y.; Gileadi, O.; McHugh, P.J.; Walsh, T.R.; McDonough, M.A.; Schofield, C.J. Structural Basis of Metallo-β-Lactamase Inhibition by Captopril Stereoisomers. Antimicrob. Agents Chemother.2016, 60, 142-150.

[35] Rydzik, A.M.; Brem, J.; van Berkel, S.S.; Pfeffer, I.; Makena, A.; Claridge, T.D.; Schofield, C.J. Monitoring conformational changes in the NDM-1 metallo-β-lactamase by 19F NMR spectroscopy. Angew. Chem.Int. Chem. 2014, 53, 3129-3133.

[36] Heinz, U.; Bauer, R.; Wommer, S.; Meyer-Klaucke, W.; Papamichaels, C.; Bateson, J.; Adolph, H.W. Coordination

The Development of New Small-Molecule Inhibitors Current Topics in Medicinal Chemistry, 2018, Vol. 18, No. 00 9

geometries of metal ions in D- or L-captopril-inhibited metallo-β-lactamases.J. Biol. Chem.2003, 278, 20659-20666.

[37] Li, G.B.; Abboud, M.I.; Brem, J.; Someya, H.; Lohans, C.T.; Yang, S.Y.; Spencer, J.; Wareham, D.W.; McDonough, M.A.; Schofield, C.J. NMR-filtered virtual screening leads to non-metal chelating metallo-β-lactamase inhibitors. Chem. Sci.2017, 8, 928-937.

[38] Li, N.; Xu, Y.; Xia, Q.; Bai, C.; Wang, T.; Wang, L.; He, D.; Xie, N.; Li, L.; Wang, J.; Zhou, H.G.; Xu, F.; Yang, C.; Zhang, Q.; Yin, Z.; Guo, Y.; Chen, Y. Simplified captopril analogues as NDM-1 inhibitors. Bioorg. Med. Chem. Lett.2014, 24, 386-389.

[39] Li, G.B.; Brem, J.; Lesniak, R.; Abboud, M.I.; Lohans, C.T.; Clifton, I.J.; Yang, S.Y.; Jimenez-Castellanos, J.C.; Avison, M.B.; Spencer, J.; McDonough, M.A.; Schofield, C.J. Crystallographic analyses of isoquinoline complexes reveal a new mode of metallo-β-lactamase inhibition. Chem. Commun.2017, 53, 5806-5809.

[40] Yusof, Y.; Tan, D.T.C.; Arjomandi, O.K.; Schenk, G.; McGeary, R.P. Captopril analogues as metallo-β-lactamase inhibitors. Bioorg. Med. Chem. Lett.2016, 26, 1589-1593.

[41] Klingler, F.M.; Wichelhaus, T.A.; Frank, D.; Cuesta-Bernal, J.; El-Delik, J.; Muller, H.F.; Sjuts, H.; Gottig, S.; Koenigs, A.; Pos, K.M.; Pogoryelov, D.; Proschak, E. Approved Drugs Containing Thiols as Inhibitors of Metallo-β-lactamases: Strategy To Combat Multidrug-Resistant Bacteria. J. Med. Chem.2015, 58, 3626-3630.

[42] Faridoon; Hussein, W.M.; Vella, P.; Islam, N.U.; Ollis, D.L.; Schenk, G.; McGeary, R.P. 3-mercapto-1,2,4-triazoles and N-acylated thiosemicarbazides as metallo-β-lactamase inhibitors. Bioorg. Med. Chem. Lett.2012, 22, 380-386.

[43] Arjomandi, O.K.; Hussein, W.M.; Vella, P.; Yusof, Y.; Sidjabat, H.E.; Schenk, G.; McGeary, R.P. Design, synthesis, and in vitro and biological evaluation of potent amino acid-derived thiol inhibitors of the metallo-β-lactamase IMP-1. Eur. J. Med. Chem.2016, 114, 318-327.

[44] Skagseth, S.; Akhter, S.; Paulsen, M.H.; Muhammad, Z.; Lauksund, S.; Samuelsen, O.; Leiros, H.S.; Bayer, A. Metallo-β-lactamase inhibitors by bioisosteric replacement: Preparation, activity and binding. Eur. J. Med. Chem.2017, 135, 159-173.

[45] Chang, Y.N.; Xiang, Y.; Zhang, Y.J.; Wang, W.M.; Chen, C.; Oelschlaeger, P.; Yang, K.W. Carbamylmethyl Mercaptoacetate Thioether: A Novel Scaffold for the Development of L1 Metallo-β-lactamase Inhibitors. ACS. Med. Chem. Lett.2017, 8, 527-532.

[46] Tehrani, K.; Martin, N.I. Thiol-Containing Metallo-β-Lactamase Inhibitors Resensitize Resistant Gram-Negative Bacteria to Meropenem. ACS. infect. Dis.2017, 3, 711-717.

[47] Lassaux, P.; Hamel, M.; Gulea, M.; Delbruck, H.; Mercuri, P.S.; Horsfall, L.; Dehareng, D.; Kupper, M.; Frere, J.M.; Hoffmann, K.; Galleni, M.; Bebrone, C. Mercaptophosphonate compounds as broad-spectrum inhibitors of the metallo-β-lactamases. J. Med. Chem.2010, 53, 4862-4876.

[48] Buttner, D.; Kramer, J.S.; Klingler, F.M.; Wittmann, S.K.; Hartmann, M.R.; Kurz, C.G.; Kohnhauser, D.; Weizel, L.; Bruggerhoff, A.; Frank, D.; Steinhilber, D.; Wichelhaus, T.A.; Pogoryelov, D.; Proschak, E. Challenges in the Development of a Thiol-Based Broad-Spectrum Inhibitor for Metallo-β-Lactamases. ACS. infect. Dis.2018, 4, 360-372.

[49] Horsfall, L.E.; Garau, G.; Lienard, B.M.; Dideberg, O.; Schofield, C.J.; Frere, J.M.; Galleni, M. Competitive inhibitors of the CphA metallo-β-lactamase from Aeromonas hydrophila. Antimicrob. Agents Chemother.2007, 51, 2136-2142.

[50] Chen, A.Y.; Thomas, P.W.; Stewart, A.C.; Bergstrom, A.; Cheng, Z.; Miller, C.; Bethel, C.R.; Marshall, S.H.; Credille, C.V.; Riley, C.L.; Page, R.C.; Bonomo, R.A.; Crowder, M.W.; Tierney, D.L.; Fast, W.; Cohen, S.M. Dipicolinic Acid Derivatives as Inhibitors of New Delhi Metallo-β-lactamase-1. J. Med. Chem.2017, 60, 7267-7283.

[51] Shin, W.S.; Bergstrom, A.; Bonomo, R.A.; Crowder, M.W.; Muthyala, R.; Sham, Y.Y. Discovery of 1-Hydroxypyridine-2(1H)-thione-6-carboxylic Acid as a First-in-Class Low-Cytotoxic Nanomolar Metallo β-Lactamase Inhibitor. Chem. Med. Chem.2017, 12, 845-849.

[52] Hiraiwa, Y.; Morinaka, A.; Fukushima, T.; Kudo, T. Metallo-β-lactamase inhibitory activity of phthalic acid derivatives. Bioorg. Med. Chem. Lett.2009, 19, 5162-5165.

[53] Hiraiwa, Y.; Morinaka, A.; Fukushima, T.; Kudo, T. Metallo-β-lactamase inhibitory activity of 3-alkyloxy and 3-amino phthalic acid derivatives and their combination effect with carbapenem. Bioorg. Med. Chem. 2013, 21, 5841-5850.

[54] Ishii, Y.; Eto, M.; Mano, Y.; Tateda, K.; Yamaguchi, K. In vitro potentiation of carbapenems with ME1071, a novel metallo-β-lactamase inhibitor, against metallo-β-lactamase-producing Pseudomonas aeruginosa clinical isolates. Antimicrob. Agents Chemother.2010, 54, 3625-3629.

[55] ivermore, D.M.; Mushtaq, S.; Morinaka, A.; Ida, T.; Maebashi, K.; Hope, R. Activity of carbapenems with ME1071 (disodium 2,3-diethylmaleate) against Enterobacteriaceae and Acinetobacter spp. with carbapenemases, including NDM enzymes. J. Antimicrob Chemother.2013, 68, 153-158.

[56] Hen, B.; Yu, Y.; Chen, H.; Cao, X.; Lao, X.; Fang, Y.; Shi, Y.; Chen, J.; Zheng, H. Inhibitor discovery of full-length New Delhi metallo-β-lactamase-1 (NDM-1). PloS One2013, 8, e62955.

[57] Brem, J.; Cain, R.; Cahill, S.; McDonough, M.A.; Clifton, I.J.; Jimenez-Castellanos, J.C.; Avison, M.B.; Spencer, J.; Fishwick, C.W.; Schofield, C.J. Structural basis of metallo-β-lactamase, serine-β-lactamase and penicillin-binding protein inhibition by cyclic boronates. Nat.Commun.2016, 7, 12406.

[58] Cahill, S.T.; Cain, R.; Wang, D.Y.; Lohans, C.T.; Wareham, D.W.; Oswin, H.P.; Mohammed, J.; Spencer, J.; Fishwick, C.W.; McDonough, M.A.; Schofield, C.J.; Brem, J. Cyclic Boronates Inhibit All Classes of β-Lactamases. Antimicrob. Agents Che-mother.2017, 61, e02260–16.

[59] Yang, S.K.; Kang, J.S.; Oelschlaeger, P.; Yang, K.W. Azolylthioacetamide: A Highly Promising Scaffold for the Development of Metallo-β-lactamase Inhibitors. ACS. Med. Chem. Lett.2015, 6, 455-460.

[60] Zhai, L.; Zhang, Y.L.; Kang, J.S.; Oelschlaeger, P.; Xiao, L.; Nie, S.S.; Yang, K.W. Triazolylthioacetamide: A Valid Scaffold for the Development of New Delhi Metallo-beta-Lactmase-1 (NDM-1) Inhibitors. ACS. Med. Chem. Lett.2016, 7, 413-417.

[61] Sevaille, L.; Gavara, L.; Bebrone, C.; De Luca, F.; Nauton, L.; Achard, M.; Mercuri, P.; Tanfoni, S.; Borgianni, L.; Guyon, C.; Lonjon, P.; Turan-Zitouni, G.; Dzieciolowski, J.; Becker, K.; Benard, L.; Condon, C.; Maillard, L.; Martinez, J.; Frere, J.M.; Dideberg, O.; Galleni, M.; Docquier, J.D.; Hernandez, J.F. 1,2,4-Triazole-3-thione Compounds as Inhibitors of Dizinc Metallo-β-lactamases. Chem. Med. Chem.2017, 12, 972-985.

[62] Weide, T.; Saldanha, S.A.; Minond, D.; Spicer, T.P.; Fotsing, J.R.; Spaargaren, M.; Frere, J.M.; Bebrone, C.; Sharpless, K.B.; Hodder, P.S.; Fokin, V.V. NH-1,2,3-Triazole-based Inhibitors of the VIM-2 Metallo-β-Lactamase: Synthesis and Structure-Activity Studies. ACS. Med. Chem. Lett.2010, 1, 150-154.

[63] King, A.M.; Reid-Yu, S.A.; Wang, W.; King, D.T.; De Pascale, G.; Strynadka, N.C.; Walsh, T.R.; Coombes, B.K.; Wright, G.D. Aspergillomarasmine A overcomes metallo-β-lactamase antibiotic resistance. Nature2014, 510, 503-506.

[64] Zhang, J.; Wang, S.; Wei, Q.; Guo, Q.; Bai, Y.; Yang, S.; Song, F.; Zhang, L.; Lei, X. Synthesis and biological evaluation of Aspergillomarasmine A derivatives as novel NDM-1 inhibitor to overcome antibiotics resistance. Bioorg. Med. Chem.2017, 25, 5133-5141.

[65] Thakur, P.K.; Kumar, J.; Ray, D.; Anjum, F.; Hassan, M.I. Search of potential inhibitor against New Delhi metallo-β-lactamase 1 from a series of antibacterial natural compounds. J. Nat. Sci. Biol. Med.2013, 4, 51-56.

[66] Chetia, H.; Sharma, D.K.; Sarma, R.; Verma, A. An In Silico Approach To Discover Potential Inhibitors Against Multi-Drug Resistant Bacteria Producing New-Delhi Metallo-β-Lactamase 1 (Ndm-1) Enzyme. Int. J. Pharm. Pharm. Sci.2014, 6, 299-303.

[67] Bergstrom, A.; Katko, A.; Adkins, Z.; Hill, J.; Cheng, Z.; Burnett, M.; Yang, H.; Aitha, M.; Mehaffey, M.R.; Brodbelt, J.S.; Tehrani, K.; Martin, N.I.; Bonomo, R.A.; Page, R.C.; Tierney, D.L.; Fast, W.; Wright, G.D.; Crowder, M.W. Probing the Interaction of Aspergillomarasmine A with Metallo-β-lactamases NDM-1, VIM-2, and IMP-7. ACS. infect. Dis.2018, 4, 135-145.

[68] Rotondo, C.M.; Marrone, L.; Goodfellow, V.J.; Ghavami, A.; Labbe, G.; Spencer, J.; Dmitrienko, G.I.; Siemann, S. Arginine-containing peptides as potent inhibitors of VIM-2 metallo-β-lactamase. Biochim. Biophys Acta.2015, 1850, 2228-2238.

[69] McGeary, R.P.; Tan, D.T.C.; Selleck, C.; Monteiro Pedroso, M.; Sidjabat, H.E.; Schenk, G. Structure-activity relationship study and optimisation of 2-aminopyrrole-1-benzyl-4,5-diphenyl-1H-pyrrole-3-carbonitrile as a broad spectrum metallo-β-lactamase inhibitor. Eur. J. Med. Chem.2017, 137, 351-364.

10 Current Topics in Medicinal Chemistry, 2018, Vol. 18, No. 00 Wang et al.

[70] Feng, L.; Yang, K.W.; Zhou, L.S.; Xiao, J.M.; Yang, X.; Zhai, L.; Zhang, Y.L.; Crowder, M.W. N-heterocyclic dicarboxylic acids: broad-spectrum inhibitors of metallo-β-lactamases with co-antibacterial effect against antibiotic-resistant bacteria. Bioorg. Med. Chem. Lett.2012, 22, 5185-5189.

[71] Lienard, B.M.; Horsfall, L.E.; Galleni, M.; Frere, J.M.; Schofield, C.J. Inhibitors of the FEZ-1 metallo-β-lactamase. Bioorg. Med. Chem. Lett.2007, 17, 964-968.

[72] Somboro, A.M.; Tiwari, D.; Bester, L.A.; Parboosing, R.; Chonco, L.; Kruger, H.G.; Arvidsson, P.I.; Govender, T.; Naicker, T.; Essack, S.Y. NOTA: a potent metallo-β-lactamase inhibitor. J. An-timicrob Chemother.2015, 70, 1594-1596.

[73] Hinchliffe, P.; Gonzalez, M.M.; Mojica, M.F.; Gonzalez, J.M.; Castillo, V.; Saiz, C.; Kosmopoulou, M.; Tooke, C.L.; Llarrull, L.I.; Mahler, G.; Bonomo, R.A.; Vila, A.J.; Spencer, J. Cross-class metallo-β-lactamase inhibition by bisthiazolidines reveals multiple binding modes. Proc. Natl Acad. Sci USA2016, 113, E3745-3754.

[74] Gonzalez, M.M.; Kosmopoulou, M.; Mojica, M.F.; Castillo, V.; Hinchliffe, P.; Pettinati, I.; Brem, J.; Schofield, C.J.; Mahler, G.; Bonomo, R.A.; Llarrull, L.I.; Spencer, J.; Vila, A.J. Bisthiazolidines: A Substrate-Mimicking Scaffold as an Inhibitor of the NDM-1 Carbapenemase. ACS. infect. Dis.2015, 1, 544-554.

[75] Kim, S.K.; Sims, C.L.; Wozniak, S.E.; Drude, S.H.; Whitson, D.; Shaw, R.W. Antibiotic resistance in bacteria: novel metalloenzyme inhibitors. Chem. Biol. Drug. Des.2009, 74, 343-348.

[76] Wang, X.; Lu, M.; Shi, Y.; Ou, Y.; Cheng, X. Discovery of novel new Delhi metallo-β-lactamases-1 inhibitors by multistep virtual screening. PloS One2015, 10, e0118290.

[77] Christopeit, T.; Albert, A.; Leiros, H.S. Discovery of a novel covalent non-beta-lactam inhibitor of the metallo-β-lactamase NDM-1. Biol. Med. Chem.2016, 24, 2947-2953.

[78] Christopeit, T.; Leiros, H.K. Fragment-based discovery of inhibitor scaffolds targeting the metallo-β-lactamases NDM-1 and VIM-2. Bioorg. Med. Chem. Lett.2016, 26, 1973-1977.

[79] Brindisi, M.; Brogi, S.; Giovani, S.; Gemma, S.; Lamponi, S.; De Luca, F.; Novellino, E.; Campiani, G.; Docquier, J.D.; Butini, S. Targeting clinically-relevant metallo-β-lactamases: from high-throughput docking to broad-spectrum inhibitors. J. EnzymeInhib. Med. Chem.2016, 31, 98-109.

[80] Salahuddin, P.; Kumar, A.; Khan, A. Structure, function of serine and metallo-β-lactamases and their inhibitors. Curr. Protein Pept. Sci.2018, 19, 130-144.

[81] Khan, S.; Ali, A.; Khan, A.U. Structural and functional insight of New Delhi Metallo-β-lactamase-1 variants. Future. Med. Chem.2018, 10, 221-229.

[82] Bahr, G.; Vitor-Horen, L.; Bethel, C.; Bonomo, R.; González, L.; Vila, A. Clinical evolution of New Delhi metallo-β-lactamase (NDM) optimizes resistance under Zn(II) deprivation. Antimicrob. Agents Chemother. 2018, 62, e01849-01817.

[83] González, L.; Stival, C.; Puzzolo, J.; Moreno, D.; Vila, A. Shaping substrate selectivity in a broad-spectrum metallo-β-lactamase. Antimicrob. Agents Chemother. 2018, 62, e02079-02017.

[84] Abboud, M.I.; Kosmopoulou, M.; Krismanich, A.P.; Johnson, J.W.; Hinchliffe, P.; Brem, J.; Claridge, T.D.W.; Spencer, J.; Schofield, C.J.; Dmitrienko, G.I. Cyclobutanone Mimics of Intermediates in Metallo-β-Lactamase Catalysis. Chem.Eur. J.2018, 24, 5734–5737.

[85] Jiang, X.W.; Cheng, H.; Huo, Y.Y.; Xu, L.; Wu, Y.H.; Liu, W.H.; Tao, F.F.; Cui, X.J.; Zheng, B.W. Biochemical and genetic characterization of a novel metallo-β-lactamase from marine bacterium Erythrobacter litoralis HTCC 2594. Sci. Rep.2018, 8, 803.

[86] Marcoccia, F.; Leiros, H.; Aschi, M.; Amicosante, G.; Perilli, M. Exploring the role of L209 residue in the active site of NDM-1 ametallo-β-lactamase. PLoS One2018, 13, e0189686.

[87] Duan, J.; Hu, C.; Guo, J.; Guo, L.; Sun, J.; Zhao, Z. A molecular dynamics study of the complete binding process of meropenem to New Delhi metallo-β-lactamase 1. Phys. Chem. Chem. Phys.2018, 20, 6409-6420.

[88] Khrenova, M.G.; Nemukhin, A.V. Modeling the Transient Kinetics of the L1 Metallo-β-Lactamase. J. Phys. Chem. B.2018, 122, 1378-1386.

[89] Wang, Q.; He, Y.; Lu, R.; Wang, W. M.; Yang, K. W.; Fan, H. M.; Jin, Y.; Blackburn, G. M. Thermokinetic profile of NDM-1 and its inhibition by small carboxylic acids.Biosci. Rep.2018, 38, BSR20180244.

[90] Liu, S.; Jing, L.; Yu, Z.J.; Wu, C.; Zheng, Y.; Zhang, E.; Chen, Q.; Yu, Y.; Guo, L.; Wu, Y.; Li, G.B. ((S)-3-Mercapto-2-methylpropanamido)acetic acid derivatives as metallo-β-lactamase inhibitors: Synthesis, kinetic and crystallographic studies. Eur. J. Med. Chem.2018, 145, 649-660.

[91] Proschak, A.; Kramer, J.; Proschak, E.; Wichelhaus, T.A. Bacterial zincophore [S,S]-ethylenediamine-N,N'-disuccinic acid is an effective inhibitor of MBLs. J. Antimicrob Chemother.2018, 73, 425-430.

[92] Wang, R.; Lai, T.P.; Gao, P.; Zhang, H.; Ho, P.L.; Woo, P.C.; Ma, G.; Kao, R.Y.; Li, H.; Sun, H. Bismuth antimicrobial drugs serve as broad-spectrum metallo-β-lactamase inhibitors. Nat. Commun.2018, 9, 439.

[93] Djoko, K.Y.; Achard, M.E.S.; Phan, M.D.; Lo, A.W.; Miraula, M.; Prombhul, S.; Hancock, S.J.; Peters, K.M.; Sidjabat, H.E.; Harris, P.N.; Mitic, N.; Walsh, T.R.; Anderson, G.J.; Shafer, W.M.; Paterson, D.L.; Schenk, G.; McEwan, A.G.; Schembri, M.A. Copper Ions and Coordination Complexes as Novel Carbapenem Adjuvants. Antimicrob. Agents Chemother.2018, 62, e02280-17.

[94] Hinchliffe, P.; Tanner, C.A.; Krismanich, A.P.; Labbe, G.; Goodfellow, V.J.; Marrone, L.; Desoky, A.Y.; Calvopina, K.; Whittle, E.E.; Zeng, F.; Avison, M.B.; Bols, N.C.; Siemann, S.; Spencer, J.; Dmitrienko, G.I. Structural and Kinetic Studies of the Potent Inhibition of Metallo-β-lactamases by 6-Phosphonomethylpyridine-2-carboxylates. Biochemistry 2018, 57, 1880-1892.

[95] Xiang, Y.; Chen, C.; Wang, W.-M.; Xu, L.-W.; Yang, K.-W.; Oelschlaeger, P.; He, Y. Rhodanine as a potent Scaffold for the development of broad-spectrum metallo-β-lactamase inhibitors. ACS Med. Chem. Lett.2018, 9, 359-364.

[96] Zhang, E.; Wang, M.M.; Huang, S.C.; Xu, S.M.; Cui, D.Y.; Bo, Y.L.; Bai, P.Y.; Hua, Y.G.; Xiao, C.L.; Qin, S. NOTA analogue: A first dithiocarbamate inhibitor of metallo-β-lactamases. Bioorg. Med. Chem. Lett.2018, 28, 214-221.

[97] Ain, R.; Brem, J.; Zollman, D.; McDonough, M.A.; Johnson, R.M.; Spencer, J.; Makena, A.; Abboud, M.I.; Cahill, S.; Lee, S.Y.; McHugh, P.J.; Schofield, C.J.; Fishwick, C.W.G. In Silico Fragment-Based Design Identifies Subfamily B1 Metallo-β-lactamase Inhibitors. J. Med. Chem.2018, 61, 1255-1260.

[98] Spyrakis, F.; Celenza, G.; Marcoccia, F.; Santucci, M.; Cross, S.; Bellio, P.; Cendron, L.; Perilli, M.; Tondi, D. Structure-Based Virtual Screening for the Discovery of Novel Inhibitors of New Delhi Metallo-β-lactamase-1. ACS Med. Chem. Lett.2018, 9, 45-50.

[99] Yu, Z.J.; Liu, S.; Zhou, S.; Li, H.; Yang, F.; Yang, L.L.; Wu, Y.; Guo, L.; Li, G.B. Virtual target screening reveals rosmarinic acid and salvianolic acid A inhibiting metallo- and serine-β-lactamases. Bioorg. Med. Chem. Lett.2018, 28, 1037-1042.

DISCLAIMER: The above article has been published in Epub (ahead of print) on the basis of the materials provided by the author. The Editorial Department reserves the right to make minor modifications for further improvement of the manuscript.