Kinetic study of interaction between BRL 42715, beta-lactamases, and D-alanyl-D-alanine peptidases

β-Lactamase Inhibitors To Restore the Efficacy of Antibiotics against Superbugs

Infections caused by resistant bacteria are nowadays too common, and some pathogens have even become resistant to multiple types of antibiotics, in which case few or even no treatments are available. In recent years, the most successful strategy in anti-infective drug discovery for the treatment of such problematic infections is the combination therapy "antibiotic + inhibitor of resistance". These inhibitors allow the repurposing of antibiotics that have already proven to be safe and effective for clinical use. Three main types of compounds have been developed to block the principal bacterial resistance mechanisms: (i) β-lactamase inhibitors; (ii) outer membrane permeabilizers; (iii) efflux pump inhibitors. This Perspective is focused on β-lactamase inhibitors that disable the most prevalent cause of antibiotic resistance in Gram-negative bacteria, i.e., the deactivation of the most widely used antibiotics, β-lactams (penicillins, cephalosporines, carbapenems, and monobactams), by the production of β-lactamases. An overview of the most recently identified β-lactamase inhibitors and of combination therapy is provided. The article also covers the mechanism of action of the different types of β-lactamase enzymes as a basis for inhibitor design and target inactivation.

Intrinsic carbapenem-hydrolyzing oxacillinases from members of the genus Pandoraea

We analyzed the oxacillinases of isolates of six different species of Pandoraea, a genus that colonizes the respiratory tract of cystic fibrosis patients. The isolates produced carbapenem-hydrolyzing enzymes causing elevated MICs for amoxicillin, piperacillin, meropenem, and imipenem when expressed in an Escherichia coli host strain. Sequencing revealed nine new oxacillinases (OXA-151 to OXA-159) with a high degree of identity among isolates of the same species; however, they had much lower interspecies similarities. The intrinsic oxacillinase genes might therefore be helpful for correct identification of Pandoraea isolates.

Phenotypic and enzymatic comparative analysis of the KPC variants, KPC-2 and its recently discovered variant KPC-15

Sixteen different variants (KPC-2 to KPC-17) in the KPC family have been reported, and most current studies are focusing on KPC-2 and KPC-3. The KPC-15 variant, which isolated from Klebsiella pneumoniae in a Chinese hospital, was a recently discovered KPC enzyme. To compare the characteristics of KPC-15 and KPC-2, the variants were determined by susceptibility testing, PCR amplification and sequencing, and study of kinetic parameters. The strain harboring the KPC-15 showed resistance to 18 conventional antimicrobial agents, especially to cabapenem antibiotics, and the strain involving the KPC-2 also indicated resistance to cabapenem antibiotics, but both strains were susceptible to polymyxin B and colistin. The conjugation experiments showed that the changes of MIC values to the antibiotics were due to the transferred plasmids. The differences of amino acids were characterised at sites of 119 leucine and 146 lysine with KPC-15 and KPC-2. The minimum evolution tree indicated the KPC alleles evolution, and showed that the KPC-15 appeared to be homogenous with KPC-4 closely. Steady-state kinetic parameters showed the catalytic efficiency of KPC-15 was higher than that of KPC-2 for all tested antibiotics in this study. The catalytic efficiency of KPC-15 caused resistance to β-lactam antibiotics was higher than that of KPC-2. Meanwhile, an evolutionary transformation changed KPC from an efficient carbapenemase to its variants (KPC-15) with better ceftazidimase catalytic efficiency, and the old antibiotics polymyxin B and colistin might play a role in the therapy for multi-resistant strains.

Kinetic study of the effect of histidines 240 and 164 on TEM-149 enzyme probed by β-lactam inhibitors

In the present study, we performed a detailed kinetic analysis of the enzymes TEM-149, TEM-149(H240), and TEM-149(H164-H240) versus a large panel of inhibitors/inactivators, including penicillins, penems, carbapenems, monobactams, cephamycin, and carbacephem. These compounds behaved as poor substrates versus TEM-149, TEM-149(H240), and TEM-149(H164-H240) β-lactamases, and the Ki (inhibition constant), K (dissociation constant of the Henri-Michaelis complex), k+2 and k+3 (first-order acylation and deacylation constants, respectively), and k+2/K values were calculated.

Class D β-lactamases: a reappraisal after five decades

Despite 70 years of clinical use, β-lactam antibiotics still remain at the forefront of antimicrobial chemotherapy. The major challenge to these life-saving therapeutics is the presence of bacterial enzymes (i.e., β-lactamases) that can hydrolyze the β-lactam bond and inactivate the antibiotic. These enzymes can be grouped into four classes (A-D). Among the most genetically diverse are the class D β-lactamases. In this class are β-lactamases that can inactivate the entire spectrum of β-lactam antibiotics (penicillins, cephalosporins, and carbapenems). Class D β-lactamases are mostly found in Gram-negative bacteria such as Pseudomonas aeruginosa , Escherichia coli , Proteus mirabilis , and Acinetobacter baumannii . The active-sites of class D β-lactamases contain an unusual N-carboxylated lysine post-translational modification. A strongly hydrophobic active-site helps create the conditions that allow the lysine to combine with CO2, and the resulting carbamate is stabilized by a number of hydrogen bonds. The carboxy-lysine plays a symmetric role in the reaction, serving as a general base to activate the serine nucleophile in the acylation reaction, and the deacylating water in the second step. There are more than 250 class D β-lactamases described, and the full set of variants shows remarkable diversity with regard to substrate binding and turnover. Narrow-spectrum variants are most effective against the earliest generation penicillins and cephalosporins such as ampicillin and cephalothin. Extended-spectrum variants (also known as extended-spectrum β-lactamases, ESBLs) pose a more dangerous clinical threat as they possess a small number of substitutions that allow them to bind and hydrolyze later generation cephalosporins that contain bulkier side-chain constituents (e.g., cefotaxime, ceftazidime, and cefepime). Mutations that permit this versatility seem to cluster in the area surrounding an active-site tryptophan resulting in a widened active-site to accommodate the oxyimino side-chains of these cephalosporins. More concerning are the class D β-lactamases that hydrolyze clinically important carbapenem β-lactam drugs (e.g., imipenem). Whereas carbapenems irreversibly acylate and inhibit narrow-spectrum β-lactamases, class D carbapenemases are able to recruit and activate a deacylating water. The rotational orientation of the C6 hydroxyethyl group found on all carbapenem antibiotics likely plays a role in whether the deacylating water is effective or not. Inhibition of class D β-lactamases is a current challenge. Commercially available inhibitors that are active against other classes of β-lactamases are ineffective against class D enzymes. On the horizon are several compounds, consisting of both β-lactam derivatives and non-β-lactams, that have the potential of providing novel leads to design new mechanism-based inactivators that are effective against the class D enzymes. Several act synergistically when given in combination with a β-lactam antibiotic, and others show a unique mechanism of inhibition that is distinct from the traditional β-lactamase inhibitors. These studies will bolster structure-based inhibitor design efforts to facilitate the optimization and development of these compounds as class D inactivators.

Characterization of the inhibitor-resistant SHV β-lactamase SHV-107 in a clinical Klebsiella pneumoniae strain coproducing GES-7 enzyme

The clinical Klebsiella pneumoniae INSRA6884 strain exhibited nonsusceptibility to all penicillins tested (MICs of 64 to >2,048 μg/ml). The MICs of penicillins were weakly reduced by clavulanate (from 2,048 to 512 μg/ml), and tazobactam restored piperacillin susceptibility. Molecular characterization identified the genes bla(GES-7) and a new β-lactamase gene, bla(SHV-107), which encoded an enzyme that differed from SHV-1 by the amino acid substitutions Leu35Gln and Thr235Ala. The SHV-107-producing Escherichia coli strain exhibited only a β-lactam resistance phenotype with respect to amoxicillin, ticarcillin, and amoxicillin-clavulanate combination. The kinetic parameters of the purified SHV-107 enzyme revealed a high affinity for penicillins. However, catalytic efficiency for these antibiotics was lower for SHV-107 than for SHV-1. No hydrolysis was detected against oxyimino-β-lactams. The 50% inhibitory concentration (IC(50)) for clavulanic acid was 9-fold higher for SHV-107 than for SHV-1, but the inhibitory effects of tazobactam were unchanged. Molecular dynamics simulation suggested that the Thr235Ala substitution affects the accommodation of clavulanate in the binding site and therefore its inhibitory activity.

Current challenges in antimicrobial chemotherapy: focus on ß-lactamase inhibition

The use of the three classical beta-lactamase inhibitors (clavulanic acid, tazobactam and sulbactam) in combination with beta-lactam antibacterials is currently the most successful strategy to combat beta-lactamase-mediated resistance. However, these inhibitors are efficient in inactivating only class A beta-lactamases and the efficiency of the inhibitor/antibacterial combination can be compromised by several mechanisms, such as the production of naturally resistant class B or class D enzymes, the hyperproduction of AmpC or even the production of evolved inhibitor-resistant class A enzymes. Thus, there is an urgent need for the development of novel inhibitors. For serine active enzymes (classes A, C and D), derivatives of the beta-lactam ring such as 6-beta-halogenopenicillanates, beta-lactam sulfones, penems and oxapenems, monobactams or trinems seem to be potential starting points to design efficient molecules (such as AM-112 and LK-157). Moreover, a promising non-beta-lactam molecule, NXL-104, is now under clinical development. In contrast, an ideal inhibitor of metallo-beta-lactamases (class B) remains to be found, despite the huge number of potential molecules already described (biphenyl tetrazoles, cysteinyl peptides, mercaptocarboxylates, succinic acid derivatives, etc.). The search for such an inhibitor is complicated by the absence of a covalent intermediate in their catalytic mechanisms and the fact that beta-lactam derivatives often behave as substrates rather than as inhibitors. Currently, the most promising broad-spectrum inhibitors of class B enzymes are molecules presenting chelating groups (thiols, carboxylates, etc.) combined with an aromatic group. This review describes all the types of molecules already tested as potential beta-lactamase inhibitors and thus constitutes an update of the current status in beta-lactamase inhibitor discovery.

Three decades of beta-lactamase inhibitors

Since the introduction of penicillin, beta-lactam antibiotics have been the antimicrobial agents of choice. Unfortunately, the efficacy of these life-saving antibiotics is significantly threatened by bacterial beta-lactamases. beta-Lactamases are now responsible for resistance to penicillins, extended-spectrum cephalosporins, monobactams, and carbapenems. In order to overcome beta-lactamase-mediated resistance, beta-lactamase inhibitors (clavulanate, sulbactam, and tazobactam) were introduced into clinical practice. These inhibitors greatly enhance the efficacy of their partner beta-lactams (amoxicillin, ampicillin, piperacillin, and ticarcillin) in the treatment of serious Enterobacteriaceae and penicillin-resistant staphylococcal infections. However, selective pressure from excess antibiotic use accelerated the emergence of resistance to beta-lactam-beta-lactamase inhibitor combinations. Furthermore, the prevalence of clinically relevant beta-lactamases from other classes that are resistant to inhibition is rapidly increasing. There is an urgent need for effective inhibitors that can restore the activity of beta-lactams. Here, we review the catalytic mechanisms of each beta-lactamase class. We then discuss approaches for circumventing beta-lactamase-mediated resistance, including properties and characteristics of mechanism-based inactivators. We next highlight the mechanisms of action and salient clinical and microbiological features of beta-lactamase inhibitors. We also emphasize their therapeutic applications. We close by focusing on novel compounds and the chemical features of these agents that may contribute to a "second generation" of inhibitors. The goal for the next 3 decades will be to design inhibitors that will be effective for more than a single class of beta-lactamases.

Inhibitor resistance in the KPC-2 beta-lactamase, a preeminent property of this class A beta-lactamase

As resistance determinants, KPC beta-lactamases demonstrate a wide substrate spectrum that includes carbapenems, oxyimino-cephalosporins, and cephamycins. In addition, clinical strains harboring KPC-type beta-lactamases are often identified as resistant to standard beta-lactam-beta-lactamase inhibitor combinations in susceptibility testing. The KPC-2 carbapenemase presents a significant clinical challenge, as the mechanistic bases for KPC-2-associated phenotypes remain elusive. Here, we demonstrate resistance by KPC-2 to beta-lactamase inhibitors by determining that clavulanic acid, sulbactam, and tazobactam are hydrolyzed by KPC-2 with partition ratios (kcat/kinact ratios, where kinact is the rate constant of enzyme inactivation) of 2,500, 1,000, and 500, respectively. Methylidene penems that contain an sp2-hybridized C3 carboxylate and a bicyclic R1 side chain (dihydropyrazolo[1,5-c][1,3]thiazole [penem 1] and dihydropyrazolo[5,1-c][1,4]thiazine [penem 2]) are potent inhibitors: Km of penem 1, 0.06+/-0.01 microM, and Km of penem 2, 0.006+/-0.001 microM. We also demonstrate that penems 1 and 2 are mechanism-based inactivators, having partition ratios (kcat/kinact ratios) of 250 and 50, respectively. To understand the mechanism of inhibition by these penems, we generated molecular representations of both inhibitors in the active site of KPC-2. These models (i) suggest that penem 1 and penem 2 interact differently with active site residues, with the carbonyl of penem 2 being positioned outside the oxyanion hole and in a less favorable position for hydrolysis than that of penem 1, and (ii) support the kinetic observations that penem 2 is the better inhibitor (kinact/Km=6.5+/-0.6 microM(-1) s(-1)). We conclude that KPC-2 is unique among class A beta-lactamases in being able to readily hydrolyze clavulanic acid, sulbactam, and tazobactam. In contrast, penem-type beta-lactamase inhibitors, by exhibiting unique active site chemistry, may serve as an important scaffold for future development and offer an attractive alternative to our current beta-lactamase inhibitors.

Inhibition of OXA-1 beta-lactamase by penems

The partnering of a beta-lactam with a beta-lactamase inhibitor is a highly effective strategy that can be used to combat bacterial resistance to beta-lactam antibiotics mediated by serine beta-lactamases (EC 3.2.5.6). To this end, we tested two novel penem inhibitors against OXA-1, a class D beta-lactamase that is resistant to inactivation by tazobactam. The K(i) of each penem inhibitor for OXA-1 was in the nM range (K(i) of penem 1, 45 +/- 8 nM; K(i) of penem 2, 12 +/- 2 nM). The first-order rate constant for enzyme and inhibitor complex inactivation of penems 1 and 2 for OXA-1 beta-lactamase were 0.13 +/- 0.01 s(-1) and 0.11 +/- 0.01 s(-1), respectively. By using an inhibitor-to-enzyme ratio of 1:1, 100% inactivation was achieved in <or=900 s and the recovery of OXA-1 beta-lactamase activity was not detected at 24 h. Covalent adducts of penems 1 and 2 (changes in molecular masses, +306 +/- 3 and +321 +/- 3 Da, respectively) were identified by electrospray ionization mass spectrometry (ESI-MS). After tryptic digestion of OXA-1 inactivated by penems 1 and 2, ESI-MS and matrix-assisted laser desorption ionization-time-of-flight MS identified the adducts of 306 +/- 3 and 321 +/- 3 Da attached to the peptide containing the active-site Ser67. The base hydrolysis of penem 2, monitored by serial (1)H nuclear magnetic resonance analysis, suggested that penem 2 formed a linear imine species that underwent 7-endo-trig cyclization to ultimately form a cyclic enamine, the 1,4-thiazepine derivative. Susceptibility testing demonstrated that the penem inhibitors at 4 mg/liter effectively restored susceptibility to piperacillin. Penem beta-lactamase inhibitors which demonstrate high affinities and which form long-lived acyl intermediates may prove to be extremely useful against the broad range of inhibitor-resistant serine beta-lactamases present in gram-negative bacteria.

Novel carbapenem-hydrolyzing oxacillinase OXA-62 from Pandoraea pnomenusa

Pandoraea spp. are gram-negative, glucose nonfermenting rods detectable in blood cultures and sputa of cystic fibrosis patients. They are resistant to various antibiotic groups, with imipenem being the only active beta-lactam. We isolated an imipenem-resistant (MIC, 64 microg/ml) Pandoraea pnomenusa strain from a cystic fibrosis patient. Cloning and sequencing identified two beta-lactamases of Bush group 2d, namely, the known OXA-33, located on an integron, and the novel carbapenem-hydrolyzing oxacillinase OXA-62. OXA-62 is only distantly related to other oxacillinases (OXA-50 being closest with 43% amino acid identity). It hydrolyzes penicillins, oxacillin, imipenem, and meropenem but not expanded-spectrum cephalosporins. The blaOXA-62 gene is chromosome located. No transposable elements were found in its genetic neighborhood. With OXA-62-specific primers, blaOXA-62 could be identified in all P. pnomenusa strains and appears to be species specific. This additional mechanism of carbapenem resistance further complicates the treatment of infections caused by P. pnomenusa.

Crystal structure of BRL 42715, C6-(N1-methyl-1,2,3-triazolylmethylene)penem, in complex with Enterobacter cloacae 908R beta-lactamase: evidence for a stereoselective mechanism from docking studies

BRL 42715, C6-(N1-methyl-1,2,3-triazolylmethylene)penem, is an active-site-directed inactivator of bacterial beta-lactamases. The crystal structure of Enterobacter cloacae 908R class C beta-lactamase in complex with BRL 42715, docking, and energy minimization studies explain stereoselectivity of the binding of C6-(heterocyclic methylene)penems against class C beta-lactamase.

Structure−Activity Relationship of 6-Methylidene Penems Bearing Tricyclic Heterocycles as Broad-Spectrum β-Lactamase Inhibitors: Crystallographic Structures Show Unexpected Binding of 1,4-Thiazepine Intermediates

The design and synthesis of a series of seven tricyclic 6-methylidene penems as novel class A and C serine beta-lactamase inhibitors is described. These compounds proved to be very potent inhibitors of the TEM-1 and AmpC beta-lactamases and less so against the class B metallo-beta-lactamase CcrA. In combination with piperacillin, their in vitro activities enhanced susceptibility of all class C resistant strains from various bacteria. Crystallographic structures of a serine-bound reaction intermediate of 17 with the class A SHV-1 and class C GC1 enzymes have been established to resolutions of 2.0 and 1.4 A, respectively, and refined to R-factors equal 0.163 and 0.145. In both beta-lactamases, a seven-membered 1,4-thiazepine ring has formed. The stereogenic C7 atom in the ring has the R configuration in the SHV-1 intermediate and has both R and S configurations in the GC1 intermediate. Hydrophobic stacking interactions between the tricyclic C7 substituent and a tyrosine side chain, rather than electrostatic or hydrogen bonding by the C3 carboxylic acid group, dominate in both complexes. The formation of the 1,4- thiazepine ring structures is proposed based on a 7-endo-trig cyclization.

Novel imidazole substituted 6-methylidene-penems as broad-spectrum β-lactamase inhibitors

Beta-lactamases are serine and metallo-dependent enzymes produced by the bacteria in defense against beta-lactam antibiotics. Production of class-A, class-B, and class-C enzymes by the bacteria make the use of beta-lactam antibiotics ineffective in certain cases. To overcome resistance to beta-lactam antibiotics, several beta-lactamase inhibitors such as clavulanic acid, sulbactam, and tazobactam are widely used in the clinic in combination with beta-lactam antibiotics. However, single point mutations within these enzymes have allowed bacteria to overcome the inhibitory effect of the commercially approved beta-lactamase inhibitors. Although the commercially available beta-lactamase inhibitor/beta-lactam antibiotic combinations are effective against class-A producing bacteria and many extended spectrum beta-lactamase (ESBL's) producing bacteria they are less effective against class-C enzymes expressing bacteria. To circumvent this problem, based on modeling studies several novel imidazole substituted 6-methylidene-penem derivatives were synthesized and tested against various beta-lactamase producing isolates. The present paper deals with the synthesis and structure-activity relationships (SAR) of these compounds.

Inhibition of class A and class C beta-lactamases by penems: crystallographic structures of a novel 1,4-thiazepine intermediate

A new beta-lactamase inhibitor, a methylidene penem having a 5,6-dihydro-8H-imidazo[2,1-c][1,4]oxazine heterocyclic substituent at the C6 position with a Z configuration, irreversibly inhibits both class A and class C serine beta-lactamases with IC(50) values of 0.4 and 9.0 nM for TEM-1 and SHV-1 (class A), respectively, and 4.8 nM in AmpC (class C) beta-lactamases. The compound also inhibits irreversibly the class C extended-spectrum GC1 beta-lactamase (IC(50) = 6.2 nM). High-resolution crystallographic structures of a reaction intermediate of (5R)-(6Z)-6-(5,6-dihydro-8H-imidazo[2,1-c][1,4]oxazin-2-ylmethylene)-7-oxo-4-thia-1-azabicyclo[3.2.0]hept-2-ene-3-carboxylic acid 1 with the SHV-1 beta-lactamase and with the GC1 beta-lactamase have been determined by X-ray diffraction to resolutions of 1.10 and 1.38 A, respectively. The two complexes were refined to crystallographic R-factors (R(free)) of 0.141 (0.186) and 0.138 (0.202), respectively. Cryoquenching of the reaction of 1 with each beta-lactamase crystal produced a common, covalently bound intermediate. After acylation of the serine, a nucleophilic attack by the departing thiolate on the C6' atom yielded a novel seven-membered 1,4-thiazepine ring having R stereochemistry at the new C7 moiety. The orientation of this ring in each complex differs by a 180 degrees rotation about the bond to the acylated serine. The acyl ester bond is stabilized to hydrolysis through resonance stabilization with the dihydrothiazepine ring and by low occupancy or disorder of hydrolytic water molecules. In the class A complex, the buried water molecule on the alpha-face of the ester bond appears to be loosely bound or absent. In the class C complex, a water molecule on the beta-face is disordered and poorly activated for hydrolysis. Here, the acyl intermediate is unable to assist its own hydrolysis, as is thought to occur with many class C substrates.

[Phenotypes of beta-lactam resistance in the genus Aeromonas]

This work aimed to investigate resistance profiles towards beta-lactam antibiotics in correlation with beta-lactamases production in the genus Aeromonas. In a series of 417 wild-type strains, biochemical identification and testing with 11 beta-lactams by the disk-diffusion method revealed 5 predominant phenotypes: A. hydrophila complex/class B, C and D beta-lactamases; A. caviae complex/class C and D beta-lactamases; A. veronii complex/class B and D beta-lactamases; A. schubertii spp./class D beta-lactamase; A. trota spp./class C beta-lactamase. A subgroup of 64 representative strains was submitted to MIC determination with 8 beta-lactam compounds alone and in combination with 3 beta-lactamase inhibitors (clavulanic acid, tazobactam and BRL 42715). Visualisation of beta-lactamases and pI determination were performed in all these 64 isolates by isoelectric focusing from crude extracts. The different Aeromonas species produced 1 to 3 of the following inducible enzymes: an imipenemase with low expression, which is difficult to detect with routine phenotype studies (class B, pI 8, imipenem MIC > 2 micrograms/ml), a cephalosporinase (class C, pI > 7 +/- 0.5, cephalothin MIC > 256 micrograms/ml), and an oxacillinase widely produced in the genus Aeromonas (class D, pI > 8.5, ticarcillin MIC > 256 micrograms/ml). In Aeromonas spp. resistance profile to beta-lactam antibiotics is correlated with naturally occurring phenotypes of beta-lactamases production. As a conclusion, the characterisation of these different enzymes is of therapeutic and taxonomic interest, in species notoriously difficult to identify.

Analysis of the importance of the metallo-beta-lactamase active site loop in substrate binding and catalysis

The role of the mobile loop comprising residues 60-66 in metallo-beta-lactamases has been studied by site-directed mutagenesis, determination of kinetic parameters for six substrates and two inhibitors, pre-steady-state characterization of the interaction with chromogenic nitrocefin, and molecular modeling. The W64A mutation was performed in IMP-1 and BcII (after replacement of the BcII 60-66 peptide by that of IMP-1) and always resulted in increased K(i) and K(m) and decreased k(cat)/K(m) values, an effect reinforced by complete deletion of the loop. k(cat) values were, by contrast, much more diversely affected, indicating that the loop does not systematically favor the best relative positioning of substrate and enzyme catalytic groups. The hydrophobic nature of the ligand is also crucial to strong interactions with the loop, since imipenem was almost insensitive to loop modifications.

Kinetic study of two novel enantiomeric tricyclic beta-lactams which efficiently inactivate class C beta-lactamases

A detailed kinetic study of the interaction between two ethylidene derivatives of tricyclic carbapenems, Lek 156 and Lek 157, and representative beta-lactamases and D-alanyl-D-alanine peptidases (DD-peptidases) is presented. Both compounds are very efficient inactivators of the Enterobacter cloacae 908R beta-lactamase, which is usually resistant to inhibition. Preliminary experiments indicate that various extended-spectrum class C beta-lactamases (ACT-1, CMY-1, and MIR-1) are also inactivated. With the E. cloacae 908R enzyme, complete inactivation occurs with a second-order rate constant, k(2)/K', of 2 x 10(4) to 4 x 10(4) M(-1) s(-1), and reactivation is very slow, with a half-life of >1 h. Accordingly, Lek 157 significantly decreases the MIC of ampicillin for E. cloacae P99, a constitutive class C beta-lactamase overproducer. With the other serine beta-lactamases tested, the covalent adducts exhibit a wide range of stabilities, with half-lives ranging from long (>4 h with the TEM-1 class A enzyme), to medium (10 to 20 min with the OXA-10 class D enzyme), to short (0.2 to 0.4 s with the NmcA class A beta-lactamase). By contrast, both carbapenems behave as good substrates of the Bacillus cereus metallo-beta-lactamase (class B). The Streptomyces sp. strain R61 and K15 extracellular DD-peptidases exhibit low levels of sensitivity to both compounds.

Inhibition of beta-lactamases by 6,6-bis(hydroxylmethyl)penicillanate

beta-Lactamases of classes A and C are the two most prevalent resistant determinants to beta-lactam antibiotics among bacterial pathogens. Both these enzymes pursue different mechanisms for their catalytic processes, highlighted by the fact that the hydrolytic water molecule in each approaches the ester of the intermediary acyl-enzyme species from the opposite ends. 6,6-Bis(hydroxylmethyl)penicillanate was designed as an inhibitor that would impair the approach of the hydrolytic water molecule in either of these enzymes upon formation of the acyl-enzyme species. The design, synthesis, and kinetic evaluation of this inhibitor are disclosed herein.

beta-Lactamase epidemiology and the utility of established and novel beta-lactamase inhibitors

beta-Lactamase inhibitor:beta-lactam combinations remain one of the most successful strategies for the treatment of bacterial infections. Over the last 20 years the number and diversity of serine and metallo active site beta-lactamases has increased dramatically. This review highlights some of the new additions to the beta-lactamase arena and discusses how the commercially available beta-lactamase inhibitors are keeping pace with the changing epidemiology of beta-lactamases. In addition, we survey the progress with the design of novel inhibitors of serine and metallo-beta-lactamases. Focus is given to the recent advances in the design of metallo-beta-lactamase inhibitors as these enzymes pose a serious emerging threat to the use of all beta-lactam based therapies.

Inhibition studies on the metallo-beta-lactamase L1 from Stenotrophomonas maltophilia

In an effort to identify a competitive inhibitor that can be used in future spectroscopic and crystallographic studies and to better understand the interaction of a mercaptoacetic acid-thiolester-containing compound with metallo-beta-lactamase L1 from Stenotrophomonas maltophilia, inhibition studies using two thiol-containing compounds were conducted. N-(2'-Mercaptoethyl)-2-phenylacetamide is a competitive inhibitor of L1 with a K(i) of 50 +/- 3 microM, and this compound is not a time-dependent inactivator of L1. N-Benzylacetyl-d-alanylthioacetic acid is a competitive inhibitor of L1 with a K(i) of 1.6 +/- 0.3 microM. Matrix-assisted laser desorption ionization time-of-flight mass spectrometric studies revealed that 2 mol of mercaptoacetate covalently bind to L1 upon incubation of the enzyme with N-benzylacetyl-d-alanylthioacetic acid; however, this covalently modified enzyme has the same activity as wild-type L1. Last, inhibition studies were used to demonstrate that 4-morpholinoethanesulfonic acid does not inhibit L1, even at concentrations up to 300 mM. This work identifies two possible competitive inhibitors which can be used in future structural studies and further demonstrates inhibitory heterogeneity among the metallo-beta-lactamases.

Overexpression, purification, and characterization of the cloned metallo-beta-lactamase L1 from Stenotrophomonas maltophilia

The metallo-beta-lactamase L1 from Stenotrophomonas maltophilia was cloned, overexpressed, and characterized by spectrometric and biochemical techniques. Results of metal analyses were consistent with the cloned enzyme having 2 mol of tightly bound Zn(II) per monomer. Gel filtration chromatography demonstrated that the cloned enzyme exists as a tightly held tetramer with a molecular mass of ca. 115 kDa, and matrix-assisted laser desorption ionization and time-of-flight mass spectrometry indicated a monomeric molecular mass of 28.8 kDa. Steady-state kinetic studies with a number of diverse penicillin and cephalosporin antibiotics demonstrated that L1 effectively hydrolyzes all tested compounds, with k(cat)/Km values ranging between 0.002 and 5.5 microM(-1) s(-1). These characteristics of the recombinant enzyme are contrasted to those previously reported for metallo-beta-lactamases isolated directly from S. maltophilia.