Comparative stability of carbapenem and penem antibiotics to human recombinant dehydropeptidase-I

Arginine Modulates Carbapenem Deactivation by OXA-24/40 in Acinetobacter baumannii

The resistance of Gram-negative bacteria to β-lactam antibiotics stems mainly from β-lactamase proteins that hydrolytically deactivate the β-lactams. Of particular concern are the β-lactamases that can deactivate a class of β-lactams known as carbapenems. Carbapenems are among the few anti-infectives that can treat multi-drug resistant bacterial infections. Revealing the mechanisms of their deactivation by β-lactamases is a necessary step for preserving their therapeutic value. Here, we present NMR investigations of OXA-24/40, a carbapenem-hydrolyzing Class D β-lactamase (CHDL) expressed in the gram-negative pathogen, Acinetobacter baumannii. Using rapid data acquisition methods, we were able to study the "real-time" deactivation of the carbapenem known as doripenem by OXA-24/40. Our results indicate that OXA-24/40 has two deactivation mechanisms: canonical hydrolytic cleavage, and a distinct mechanism that produces a β-lactone product that has weak affinity for the OXA-24/40 active site. The mechanisms issue from distinct active site environments poised either for hydrolysis or β-lactone formation. Mutagenesis reveals that R261, a conserved active site arginine, stabilizes the active site environment enabling β-lactone formation. Our results have implications not only for OXA-24/40, but the larger family of CHDLs now challenging clinical settings on a global scale.

Have we realized the full potential of β-lactams for treating drug-resistant TB?

β-lactams are the most widely used antibiotics and are effective against a spectrum of pathogenic bacteria. Here, we focus on the state-of-the-art understanding of the molecular underpinnings that determine the overall efficacy of β-lactams against TB and include historical perspectives of this antibiotic class against this ancient disease. We summarize literature that describes why earlier generations of β-lactams are ineffective and the potential promise of newer β-lactams that exhibit improved efficacy against TB. Emerging evidence warrants renewed consideration of newer β-lactams in regimens for treatment of drug-resistant TB. © 2018 IUBMB Life, 70(9):881-888, 2018.

Treatment ofPseudomonas aeruginosainfection in critically ill patients

Critically ill patients are on the increase in the present clinical setting. Aging of our population and increasingly aggressive medical and therapeutic interventions, including implanted foreign bodies, organ transplantation and advances in the chemotherapy of malignant diseases, have created a cohort of particularly vulnerable patients. Pseudomonas aeruginosa is one of the leading gram-negative organisms associated with nosocomial infections. This organism is frequently feared because it causes severe hospital-acquired infections, especially in immunocompromised hosts, and is often antibiotic resistant, complicating the choice of therapy. The epidemiology, microbiology, mechanisms of resistance and currently available and future treatment options for the most relevant infections caused by P. aeruginosa are reviewed.

Structure of apo- and monometalated forms of NDM-1--a highly potent carbapenem-hydrolyzing metallo-β-lactamase

The New Delhi Metallo-β-lactamase (NDM-1) gene makes multiple pathogenic microorganisms resistant to all known β-lactam antibiotics. The rapid emergence of NDM-1 has been linked to mobile plasmids that move between different strains resulting in world-wide dissemination. Biochemical studies revealed that NDM-1 is capable of efficiently hydrolyzing a wide range of β-lactams, including many carbapenems considered as "last resort" antibiotics. The crystal structures of metal-free apo- and monozinc forms of NDM-1 presented here revealed an enlarged and flexible active site of class B1 metallo-β-lactamase. This site is capable of accommodating many β-lactam substrates by having many of the catalytic residues on flexible loops, which explains the observed extended spectrum activity of this zinc dependent β-lactamase. Indeed, five loops contribute "keg" residues in the active site including side chains involved in metal binding. Loop 1 in particular, shows conformational flexibility, apparently related to the acceptance and positioning of substrates for cleavage by a zinc-activated water molecule.

Doripenem: a new carbapenem antibiotic

PURPOSE

The chemistry, pharmacology, antimicrobial activity, pharmacokinetics, pharmacodynamics, efficacy and safety in humans, and formulary considerations of doripenem are reviewed.

SUMMARY

Doripenem, a member of the β-lactam class of antibiotics, is the newest addition to the carbapenems. It exhibits concentration-independent bactericidal activity against gram-positive bacteria; enteric and nonenteric gram-negative bacteria, including extended-spectrum β-lactamase-producing strains; and anaerobic pathogens. Doripenem was found to be noninferior to meropenem in the treatment of complicated intraabdominal infections and noninferior to levofloxacin in the treatment of complicated urinary tract infections including pyelonephritis and was granted marketing approval by the Food and Drug Administration for these two indications. Doripenem was also found to be noninferior to imipenem in the treatment of ventilator-associated pneumonia and noninferior to piperacillin-tazobactam in the treatment of hospital-acquired pneumonia. It has a favorable safety profile, with gastrointestinal complaints and headache being the most common adverse effects and allergic reactions the most serious adverse effects. Doripenem has a relatively low potential to induce seizures. The only known clinically relevant drug interaction is that coadministration with valproic acid may result in reductions of valproic acid serum concentrations. As with most renally eliminated antibiotics, the dose of doripenem should be adjusted according to kidney function.

CONCLUSION

Doripenem is an injectable carbapenem antibiotic with a spectrum of activity comparable to that of imipenem and meropenem. Its safety is similar to that of other carbapenems.

Characteristics of doripenem: a new broad-spectrum antibiotic

Doripenem (S-4661) is a new parenteral antibiotic from the carbapenem class; similarly to imipenem and meropenem, it has a broad-spectrum activity against Gram-positive, Gram-negative, and anaerobic bacteria. It is active against multiresistant Gram-negative bacilli such as extended-spectrum beta-lactamase-producing (ESBL) Gram-negative Enterobacteriaceae and nonfermentative Gram-negative bacilli including some strains of Pseudomonas aeruginosa that are resistant to other carbapenems. Doripenem’s chemical structure is similar to that of meropenem (substitution of one sulfamoxil-aminomethyl chain for the dimethyl-carboxyl chain), and has one 1-beta-methyl chain which provides resistance to dehydropeptidase-I enzyme. The clinical trials conducted so far have focused on the treatment of severe infections such as complicated intra-abdominal infections, complicated urinary tract infections and pyelonephritis, nosocomial pneumonia, and ventilator-associated pneumonia. Given its activity profile and the results from the clinical trials, this antibiotic may be used for empirical treatment of multibacterial infections produced by potentially multiresistant Gram-negative bacilli. In 2007, the US Food and Drug Administration approved the use of doripenem for the treatment of complicated intra-abdominal infections and complicated urinary tract infections. The European Medicines Agency has approved the use of doripenem for the same indications in addition to nosocomial pneumonia regardless of whether it is ventilator-associated or not.

Beta-lactams and beta-lactamase-inhibitors in current- or potential-clinical practice: a comprehensive update

The use of successive generations of beta-lactams has selected successive generations of beta-lactamases including CTX-M ESBLs, AmpC beta-lactamases, and KPC carbapenamases in Enterobacteriaceae. Moreover, this cephalosporin resistance, along with rising resistance to fluoroquinolones, is now driving the use of carbapenems and unfortunately the carbapenem resistance has emerged markedly, especially in Acinetobacter spp. due to OXA- and metallo-carbapenemases. The industry responded to the challenge of rising resistance and recently developed some novel beta-lactams such as ceftobiprole, ceftaroline etc. and many beta-lactam compounds, including beta-lactamase-inhibitors, such as BMS-247243, S-3578, RWJ-54428, CS-023, SMP-601, NXL 104, BAL 30376, LK 157, and so on are under trials. This review provides the comprehensive accounts of the developments in penicillins, cephalosporins, carbapenems, and beta-lactamase-inhibitors, and the insight about medicinal chemistry, mechanism(s) of action and resistance, potential strategies to overcome resistance due to beta-lactamases, and also the recent advancements in the development of newer beta-lactam compounds; some of which are still under trials and yet to be classified. This review will fill the gap since previously published reviews and will serve as a comprehensive update on the current topic.

The use of carbapenems in the treatment of serious infections

Inadequate initial antimicrobial treatment in serious infections leads to increased mortality. Achieving adequate treatment is increasingly difficult because of the increasing prevalence of multidrug-resistant (MDR) pathogens. The carbapenems are potent, broad-spectrum antibiotics that have been shown to be safe and efficacious therapies in the treatment of serious infections. This review is intended to compare the 4 major members of the carbapenem class, which include imipenem, meropenem, ertapenem, and doripenem, with other widely used antimicrobial agents in the intensive care unit (ICU). The carbapenems are potent, broad-spectrum antibiotics that have been shown to be safe and efficacious therapies in the treatment of serious infections. They provide better gram-negative coverage than other beta-lactams and are stable against extended-spectrum beta-lactamases and AmpC beta-lactamases, making them effective in the treatment of many MDR bacteria. The newly approved carbapenem, doripenem, may help preserve the utility of the carbapenem class.

New developments in carbapenems

Antibiotic resistance among Gram-negative pathogens in hospitals is a growing threat to patients and is driving the increased use of carbapenems. Carbapenems are potent members of the beta-lactam family of antibiotics, with a history of safety and efficacy for serious infections that exceeds 20 years. Original and review articles were identified from a Medline search (1979-2008). Reference citations from identified publications, abstracts from the Interscience Conferences on Antimicrobial Agents and Chemotherapy and package inserts were also used. Carbapenems are effective in treating severe infections at diverse sites, with relatively low resistance rates and a favourable safety profile. Carbapenems are the beta-lactams of choice for the treatment of infections caused by multidrug-resistant organisms. Optimized dosing of carbapenems should limit the emergence of resistance and prolong the utility of these agents. The newly approved doripenem should prove to be a valuable addition to the currently available carbapenems: imipenem, meropenem and ertapenem.

Carbapenems: a potent class of antibiotics

The purpose of this review is to assess the relative strengths and weaknesses of individual members of the carbapenem class of antibiotics. Clinical trials and review articles were identified from a Medline search (1979 - July 2006), in addition to, reference citations from identified publications, abstracts from the Interscience Conferences on Antimicrobial Agents and Chemotherapy and the 12th International Congress on Infectious Disease, and package inserts. Articles in English were reviewed, with emphasis on those containing efficacy or safety data. Carbapenems bind to critical penicillin-binding proteins, disrupting the growth and structural integrity of bacterial cell walls. They provide enhanced anaerobic and Gram-negative coverage as compared with other beta-lactams and their stability against extended-spectrum beta-lactamases (ESBLs) makes them an effective treatment option. The most common adverse effects are infusion-site complications and gastrointestinal distress. Ertapenem has limited efficacy against non-fermenting, Gram-negative bacteria, restricting its use to community-acquired infections. Imipenem is slightly more effective against Gram-positive organisms and meropenem slightly more effective against Gram-negative organisms. However, both have broad-spectrum activity, including non-fermenting, Gram-negative bacteria. Among non-fermenting, Gram-negatives, resistance to imipenem in particular is increasing. Doripenem is in late-stage clinical development and combines the broad-spectrum coverage of imipenem and meropenem, and more potent activity against Pseudomonas aeruginosa. Due to the increasing challenges represented by ESBLs and multi-drug resistant organisms, the carbapenems are assuming a greater role in the treatment of serious infections. Imipenem and meropenem are presently available and have been shown to be effective against nosocomial infections. Doripenem is an investigational carbapenem that has completed Phase III clinical trials and that has the potential to improve on this efficacy and minimize the emergence of resistance to the carbapenem class.

Investigational treatments for postoperative surgical site infections

Surgical site infections rank third among nosocomial infections, representing a global threat, associated with the emergence of multi-drug-resistant bacteria. The pharmaceutical industry has recently curtailed developmental programmes; however, the need for new compounds is extremely important. This article reviews new antimicrobials and immunointerventional targets for their potential to treat surgical site infections in comparison with recently licensed compounds. Daptomycin, dalbavancin, oritavancin, telavancin, iclaprim and ranbezolid seem to be promising agents against infections caused by Gram-positive pathogens and effectively address the present problems of multi-resistance in Gram-positive infections. Peptide deformylase inhibitors and immunostimulating agents open new perspectives in this field; however, very few compounds targeting Gram-negative problematic pathogens are in the pipeline of the future. Tigecycline (recently marketed) ceftobiprole, ceftaroline and doripenem seem to possess an extended anti-Gram-positive and -negative spectrum. Among these compounds, only doripenem demonstrates activity against Pseudomonas aeruginosa, for which there is a clear unmet need for new compounds, focusing on new targets.

In vitro activities of doripenem and comparator agents against 364 anaerobic clinical isolates

The in vitro activities of doripenem against 364 anaerobic isolates were measured and compared to those of ertapenem, imipenem, meropenem, ceftriaxone, and levofloxacin. All of the carbapenems were active against nearly all Bacteroides fragilis group isolates. Doripenem was either comparable to or slightly less active than imipenem and meropenem against most isolates but more active than the other penems against Clostridium difficile. Doripenem appears to have excellent activity against a broad range of anaerobes.

Antimicrobial activity of doripenem (S-4661): a global surveillance report (2003)

The spectrum of activity and potency of doripenem, a broad-spectrum parenteral carbapenem currently in clinical development, was evaluated using 16 008 clinical bacterial isolates collected as part of an international surveillance project during 2003. Using reference broth microdilution methods, doripenem was found to be highly active against oxacillin-susceptible Staphylococcus aureus and coagulase-negative staphylococci (2705 and 297 isolates, respectively; MIC90s 0.06 mg/L), with a potency greater than that of other carbapenem antibiotics. Against enterococci (1474 isolates), with the exception of Enterococcus faecium, doripenem displayed modest activity (MIC50 4). Doripenem was among the most potent agents tested against Streptococcus pneumoniae, viridans group streptococci and beta-haemolytic streptococci (885, 140 and 397 isolates; MIC(90)s 0.5, 0.5 and 0.03 mg/L, respectively). For Enterobacteriaceae (> 6200 isolates), doripenem was four- to 32-fold more active than imipenem against wild-type isolates (MIC90s 0.03-0.5 mg/L). MIC90s for confirmed extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae (121 and 155 isolates; 0.06 and 0.12 mg/L, respectively) were two-fold higher than for wild-type isolates. Doripenem was also active against Citrobacter spp., Enterobacter spp. and Serratia spp. (MIC90s 0.06-0.25 mg/L), including ceftazidime-resistant isolates. Doripenem and meropenem were the most active agents among all beta-lactams against Pseudomonas aeruginosa (829 isolates; MIC50/90s 0.5/8 and 0.5/16 mg/L, respectively), whereas doripenem and imipenem were the most active agents against Acinetobacter spp. (155 isolates; MIC50/90s 0.5/4 and <or= 0.5/2 mg/L, respectively). Doripenem was slightly more potent (MIC50 2 mg/L) than ertapenem and imipenem (MIC50 4 mg/L), and had a potency similar to that of meropenem (MIC50 2 mg/L), against Burkholderia cepacia (20 isolates). Both Haemophilus influenzae (1824 isolates) and Moraxella catarrhalis (108 isolates), including beta-lactamase-positive isolates, were susceptible to doripenem (MIC90s 0.25 and 0.03 mg/L, respectively). Doripenem displays the favourable characteristics of other carbapenems, and appears to offer certain advantages in terms of potency, spectrum and beta-lactamase stability when compared with some carbapenems used currently to treat nosocomial infections.

Comparative activity of doripenem and three other carbapenems tested against Gram-negative bacilli with various beta-lactamase resistance mechanisms

Doripenem (formerly S-4661), a novel carbapenem antimicrobial, was compared with ertapenem, imipenem, and meropenem using reference broth microdilution test methods against wild-type and various resistant microbial subsets (380 strains). Doripenem and meropenem were consistently more potent than ertapenem or imipenem when tested against Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter spp. Ertapenem exhibited minimum inhibitory concentration (MIC) elevations for some isolates producing AmpC and extended-spectrum beta-lactamases, in contrast to greater enzyme stability for doripenem and other carbapenems tested. Multiple beta-lactamase (TEM, SHV, CTX-M, OXA, CMY types)-producing Escherichia coli had doripenem MIC values at </=0.016 mug/mL (with higher values for ertapenem). Doripenem appears to be a promising, potent carbapenem for parenteral use against contemporary Gram-negative bacilli producing various beta-lactamases.

Activities of doripenem (S-4661) against drug-resistant clinical pathogens

Doripenem (formerly S-4661), a new 1-beta-methyl carbapenem, was challenged with a worldwide collection of 394 drug-refractory isolates. For endemic extended-spectrum beta-lactamase- and stably derepressed AmpC-producing enteric bacilli, the doripenem MICs at which 90% of the isolates were inhibited (MIC90s) were 0.03 to 0.5 microg/ml, generally lower than those of comparator carbapenems. A greater proportion of strains among carbapenem-resistant nonfermentative gram-negative bacilli were inhibited by doripenem at < or =4 microg/ml, and doripenem was the most active carbapenem (MIC90, 1 to 4 microg/ml) against penicillin-resistant streptococci.

Comparative activities of doripenem versus isolates, mutants, and transconjugants of Enterobacteriaceae and Acinetobacter spp. with characterized beta-lactamases

Doripenem (S-4661), a new parenteral carbapenem, was tested against over 250 clinical isolates, mutants, and transconjugants of Enterobacteriaceae and Acinetobacter spp., selected or derived for their beta-lactamase expression characteristics. Imipenem, meropenem, and ertapenem were tested as comparators, along with cephalosporins and piperacillin-tazobactam, by using National Committee for Clinical Laboratory Standards agar dilution methodology. Doripenem MICs were from 0.03 to 0.25 microg/ml for Klebsiella isolates, irrespective of the presence of extended-spectrum beta-lactamases (ESBLs) or plasmid-mediated AmpC or hyperproduced K1 beta-lactamase. Similarly, MICs of doripenem for both AmpC-inducible and -derepressed Enterobacter isolates were 0.06 to 0.5 microg/ml. ESBL production did not raise the MICs of doripenem for Escherichia coli transconjugants, and studies with known expression mutants confirmed that neither inducible nor depressed AmpC beta-lactamase expression was protective in Enterobacter cloacae, Citrobacter freundii, Serratia marcescens, or Morganella morganii. In all of these respects, doripenem resembled meropenem and imipenem, whereas the MICs of ertapenem were raised (but still < or =1 microg/ml) for many ESBL-producing klebsiellas and AmpC-derepressed E. cloacae and C. freundii strains. Resistance to all carbapenems, including doripenem (MICs of mostly 16 to 64 microg/ml, compared with 0.25 to 1 microg/ml for typical strains), was seen in Acinetobacter isolates with metallo-beta-lactamases or OXA-carbapenemases. Isolates of Klebsiella and Serratia spp. with IMP, KPC, and SME beta-lactamases also were resistant to doripenem (MICs, 8 to >64 microg/ml) and to other carbapenems, although the continued apparent susceptibility (MICs, < or =0.5 microg/ml) of E. coli derivatives with cloned IMP-1 and NMC-A beta-lactamases suggested that carbapenem resistance might require other factors besides the enzymes.

In vitro antimicrobial activity of doripenem, a new carbapenem

The doripenem MICs at which 90% of the tested strains were inhibited ranged from 0.03 to 1 microg/ml for 10 species of Enterobacteriaceae (n = 351), from 0.03 to 0.12 microg/ml for oxacillin-susceptible staphylococci (n = 119), from 4 to 32 microg/ml for oxacillin-resistant staphylococci (n = 64), from < or =0.008 to 0.06 microg/ml for penicillin-susceptible streptococci (n = 132), and from 1 to 4 microg/ml for penicillin-resistant streptococci (n = 51). Overall, doripenem demonstrated in vitro activity similar to that of meropenem against gram-negative pathogens and to that of imipenem against gram-positive pathogens.

Biapenem

Biapenem is a new parenteral carbapenem antibacterial agent with a broad spectrum of in vitro antibacterial activity encompassing many Gram-negative and Gram-positive aerobic and anaerobic bacteria, including species producing beta-lactamases. Biapenem is more stable than imipenem, meropenem and panipenem to hydrolysis by human renal dihydropeptidase-I (DHP-I), and therefore does not require the coadministration of a DHP-I inhibitor. After intravenous administration, biapenem is widely distributed and penetrates well into various tissues (e.g. lung tissue) and body fluids (e.g. sputum, pleural effusion, abdominal cavity fluid). In randomised, nonblind or double-blind clinical trials, biapenem showed good clinical and bacteriological efficacy (similar to that of imipenem/ cilastatin) in the treatment of adult patients with intra-abdominal infections, lower respiratory infections or complicated urinary tract infections. Biapenem is generally well tolerated. The most common adverse events in clinical trials were skin eruptions/rashes, nausea and diarrhoea.

Emerging Strategies in Infectious Diseases

Beta-lactam antibiotics represent the most commonly prescribed antibacterial agents. New beta-lactams have been introduced continuously as many bacteria have developed resistance to older agents. In the late 1970s, a new class of exceptionally broad spectrum beta-lactams, the carbapenems, was identified. Despite being a very potent compound, the antibacterial activity of the first carbapenem, imipenem, was compromised because of hydrolysis by the renal dehydropeptidase enzyme (DHP-1), and it is now coadministered with a potent competitive inhibitor of the DHP-1 enzyme, cilastin. Molecular modifications in the carbapenem nucleus were able to increase stability to DHP-1 and retain the antibacterial activity. However, some important pathogenic bacteria were found to be resistant to this new class of agents. In addition, other clinically important gram-negative species, such as Pseudomonas aeruginosa, developed resistance mainly by the production of potent beta-lactamases and reduced permeability of the outer membrane. Since the discovery of imipenem/cilastatin, a great number of carbapenems have been developed, and a few of them have been marketed. Stability to hydrolysis by DHP-1 and decrease in toxicity were achieved by meropenem and biapenem. However, only a slight increase in the antibacterial potency and spectrum has been accomplished with either the new marketed or experimental parenteral compounds. In addition, compounds that can be administered orally, such as the carbapenens faropenem, CS-834 and MK-826, and the trinem sanfetrinem, have been developed. However, when compared with the parenterally administered compounds, the oral agents seem to lose some in vitro antibacterial activity, especially against P. aeruginosa.

In vitro antibacterial activity of LJC 11,036, an active metabolite of L-084, a new oral carbapenem antibiotic with potent antipneumococcal activity

LJC 11,036 is the active metabolite of L-084, a novel oral carbapenem that exhibits potent broad-spectrum activity. Antibacterial activities of LJC 11,036 against clinical isolates from respiratory infections, such as Streptococcus pneumoniae (n = 52), Streptococcus pyogenes (n = 19), Haemophilus influenzae (n = 50), Klebsiella pneumoniae (n = 53), and Moraxella catarrhalis (n = 53), and from urinary-tract infections, such as Escherichia coli (n = 53) (MICs at which 90% of the isolates were inhibited [MIC(90)s], 0.1, </=0.006, 0.39, 0.05, 0.05, and 0.05 microg/ml, respectively), were 2- to 64-fold higher than those of imipenem, cefdinir, and faropenem. Moreover, against these bacterial species, except for H. influenzae, the MIC(90)s of LJC 11,036 were 4- to 512-fold lower than those of levofloxacin. LJC 11,036 showed bactericidal activity equal or superior to that of imipenem. Bactericidal activity against penicillin-resistant S. pneumoniae (PRSP) did not vary with the phase of growth. LJC 11,036 had potent activity against various beta-lactamase-producing strains, excluding carbapenemase producers. Against renal dehydropeptidase-I, LJC 11,036 was more stable than imipenem. Furthermore, LJC 11,036 produced in vitro postantibiotic sub-MIC effects against PRSP HSC-3 (6.0 h at one-fourth the MIC) and H. influenzae LJ5 (9.2 h at one-half the MIC). LJC 11,036 showed high binding affinities for PBP1A, -1B, -2A/2X, -2B, and -3 of PRSP and for PBP1B, -2, -3A, and -3B of H. influenzae.