Limited treatment options exist to combat infections caused by multidrug-resistant (MDR) Gram-negative bacteria possessing broad-spectrum β-lactamases. The design of novel β-lactamase inhibitors is of paramount importance. Here, three novel diazabicyclooctanes (DBOs), WCK 5153, zidebactam (WCK 5107), and WCK 4234 (compounds 1-3, respectively), were synthesized and biochemically characterized against clinically important bacteria. Compound 3 inhibited class A, C, and D β-lactamases with unprecedented k/ K values against OXA carbapenemases. Compounds 1 and 2 acylated class A and C β-lactamses rapidly but not the tested OXAs. Compounds 1-3 formed highly stable acyl-complexes as demonstrated by mass spectrometry. Crystallography revealed that 1-3 complexed with KPC-2 adopted a "chair conformation" with the sulfate occupying the carboxylate binding region. The cefepime-2 and meropenem-3 combinations were effective in murine peritonitis and neutropenic lung infection models caused by MDR Acinetobacter baumannii. Compounds 1-3 are novel β-lactamase inhibitors that demonstate potent cross-class inhibition, and clinical studies targeting MDR infections are warranted.

Zidebactam and WCK 5153 are novel ␤-lactam enhancers that are bicyclo-acyl hydrazides (BCH), derivatives of the diazabicyclooctane (DBO) scaffold, targeted for the treatment of serious infections caused by highly drug-resistant Gram-negative pathogens. In this study, we determined the penicillin-binding protein (PBP) inhibition profiles and the antimicrobial activities of zidebactam and WCK 5153 against Pseudomonas aeruginosa, including multidrug-resistant (MDR) metallo-␤-lactamase (MBL)-producing high-risk clones. MIC determinations and time-kill assays were conducted for zidebactam, WCK 5153, and antipseudomonal ␤-lactams using wild-type PAO1, MexAB-OprM-hyperproducing (mexR), porin-deficient (oprD), and AmpC-hyperproducing (dacB) derivatives of PAO1, and MBL-expressing clinical strains ST175 (bla VIM-2 ) and ST111 (bla VIM-1 ). Furthermore, steady-state kinetics was used to assess the inhibitory potential of these compounds against the purified VIM-2 MBL. Zidebactam and WCK 5153 showed specific PBP2 inhibition and did not inhibit VIM-2 (apparent K i [K i app ] Ͼ 100 M). MICs for zidebactam and WCK 5153 ranged from 2 to 32 g/ml (amdinocillin MICs Ͼ 32 g/ml). Time-kill assays revealed bactericidal activity of zidebactam and WCK 5153. LIVE-DEAD staining further supported the bactericidal activity of both compounds, showing spheroplast formation. Fixed concentrations (4 or 8 g/ml) of zidebactam and WCK 5153 restored susceptibility to all of the tested ␤-lactams for each of the P. aeruginosa mutant strains. Likewise, antipseudomonal ␤-lactams (CLSI breakpoints), in combination with 4 or 8 g/ml of zidebactam or WCK 5153, resulted in enhanced killing. Certain combinations determined full bacterial eradication, even with MDR MBL-producing high-risk clones. ␤-Lactam-WCK enhancer combinations represent a promising ␤-lactam "enhancerbased" approach to treat MDR P. aeruginosa infections, bypassing the need for MBL inhibition.

Levonadifloxacin and its prodrug alalevonadifloxacin are novel broad-spectrum anti-MRSA agents belonging to the benzoquinolizine subclass of quinolone, formulated for intravenous and oral administration, respectively. Various in vitro and in vivo studies have established their antimicrobial spectrum against clinically significant Gram-positive, Gram-negative, atypical, and anaerobic pathogens. The potent activity of levonadifloxacin against MRSA, quinolone-resistant Staphylococcus aureus, and hetero-vancomycin-intermediate strains is an outcome of its welldifferentiated mechanism of action involving preferential targeting to DNA gyrase. Potent antistaphylococcal activity of levonadifloxacin was also observed in clinically relevant experimental conditions such as acidic pH, the intracellular environment, and biofilms, suggesting that the drug is bestowed with enabling features for the treatment of difficult-to-treat MRSA infections. Levonadifloxacin also retains clinically relevant activity against resistant respiratory pathogens such as macrolide-and penicillin-resistant Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, and Moraxella catarrhalis and, in conjunction with clinically established best-in-class human epithelial lung fluid concentration, has promising potential in the management of recalcitrant respiratory infections. Attractive features, such as resistance to NorA efflux, divergent mechanism of action in S. aureus, cidality against high-inoculum cultures, and low mutant prevention concentration, are likely to confer favorable resistance-suppression features to both agents. In vivo studies have shown promising efficacy in models of acute bacterial skin and skin structure infection, respiratory infections, pyelonephritis, and peritonitis at human-equivalent mouse doses. Both formulations were well tolerated in multiple phase I studies and overall showed a dose-dependent exposure. In particular, oral alalevonadifloxacin showed excellent bioavailability (~90%), almost mirroring the pharmacokinetic profile of intravenous levonadifloxacin, indicating the prodrug's seamless absorption and efficient cleavage to release the active parent drug. Hepatic impairment studies showed that clinical doses of levonadifloxacin/alalevonadifloxacin are not required to be adjusted for various degrees of hepatic impairment. With the successful completion of phase II and phase III studies for both levonadifloxacin and alalevonadifloxacin, they represent clinically attractive therapeutic options for the treatment of infections caused by multi-drugresistant Gram-positive organisms. Herein, we review the current evidence on therapeutically appealing attributes of levonadifloxacin and alalevonadifloxacin, which are based on a range of nonclinical in vitro and in vivo investigations and clinical studies.

Multidrug-resistant has rapidly spread worldwide, resulting in a serious threat to hospitalized patients. Zidebactam and WCK 5153 are novel non-β-lactam bicyclo-acyl hydrazide β-lactam enhancer antibiotics being developed to target multidrug-resistant The objectives of this work were to determine the 50% inhibitory concentrations (ICs) for penicillin-binding proteins (PBP), the OXA-23 inhibition profiles, and the antimicrobial activities of zidebactam and WCK 5153, alone and in combination with β-lactams, against multidrug-resistant MICs and time-kill kinetics were determined for an clinical strain producing the carbapenemase OXA-23 and belonging to the widespread European clone II of sequence type 2 (ST2). Inhibition of the purified OXA-23 enzyme by zidebactam, WCK 5153, and comparators was assessed. All of the compounds tested displayed apparent values of>100 μM, indicating poor OXA-23 β-lactamase inhibition. The ICs of zidebactam, WCK 5153, cefepime, ceftazidime, meropenem, and sulbactam (range of concentrations tested, 0.02 to 2 μg/ml) for PBP were also determined. Zidebactam and WCK 5153 demonstrated specific high-affinity binding to PBP2 of (0.01 μg/ml for both of the compounds). The MICs of zidebactam and WCK 5153 were>1,024 μg/ml for wild-type and multidrug-resistant strains. Importantly, combinations of cefepime with 8 μg/ml of zidebactam or WCK 5153 and sulbactam with 8 μg/ml of zidebactam or WCK 5153 led to 4- and 8-fold reductions of the MICs, respectively, and showed enhanced killing. Notably, several of the combinations resulted in full bacterial eradication at 24 h. We conclude that zidebactam and WCK 5153 are PBP2 inhibitors that show a potent β-lactam enhancer effect against, including a multidrug-resistant OXA-23-producing ST2 international clone.

The activity of WCK 771, an experimental quinolone developed to overcome quinolone resistance in staphylococci and other bacteria, was determined against quinolone-susceptible and -resistant Staphylococcus aureus and S. epidermidis. WCK 771 MICs for 50 and 90% of the strains tested (MIC 50 and MIC 90 , respectively) were 0.008 and 0.015 g/ml for S. aureus (n ‫؍‬ 43) and 0.015 and 0.03 g/ml for S. epidermidis (n ‫؍‬ 44) for quinolone-susceptible isolates, compared to ciprofloxacin values of 0.12 and 0.25 g/ml and 0.25 and 0.5 g/ml, respectively. Values for levofloxacin were 0.12 and 0.25 g/ml and 0.12 and 0.25 g/ml, those for clinafloxacin were 0.015 and 0.03 g/ml and 0.015 and 0.03 g/ml, those for moxifloxacin were 0.03 and 0.06 g/ml and 0.06 and 0.12 g/ml, and those for gatifloxacin were 0.06 and 0.12 g/ml and 0.12 and 0.25 g/ml, respectively. The WCK 771 MIC 50 and MIC 90 , respectively, were 0.5 and 1 g/ml for both species of staphylococci (n ‫؍‬ 73 for S. aureus, n ‫؍‬ 70 for S. epidermidis) for isolates highly resistant to ciprofloxacin (MIC 50 and MIC 90 , >32 and >32 g/ml, respectively). Values for levofloxacin were 8 and 32 g/ml and 8 and 32 g/ml, those for clinafloxacin were 1 and 2 g/ml and 0.5 and 2 g/ml, those for moxifloxacin 4 and >4 g/ml and 4 and >4 g/ml, and those for gatifloxacin were 4 and >4 g/ml and 2 and >4 g/ml, respectively. WCK 771 and clinafloxacin demonstrated MICs of 1 g/ml against three vancomycin-intermediate strains. WCK 771 showed concentration-independent killing for up to 24 h at 2, 4, and 8 times the MICs against quinolone-resistant staphylococci and was also bactericidal after 8 h for high-density inocula (10 8 CFU/ml) of quinolone-resistant strains at 5 g/ml, whereas moxifloxacin at 7.5 g/ml was bacteriostatic. WCK 771 was not a substrate of the NorA efflux pump as evident from the similar MICs against both an efflux-positive and an efflux-negative strain. Overall, WCK 771 was the most potent quinolone tested against the staphylococci tested, regardless of quinolone susceptibility.As the prevalence of multidrug-resistant strains of Staphylococcus aureus and coagulase-negative staphylococci has increased worldwide, there has been an attendant need for effective new agents. Strains of Staphylococcus species have showed increasing resistance to ␤-lactam compounds. As early as the 1970s, 70 to 85% of S. aureus isolates were penicillin resistant (4). Previously a problem of nosocomial transmission-methicillin-resistant S. aureus (MRSA) prevalence in hospitals was estimated by the Centers for Disease Control and Prevention to be approximately 50% in 1998-it is increasingly a problem in the community (4). Methicillin resistance is often accompanied by resistance to other antimicrobial agents, including quinolones. A Mexican study of 211 strains of S. aureus (30 methicillin resistant) and 998 strains of coagulase-negative staphylococci (533 methicillin resistant) showed only 10% ciprofloxacin susceptibility among S. aureus isolates and 43% susceptibility to ciprofloxacin in the coagu...