Successful Use of Cefepime-Zidebactam (WCK 5222) as a Salvage Therapy for the Treatment of Disseminated Extensively Drug-Resistant New Delhi Metallo-β-Lactamase-Producing Pseudomonas aeruginosa Infection in an Adult Patient with Acute T-Cell Leukemia

With limited and often toxic treatment options, carbapenem-resistant Gram-negative infections are associated with significant mortality. Cefepime-zidebactam is a promising antibiotic option undergoing a phase 3 trial that has activity against diverse antibiotic-resistant mechanisms in Gram-negative pathogens due to its β-lactam enhancer mechanism, mediating multiple PBP binding. We report a case of disseminated infection caused by a New Delhi metallo-β-lactamase-producing, extensively drug-resistant Pseudomonas aeruginosa isolate in a patient with acute T-cell leukemia, successfully managed with cefepime-zidebactam as a salvage therapy.

Molecular Characterization of WCK 5222 (Cefepime/Zidebactam)-Resistant Mutants Developed from a Carbapenem-Resistant Pseudomonas aeruginosa Clinical Isolate

WCK 5222 (cefepime/zidebactam) is a β-lactam/β-lactamase inhibitor combination that is effective against a broad range of highly drug-resistant bacterial pathogens, including those producing metallo-β-lactamase. In this study, we isolated a multidrug-resistant Pseudomonas aeruginosa clinical strain that is resistant to a variety of β-lactam antibiotics and the ceftazidime-avibactam combination. A metallo-β-lactamase gene blaDIM-2 was identified on a self-transmissible megaplasmid in the strain, which confers the resistance to β-lactam antibiotics, leaving WCK 5222 potentially one of the last treatment resorts. In vitro passaging assay combined with whole-genome sequencing revealed mutations in the pbpA gene (encoding the zidebactam target protein PBP2) in the evolved resistant mutants. Among the mutations, a V516M mutation increased the bacterial virulence in a murine acute pneumonia model. Reconstitution of the mutations in the reference strain PAO1 verified their roles in the resistance to zidebactam and revealed their influences on cell morphology in the absence and presence of zidebactam. Microscale thermophoresis (MST) assays demonstrated that the mutations reduced the affinity between PBP2 and zidebactam to various extents. Overall, our results revealed that mutations in the pbpA gene might be a major cause of evolved resistance to WCK 5222 in clinical settings. IMPORTANCE Antibiotic resistance imposes a severe threat on human health. WCK 5222 is a β-lactam/β-lactamase inhibitor combination that is composed of cefepime and zidebactam. It is one of the few antibiotics in clinical trials that are effective against multidrug-resistant Pseudomonas aeruginosa, including those producing metallo-β-lactamases. Understanding the mechanisms and development of bacterial resistance to WCK 5222 may provide clues for the development of strategies to suppress resistant evolvement. In this study, we performed an in vitro passaging assay by using a multidrug-resistant P. aeruginosa clinical isolate. Our results revealed that mutations in the zidebactam target protein PBP2 play a major role in the bacterial resistance to WCK 5222. We further demonstrated that the mutations reduced the affinities between PBP2 and zidebactam and resulted in functional resistance of PBP2 to zidebactam.

In Vitro Activity of WCK 5222 (Cefepime-Zidebactam) against Worldwide Collected Gram-Negative Bacilli Not Susceptible to Carbapenems

WCK 5222 (cefepime-zidebactam, 2 g + 1g, every 8 h [q8h]) is in clinical development for the treatment of infections caused by carbapenem-resistant and multidrug-resistant (MDR) Gram-negative bacilli. We determined the in vitro susceptibility of 1,385 clinical isolates of non-carbapenem-susceptible Enterobacterales, MDR Pseudomonas aeruginosa (also non-carbapenem susceptible), Stenotrophomonas maltophilia, and Burkholderia spp. collected worldwide (49 countries) from 2014 to 2016 to cefepime-zidebactam (1:1 ratio), ceftazidime-avibactam, imipenem-relebactam, ceftolozane-tazobactam, and colistin using the CLSI broth microdilution method. Cefepime-zidebactam inhibited 98.5% of non-carbapenem-susceptible Enterobacterales (n = 1,018) at ≤8 μg/ml (provisional cefepime-zidebactam-susceptible MIC breakpoint). Against the subset of metallo-β-lactamase (MBL)-positive Enterobacterales (n = 214), cefepime-zidebactam inhibited 94.9% of isolates at ≤8 μg/ml. Further, it inhibited 99.6% of MDR P. aeruginosa (n = 262) isolates at ≤32 μg/ml (proposed cefepime-zidebactam-susceptible pharmacokinetic/pharmacodynamic MIC breakpoint), including all MBL-positive isolates (n = 94). Moreover, cefepime-zidebactam was active against the majority of isolates of Enterobacterales (≥95%) and P. aeruginosa (99%) that were not susceptible to ceftazidime-avibactam, ceftolozane-tazobactam, imipenem-relebactam, and colistin. Most isolates (99%) of S. maltophilia (n = 101; MIC₅₀, 8 μg/ml; MIC₉₀, 32 μg/ml) and Burkholderia spp. (n = 4; MIC range, 16 to 32 μg/ml) were also inhibited by cefepime-zidebactam at ≤32 μg/ml. The activity of cefepime-zidebactam against carbapenem-resistant Gram-negative bacteria is ascribed to its β-lactam enhancer mechanism of action (i.e., zidebactam binding to penicillin binding protein 2 [PBP2] and its universal stability to both serine β-lactamases and MBLs). The results from this study support the continued development of cefepime-zidebactam as a potential therapy for infections caused by Enterobacterales, P. aeruginosa, and other nonfermentative Gram-negative bacilli where resistance to marketed antimicrobial agents is a limiting factor.

Comparative Evaluation of the In Vitro Activities of WCK 5222 (Cefepime-Zidebactam) and Combination Antibiotic Therapies against Carbapenem-Resistant Pseudomonas aeruginosa

The in vitro activity of WCK 5222 (cefepime-zidebactam) was compared to that of several available combination therapies among 30 clinical carbapenem-resistant Pseudomonas aeruginosa (CRP) strains using gradient diffusion strips. The combinations included nonsusceptible β-lactams (cefepime, ceftolozane-tazobactam, and meropenem) with amikacin and fosfomycin. WCK 5222 MICs ranged from 2 to 32 mg/liter, and 97% were ≤16 mg/liter, while 105/146 (72%) combinations demonstrated inhibition below established susceptibility breakpoints. WCK 5222 monotherapy may be preferred over the combinations assessed for CRP infections.

Evaluation of the in vitro activity of WCK 5222 (cefepime/zidebactam) and currently available combination therapies against single- and double-carbapenemase producing Enterobacteriaceae: Expanding the zone of hope

Cefepime/zidebactam (WCK 5222) is a β-lactam/β-lactam enhancer antibiotic designed to retain in vitro activity against Enterobacteriaceae that simultaneously produce metallo-β-lactamase (MBL) and serine-β-lactamase (SBL). Aztreonam (ATM) plus ceftazidime/avibactam (CZA) or meropenem/vaborbactam (M/V) is an attractive option for coverage of such strains, but clinical laboratories are not equipped to distinguish which is the more potent regimen to inform treatment decisions. We evaluated Enterobacteriaceae that expressed MBL and ≥1 SBL (n=15) using gradient diffusion strip (GDS) methods to (1) determine the minimum inhibitory concentration (MIC) of WCK 5222 and (2) compare the in vitro potency of CZA+ATM vs. M/V+ATM. All isolates were non-susceptible to ATM, CZA, and M/V and were inhibited by WCK 5222 at cefepime concentrations ≥2 log₂ dilutions below the susceptible-dose dependent breakpoint of 8 mg/L (MIC_50/90, 1/2 mg/L). Activity of CZA+ATM vs. M/V+ATM was compared using the zone of hope (ZOH) product, quantitated by multiplying the length (in mm) of inhibited growth adjacent to each GDS from the point of intersection. The median (interquartile range) ZOH product for CZA+ATM and M/V+ATM was 75.4 (62.8-93.7) and 23.5 (14.1-60.4), respectively (P=0.002). In strains with one carbapenemase (the MBL), the median ZOH products were not statistically different, but in strains with an OXA-type carbapenemase (n=6), the median product for CZA+ATM and M/V+ATM was 78.1 and 20.7, respectively (P=0.004). Thus, CZA+ATM may offer enhanced coverage over M/V+ATM of Enterobacteriaceae co-expressing MBL and SBL. Further preclinical in vivo evaluations of WCK 5222 monotherapy are warranted.

The Novel β-Lactam Enhancer Zidebactam Augments the In Vivo Pharmacodynamic Activity of Cefepime in a Neutropenic Mouse Lung Acinetobacter baumannii Infection Model

WCK 5222 is a combination of cefepime and the high-affinity PBP2-binding β-lactam enhancer zidebactam. The cefepime-zidebactam combination is active against multidrug-resistant Gram-negative bacteria, including carbapenemase-expressing Acinetobacter baumannii The mechanism of action of the combination involves concurrent multiple penicillin binding protein inhibition, leading to the enhanced bactericidal action of cefepime. The aim of the present study was to assess the impact of the zidebactam-mediated enhanced in vitro bactericidal action in modulating the percentage of the time that the free drug concentration remains above the MIC (percent fT>MIC) for cefepime required for the in vivo killing of A. baumannii Cefepime and cefepime-zidebactam MICs were comparable and ranged from 2 to 16 mg/liter for the A. baumannii strains (n = 5) employed in the study. Time-kill studies revealed the improved killing of these strains by the cefepime-zidebactam combination compared to that by the constituents alone. Employing a neutropenic mouse lung infection model, exposure-response analyses for all the A. baumannii strains showed that the cefepime fT>MIC required for 1-log₁₀ kill was 38.9%. In the presence of a noneffective dose of zidebactam, the cefepime fT>MIC requirement dropped significantly to 15.5%, but it still rendered a 1-log₁₀ kill effect. Thus, zidebactam mediated the improvement in cefepime's bactericidal effect observed in time-kill studies, manifested in vivo through the lowering of cefepime's pharmacodynamic requirement. This is a first-ever study demonstrating a β-lactam enhancer role of zidebactam that helps augment the in vivo activity of cefepime by reducing the magnitude of its pharmacodynamically relevant exposures against A. baumannii.

Plasma and Intrapulmonary Concentrations of Cefepime and Zidebactam following Intravenous Administration of WCK 5222 to Healthy Adult Subjects

WCK 5222 is a combination of cefepime and the novel β-lactam enhancer zidebactam being developed for the treatment of serious Gram-negative bacterial infections. The objective of this study was to compare plasma (total), epithelial lining fluid (ELF), and alveolar macrophage (AM) concentrations of cefepime and zidebactam in healthy adult subjects. The WCK 5222 dosing regimen was 2 g cefepime/1 g zidebactam administered as a 1-h intravenous infusion every 8 h for a total of 7 doses. Subjects were assigned to one bronchoalveolar lavage (BAL) sampling time at 0.5, 1.25, 3, 6, 8, or 10 h after the seventh dose. Noncompartmental pharmacokinetic parameters were determined from serial plasma concentrations collected over 8-hour and 10-hour intervals following the first and seventh doses, respectively. Penetration ratios were calculated from the area under the plasma concentration-time curve from 0 to 8 h (AUC_0-8) for plasma, ELF, and AM using mean and median concentrations at each BAL sampling time. The plasma maximum concentration of drug (C_max) and AUC values of cefepime and zidebactam increased by 8% to 9% after the seventh versus the first dose of WCK 5222. The respective AUC_0-8 values based on mean concentrations of cefepime and zidebactam in ELF were 127.9 and 52.0 mg · h/liter, and 87.9 and 13.2 mg · h/liter in AM. The ELF to total plasma penetration ratios of cefepime and zidebactam based on mean AUC_0-8 values were 0.39 and 0.38, respectively. The AM to total plasma ratios were 0.27 and 0.10, respectively. The observed plasma, ELF, and AM concentrations of cefepime and zidebactam support studies of WCK 5222 for treatment of pneumonia caused by susceptible pathogens.