Advances in contezolid: novel oxazolidinone antibacterial in Gram-positive treatment

PURPOSE

The principal objective of this project was to review and thoroughly examine the chemical characteristics, pharmacological activity, and quantification methods associated with contezolid.

METHODS

The article was based on published and ongoing preclinical and clinical studies on the application of contezolid. These studies included experiments on the physicochemical properties of contezolid, in vitro antimicrobial research, in vivo antimicrobial research, and clinical trials in various phases. There were no date restrictions on these studies.

RESULTS

In June 2021, contezolid was approved for treating complicated skin and soft tissue infections. The structural modification of contezolid has resulted in better efficacy compared to linezolid. It inhibits bacterial growth by preventing the production of the functional 70S initiation complex required to translate bacterial proteins. The current evidence has indicated a substantial decline in myelosuppression and monoamine oxidase inhibition without impairing its antibacterial properties. Contezolid was found to have a more significant safety profile and to be metabolised by flavin monooxygenase 5, reducing the risk of harmful effects due to drug-drug interactions. Adjusting doses is unnecessary for patients with mild to moderate renal or hepatic insufficiency.

CONCLUSION

As an oral oxazolidinone antimicrobial agent, contezolid is effective against multi-drug resistant Gram-positive bacteria. The introduction of contezolid provided a new clinical option.

Contezolid-Containing Regimen Successfully Treated Multiple Drug Resistance Mycobacterium Abscessus Complex Infection of Skin: A Case Report and Literature Review

Background

In recent decades, there has been a substantial surge in the incidence of non-tuberculous Mycobacteria (NTM) infections. However, the diagnosis and management of NTM globally present significant challenges, particularly in cases involving Mycobacterium abscessus complex (MABC) infection where effective therapeutic options are limited.

Case Presentation

We reported a 38-year-old female patient who was infected with MABC of skin due to "beauty needle" at a beauty salon, with mass on both cheeks, accompanied by redness, and pain, and some of them was ulcered and effused. Puncture pumping pus from bilateral cheek mass for many times, rinsed with "metronidazole", and oral "cephalosporin" treatment did not work. Therefore, she came to our hospital. MABC was detected in abscess paracentesis pus by nucleic acid mass spectrometry, and was proved by the cultured result of the pus. Thus, the patient was diagnosed as skin MABC infection, and anti-NTM treatment was taken. However, adverse reactions such as tinnitus, hepatotoxicity and neurovirulence occurred during the initial treatment. After adjusting to the contezolid-containing regimen, these adverse reactions improved. After nearly 6 months of treatment, the cheek mass was gradually reduced and the skin ruptures were gradually healed. Follow-up for 10 months showed that the patient's facial symptoms were significantly improved, and no drug-related adverse reactions happened.

Conclusion

This was the first successful case of multiple drug resistance MABC infection of skin treated with contezolid-containing antibiotic management strategies, which exhibited remarkable efficacy and good safety in this intractable disease.

Tuberculosis patients with special clinical conditions treated with contezolid: three case reports and a literature review

Background

Contezolid is a novel oxazolidinone antibacterial agent, but there have been no reports of any pertinent clinical studies for the treatment of tuberculosis (TB). This was the first report of three TB patients who were successfully treated with contezolid.

Case presentation

Case 1 was TB complicated by myelosuppression syndrome. Case 2 was drug-resistant TB complicated by cirrhosis and anemia. Case 3 was drug-resistant TB complicated by liver transplantation that developed severe anemia after linezolid treatment. Following contezolid therapy, the three patients' symptoms improved significantly, and no adverse reactions were observed. The chest computed tomography (CT) examination also indicated that the therapeutic effect of this anti-TB regimen was as expected.

Conclusion

Contezolid showed good efficacy and fewer side effects in the treatment of TB. It may be a promising TB treatment.

Staph wars: the antibiotic pipeline strikes back

Antibiotic chemotherapy is widely regarded as one of the most significant medical advancements in history. However, the continued misuse of antibiotics has contributed to the rapid rise of antimicrobial resistance (AMR) globally. Staphylococcus aureus, a major human pathogen, has become synonymous with multidrug resistance and is a leading antimicrobial-resistant pathogen causing significant morbidity and mortality worldwide. This review focuses on (1) the targets of current anti-staphylococcal antibiotics and the specific mechanisms that confirm resistance; (2) an in-depth analysis of recently licensed antibiotics approved for the treatment of S. aureus infections; and (3) an examination of the pre-clinical pipeline of anti-staphylococcal compounds. In addition, we examine the molecular mechanism of action of novel antimicrobials and derivatives of existing classes of antibiotics, collate data on the emergence of resistance to new compounds and provide an overview of key data from clinical trials evaluating anti-staphylococcal compounds. We present several successful cases in the development of alternative forms of existing antibiotics that have activity against multidrug-resistant S. aureus. Pre-clinical antimicrobials show promise, but more focus and funding are required to develop novel classes of compounds that can curtail the spread of and sustainably control antimicrobial-resistant S. aureus infections.

Analytical Methodologies for the Estimation of Oxazolidinone Antibiotics as Key Members of anti-MRSA Arsenal: A Decade in Review

Gram-positive bacterial infections are among the most serious diseases related with high mortality rates and huge healthcare costs especially with the rise of antibiotic-resistant strains that limits treatment options. Thus, development of new antibiotics combating these multi-drug resistant bacteria is crucial. Oxazolidinone antibiotics are the only totally synthetic group of antibiotics that showed activity against multi-drug resistant Gram positive bacteria including MRSA because of their unique mechanism of action in targeting protein synthesis. This group include approved marketed members (tedizolid, linezolid and contezolid) or those under development (delpazlolid, radezolid and sutezolid). Due to the significant impact of this class, larger number of analytical methods were required to meet the needs of both clinical and industrial studies. Analyzing these drugs either alone or with other antimicrobial agents commonly used in ICU, in the presence of pharmaceutical or endogenous biological interferences, or in the presence of matrix impurities as metabolites and degradation products poses a big analytical challenge. This review highlights current analytical approaches published in the last decade (2012-2022) that dealt with the determination of these drugs in different matrices and discusses their advantages and disadvantages. Various techniques have been described for their determination including chromatographic, spectroscopic, capillary electrophoretic and electroanalytical methods. The review comprises six sections (one for each drug) with their related tables that depict critical figures of merit and some experimental conditions for the reviewed methods. Furthermore, future perspectives about the analytical methodologies that can be developed in the near future for determination of these drugs are suggested.

Dose adjustment not required for contezolid in patients with moderate hepatic impairment based on pharmacokinetic/pharmacodynamic analysis

Objective: Contezolid is an oxazolidinone antimicrobial agent newly approved for treatment of Gram-positive bacterial infections. It is primarily metabolized by the liver. This study aimed to assess whether it is required to adjust the dose of contezolid in patients with moderate hepatic impairment for clinicians to use the drug more rationally.

Methods: A single-center, open-label, parallel-group study was conducted to compare the pharmacokinetic (PK) parameters of contezolid and its metabolite M2 between the patients with moderate hepatic impairment and healthy controls with normal liver function after oral administration of 800 mg contezolid tablets. Monte Carlo simulation was performed to calculate the probability of target attainment (PTA) and cumulative fraction of response (CFR) of contezolid based on the PK and pharmacodynamic data.

Results: Oral treatment with 800 mg contezolid tablets was safe and well tolerated in both the patients with moderate hepatic impairment and healthy controls. Moderate hepatic impairment did not result in substantial difference in the area under the concentration-time curve from 0 to 24 h (AUC0–24h, 106.79 vs. 97.07 h μg/mL) of contezolid even though lower maximum concentration (Cmax, 19.03 vs. 34.49 μg/mL) compared with healthy controls. The mean cumulative amount excreted in urine from 0 to 48 h (Ae0–48h) and renal clearance (CLR) of contezolid did not show significant difference between the two groups. Moderate hepatic impairment was associated with lower Cmax, slightly lower AUC and Ae0–48h of M2 compared to the healthy controls. fAUC/MIC was the best PK/PD index to predict the clinical efficacy of contezolid. Monte Carlo simulation results indicated that at the proposed fAUC/MIC target value of 2.3, the dosing regimen of oral contezolid 800 mg q12h could achieve satisfactory PTA and CFR (both >90%) for the target pathogen (methicillin-resistant S. aureus, MIC ≤4 mg/L) in patients with moderate hepatic impairment.

Conclusion: Our preliminary data suggest that dose adjustment is not required for contezolid in patients with moderate hepatic impairment.

Clinical Trial Registration:https://chinadrugtrials.org.cn, identifier: CTR20171377.

Sequential Therapy of Linezolid and Contezolid to Treat Vancomycin-Resistant Enterococcus faecium Pneumonia in a Centenarian Patient: Case Report

Enterococcus faecium (E. faecium) is one of the core components of enterococci and causes serious illnesses in the elderly and immunocompromised patients. Due to its adaptive traits and antibiotic resistance, E. faecium has evolved as a worldwide hospital-associated pathogen, especially vancomsycin-resistant Enterococcus faecium (VREfm). Pneumonia caused by VREfm is quite rare in clinical settings, and optimal treatment has not yet been determined. Here, we present a case of nosocomial VREfm pneumonia with lung cavitation following adenovirus infection, which was successfully treated with linezolid and contezolid.

Contezolid, a novel oxazolidinone antibiotic, may improve drug-related thrombocytopenia in clinical antibacterial treatment

One of the major limitations in the clinical use of existing oxazolidinone antibiotics is their characteristic adverse reactions, in particular thrombocytopenia. In anti-infective treatment, if patients are suspected of having drug-induced thrombocytopenia, the first step is to immediately discontinue the offending drug. Even in patients with severe infections, the antibacterial drug may need to be changed or the antibacterial treatment may need to be discontinued because thrombocytopenia may have a more serious clinical prognosis. In addition, if the patient needs to continue antibacterial treatment after discharge, the lack of conditions for monitoring platelet levels may also pose hidden dangers to the patient. Contezolid is an orally administered oxazolidinone antibacterial agent approved by the National Medical Products Administration of China in 2021. We found that contezolid may have an improved safety profile with a significantly reduced potential for myelosuppression based on the results of our observational clinical study. In this article, we review the advantages of contezolid as a new oxazolidinone antibiotic and describe three typical clinical cases of patients who experienced drug-induced thrombocytopenia after using linezolid. The platelet levels of these different patients were all significantly improved to varying degrees after initiation of contezolid treatment.

Drug Degradation Caused by mce3R Mutations Confers Contezolid (MRX-I) Resistance in Mycobacterium tuberculosis

Contezolid (MRX-I), a safer antibiotic of the oxazolidinone class, is a promising new antibiotic with potent activity against Mycobacterium tuberculosis (MTB) both in vitro and in vivo. To identify resistance mechanisms of contezolid in MTB, we isolated several in vitro spontaneous contezolid-resistant MTB mutants, which exhibited 16-fold increases in the MIC of contezolid compared with the parent strain but were still unexpectedly susceptible to linezolid. Whole-genome sequencing revealed that most of the contezolid-resistant mutants bore mutations in the mce3R gene, which encodes a transcriptional repressor. The mutations in mce3R led to markedly increased expression of a monooxygenase encoding gene Rv1936. We then characterized Rv1936 as a putative flavin-dependent monooxygenase that catalyzes the degradation of contezolid into its inactive 2,3-dihydropyridin-4-one (DHPO) ring-opened metabolites, thereby conferring drug resistance. While contezolid is an attractive drug candidate with potent antimycobacterial activity and low toxicity, the occurrence of mutations in Mce3R should be considered when designing combination therapy using contezolid for treating tuberculosis.

Clinical Pharmacology and Utility of Contezolid in Chinese Patients with Complicated Skin and Soft-Tissue Infections

This study aimed to build a population pharmacokinetic (PopPK) model for contezolid tablet (MRX-I) in healthy subjects and adults with complicated skin and soft-tissue infections (cSSTIs) to further evaluate the efficacy and safety of contezolid and recommend the optimal dosing regimen based on pharmacokinetic/pharmacodynamic (PK/PD) analysis. PopPK analysis was performed using a nonlinear mixed-effects model (NONMEM) to examine the effects of age, body weight, sex, liver and renal functions, albumin, food, dosage strength, and subject type on the PK parameters of contezolid. PK/PD analysis was combined with the MIC of contezolid, clinical/microbiological efficacy, and nonclinical study data. Adverse events (AEs) and study drug-related AEs reported were summarized to examine the relationship between contezolid exposure level and safety measures. A two-compartment model was built. An exponential model was used to describe the interindividual variation. A proportional model was used to describe the intraindividual variation of PK parameters. Good clinical and microbiological efficacy are expected for the infections caused by S. aureus when contezolid is administered at 600 mg or 800 mg every 12 h (q12h). The area under the concentration-time curve from 0 to 24 h at steady state and maximum concentration of drug in serum at steady state of contezolid did not show significant association with the incidence of any AE. The dosing regimen of contezolid at 800 mg q12h administered postprandially for 7 to 14 days is expected to achieve satisfactory clinical and microbiological efficacy in cSSTIs, which is slightly better than that of 600 mg contezolid. This administration has been added to the prescribing information of contezolid tablets.

Roles of selected non-P450 human oxidoreductase enzymes in protective and toxic effects of chemicals: review and compilation of reactions

This is an overview of the metabolic reactions of drugs, natural products, physiological compounds, and other (general) chemicals catalyzed by flavin monooxygenase (FMO), monoamine oxidase (MAO), NAD(P)H quinone oxidoreductase (NQO), and molybdenum hydroxylase enzymes (aldehyde oxidase (AOX) and xanthine oxidoreductase (XOR)), including roles as substrates, inducers, and inhibitors of the enzymes. The metabolism and bioactivation of selected examples of each group (i.e., drugs, “general chemicals,” natural products, and physiological compounds) are discussed. We identified a higher fraction of bioactivation reactions for FMO enzymes compared to other enzymes, predominately involving drugs and general chemicals. With MAO enzymes, physiological compounds predominate as substrates, and some products lead to unwanted side effects or illness. AOX and XOR enzymes are molybdenum hydroxylases that catalyze the oxidation of various heteroaromatic rings and aldehydes and the reduction of a number of different functional groups. While neither of these two enzymes contributes substantially to the metabolism of currently marketed drugs, AOX has become a frequently encountered route of metabolism among drug discovery programs in the past 10–15 years. XOR has even less of a role in the metabolism of clinical drugs and preclinical drug candidates than AOX, likely due to narrower substrate specificity.

Discovery and Development of Antibacterial Agents: Fortuitous and Designed

Today, antibacterial drug resistance has turned into a significant public health issue. Repeated intake, suboptimal and/or unnecessary use of antibiotics, and, additionally, the transfer of resistance genes are the critical elements that make microorganisms resistant to conventional antibiotics. A substantial number of antibacterials that were successfully utilized earlier for prophylaxis and therapeutic purposes have been rendered inadequate due to this phenomenon. Therefore, the exploration of new molecules has become a continuous endeavour. Many such molecules are at various stages of investigation. A surprisingly high number of new molecules are currently in the stage of phase 3 clinical trials. A few new agents have been commercialized in the last decade. These include solithromycin, plazomicin, lefamulin, omadacycline, eravacycline, delafloxacin, zabofloxacin, finafloxacin, nemonoxacin, gepotidacin, zoliflodacin, cefiderocol, BAL30072, avycaz, zerbaxa, vabomere, relebactam, tedizolid, cadazolid, sutezolid, triclosan and afabiacin. This article aims to review the investigational and recently approved antibacterials with a focus on their structure, mechanisms of action/resistance, and spectrum of activity. Delving deep, their success or otherwise in various phases of clinical trials is also discussed while attributing the same to various causal factors.

Regulatory utility of pharmacometrics in the development and evaluation of antimicrobial agents and its recent progress in China

Pharmacometrics is an emerging science that interprets drug, disease, and trial information in a mathematical fashion to inform and facilitate efficient drug development and/or regulatory decisions. Pharmacometrics study is increasingly adopted in the regulatory review of new antimicrobial agents. We summarized the 31 antimicrobial agents approved by the US Food and Drug Administration (FDA) and the 26 antimicrobial agents approved by European Medicines Agency (EMA) from January 2001 to May 2019. We also reviewed recent examples of utilizing pharmacometrics to support antimicrobial agent's registration in China, including modeling and simulation methods, effects of internal/external factors on pharmacokinetic (PK) parameters, safety and efficacy evaluation in terms of exposure-response analysis, refinement of the wording of product labeling and package leaflet, and possible postmarketing clinical trial. Ongoing communication among regulator, academia, and industry regarding pharmacometrics is encouraged to streamline and facilitate the development of new antimicrobial agents. The industry can maximize its benefit in drug development through continued pharmacometrics education/training.

Non-cytochrome P450 enzymes involved in the oxidative metabolism of xenobiotics: Focus on the regulation of gene expression and enzyme activity

Oxidative metabolism is one of the major biotransformation reactions that regulates the exposure of xenobiotics and their metabolites in the circulatory system and local tissues and organs, and influences their efficacy and toxicity. Although cytochrome (CY)P450s play critical roles in the oxidative reaction, extensive CYP450-independent oxidative metabolism also occurs in some xenobiotics, such as aldehyde oxidase, xanthine oxidoreductase, flavin-containing monooxygenase, monoamine oxidase, alcohol dehydrogenase, or aldehyde dehydrogenase-dependent oxidative metabolism. Drugs form a large portion of xenobiotics and are the primary target of this review. The common reaction mechanisms and roles of non-CYP450 enzymes in metabolism, factors affecting the expression and activity of non-CYP450 enzymes in terms of inhibition, induction, regulation, and species differences in pharmaceutical research and development have been summarized. These non-CYP450 enzymes are detoxifying enzymes, although sometimes they mediate severe toxicity. Synthetic or natural chemicals serve as inhibitors for these non-CYP450 enzymes. However, pharmacokinetic-based drug interactions through these inhibitors have rarely been reported in vivo. Although multiple mechanisms participate in the basal expression and regulation of non-CYP450 enzymes, only a limited number of inducers upregulate their expression. Therefore, these enzymes are considered non-inducible or less inducible. Overall, this review focuses on the potential xenobiotic factors that contribute to variations in gene expression levels and the activities of non-CYP450 enzymes.

In vitro Activity of Contezolid Against Methicillin-Resistant Staphylococcus aureus, Vancomycin-Resistant Enterococcus, and Strains With Linezolid Resistance Genes From China

Contezolid is a novel oxazolidinone, which exhibits potent activity against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), and penicillin-resistant Streptococcus pneumoniae (PRSP). In this study, the in vitro activity of contezolid was compared with linezolid (LZD), tigecycline (TGC), teicoplanin (TEC), vancomycin (VA), daptomycin (DAP), and florfenicol (FFC) against MRSA and VRE strains isolated from China. Contezolid revealed considerable activity against MRSA and VRE isolates with MIC₉₀ values of 0.5 and 1.0 μg/mL, respectively. For VRE strains with different resistance genotypes, including vanA- and vanM-type strains, contezolid did not exhibit significantly differential antibacterial activity. Furthermore, the antimicrobial activity of contezolid is similar to or slightly better than that of linezolid against MRSA and VRE strains. Subsequently, the activity of contezolid was tested against strains carrying linezolid resistance genes, including Staphylococcus capitis carrying cfr gene and Enterococcus faecalis carrying optrA gene. The results showed that contezolid exhibited similar antimicrobial efficacy to linezolid against strains with linezolid resistance genes. In general, contezolid may have potential benefits to treat the infections caused by MRSA and VRE pathogens.

Pharmacokinetics and Disposition of Contezolid in Humans-Resolution of a Disproportionate Human Metabolite for Clinical Development

Contezolid (MRX-I), a novel oxazolidinone antibiotic, was recently approved for the treatment of serious Gram-positive infections. The pharmacokinetics and disposition of [¹⁴C]contezolid were investigated in a single-dose human mass balance study. Cross-species comparison of plasma exposure for contezolid and metabolites was performed, and the safety of the disproportionate metabolite in human was evaluated with additional nonclinical studies. After an oral administration of 99.1 μCi/602 mg dose of [¹⁴C]contezolid, approximately 91.5% of the radioactivity was recovered in 0-168 h postdose, mainly in urine and followed by feces. The principal metabolic pathway of contezolid in human comprised an oxidative ring opening of 2,3-dihydropyridin-4-one fragment into polar metabolites MRX445-1 and MRX459, with recovery of approximately 48% and 15% of the dose, respectively, in urine and feces. Contezolid, MRX445-1, and MRX459 accounted for 68.0%, 19.5%, and 4.84% of the plasma exposure of the total radioactivity, respectively. Metabolites MRX445-1 and MRX459 were observed in disproportionately higher amounts in human plasma as compared to that rat or dog, the rodent and nonrodent species used for the general nonclinical safety assessment of this molecule. This discrepancy was resolved with additional nonclinical studies, wherein the primary metabolite, MRX445-1, was further characterized. The no observed adverse effect level (NOAEL) of MRX445-1 was determined as 360 mg/kg/day in 14-day repeat-dose test in pregnant and non-pregnant SD rats. Furthermore, MRX445-1 exhibited no antibacterial activity in vitro. Thus, MRX445-1 is not expected to exert clinically relevant pharmacology and toxicity.

Contezolid: First Approval

Contezolid 康替唑胺 (Youxitai 优喜泰^®), an orally administered oxazolidinone antibacterial agent, is being developed by Shanghai MicuRx Pharmaceutical Co., Ltd. for the treatment of multidrug-resistant (MDR) Gram-positive bacterial infections, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci. In June 2021, it was approved by the National Medical Products Administration of China for the treatment of complicated skin and soft tissue infections (cSSTI), including, but not limited to, methicillin-susceptible S. aureus, MRSA, Streptococcus pyogenes and Streptococcus agalactiae. The recommended dosage of contezolid is 800 mg (i.e. two 400 mg tablets) every 12 h for 7–14 days. Contezolid is also undergoing clinical development for acute bacterial skin and skin structure infections (ABSSSI) in the USA, and for diabetic foot infections. This article summarizes the milestones in the development of contezolid leading to this first approval for the treatment of cSSTI.

Metabolic Study of Stable Isotope Labeled Indolinone Derivative in Hepatocyte Cell by UPLC/Q TOF MS

The aggregation process of α-synuclein (α-syn) is substantial in the pathogenesis of Parkinson's disease. Indolinone derivatives are inhibitors of α-syn aggregates and can be used as PET-based radiotracers for imaging α-syn fibrils. However, no investigations on the metabolism of indolinone derivatives have been reported until now. In the present research, a ¹³C and ¹⁵N isotope labeling strategy was developed to synthesize compound [¹³C₂,¹⁵N]-(Z)-1-(4-aminobenzyl)-3-((E)-(3-phenyl)allylidene)indolin-2-one (M0'), which was then used in a study of metabolism in hepatocytes. The metabolites were characterized using accurate mass and characteristic ion measurements. In the metabolic system, compound M0' was the main component (accounting for 97.5% of compound-related components) after incubation in hepatocytes for 3 h, which indicated that compound M0' possessed great metabolic stability. Seven metabolites have been successfully verified by UPLC/Q TOF MS in metabolic studies, including hydroxyl M0' (M1'), hydroxyl and methylated M0' (M2'), N-acetylated M0' (M3'), sulfate of hydroxyl M0' (M4'), the glucose conjugate of M0' (M5'), glucuronide conjugate of M0' (M6'), and glucuronide conjugate of hydroxyl M0' (M7'). The study on metabolism provides the important information to develop effective α-syn aggregate inhibitors and new PET-tracer-related indolinone derivatives.

Role of human flavin-containing monooxygenase (FMO) 5 in the metabolism of nabumetone: Baeyer-Villiger oxidation in the activation of the intermediate metabolite, 3-hydroxy nabumetone, to the active metabolite, 6-methoxy-2-naphthylacetic acid in vitro

Nabumetone (NAB) is a non-steroidal anti-inflammatory drug used clinically, and its biotransformation includes the major active metabolite 6-methoxy-2-naphthylacetic acid (6-MNA). One of the key intermediates between NAB and 6-MNA may be 3-hydroxy nabumetone (3-OH-NAB). The aim of the present study was to investigate the role of flavin-containing monooxygenase (FMO) isoform 5 in the formation of 6-MNA from 3-OH-NAB. To elucidate the biotransformation of 3-OH-NAB to 6-MNA, an authentic standard of 3-OH-NAB was synthesised and used as a substrate in an incubation with human liver samples or recombinant enzymes. The formation of 3-OH-NAB was observed after the incubation of NAB with various cytochrome P450 (CYP) isoforms. However, 6-MNA itself was rarely detected from NAB and 3-OH-NAB. Further experiments revealed a 6-MNA peak derived from 3-OH-NAB in human hepatocytes. 6-MNA was also detected in the extract obtained from 3-OH-NAB by a combined incubation of recombinant human FMO5 and human liver S9. We herein demonstrated that the reaction involves carbon-carbon cleavage catalyzed by the Baeyer-Villiger oxidation (BVO) of a carbonyl compound, the BVO substrate, such as a ketol, by FMO5. Further in vitro inhibition experiments showed that multiple non-CYP enzymes are involved in the formation of 6-MNA from 3-OH-NAB.

A review of recent advances in anti-tubercular drug development

Tuberculosis is a global threat but in particular affects people from developing countries. It is thought that nearly a third of the population of the world live with its causative bacteria in a dormant form. Although tuberculosis is a curable disease, the chances of cure become slim as the disease becomes multidrug-resistant and the situation gets even worse as the disease becomes extensively drug-resistant. After approximately 5 decades without any new TB drug in the pipeline, there has been some good news in the recent years with the discovery of new drugs such as bedaquiline and delamanid as well as the discovery of new classes of anti-tubercular drugs. Some old drugs such as clofazimine, linezolid and many others which were not previously indicated for tuberculosis have been also repurposed for tuberculosis and they are performing well.

Evaluation of the Effect of Contezolid (MRX-I) on the Corrected QT Interval in a Randomized, Double-Blind, Placebo- and Positive-Controlled Crossover Study in Healthy Chinese Volunteers

Contezolid (MRX-I), a new oxazolidinone, is an antibiotic in development for treating complicated skin and soft tissue infections caused by resistant Gram-positive bacteria. This was a thorough QT study conducted in 52 healthy subjects who were administered oral contezolid at a therapeutic (800 mg) dose, a supratherapeutic (1,600 mg) dose, placebo, and oral moxifloxacin at 400 mg in four separate treatment periods. The pharmacokinetic profile of contezolid was also evaluated. Time point analysis indicated that the upper bounds of the two-sided 90% confidence interval (CI) for placebo-corrected change-from-baseline QTc (ΔΔQTc) were <10 ms for the contezolid therapeutic dose at each time point. The upper bound of the 90% CI for ΔΔQTc was slightly more than 10 ms with the contezolid supratherapeutic dose at 3 and 4 h postdose, and the prolongation effect on the QT/QTc interval was less than that of the positive control, moxifloxacin, at 400 mg. At 3 and 4 h after the moxifloxacin dose, the moxifloxacin group met the assay sensitivity criteria outlined in ICH Guidance E14 by having a lower confidence bound of ≥5 ms. The results of a linear exposure-response model which were similar to that of a time point analysis demonstrated a slightly positive relationship between contezolid plasma levels and ΔQTcF interval with a slope of 0.227 ms per mg/liter (90% CI, 0.188 to 0.266). In summary, contezolid did not prolong the QT interval at a therapeutic dose and may have a slight effect on QT interval prolongation at a supratherapeutic dose.

Transformation of Prostaglandin D2 to 11-Dehydro Thromboxane B2 by Baeyer-Villiger Oxidation

Prostaglandin D₂ is one of five chief prostanoids formed in the cyclooxygenase pathway of arachidonic acid oxidation. Except for a single oxygen atom, PGD₂ is structurally identical to 11-dehydro thromboxane B₂ (11d-TxB₂ ), a urinary metabolite of the pro-aggregatory platelet activator, thromboxane A₂ . The close structural relationship suggested that one might be transformed to the other. Accordingly, we tested whether the cyclopentanone of PGD₂ can be expanded to the δ-lactone of 11d-TxB₂ in a Baeyer-Villiger oxidation. Oxidation of PGD₂ with two standard oxidants showed that 11d-TxB₂ was formed only with H₂ O₂ but not with peracetic acid. Byproducts of the H₂ O₂ -mediated oxidation were hydroperoxide derivatives and isomers of PGD₂ . Chemical oxidation of PGD₂ to 11d-TxB₂ may be a model for an equivalent enzymatic transformation, suggesting a possible link in the metabolism of PGD₂ and thromboxane A₂ .

Current trends in drug metabolism and pharmacokinetics

Pharmacokinetics (PK) is the study of the absorption, distribution, metabolism, and excretion (ADME) processes of a drug. Understanding PK properties is essential for drug development and precision medication. In this review we provided an overview of recent research on PK with focus on the following aspects: (1) an update on drug-metabolizing enzymes and transporters in the determination of PK, as well as advances in xenobiotic receptors and noncoding RNAs (ncRNAs) in the modulation of PK, providing new understanding of the transcriptional and posttranscriptional regulatory mechanisms that result in inter-individual variations in pharmacotherapy; (2) current status and trends in assessing drug-drug interactions, especially interactions between drugs and herbs, between drugs and therapeutic biologics, and microbiota-mediated interactions; (3) advances in understanding the effects of diseases on PK, particularly changes in metabolizing enzymes and transporters with disease progression; (4) trends in mathematical modeling including physiologically-based PK modeling and novel animal models such as CRISPR/Cas9-based animal models for DMPK studies; (5) emerging non-classical xenobiotic metabolic pathways and the involvement of novel metabolic enzymes, especially non-P450s. Existing challenges and perspectives on future directions are discussed, and may stimulate the development of new research models, technologies, and strategies towards the development of better drugs and improved clinical practice.

Metabolism of Strained Rings: Glutathione S-transferase-Catalyzed Formation of a Glutathione-Conjugated Spiro-azetidine without Prior Bioactivation

AZD1979 [(3-(4-(2-oxa-6-azaspiro[3.3]heptan-6-ylmethyl)phenoxy)azetidin-1-yl)(5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl)methanone] is a melanin-concentrating hormone receptor 1 antagonist designed for the treatment of obesity. In this study, metabolite profiles of AZD1979 in human hepatocytes revealed a series of glutathione-related metabolites, including the glutathionyl, cysteinyl, cysteinylglycinyl, and mercapturic acid conjugates. The formation of these metabolites was not inhibited by coincubation with the cytochrome P450 (P450) inhibitor 1-aminobenzotriazole. In efforts to identify the mechanistic features of this pathway, investigations were performed to characterize the structure of the glutathionyl conjugate M12 of AZD1979 and to identify the enzyme system catalyzing its formation. Studies with various human liver subcellular fractions established that the formation of M12 was NAD(P)H-independent and proceeded in cytosol and S9 fractions but not in microsomal or mitochondrial fractions. The formation of M12 was inhibited by ethacrynic acid, an inhibitor of glutathione S-transferases (GSTs). Several human recombinant GSTs, including GSTA1, A2-2, M1a, M2-2, T1-1, and GST from human placenta, were incubated with AZD1979. All GSTs tested catalyzed the formation of M12, with GSTA2-2 being the most efficient. Metabolite M12 was purified from rat liver S9 incubations and its structure elucidated by NMR. These results establish that M12 is the product of the GST-catalyzed glutathione attack on the carbon atom α to the nitrogen atom of the strained spiro-azetidinyl moiety to give, after ring opening, the corresponding amino-thioether conjugate product, a direct conjugation pathway that occurs without the prior substrate bioactivation by P450. SIGNIFICANCE STATEMENT: The investigated compound, AZD1979, contains a 6-substituted-2-oxa-6-azaspiro[3.3]heptanyl derivative that is an example of strained heterocycles, including spiro-fused ring systems, that are widely used in synthetic organic chemistry. An unusual azetidinyl ring-opening reaction involving a nucleophilic attack by glutathione, which does not involve prior cytochrome P450-catalyzed bioactivation of the substrate and which is catalyzed by glutathione transferases, is reported. We propose a mechanism involving the protonated cyclic aminyl intermediate that undergoes nucleophilic attack by glutathione thiolate anion in this reaction, catalyzed by glutathione transferases.

MetScore: Site of Metabolism Prediction Beyond Cytochrome P450 Enzymes

The metabolism of xenobiotics by humans and other organisms is a complex process involving numerous enzymes that catalyze phase I (functionalization) and phase II (conjugation) reactions. Herein we introduce MetScore, a machine learning model that can predict both phase I and phase II reaction sites of drugs in a single prediction run. We developed cheminformatics workflows to filter and process reactions to obtain suitable phase I and phase II data sets for model training. Employing a recently developed molecular representation based on quantum chemical partial charges, we constructed random forest machine learning models for phase I and phase II reactions. After combining these models with our previous cytochrome P450 model and calibrating the combination against Bayer in-house data, we obtained the MetScore model that shows good performance, with Matthews correlation coefficients of 0.61 and 0.76 for diverse phase I and phase II reaction types, respectively. We validated its potential applicability to lead optimization campaigns for a new and independent data set compiled from recent publications. The results of this study demonstrate the usefulness of quantum-chemistry-derived molecular representations for reactivity prediction.

Formation and Cleavage of C-C Bonds by Enzymatic Oxidation-Reduction Reactions

Many oxidation-reduction (redox) enzymes, particularly oxygenases, have roles in reactions that make and break C-C bonds. The list includes cytochrome P450 and other heme-based monooxygenases, heme-based dioxygenases, nonheme iron mono- and dioxygenases, flavoproteins, radical S-adenosylmethionine enzymes, copper enzymes, and peroxidases. Reactions involve steroids, intermediary metabolism, secondary natural products, drugs, and industrial and agricultural chemicals. Many C-C bonds are formed via either (i) coupling of diradicals or (ii) generation of unstable products that rearrange. C-C cleavage reactions involve several themes: (i) rearrangement of unstable oxidized products produced by the enzymes, (ii) oxidation and collapse of radicals or cations via rearrangement, (iii) oxygenation to yield products that are readily hydrolyzed by other enzymes, and (iv) activation of O₂ in systems in which the binding of a substrate facilitates O₂ activation. Many of the enzymes involve metals, but of these, iron is clearly predominant.

Functional assessment of rat pulmonary flavin-containing monooxygenase activity

The expression of flavin-containing monooxygenase (FMO) varies extensively between human and commonly used preclinical species such as rat and mouse. The aim of this study was to investigate the pulmonary FMO activity in rat using benzydamine. Furthermore, the contribution of rat lung to the clearance of benzydamine was investigated using an in vivo pulmonary extraction model. Benzydamine N-oxygenation was observed in lung microsomes and lung slices. Thermal inactivation of FMO and CYP inhibition suggested that rat pulmonary N-oxygenation is predominantly FMO mediated while any contribution from CYPs is negligible. The predicted lung clearance (CL_lung) estimated from microsomes and slices was 16 ± 0.6 and 2.1 ± 0.3 mL/min/kg, respectively. The results from in vivo pulmonary extraction indicated no pulmonary extraction following intravenous and intra-arterial dosing to rats. Interestingly, the predicted CL_lung using rat lung microsomes corresponded to approximately 35% of rat CL_liver suggesting that the lung makes a smaller contribution to the whole body clearance of benzydamine. Although benzydamine clearance in rat appears to be predominantly mediated by hepatic metabolism, the data suggest that the lung may also make a smaller contribution to its whole body clearance.

Baeyer-Villiger Monooxygenase FMO5 as Entry Point in Drug Metabolism

Flavin-containing monooxygenases (FMOs) are emerging as effective players in oxidative drug metabolism. Until recently, the functions of the five human FMO isoforms were mostly linked to their capability of oxygenating molecules containing soft N- and S-nucleophiles. However, the human FMO isoform 5 was recently shown to feature an atypical activity as Baeyer-Villiger monooxygenase. With the aim of evaluating such an alternative entry point in the metabolism of active pharmaceutical ingredients, we selected and tested drug molecules bearing a carbonyl group on an aliphatic chain. Nabumetone and pentoxifylline, two widely used pharmaceuticals, were thereby demonstrated to be efficiently oxidized in vitro by FMO5 to the corresponding acetate esters with high selectivity. The proposed pathways explain the formation of a predominant plasma metabolite of pentoxifylline as well as the crucial transformation of the pro-drug nabumetone into the pharmacologically active compound. Using the recombinant enzyme, the ester derivatives of both drugs were obtained in milligram amounts, purified, and fully characterized. This protocol can potentially be extended to other FMO5 candidate substrates as it represents an effective and robust bench-ready platform applicable to API screening and metabolite synthesis.

Identification of Flavin-Containing Monooxygenase 5 (FMO5) as a Regulator of Glucose Homeostasis and a Potential Sensor of Gut Bacteria

We have previously identified flavin-containing monooxygenase 5 (FMO5) as a regulator of metabolic aging. The aim of the present study was to investigate the role of FMO5 in glucose homeostasis and the impact of diet and gut flora on the phenotype of mice in which the Fmo5 gene has been disrupted (Fmo5^−/− mice). In comparison with wild-type (WT) counterparts, Fmo5^−/− mice are resistant to age-related changes in glucose homeostasis and maintain the higher glucose tolerance and insulin sensitivity characteristic of young animals. When fed a high-fat diet, they are protected against weight gain and reduction of insulin sensitivity. The phenotype of Fmo5^−/− mice is independent of diet and the gut microbiome and is determined solely by the host genotype. Fmo5^−/− mice have metabolic characteristics similar to those of germ-free mice, indicating that FMO5 plays a role in sensing or responding to gut bacteria. In WT mice, FMO5 is present in the mucosal epithelium of the gastrointestinal tract where it is induced in response to a high-fat diet. In comparison with WT mice, Fmo5^−/− mice have fewer colonic goblet cells, and they differ in the production of the colonic hormone resistin-like molecule β. Fmo5^−/− mice have lower concentrations of tumor necrosis factor α in plasma and of complement component 3 in epididymal white adipose tissue, indicative of improved inflammatory tone. Our results implicate FMO5 as a regulator of body weight and of glucose disposal and insulin sensitivity and, thus, identify FMO5 as a potential novel therapeutic target for obesity and insulin resistance.

Drug metabolism by flavin-containing monooxygenases of human and mouse

INTRODUCTION

Flavin-containing monooxygenases (FMOs) play an important role in drug metabolism. Areas covered: We focus on the role of FMOs in the metabolism of drugs in human and mouse. We describe FMO genes and proteins of human and mouse; the catalytic mechanism of FMOs and their significance for drug metabolism; differences between FMOs and CYPs; factors contributing to potential underestimation of the contribution of FMOs to drug metabolism; the developmental and tissue-specific expression of FMO genes and differences between human and mouse; and factors that induce or inhibit FMOs. We discuss the contribution of FMOs of human and mouse to the metabolism of drugs and how genetic variation of FMOs affects drug metabolism. Finally, we discuss the utility of animal models for FMO-mediated drug metabolism in humans. Expert opinion: The contribution of FMOs to drug metabolism may be underestimated. As FMOs are not readily induced or inhibited and their reactions are generally detoxifications, the design of drugs that are metabolized predominantly by FMOs offers clinical advantages. Fmo1^(-/-),Fmo2^(-/-),Fmo4^(-/-) mice provide a good animal model for FMO-mediated drug metabolism in humans. Identification of roles for FMO1 and FMO5 in endogenous metabolism has implications for drug therapy and initiates an exciting area of research.

C. elegans flavin-containing monooxygenase-4 is essential for osmoregulation in hypotonic stress

Studies in Caenorhabditis elegans have revealed osmoregulatory systems engaged when worms experience hypertonic conditions, but less is known about measures employed when faced with hypotonic stress. Inactivation of fmo-4, which encodes flavin-containing monooxygenase-4, results in dramatic hypoosmotic hypersensitivity; worms are unable to prevent overwhelming water influx and swell rapidly, finally rupturing due to high internal hydrostatic pressure. fmo-4 is expressed prominently in hypodermis, duct and pore cells but is excluded from the excretory cell. Thus, FMO-4 plays a crucial osmoregulatory role by promoting clearance of excess water that enters during hypotonicity, perhaps by synthesizing an osmolyte that acts to establish an osmotic gradient from excretory cell to duct and pore cells. C. elegans FMO-4 contains a C-terminal extension conserved in all nematode FMO-4s. The coincidently numbered human FMO4 also contains an extended C-terminus with features similar to those of FMO-4. Although these shared sequence characteristics suggest potential orthology, human FMO4 was unable to rescue the fmo-4 osmoregulatory defect. Intriguingly, however, mammalian FMO4 is expressed predominantly in the kidney - an appropriate site if it too is, or once was, involved in osmoregulation.

Going Beyond Common Drug Metabolizing Enzymes: Case Studies of Biotransformation Involving Aldehyde Oxidase, γ-Glutamyl Transpeptidase, Cathepsin B, Flavin-Containing Monooxygenase, and ADP-Ribosyltransferase

The significant roles that cytochrome P450 (P450) and UDP-glucuronosyl transferase (UGT) enzymes play in drug discovery cannot be ignored, and these enzyme systems are commonly examined during drug optimization using liver microsomes or hepatocytes. At the same time, other drug-metabolizing enzymes have a role in the metabolism of drugs and can lead to challenges in drug optimization that could be mitigated if the contributions of these enzymes were better understood. We present examples (mostly from Genentech) of five different non-P450 and non-UGT enzymes that contribute to the metabolic clearance or bioactivation of drugs and drug candidates. Aldehyde oxidase mediates a unique amide hydrolysis of GDC-0834 (N-[3-[6-[4-[(2R)-1,4-dimethyl-3-oxopiperazin-2-yl]anilino]-4-methyl-5-oxopyrazin-2-yl]-2-methylphenyl]-4,5,6,7-tetrahydro-1-benzothiophene-2-carboxamide), leading to high clearance of the drug. Likewise, the rodent-specific ribose conjugation by ADP-ribosyltransferase leads to high clearance of an interleukin-2-inducible T-cell kinase inhibitor. Metabolic reactions by flavin-containing monooxygenases (FMO) are easily mistaken for P450-mediated metabolism such as oxidative defluorination of 4-fluoro-N-methylaniline by FMO. Gamma-glutamyl transpeptidase is involved in the initial hydrolysis of glutathione metabolites, leading to formation of proximate toxins and nephrotoxicity, as is observed with cisplatin in the clinic, or renal toxicity, as is observed with efavirenz in rodents. Finally, cathepsin B is a lysosomal enzyme that is highly expressed in human tumors and has been targeted to release potent cytotoxins, as in the case of brentuximab vedotin. These examples of non-P450- and non-UGT-mediated metabolism show that a more complete understanding of drug metabolizing enzymes allows for better insight into the fate of drugs and improved design strategies of molecules in drug discovery.

Biocatalytic Characterization of Human FMO5: Unearthing Baeyer-Villiger Reactions in Humans

Flavin-containing mono-oxygenases are known as potent drug-metabolizing enzymes, providing complementary functions to the well-investigated cytochrome P450 mono-oxygenases. While human FMO isoforms are typically involved in the oxidation of soft nucleophiles, the biocatalytic activity of human FMO5 (along its physiological role) has long remained unexplored. In this study, we demonstrate the atypical in vitro activity of human FMO5 as a Baeyer-Villiger mono-oxygenase on a broad range of substrates, revealing the first example to date of a human protein catalyzing such reactions. The isolated and purified protein was active on diverse carbonyl compounds, whereas soft nucleophiles were mostly non- or poorly reactive. The absence of the typical characteristic sequence motifs sets human FMO5 apart from all characterized Baeyer-Villiger mono-oxygenases so far. These findings open new perspectives in human oxidative metabolism.

Investigational drugs to treat methicillin-resistant Staphylococcus aureus

INTRODUCTION

Staphylococcus aureus remains one of the leading causes of morbidity and mortality worldwide. This is to a large extent due to antibiotic-resistant strains, in particular methicillin-resistant S. aureus (MRSA). While the toll of invasive MRSA infections appears to decrease in U.S. hospitals, the rate of community-associated MRSA infections remains constant and there is a surge of MRSA in many other countries, a situation that calls for continuing if not increased efforts to find novel strategies to combat MRSA infections.

AREAS COVERED

This review provides an overview of current investigational drugs and therapeutic antibodies against S. aureus in early clinical development (up to phase II clinical development). It includes a short description of the mechanism of action and a presentation of microbiological and clinical data.

EXPERT OPINION

Increased recent antibiotic development efforts and results from pathogenesis research have led to several new antibiotics and therapies, such as anti-virulence drugs, as well as a more informed selection of targets for vaccination efforts against MRSA. This developing portfolio of novel anti-staphylococcal drugs will hopefully provide us with additional and more efficient ways to combat MRSA infections in the near future and prevent us from running out of treatment options, even if new resistances arise.

Carbon-carbon bond cleavage and formation reactions in drug metabolism and the role of metabolic enzymes

Elimination of xenobiotics from the human body is often facilitated by a transformation to highly water soluble and more ionizable molecules. In general, oxidation-reduction, hydrolysis, and conjugation reactions are common biotransformation reactions that are catalyzed by various metabolic enzymes including cytochrome P450s (CYPs), non-CYPs, and conjugative enzymes. Although carbon-carbon (C-C) bond formation and cleavage reactions are known to exist in plant secondary metabolism, these reactions are relatively rare in mammalian metabolism and are considered exceptions. However, various reactions such as demethylation, dealkylation, dearylation, reduction of alkyl chain, ring expansion, ring contraction, oxidative elimination of a nitrile through C-C bond cleavage, and dimerization, and glucuronidation through C-C bond formation have been reported for drug molecules. Carbon-carbon bond cleavage reactions for drug molecules are primarily catalyzed by CYP enzymes, dimerization is mediated by peroxidases, and C-glucuronidation is catalyzed by UGT1A9. This review provides an overview of C-C bond cleavage and formation reactions in drug metabolism and the metabolic enzymes associated with these reactions.