Role of mixed ion channel effects in the cardiovascular safety assessment of the novel anti-MRSA fluoroquinolone JNJ-Q2

Emerging treatment options for skin and soft tissue infections tailoring drug selection to individual patients

PURPOSE OF REVIEW

To provide a brief overview of drugs in Phase II and III of development for the treatment of acute bacterial skin and skin structure infections (ABSSSI), offering insights into potential customized treatment options.

RECENT FINDINGS

Several drugs are currently in advanced stages of evaluation for the treatment of ABSSSI, and numerous molecules are entering in the early development phases. Notably, many of these drugs exhibit unique mechanisms of action and interesting antimicrobial spectrum.

SUMMARY

Tailoring antibiotic therapy based on patient characteristics, likely pathogens, type, site and severity of ABSSSI is crucial. Given the inherent limitations of available treatments, the development of novel agents is a pivotal avenue. Such advancements hold promise for enhancing treatment efficacy and simplifying drug selection for ABSSSI in everyday clinical practice.

Innovative therapies for acute bacterial skin and skin-structure infections (ABSSSI) caused by methicillin-resistant Staphylococcus aureus: advances in phase I and II trials

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) is among the most frequent causative agents of acute bacterial skin and skin-structure infections (ABSSSI) and has been associated with increased risks of invasive disease and of treatment failure.

AREAS COVERED

In this review, we focus on those novel anti-MRSA agents currently in phase I or II of clinical development that may enrich the armamentarium against ABSSSI caused by MRSA in the future.

EXPERT OPINION

Promising agents belonging to either old or novel antibiotic classes are currently in early phases of clinical development and may become available in the future for the effective treatment of ABSSSI caused by MRSA. In particular, the future availability of agents belonging to novel classes will be important for guaranteeing an effective treatment and for allowing outpatient treatment/early discharge, with a consequent reduced impact on healthcare resources. However, this does not mean that we can relax our efforts directed toward improving the responsible use of already available agents. Indeed, preserving their activity in the long term is crucial for optimizing the use of healthcare resources.

Drug-induced Inhibition and Trafficking Disruption of ion Channels: Pathogenesis of QT Abnormalities and Drug-induced Fatal Arrhythmias

Risk of severe and fatal ventricular arrhythmias, presenting as Torsade de Pointes (TdP), is increased in congenital and acquired forms of long QT syndromes (LQTS). Drug-induced inhibition of K+ currents, IKs, IKr, IK1, and/or Ito, delay repolarization, prolong QT, and increase the risk of TdP. Drug-induced interference with IKr is the most common cause of acquired LQTS/TdP. Multiple drugs bind to KNCH2-hERG-K+ channels affecting IKr, including antiarrythmics, antibiotics, antivirals, azole-antifungals, antimalarials, anticancer, antiemetics, prokinetics, antipsychotics, and antidepressants. Azithromycin has been recently added to this list. In addition to direct channel inhibition, some drugs interfere with the traffic of channels from the endoplasmic reticulum to the cell membrane, decreasing mature channel membrane density; e.g., pentamidine, geldalamicin, arsenic trioxide, digoxin, and probucol. Other drugs, such as ketoconazole, fluoxetine, norfluoxetine, citalopram, escitalopram, donepezil, tamoxifen, endoxifen, atazanavir, and roxitromycin, induce both direct channel inhibition and impaired channel trafficking. Although many drugs prolong the QT interval, TdP is a rare event. The following conditions increase the risk of drug-induced TdP: a) Disease states/electrolyte levels (heart failure, structural cardiac disease, bradycardia, hypokalemia); b) Pharmacogenomic variables (presence of congenital LQTS, subclinical ion-channel mutations, history of or having a relative with history of drug-induced long QT/TdP); c) Pharmacodynamic and kinetic factors (high doses, women, elderly, metabolism inhibitors, combining two or more QT prolonging drugs, drugs that prolong the QT and increase QT dispersion, and drugs with multiple actions on ion channels). Because most of these conditions are preventable, careful evaluation of risk factors and increased knowledge of drug use associated with repolarization abnormalities are strongly recommended.

Pharmacokinetic-pharmacodynamic modelling of drug-induced QTc interval prolongation in man: prediction from in vitro human ether-à-go-go-related gene binding and functional inhibition assays and conscious dog studies

BACKGROUND AND PURPOSE

Functional measures of human ether-à-go-go-related gene (hERG; Kv 11.1) channel inhibition have been prioritized as an in vitro screening tool for candidate molecules. However, it is unclear how these results can be translated to humans. Here, we explore how data on drug binding and functional inhibition in vitro relate to QT prolongation in vivo. Using cisapride, sotalol and moxifloxacin as paradigm compounds, we assessed the relationship between drug concentrations, binding, functional measures and in vivo effects in preclinical species and humans.

EXPERIMENTAL APPROACH

Pharmacokinetic-pharmacodynamic modelling was used to characterize the drug effects in hERG functional patch clamp, hERG radio-labelled dofetilide displacement experiments and QT interval in conscious dogs. Data were analysed in parallel to identify potential correlations between pharmacological activity in vitro and in vivo.

KEY RESULTS

An Emax model could not be used due to large variability in the functional patch clamp assay. Dofetilide displacement revealed that binding curves are unrelated to the in vivo potency estimates for QTc prolongation in dogs and humans. Mean in vitro potency estimates ranged from 99.9 nM for cisapride to 1030 μM for moxifloxacin.

CONCLUSIONS AND IMPLICATIONS

The lack of standardized protocols for in vitro assays leads to significant differences in experimental conditions, making the assessment of in vitro-in vivo correlations unreliable. Identification of an accurate safety window during the screening of candidate molecules requires a quantitative framework that disentangles system- from drug-specific properties under physiological conditions, enabling translation of the results to humans. Similar considerations will be relevant for the comprehensive in vitro pro-arrhythmia assay initiative.

Focus on JNJ-Q2, a novel fluoroquinolone, for the management of community-acquired bacterial pneumonia and acute bacterial skin and skin structure infections

JNJ-Q2 is a novel, fifth-generation fluoroquinolone that has excellent in vitro and in vivo activity against a variety of Gram-positive and Gram-negative organisms. In vitro studies indicate that JNJ-Q2 has potent activity against pathogens responsible for acute bacterial skin and skin structure infections (ABSSSI) and community-acquired bacterial pneumonia (CABP), such as Staphylococcus aureus and Streptococcus pneumoniae. JNJ-Q2 also has been shown to have a higher barrier to resistance compared to other agents in the class and it remains highly active against drug-resistant organisms, including methicillin-resistant S. aureus, ciprofloxacin-resistant methicillin-resistant S. aureus, and drug-resistant S. pneumoniae. In two Phase II studies, the efficacy of JNJ-Q2 was comparable to linezolid for ABSSSI and moxifloxacin for CABP. Furthermore, JNJ-Q2 was well tolerated, with adverse event rates similar to or less than other fluoroquinolones. With an expanded spectrum of activity and low potential for resistance, JNJ-Q2 shows promise as an effective treatment option for ABSSSI and CABP. Considering its early stage of development, the definitive role of JNJ-Q2 against these infections and its safety profile will be determined in future Phase III studies.

PK/PD Modelling of the QT Interval: a Step Towards Defining the Translational Relationship Between In Vitro, Awake Beagle Dogs, and Humans

Inhibiting the human ether-a-go-go-related gene (hERG)-encoded potassium ion channel is positively correlated with QT-interval prolongation in vivo, which is considered a risk factor for the occurrence of Torsades de Pointes (TdP). A pharmacokinetic/pharmacodynamic model was developed for four compounds that reached the clinic, to relate drug-induced QT-interval change in awake dogs and humans and to derive a translational scaling factor a 1. Overall, dogs were more sensitive than humans to QT-interval change, an a 1 of 1.5 was found, and a 10% current inhibition in vitro produced a higher percent QT-interval change in dogs as compared to humans. The QT-interval changes in dogs were predictive for humans. In vitro and in vivo information could reliably describe the effects in humans. Robust translational knowledge is likely to reduce the need for expensive thorough QT studies; therefore, expanding this work to more compounds is recommended.

Can an early phase clinical pharmacology study replace a thorough QT study? Experience with a novel H3-receptor antagonist/inverse agonist

OBJECTIVE

The objective of the present study was to compare the effects of pitolisant on QTcF interval in a single ascending dose (SAD) study and a thorough QT (TQT) study.

METHODS

The SAD study at three dose levels of pitolisant enrolled 24 males and the TQT study at two dose levels 25 males. Both studies intensively monitored ECGs and pitolisant exposure. Effect on QTcF interval was analysed by Intersection Union Test (IUT) and by exposure-response (ER) analysis. Results from the two studies were compared.

RESULTS

In both studies, moxifloxacin effect established assay sensitivity. IUT analysis revealed comparable pitolisant-induced maximum mean (90 % confidence interval (CI)) placebo-corrected increase from baseline (ΔΔQTcF) in both the studies, being 13.3 (8.1; 18.5) ms at 200-mg and 9.9 (4.7; 15.1) ms at 240-mg doses in SAD study and 5.27 (2.35; 8.20) ms at 120-mg dose in TQT study. ER analysis revealed that ER slopes in SAD and TQT studies were comparable and significantly positive (0.031 vs 0.027 ms/ng/mL, respectively). At geometric mean concentrations, bootstrap predicted ΔΔQTcF (90 % CI) were 9.23 (4.68; 14.4) ms at 279 ng/mL (240-mg dose) in the SAD study and 4.97 (3.42; 8.19) ms at 156 ng/mL (120-mg dose) in the TQT study.

CONCLUSION

Pitolisant lacked an effect of regulatory concern on QTc interval in both the studies, however analysed, suggesting that the results from the SAD study could have mitigated the need for a TQT study. Our findings add to the growing evidence that intensive ECG monitoring in early phase clinical studies can replace a TQT study.

Clinical ECG Assessment

With the adoption of the ICH E14 guidance, the thorough QT/QTc (TQT) study has become the focus of clinical assessment of an NCE's effects on ECG parameters. The TQT study is used as a guide to the liability of a drug to cause proarrhythmias on the basis of delayed cardiac repolarization. Around 300 TQT studies have been performed since 2005 and through interactions between sponsors and regulators, especially FDA's Interdisciplinary Review Team (IRT) for QT studies. These studies can today be performed more effectively and with great confidence in the generated data. This chapter will discuss technical features and the design and analysis of TQT studies, how assay sensitivity is demonstrated, and examples from recently conducted studies. ECG assessment for drugs that cannot be safely given to healthy volunteers is also addressed, and examples from studies in cancer patients and in healthy volunteers with tyrosine kinase inhibitors are discussed. The TQT study is resource intensive and designed to solely evaluate whether an NCE prolongs the QTc interval. If data with similar confidence can be generated from other studies that are routinely performed as part of the clinical development, this would represent a more optimal use of human resources. Methods and approaches to increase the confidence in ECG data derived from "early QT assessment" in single-ascending/multiple-ascending dose studies are therefore discussed, and a path toward replacing the TQT study using these approaches will be outlined.

Renaissance of antibiotics against difficult infections: Focus on oritavancin and new ketolides and quinolones

Lipoglycopeptide, ketolide, and quinolone antibiotics are currently in clinical development, with specific advantages over available molecules within their respective classes. The lipoglycopeptide oritavancin is bactericidal against MRSA, vancomycin-resistant enterococci, and multiresistant Streptococcus pneumoniae, and proved effective and safe for the treatment of acute bacterial skin and skin structure infection (ABSSSI) upon administration of a single 1200 mg dose (two completed phase III trials). The ketolide solithromycin (two phase III studies recruiting for community-acquired pneumonia) shows a profile of activity similar to that of telithromycin, but in vitro data suggest a lower risk of hepatotoxicity, visual disturbance, and aggravation of myasthenia gravis due to reduced affinity for nicotinic receptors. Among quinolones, finafloxacin and delafloxacin share the unique property of an improved activity in acidic environments (found in many infection sites). Finafloxacin (phase II completed; activity profile similar to that of ciprofloxacin) is evaluated for complicated urinary tract and Helicobacter pylori infections. The other quinolones (directed towards Gram-positive pathogens) show improved activity on MRSA and multiresistant S. pneumoniae compared to current molecules. They are in clinical evaluation for ABSSSI (avarofloxacin (phase II completed), nemonoxacin and delafloxacin (ongoing phase III)), respiratory tract infections (zabofloxacin and nemonoxacin (ongoing phase III)), or gonorrhea (delafloxacin).