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

BACKGROUND AND PURPOSE: JNJ-Q2, a novel broad-spectrum fluoroquinolone with anti-methicillin-resistant Staphylococcus aureus activity, was evaluated in a comprehensive set of non-clinical and clinical cardiovascular safety studies. The effect of JNJ-Q2 on different cardiovascular parameters was compared with that of moxifloxacin, sparfloxacin and ofloxacin. Through comparisons with these well-known fluoroquinolones, the importance of effects on compensatory ion channels to the cardiovascular safety of JNJ-Q2 was investigated. EXPERIMENTAL APPROACH: JNJ-Q2 and comparator fluoroquinolones were evaluated in the following models/test systems: hERG-transfected HEK293 cells sodium channel-transfected CHO cells, guinea pig right atria, arterially perfused rabbit left ventricular wedge preparations and in vivo studies in anaesthetized guinea pigs, anaesthetized and conscious telemetered dogs, and a thorough QT study in humans. KEY RESULTS: The trend for effects of JNJ-Q2 on Tp-Te, QT, QRS and PR intervals in the non-clinical models and the plateau in QTc with increasing plasma concentration in humans are consistent with offsetting sodium and calcium channel activities that were observed in the non-clinical studies. These mixed ion channel activities result in the less pronounced or comparable increase in QTc interval for JNJ-Q2 compared with moxifloxacin and sparfloxacin despite its greater in vitro inhibition of I(Kr). CONCLUSIONS AND IMPLICATIONS: Based on the non-clinical and clinical cardiovascular safety assessment, JNJ-Q2 has a safe cardiovascular profile for administration in humans with comparable or reduced potential to prolong QT intervals, compared with moxifloxacin. The results demonstrate the importance of compensatory sodium and calcium channel activity in offsetting potassium channel activity for compounds with a fluoroquinolone core.

Impact of gavage dosing procedure and gastric content on adverse respiratory effects and mortality in rat toxicity studies.

Unscheduled mortality preceded by adverse respiratory clinical signs in rats dosed by oral gavage may not only be caused by technical gavage error or systemic toxicity but may also be caused by gastro-esophageal reflux and subsequent aspiration of high concentrations of drug formulation. In a 3 week oral gavage rat toxicity study for an early drug development compound, preterminal deaths (approximately 20% of animals) at high doses (≥1000 mg kg(-1) ) and concentrations (≥60 mg ml(-1) ) were preceded by recurrent dyspnea, rales or excessive salivation, without evidence of accidental intrapulmonary gavage error. Histological evaluation revealed extensive necrosis and inflammatory changes in the upper respiratory tract, especially in the nasal turbinates and/or nasopharynx. The presence of food particles in inflammatory exudates suggested a retrograde aspiration of stomach content with test formulation via the nasopharyngeal duct into the posterior region of the nose. In contrast, no mortality or adverse respiratory effects were observed in rats following 2 week intravenous administration at comparable exposures or oral gavage administration at lower concentrations (≤20 mg ml(-1) ). In a pharmacology study, the compound caused a dose-dependent increase in gastric content (partly due to inhibition of gastric emptying), providing a pharmacological basis for the suspected gavage-mediated gastroesophageal reflux. Reducing the dose volume and dosing fasted animals substantially reduced or eliminated the respiratory effects and mortality at the high test article concentrations, demonstrating that the adverse effects are related to the gavage method.