A Search to Predict Potential for Drug-Induced Cardiovascular Toxicity

A randomized open label trial of tamoxifen combined with amphotericin B and fluconazole for cryptococcal meningitis

Background: Cryptococcal meningitis is a leading cause of death in HIV-infected patients. International treatment guidelines recommend induction therapy with amphotericin B and flucytosine. This antifungal combination is most effective, but unfortunately flucytosine is expensive and unavailable where the burden of disease is greatest. Where unavailable, guidelines recommend treatment with amphotericin and fluconazole, but this is less effective, with mortality rates of 40-50%. Faster rates of clearance of yeast from cerebrospinal fluid (CSF) are associated with better outcomes - improving the potency of antifungal therapy is likely to be an effective strategy to improve survival. Tamoxifen, a selective estrogen receptor modulator used to treat breast cancer, has anti-cryptococcal activity, appearing synergistic when combined in vitro with amphotericin, and fungicidal when combined with fluconazole. It is concentrated in the brain and macrophages, off-patent, cheap and widely available. We designed a randomized trial to deliver initial efficacy and safety data for tamoxifen combined with amphotericin and fluconazole. Method: A phase II, open-label, randomized (1:1) controlled trial of tamoxifen (300mg/day) combined with amphotericin (1mg/kg/day) and fluconazole (800mg/day) for the first 2 weeks therapy for HIV infected or uninfected adults with cryptococcal meningitis. The study recruits at Cho Ray Hospital and the Hospital for Tropical Diseases, Ho Chi Minh City, Vietnam. The primary end point is Early Fungicidal Activity (EFA-the rate of yeast clearance from CSF), over the first two weeks of treatment. 50 patients will be recruited providing ≈80% and 90% power to detect a difference in the EFA of -0.11 or -0.13 log10CFU/ml/day, respectively. Discussion: The results of the study will inform the decision to proceed to a larger trial powered to mortality. The size of effect detectable has previously been associated with reduced mortality from this devastating disease. Particular side effects of interest include QT prolongation. Trial registration: Clinicaltrials.gov NCT03112031 (11/04/2017).

A Historical View and Vision into the Future of the Field of Safety Pharmacology

Professor Gerhard Zbinden recognized in the 1970s that the standards of the day for testing new candidate drugs in preclinical toxicity studies failed to identify acute pharmacodynamic adverse events that had the potential to harm participants in clinical trials. From his vision emerged the field of safety pharmacology, formally defined in the International Conference on Harmonization (ICH) S7A guidelines as "those studies that investigate the potential undesirable pharmacodynamic effects of a substance on physiological functions in relation to exposure in the therapeutic range and above." Initially, evaluations of small-molecule pharmacodynamic safety utilized efficacy models and were an ancillary responsibility of discovery scientists. However, over time, the relationship of these studies to overall safety was reflected by the regulatory agencies who, in directing the practice of safety pharmacology through guidance documents, prompted transition of responsibility to drug safety departments (e.g., toxicology). Events that have further shaped the field over the past 15 years include the ICH S7B guidance, evolution of molecular technologies leading to identification of new therapeutic targets with uncertain toxicities, introduction of data collection using more sophisticated and refined technologies, and utilization of transgenic animal models probing critical scientific questions regarding novel targets of toxicity. The collapse of the worldwide economy in the latter half of the first decade of the twenty-first century, continuing high rates of compound attrition during clinical development and post-approval and sharply increasing costs of drug development have led to significant strategy changes, contraction of the size of pharmaceutical organizations, and refocusing of therapeutic areas of investigation. With these changes has come movement away from dedicated internal safety pharmacology capability to utilization of capabilities within external contract research organizations. This movement has created the opportunity for the safety pharmacology discipline to come "full circle" and return to the drug discovery arena (target identification through clinical candidate selection) to contribute to the mitigation of the high rate of candidate drug failure through better compound selection decision making. Finally, the changing focus of science and losses in didactic training of scientists in whole animal physiology and pharmacology have revealed a serious gap in the future availability of qualified individuals to apply the principles of safety pharmacology in support of drug discovery and development. This is a significant deficiency that at present is only partially met with academic and professional society programs advancing a minimal level of training. In summary, with the exception that the future availability of suitably trained scientists is a critical need for the field that remains to be effectively addressed, the prospects for the future of safety pharmacology are hopeful and promising, and challenging for those individuals who want to assume this responsibility. What began in the early part of the new millennium as a relatively simple model of testing to assure the safety of Phase I clinical subjects and patients from acute deleterious effects on life-supporting organ systems has grown with experience and time to a science that mobilizes the principles of cellular and molecular biology and attempts to predict acute adverse events and those associated with long-term treatment. These challenges call for scientists with a broad range of in-depth scientific knowledge and an ability to adapt to a dynamic and forever changing industry. Identifying individuals who will serve today and training those who will serve in the future will fall to all of us who are committed to this important field of science.

Investigation of mechanism of drug-induced cardiac injury and torsades de pointes in cynomolgus monkeys

BACKGROUND AND PURPOSE

Drug candidates must be thoroughly investigated for their potential cardiac side effects. During the course of routine toxicological assessment, the compound RO5657, a CCR5 antagonist, was discovered to have the rare liability of inducing torsades de pointes (polymorphic ventricular arrhythmia) in normal, healthy animals. Studies were conducted to determine the molecular mechanism of this arrhythmia.

EXPERIMENTAL APPROACH

Toxicological effects of repeat dosing were assessed in naïve monkeys. Cardiovascular effects were determined in conscious telemetry-implanted monkeys (repeat dosing) and anaesthetized instrumented dogs (single doses). Mechanistic studies were performed in guinea-pig isolated hearts and in cells recombinantly expressing human cardiac channels.

KEY RESULTS

In cynomolgus monkeys, RO5657 caused a low incidence of myocardial degeneration and a greater incidence of ECG abnormalities including prolonged QT/QTc intervals, QRS complex widening and supraventricular tachycardia. In telemetry-implanted monkeys, RO5657 induced arrhythmias, including torsades de pointes and in one instance, degeneration to fatal ventricular fibrillation. RO5657 also depressed both heart rate (HR) and blood pressure (BP), with no histological evidence of myocardial degeneration. In the anaesthetized dog and guinea-pig isolated heart studies, RO5657 induced similar cardiovascular effects. RO5657 also inhibited Kv11.1 and sodium channel currents.

CONCLUSIONS AND IMPLICATIONS

The molecular mechanism of RO5657 is hypothesized to be due to inhibition of cardiac sodium and Kv11.1 potassium channels. These results indicate that RO5657 is arrhythymogenic due to decreased haemodynamic function (HR/BP), decreased conduction and inhibition of multiple cardiac channels, which precede and are probably the causative factors in the observed myocardial degeneration.