Clinical Implications and Translation of an Off-Target Pharmacology Profiling Hit: Adenosine Uptake Inhibition In Vitro

Preclinical mitigation of 5-HT2B agonism-related cardiac valvulopathy revisited

Cardiac valvulopathy (Cardiac Valve Disease; CVD) associated with off-target activation of the 5-hydroxytryptamine (5-HT) 2B receptor has been well recognized, but is still poorly predicted during drug development. The regulatory guidance proposes the use of 5-HT2B binding data (i.e., Ki values) and free maximum therapeutic exposure (Cmax) to calculate safety margins as a threshold of detection (>10) for eliminating the risk of drug-induced cardiac valvulopathy. In this paper, we provide additional recommendations for preclinical prediction of CVD risk based on clinical pharmacodynamic and pharmacokinetic data obtained from drugs with or without 5-HT2B receptor activation. Our investigations showed that 5-HT2B agonist affinity of molecules tested in an in vitro 5-HT2B cell-based functional assay, placed in perspective to their sustained plasma exposure (AUCs) and not to their peak plasma exposure, Cmax (i.e., maximum therapeutic exposure) provide a solid basis for interpreting 5-HT2B data, for calculating safety margins and then, accurately differentiate drugs associated with a clinical risk of CVD from those which are not (despite having some agonist 5-HT2B activity). In addition, we discuss the risk of multi-organ fibrosis linked to 5-HT2B receptor activation, often underestimated, however well reported in FAERS for 5-HT2B agonists. We believe that our recommendations have the potential to mitigate the risk for the clinical development of CVD and fibrosis.

Migraine signaling pathways: purine metabolites that regulate migraine and predispose migraineurs to headache

Migraine is a debilitating disorder that afflicts over 1 billion people worldwide, involving attacks that result in a throbbing and pulsating headache. Migraine is thought to be a neurovascular event associated with vasoconstriction, vasodilation, and neuronal activation. Understanding signaling in migraine pathology is central to the development of therapeutics for migraine prophylaxis and for mitigation of migraine in the prodrome phase before pain sets in. The fact that both vasoactivity and neural sensitization are involved in migraine indicates that agonists which promote these phenomena may very well be involved in migraine pathology. One such group of agonists is the purines, in particular, adenosine phosphates and their metabolites. This manuscript explores what is known about the relationship between these metabolites and migraine pathology and explores the potential for such relationships through their known signaling pathways. Reported receptor involvement in vasoaction and nociception.

Zebrafish toxicological screening could aid Leishmaniosis drug discovery

BACKGROUND

Recently a screen from a library of 1.8 million compounds identified in vitro a potent activity of the 2-aminobenzimidazoles series against Leishmania infantum, the etiological agent responsible by over 20.000 deaths each year. Several analogs were synthesized and in vitro tested through an optimization program, leading to a promising 2-aminobenzimidazoles derived compound (2amnbzl-d) that was progressed to in vivo mice studies. However, the not expected toxic effects prevented its progression to more advanced preclinical and clinical phases of drug development. Due to limitations of cell models in detecting whole organism complex interactions, 90% of the compounds submitted to pre-clinical tests are reproved. The use of Zebrafish embryo models could improve this rate, saving mammals, time and costs in the development of new drugs. To test this hypothesis, we compared 2amnbzl-d with two compounds with already established safety profile: carbamazepine and benznidazole, using an embryo Zebrafish platform based on acute toxicity, hepatotoxicity, neurotoxicity and cardiotoxicity assays (Pltf-AcHpNrCd).

RESULTS

Tests were performed blindly, and the results demonstrated the presence of lethal and teratogenic effects (CL50%: 14.8 µM; EC50%: 8.6 µM), hepatotoxic in concentrations above 7.5 µM and neurotoxic in embryos exposed to 15 µM of 2amnbzl-d. Nevertheless, benznidazole exposition showed no toxicity and only the 100 µM of carbamazepine induced a bradycardia.

CONCLUSIONS

Results using Pltf-AcHpNrCd with zebrafish reproduced that found in the toxicological tests with mammals to a portion of the costs and time of experimentation.

Safety pharmacology during the COVID pandemic

This editorial summarizes the content of the current themed issue of J Pharmacol Toxicol Methods derived from the 2020 Annual Safety Pharmacology Society (SPS) meeting that was held virtually September 14–17, 2020 due to the ongoing COVID-19 global pandemic. A selection of articles arising from the virtual meeting is summarized. Like previous years they continue to reflect current areas of innovation in SP including new methodologies to predict human safety, best practices for IKr current measurement, and best practice considerations for the conduct of in vivo nonclinical QT studies. The meeting included scientific content from 94 abstracts (reproduced in the current volume of J Pharmacol Toxicol Methods). This continued innovation reflects a rubric in SP that identifies problems, seeks solutions and, importantly, validates the solutions.

Evaluation of moxifloxacin in canine and non-human primate telemetry assays: Comparison of QTc interval prolongation by timepoint and concentration-QTc analysis

The in vivo correct QT (QTc) assay is used by the pharmaceutical industry to characterize the potential for delayed ventricular repolarization and is a core safety assay mentioned in International Conference on Harmonization (ICH) S7B guideline. The typical telemetry study involves a dose‐response analysis of QTc intervals over time using a crossover (CO) design. This method has proven utility but does not include direct integration of pharmacokinetic (PK) data. An alternative approach has been validated and is used routinely in the clinical setting that pairs pharmacodynamic (PD) responses with PK exposure (e.g., concentration‐QTc (C‐QTc) analysis. The goal of our paper was to compare the QTc sensitivity of two experimental approaches in the conscious dog and non‐human primate (NHP) QTc assays. For timepoint analysis, a conventional design using eight animals (8 × 4 CO) to detect moxifloxacin‐induced QTc prolongation was compared to a PK/PD design in a subset (N = 4) of the same animals. The findings demonstrate that both approaches are equally sensitive in detecting threshold QTc prolongation on the order of 10 ms. Both QTc models demonstrated linearity in the QTc prolongation response to moxifloxacin dose escalation (6 to 46 ms). Further, comparison with human QTc findings with moxifloxacin showed agreement and consistent translation across the three species: C‐QTc slope values were 0.7‐ (dog) and 1.2‐ (NHP) fold of the composite human value. In conclusion, our data show that dog and NHP QTc telemetry with an integrated PK arm (C‐QTc) has the potential to supplement clinical evaluation and improve integrated QTc risk assessment.

Adenosine-Related Mechanisms in Non-Adenosine Receptor Drugs

Many ligands directly target adenosine receptors (ARs). Here we review the effects of noncanonical AR drugs on adenosinergic signaling. Non-AR mechanisms include raising adenosine levels by inhibiting adenosine transport (e.g., ticagrelor, ethanol, and cannabidiol), affecting intracellular metabolic pathways (e.g., methotrexate, nicotinamide riboside, salicylate, and 5-aminoimidazole-4-carboxamide riboside), or undetermined means (e.g., acupuncture). However, other compounds bind ARs in addition to their canonical ‘on-target’ activity (e.g., mefloquine). The strength of experimental support for an adenosine-related role in a drug’s effects varies widely. AR knockout mice are the ‘gold standard’ method for investigating an AR role, but few drugs have been tested on these mice. Given the interest in AR modulation for treatment of cancer, CNS, immune, metabolic, cardiovascular, and musculoskeletal conditions, it is informative to consider AR and non-AR adenosinergic effects of approved drugs and conventional treatments.