Is schedule IV suvorexant an appropriate reference drug of abuse to use in preclinical abuse liability testing in the rat?

The abuse potential of novel CNS-active drug candidates with low specificity for known receptors involved in abuse might be complex to test preclinically relative to an appropriate reference drug of abuse. Suvorexant, a Schedule IV dual orexin receptor antagonist was investigated for its potential use as a reference drug in Drug Discrimination Learning (DDL) studies. Firstly, toxicokinetic properties of suvorexant were determined in male and female rats after single oral doses of 160 and 325 mg/kg in MC and PEG400. Thereafter the subjective effects of suvorexant at 325 mg/kg versus vehicle were evaluated in a DDL paradigm and plasma exposures were measured. Mean maximum plasma exposures in male rats after a single dose of 325 mg/kg suvorexant were 2.5- (MC) to 10.5-fold (PEG400) the human exposure at supratherapeutic doses of 40 mg q.d. (Cmax:1.1 µM), and 4.9- (MC) to 20.8-fold (PEG400) the approved maximum human efficacious dose (20 mg q.d.; 0.557 µM). Training male rats at 325 mg/kg in the DDL study however did not result in discriminative stimulus generalisation versus respective vehicles. Suvorexant, a Schedule IV dual orexin receptor antagonist failed to serve as a robust reference drug of abuse in the DDL paradigm in rats despite appropriate exposures.

Postmortem redistribution of fentanyl in the rabbit blood.

Postmortem redistribution of fentanyl in the rabbit was investigated after application of the 50-µg/h Durogesic pain patch. Patches were applied for 48 hours. Two cycles of patch administration were used before characterization of the postmortem redistribution. Fentanyl showed marked redistribution into the femoral and pulmonary veins of the rabbit through 48 hours after the animals were humanely killed and the pain patches removed. The plasma concentration of 2.34 ng/mL in the femoral blood before killing the animals increased 5.6-fold by 48 hours after patch removal to 13.2 ng/mL. This postmortem concentration is approximately 3-fold the C(max) determined during antemortem pharmacokinetic analysis, 4 ng/mL, which was achieved 24 hours after the application of the second 50-µg/h Durogesic pain patch. After blood sampling for 48 hours after animal termination with patch removal compared with sampling for 48 hours from animals not terminated and with patch removal, the exposure ratios in the terminated animals were approximately 30-fold, indicating that between the postmortem redistribution of fentanyl and the cessation of hepatic clearance of fentanyl in the rabbit, the postmortem redistribution of fentanyl leads to an elevated measures of postmortem blood concentrations relative to antemortem blood concentrations.

Reprint of: Nonclinical species sensitivity to convulsions: An IQ DruSafe consortium working group initiative.

Clinical development of compounds that carry a convulsion liability is typically limited by safety margins based on the most sensitive nonclinical species. To better understand differences in sensitivity to drug-induced convulsion of commonly used preclinical species, a survey was distributed amongst pharmaceutical companies through an IQ consortium (International Consortium for Innovation and Quality in Pharmaceutical Development) resulting in convulsion-related data on 80 unique compounds from 11 companies. The lowest free drug plasma concentration at which convulsions were observed and the no observed effect level for convulsions were compared between species to determine their relative sensitivity. Additionally, data were collected on other endpoints including use of electroencephalography, premonitory signs, convulsion type, the reason why development was stopped, and the highest development phase reached. The key outcomes were: (1) the dog was most often determined to be the most sensitive species by both non-exposure and exposure-based analyses, (2) there was not a clear sensitivity ranking of other species (NHP, rat and mouse), (3) CNS symptoms were frequently present at exposures that were not associated with convulsions, but no single reliable premonitory indicator of convulsion was identified, and (4) the lack of convulsions in the compounds that were tested in humans in this dataset may suggest that convulsion liability is well mitigated via current drug development strategies.

Nonclinical species sensitivity to convulsions: An IQ DruSafe consortium working group initiative.

Clinical development of compounds that carry a convulsion liability is typically limited by safety margins based on the most sensitive nonclinical species. To better understand differences in sensitivity to drug-induced convulsion of commonly used nonclinical species, a survey was distributed amongst pharmaceutical companies through an IQ consortium (International Consortium for Innovation and Quality in Pharmaceutical Development) resulting in convulsion-related data on 80 unique compounds from 11 companies. The lowest free drug plasma concentration at which convulsions were observed and the no observed effect level for convulsions were compared between species to determine their relative sensitivity. Additionally, data were collected on other endpoints including use of electroencephalography, premonitory signs, convulsion type, the reason why development was stopped, and the highest development phase reached. The key outcomes were: (1) the dog was most often determined to be the most sensitive species by both non-exposure and exposure-based analyses, (2) there was not a clear sensitivity ranking of other species (NHP, rat and mouse), (3) CNS symptoms were frequently present at exposures that were not associated with convulsions, but no single reliable premonitory indicator of convulsion was identified, and (4) the lack of convulsions when compounds were tested in humans in this dataset may suggest that convulsion liability is well mitigated via current drug development strategies.

Role of Kv7.2/Kv7.3 and M1 muscarinic receptors in the regulation of neuronal excitability in hiPSC-derived neurons.

The Kv7 family of voltage-dependent non-inactivating potassium channels is composed of five members, of which four are expressed in the CNS. Kv7.2, 7.3 and 7.5 are responsible for the M-current, which plays a critical role in the regulation of neuronal excitability. Stimulation of M1 muscarinic acetylcholine receptor, M1 receptor, increases neuronal excitability by suppressing the M-current generated by the Kv7 channel family. The M-current modulation via M1 receptor is well-described in in vitro assays using cell lines and in native rodent tissue. However, this mechanism was not yet reported in human induced pluripotent stem cells (hiPSC) derived neurons. In the present study, we investigated the effects of both agonists and antagonists of Kv7.2/7.3 channel and M1 receptor in hiPSC derived neurons and in primary rat cortical neuronal cells. The role of M1 receptors in the modulation of neuronal excitability could be demonstrated in both rat primary and hiPSC neurons. The M1 receptors agonist, xanomeline, increased neuronal excitability in both rat cortical and the hiPSC neuronal cells. Furthermore, M1 receptor agonist-induced neuronal excitability in vitro was reduced by an agonist of Kv7.2/7.3 in both neuronal cells. These results show that hiPSC derived neurons recreate the modulation of the M-current by the muscarinic receptor in hiPSC neurons similarly to rat native neurons. Thus, hiPSC neurons could be a useful human-based cell assay for characterization of drugs that affect neuronal excitability and/or induce seizure activity by modulation of M1 receptors or inhibition of Kv7 channels.

Abuse liability assessment in preclinical drug development: predictivity of a translational approach for abuse liability testing using methylphenidate in four standardized preclinical study models.

OBJECTIVES: Preclinical abuse liability assessment of novel clinical CNS-active candidates involves several tests, addressing different aspects characteristic for abuse potential, which are considered predictive for substance abuse of these candidates, thus ensuring an appropriate translational approach. To demonstrate how such a strategy could work, a known drug of abuse, methylphenidate was evaluated in a full rodent test battery, comprising four test models, and in accordance with the requirements of the FDA, ICH and EMA guidelines. METHODS: Methylphenidate was tested orally at 2.5, 5 or 10mg/kg for its physical dependence potential in a repeated dose non-precipitated withdrawal test, for its drug profiling in a drug discrimination learning procedure (single escalating doses), and for its reinforcing properties in a conditioned place preference test (alternate dosing days) and an intravenous self-administration procedure (0.05 to 1mg/kg/IV infusion during 5 daily 1-h test sessions). The stimulant d-amphetamine served as positive control and was administered subcutaneously at 0.8mg/kg in the first three test models. In the intravenous self-administration procedure rats were habituated to intravenously self-administer d-amphetamine at 0.06mg/kg/IV infusion prior to methylphenidate substitution. RESULTS: Cessation of subchronic dosing up to 10mg/kg methylphenidate led to sustained or even exacerbated effects on locomotion and behavior, body temperature, body weight, food consumption, and alteration of the diurnal rhythm during withdrawal. Clear generalization to d-amphetamine was obtained in the drug discrimination test at 5 and 10mg/kg. Distinct reinforcing properties were present in the conditioned place preference test at 10mg/kg and in the intravenous self-administration study from 0.05mg/kg/IV infusion onwards. The maximum plasma exposure after oral administration of methylphenidate over the dose ranges tested in the present rat studies covered at least 1.9-fold to 18.9-fold the recommended human therapeutic exposure of 10ng/ml, a plasma level that is considered representative of the human efficacious methylphenidate dose. The ratio Cmax Hu/rat calculated from the intravenous self-administration data ranged from 14.9 to 576.5. Consequently the regulatory requirements, stating that preclinical drug abuse liability studies should include high doses that produce plasma levels that are multiples of the therapeutic dose were fulfilled (FDA, EMA, ICH). DISCUSSION: The presented preclinical models, implemented within a drug development environment, were considered highly predictive to assess the abuse potential of methylphenidate, and in accordance with the regulatory requirements of drug licensing authorities in terms of appropriate methods, dose selection and subsequent plasma exposure.

A high-dimensional joint model for longitudinal outcomes of different nature.

In repeated dose-toxicity studies, many outcomes are repeatedly measured on the same animal to study the toxicity of a compound of interest. This is only one example in which one is confronted with the analysis of many outcomes, possibly of a different type. Probably the most common situation is that of an amalgamation of continuous and categorical outcomes. A possible approach towards the joint analysis of two longitudinal outcomes of a different nature is the use of random-effects models (Models for Discrete Longitudinal Data. Springer Series in Statistics. Springer: New York, 2005). Although a random-effects model can easily be extended to jointly model many outcomes of a different nature, computational problems arise as the number of outcomes increases. To avoid maximization of the full likelihood expression, Fieuws and Verbeke (Biometrics 2006; 62:424-431) proposed a pairwise modeling strategy in which all possible pairs are modeled separately, using a mixed model, yielding several different estimates for the same parameters. These latter estimates are then combined into a single set of estimates. Also inference, based on pseudo-likelihood principles, is indirectly derived from the separate analyses. In this paper, we extend the approach of Fieuws and Verbeke (Biometrics 2006; 62:424-431) in two ways: the method is applied to different types of outcomes and the full pseudo-likelihood expression is maximized at once, leading directly to unique estimates as well as direct application of pseudo-likelihood inference. This is very appealing when interested in hypothesis testing. The method is applied to data from a repeated dose-toxicity study designed for the evaluation of the neurofunctional effects of a psychotrophic drug. The relative merits of both methods are discussed.