Geert Jan Groeneveld

The Use of Biomarkers in Human Pharmacology (Phase I) Studies

The development of a new medicine is a risky and costly undertaking that requires careful planning. This planning is largely applied to the operational aspects of the development and less so to the scientific objectives and methodology. The drugs that will be developed in the future will increasingly affect pathophysiological pathways that have been largely unexplored. Such drug prototypes cannot be immediately introduced in large clinical trials. The effects of the drug on normal physiology, pathophysiology, and eventually the desired clinical effects will need to be evaluated in a structured approach, based on the definition of drug development as providing answers to important questions by appropriate clinical studies. This review describes the selection process for biomarkers that are fit-for-purpose for the stage of drug development in which they are used. This structured and practical approach is widely applicable and particularly useful for the early stages of innovative drug development.

Fentanyl Utility Function: A Risk-Benefit Composite of Pain Relief and Breathing Responses

Introduction:Integrating opioid risk and benefit into a single function may give a useful single measure of the opioid’s positive and negative effects. An explorative study on the effects of fentanyl on antinociception and respiratory depression was performed to construct fentanyl risk–benefit (utility) functions. Methods:Twelve volunteers received a 3.5-&mgr;g/kg fentanyl intravenous injection on 2 separate study days. On one occasion, ventilation at a clamped increased carbon dioxide concentration was measured and on another the pain tolerance to electrical stimulation. In both sessions, arterial plasma samples were obtained. The data were analyzed with a population pharmacokinetic–pharmacodynamic model. A simulation study was performed, using the model parameter estimates and their variances, in which simulated subjects received 3.5 &mgr;g/kg of fentanyl. The resultant distributions were used to calculate the utility functions, defined as the probability of at least 50% analgesia (an increase in pain tolerance by ≥50%) minus the probability of at least 50% respiratory depression (a reduction in ventilation by ≥50%). Utility functions were constructed in concentration and time domains. Results:Fentanyl produced significant respiratory depression and analgesia. The pharmacokinetic and pharmacodynamic models adequately described the data. The constructed utility functions were negative at effect-site concentrations of greater than 0.5 ng/ml in the first 90 min after the 3.5 &mgr;g/kg bolus infusion. Conclusions:Utility functions based on fentanyl’s experimental effects on respiration and pain relief were successfully constructed. These functions are useful in multiple effect comparisons among experimental drugs. Further studies are required to assess whether this risk–benefit analysis is valuable in clinical practice.

Respiratory Effects of the Nociceptin/Orphanin FQ Peptide and Opioid Receptor Agonist, Cebranopadol, in Healthy Human Volunteers

Background: Cebranopadol is a novel strong analgesic that coactivates the nociceptin/orphanin FQ receptor and classical opioid receptors. There are indications that activation of the nociceptin/orphanin FQ receptor is related to ceiling in respiratory depression. In this phase 1 clinical trial, we performed a pharmacokinetic-pharmacodynamic study to quantify cebranopadol’s respiratory effects. Methods: Twelve healthy male volunteers received 600 &mgr;g oral cebranopadol as a single dose. The following main endpoints were obtained at regular time intervals for 10 to 11 h after drug intake: ventilation at an elevated clamped end-tidal pressure of carbon dioxide, pain threshold and tolerance to a transcutaneous electrical stimulus train, and plasma cebranopadol concentrations. The data were analyzed using sigmoid Emax (respiration) and power (antinociception) models. Results: Cebranopadol displayed typical opioid-like effects including miosis, analgesia, and respiratory depression. The blood-effect-site equilibration half-life for respiratory depression and analgesia was 1.2 ± 0.4 h (median ± standard error of the estimate) and 8.1 ± 2.5 h, respectively. The effect-site concentration causing 50% respiratory depression was 62 ± 4 pg/ml; the effect-site concentration causing 25% increase in currents to obtain pain threshold and tolerance was 97 ± 29 pg/ml. The model estimate for minimum ventilation was greater than zero at 4.9 ± 0.7 l/min (95% CI, 3.5 to 6.6 l/min). Conclusions: At the dose tested, cebranopadol produced respiratory depression with an estimate for minimum ventilation greater than 0 l/min. This is a major advantage over full &mgr;-opioid receptor agonists that will produce apnea at high concentrations. Further clinical studies are needed to assess whether such behavior persists at higher doses.

A literature review on the pharmacological sensitivity of human evoked hyperalgesia pain models

AIMS Human evoked pain models can be used to determine the efficacy of new and existing analgesics and to aid in the identification of new targets. Aspects of neuropathic pain can be simulated by inducing hyperalgesia resulting from provoked sensitization. The present literature review aimed to provide insight into the sensitivity of different hyperalgesia and allodynia models of pharmacological treatment. METHODS A literature search was performed to identify randomized, double-blind, placebo-controlled studies that included human hyperalgesia pain models and investigated the pharmacodynamic effects of different classes of drugs. RESULTS Three hyperalgesia models [ultraviolet B (UVB) irradiation, capsaicin and thermode burn] have been used extensively. Assessment of hyperalgesia/allodynia and pharmacological effect are measured using challenge tests, which generally comprise thermal (heat/cold) or mechanical stimulation (pin-prick, stroking or impact). The UVB model was sensitive to the antihyperalgesic effects of nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids. The capsaicin model was partially sensitive to opioids. The burn model did not detect any antihyperalgesic effects when NSAIDs or local anaesthetics were administered but responded to the effects of N-methyl D-aspartate (NMDA) receptor antagonists by moderately reducing mechanical hyperalgesia. CONCLUSIONS Based on pharmacological sensitivity, the UVB model adequately reflects inflammatory pain and was sensitive to NSAIDs and opioids. Findings from the capsaicin and burn models raised questions about the translatability of these models to the treatment of neuropathic pain. There is a need for a reproducible and predictive model of neuropathic pain, either in healthy subjects or in patients.

The use of a battery of pain models to detect analgesic properties of compounds : a two-part four-way crossover study

Aim The aim was to investigate the ability of a battery of pain models to detect analgesic properties of commonly used analgesics in healthy subjects. Methods The battery consisted of tests eliciting electrical, mechanical and thermal (contact heat and cold pressor)‐pain and included a UVB model, the thermal grill illusion and a paradigm of conditioned pain modulation. Subjects were administered fentanyl 3 &mgr;g kg–1, phenytoin 300 mg, (S)‐ketamine 10 mg and placebo (part I), or imipramine 100 mg, pregabalin 300 mg, ibuprofen 600 mg and placebo (part II). Pain measurements were performed at baseline and up to 10 h post‐dose. Endpoints were analysed using a mixed model analysis of variance. Results Sixteen subjects (8 female) completed each part. The pain tolerance threshold (PTT) for electrical stimulation was increased (all P < 0.05) compared to placebo for (S)‐ketamine (+10.1%), phenytoin (+8.5%) and pregabalin (+10.8%). The PTT for mechanical pain was increased by pregabalin (+14.1%). The cold pressor PTT was increased by fentanyl (+17.1%) and pregabalin (+46.4%). Normal skin heat pain detection threshold was increased by (S)‐ketamine (+3.3%), fentanyl (+2.8%) and pregabalin (+4.1%). UVB treated skin pain detection threshold was increased by fentanyl (+2.6%) and ibuprofen (+4.0%). No differences in conditioned pain modulation were observed. Conclusion This study shows that these pain models are able to detect changes in pain thresholds after administration of different classes of analgesics in healthy subjects. The analgesic compounds all showed a unique profile in their effects on the pain tasks administered.

Relationships Between Type 2 Diabetes, Neuropathy, and Microvascular Dysfunction: Evidence From Patients With Cryptogenic Axonal Polyneuropathy

OBJECTIVE This study investigated whether the relationship between neuropathy and microvascular dysfunction in patients with type 2 diabetes is independent of diabetes-related factors. For this purpose, we compared skin microvascular function in patients with type 2 diabetes with that of patients with cryptogenic axonal polyneuropathy (CAP), a polyneuropathy of unknown etiology. RESEARCH DESIGN AND METHODS Cross-sectional information was collected from 16 healthy controls (HCs), 16 patients with CAP, 15 patients with type 2 diabetes with polyneuropathy (DPN), and 11 patients with type 2 diabetes without polyneuropathy. Axonal degeneration was assessed with skin biopsy and nerve conduction studies. Microvascular skin vasodilation was measured using laser Doppler fluxmetry combined with iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP). RESULTS Patients with CAP and DPN demonstrated a similar decrease in intraepidermal nerve fiber density and sural sensory nerve action potential compared with HCs. The vasodilator response to ACh was similar among patients with CAP (relative mean difference based on log values 13.3%; 95% CI −35.0 to 97.7%; P = 0.652) but was lower in the patients with diabetes with neuropathy (157.5%; 42.0–366.7%; P = 0.003) and without neuropathy (174.2%; 44.2–421.3%; P = 0.003) compared with HCs. No significant differences were found between the groups of patients with diabetes (P = 0.845). The vasodilator response to SNP was not significantly different among the groups (P = 0.082). CONCLUSIONS In this study, endothelium-dependent vasodilation was reduced in patients with type 2 diabetes regardless of the presence of polyneuropathy, whereas microvascular vasodilation was normal in patients with CAP. These data suggest that in type 2 diabetes, neuropathy does not contribute to impaired microvascular endothelium-dependent vasodilation and vice versa. In addition, this study suggests that impaired microvascular vasodilation does not contribute to CAP.

Pharmacokinetics and pharmacodynamics of intrathecally administered Xen2174, a synthetic conopeptide with norepinephrine reuptake inhibitor and analgesic properties

AIM Xen2174 is a synthetic 13‐amino acid peptide that binds specifically to the norepinephrine transporter, which results in inhibition of norepinephrine uptake. It is being developed as a possible treatment for moderate to severe pain and is delivered intrathecally. The current study was performed to assess the pharmacodynamics (PD) and the cerebrospinal fluid (CSF) pharmacokinetics (PK) of Xen2174 in healthy subjects. METHODS This was a randomized, blinded, placebo‐controlled study in healthy subjects. The study was divided into three treatment arms. Each group consisted of eight subjects on active treatment and two or three subjects on placebo. The CSF was sampled for 32 h using an intrathecal catheter. PD assessments were performed using a battery of nociceptive tasks (electrical pain, pressure pain and cold pressor tasks). RESULTS Twenty‐five subjects were administered Xen2174. CSF PK analysis showed a higher area under the CSF concentration–time curve of Xen2174 in the highest dose group than allowed by the predefined safety margin based on nonclinical data. The most common adverse event was post‐lumbar puncture syndrome, with no difference in incidence between treatment groups. Although no statistically significant differences were observed in the PD assessments between the different dosages of Xen2174 and placebo, pain tolerability in the highest dose group was higher than in the placebo group [contrast least squares mean pressure pain tolerance threshold of Xen2174 2.5 mg–placebo (95% confidence interval), 22.2% (−5.0%, 57.1%); P = 0.1131]. CONCLUSIONS At the Xen2174 dose level of 2.5 mg, CSF concentrations exceeded the prespecified exposure limit based on the nonclinical safety margin. No statistically significant effects on evoked pain tests were observed.

Measuring blood–brain barrier penetration using the NeuroCart, a CNS test battery

To systematically study the pharmacodynamics of a CNS drug early in the development process, we developed and validated a battery of drug-sensitive CNS tests, which we call NeuroCart. Using this test battery, data-intensive phase 1 studies in healthy subjects can be performed to demonstrate the specific, time- and dose-dependent, neurophysiological and/or neuropsychological effects of a compound, thereby confirming whether the test compound reaches its intended target in the CNS - or does not reach its intended target. We use this test battery to demonstrate that a compound passes the blood-brain barrier.

EEG machine learning for accurate detection of cholinergic intervention and Alzheimer's disease

Monitoring effects of disease or therapeutic intervention on brain function is increasingly important for clinical trials, albeit hampered by inter-individual variability and subtle effects. Here, we apply complementary biomarker algorithms to electroencephalography (EEG) recordings to capture the brain’s multi-faceted signature of disease or pharmacological intervention and use machine learning to improve classification performance. Using data from healthy subjects receiving scopolamine we developed an index of the muscarinic acetylcholine receptor antagonist (mAChR) consisting of 14 EEG biomarkers. This mAChR index yielded higher classification performance than any single EEG biomarker with cross-validated accuracy, sensitivity, specificity and precision ranging from 88–92%. The mAChR index also discriminated healthy elderly from patients with Alzheimer’s disease (AD); however, an index optimized for AD pathophysiology provided a better classification. We conclude that integrating multiple EEG biomarkers can enhance the accuracy of identifying disease or drug interventions, which is essential for clinical trials.

Pharmacokinetics and pharmacodynamics of oral mecamylamine - development of a nicotinic acetylcholine receptor antagonist cognitive challenge test using modelling and simulation.

A pharmacologic challenge model with a nicotinic antagonist could be an important tool not only to understand the complex role of the nicotinic cholinergic system in cognition, but also to develop novel compounds acting on the nicotinic acetylcholine receptor. The objective was to develop a pharmacokinetic–pharmacodynamic (PKPD) model using nonlinear mixed effects (NLME) methods to quantitate the pharmacokinetics of three oral mecamylamine doses (10, 20 and 30 mg) and correlate the plasma concentrations to the pharmacodynamic effects on a cognitive and neurophysiologic battery of tests in healthy subjects. A one-compartment linear kinetic model best described the plasma concentrations of mecamylamine. Mecamylamine’s estimated clearance was 0.28 ± 0.015 L min−1. The peripheral volume of distribution (291 ± 5.15 L) was directly related to total body weight. Mecamylamine impaired the accuracy and increased the reaction time in tests evaluating short term working memory with a steep increase in the concentration-effect relationship at plasma concentrations below 100 μg L−1. On the other hand, mecamylamine induced a decrease in performance of tests evaluating visual and fine motor coordination at higher plasma concentrations (EC50 97 μg L−1). Systolic and diastolic blood pressure decreased exponentially after a plasma mecamylamine concentration of 80 μg L−1, a known effect previously poorly studied in healthy subjects. The developed mecamylamine PKPD model was used to quantify the effects of nicotinic blockade in a set of neurophysiological tests in humans with the goal to provide insight into the physiology and pharmacology of the nicotinic system in humans and the possibility to optimize future trials that use mecamylamine as a pharmacological challenge.