Pharmacology in translation: the preclinical and early clinical profile of the novel α2/3 functionally selective GABAA receptor positive allosteric modulator PF-06372865

Abstract

Background and purpose: Benzodiazepines, non-selective positive allosteric modulators (PAMs) of GABAA receptors, have significant side effects that limit their clinical utility. As many of these side effects are mediated by the α1 subunit, there has been a concerted effort to develop α2/3 subtype-selective PAMs.

Experimental approach: In vitro screening assays were used to identify molecules with functional selectivity for receptors containing α2/3 subunits over those containing α1 subunits. In vivo receptor occupancy (RO) was conducted, prior to confirmation of in vivo α2/3 and α1 pharmacology through quantitative EEG (qEEG) beta frequency and zolpidem drug discrimination in rats respectively. PF-06372865 was then progressed to Phase 1 clinical trials.

Key results: PF-06372865 exhibited functional selectivity for those receptors containing α2/3/5 subunits, with significant positive allosteric modulation (90-140%) but negligible activity (≤20%) at GABAA receptors containing α1 subunits. PF-06372865 exhibited concentration-dependent occupancy of GABAA receptors in preclinical species. There was an occupancy-dependent increase in qEEG beta frequency and no generalization to a GABAA α1 cue in the drug-discrimination assay, clearly demonstrating the lack of modulation at the GABAA receptors containing an α1 subtype. In a Phase 1 single ascending dose study in healthy volunteers, evaluation of the pharmacodynamics of PF-06372865 demonstrated a robust increase in saccadic peak velocity (a marker of α2/3 pharmacology), increases in beta frequency qEEG and a slight saturating increase in body sway.

Conclusions and implications: PF-06372865 has a unique clinical pharmacology profile and a highly predictive translational data package from preclinical species to the clinical setting.

© 2017 The British Pharmacological Society.

Figures

Figure 1

Chemical structure of PF‐06372865.

Figure 2

(A) Concentration–response curves for PF‐06372865 in [3H]‐flumazenil competition‐binding assays to membranes containing GABAA receptors expressing different α subunits. Data are representative, duplicate, determinations from between 5 and 8 separate experiments. (B) Example of GABAA current response to the co‐application of GABA and 0.1% DMSO (first pipette mark), the co‐application of GABA and PF‐06372865 (second pipette mark), followed by a wash with extracellular solution (third pipette mark); peak recording is indicated by the line. (C) Example of GABAA current response to the co‐application of GABA and 0.1% DMSO (first pipette mark), followed by a second co‐application of GABA and 0.1% DMSO (second pipette mark), followed by a wash with extracellular solution (third pipette mark); peak recording is indicated by the line. (D) Concentration–response curves of QPatch functional response for human GABAA receptors containing different α subunits. Graphs are the mean ± SEM data from all experiments (n = 3–7).

Figure 3

(A) In vivo GABAA receptor occupancy (RO) of PF‐06372865 in rats at 1 h post‐dose. Values are expressed as percentage inhibition of [3H]‐flumazenil binding relative to vehicle, shown as mean ± SEM (n = 4 per group); (B) relationship of total and free plasma to brain RO.

Figure 4

The effect of vehicle and 1, 3 and 10 mg·kg−1 PF‐06372865 0–6 h post‐treatment on qEEG recordings in the light phase. Data are expressed as mean ± SEM (n = 8) delta (0.75–4 Hz), theta (6–9 Hz), alpha (8–13 Hz), beta (14–40 Hz) and gamma (40–80 Hz) power (mV2) in the 6 h period post‐administration, and were analysed with a one‐way ANOVA with the significance level set at P < 0.05.

Figure 5

(A) Drug‐discrimination of PF‐06372865 in zolpidem‐trained rats. Data show mean percentage zolpidem‐appropriate responding (left axis) or responses.min‐1 (right axis) (±SEM) during training or generalization tests with PF‐06372865. (B) Effects of PF‐06372865 on core body temperature. Data show mean rectal temperature (±SEM) 65–75 min post‐dosing. (C) Effects of PF‐06372865 on locomotor activity during test session. Data show mean locomotor counts (±SEM) during training or generalization tests. FR, fixed ratio.

Figure 6

Median plasma PF‐06372865 concentration–time profiles following single p.o. doses (semi‐logarithmic plot).

Figure 7

Incidence of dizziness and somnolence: treatment‐emergent adverse events. Plot of the percentage of subjects reporting a treatment‐emergent adverse event of dizziness or somnolence (all causality) by dose from both the SAD and PET studies. Shape represents the treatment, and colour represents the study/cohort. LRZ, lorazepam; (T), tablet.

Figure 8

Plot of difference to placebo in overall LSmeans for (A) SPV, (B) body sway and (C) qEEG frequency band by dose (SAD study). LSmeans represent the average treatment effect versus placebo across the first 6 h post‐dose along with 95% CIs. Error bars that do not intersect the horizontal dashed line indicate a statistically significant effect versus placebo (P < 0.05). Shape represents the cohort, and colour represents the treatment. LRZ, lorazepam; (T), tablet.

Figure 9

(A) Representative PET and MRI images in healthy human subjects. (A) MRI, (B) baseline PET, (C) first post‐drug PET at 1.5 h (~66% RO) and (D) second post‐drug PET at 24 h (~27% RO). All images were from the same subject who was dosed with 10 mg of PF‐06372865. Images are displayed along three orthogonal views (coronal, transverse and sagittal views from left to right columns). PET images are in VT units (mL blood.cm‐3 tissue). (B) PET RO versus plasma PF‐06372865 concentration relationship in human subjects. The individual dots are the brain GABAA RO measured, while the line is the fitted relationship with an Emax model.