Brain translocator protein occupancy by ONO-2952 in healthy adults: A Phase 1 PET study using [11 C]PBR28.

ONO-2952, a novel antagonist of translocator protein 18 kDa (TSPO), binds with high affinity to TSPO in rat brain and human tumor cell line membrane preparations. This study used the TSPO-specific PET radioligand [11 C]PBR28 to confirm binding of ONO-2952 to brain TSPO in human subjects, and evaluate brain TSPO occupancy and its relationship with ONO-2952 plasma concentration. Sixteen healthy subjects received a single oral dose of 200, 60, 20, or 6 mg ONO-2952 (n = 4 per dose). Two PET scans with [11 C]PBR28 were conducted ≤7 days apart: at baseline and 24 h after ONO-2952 administration. [11 C]PBR28 regional distribution volume (VT ) was derived with kinetic modeling using the arterial input function and a two tissue compartment model. Nonspecific binding (VND ) was obtained on an individual basis for each subject using linear regression as the x-intercept of the Lassen plot. The binding potential relative to VND (BPND ) was derived as the difference between VT in the ROI (VT ROI) and VND , normalized to VND ; BPND = (VT ROI - VND )/VND . TSPO occupancy was calculated as the change in BPND (ΔBPND ) from individual's baseline scan to the on-medication scan to the baseline BPND value. TSPO occupancy by ONO-2952 was dose dependent between 20-200 mg, approaching saturation at 200 mg both in the whole brain and in 15 anatomic regions of interest (ROI). Estimated Ki values ranged from 24.1 to 72.2 nM. This open-label, single-center, single-dose study demonstrated engagement of ONO-2952 to brain TSPO. The relationship between pharmacokinetics and TSPO occupancy observed in this study support the hypothesis that ONO-2952 could potentially modulate neurosteroid production by binding to brain TSPO.

Quantification of ONO-2952 Occupancy of 18-kDaTranslocator Protein in Conscious Monkey Brains using Positron Emission Tomography.

We have previously shown that ONO-2952, a novel 18-kDa translocator protein (TSPO) antagonist, inhibits stress-induced accumulation of neurosteroids and noradrenaline release in the rat brain and alleviates the subsequent symptomatic responses with a brain TSPO occupancy of 50% or more. In this study, we measured ONO-2952 brain TSPO occupancy in conscious rhesus monkeys using positron emission tomography (PET) with 11C-PBR28 as ligand for translational research to clinical application. PET scans were performed after single and repeated oral administration of ONO-2952 at several dose levels for each animal, with sequential arterial blood sampling. In vitro binding studies showed that ONO-2952 potently binds to brain TSPO in monkeys with an affinity equivalent to that in rats. ONO-2952, given orally before PET scans, dose dependently decreased 11C-PBR28 uptake without marked brain region specificity. Results of the quantitative analysis using arterial input function revealed that TSPO occupancy after ONO-2952 single and repeated oral administration tended to increase in parallel with its plasma concentration, reaching the highest level of 100%. These findings indicate that ONO-2952 has sufficient brain distribution in primates and that ONO-2952 TSPO occupancy in humans can also be determined using PET.

Anti-stress effects of ONO-2952, a novel translocator protein 18 kDa antagonist, in rats.

Accumulating evidence has shown the pathophysiological significance of the translocator protein 18 kDa (TSPO) in the central nervous system. In this study, we evaluated the beneficial effects of ONO-2952, a novel TSPO antagonist in rat stress models. ONO-2952 potently bound both rat and human TSPO (Ki=0.330-9.30 nmol/L) with high selectivity over other receptors, transporters, ion channels and enzymes. ONO-2952 inhibited both neurosteroid accumulation and noradrenaline release in the brain of rats exposed to acute stress. The inhibitory effect of ONO-2952 on stress-induced noradrenaline release was attenuated by co-treatment with the TSPO agonist CB34 in a dose-dependent manner. ONO-2952, at 0.3 mg/kg or higher, dose-dependently suppressed restraint stress-induced defecation in rats with brain TSPO occupancy of more than 50%. In addition, ONO-2952, at 1 mg/kg or higher, suppressed conditioned fear stress-induced freezing behavior in rats with an efficacy equivalent to that of diazepam, given orally at 3 mg/kg. Results of the passive avoidance learning test revealed that ONO-2952, unlike diazepam, did not affect learning and memory even at doses 10 times higher than its effective doses in the stress models. The present findings indicate that ONO-2952 is a promising candidate for the treatment of stress-related disorders.

Study of active substances involved in skin dysfunction induced by crowding stress. I. Effect of crowding and isolation on some physiological variables, skin function and skin blood perfusion in hairless mice.

The effects of five levels of population density on various organs, the neuroendocrine system, skin function, skin blood perfusion, and blood parameters were studied in the hairless mouse. Skin barrier recovery was evaluated by measuring transepidermal water loss after tape stripping. Blood perfusion was measured by means of a laser Doppler imaging technique. The effect of a parasympathetic nerve stimulator, carpronium chloride, on skin function in the crowded animal model was also examined. A 7 d crowding (10, 15, 20 mice/cage) significantly increased the levels of corticosterone, catecholamines (norepinephrine, epinephrine and dopamine), glucose and serum lactate dehydrogenase activity in circulating blood, induced atrophy of kidney, ovary and thymus and hypertrophy of adrenal glands, and decreased body weight gain in comparison with the control (5 mice/cage). Crowding also increased epidermal thickness and epidermal proliferative activity, and decreased corneocyte size, rate of barrier recovery and skin blood perfusion. Most of these changes became more marked with increasing population density and/or longer exposure to a crowded environment. Isolation (1 mouse/cage) increased the level of norepinephrine and rate of skin blood perfusion, and significantly delayed barrier recovery. Repeated topical applications of carpronium chloride for 7 d improved the changes in skin blood perfusion, barrier recovery, kidney and ovary, and epidermal morphology induced by crowding. The crowded animal model could be useful for quantifying objectively the influence of crowded environment-induced stress on cutaneous function and blood perfusion.