Biochemical and behavioral effects of PDE10A inhibitors: Relationship to target site occupancy

Phosphodiesterase 10A (PDE10A) inhibitors increase the functionality of striatal medium spiny neurons and produce antipsychotic-like effects in rodents by blocking PDE10A mediated hydrolysis of cAMP and/or cGMP. In the current study, we characterized a radiolabeled PDE10A inhibitor, [3H]BMS-843496, and developed an ex vivo PDE10 binding autoradiographic assay to explore the relationship between PDE10 binding site occupancy and the observed biochemical and behavioral effects of PDE10 inhibitors in mice. [3H]BMS-843496 is a potent PDE10A inhibitor with a binding affinity (KD) of 0.15 nM and a functional selectivity of \u3e100-fold over other PDE subtypes tested. Specific [3H]BMS-843496 binding sites were dominant in the basal ganglia, especially the striatum, with low to moderate binding in the cortical and hippocampal areas, of the mouse and monkey brain. Systemic administration of PDE10 inhibitors produced a dose- and plasma/brain concentration-dependent increase in PDE10A occupancy measured in the striatum. PDE10A occupancy was positively correlated with striatal pCREB expression levels. PDE10A occupancy was also correlated with antipsychotic-like effects measured using the conditioned avoidance response model; a minimum of ∼40% occupancy was typically required to achieve efficacy. In contrast, a clear relationship between PDE10A occupancy and catalepsy scores, a potential extrapyramidal symptom readout in rodent, was not evident

The Novel, Nicotinic Alpha7 Receptor Partial Agonist, BMS-933043, Improves Cognition and Sensory Processing in Preclinical Models of Schizophrenia.

The development of alpha7 nicotinic acetylcholine receptor agonists is considered a promising approach for the treatment of cognitive symptoms in schizophrenia patients. In the present studies we characterized the novel agent, (2R)-N-(6-(1H-imidazol-1-yl)-4-pyrimidinyl)-4'H-spiro[4-azabicyclo[2.2.2]octane-2,5'-[1,3]oxazol]-2'-amine (BMS-933043), in vitro and in rodent models of schizophrenia-like deficits in cognition and sensory processing. BMS-933043 showed potent binding affinity to native rat (Ki = 3.3 nM) and recombinant human alpha7 nicotinic acetylcholine receptors (Ki = 8.1 nM) and agonist activity in a calcium fluorescence assay (EC50 = 23.4 nM) and whole cell voltage clamp electrophysiology (EC50 = 0.14 micromolar (rat) and 0.29 micromolar (human)). BMS-933043 exhibited a partial agonist profile relative to acetylcholine; the relative efficacy for net charge crossing the cell membrane was 67% and 78% at rat and human alpha7 nicotinic acetylcholine receptors respectively. BMS-933043 showed no agonist or antagonist activity at other nicotinic acetylcholine receptor subtypes and was at least 300 fold weaker at binding to and antagonizing human 5-HT3A receptors (Ki = 2,451 nM; IC50 = 8,066 nM). BMS-933043 treatment i) improved 24 hour novel object recognition memory in mice (0.1-10 mg/kg, sc), ii) reversed MK-801-induced deficits in Y maze performance in mice (1-10 mg/kg, sc) and set shift performance in rats (1-10 mg/kg, po) and iii) reduced the number of trials required to complete the extradimensional shift discrimination in neonatal PCP treated rats performing the intra-dimensional/extradimensional set shifting task (0.1-3 mg/kg, po). BMS-933043 also improved auditory gating (0.56-3 mg/kg, sc) and mismatch negativity (0.03-3 mg/kg, sc) in rats treated with S(+)ketamine or neonatal phencyclidine respectively. Given this favorable preclinical profile BMS-933043 was selected for further development to support clinical evaluation in humans

Summary of BMS-933043 Results in Preclinical Models of Schizophrenia.

<p>Summary of BMS-933043 Results in Preclinical Models of Schizophrenia.</p

BMS-933043 improves EDS performance in neonatal PCP-treated rats.

<p>Results are presented as the mean ± SEM number of trials required to reach the performance criterion of 6 successive correct entries into the baited pot for each discrimination (n = 9–10/treatment). Results were analyzed by 2 way repeated measures ANOVA followed by Dunnett’s post hoc analysis; **** p = 0.0001 compared to neonatal PCP/Vehicle treated rats.</p

BMS-933043 improves 24 h recognition memory in mice.

<p>Subjects were treated 30 min prior to the training session with either A/B) vehicle or low doses of BMS-933043 (n = 11–13/group), C/D) vehicle or high doses of BMS-933043 (n = 10–13/group) or E/F) vehicle or NS-6740 (10 mg/kg, sc) 10 min prior to BMS-933043 (0.3 mg/kg, sc; n = 15–16/group) and then tested for memory retention 24 h later. Results are presented as the mean ± SEM % discrimination index for the training (A, C, E) and test sessions (B, D, F) and were analyzed by ANOVA followed by Dunnett’s test; ** p<0.01, *** p<0.001 versus vehicle or vehicle/BMS-933043 treated mice.</p

Functional efficacy at recombinant human α7 nACh and 5-HT_3A receptors determined by Ca²⁺ flux (FLIPR) assays.

<p>Functional efficacy at recombinant human α7 nACh and 5-HT_3A receptors determined by Ca²⁺ flux (FLIPR) assays.</p

BMS-933043 improves MMN in neonatal PCP-treated rats.

<p>Results from 3 independent studies are presented as the mean ± SEM AUC determined from the averaged difference wave for each subject after treatment with either vehicle or BMS-933043 (n = 12–13/group). For reference, the dashed line shows the average AUC in untreated adult rats determined in separate studies. Each treatment was analyzed by one sample, two tailed t test; ** p<0.01 compared to a hypothetical zero.</p

Relationship between dose, plasma exposure and ex vivo α7 nAChR occupancy in rodents.

<p>A) Results show the mean ± SEM occupancy determined 30 min after sc dosing in mice (open circles) or 90 min after po dosing in rats (n = 4/dose). B) Individual occupancy/exposure results for mice (open circles) and composite plot showing results for rats (closed circles) treated po (as above), sc (30 min post-dose) and experimental set shift subjects (150 min post-dose).</p

Displacement of [³H]-A-585539 binding to rat brain or recombinant human α7 nAChR.

<p>Displacement of [³H]-A-585539 binding to rat brain or recombinant human α7 nAChR.</p