- [1-(4-fluorobenzyl)-5-hydroxy-indole-3-yl]-glyoxylic acid amide (AWD 12-281) is a highly potent and selective phosphodiesterase 4 (PDE4) inhibitor that was designed to have a metabolic profile that was optimized for topical administration. The aim of the current study was to explore the pharmacological profile of intratracheally administered AWD 12-281 in different models of asthma and chronic obstructive pulmonary disease (COPD) in comparison with steroids. To assess the anti-inflammatory potential of AWD 12-281, the antigen-induced cell infiltration in bronchoalveolar lavage fluid (BALF) of Brown Norway rats was determined. AWD 12-281 (ID 50 of 7 g/kg i.t.) as well as beclomethasone (0.1 g/kg i.t.) suppresses late-phase eosinophilia when administered intrapulmonary. Furthermore, AWD 12-281 has also strong anti-inflammatory properties when tested in lipopolysaccharide-induced acute lung neutrophilia in Lewis rats (ID 50 of 0.02 g/kg i.t.), ferrets (ID 50 of 10 g/kg i.t.), and domestic pigs (2-4 mg/pig i.t. or 1 mg/kg i.v.). In pigs, AWD 12-281 was as effective as beclomethasone (0.4 mg/pig i.t.) and dexamethasone (0.28 mg/kg i.v.), although at 3 to 10 times the dosage. The bronchodilatory activity of AWD 12-281 was assessed in sensitized guinea pigs. AWD 12-281 (1.5 mg/kg i.t., 1-h pretreatment) inhibited allergen-induced bronchoconstriction by 68% (parameter airway resistance). In sensitized BP-2 mice AWD 12-281 abolished the allergen-induced bronchial hyperresponsiveness and eosinophilia in BALF, showing dose dependence. When given orally, i.v. or i.t., AWD 12-281 has a considerably lower emetic potential than cilomilast in ferrets and roflumilast in pigs. When given topically by inhalation, no emesis could be induced in dogs up to the highest feasible dose (15 mg/kg in 50% lactose blend). These results indicate that AWD 12-281 is a unique potential new drug for the topical treatment of asthma and COPD.

The identification of highly potent and orally active phenylpyrazines for the inhibition of PDE10A is reported. The new analogues exhibit subnanomolar potency for PDE10A, demonstrate high selectivity against all other members of the PDE family, and show desired druglike properties. Employing structure-based drug design approaches, we methodically explored two key regions of the binding pocket of the PDE10A enzyme to alter the planarity of the parent compound 1 and optimize its affinity for PDE10A. Bulky substituents at the C9 position led to elimination of the mutagenicity of 1, while a crucial hydrogen bond interaction with Glu716 markedly enhanced its potency and selectivity. A systematic assessment of the ADME and PK properties of the new analogues led to druglike development candidates. One of the more potent compounds, 96, displayed an IC(50) for PDE10A of 0.7 nM and was active in predictive antipsychotic animal models.

The possibility to substitute PCP by MK-801 in this model indicates that the effect is mediated by their common mechanism of NMDA antagonism. PDE10A inhibitors similar to clozapine significantly antagonize the increase of immobility, suggesting a therapeutic potential for the treatment of negative symptoms. However, further validation of the model is necessary.

Cyclic nucleotide phosphodiesterase 10A (PDE10A) regulates the level of the second messengers cAMP and cGMP in particular in brain regions assumed to be associated with neurodegenerative and psychiatric diseases. A better understanding of the pathophysiological role of the expression of PDE10A could be obtained by quantitative imaging of the enzyme by positron emission tomography (PET). Thus, in this study we developed, radiolabeled, and evaluated a new PDE10A radioligand, 8-bromo-1-(6-[ F]fluoropyridin-3-yl)-3,4-dimethylimidazo[1,5-a]quinoxaline ([ F]AQ28A). [ F]AQ28A was radiolabeled by both nucleophilic bromo-to-fluoro or nitro-to-fluoro exchange using K[ F]F-K -carbonate complex with different yields. Using the superior nitro precursor, we developed an automated synthesis on a Tracerlab FX F-N module and obtained [ F]AQ28A with high radiochemical yields (33 ± 6%) and specific activities (96-145 GBq·μmol ) for further evaluation. Initially, we investigated the binding of [ F]AQ28A to the brain of different species by autoradiography and observed the highest density of binding sites in striatum, the brain region with the highest PDE10A expression. Subsequent dynamic PET studies in mice revealed a region-specific accumulation of [ F]AQ28A in this region, which could be blocked by preinjection of the selective PDE10A ligand MP-10. In conclusion, the data suggest [ F]AQ28A is a suitable candidate for imaging of PDE10A in rodent brain by PET.

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