Preclinical characterization of WAY-211612: a dual 5-HT uptake inhibitor and 5-HT (1A) receptor antagonist and potential novel antidepressant

BACKGROUND AND PURPOSE

As a combination of 5-HT selective reuptake inhibitor (SSRI) with 5-HT(1A) receptor antagonism may yield a rapidly acting antidepressant, WAY-211612, a compound with both SSRI and 5-HT(1A) receptor antagonist activities, was evaluated in preclinical models.

EXPERIMENTAL APPROACH

Occupancy studies confirmed the mechanism of action of WAY-211612, while its in vivo profile was characterized in microdialysis and behavioural models.

KEY RESULTS

WAY-211612 inhibited 5-HT reuptake (K(i) = 1.5 nmol.L(-1); K(B) = 17.7 nmol.L(-1)) and exhibited full 5-HT(1A) receptor antagonist activity (K(i) = 1.2 nmol.L(-1); K(B) = 6.3 nmol.L(-1); I(max) 100% in adenyl cyclase assays; K(B) = 19.8 nmol.L(-1); I(max) 100% in GTPgammaS). WAY-211612 (3 and 30 mg.kg(-1), po) occupied 5-HT reuptake sites in rat prefrontal cortex (56.6% and 73.6% respectively) and hippocampus (52.2% and 78.5%), and 5-HT(1A) receptors in the prefrontal cortex (6.7% and 44.7%), hippocampus (8.3% and 48.6%) and dorsal raphe (15% and 83%). Acute or chronic treatment with WAY-211612 (3-30 mg.kg(-1), po) raised levels of cortical 5-HT approximately twofold, as also observed with a combination of an SSRI (fluoxetine; 30 mg.kg(-1), s.c.) and a 5-HT(1A) antagonist (WAY-100635; 0.3 mg.kg(-1), s.c). WAY-211612 (3.3-30 mg.kg(-1), s.c.) decreased aggressive behaviour in the resident-intruder model, while increasing the number of punished crossings (3-30 mg.kg(-1), i.p. and 10-56 mg.kg(-1), po) in the mouse four-plate model and decreased adjunctive drinking behaviour (56 mg.kg(-1), i.p.) in the rat scheduled-induced polydipsia model.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that WAY-211612 may represent a novel antidepressant.

Side effects of brequinar and brequinar analogues, in combination with cyclosporine, in the rat

Brequinar is an immunosuppressant with the potential to be combined with cyclosporine in synergistic combination therapy. The drug tends to accumulate when given daily per os, and pharmacokinetic interaction with cyclosporine appears to enhance toxicity. Analogues with similar immunosuppressive activity have been identified at Du Pont Merck Pharmaceutical Co., that do not accumulate upon daily oral dosing in rats, and hence could have an improved potential in combination treatment with cyclosporine. We performed a toxicity study with brequinar and two brequinar analogues, administered orally once daily for 4 weeks, either alone or in combination with cyclosporine (Neoral, Novartis Pharma AG). In a first study relatively high doses were evaluated with cyclosporine at non-toxic doses of 5 and 10 mg/kg/d. The maximum tolerated dose of brequinar alone was estimated between 5 and 10 mg/kg/d; that of the analogues was estimated between 10 and 20 mg/kg/d, and above 20 mg/kg/d, respectively. In combination with cyclosporine at 5 and 10 mg/kg/d, approximately a 2-fold reduction in the maximum tolerated dose was observed. In a second study lower doses were evaluated in combination with cyclosporine at 2.5 and 5 mg/kg/d. Also this study revealed increased toxicity of brequinar (analogues) when given in combination with cyclosporine. The side effects observed were typical for drugs in the brequinar class and included leukocytopenia and thrombocytopenia, reduced body weight gain or body weight loss, thymic atrophy, cellular depletion of bone marrow and splenic white pulp, and villous atrophy in jejunum. Concentrations of brequinar (analogues) were determined in blood sampled 4 h after administration at day 1, 14 and 21-28 of the experiment. There was a tendency for drug accumulation in some groups treated with brequinar and cyclosporine. For one of the analogues at a low dose, higher concentrations were measured in groups treated with combinations of this compound and cyclosporine. We conclude that a potential synergism in immunosuppression using combinations of brequinar (analogues) and cyclosporine can be complicated by enhanced toxicity of the compounds. This indicates the need for a careful evaluation of the therapeutic window in a combined treatment together with detailed pharmacokinetics.

Preservation of ischemic myocardium by pinane thromboxane A2

Pinane thromboxane A2 (PTA2), a thromboxane A2 analog has been shown to antagonize the vasoconstriction and platelet aggregation induced by thromboxane A2, in addition to specifically inhibiting thromboxane synthetase. Because thromboxane A2 generation would be detrimental in acute myocardial ischemia (MI) by both decreasing coronary blood flow and increasing platelet aggregation, inhibition of thromboxane production and action may be beneficial in myocardial ischemia. In pentobarbital-anesthetized cats, the left anterior descending coronary artery was ligated, and PTA2 (0.5 mumol . kg-1 . h-1) or a Na2CO3 vehicle was infused 30 min post-MI for 270 min. Compared to vehicle-treated MI cats, PTA2 prevented the increase in plasma thromboxane levels seen at 2 through 5 h (P less than 0.005 at 2 through 5 h) and prevented the large increase in plasma CK activities at 4 and 5 h (P less than 0.025). In addition, PTA2 treatment abolished the differences in myocardial CK activities between ischemic and nonischemic regions and prevented the decrease in percent-bound cathepsin D in the ischemic region. Moreover, ECG analysis revealed a decreased incidence of premature beats in PTA2-treated MI cats as compared to MI-vehicle cats. In summary, these data indicate that PTA2 protects the ischemic myocardium and provide further evidence that inhibition of thromboxane formation, in addition to antagonism of its activity, is beneficial during the early stages of acute myocardial ischemia.