Partial agonism and fast dissociation of LASSBio-579 at dopamine D2 receptor

Abstract

In an attempt to better understand the molecular mechanism of action of the antipsychotic lead LASSBio-579 and of its main metabolite LQFM 037, the aim of this work was to evaluate their intrinsic activity and binding kinetics at the dopamine D2 receptor. In transfected HEK cells expressing the D2L receptor under an inducible promoter, LASSBio-579 and LQFM 037, but not clozapine, behaved as weak partial agonists in [(35)S]-GTPγS binding assays performed in optimized conditions previously shown to evidence the partial agonist profile of aripiprazole. Besides, data obtained in radioligand competition assays on rat striatal membranes suggested a rapid association to and dissociation from the D2-like receptors. Using the kinetic rate index based on the strategy of the dual-point competition association assay, we showed that our compounds share a similar kinetic profile with clozapine, distinct from the typical antipsychotic haloperidol. These two characteristics could contribute to the atypical-like profile observed after administration of LASSBio-579 to rodents, in models of positive and negative symptoms of schizophrenia.

Evaluation of Functional Selectivity of Haloperidol, Clozapine, and LASSBio-579, an Experimental Compound With Antipsychotic-Like Actions in Rodents, at G Protein and Arrestin Signaling Downstream of the Dopamine D2 Receptor

“…Regarding the ligand-dependent coupling of G i protein, our BRET assay showed that LASSBio-579 and LQFM 037, in a smaller extent, exhibited a (very) weak intrinsic activity. This finding is in agreement with our previous data using a [ 35 S]-GTPγS binding assay and a membrane preparation of Hela Tet-On cells overexpressing the mouse D 2L R. Indeed, we reported that LASSBio-579 and LQFM 037, like aripiprazole but not clozapine, were weak partial agonists of the D 2 R when using such assay, especially in the absence of sodium ions in the incubation medium (Pompeu et al, 2015). These experimental conditions were previously shown to increase the sensitivity to detect weak partial agonists such as aripiprazole, since sodium ions disfavor the formation of the ternary complex of GPCRs (Lin et al, 2006).…”

“…LASSBio-579 and LQFM 037 also antagonized the effect of dopamine in a concentration-dependent manner, but we were not able to obtain complete inhibition curves due to their lack of solubility at higher concentrations. However, the estimated I max are not maximal, as expected for weak partial agonists, as we observed for blocking of [ 35 S]-GTPγS binding stimulation by dopamine (Pompeu et al, 2015).…”

“…The main phase I metabolite of LASSBio-579 in rats, identified as the p -hydroxylated derivative LQFM 037 ( 2 ) ( Figure 1 ), was a ligand of the D 2 and D 4 receptors at submicromolar concentrations, indicating that it could participate in the in vivo effects of LASSBio-579 (Gomes et al, 2013). More recently, we showed that both LASSBio-579 and its metabolite were weak partial agonists of the D 2 R at the G-protein pathway and shared with clozapine the particularity to have rapid dissociation kinetics, contrary to haloperidol (Pompeu et al, 2015). We concluded that these two characteristics could explain, at least partially, the atypical-like profile previously reported when LASSBio-579 was administered to rodents.…”