In Vitro and In Vivo Identification of Novel Positive Allosteric Modulators of the Human Dopamine D2 and D3 Receptor

Agonists at dopamine D2 and D3 receptors are important therapeutic agents in the treatment of Parkinson's disease. Compared with the use of agonists, allosteric potentiators offer potential advantages such as temporal, regional, and phasic potentiation of natural signaling, and that of receptor subtype selectivity. We report the identification of a stereoselective interaction of a benzothiazol racemic compound that acts as a positive allosteric modulator (PAM) of the rat and human dopamine D2 and D3 receptors. The R isomer did not directly stimulate the dopamine D2 receptor but potentiated the effects of dopamine. In contrast the S isomer attenuated the effects of the PAM and the effects of dopamine. In radioligand binding studies, these compounds do not compete for binding of orthosteric ligands, but indeed the R isomer increased the number of high-affinity sites for [(3)H]-dopamine without affecting K(d). We went on to identify a more potent PAM for use in native receptor systems. This compound potentiated the effects of D2/D3 signaling in vitro in electrophysiologic studies on dissociated striatal neurons and in vivo on the effects of L-dopa in the 6OHDA (6-hydroxydopamine) contralateral turning model. These PAMs lacked activity at a wide variety of receptors, lacked PAM activity at related Gi-coupled G protein-coupled receptors, and lacked activity at D1 receptors. However, the PAMs did potentiate [(3)H]-dopamine binding at both D2 and D3 receptors. Together, these studies show that we have identified PAMs of the D2 and D3 receptors both in vitro and in vivo. Such compounds may have utility in the treatment of hypodopaminergic function.

Synthesis and structure-activity relationship of new 1,5-dialkyl-1,5-benzodiazepines as cholecystokinin-2 receptor antagonists

This article deals with the synthesis and the activities of some 1,5-dialkyl-3-arylureido-1,5-benzodiazepin-2,4-diones which were prepared as potential CCK2 antagonists, with the intention to find a possible follow up of our lead compound GV150013, showing an improved pharmacokinetic profile. The phenyl ring at N-5 was replaced with more hydrophilic substituents, like alkyl groups bearing basic functions. In some cases, the resolution of the racemic key intermediates 3-amino-benzodiazepines was also accomplished. Among the compounds synthesized and characterised so far in this class, the 5-morpholinoethyl derivative 54, was selected as potential follow up of GV150013 and submitted for further evaluation.

First time in human for GV196771: interspecies scaling applied on dose selection

The utility of interspecies scaling in early drug development has been extensively debated. The authors discuss the dose selection strategy for a first time into man (FTIM) study for GV196771, a new glycine antagonist, using techniques of interspecies scaling. The FTIM dose selection strategy was based on predicted plasma profiles of GV196771 in humans using allometric scaling and considerations of safety and pharmacological activity in animals. Allometric techniques were first retrospectively applied to data obtained in humans and animals for GV150526, a glycine antagonist with similar pharmacokinetic characteristics to GV196771. GV196771 and GV150526 are extensively protein bound; thus, protein binding differences among species were considered in the scaling. Using the scaled pharmacokinetic parameters, compartmental modeling was performed to prospectively simulate concentration profiles for the oral administration of GV196771. This article will discuss the outcome of the prospective dose selection strategy for GV196771 compared to the actual concentration profiles observed in the FTIM study.