Development Of Partial Agonists Research Articles

Structure-Activity Relationship Development Efforts towards Peripherally Selective Analogs of the Cannabinoid Receptor Partial Agonist BAY 59-3074.

Selective modulation of peripheral cannabinoid receptors (CBRs) has potential therapeutic applications in medical conditions, including obesity, diabetes, liver diseases, GI disorders and pain. While there have been considerable efforts to produce selective antagonists or full agonists of CBRs, there has been limited reports on the development of partial agonists. Partial agonists targeting peripheral CBRs may have desirable pharmacological profiles while not producing centrally mediated dissociative effects. Bayer reported that BAY 59-3074 is a CNS penetrant partial agonist of both CB1 and CB2 receptors with efficacy in rat models of neuropathic and inflammatory pain. In this report, we demonstrate our efforts to synthesize analogs that would favor peripheral selectivity, while maintaining partial agonism of CB1. Our efforts led to the identification of a novel compound, which is a partial agonist of the human CB1 (hCB1) receptor with vastly diminished brain exposure compared to BAY 59-3074.

Design and synthesis of peptidic partial agonists of human neuromedin U receptor 1 with enhanced serum stability

Neuromedin U (NMU) activates two receptors (NMUR1 and NMUR2) and is a promising candidate for development of drugs to combat obesity. Previously, we obtained hexapeptides as selective full NMUR agonists. Development of a partial agonist which mildly activates receptors is an effective strategy which lead to an understanding of the functions of NMU receptors. In 2014, we reported hexapeptide 3 (CPN-124) as an NMUR1-selective partial agonist but its selectivity and serum stability were unsatisfactory. Herein, we report the development of a hexapeptide-type partial agonist (8, CPN-223) based on a peptide (3) but with higher NMUR1-selectivity and enhanced serum stability. A structure-activity relationship study of synthetic pentapeptide derivatives suggested that a hexapeptide is a minimum structure consistent with both good NMUR1-selective agonistic activity and serum stability.

Exploration of the molecular architecture of the orthosteric binding site in the α4β2 nicotinic acetylcholine receptor with analogs of 3-(dimethylamino)butyl dimethylcarbamate (DMABC) and 1-(pyridin-3-yl)-1,4-diazepane

X-ray crystal structures of acetylcholine binding proteins (AChBPs) have revealed two different possible extensions to the classical ligand binding pocket known to accommodate various nicotinic agonists. One of the pockets is limited in size while the other is of considerable dimensions and protrudes along the interfacial cleft between subunits. To probe these putative extensions in functional nicotinic acetylcholine receptors (nAChRs), elongated analogs of 3-(dimethylamino)butyl dimethylcarbamate (DMABC) and 1-(pyridine-3-yl)-1,4-diazepane were prepared and characterized pharmacologically at neuronal heteromeric nAChRs. Although the new analogs, relative to parent compounds, displayed lower binding affinities, functional characterization of selected compounds revealed that they had retained partial α4β2 nAChR agonist activity. The structure–activity relationship data did not indicate an upper limit to the size of substituents as would have been expected if the ligand was bound in the smaller pocket. The data were better in agreement with a binding mode in which substituents protrude along the interfacial cleft of the receptor. This was further supported by docking into a homology model of the α4-β2 nAChR interface and by surface plasmon resonance biosensor analysis of binding of the compounds to acetylcholine-binding proteins, where they exhibit preference for Lymnaea stagnalis ACh binding protein (Ls-AChBP) over the Aplysia california ACh binding protein (Ac-AChBP). These results suggest new opportunities for expanding chemical space in the development of partial agonist and may be of interest in relation to development of novel smoking cessation aids.

The Pharmacology of Imepitoin: The First Partial Benzodiazepine Receptor Agonist Developed for the Treatment of Epilepsy

Although benzodiazepines (BZDs) offer a wide spectrum of antiepileptic activity against diverse types of epileptic seizures, their use in the treatment of epilepsy is limited because of adverse effects, loss of efficacy (tolerance), and development of physical and psychological dependence. BZDs act as positive allosteric modulators of the inhibitory neurotransmitter GABA by binding to the BZD recognition site ("BZD receptor") of the GABAA receptor. Traditional BZDs such as diazepam or clonazepam act as full agonists at this site, so that one strategy to resolve the disadvantages of these compounds would be the development of partial agonists with lower intrinsic efficacy at the BZD site of the GABAA receptor. Several BZD site partial or subtype selective compounds, including bretazenil, abecarnil, or alpidem, have been developed as anxioselective anxiolytic drugs, but epilepsy was not a target indication for such compounds. More recently, the imidazolone derivatives imepitoin (ELB138) and ELB139 were shown to act as low-affinity partial agonists at the BZD site of the GABAA receptor, and imepitoin was developed for the treatment of epilepsy. Imepitoin displayed a broad spectrum of anticonvulsant activity in diverse seizure and epilepsy models at tolerable doses, and, as expected from its mechanism of action, lacked tolerance and abuse liability in rodent and primate models. The more favorable pharmacokinetic profile of imepitoin in dogs versus humans led to the decision to develop imepitoin for the treatment of canine epilepsy. Based on randomized controlled trials that demonstrated antiepileptic efficacy and high tolerability and safety in epileptic dogs, the drug was recently approved for this indication in Europe. Hopefully, the favorable profile of imepitoin for the treatment of epilepsy in dogs will reactivate the interest in partial BZD site agonists as new treatments for human epilepsy.