G-Protein-coupled receptors (GPCRs) represent the largest class of drug targets, accounting for more than 40% of marketed drugs; however, discovery efforts for many GPCRs have failed to provide viable drug candidates. Historically, drug discovery efforts have focused on developing ligands that act at the orthosteric site of the endogenous agonist. Recently, efforts have focused on functional assay paradigms and the discovery of ligands that act at allosteric sites to modulate receptor function in either a positive, negative, or neutral manner. Allosteric modulators have numerous advantages over orthosteric ligands, including high subtype selectivity; the ability to mimic physiological conditions; the lack of densensitization, downregulation, and internalization; and reduced side effects. Despite these virtues, challenging issues have now arisen for allosteric modulators of metabotropic glutamate receptors (mGluRs): shallow SAR, ligand-directed trafficking, and the identification of subtle “molecular switches” that modulate the modes of pharmacology. Here, we will discuss the impact of modest structural changes to multiple mGluR allosteric ligands scaffolds that unexpectedly modulate pharmacology and raise concerns over metabolism and the pharmacology of metabolites.

Accumulating evidence suggests that selective M 4 muscarinic acetylcholine receptor (mAChR) activators may offer a novel strategy for the treatment of psychosis. However, previous efforts to develop selective M 4 activators were unsuccessful because of the lack of M 4 mAChR subtype specificity and off-target muscarinic adverse effects. We recently developed VU0152100, a highly selective M 4 positive allosteric modulator (PAM) that exerts central effects after systemic administration. We now report that VU0152100 dose-dependently reverses amphetamine-induced hyperlocomotion in rats and wild-type mice, but not in M4 KO mice. VU0152100 also blocks amphetamine-induced disruption of the acquisition of contextual fear conditioning and prepulse inhibition of the acoustic startle reflex. These effects were observed at doses that do not produce catalepsy or peripheral adverse effects associated with non-selective mAChR agonists. To further understand the effects of selective potentiation of M 4 on region-specific brain activation, VU0152100 alone and in combination with amphetamine were evaluated using pharmacologic magnetic resonance imaging (phMRI). Key neural substrates of M 4 -mediated modulation of the amphetamine response included the nucleus accumbens (NAS), caudate-putamen (CP), hippocampus, and medial thalamus. Functional connectivity analysis of phMRI data, specifically assessing correlations in activation between regions, revealed several brain networks involved in the M 4 modulation of amphetamine-induced brain activation, including the NAS and retrosplenial cortex with motor cortex, hippocampus, and medial thalamus. Using in vivo microdialysis, we found that VU0152100 reversed amphetamine-induced increases in extracellular dopamine levels in NAS and CP. The present data are consistent with an antipsychotic drug-like profile of activity for VU0152100. Taken together, these data support the development of selective M 4 PAMs as a new approach to the treatment of psychosis and cognitive impairments associated with psychiatric disorders such as schizophrenia.

T-type Ca2+ channel inhibitors hold tremendous therapeutic potential for the treatment of pain, epilepsy, sleep disorders, essential tremor and other neurological disorders; however, a lack of truly selective tools has hindered basic research, and selective tools from the pharmaceutical industry are potentially burdened with intellectual property (IP) constraints. Thus, an MLPCN high-throughput screen (HTS) was conducted to identify novel T-type Ca2+ channel inhibitors free from IP constraints, and freely available through the MLPCN, for use by the biomedical community to study T-type Ca2+ channels. While the HTS provided numerous hits, these compounds could not be optimized to the required level of potency to be appropriate tool compounds. Therefore, a scaffold hopping approach, guided by SurflexSim, ultimately afforded ML218 (CID 45115620) a selective T-Type Ca2+ (Cav3.1, Cav3.2, Cav3.3) inhibitor (Cav3.2, IC50 = 150 nM in Ca2+ flux; Cav3.2 IC50 = 310 nM and Cav3.3 IC50 = 270 nM, respectively in patch clamp electrophysiology) with good DMPK properties, acceptable in vivo rat PK and excellent brain levels. Electrophysiology studies in subthalamic nucleus (STN) neurons demonstrated robust effects of ML218 on the inhibition of T-Type calcium current, inhibition of low threshold spike and rebound burst activity. Based on the basal ganglia circuitry in Parkinson’s disease (PD), the effects of ML218 in STN neurons suggest a therapeutic role for T-type Ca2+ channel inhibitors, and ML218 was found to be orally efficacious in haloperidol-induced catalepsy, a preclinical PD model, with comparable efficacy to an A2A antagonist, a clinically validated PD target. ML218 proves to be a powerful new probe to study T-Type Ca2+ function in vitro and in vivo, and freely available.

Schizophrenia is a complex and highly heterogeneous psychiatric disorder whose precise etiology remains elusive. While genome-wide association studies (GWAS) have identified risk genes, they have failed to determine if rare coding single nucleotide polymorphisms (nsSNPs) contribute in schizophrenia. Recently, two independent studies identified 12 rare, deleterious nsSNPS in the GRM1 gene, which encodes the metabotropic glutamate receptor subtype 1 (mGlu1), in schizophrenic patients. Here, we generated stable cell lines expressing the mGlu1 mutant receptors and assessed their pharmacology. Using both the endogenous agonist glutamate and the synthetic agonist DHPG, we found that several of the mutant mGlu1 receptors displayed a loss of function that was not due to a loss in plasma membrane expression. Due to a lack of mGlu1 positive allosteric modulators (PAM) tool compounds active at human mGlu1, we optimized a known mGlu4 PAM/mGlu1 NAM chemotype into a series of potent and selective mGlu1 PAMs by virtue of a double “molecular switch”. Employing mGlu1 PAMs from multiple chemotypes, we demonstrate that the mutant receptors can be potentiated by small molecules and in some cases efficacy restored to that comparable to wild type mGlu1 receptors, suggesting deficits in patients with schizophrenia due to these mutations may be amenable to intervention with an mGlu1 PAM. However, in wild type animals, mGlu1 negative allosteric modulators (NAMs) are efficacious in classic models predictive of antipsychotic activity, whereas we show that mGlu1 PAMs have no effect to slight potentiation in these models. These data further highlight the heterogeneity of schizophrenia and the critical role of patient selection strategies in psychiatric clinical trials to match genotype with therapeutic mechanism.

The synthesis of phidianidines A and B, the first 1,2,4-oxadiazole-containing alkaloid, from the marine opisthobranch mollusk Phidiana militaris is reported. The synthesis proceeds in six steps from known indole acetic acids in 39.9% (phidianidine A) and 21% (phidianidine B) overall yields from commercially available materials. Biological characterization found that phidianidines A and B are selective inhibitors of DAT (versus SERT and NET) and a selective, potent ligand and partial agonist of the μ opioid receptor (versus δ-and κ-opioid receptors). Moreover, neither phidianidines A and B are cytotoxic, and thus represent an attractive starting point for chemical optimization; therefore, we piloted a number of chemistries and prepared a diverse series of unnatural analogs.

The five subtypes of the muscarinic acetylcholine receptor (mAChR [1][2][3][4][5] or M 1-5 ) are differentially expressed G protein-coupled receptors (GPCRs) important to a variety of physiological functions, including attention, learning and memory, pain, sleep, movement, gastrointestinal motility and cardiovascular regulation, among others. [1][2][3][4][5] Based on mounting data, M 1 and M 4 receptors are considered potential therapeutic targets for numerous CNS diseases and disorders such as Alzheimer's disease and schizophrenia. [6][7][8][9] However, due to high sequence conservation of the orthosteric binding site across subtypes, discovery of truly subtype-selective compounds has proven historically challenging. Indeed, M 2 -and M 3 -related side effects (e.g. GI disturbance, salivation, lacrimation and bradycardia) have contributed to failure in the clinical development of muscarinic agonists despite promising therapeutic efficacy. [6,7] Furthermore, deep biological insight into the specific roles of the mAChRs in both basic neurobiology and CNS pathologies has been hindered by the paucity of selective tools. The additional drug metabolism/pharmacokinetic (DMPK)-related challenges inherent to CNS drug discovery have also hampered progress in this area. Despite these hurdles, a number of novel subtype-selective and centrally penetrating muscarinic compounds, including agonists, antagonists, and potentiators, have recently emerged from functional cell-based screening approaches. [10][11][12][13][14][15] We previously reported the identification of a series of novel M 4 -selective potentiators (positive allosteric modulators or PAMs) that enhance receptor activation in response to acetylcholine (ACh) by an allosteric mechanism (Figure 1). [10,12] These compounds increase the potency of ACh at M4 but lack intrinsic agonist activity on their own. Initial optimization focused on improving the physiochemical properties of lead compound VU10010 (1), which possessed an EC 50 value of 400 nM and elicited a 47-fold leftward shift of an ACh concentration-response curve (CRC) by Ca 2+ mobilization assay in rat M 4 /G qi5 -expressing cells, but suffered from solubility issues and lack of brain penetration. [10,12] This limited effort produced two analogues, VU0152099 (2) and VU0152100 (3), which had similar potency and comparable efficacy to the parent compound i but were centrally penetrating and displayed in vivo activity in a rodent behavioral model predictive of antipsychotic efficacy.[10] These compounds were also devoid of ancillary pharmacological activity when evaluated against a large number of GPCRs, ion channels, and enzymes.[10] Despite the utility of compounds 2 and 3 for in vitro and in vivo pharmacological studies, we sought to further explore the SAR in this series with a more exhaustive optimization campaign by employing an iterative analogue library approach. The rationale for this effort stemmed in part from an initial limited lead optimization campaign, poor metabolic stability of compounds 2 and 3...

The first total synthesis of dispyrin, a recently reported bromopyrrole alkaloid from Agelas dispar with an unprecedented bromopyrrole tyramine motif, was achieved in three steps on a gram scale (68.4% overall). No biological activity was reported for dispyrin, so we evaluated synthetic dispyrin against>200 discrete molecular targets in radioligand binding and functional assays. Unlike most marine natural products, dispyrin (1) possesses no antibacterial or anticancer activity, but was found to be a potent ligand and antagonist of several therapeutically relevant GPCRs, the alpha1D and alpha2A adrenergic receptors and the H2 and H3 histamine receptors.

This Letter describes the first account of the synthesis and SAR, developed through an iterative analogue library approach, of analogues of the highly selective M1 allosteric agonist TBPB. With slight structural changes, mAChR selectivity was maintained, but the degree of partial M1 agonism varied considerably.