Peter J. Scammells

Opioid analgesics remain essential for pain management but are associated with significant adverse effects, including respiratory depression, tolerance, and dependence. The δ-opioid receptor (δOR) represents a promising therapeutic target for developing safer opioid analgesics with reduced adverse effects compared to conventional μ-opioid receptor-targeting drugs. Positive allosteric modulators (PAMs) offer advantages over direct agonists by enhancing endogenous opioid signaling while preserving natural spatiotemporal activation patterns, potentially avoiding tolerance and dependence issues. Here, we present high-resolution cryo-EM structures of δOR complexed with the peptide agonist DADLE and the PAM MIPS3614, revealing a lipid-facing allosteric binding site formed by transmembrane helices 2, 3, and 4. MIPS3614 stabilizes the active receptor conformation through a critical hydrogen bond with residue N131^3.35 in the conserved sodium binding site, a key regulatory region controlling GPCR activation. Comprehensive mutagenesis, molecular dynamics simulations, and structure-activity relationships validate this proposed mechanism. Structure-guided optimization yields MIPS3983 with enhanced binding affinity and retained cooperativity. Our findings describe a molecular basis for δOR allosteric modulation and provide structural information relevant to the rational design of opioid therapeutics with improved safety profiles.

The M4R has emerged as a promising therapeutic target for schizophrenia, highlighted by the recent FDA approval of Cobenfy (xanomeline coformulated with trospium chloride). However, xanomeline itself exhibits limited subtype selectivity and moderate efficacy. To address this, we applied a bitopic ligand strategy by combining xanomeline with the M4 muscarinic acetylcholine receptor (M4R) positive allosteric modulator MK cpd-97. Herein, we report on the design, synthesis, and pharmacological evaluation of a series of bitopic ligands featuring various aliphatic linkers. Derivatives with different linker lengths and types were tested across muscarinic receptor subtypes. Polymethylene-linked compounds showed minimal signaling bias and poor subtype selectivity, whereas PEG and polyamide linkers improved both properties. Notably, bitopic ligands incorporating diglycyl polyamide linkers exhibited the highest subtype preference with pronounced signaling bias. These findings provide insights into muscarinic ligand–receptor interactions and offer guidance for future bitopic ligand development.

Malaria remains a global health burden and the emergence of parasite-resistance to frontline drugs highlights an urgent need for new therapeutics with novel mechanisms of action. Inhibiting aminopeptidases, in particular the Plasmodium falciparum M1 and M17 aminopeptidases (PfA-M1 and PfA-M17 respectively) has been shown to cause parasite death. In this study, both ligand-based and structure-based design strategies were utilized to identify novel scaffolds that act as dual inhibitors of these enzymes. Structural studies supported the improved activity showing strong hydrophobic and additional hydrogen interactions between the new cores and the S1 pocket of the enzymes. These inhibitors were highly effective against Plasmodium vivax and Plasmodium berghei, showing cross-peptidase and cross-species activity while also retaining activity against multidrug resistant P. falciparum strains. Progression to in vivo efficacy studies showed reduction in parasitaemia in mice infected with P. berghei demonstrating encouraging prospects to develop suitable drug-like candidates for the treatment of malaria.

The N-demethylation of alkaloids is a critical step in the synthesis of useful pharmaceutical agents such as Naltrexone, 1, and Naloxone, 2, used in the battle against drug dependency and opioid use disorder. Efforts to make this process more sustainable have been ongoing for a number of years, using a range of iron (0) catalysts, green solvents, and different energy sources to initiate reaction. The use of a sonochemical, iron catalyzed methodology for the N-demethylation of the model alkaloid compound, dextromethorphan, 4, is described herein. The sonochemical demethylation chemistry is comparable to other methods developed in the Singer and Scammells labs. However, when electrical energy consumption is examined, conventional stirring reveals itself as least demanding while liquid assisted grinding and sonochemical approaches were most demanding. Any future scale up of this chemistry using a touted “green and sustainable approach” should therefore consider all green chemistry parameters and metrics collectively.

G protein–coupled receptors (GPCRs), the largest superfamily of human membrane proteins with >800 members, are primary targets for ~1/3 of all marketed drugs. Recent fluorescence experiments underscored the pivotal role of GPCR–G protein complex lifetime in their coupling efficiency and selectivity. However, these experiments are often expensive, time-consuming, and limited to a small number of GPCR–G protein systems. On the other hand, it is challenging to simulate GPCR–G protein dissociation using molecular dynamics (MD) methods. Here, we have employed Protein–Protein Interaction Gaussian accelerated MD (PPI-GaMD) simulations and experiments to probe the kinetics and pathways of G protein dissociation from GPCRs. For five systems with published experimental kinetic data, PPI-GaMD simulations successfully captured G protein dissociation from the GPCRs, including the adrenergic, adenosine, and muscarinic receptors. The simulations allowed identification of two distinct dissociation pathways and calculation of the G protein dissociation rates, which were in good agreement with experimental data. Additionally, we simulated the effect of positive allosteric modulators (PAMs) of the adenosine A ₁ receptor (A ₁ R) in Gi protein dissociation and supported simulation findings with bioluminescence resonance energy transfer biosensor experiments evaluating G _βγ kinetics following A ₁ R activation. A ₁ R PAMs were found to strengthen the agonist–receptor and receptor–G protein interactions and significantly reduce dissociation rates of the Gi protein. In summary, complementary PPI-GaMD simulations and kinetic assays have enabled detailed characterization of the kinetics and pathways of G protein dissociation, a critical event in the GPCR signaling cascade, and the effects of GPCR allosteric modulators.

Therapies enhancing remyelination offer the exciting prospect of disease-modifying treatments across a number of poorly treated neurological disorders. The class A orphan GPCR, GPR17, is one of the most studied receptors in remyelination; and antagonists of GPR17 have attracted significant attention as potential pro-myelinating medicines. Despite this, the signaling pathways linking GPR17 to remyelination and the molecular mechanisms of action of GPR17 antagonists are not well-defined. In the present study, we characterized GPR17 signaling and inhibition by three chemically distinct GPR17 antagonists: pranlukast, HAMI-3379, and a patent literature antagonist, RWT9996. In HEK293 cells recombinantly expressing GPR17- and BRET-based biosensors, pranlukast preferentially inhibited G protein activation over β-arrestin-2 recruitment, whereas HAMI3379 and RWT9996 equally inhibited all signal transduction tested. Follow-up studies using pharmacological inhibitors and GPR17 antagonists in Oli-neu cells, an immortalized mouse oligodendrocyte precursor cell (OPC) line with endogenous GPR17 expression, corroborated the G protein and β-arrestin coupling profile observed in recombinant cells. Specifically, the generated bias profile suggests that β-arrestin potentiates Gα_q signaling from GPR17, conferring differential regulation of Gα_q signaling by biased GPR17 antagonists. These findings highlight an unappreciated potential for biased signaling in the pharmacology of GPR17 ligands. We anticipate that these insights will help to inform the translation of GPR17-targeted therapies and improve our understanding of GPR17-mediated signaling pathways in governing myelination.

A series comprised of N6-substituted adenosines designed from the A2B adenosine agonist 4 were synthesized and their A2BR potency was assessed in a cAMP accumulation assay using FlpINCHO cells stably expressing the human A2BR. This study identified 12 novel A2BR agonists which exhibited subnanomolar potency at the A2BR. The most potent compounds possessed a 5′-N-ethyl carboxamide moiety (7, pEC50 = 10.24) or a slightly shorter N6-alkyl linker (8, pEC50 = 10.17) relative to 4. Both compounds were also highly receptor subtype selective versus the A1R, A2AR, and A3R. In terms of cellular activity, both the parent 4 and the 5′-N-ethyl carboxamide 7 ameliorated AngII stimulating effects in both cardiac myocytes and fibroblasts. Furthermore, compounds 4 and 7 attenuated TGFβ-stimulated collagen synthesis in cardiac fibroblasts. These antihypertrophy and antifibrotic effects suggest that selective A2BR compounds may have therapeutic potential for cardiovascular disease where cardiac remodeling is a major driver.

Opioid analgesics remain essential for pain management but are associated with significant adverse effects, including respiratory depression, tolerance, and dependence. The δ-opioid receptor (δOR) represents a promising therapeutic target for developing safer opioid analgesics with reduced adverse effects compared to conventional μ-opioid receptor-targeting drugs. Positive allosteric modulators (PAMs) offer advantages over direct agonists by enhancing endogenous opioid signaling while preserving natural spatiotemporal activation patterns, potentially avoiding tolerance and dependence issues. Here, we present high-resolution cryo-EM structures of δOR complexed with the peptide agonist DADLE and the PAM MIPS3614, revealing a novel lipid-facing allosteric binding site formed by transmembrane helices 2, 3, and 4. MIPS3614 stabilizes the active receptor conformation through a critical hydrogen bond with residue N131 ^{3 .35} in the conserved sodium binding site, a key regulatory region controlling GPCR activation. Comprehensive mutagenesis, molecular dynamics simulations, and structure-activity relationships validate this proposed mechanism. Structure-guided optimization yielded MIPS3983 with enhanced binding affinity and retained cooperativity. Our findings establish the first molecular framework for δOR allosteric modulation and provide a structural foundation for the rational design of safer opioid therapeutics.

Chronic pain and depression are widely prevalent comorbid conditions with limited safe, yet effective treatments. While μ-opioid receptor (MOR) agonists are effective for treating pain, they are plagued with significant drawbacks, including dependence, addiction, and respiratory depression. The δ-opioid receptor (DOR) offers a promising alternative due to its potential ability to reduce pain but with a reduced side effect profile. Previous studies have identified potent DOR positive allosteric modulators (PAMs) capable of eliciting bias through allostery. Our research has focused on developing the structure-activity relationship (SAR) around these PAMs, investigating DOR vs MOR/KOR selectivity, and lowering lipophilicity. We have developed a novel tetrazoloquinazolinone scaffold, which exhibits G protein-pathway favorability over β-arrestin2 recruitment. This scaffold offers a promising avenue for designing drug-like, DOR-targeted therapeutics with specific signaling profiles, potentially leading to new treatment options for chronic pain and depression, as well as providing an avenue for utilization in further structural studies.