Molecular Pharmacology

GPR65 is a proton-sensing G protein-coupled receptor implicated in inflammatory pain. In fibroblast-like synoviocytes (FLS), GPR65 activation promotes the release of proinflammatory cytokines capable of sensitizing sensory neurons. Following stimulation by protons, the synthetic agonist BTB09089, and the glycosphingolipid psychosine GPR65 undergoes internalization; however, the contribution of this trafficking to downstream signaling remains unclear. Using heterologous cell systems, the molecular mechanisms governing GPR65 internalization were first defined. Pharmacological and genetic inhibition of internalization revealed that intracellular trafficking is required for activation of extracellular-signal-related kinase (ERK) in the nucleus and transcriptional responses, indicating a spatially restricted signaling program originating from endosomes. The physiological relevance of this pathway was then examined in primary mouse FLS. Inhibition of endogenous GPR65 internalization reduced the ability of the conditioned media from BTB09089 stimulated FLS to sensitize dorsal root ganglia sensory neurons, thus linking receptor trafficking to pro-nociceptive function. Together these findings identify receptor internalization as a key determinant of nuclear ERK signaling and transcription downstream of GPR65 and demonstrate that endosomal signaling is required for pro-nociceptive activity of GPR65 in FLS. One-sentence summaryEndosomal internalization of GPR65 is required to coordinate gene transcription and proinflammatory cytokine production that drive neuronal sensitization.

Bitter taste receptors (TAS2Rs) are G-protein coupled receptors that detect chemically diverse compounds, including many clinically used drugs. TAS2R14 is expressed in many extraoral tissues and is activated by hundreds of ligands, including pharmaceutical drugs. Recent cryo-EM structures revealed a previously unrecognized intracellular binding pocket in TAS2R14, raising new questions regarding ligand binding modes. Here, we investigated the activation of TAS2R14 by Tamoxifen, Carbimazole, and Lidocaine using cell-based assays measuring proximal G-protein recruitment (BRET2) and downstream signaling (IP-One). Tamoxifen and Carbimazole activated TAS2R14 with EC50 values in the low micromolar range, whereas Lidocaine required substantially higher concentrations. Targeted receptor mutations were used to evaluate the contribution of extracellular and intracellular binding regions to agonist activity. Carbimazole and Lidocaine showed greater dependence on the intracellular and extracellular positions, respectively, while Tamoxifen displayed assay-dependent, but overall modest sensitivity to the tested mutations. Thus, although existing drugs can activate TAS2R14 through distinct binding modes, TAS2R14-directed repurposing will depend on whether effective local receptor concentrations can be achieved through appropriate delivery strategies.

Volume-regulated anion channels (VRACs), formed by leucine-rich repeat-containing 8 (LRRC8) proteins, are ubiquitously expressed chloride channels essential for cell volume regulation and implicated in diverse physiological and pathological processes. Small-molecule VRAC inhibitors have been reported to modulate paracrine signaling, proliferation, differentiation, migration, and apoptosis, and have been patented for potential therapeutic applications in stroke, cardiovascular and metabolic diseases, and cancer. However, growing evidence indicates that many commonly used VRAC blockers exert substantial off-target effects and frequently fail to reproduce phenotypes observed after deletion of the essential VRAC subunit LRRC8A. Here, we systematically compared effects of several widely used pharmacological VRAC inhibitors with outcomes of molecular downregulation of LRRC8A in limiting proliferation of malignant glioblastoma cells derived from surgical specimens. NIH/3T3 fibroblasts served as a non-malignant control. In serum-containing media, structurally diverse VRAC blockers (DCPIB, DIDS, carbenoxolone, phloretin, and bromadiolone) reduced proliferation in a non-uniform manner, with potencies that did not correlate with reported VRAC affinities and varied markedly among cell lines. Radiotracer-based measurements of VRAC activity indicated that these discrepancies were largely attributable to binding of inhibitors to serum albumin. When experiments were repeated under serum-free conditions, all inhibitors except DIDS and phloretin induced extensive death of both malignant and non-malignant cells, confirmed by microscopy and LDH release assays. This cytotoxicity was accompanied by a marked reduction in intracellular ATP levels, consistent with previously reported mitochondrial uncoupling effects. In contrast, LRRC8A knockdown reduced proliferation without substantial cell death. Together, these findings demonstrate that most commercially available VRAC blockers limit proliferation and viability predominantly through VRAC-independent mechanisms. Under standard culture conditions, serum albumin masks much of their intrinsic cytotoxicity. These results underscore the need for rigorous molecular controls in pharmacological studies and provide basis for developing more selective and less toxic VRAC-targeting agents.

G protein-gated inwardly rectifying potassium (GIRK2) channels regulate neuronal excitability and are implicated in neurodevelopmental disorders. A rare KCNJ6 variant, G154C (hGIRK2G154C), was identified in a patient with mild Keppen-Lubinsky syndrome features, contrasting with severe phenotypes linked to other selectivity filter mutations. Here we combined molecular dynamics simulations and patch-clamp electrophysiology to characterize the hGIRK2G154C mutant, revealing a widened selectivity filter that resulted in loss of potassium selectivity, aberrant sodium permeation, and loss of inward rectification, indicating a severe gain-of-function phenotype. An in silico and electrophysiological drug screen identified FDA-approved compounds, including nefazodone and eletriptan, that potently inhibited GIRK2 and GIRK2G154C through distinct blocking mechanisms. These findings elucidate the structural and functional impact of the G154C mutation and highlight potential pharmacological tools and therapeutic candidates for the treatment of GIRK2 channelopathies.

Chemokines orchestrate immune cell trafficking through receptor-mediated signaling and are implicated in inflammatory, autoimmune, and neuropathic disorders. The XCL1-XCR1 axis is of particular interest because XCR1 is selectively expressed on mature conventional type 1 dendritic cells (cDC1s), where it supports communication with activated CD8+ T cells and NK cells and promotes antigen cross-presentation. This selectivity has made XCR1 an attractive target for dendritic cell-based cancer vaccines, while emerging evidence also links XCL1-XCR1 signaling to neuroinflammation and pain. Despite its therapeutic potential, the mechanisms governing XCR1 activation and trafficking remain understudied. Here, we characterize XCR1 expression, membrane trafficking, and basal internalization to define mechanisms that may influence therapeutic targeting. We show that XCR1 undergoes constitutive internalization through a {beta}-arrestin-independent but adaptor protein 2 (AP2)-dependent pathway, distinguishing it from other chemokine receptors with constitutive endocytosis. Furthermore, we identify specific sequence motifs critical for its subcellular localization and intracellular trafficking. These findings provide new mechanistic insights into XCR1 regulation and may inform the development of targeted therapeutics and antigen-delivery strategies in cancer and inflammation.

G-protein-coupled receptors (GPCRs) signal through multiple heterotrimeric G proteins, {beta}-arrestins, GPCR kinases (GRKs), and downstream effectors, whose combinatorial interactions shape cellular responses. These events are typically measured with separate assay formats that each capture only part of the network, making comparison across signaling layers difficult. Here, we consolidate a broad set of previously reported GPCR signaling interactions and assay concepts, together with newly designed sensors, into a single NanoBiT split-luciferase framework, allowing multiple layers of signal transduction to be examined side by side in living cells. We show that rational sensor engineering, in particular the positioning of NanoBiT fragments and targeted modification of the tagged proteins, is essential for detecting transient protein-protein interactions. The framework implements assays for G-protein dissociation, {beta}-arrestin recruitment, conformational activation and trafficking, and GRK recruitment, and extends to G-protein-effector and inter-effector interactions across diverse G, G{beta}, G{gamma}, {beta}-arrestin, GRK, adenylyl cyclase, PLC{beta}, and RhoGEF subtypes. It also enables real-time monitoring of the difficult-to-access G12/13-RhoGEF-RhoA pathway. Together, these assays provide a unified NanoBiT readout for systematic, side-by-side dissection of GPCR signaling.

Pregnancy induces or represses hepatic drug metabolism. Whether pregnancy affects hepatic drug transport is unexplored. We previously showed that a cocktail of pregnancy-related hormones (PRHC) induces mRNA expression and activity of sodium/taurocholate cotransporting polypeptide (NTCP), organic anion transporter 2 (OAT2), and organic cation transporter 1 (OCT1, mRNA only) in differentiated HepaRG cells. Here, using HepaRG cells, we identified cortisol as the hormone primarily responsible for this induction and explored the underlying mechanisms. Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9-mediated knockdown studies in HepaRG cells showed that the glucocorticoid receptor (GR) is the primary mediator of this response. GR knockdown markedly attenuated cortisol-induced NTCP, OAT2, and OCT1 mRNA expression and activity. Cortisol also induced the mRNA expression of regulatory factors, including pregnane X receptor (PXR), constitutive androstane receptor (CAR), and hepatocyte nuclear factor (HNF) 4 alpha (HNF4). HNF4 knockdown selectively attenuated OAT2 and OCT1 induction, whereas HNF1 knockdown enhanced NTCP induction, attenuated OCT1 induction, and reduced basal organic anion transporting polypeptide 1B1 (OATP1B1) expression. In contrast, knockdown of CAR or PXR did not significantly alter cortisol-mediated transporter regulation. These data identify cortisol as the principal PRH driving regulation of the hepatic OAT2, NTCP, and OCT1 in HepaRG cells and indicate that this response is mediated primarily by GR, with selective downstream contributions from HNF4 and HNF1. These findings provide mechanistic insights into pregnancy-associated changes in hepatic transporter-mediated drug disposition, including when antenatal corticosteroids are administered to pregnant women to prevent respiratory distress syndrome in their prematurely born infants. Significance StatementThe extent and mechanisms by which pregnancy-related hormones regulate hepatic uptake transporters remain poorly defined. This study identifies cortisol as the principal pregnancy-related hormone driving NTCP, OAT2, and OCT1 induction in HepaRG cells and shows that this response is mediated primarily through GR, with transporter-specific contributions from HNF4 and HNF1.

Background. Polypharmacy is an important source of phenoconversion caused by drug interactions potentially modulated by genetic variability. Aims. To develop a linear phenoconversion model for TDM data and provide quantitative estimates of drug-drug-gene interactions (DDGIs) in the pharmacogenetic phenotype groups of CYP2C19. Methods. Escitalopram TDM data in a large real-world sample (n=2,852) was analysed for phenoconversion of CYP2C19 activity. Co-medication was identified by reprocessing high-resolution mass-spectra (Orbitrap). We developed a statistical model to identify inhibition from co-medication in the CYP2C19 and in alternative elimination pathways. We extended the model to estimate the inhibition ensuing from individual co-medications, using a single model for all data to account for multiple co-medications and confounders simultaneously. A Bayesian approach allowed us to stabilize the fit and provide well-calibrated credibility intervals. Results. Reprocessing of TDM analyses identified 17 co-medications, which were shown to phenoconvert CYP2C19 activity proportionally to the activity in non-medicated phenotypes. Phenoconversion decreased the original CYP2C19 activity by about one third for a co-medication that corresponded to a 100% substrate of CYP2C19. The extent of CYP2C19 phenoconversion correlated strongly with the fractional contribution of CYP2C19 to the metabolism of the specific co-medication reported in the pharmacogenetic literature (R2=0.55) so long as the mechanism was competitive inhibition. Conclusion. We provide the statistical methodology to estimate phenoconversion from co-medication in TDM data and combine TDM and pharmacogenetic datasets in future studies aiming at establishing quantitative models of DDGIs.

Cholesterol is a key membrane component that regulates G protein-coupled receptor (GPCR) function, yet its molecular mechanisms remain unclear. Here, we combine chemical extraction of membrane sterols with functional signaling assays and single-molecule fluorescence resonance energy transfer (smFRET) to define how cholesterol controls activation of chemokine receptors. Reduction of membrane cholesterol in mammalian cells selectively decreased constitutive and agonist-induced signaling across CXCR1, CXCR2, CXCR4, while it activated ACKR3, and did not affect CXCR3, revealing receptor-specific dependence on membrane sterols. Mechanistically, cholesterol regulation partly required the conserved class A GPCR residue Trp4.50 and shifted agonist-bound CXCR4 toward active conformational states, providing a molecular explanation for its functional effects. In contrast, replenishment with oxidized cholesterol species failed to restore receptor activity, distinguishing cholesterol from oxysterols as modulators of receptor activation. Our findings identify cholesterol as an allosteric regulator of chemokine receptors and suggest that oxysterols may reshape inflammatory signaling by selectively modulating GPCR activity.

Schizophrenia is a debilitating neuropsychiatric disease that lacks effective treatments for many symptom domains including negative, cognitive and sleep disturbances. Lack of clear disease etiology has hampered the development of new, effective treatments for the unmet needs of people with schizophrenia. Large scale human genetics have identified rare loss of function mutations that substantially increase risk of developing schizophrenia, including in GRIA3, the gene that encodes the GluA3 receptor subunit of the AMPA receptor (AMPAR). Several drug discovery programs have been aimed at developing AMPAR positive allosteric modulators (PAMs) as a novel treatment for schizophrenia. Despite intense drug discovery efforts, there are no FDA approved AMPAR PAMs. We therefore hypothesized that selectively targeting GluA3, the AMPAR subunit implicated by human genetics, could yield a safer and more effective AMPAR PAM for the potential treatment of schizophrenia. Using a combination of medicinal chemistry, in vitro, and in vivo studies, we discovered BRD3290, a GluA3-preferring AMPAR PAM with reasonable potency in heterologous cells, as well as favorable tolerability and brain exposure. Peripheral administration of BRD3290 engaged an established AMPAR PAM target engagement biomarker but did not improve performance of wildtype mice in the novel object recognition task (NOR), in contrast to the nonselective AMPAR PAM PF-4778574, which improved mouse NOR. These findings suggest that the GluA3 selectivity profile of BRD3290 was insufficient to enhance cognitive function in this mouse NOR paradigm. This work highlights the challenges of AMPAR subtype-selective modulation and provides molecular insights into the ability to develop subtype-selective AMPAR PAMs. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/740780v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@1c14b74org.highwire.dtl.DTLVardef@140b2b3org.highwire.dtl.DTLVardef@942636org.highwire.dtl.DTLVardef@58bc24_HPS_FORMAT_FIGEXP M_FIG C_FIG

We published recently that one of the main constituents of cannabis products, cannabidiol (CBD), is an efficacious negative allosteric modulator (NAM) of the mu opioid receptor (MOR1) (Bosquez-Berger et al., 2023). Here, we investigated how the presence of cannabidiol (CBD) is associated with fentanyl (FEN) binding across MOR1 conformations. We performed molecular dynamics simulations of systems containing FEN alone or FEN+CBD in three mouse MOR1 conformational backgrounds: active-like 5C1M, inactive-like 4DKL, and a modeled Morph50 intermediate between the 5C1M and 4DKL conformations. Three independently seeded 200 ns trajectories were analyzed per model and condition (18 trajectories total), with the trajectory treated as the independent unit. Across the matched 0-200 ns window, consensus CBD contacts and CBD-associated changes in FEN contacts were strongly state dependent. Corrected intracellular TM3 to TM6 analyses separated the expected active-like, intermediate, and inactive-like backgrounds but did not identify a CBD-associated shift that was consistent across both geometric definitions and all three replicates. Equal-weight replicate-composite density maps preserved both the shared ligand distributions and this between-trajectory variability. These descriptive results support receptor-state-dependent CBD, FEN, MOR1 interactions while emphasizing the limited inferential power of three trajectories per condition.

Background & Aims: Activation of apoptosis signal-regulating kinase 1 (ASK1), a ubiquitous redox-sensitive kinase, results in inflammation, apoptosis, and fibrosis, key common pathways in human liver disease. SRT-015 is a novel, small molecule inhibitor of ASK1. This study evaluated the in vitro efficacy of SRT-015, compared it to other ASK1 inhibitors, and determined the in vivo efficacy of SRT-015 across multiple acute and chronic liver disease models. Methods: In vitro studies determined the kinase potency and selectivity of SRT-015, and cellular studies were used to demonstrate direct mechanisms of action. The cardiac hERG channel inhibition was assessed and PK determined in rodents and nonhuman primates. In vivo studies evaluated SRT-015 efficacy in rodent models of drug-induced hepatotoxicity (acetaminophen (APAP) overdose), alcohol-associated liver disease (ALD), metabolic-disease associated steatohepatitis (MASH) and cholestatic disease (bile duct ligation, BDL). Results: SRT-015, was demonstrated a selective ASK1 kinase, and SRT-015 treatment directly inhibited fibrosis, apoptosis and inflammation in activated human fibroblasts, hepatocytes and PBMCs, respectively without safety signals or hERG inhibition. Other ASK1 inhibitors had safety concerns or limited functional activity. Liver and kidney selective PK were observed for SRT-015 in all species evaluated. In vivo, SRT-015 treatment was efficacious in the acute mouse APAP overdose and ALD model significantly (P<0.05) decreasing serum ALT. Using a therapeutic diet-induced obesity (DIO)-MASH model with biopsy-verified fibrosis, SRT-015 treatment significantly (P<0.05) inhibited DIO-induced liver enzymes, hepatomegaly, fibrosis, inflammation, and apoptosis independent of body weight loss whereas treatment with selonsertib was ineffective. In a rat cholestatic model, SRT-015 treatment significantly (P<0.05) decreased fibrosis and stellate cell activation. Conclusions: These findings support SRT-015 as a potential therapeutic for human liver diseases of any etiology.

GPR27/SREB1 is a highly conserved orphan class A G-protein coupled receptor implicated in insulin production, metabolic regulation, tumour biology, neurodegeneration and L-lactate homeostasis, but its immediate second-messenger signalling remains poorly defined. We used single-cell Forster resonance energy transfer nanosensors to monitor cytosolic Ca2+ and cAMP in wild-type 3T3 MEF cells, CRISPR-Cas9 GPR27-knockout cells (GPR27KO) and GPR27-knockout cells transiently re-expressing FLAG-tagged GPR27 (GPR27-rescued). The GPR27 surrogate agonist 8535n (1 {micro}M) increased intracellular Ca2+ in wild-type and rescued cells but not in GPR27-knockout cells and produced no significant cAMP response in wild-type cells. Basal Ca2+ and cAMP levels were unaffected by GPR27 deletion. Extracellular L-lactate (2 mM) induced a GPR27-dependent increase in Ca2+ and cAMP in wild-type and rescued cells, but not in knockout cells, raising the possibility that L-lactate acts as an endogenous ligand or modulator of GPR27. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=111 SRC="FIGDIR/small/743761v1_ufig1.gif" ALT="Figure 1"> View larger version (10K): org.highwire.dtl.DTLVardef@2af45dorg.highwire.dtl.DTLVardef@113e2corg.highwire.dtl.DTLVardef@8dea4org.highwire.dtl.DTLVardef@50ec49_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIGPR27 surrogate agonist 8535n increases intracellular Ca2+ but not cAMP in 3T3 cells. C_LIO_LIExtracellular L-lactate induces GPR27-dependent intracellular Ca2+ and cAMP increases in 3T3 cells. C_LIO_LIThese findings identify GPR27 as a putative candidate lactate sensor. C_LI

Small molecule targeting of suppressive myeloid immune checkpoints remains a major challenge in cancer immunotherapy, particularly for non-enzymatic receptors lacking conventional druggable active sites. Leukocyte immunoglobulin-like receptor B4 (LILRB4/ILT3) is an immunosuppressive myeloid checkpoint implicated in tumor immune evasion, T-cell dysfunction, and resistance to immunotherapy across both solid and hematologic malignancies. Here, we report the discovery and characterization of GL-4512, a direct small molecule modulator of LILRB4 identified through a Dianthus-based temperature-related intensity change (TRIC) screening platform. Orthogonal biophysical studies, including microscale thermophoresis, surface plasmon resonance, and cellular thermal shift assays, confirmed direct target engagement with nanomolar affinity. Extensive microsecond molecular dynamics simulations combined with site-directed mutagenesis identified a previously unrecognized ligandable pocket within the flexible extracellular domain of LILRB4. Functionally, GL-4512 disrupted the immunosuppressive LILRB4-SCG2 signaling axis and suppressed downstream SHP1/SHP2 and STAT3 signaling. In patient-derived colorectal cancer and acute myeloid leukemia co-culture systems, pharmacological inhibition of LILRB4 restored anti-tumor immune activity, enhanced IFN-{gamma} and IL-2 production, increased cytotoxic T-cell activation, and reduced tumor-cell viability. GL-4512 additionally demonstrated favorable pharmacokinetic and safety properties supporting oral in vivo administration. In immunocompetent CT26 syngeneic colorectal tumors, once-daily oral treatment significantly suppressed tumor growth and enhanced intratumoral immune activation. Collectively, these findings establish LILRB4 as a tractable target for direct small molecule immunomodulation and support therapeutic targeting of suppressive myeloid immune checkpoints for cancer using non-biologic modalities.

Confounding the treatment options available to patients with triple-negative breast cancer (TNBC) are not only its purported lack of hormone receptor and growth factor receptor targets (ER-/ PR-/ HER2-), but its enrichment in plastic and chemoresistant breast cancer stem cells (BCSCs). Although descriptions of non-canonical PR expression in TNBC are rife in the literature, only canonical PR is considered in the definition of TNBC and is used to determine therapeutic strategy, not least because the utility of non-canonical PR modulation in TNBC chemoresistance is largely unexplored and poorly understood. Here we document the expression of three non-canonical PRs and the canonical PR (PGR) phosphorylated at Ser345 (p-PGR S345) in a panel of TNBC and luminal breast cancer cell lines, and employ combined PR agonists and antagonists to investigate the influence of PR activity on TNBC cell viability and PI3K inhibitor cytotoxicity. To examine the contributions of non-canonical membrane-associated PRs mPR{beta} and PGRMC1, we tested the agonist Org OD 02-0, a synthetic progestin targeted to mPRs; the PGRMC1 antagonist Ag-205; and the antagonist SPA70 against the cytosolic/nuclear PXR, in the background of pan-PI3K inhibition with Buparlisib (BUP). We also reveal that combinations of agonists and antagonists targeted to canonical and non-canonical PRs robustly potentiate the cytotoxic effects of PI3K inhibition, and also exhibit significant cytotoxicity on their own. Using functional assays, flow cytometry, immunocytochemistry and protein expression analyses, we found that simultaneously perturbing PRs and inhibiting PI3K function resulted in significantly greater cell death than vehicle control or BUP alone, and reduced the proportion of ALDH1+ BCSCs in two TNBC cell lines. We conclude that four types of PR are tractable targets in TNBC which participate in cell viability and enhance chemotherapy-induced cytotoxicity, and should be re-evaluated in an evolving definition of this challenging disease.

Mcl1 is a major driver of therapeutic resistance across hematologic malignancies, but direct Mcl1 inhibition has been limited by on-target cardiotoxicity. Here, building on our development of an Mcl1-targeting autophagy-targeting chimera (AUTAC), we show that AUTAC-mediated degradation creates a tumor-selective therapeutic window that spares the heart. AUTAC induced robust cytotoxicity and Mcl1 degradation in multiple myeloma models, while showing minimal toxicity in cardiac cell lines, primary cardiomyocytes, and murine heart tissue. In vivo, AUTAC reduced tumor Mcl1 without measurably affecting cardiac Mcl1. Mechanistically, this selectivity was associated with lower expression of the p62/SQSTM1, TRAF6, and UBC13 machinery required for AUTAC activity in cardiac cells, together with lower intracellular AUTAC accumulation relative to tumor cells. AUTAC also enhanced the antitumor activity of carfilzomib and venetoclax, including in resistant models, without worsening cardiotoxicity or promoting cardiac Mcl1 loss. Compared with classical Mcl1 inhibitors, AUTAC caused markedly less cardiomyocyte death, mitochondrial depolarization, and apoptotic signaling. These findings identify AUTAC-mediated Mcl1 degradation as a cardiac-sparing strategy to target an otherwise clinically constrained vulnerability and support tumor-selective lysosomal degradation as a path to safer Mcl1-directed therapy.

BackgroundMedulloblastoma is the most common malignant pediatric brain tumor. Although advances in conventional therapies have improved survival over the years, acquired drug resistance remains a major barrier to durable cure. As dysregulation of epigenetic mechanisms is increasingly recognized as a driver of medulloblastoma pathogenesis and therapeutic adaptation, targeting epigenetic vulnerabilities represents a promising strategy to overcome treatment resistance. MethodsWe generated vincristine-resistant medulloblastoma cell line models and performed chemical screening to identify therapeutically targetable vulnerabilities. Candidate hits were validated using transcriptomic analyses, chromatin immunoprecipitation, and CRISPR-mediated genetic ablation to define the molecular mechanisms underlying drug sensitivity. ResultsChemical screening identified multiple active epigenetic compound classes capable of resensitizing vincristine-resistant medulloblastoma cells, including histone methyltransferase inhibitors, histone deacetylase inhibitors, and bromodomain inhibitors. Among these, the CBP/p300 bromodomain inhibitor SGC-CBP30 emerged as the most potent sensitizer to vincristine. Transcriptomic profiling revealed that, while ABCB1 was among the most highly upregulated genes in resistant cells, SGC-CBP30 treatment selectively downregulated ABCC3 and ABCA4, an effect not observed in parental cells. Mechanistically, chromatin immunoprecipitation demonstrated enrichment of p300 and H3K27ac at the ABCC3 and ABCA4 promoters in resistant cells, which was markedly reduced following SGC-CBP30 treatment. Consistent with these findings, genetic ablation of CREBBP or EP300 phenocopied the effects of pharmacological inhibition. Analysis of patient datasets further demonstrated elevated CREBBP, EP300, and ABCC3 expression in SHH MB, with positive correlations between ABCC3 and both CREBBP and EP300, supporting the clinical relevance of this regulatory axis. ConclusionsTogether, our findings demonstrate that CBP/p300 activity contributes to acquired vincristine-resistance in medulloblastoma. Targeting this axis represents a promising strategy to overcome drug resistance and enhance the efficacy of vincristine-based chemotherapy particularly in the context of relapsed or refractory disease. PLAIN ENGLISH SUMMARYMedulloblastoma is the most common cancerous brain tumor in children. Although many children respond well to the treatment, some tumors become resistant to chemotherapy, making them much harder to treat. Understanding why this resistance develops could lead to better treatment options for children whose cancer returns or no longer respond to therapy. In this study, we created laboratory models of medulloblastoma that had become resistant to the chemotherapy drug vincristine. We then tested a collection of drugs to identify compounds, which would restore the cancer cells sensitivity to treatment. We have discovered that several drugs were effective, with one compound, called SGC-CBP30, showing particularly strong activity. We investigated how SGC-CBP30 works and found that it decreases the activity of genes that are linked to chemotherapy resistance. Using multiple complementary experimental approaches, we confirmed that this gene-regulating pathway plays an important role in helping medulloblastoma cells survive treatment. Our findings suggest that targeting this pathway could restore the effectiveness of chemotherapy in drug-resistant tumors. Although further research is needed before this approach can be used in patients, these results provide a promising foundation for developing new treatments for children with relapsed or treatment-resistant medulloblastoma.

The platelet P2Y1 receptor (P2Y1R) is necessary for inflammation, signalling via Rho-GTPase pathways to elicit functions that are distinct from aggregation (PLC-dependent canonical signalling pathway). Whether these distinct platelet inflammatory functions can be selectively suppressed to preserve hemostasis through the rational design of P2Y1R antagonists has not been explored. In silico molecular docking analysis examined biased nucleotide interactions within the P2Y1R binding pocket. The identified possible key amino acid residues guided rational design to synthesize compounds for pathway selective inhibition, evolving from nucleotide to non-nucleotide structures. The nucleotide analogue KMR-82-13 was predicted to engage distinct regions of the binding pocket and selectively inhibited platelet chemotaxis while preserving aggregation. These findings informed the design of a non-nucleotide compound KSN-159-27, aiming to retain key KMR-82-13-like interactions while improving drug-like properties. Docking and molecular dynamics simulation supported a stable but dynamic binding mode for KSN-159-27 within the P2Y1R pocket, consistent with pathway-selective inhibition. KSN-159-27 displayed characteristics of a pathway selective inverse agonist at P2Y1R towards G12/13-mediated pathways, but not those associated by Gq activation in P2Y1R-transfected HEK293T cells. KSN-159-27 showed functionally selective inhibition for platelet P2Y1R-mediated functions. In vivo, KSN-159-27 suppressed inflammatory cell recruitment, whilst preserving bleeding time and ADP-induced thromboembolic responses, in contrast to the neutral P2Y1R antagonist MRS2500. This first demonstration for the rational design of a pathway selective inverse agonist at platelet P2Y1Rs has significant implications for novel therapeutic strategies developed to safely target platelet activation during inflammation, in contrast to current anti-platelet drugs used in the prevention of thrombosis. Key PointsO_LIBiased inverse platelet P2Y1R agonists selectively supress inflammation whilst preserving hemostasis and the ability of platelets to aggregate. C_LIO_LIBiased inverse agonism selectively inhibited P2Y1R G12/13 (Rho-GTPAse functions) but not Gq activities (PLC functions). C_LI

Cav1.2 is an L-type voltage-gated Ca2+ channel (VGCC) that supports Ca2+ influx in response to membrane depolarization. Ca2+ entering via Cav1.2 alters gene expression, activates Ca2+-dependent enzymes and has been implicated in synaptic plasticity. ORL-1 is a Gi/o-coupled G protein-coupled receptor (GPCR) that is expressed in the peripheral and central nervous systems. Both Cav1.2 and ORL-1 are expressed in the hippocampus, where they have been implicated in learning and memory. It is well-documented that ORL-1 interacts with another VGCC, Cav2.2. However, less is known about potential interactions between Cav1.2 and ORL-1. Here, we examine the interplay between Cav1.2 (Cav1c, Cav2{delta}-1, Cav{beta}1) and ORL-1 co-expressed in tsA-201 cells by using biochemical, electrophysiological and confocal imaging analysis. Co-immunoprecipitations revealed that ORL-1 independently interacts with Cav1c and Cav2{delta}-1 subunits of the Cav1.2 channel complex. Electrophysiological recordings revealed that co-expression with ORL-1 reduced Cav1.2 peak current density without altering its biophysical properties. Acute perfusion with the ORL-1 receptor agonist nociceptin (1 M) did not alter Cav1.2 current density. Confocal imaging experiments revealed that ORL-1 significantly decreases Cav1.2 plasma membrane expression by disrupting forward trafficking. Interestingly, ORL-1 did not affect Cav1.2 endocytosis. Overall, our results demonstrate a previously unrecognized interaction between ORL-1 and Cav1.2 that alters Cav1.2 membrane expression without affecting biophysical properties.

Background: Subtype-selectivity predictions are scored against measured selectivity and judged against an assumed noise ceiling. We asked what an 2-adrenergic benchmark rewards and which controls change its interpretation. Research design and methods: On a frozen benchmark of 586 paired 2A/2C compounds we evaluated Glide SP docking, CNN rescoring, ligand-only fingerprint models, receptor descriptors and pose contacts, with dopamine D3/D2 as comparator, applying five controls: a measured ceiling, a cluster-identity null, a nonselective reference, a same-receptor floor and a trivial-descriptor baseline. Results: Five descriptors from SMILES reached Spearman 0.645, 72% of the measured ceiling, against 0.071 for Glide SP and 0.188 for CNN rescoring; receptor properties and pose contacts reduced to size under control, while a non-size signal of 0.258 survived. Measured rather than propagated noise raised that ceiling from 0.704 to 0.897; cluster identity alone reached R2 0.499 on D3/D2 and none on 2; a nonselective reference received +1.43 to +4.79 kcal/mol where zero is expected; and a same-receptor floor reached 1.77-fold against 1.88-fold across subtypes. Conclusions: Such benchmarks reward molecular size first; a method must exceed 0.645 before its score indicates structural reasoning. The controls are inexpensive; conclusions rest on two receptor pairs, a three-pair floor and static structures.