Background and purpose: Lactate, historically viewed as a metabolic by-product, has emerged as a signalling molecule via the G protein-coupled receptor Hydroxycarboxylic Acid Receptor 1 (HCAR1). The receptor is primarily expressed in adipocytes but also found in various other tissues. HCAR1 activation has been shown to regulate lipolysis and improve insulin sensitivity, positioning it as a promising therapeutic target for metabolic disorders such as obesity and type 2 diabetes. Despite its potential, its role in cancer progression and the limited availability of characterized ligands necessitate further investigation into its signalling mechanisms. This study aimed to broaden the pharmacological understanding of HCAR1 by investigating previously uncharacterized ligands and profiling their signalling properties.
Experimental approach: We employed enhanced bystander bioluminescence resonance energy transfer (ebBRET) assays to investigate G protein activation and β-arrestin recruitment following ligand stimulation of HCAR1. A panel of compounds was screened to identify more potent agonists and modulators of HCAR1 signalling.
Key results: We identified AZ7136 as a relatively potent HCAR1 agonist, AZ2114 as a partial agonist, and GPR81 agonist 1 as an ago-positive allosteric modulator. HCAR1 preferentially activated Gαi/o and Gαs pathways without recruiting β-arrestins, revealing a distinct signalling profile.
Conclusion and implications: These findings expand our understanding of HCAR1 signalling and introduce new molecular tools for probing its physiological and pathological roles. The characterized ligands may support future therapeutic strategies targeting HCAR1 in metabolic disorders while informing approaches to mitigate potential oncogenic effects.
Keywords: G‐protein‐coupled; allosteric modulation; drug screening assay; metabolism; receptors; signal transduction.
© 2025 The Author(s). British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.