HCAR3 and Kynurenic Acid in Cancer: A Promising Axis of Immunometabolic Regulation or a Scientific Mirage?

The hydroxycarboxylic acid receptor (HCAR) family belongs to G-protein-coupled receptors (GPCRs) implicated in a diverse array of physiological and pathological mechanisms. Kynurenic acid, a metabolite of the tryptophan catabolic pathway, has been proposed as a putative ligand of HCAR3. This receptor, among other HCARs, has garnered particular attention due to its exclusive expression in humans and closely related primates, and its emerging role in immunometabolic regulation. This review focuses on the potential role of HCAR3 in cancer initiation, progression, and metastasis. Moreover, it presents a comprehensive analysis of the potential functional and molecular interactions between kynurenic acid and HCAR3 in the context of cancer pathophysiology, which may have significant implications for tumor immunomodulation and the development of new therapeutic strategies.