Lidocaine Induces Apoptosis in Head and Neck Squamous Cell Carcinoma Cells Through Activation of Bitter Taste Receptor T2R14

Abstract

Head and Neck Squamous Cell Carcinomas (HNSCCs) have high mortality due to late stage diagnosis, high metastasis rates, and poor treatment options. Current therapies are invasive and aggressive, leading to a severe decline in patient quality of life (QoL). It is vital to create new therapies that are both potent and localized and/or targeted to prolong survival while maintaining QoL. Lidocaine is a local anesthetic used in HNSCC surgery settings. Lidocaine also activates bitter taste (taste family 2) receptor 14 (T2R14). T2Rs are G-protein coupled receptors (GPCRs) that increase intracellular Ca²⁺ when activated. T2Rs are expressed in mucosal epithelia, including internal regions of the head and neck, and are accessible drug targets. Here, we show that lidocaine increases intracellular Ca²⁺ and decreases cAMP in several HNSCC cell lines. Ca²⁺ release from the ER results in Ca²⁺ uptake into the mitochondria. Ca²⁺ mobilization is blocked with GPCR inhibitors and T2R14 antagonist, 6-methoxyflavanone. Lidocaine activation of T2R14 depolarizes the mitochondrial membrane, inhibits cell proliferation, and induces apoptosis. Lidocaine activates caspase-3 and -7 cleavage and also increases total caspase protein levels despite no changes in mRNA production. Both total and cleaved caspase products were upregulated even in the presence of cycloheximide, an inhibitor of protein synthesis. This suggests inhibition of the ubiquitin-proteasome system. It is vital to understand Lidocaine-induced apoptosis in HSNCCs to utilize its chemotherapeutic effects as a treatment option. In addition, future studies on T2R14 expression in HNSCC patients could provide insight for implementing lidocaine as a targeted topical therapy.