Better management of head and neck squamous cell carcinomas (HNSCCs) requires a clearer understanding of tumor biology and disease risk. Bitter taste receptors (T2Rs) have been studied in several cancers, including thyroid, salivary, and GI, but their role in HNSCC has not been explored. We found that HNSCC patient samples and cell lines expressed functional T2Rs on both the cell and nuclear membranes. Bitter compounds, including bacterial metabolites, activated T2R‐mediated nuclear Ca2+ responses leading to mitochondrial depolarization, caspase activation, and ultimately apoptosis. Buffering nuclear Ca2+ elevation blocked caspase activation. Furthermore, increased expression of T2Rs in HNSCCs from The Cancer Genome Atlas is associated with improved overall survival. This work suggests that T2Rs are potential biomarkers to predict outcomes and guide treatment selection, may be leveraged as therapeutic targets to stimulate tumor apoptosis, and may mediate tumor‐microbiome crosstalk in HNSCC.

T2R bitter taste receptors in airway motile cilia increase ciliary beat frequency (CBF) and nitric oxide (NO) production. Polymorphisms in some T2Rs are linked to disease outcomes in chronic rhinosinusitis (CRS) and cystic fibrosis (CF). We examined the expression of cilia T2Rs during the differentiation of human nasal epithelial cells grown at air–liquid interface (ALI). The T2R expression increased with differentiation but did not vary between CF and non-CF cultures. Treatment with Pseudomonas aeruginosa flagellin decreased the expression of diphenhydramine-responsive T2R14 and 40, among others. Diphenhydramine increased both NO production, measured by fluorescent dye DAF-FM, and CBF, measured via high-speed imaging. Increases in CBF were disrupted after flagellin treatment. Diphenhydramine impaired the growth of lab and clinical strains of P. aeruginosa, a major pathogen in CF and CF-related CRS. Diphenhydramine impaired biofilm formation of P. aeruginosa, measured via crystal violet staining, as well as the surface attachment of P. aeruginosa to CF airway epithelial cells, measured using colony-forming unit counting. Because the T2R agonist diphenhydramine increases NO production and CBF while also decreasing bacterial growth and biofilm production, diphenhydramine-derived compounds may have potential clinical usefulness in CF-related CRS as a topical therapy. However, utilizing T2R agonists as therapeutics within the context of P. aeruginosa infection may require co-treatment with anti-inflammatories to enhance T2R expression.

The transition metal copper (Cu) is an essential micronutrient required for development and proliferation, but the molecular mechanisms by which Cu contributes to these processes is not fully understood. Although traditionally studied as a static cofactor critical for the function of Cu-dependent enzymes, an expanding role for Cu is emerging to include its novel function as a dynamic mediator of signaling processes through the direct control of protein kinase activity. We now appreciate that Cu directly binds to and influences MEK1/2 and ULK1/2 kinase activity, and show here that reductions in MAPK and autophagic signaling are associated with dampened growth and survival of oncogenic BRAF-driven lung adenocarcinoma cells upon loss of Ctr1. Efficient autophagy, clonogenic survival, and tumorigenesis of BRAF-mutant cells required ULK1 Cu-binding. Although treatment with canonical MAPK inhibitors resulted in the upregulation of protective autophagy, mechanistically, the Cu chelator tetrathiomolybdate (TTM) was sufficient to target both autophagic and MAPK signaling as a means to blunt BRAF-driven tumorigenic properties. These findings support leveraging Cu chelation with TTM as an alternative therapeutic strategy to impair autophagy and MAPK signaling. As traditional MAPK monotherapies initiate autophagy signaling and promote cancer cell survival. Implications: We establish that copper chelation therapy inhibits both autophagy and MAPK signaling in BRAFV600E-driven lung adenocarcinoma, thus overcoming the upregulation of protective autophagy elicited by canonical MAPK pathway inhibitors.

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.