P2RX3 and head and neck squamous cell carcinoma: Application of two different classes of P2X3 and P2X2/3 receptor antagonists, a competitive antagonist A-317491 and an allosteric antagonist AF-353, resulted in a significant decrease in the percentage of neurons responding to HNSCC supernatant (Figure 2d): 16% (16/99) following A-317491 treatment, and 15% (14/96) following AF-353 treatment.