PNP and head and neck squamous cell carcinoma: E. coli PNP‐based nucleoside cleavage represents an emerging experimental therapy for HNSCC, and optimizing this strategy depends on availability of well validated preclinical model systems.3, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19