PLAU and head and neck squamous cell carcinoma: Three of the HNSCC cell lines (Cal27, HN6, HN12) were sensitive to the intercomplementing toxin (LD50, 0.5 nM to 8 nM), demonstrating functional uPA and MMP expression, while the two other cell lines, Hep2 and HN30 were resistant, indicating the absence of either functional uPA or MMP activity, or both.