PLAU and head and neck squamous cell carcinoma: Thus, although all of the four tumors resulting from the HNSCC cell lines were efficiently treated with the intercomplementing toxin when xenografted to mice, none of the cell lines displayed significant sensitivity to LF in culture (wildtype PA with LF, Figure 1C), and one cell line did not express sufficient cell surface uPA and MMP activity for functional PA heptamer formation (Hep2 cells, intercomplementing toxin with FP59, Figure 1B).