Cytotoxicity and Viability Assay for HNSCC

The Crystal Violet Assay Kit (#ab232855; Abcam, Cambridge, UK) was used for cell cytotoxicity and cell viability studies, as previously described [22 (link)]. Briefly, the HNSCC cells were plated 3000–4000/well in 96-well plates and treated with hDT806, cetuximab (#A2000; Selleckchem, Houston, TX, USA), or erlotinib (#S1023; Selleckchem) following a 2-fold serial dilution. Five to seven days later, a crystal violet staining assay was performed according to the manufacturer’s instruction to determine cytotoxicity and cell viability. Optical density (O.D.) of each well was measured at 595 nm on a microplate reader. The percentage of viable (attached) cells against the values of untreated control samples were calculated to represent cell viability [23 (link)].