GS reduces cell viability of HNSCC cell lines. Cell viability was determined in SCC4 and HSC2 cells after 24 h - 72 h of incubation with 5, 10, 20, 50, 75 and 100 μM GS. Viable cell number was assayed by MTT uptake. Graphs show % of viable (a) SCC4 and (b) HSC2 cells on treatment with GS in a dose- and time-dependent manner. Each data point represents the mean ± standard deviation (S.D.) of 3 independent experiments.