Figure 6. CDDP-resistant SCCHN cells show cross-resistance to ATO whereas cetuximab-resistant cells display increased ATO sensitivity.

The sensitivity of (A) cetuximab-resistant UT-SCC-9 cells (UT-SCC-9_CET-R) to ATO (left panel) or cetuximab (right panel) compared to their parental sensitive counterparts (UT-SCC-9_CET-S) was determined by the MTT assay. In addition, (B) the sensitivity of cisplatin-resistant FaDu cells (FaDu_CDDP-R) and parental FaDu_CDDP-S to ATO or CDDP treatment was determined. Briefly, cells were treated for 10 days with the drugs at the indicated concentrations. Cell viability was assessed by measuring the absorbance of the formazan solution. Each sample was analyzed in six technical replicates and the experimental series were repeated for four times. Survival fractions were calculated on the basis of untreated cells. The mean surviving fractions ± SEM are presented.