Effects of sensitization with anti-epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) on ovarian cancer cell viability and antiproliferative activity of cetuximab (Cet). Cell viability (%) of (a) IGROV-1 and (d) SKOV-3 after short-term treatment (72 h) with erlotinib (E), gefitinib (G), and vandetanib (V) is shown in white columns. Striped columns indicate addition of cetuximab. Cell viability was assessed by performing MTT assay. (b,c,e,f): Cell viability of (b+c) IGROV-1 and (e+f) SKOV-3 sensitized with erlotinib (sE), gefitinib (sG), and vandetanib (sV) (1 µM) for 7 days and 6 weeks, respectively. White columns illustrate cell viability under continuous anti-EGFR treatment, grey columns document cell viability 72 h after discontinuation of TKI treatment. Striped columns show addition of cetuximab. Bars show means +/- standard deviation (SD) of four to six independent experiments. For illustration purposes, the cell viability of treated and sensitized cells is shown in relation to untreated and unsensitized tumor cells (w/o) in (a) and (d). Unpaired t-test was applied for statistical analysis, statistical significance (p < 0.05) is indicated (*).