Dual blockade of HER3 and EGFR can effectively inhibit the proliferation of CtxRclones. (A) Combinatorial treatment of CtxR clones with cetuximab and U3-1287 leads to proliferation inhibition. Cell proliferation was measured using crystal violet assay and plotted as a percentage of proliferation relative to the vehicle control cells. Data points are represented as mean ± s.e.m. (n = 3). (B) Combinatorial treatment with cetuximab and U3-1287 leads to loss of HER3 expression in CtxR clones. Protein lysates were fractionated on SDS–PAGE followed by immunoblotting for the indicated proteins. α-Tubulin was used as a loading control.