Cell lines resistant to CCI-779 demonstrate higher expression levels of EGFR mRNA and elevated p-EGFR protein levels. (A) EGFR mRNA levels were measured by Real Time RT-PCR and correlated to the housekeeper gene Tubulin alpha-6. The relative EGFR mRNA expression was calculated using UM-SCC-74B with the lowest EGFR expression levels as reference and is given as fold levels. (B) To quantify the basal expression of phosphorylated, activated EGFR (p-EGFR Tyr1068) flow cytometry was used. Results are given as the median specific fluorescence intensity (MFI) of cells stained with the specific antibody divided by the intensity of cells stained with the isotype control antibody.