Effects of HER1-HER2 axis inhibitors measured by VeraTag™ lysate assays. SKOV3 cells were serum-starved overnight then treated with 2C4, erlotinib, or lapatinib for two hours at the indicated concentrations, in units of μg/mL for 2C4 and in μM for erlotinib and lapatinib. A final concentration of 16 nM EGF was added or mock-added to the drug-containing media for 10 minutes prior to harvesting cells for lysate or FFPE. VeraTag™ lysate assays were used to examine A) effects of 2C4, B) effects of lapatinib and C) effects of erlotinib on HER1-HER2 heterodimerization (top row), phosphorylation of HER2 (second row), phosphorylation of HER1 (third row), and HER1-HER1 homodimerization (bottom row). Each experiment, beginning with a new growth of SKOV3 cells, was performed twice with consistent results.