The epidermal growth factor receptor (EGFR) is a central regulator of proliferation and progression in human being cancers. In addition, cetuximab-resistant cells manifested strong activation of HER2, HER3 and cMET. EGFR upregulation promoted increased dimerization with HER2 and HER3 leading to their transactivation. Blockade of EGFR and HER2 led to loss of HER3 and PI(3)K/Akt activity. These data suggest that acquired-resistance to cetuximab is accompanied by dysregulation of EGFR internalization/degradation and subsequent EGFR-dependent activation of HER3. Taken together these findings suggest a rationale for the clinical evaluation of combinatorial anti-HER targeting approaches in tumors manifesting acquired resistance to cetuximab. following long-term exposure to cetuximab in NSCLC (H226) and HNSCC (SCC-1) cell lines. Following establishment of stable clones, we performed high-throughput screening to examine the activity of 42 membrane receptor tyrosine kinases (RTKs). Through comparative analysis of cetuximab-resistant versus parental lines, we identified that EGFR along with HER2, HER3 and cMET are all highly activated in the resistant clones. Further studies suggest that acquired resistance to cetuximab reflects dysregulation of EGFR internalization/degradation and subsequent EGFR-dependent activation of HER3. RESULTS Establishment of cetuximab-resistant lines We established cetuximab resistant tumor cell lines using the human NSCLC line NCI-H226 (H226) and the HNSCC line UMSCC-1 (SCC1) to use as a model system to elucidate molecular mechanisms of acquired-resistance to cetuximab. These lines were chosen based on three primary criteria; 1) Cetuximab is used in therapy for both tumor types, 2) the cell lines are sensitive to cetuximab and 3) the cell lines have no TKD mutations. To generate resistant lines, H226 and SCC1 cells were continuously exposed to increasing concentrations of cetuximab over six months. Following the development of heterogeneous populations of cetuximab-resistant cells we isolated individual subclones of cetuximab-resistant lines. This process resulted in six stable resistant clones for the H226 NSCLC line designated HC1, HC4, HC5, HC6, HC7 and HC8. The sensitive parental line was designated HP. For the PD 169316 SCC1 HNSCC line six stable resistant clones were produced (SC1, SC2, SC5, SC6, SC7, SC8). As demonstrated in Shape 1A, all HC clones shown a powerful cetuximab-resistant phenotype when challenged with raising concentrations of cetuximab when compared with parental controls. Identical results were noticed using the SCC1 cetuximab-resistant clones (Shape 1B). Sequence evaluation from the EGFR TKD in H226 cells following the establishment of resistant clones indicated no mutations created through the selection procedure PD 169316 in either the resistant or PD 169316 parental cells (data not really shown). Shape 1 phospho-receptor tyrosine kinase (RTK) array in NSCLC HNSCC and H226 SCC1 cells demonstrate upregulation of EGFR, HER2, HER3 and cMET Upregulation of activation and EGFR of HER2, HER3 and cMet After effective establishment of cetuximab-resistant clones, we performed high-throughput comparative analyses calculating phosphorylated RTKs in the resistant PD 169316 vs. parental lines to check the hypothesis that obtained level of resistance to EGFR inhibition outcomes from the activation of alternate RTKs that talk about overlapping sign transduction elements using the EGFR. To check this hypothesis, we screened the experience of a -panel of triggered RTKs using an antibody-based array from R&D Systems (Minneapolis, As shown in Shape 1C MN). Pursuing quantification of PD 169316 scanned pictures using ImageQuant Mouse monoclonal to CD8/CD38 (FITC/PE). software program, the relative manifestation of particular phosphorylated RTKs between cetuximab-resistant and parental cells was established (Shape 1D). Exactly the same experimental strategy was performed using the SCC1 cetuximab-resistant lines and parental control (Shape 1E and F). Out of this high-throughput display, many phosphorylated RTKs had been notably up-regulated in both cetuximab-resistant NSCLC and HNSCC tumor lines including HER family (EGFR, HER2 and HER3) as well as the hepatocyte development element receptor (HGFR, c-MET). These total outcomes indicated these 3rd party tumor cell lines, challenged with cetuximab chronically, manifested highly similar patterns of altered RTK expression and or activation. To validate results of the phospho-RTK array in individual cetuximab-resistant clones we performed standard Western blot analysis on the parental and cetuximab-resistant clones of H226 to measure levels of EGFR, HER2, HER3, cMET, and members of their downstream signaling cascades, including the phosphorylated forms of MAPK and Akt. The results demonstrated that findings from the phospho-RTK array were consistent in all of the cetuximab-resistant clones (Figure 2A). Although the activity of EGFR, HER2, HER3 and cMET was increased relative to the parental line, only EGFR steady-state expression was dramatically increased in cetuximab-resistant clones. Furthermore, analysis of EGFR binding partners using immunoprecipitation techniques indicated that EGFR displayed increased.