The anti-vascular and anti-tumor response of human lung cancer growing orthotopically in mice to AEE788, a tyrosine kinase inhibitor of EGFR and VEGFR, is dependent upon EGF/TGFα expression

Proc Amer Assoc Cancer Res, Volume 46, 2005 3031 Introduction: Targeting of EGFR has been extensively studied in lung cancer; yet, clinical data show that only a fraction of patients can respond to EGFR inhibitors. The development and validation of strategies to identify patients likely to benefit from these agents is therefore of critical importance. We hypothesized that the expression of EGF/TGFα by tumors is needed for activation of EGFR in both tumor (autocrine) and tumor-associated endothelial (paracrine) cells and would thus be required for an anti-tumor and anti-vascular response to EGFR signal blockade. Methods: The human lung adenocarcinoma cell lines NCIH441 (EGF/TGFα+/EGFR+) and PC14PE6 (EGF/TGFα-/EGFR+) were injected into the lungs of mice. Once tumors formed, mice were randomized to treatment with AEE788 or vehicle. When control mice became moribund, animals were killed and assessed for tumor size, pleural effusion, metastasis, and immunohistochemical studies. The EGFR nucleotide sequence was analyzed in H441 and PC14PE6 cell lines. Results: EGFR was found to be wild type in both H441 and PC14PE6 cells. Treatment of mice bearing H441 lung tumors with AEE788 resulted in a significant (p < 0.01) reduction of primary tumor growth (93.5%), pleural effusion incidence (100%), pleural metastasis (75%), and lymph node metastasis (95%). In contrast, for PC14PE6 lung tumors AEE788 treatment produced a 0, 43, 37.5, and 0 percent reduction in primary tumor growth, pleural effusion incidence, pleural metastasis, and lymph node metastasis, respectively. Immunohistochemical analyses revealed that the expression of VEGF and VEGFR2 was comparable for H441 and PC14PE6 tumors. However, only H441 tumors produced EGF/TGFα with resultant expression and activation of EGFR in both tumor and tumor-associated endothelial cells. PC14PE6 tumors did not produce EGF/TGFα nor did they express activated EGFR in both the tumor and tumor-associated endothelial cells. Αnalysis of microvessel density (CD31) show that vascularization was reduced in H441 tumors but not in PC14PE6 tumors. Double labeling to assess endothelial and tumor cell proliferation (CD31/Ki67) and apoptosis (CD31/TUNEL) demonstrated that AEE788 decreased proliferation and increased apoptosis for both tumor and endothelial cells in H441 tumors but not in PC14PE6 tumors. Conclusion: We demonstrate that the response of human lung cancer growing orthotopically in mice to the EGFR and VEGFR antagonist AEE788 correlates with EGF/TGFα expression but not with EGFR expression. Further, EGF/TGFα was required for activation of EGFR on tumor cells and tumor-associated endothelial cells. Our results strongly suggest that even if wild type EGFR is expressed, only those tumors that produce the necessary ligand ( i.e. , EGF/TGFα) will respond to biologically targeted therapies against the activated EGF receptor.