Background: Non-small cell lung cancer (NSCLS) comprises about 80% of all lung cancers. The regular treatments for NSCLC are surgery, chemotherapy, radiotherapy and EGFR-targeted therapy. EGFR is frequently mutated and amplified in lung adenocarcinom as sensitive to EGFR inhibitors. The EGFR-targeted therapy, Gefitinib and Erlotinib, significantly improves disease free survival. However, it was not possible to predict super-responder of gefitinib degree of EGFR expression as a single agent. There is an imposing need for new rationally designed regimens to overcome Gefitinib resistance. The other tyrosine kinase inhibitor, Lapatinib, is a small-molecule inhibitor targeting both the HER2 and the epidermal growth factor receptor (EGFR) in solid tumors. We hypothesized that this aberrant activation of EGFR may contribute to Gefitinib resistance and dual blocking EGFR activation with EGFR and ERBB2 inhibitor will re-sensitize HER family in lung cancers.

Experimental Design: In the in vitro study, cancer cells with EGFR wild type or mutation type were treated with Tyrosine kinase inhibitor, Gefitinib, Lapatinib, or combined treatments. The responses of cells to Gefitinib or/and Lapatinib treatments were evaluated by MTS proliferation, apoptosis assay, soft agar colony formation assay and western blot. In the in vivo study, pulmonary xenograft tumors were established in ICR/SCID mouse and treated with vehicle control, Gefitinib, Lapatinib, or Gefitinib plus Lapatinib for 4 weeks. Tumor volume were monitored and further studied by immunohistochemistry on collected tumors.

Results: We selected multiple pairs of EGFR wild type and mutation type. The EGFR mutation cells have more effect under single tyrosine kinase inhibitor (Gefitinib) treatment compared with EGFR wild type cells. Dual inhibition of EGFR activation sensitized EGFR expression pulmonary cancer cells to Gefitinib treatment. Compared with single treatment, combined treatment led to a significantly more effective inhibition of cell proliferation and induced apoptosis. In a mouse pulmonary xenograft model, combination therapy with Gefitinib and Lapatinib dramatically inhibited EGFR wild type tumor growth.

Conclusions: Since the EGFR family inhibitor, Lapatinib is currently under Phase III clinical trial, combining Gefitinib with this Lapatinib, dual EGFR inhibitors is a clinically applicable strategy and a promising combinatory targeted anti-cancer therapy to overcome EGFR wild type mediated Gefitinib resistance.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 619.