Lapatinib, a dual inhibitor of EGFR and HER2, has synergistic effects with 5-fluorouracil on esophageal carcinoma.

Epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) amplification occurs in over 30% of esophageal carcinomas. Combination therapies with EGFR and HER2-targeting agents and cytotoxic agents are considered a potential therapeutic option for esophageal cancer. We evaluated the antitumor effects of lapatinib, a dual tyrosine kinase inhibitor which simultaneously inhibits EGFR and HER2, 5-fluorouracil (5-Fu) alone and in combination on esophageal cancer cells. The antiproliferative activity of lapatinib, 5-Fu and lapatinib plus 5-Fu was measured by MTT assay and the combination index (CI) values were calculated. Additionally, cell cycle distribution of lapatinib alone and the combination with 5-Fu were detected by flow cytometry analysis. Annexin V-FITC and propidium iodide stain were used for analyzing the apoptotic cells after cells were treated with either agent alone or in combination. The EGFR and HER2 activated signaling pathways were monitored by western blotting. The combination of lapatinib and 5-Fu synergistically inhibited cell proliferation and exhibited an enhanced proapoptotic effect on esophageal cancer cells. The potentiation effect of combined treatment was associated with downregulation of EGFR and HER2 signaling pathways because data from western blot analysis showed that lapatinib in combination with 5-Fu markedly reduced the phosphorylation of EGFR and HER2, and inhibited the activation of downstream signaling molecules, such as AKT and ERK. A significant G1 arrest was also observed in cell cycle analysis after exposing cells to lapatinib, however, combination with 5-Fu did not enhance G1 arrest. These results indicate that the combination of the lapatinib and 5-Fu is a promising treatment option for esophageal carcinoma with HER2 amplification.