Fucoidan increased the sensitivity to gefitinib in lung cancer cells correlates with reduction of TGFβ-mediated Slug expression.

Gefitinib is a first tyrosine kinase inhibitor (TKI) designed with an EGFR tyrosine kinase for lung cancer targeted therapy. However, some lung cancer patients with wild-type EGFR (wtEGFR) or acquired secondary EGFR mutation showed lower response rate of gefitinib. In this study, we examined the efficacy of fucoidan on altering gefitinib-sensitivity on TKI-resistant lung cancer A549 and H1975 cells. We found that the simultaneous administration of fucoidan and gefitinib synergistically inhibited lung cancer cell viability via activating apoptotic response. Moreover, we found that fucoidan effectively downregulated expressions of mesenchymal-like molecules. Mechanistically, we demonstrated that fucoidan altered the gefitinib-inhibitory rate may result from induction of proteasome-dependent Slug degradation. Abolishment of TGFβ signaling enhanced gefitinib-inhibited cell viability and reduced N-cadherin, Twist and Slug levels. Moreover, knockdown of Slug contributed the increasing the gefitinib-sensitivity of H1975 cells. Our study is the first to find that fucoidan alters the gefitinib-sensitive of TKI-resistant cells by reduction of TGFβ receptor-mediated expressions of mesenchymal-like molecules and induction of Slug degradation. Together, our current results indicate that combination of fucoidan and gefitinib may be a potential and effective therapeutic strategy in gefitinib non-sensitive lung cancer.

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