STAT3 inhibitor BBI608 enhances the antitumor effect of gefitinib on EGFR-mutated non-small cell lung cancer cells.

Gefitinib is known as epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) while an increasing number of patients with non-small cell lung cancer (NSCLC) are becoming resistant to EGFR-TKI. Therefore, innovative methods are urgently needed to overcome primary and acquired resistance to EGFR-TKIs in NSCLC patients. The viability of HCC827 cells and HCC827 Ge-resistant (Ge-r) cells treated with gefitinib and/or STAT3 inhibitor and/or Overexpression (Oe)-ROR1 was detected by CCK-8 assay. The colony formation, invasion, migration and apoptosis of HCC827 Ge-r cells treated with gefitinib and/or STAT3 inhibitor and/or Oe-ROR1 transfection were, respectively, detected by clone formation assay, transwell assay, wound healing assay and flow cytometry analysis. The protein expressions of EGFR, STAT3, invasion and migration-related proteins, ROR1/ABCB1/P53 pathway and apoptosis-related proteins were analyzed by Western blot analysis. The transfection effect of Oe-ROR1 in HCC827 Ge-r cells was confirmed by qRT-PCR and Western blot analysis. In vivo animal experiment was used to confirm the role of STAT3 in improving the sensitivity of HCC827 Ge-r cells to gefitinib. As a result, after treatment of gefitinib, the viability of HCC827 cells was lower than that of HCC827 Ge-r cells and the expression of p/t-EGFR and p/t-STAT3 was decreased in HCC827 cells and HCC827 Ge-r cells after treatment of gefitinib. STAT3 inhibitor BBI608 enhanced the ability of gefitinib to inhibit viability, invasion and migration while promoting apoptosis of HCC827 Ge-r cells treated with gefitinib, which was partially reversed by ROR1 overexpression. STAT3 inhibitor further down-regulated the expression of MMP2, MMP9, ROR1, ABCB1 and BCl2, while up-regulated the expression of p53, bax and cleaved caspase3 in HCC827 Ge-r cells treated with gefitinib, which was partially reversed by ROR1 overexpression. In vivo experiment, STAT3 inhibitor further suppressed the size of NSCLC tissues, and further down-regulated the expression of ROR1 and ABCB1 while up-regulated the expression of p53 in NSCLC tissues. In conclusion, STAT3 inhibitor enhanced the antitumor effect of gefitinib on EGFR-mutated NSCLC cells through regulating ROR1/ABCB1/P53 pathway.