Fig. 2

BBI608 significantly inhibited cell viability in EGFR-positive lung cancers, including EGFR E746-A750 HCC827, wild-type (WT) A549, and T790 M H1975. a EGFR-positive HCC827, A549, and H1975 and EGFR-negative H520 lung cancers were selected for use in identifying potential therapeutic agents. HCC827 with EGFR E746-A750 mutation triggers TKIs, whereas A549 and H1975 bearing KRAS and T790 M mutations, respectively, are resistant to TKIs. b Results from qPCR revealed that ERBB3 was expressed in HCC27, A549, and H1975 at higher levels than in H520 cells. In particular, H1975 showed the highest ERBB3 expression level. c The results of Western blot analyses demonstrated and validated that H1975 with EGFR autophosphorylation presented higher phosphorylation of STAT3 and expression of HER3 (ERBB3). d To identify potential therapeutic agents against EGFR-positive lung cancers, a panel kit containing 172 compounds was used and HCC827, A549, H1975, and H520 cells were added separately and incubated for 48 h. The detailed cell viability measurements are illustrated in Additional file 9: Figure S1, which revealed that BBI608 significantly reduced the viability of HCC827, A549, and H975 cells as opposed to the viability of H520 cells. e BBI608 significantly reduced the viability of HCC827 cells, which is similar to the results observed under afatinib, an EGFR-TKI. However, BBI608 reduced the viability of A549 and H1975 cells compared with the viability of these cells under afatinib, indicating that BBI608 overcame EGFR-TKI resistance associated with KRAS and T790 M mutations. f and g A549-derived cancer stem-like cells significantly increased cell migration, but A549 treated with BBI608 reduced cell migration. h Moreover, BBI608 significantly reduced tumor growth in A549-transplated xenografts in vivo. *p < 0.05, ***p < 0.001, NS, nonsignificant. Scale bar, 100 μm