Fig. 1. ESCC cells developed acquired resistance after continuous exposure to PI3Kα inhibition.

A A series of ESCC cells were treated with CYH33 or alpelisib for 72 h and the GI₅₀ values were determined with SRB assay (n = 3). B Parental and resistant cells were incubated with CYH33 for 72 h and cell proliferation was measured with SRB assay. Resistance factor (RF) was calculated by the ratio of GI₅₀ obtained in CYH33-resistant cells and that in parental cells (n = 3). C Parental and resistant cells were treated with CYH33 at the indicated concentrations for 72 h and cell cycle distribution was analyzed by flow cytometry (n = 3). Data are presented as mean + SD. Differences between indicated groups were analyzed using one-way ANOVA with Tukey multiple group comparison test.*P < 0.05, **P < 0.01, ***P < 0.001.