Fig. 4.

Validation of the biomarkers of drug sensitivity in vitro. a, b ZEC127 (CDKN2A/2B loss) and ZEC118 (CDKN2A/2B no CNV) were used to evaluate the sensitivity of CDK4/6 inhibitors (palbociclib and ribociclib) using colony formation assays. Three experiments were averaged, and error bars correspond to the standard deviation of colony numbers. The colony number differences between different dose groups of inhibitors were compared using a Student’s t test and *p < 0.01 and **p < 0.001. c Mutations of cell cycle checkpoint genes including CDKN2A, CDKN2B, MYC, CCND1, CDK4, RB1, TP53, CHEK1, and CCNE1 were detected in eight ESCC PDCs using targeted deep sequencing. d Z-score analysis of the expression level of cell cycle checkpoint genes in the eight ESCC PDCs, which carried either CDKN2A or CDKN2B loss, or neither