These studies have demonstrated a general effect of restored sensitivity of ABCB1 substrate drug in MDR cancer cells after ABCB1 knockout using CRISPR/Cas9 system, however, nothing was known regarding the variation in drug sensitivity of acquired MDR cell line with ABCB1 knockout comparing to that of the parental cell lines from which the MDR cell lines originated. Here, ABCB1 is linked to cancer.