ABCB1 and cancer: To this end, we investigated the effect of ABCB1 and ABCG2 on the efficacy of citarinostat in human cancer cells by examining the acetylation level of α-tubulin (Ac-tub), which is a known non-histone substrate of HDAC6 [22], in drug-sensitive cancer cell lines and multidrug-resistant variants overexpressing ABCB1 or ABCG2.