ABCB1 and neoplasm: To determine whether the peptides (HX-12A, HX-12B, and HX-12C) can reverse multi-drug resistance mediated by ABCB1 transporter, we tested the sensitivity of drug-induced resistant tumor cell line (KB-C2), the transfected ABCB1-overexpressing cell lines (HEK293/ABCB1) and their parental cell lines (KB-3-1 and HEK293/pcDNA3.1) to the peptides.