ABCB1 and cancer: To test the reversal effect of these three peptides in ABC transporter-mediated MDR, drug-selected MDR human cancer cell lines, KB-C2 and NCI-H460/MX20, and their parental cell lines, KB-3-1 and NCI-H460, were used to examine the ABCB1 substrates paclitaxel and doxorubicin and ABCG2 substrates mitoxantrone and topotecan.