ABCB1 and colorectal carcinoma: All the tested SN-38-resistant variants of CRC cell lines presented elevated expressions of several ABC proteins; however, the profiles differed among all the cell lines, as seen in Figure 1A. The expressions of main SN-38 and irinotecan transporters, i.e., ABCB1, ABCC1, ABCC2, and ABCG2, were significantly upregulated in most SN-38-resistant variants, except for HCT116 cells.