ABCB1 and colorectal carcinoma: In addition, pegylated liposomes loaded with epirubicin and antisense oligonucleotides (ASOs) against MDR1, MRP1 and MRP2 increased the antitumor activity of the drug in mice bearing CRC (CT26 cells), while administration of ASOs alone did not show significant differences between resistant and non-resistant tumors [51].