Colorectal cancer (CRC) is one of the most common cancers, and rates of incidence and diagnosis of CRC have gradually increased. Carcinoembryonic antigen (CEA) is overexpressed in patients with CRC and is associated with cell adhesion, anoikis resistance, and promotion of metastasis to the liver. 5-Fluorouracil (5-FU) is a chemotherapeutic drug used to treat cancer, including CRC. However, a major issue of 5-FU therapy is the occurrence of chemoresistance, and the fact that 5-FU induces CEA overexpression, which may induce the 5-FU resistance. We previously isolated a CEA-specific RNA aptamer that was able to inhibit hepatic metastasis of colon cancer cells in a mouse model. In the present study, we tested whether protecting CEA using the CEA aptamer could enhance 5-FU sensitivity in chemoresistant LS174T colon cancer cells. We observed that the CEA aptamer sensitized the 5-FU-resistant colon cancer cell line to 5-FU more than five-fold (IC50 ~ 5.995 μM), compared with cells treated with 5-FU alone (IC50 ~ 31.46 μM). Moreover, treatment with CEA aptamer combined with 5-FU synergistically regressed growth of chemoresistant tumors in mouse xenografted models. Combinatorial treatment of 5-FU and CEA aptamer augmented caspase-8 activity in the 5-FU-resistant colon cancer cell line via aptamer-mediated disruption of CEA interaction with death receptor 5 and in mouse xenograft tumors. In conclusion, CEA-specific aptamer improved 5-FU sensitivity in chemoresistant colon cancer cells in vitro and in vivo, and thus represents a novel 5-FU adjuvant to overcome the chemoresistance in CRC patients.
Keywords: 5-fluorouracil; Anticancer chemoresistance; Carcinoembryonic antigen; Caspase-8; Combination chemotherapy; RNA aptamer.