Differential expression of hENT1 and hENT2 in colon cancer cell lines.

Human equilibrative nucleoside transporters (hENT) 1 and 2, encoded by SLC29A1 and SLC29A2, permit the bidirectional passage of nucleoside analogues into cells and may correlate with clinical responses to chemotherapy in patients with colorectal cancer (CRC). The purpose of this study was to evaluate the expression profiles of SLC29A1 and SLC29A2 in human cancer cell lines. Using quantitative real-time polymerase chain reaction, we comprehensively profiled the transcription levels of SLC29A1 and SLC29A2 in 16 colon cancer cell lines. We validated the ubiquitous and heterogeneous distribution of SLC29A1 and SLC29A2 in human colon cancer cell lines and demonstrated that SLC29A1 was highly expressed in 25% of metastatic cell lines (Colo201 and Colo205) and 62.5% of primary cell lines (Caco2, Colo320, HCT116, RKO, and SW48). For the first time, we showed that both SLC29A1 and SLC29A2 were expressed at lower levels in colon cancer cell lines originating from metastatic sites than from primary sites. These findings indicate that most patients with metastatic CRC (mCRC) may have low hENT1 expression, and treatment with nucleoside analogues may be inefficient. However, some patients still show high hENT1 expression and have a high probability of benefiting from these drugs. Therefore, evaluating transporter expression profiles and different drug responses between primary and metastatic tumors in patients with mCRC is important. Further assessment of the association between hENTs and drug-based treatment of mCRC is required to elucidate the mechanisms of chemotherapy resistance.