TDO2 and colon adenocarcinoma: TDO2 mRNA expression was significantly higher in SK-Mel-28 cells, compared to the human colon adenocarcinoma cell line and to the human endothelium, being 4.8 ± 0.9 fold over HUVEC and 12.5 ± 5 over HCT-8 (Fig. 1a).