SLCO4A1 and colorectal carcinoma: OATP2B1 knockdown did not significantly affect E1S uptake (Figure 6B), however OATP4A1 knockdown significantly reduced E1S uptake from 21.02 ± 3.12 to 8.93 ± 2.07 pmol/mg/h (p < 0.01), suggesting this transporter may play a key role in E1S transport in CRC.