Identification of inhibitor concentrations to efficiently screen and measure inhibition Ki values against solute carrier transporters.

The objective was to identify inhibitor concentrations to efficiently screen and measure inhibition K(i) values of solute carrier (SLC) transporters. The intestinal bile acid transporter and its native substrate taurocholate were used as a model system. Inhibition experiments were conducted using 27 compounds. For each compound, the inhibition constant K(i) was obtained from the comprehensive inhibition profile, and referred as the reference K(i). K(i) values were also estimated from various partial profiles and were compared to the reference K(i). A screening K(i) was estimated from one data point and also compared to the reference K(i). Results indicate that K(i) can be accurately measured using an inhibitor concentration range of only 0-K(i) via five different inhibitor concentrations. Additionally, a screening concentration of 10-fold the substrate affinity K(t) for potent inhibitors (K(i)<20K(t)) and 100-fold K(t) for nonpotent inhibitors (K(i)>20K(t)) provided an accurate K(i) estimation. Results were validated through inhibition studies of two other SLC transporters. In conclusion, experimental conditions to screen and measure accurate transporter inhibition constant K(i) are suggested where a low range of inhibitor concentrations can be used. This approach is advantageous in that minimal compound is needed to perform studies and accommodates compounds with low aqueous solubility.