Fig. 1
A-D Cytotoxic activity of OTS964 in drug-selected, gene-transfected, or gene-knockout cells and their respective parental cells. The concentration-response curves and IC50 values for OTS964 with or without a verified ABCB1 inhibitor in A) KB-C2 and KB-3-1, B) HEK293/ABCB1 and HEK293/pcDNA3.1, C) SW620/Ad300 and SW620, and D) SW620/Ad300-ABCB1ko and SW620-ABCB1ko cells. The GraphPad software [log (inhibitor) vs. response] was used to fit nonlinear regression and to calculate IC50 values. Each dot is expressed as mean ± SD from a representative of three independent experiments. *p < 0.05 versus the respective control group. E-F Effects of OTS964 on transport function mediated by ABCB1. The intracellular accumulation of [3H]-PTX in E) KB-C2 and KB-3-1 and F) HEK293/ABCB1 and HEK293/pcDNA3.1 cells after 2 h of pretreatment with vehicle, OTS964, or VPL. Data are expressed as mean ± SD from a representative of three independent experiments. *p < 0.05 versus the respective control group. G Effects of OTS964 on ATPase activity mediated by ABCB1. Effects of 0–40 μM OTS964 with or without 1 μM tepotinib on ATPase activity of ABCB1. Concentration of OTS964 was plotted against basal level (without OTS964) of ABCB1 ATPase activity. Data are expressed as mean ± SD from a representative of three independent experiments. H-J Highest-scoring docked pose of OTS964 within human ABCB1 at substrate-binding site. H) Overview of PTX and the best-scoring pose of OTS964 in the drug binding pocket of ABCB1 protein. PTX and OTS964 are displayed as colored sticks, blue: PTX; red: OTS964. I) Details of interactions between OTS964 and ABCB1 binding pocket. Predicted bonds are displayed as colored dash lines: hydrogen bond: yellow; pi-pi stacking: blue; cation-pi interaction: green. J) 2D OTS964-ABCB1 interaction. Important amino acids are displayed as colored bubbles (green: hydrophobic; blue: polar; red: positively charged). Predicted bonds are displayed as colored lines: green line: pi-pi stacking; purple line with arrow: hydrogen bond; red line: cation-pi interaction