Application of cation-π interactions in enzyme-substrate binding: Design, synthesis, biological evaluation, and molecular dynamics insights of novel hydrophilic substrates for NQO1

Cation-pi interaction is a type of noncovalent interaction formed between the pi-electron system and the positively charged ion or moieties. In this study, we designed a series of novel NQO1 substrates by introducing aliphatic nitrogen-containing side chains to fit with the L-shaped pocket of NQO1 by the formation of cation-pi interactions. Molecular dynamics (MD) simulation indicated that the basic N atom in the side chain of NQO1 substrates, which is prone to be protonated under physiological conditions, can form cation-pi interactions with the Phe232 and Phe236 residues of the NQO1 enzyme. Compound 4 with a methylpiperazinyl substituent was identified as the most efficient substrate for NQO1 with the reduction rate and catalytic efficiency of 1263 +/- 61 mu mol NADPH/min/mmol NQO1 and 2.8 +/- 0.3 x 10(6) M(-1)s(-1), respectively. Notably, compound 4 exhibited increased water solubility (110 mu g/mL) compared to that of beta-lap (43 mu g/mL), especially under acidic condition (pH = 3, solubility > 1000 mu g/mL). Compound 4 (IC50/A549 = 2.4 +/- 0.6 mM) showed potent antitumor activity against NQO1-rich cancer cells through ROS generation via NQO1-mediated redox cycling. These results emphasized that the application of cation-pi interactions by introducing basic aliphatic amine moiety is beneficial for both the water solubility and the NQO1-substrate binding, leading to promising NQO1-targeting antitumor candidates with improved druglike properties. (C) 2021 Elsevier Masson SAS. All rights reserved.

Automated summary

In this study, a series of novel NQO1 substrates were designed by introducing aliphatic nitrogen-containing side chains to form cation-pi interactions with the L-shaped pocket of NQO1. Compound 4 was identified as the most efficient substrate for NQO1, with high reduction rate and catalytic efficiency, as well as increased water solubility. Compound 4 showed potent antitumor activity against NQO1-rich cancer cells through ROS generation, highlighting the potential of cation-pi interactions for developing promising NQO1-targeting antitumor candidates with improved druglike properties.