Buthaina Hussein, Balqis Ikhmais, Richard Bryce, Ian Stratford and Sally Freeman
Manchester Pharmacy School, The University of Manchester, Manchester, United Kingdom
Quinone reductases (QRs) are the mammalian enzyme family responsible for the two-electron reduction of quinones to hydroquinones. NRH quinone oxidoreductase 2 (NQO2) belongs to this family and evidence shows that NQO2 maybe associated with cancer initiation via the production of ROS. In addition, NQO2 may be involved in cancer progression as a consequence of its ability to act as a "nanny" protein, alter cyclin D expression and modulate the activity of NF-ĸB. Hence, there is an interest in developing pharmacological inhibitors of NQO2 in order to study these processes; however, known inhibitors such as resveratrol, casimiroin, melatonin, chloroquine and imatinib are compromised by a variety of "off-target" effects. Thus, the initial aim of this project has been to design, synthesise and evaluate novel NQO2 inhibitors with high potency and good selectivity in cancer cells in vitro.
A library of analogues containing the 4-aminoquinoline scaffold were computationally docked into the crystal structure of NQO2 (PDB protein code 1SG0) using Gold suite (version 5.2). The results of the molecular docking were used to select twenty compounds for synthesis. The potency of these compounds to inhibit the NQO2 enzyme were then determined spectrophotometrically using 2, 6-dichlorophenolindophenol as a substrate for NQO2. These compounds showed good inhibition of the recombinant NQO2 enzyme with values of IC50 ranging from 8 to 500 nM.
The 4-aminoquinolines were tested for activity in SKOV-3 ovarian cancer cells in vitro. Firstly, we evaluated the inherent cytotoxicity of the inhibitors following 24 or 96 hours exposure to SKOV-3 cells with Values of IC50 varied from 1.7 to >100μM. There was no relationship between toxicity and the ability of the compounds to inhibit recombinant NQO2. However, some of these compounds showed functional activity as NQO2 inhibitors in cells, revealed by their ability to inhibit the toxicity of CB1954 (which is NQO2 dependent) at sub-μM concentrations. The compounds may be able to act as molecular probes for the (multi-)functional activity of NQO2 in cells.
Keywords: Anticancer, NQO2, 4-aminoquinoline.