Chemical synthesis and biological evaluation of a NAD(P)H:quinone oxidoreductase-1–targeted tripartite quinone drug delivery system

NAD(P)H:quinone oxidoreductase-1 (NQO1) is a potential target for therapeutic intervention but attempts to exploit NQO1 using quinone-based bioreductive prodrugs have been largely compromised by toxicity to organs that inherently express high levels of NQO1. In an attempt to circumvent this problem, this study describes the devel- opment of a tripartite quinone-based drug delivery system, the ultimate objective of which is to release a targeted therapeutic agent following the reduction of a quinone ‘‘trigger’’ by NQO1. Molecular modeling of drug/NQO1 interactions were conducted prior to the synthesis of N -{4-[bis-(2-chloroethyl)-amino]-phenyl}-B,B,2,4,5- pentamethyl-3,6-dioxo-1,4-cyclohexadiene-1-propanamide (prodrug 1). Prodrug 1 is a good substrate for purified NQO1 (Vmax and Km values of 11.86 F 3.09 Mmol/min/mg and 2.70 F 1.14 Mmol/L, respectively) and liquid chromatography-mass spectrometry analysis of the metabolites generated showed that lactone 3 and aniline mustard 4 were generated in a time- and NQO1-dependent manner. Chemosensitivity studies showed that prodrug 1 is selectively toxic to cells that overexpress NQO1 under aerobic conditions, and comet assay analysis confirmed the presence of elevated interstrand cross-links in NQO1- rich compared with NQO1-deficient cells. Hypoxic sensi- tization (hypoxic cytotoxicity ratio = 15.8) was observed in T47D cells that overexpress cytochrome P450 reductase. In conclusion, the results of this study provide mechanistic proof of principle that a tripartite benzoquinone drug delivery system is enzymatically reduced to release an active therapeutic agent. Further development of this concept to fine-tune substrate specificity for specific reductases and/or the inclusion of alternative therapeutic agents is warranted.