Efficient NQO1 Substrates are Potent and Selective Anticancer Agents

Abstract

A major goal of personalized medicine in oncology is the identification of drugs with predictable efficacy based on a specific trait of the cancer cell, as has been demonstrated with gleevec (presence of Bcr-Abl protein), herceptin (Her2 overexpression), and iressa (presence of a specific EGFR mutation). This is a challenging task, as it requires identifying a cellular component that is altered in cancer, but not normal cells, and discovering a compound that specifically interacts with it. The enzyme NQO1 is a potential target for personalized medicine, as it is overexpressed in many solid tumors. In normal cells NQO1 is inducibly expressed, and its major role is to detoxify quinones via bioreduction; however, certain quinones become more toxic after reduction by NQO1, and these compounds have potential as selective anticancer agents. Several quinones of this type have been reported, including mitomycin C, RH1, EO9, streptonigrin, β-lapachone, and deoxynyboquinone (DNQ). However, no unified picture has emerged from these studies, and the key question regarding the relationship between NQO1 processing and anticancer activity remains unanswered. Here, we directly compare these quinones as substrates for NQO1 in vitro, and for their ability to kill cancer cells in culture in an NQO1-dependent manner. We show that DNQ is a superior NQO1 substrate, and we use computationally guided design to create DNQ analogues that have a spectrum of activities with NQO1. Assessment of these compounds definitively establishes a strong relationship between in vitro NQO1 processing and induction of cancer cell death and suggests these compounds are outstanding candidates for selective anticancer therapy.

Deoxynyboquinones as NQO1-Activated Cancer Therapeutics

“…46,50 A similar pattern of activity, at IC 50 values ∼20−100 fold higher, is observed for β-Lap (Table 1).…”

“…2,33,43−45 Recent head-to-head comparisons (as discussed herein) indicate that most of these compounds are not bioreductively activated by NQO1 in cancer cells in culture. 46 The second mechanism is inhibition of Hsp90 by hydroquinones. 47,48 It appears that certain quinones (e.g., geldanamycin and its derivative 17-AAG) upon reduction to their corresponding hydroquinones by NQO1 become potent inhibitors of Hsp90.…”

“…49 The final and most substantiated NQO1-dependent modeof-action for anticancer agents is through redox cycling. 9,46,50 Upon reduction of an appropriate quinone by NQO1, the respective hydroquinones rapidly react with molecular oxygen in the cell to give two moles of superoxide and regenerate the quinone ( Figure 1). Because these compounds rapidly and catalytically generate large quantities of toxic ROS only in NQO1-expressing cells, they have considerable potential as anticancer agents.…”

“…Remarkably, we found that DNQ is processed by NQO1 in vitro near the diffusion controlled limit (k cat /K m = 6.2 × 10 7 M −1 s −1 , Figure 3B); other known redox cyclers β-Lap and STN are less efficient NQO1 substrates ( Figure 3B). 46 The correlation between NQO1 activity in vitro and anticancer potency in cell culture was also investigated. As shown in Table 1, 2 h exposure of cells to DNQ leads to potent cell death (IC 50 values of 0.05 to 0.12 μM) in cell lines expressing a threshold level (∼200 U) of NQO1, but little-to-no activity against cell lines with low levels Scheme 1.…”

O-naphthoquinone isolated from Capraria biflora L. induces selective cytotoxicity in tumor cell lines

“…The selective induction of cell death plays a major role in decreasing the possible side effects of chemotherapy (Reichert and Wenger, 2008;Parkinson et al, 2013). The relation between cancer and apoptosis has being emphasized for a long time, suggesting that tumor progression involves the inhibition of apoptotic stages in tumor cells (Yang et al, 2006;Vasconcellos et al, 2011).…”