Tumor-Selective, Futile Redox Cycle-Induced Bystander Effects Elicited by NQO1 Bioactivatable Radiosensitizing Drugs in Triple-Negative Breast Cancers

Abstract

β-Lap showed NQO1-dependent efficacy against two triple-negative breast cancer (TNBC) xenografts. NQO1 expression variations in human breast cancer patient samples were noted, where ~60% cancers over-expressed NQO1, with little or no expression in associated normal tissue. Differential DNA damage and lethality were noted in NQO1(+) versus NQO1-deficient (NQO1(-)) TNBC cells and xenografts after β-lap treatment. β-Lap-treated NQO1(+) cells died by programmed necrosis, whereas co-cultured NQO1(-) TNBC cells exhibited DNA damage and caspase-dependent apoptosis. NQO1 inhibition (dicoumarol) or H2O2 scavenging (catalase [CAT]) blocked all responses. Only NQO1(-) cells neighboring NQO1(+) TNBC cells responded to β-lap in vitro, and bystander effects correlated well with H2O2 diffusion. Bystander effects in NQO1(-) cells in vivo within mixed 50:50 co-cultured xenografts were dramatic and depended on NQO1(+) cells. However, normal human cells in vitro or in vivo did not show bystander effects, due to elevated endogenous CAT levels. Innovation and Conclusions: NQO1-dependent bystander effects elicited by NQO1 bioactivatable drugs (β-lap or deoxynyboquinone [DNQ]) likely contribute to their efficacies, killing NQO1(+) solid cancer cells and eliminating surrounding heterogeneous NQO1(low) cancer cells. Normal cells/tissue are protected by low NQO1:CAT ratios.

Using DNA devices to track anticancer drug activity

“…The β-lap concentration dependence of the signal change was investigated across three specific concentrations: a dose typically lethal to cancer cells (2.5 μM, such as MCF-7 breast cancer cells (Wuerzberger et al 1998; Cao et al 2014), a dose at the threshold of activity (1.0 μM), and at an order of magnitude below this in vivo activity threshold (0.10 μM). Each concentration was measured against a drug-free control on the chip and normalized against the nonspecific change, ( C - D )/ C , where C is the change associated with the drug free control and D is the change associated with the drug-treated electrodes.…”

“…To investigate this effect, we performed two experiments with catalase, one with relatively low levels of catalase (10 activity units/ml, 0.0030 nmol/ml, 3.0 nM) and high levels of NQO1 (50 nM), consistent with cancerous cells, and another one with high levels of catalase (100 activity units/ml, 0.030 nmol/ml, 30 nM) and lower levels of NQO1 (5 nM), representative of a healthy cell. These ratios were selected from the relative expression levels of these enzymes from repeated trials of solid tumors (Bey et al 2007; Cao et al 2014; Chakrabarti et al 2015a; Dong et al 2007; Huang et al 2012, 2013; Moore et al 2015). Each experiment was conducted along with a drug-free control.…”

“…Cancer treatments that use inherent differences in cancer versus normal cells to induce selective DNA damage represent a promising strategy for avoiding common therapeutic resistances. Strategies are now emerging that involve drugs that respond to overexpression of enzymes and inherent differences in reactive oxygen species (Cao et al 2014; Vadukoot et al 2014). Quantifying and maximizing the effectiveness of these cancer-selective DNA-damaging drugs necessitates understanding chemical alterations of DNA and DNA-protein interactions arising from the subsequent repair processes (Rauf et al 2005).…”

“…This damage triggers specific, but overlapping, DNA repair processes, generating DNA base damage (and subsequent abasic sites), as well as single- and double- DNA strand breaks that hyperactivate poly(ADP-ribose) polymerase 1 (PARP1), ultimately leading to selective cancer programmed necrosis. NQO1 is constitutively over-expressed in most solid cancers, particularly in non-small cell lung (>85% show 10- to 50-fold elevations relative to normal tissue), pancreatic (~85% have 10- to 100-fold elevations), prostate (~60% have 5- to 100-fold elevations), and breast (~60% have 5- to 100-fold elevations) cancers (Bey et al 2007; Cao et al 2014; Chakrabarti et al 2015a; Dong et al 2007; Huang et al 2012, 2013; Moore et al 2015). Importantly, many of these same tumors concomitantly express low catalase levels compared to normal tissue (Chakrabarti et al 2015b), so H 2 O 2 levels generated by the drug are relatively long-lived compared to most reactive oxygen species.…”

“…Importantly, many of these same tumors concomitantly express low catalase levels compared to normal tissue (Chakrabarti et al 2015b), so H 2 O 2 levels generated by the drug are relatively long-lived compared to most reactive oxygen species. Furthermore, ß-lap-induced cell death avoids many resistance pathways, as studies show that the cell death induced is: (i) not dependent on the particular p53 status of the cancer cell; (ii) independent of cell cycle status; (iii) not affected by losses in expression of Bak and/or Bax; (iv) not affected by oncogenic driver or carrier mutations; and (v) not influenced by loss of caspases (Cao et al 2014; Chakrabarti et al 2015a; Huang et al 2012, 2013; Moore et al 2015). β-Lap has produced apparent cures of cancers in mice, and a modified form (ARQ761) is currently under several Phase I/Ib clinical trials.…”