- Experimental targeted cancer chemotherapies
- Breast cancer
- DNA damage and repair
- Redox signaling
- Transcriptional regulation
- Mammalian cell cultures
- Dose-response assays
- Flow cytometry
- Western blot
- Immunoprecipitation assays
- Redox signaling
- Flourescence microscopy
- RNA-seq data analysis
- Molecular cloning and transfection
- Cornet assays
The long-term goal of our research is to exploit natural products that target breast cancers for the advancement of precision medicine with notable clinical benefit. β-Lapachone (β-lap) is a naturally occurring antitumor quinone currently in Phase I clinical trials that is selectively bioactivated in tumors expressing NAD(P)H:quinone oxidoreductase 1 (NQO1). NQO1 is constitutively overexpressed in a number of solid tumors including breast (~60%) (1-3), non-small cell lung carcinomas (NSCLCs) (>85%), and pancreatic cancers (~85%) compared to associated normal tissues (4-7). Interestingly, breast tumors with mutations in breast cancer susceptibility genes BRCA1/2 also overexpress NQO1. However, the efficacy of β-lap has not been tested in these or other tumors with inherent defects in DNA repair.
Figure 1. NQO1 futile redox cycling of β-lap or IB-DNQ.
NQO1-mediated futile cycle for IB-DNQ is shown.
NQO1 metabolizes β-lap via a two-electron oxidoreduction, resulting in the generation of an unstable hydroquinone form that rapidly reverts back to the parent quinone, causing multiple rounds of redox cycling (Fig. 1). β-Lap-induced reactive oxygen species (ROS) cause DNA base damage and DNA breaks (both single (SSB) and double-stranded (DSB)(8). SSBs and cytosolic Ca2+ release from endoplasmic reticulum pools hyperactive poly(ADP-ribose) polymerase-1 (PARP-1) resulting in cell death due to NAD+ and ATP loss (8-10). Interestingly, sub-lethal doses of β-lap, in combination with DNA damaging agents such as ionizing radiation, result in tumor sensitization (11,12). Recently, a novel more potent derivative of β-lap, isobutyldeoxynyboquinone (IB-DNQ) has been generated, which kills NQO1+ cells in a manner similar to β-lap (13). We hypothesize that sub-lethal doses of β-lap or IB-DNQ will induce low-level DNA damage in NQO1+; BRCA1/2-mutant breast tumors. Existing deficits in DNA repair caused by BRCA1/2 mutations in these cells will, therefore, selectively sensitize them to sub-lethal doses of β-lap- or IB-DNQ resulting in lethality. Furthermore, combination treatment with PARP inhibitors (PARPi) will further potentiate β-lap- or IB-DNQ- induced lethality for genotype-driven cytotoxicity, and thereby, circumvent possible resistance mechanisms. Two projects will be pursued to test this hypothesis:
- To determine the mechanism of β-lap or IB-DNQ-induced cell death in NQO1+;BRCA1/2-mutant breast cancers.
- To elucidate the efficacy of β-lap or IB-DNQ treatment in NQO1+;BRCA1/2-mutant breast cancers with or without PARPi combination treatment.
The findings gleaned from our studies will provide insight into the mechanisms of precision targeting of β-lap or IB-DNQ in NQO1-expressing BRCA1/2 mutant breast tumors to increase tumor response to therapy while decreasing normal tissue toxicity.
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