Improving patient outcome by personalized
therapy involves a thorough understanding of an agent's mechanism of action. β-
Lapachone (clinical forms, Arq501/Arq761) has been developed to exploit dramatic
cancer-specific elevations in the phase II detoxifying
enzyme NAD(P)H:
quinone oxidoreductase (NQO1). NQO1 is dramatically elevated in solid
cancers, including primary and metastatic [e.g., triple-negative (ER-, PR-, Her2/Neu-)] breast
cancers. To define cellular factors that influence the efficacy of β-
lapachone using knowledge of its mechanism of action, we confirmed that NQO1 was required for lethality and mediated a futile redox cycle where ∼120 moles of
superoxide were formed per mole of β-
lapachone in 2 minutes. β-
Lapachone induced
reactive oxygen species (ROS), stimulated
DNA single-strand break-dependent
poly(ADP-ribose) polymerase-1 (PARP1) hyperactivation, caused dramatic loss of essential
nucleotides (
NAD(+)/
ATP), and elicited programmed
necrosis in
breast cancer cells. Although PARP1 hyperactivation and NQO1 expression were major determinants of β-
lapachone-induced lethality, alterations in
catalase expression, including treatment with exogenous
enzyme, caused marked cytoprotection. Thus,
catalase is an important resistance factor and highlights H2O2 as an obligate ROS for cell death from this agent. Exogenous
superoxide dismutase enhanced
catalase-induced cytoprotection. β-
Lapachone-induced cell death included
apoptosis-inducing factor (AIF) translocation from mitochondria to nuclei, TUNEL+ staining, atypical PARP1 cleavage, and
glyceraldehyde 3-phosphate dehydrogenase S-nitrosylation, which were abrogated by
catalase. We predict that the ratio of NQO1:
catalase activities in
breast cancer versus associated normal tissue are likely to be the major determinants affecting the therapeutic window of β-
lapachone and other NQO1 bioactivatable drugs.