β-Lapachone Regulates Mammalian Inositol Pyrophosphate Levels in an NQO1- and Oxygen-dependent Manner

Abstract

1Inositol pyrophosphates (PP-InsPs) are energetic signalling molecules with important functions in mammals. As their biosynthesis depends on ATP concentration, PP-InsPs are tightly connected to cellular energy homeostasis. Consequently, an increasing number of studies involves PP-InsPs in metabolic disorders, such as type 2 diabetes, aspects of tumorigenesis, and hyperphosphatemia. Research conducted in yeast suggests that the PP-InsP pathway is activated in response to reactive oxygen species (ROS). However, the precise modulation of PP-InsPs during cellular ROS signalling is unknown. Here, we report how mammalian PP-InsP levels are changing during exposure to exogenous (H2O2) and endogenous ROS. Using capillary electrophoresis electrospray ionization mass spectrometry (CE-ESI-MS), we found that PP-InsP levels decrease upon exposure to oxidative stressors in HCT116 cells. Application of quinone drugs, particularly {beta}-lapachone ({beta}-lap), under normoxic and hypoxic conditions enabled us to produce ROS in cellulo and to show that {beta}-lap treatment caused PP-InsP changes that are oxygen dependent. Experiments in MDA-MB-231 breast cancer cells deficient of NAD(P)H:quinone oxidoreductase-1 (NQO1) demonstrated that {beta}-lap requires NQO1-bioactivation to regulate the cellular metabolism of PP-InsPs. Critically, significant reductions in cellular ATP concentrations were not directly mirrored in reduced PP-InsP levels as shown in NQO1-deficient MDA-MB-231 cells treated with {beta}-lap. The data presented here unveil new aspects of {beta}-lap pharmacology and its impact on PP-InsP levels. Our identification of different quinone drugs as modulators of PP-InsP synthesis will allow to better appreciate their overall impact on cellular function. 2 Significance StatementInositol pyrophosphates (PP-InsPs) are messenger molecules regulating various functions in mammals. They are associated with the oxidative stress response, but the underlying mechanism is unclear. We investigate PP-InsP signalling in mammalian cells subjected to reactive oxygen species (ROS). Applying the quinone {beta}-lapachone ({beta}-lap) generated intracellular ROS resulting in decreased PP-InsP levels. This indicates a key role of PP-InsPs in cellular signalling under oxidative stress. Moreover, {beta}-lap mediated PP-InsP signalling required oxygen and the enzyme NAD(P)H:quinone oxidoreductase-1 (NQO1). Since quinone drugs are cytotoxic, our data provide a basis for further investigations into the role of PP-InsPs during quinone-dependent chemotherapies. This is of special relevance since a phase II clinical trial demonstrated {beta}-lap efficacy in a combination chemotherapy against pancreatic cancer.