Abstract 4614: β-lapachone suppresses glucose metabolism in a NQO1-dependent, tumor-selective manner.

Abstract

β-Lapachone (β-lap) is a very unique quinone that can be reduced by two-electron oxidoreductase, NQO1, but unlike most other quinones, its hydroquinone form is unstable and spontaneously oxidizes back to β-lap in two steps. This redox cycle occurs in a futile manner in which one mole of β-lap generates ∼120 moles of superoxide in two minutes, causing predominately DNA base and single strand break damage. This results in PARP1 hyperactivation and programmed necrosis in an NQO1-dependent manner. Most solid cancers, such as nearly 90% of pancreatic and non-small cell lung cancers have 10- to 40- fold of elevated levels of NQO1. Since β-lap causes DNA damage that is dependent on NQO1 expression, and therefore tumor-selective for most solid cancers, use of this ‘NQO1 bioactivatable’ drug is perfect for improving efficacy of cancer therapy. Our recent work also showed that β-lap efficaciously kills pancreatic cancer cells in an NQO1-dependent manner (Li et al., Clin. Cancer Res., 2011).

In mechanism of action studies of β-lap, we found that PARP1 hyperactivation led to dramatic depletion of NAD+ and ATP pools in NQO1+ cancer cells (Bentle et al., JBC, 2006). Since NAD+ is a key cofactor for many enzymes in cellular metabolism, we theorized that NAD+ loss may significantly affect cellular metabolism and energy generation. To elucidate how β-lap affects metabolism, we examined metabolites using 13C-labeled glucose. After two hours exposure of β-lap, glucose utilization in MiaPaca-2 cells was completely repressed, lasting 12 h after removal of β-lap. β-Lap treatment also inhibited lactate generation, indicating a suppression of glycolysis after β-lap treatment. In examining metabolic recovery, however, we found that the TCA cycle was not, or only moderately affected by β-lap, indicating that this metabolic process was essential for recovery from this agent. A proportion of 13C-labeled metabolites (i.e., citrate, fumarate) generated by TCA cycle increased vs untreated control cells. Consistently, ATP levels in β-lap-treated NQO1+ pancreatic cancer cells gradually recovered from <10% of untreated cells to ∼50% in 12 h. These data indicate that β-lap predominately represses glycolysis, while the TCA cycle remains functional and possibly the only source of ATP production in the cell. Our results indicated that β-lap a very unique DNA damage-inducing NQO1-dependent agent that simultaneously suppresses glucose metabolism and energy generation. This may explain why β-lap is so potent in cell death induction in comparison with other DNA damage-inducing agents. Further studies will be performed to elucidate the exact mechanism how β-lap represses glycolysis while apparently stimulating the TCA cycle. Understanding how cells recover from β-lap exposures should shed light on improved therapies for NQO1 bioactivatable drugs. This work was supported by an AACR Innovator Award from the George and June Block Foundation to DAB.

Citation Format: Xiuquan Luo, Malina Patel, Longshan Li, Ralph Deberardinis, David A. Boothman. β-lapachone suppresses glucose metabolism in a NQO1-dependent, tumor-selective manner. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4614. doi:10.1158/1538-7445.AM2013-4614