Inhibiting Base Excision Repair Synergistically Enhances Beta-Lapachone-Mediated 'Kiss Of Death' For Tumor-Selective Therapy Of Pancreatic Cancer.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Pancreatic cancer will be the second leading cause of cancer-related deaths in the US by 2020, where 5-year survival is <6%. Current standard of care therapies offer little selectivity and high toxicity. Novel, tumor-selective approaches are desperately needed. Nearly 90% of pancreatic cancers have elevated levels (10- to 40-fold) NQO1 and we recently showed that beta-lapachone (beta-lap) was efficacious against pancreatic cancers in an NQO1-dependent manner (Li et al., Clin. Cancer Res., 2011). Beta-Lap is reduced by NQO1 like most quinones, but unlike most, its hydroquinone form is unstable and spontaneously redox cycles in a futile manner where one mole of beta-lap generates ∼120 moles of superoxide in two mins., inducing predominately DNA base and single strand break (SSB) damage. This results in PARP1 hyperactivation and programmed necrosis, killing NQO1+ cancer cells independent of: i, p53; ii, cell cycle; iii, all known oncogenic drivers; and iv, apoptotic/antiapoptotic gene expression (e.g., Bax, Bak, Bcl2). This ‘NQO1 bioactivatable drug’ is tumor-selective and a perfect candidate for improving efficacy of pancreatic cancer therapy. To improve its efficacy, we examined the synergistic effects of adding the AP site-modifying drug and base excision repair (BER) inhibitor, methoxyamine (MeOX), with beta-lap against NQO1 over-expressing pancreatic cancer cells. MeOX + beta-lap synergy resulted in: a, enhanced lethality of sublethal doses of beta-lap, reducing the shoulder (Dq), increasing the lethality rate (Do), and inducing apoptosis (TUNEL+) in NQO1+, but not in NQO1-, MIA PaCa-2 cells; b, increased DNA lesion formation; c, dramatic losses in ATP levels, with little recovery; and d, dramatic suppression of glycolysis. These data strongly suggests that MeOX enhances PARP1 hyperactivation and synergistic cell killing of beta-lap. Similar results were noted in shRNA-XRCC1 knockdown cells. Mechanistically, our data suggests that PARP1 detects MeOX-AP modified sites or SSBs, allowing PARP1 hyperactivation and synergistic cell death. Since MeOX is a nontoxic agent, and both agents are currently in clinical trials (i.e., beta-lap as Arq761, Arqule, Boston, MA), combination therapies for the treatment of pancreatic, as well as other NQO1 over-expressing solid cancers could be rapidly developed. An AACR Innovator Award from the George and June Block Foundation to DAB supported this work. Citation Format: Xiuquan Luo, Longshan Li, Xiumei Huang, Lifen Cao, Zachary Moore, Ralph Deberardinis, Rolf Brekken, Stanton Gerson, Lili Liu, David A. Boothman. Inhibiting base excision repair synergistically enhances beta-lapachone-mediated ‘kiss of death’ for tumor-selective therapy of pancreatic cancer. [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 3344. doi:10.1158/1538-7445.AM2013-3344