Pharmacologic Ascorbate Primes Pancreatic Cancer Cells for Death by Rewiring Cellular Energetics and Inducing DNA Damage

Abstract

The clinical potential of pharmacologic ascorbate (P-AscH^-; intravenous delivery achieving mmol/L concentrations in blood) as an adjuvant in cancer therapy is being reevaluated. At mmol/L concentrations, P-AscH^- is thought to exhibit anticancer activity via generation of a flux of H₂O₂ in tumors, which leads to oxidative distress. Here, we use cell culture models of pancreatic cancer to examine the effects of P-AscH^- on DNA damage, and downstream consequences, including changes in bioenergetics. We have found that the high flux of H₂O₂ produced by P-AscH^- induces DNA damage. In response to this DNA damage, we observed that PARP1 is hyperactivated. Using our unique absolute quantitation, we found that P-AscH^- mediated the overactivation of PARP1, which results in consumption of NAD⁺, and subsequently depletion of ATP leading to mitotic cell death. We have also found that Chk1 plays a major role in the maintenance of genomic integrity following treatment with P-AscH^-. Hyperactivation of PARP1 and DNA repair are ATP-consuming processes. Using a Seahorse XF96 analyzer, we demonstrated that the severe decrease in ATP after challenging with P-AscH^- is because of increased demand, not changes in the rate of production. Genetic deletion and pharmacologic inhibition of PARP1 preserved both NAD⁺ and ATP; however, the toxicity of P-AscH^- remained. These data indicate that disruption of bioenergetics is a secondary factor in the toxicity of P-AscH^-; damage to DNA appears to be the primary factor. IMPLICATIONS: Efforts to leverage P-AscH^- in cancer therapy should first focus on DNA damage.