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

The clinical potential of pharmacological ascorbate (P-AscH-; IV delivery achieving mM concentrations in blood) as an adjuvant in cancer therapy is being re-evaluated. At mM concentrations, P-AscH- is thought to exhibit anti-cancer 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 poly (ADP-ribose) polymerase-1 (PARP-1) is hyperactivated. Using our unique absolute quantitation, we found that the P-AscH--mediated the overactivation of PARP-1, 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 PARP-1 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 due to increased demand, not changes in the rate of production. Genetic deletion and pharmacological inhibition of PARP-1 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.