Pharmacological ascorbate induces ‘BRCAness’ and enhances the effects of Poly(ADP‑Ribose) polymerase inhibitors against BRCA1/2 wild‑type ovarian cancer

Abstract

The promise of poly(ADP-ribose) polymerase inhibitors (PARPis) in the management of epithelial ovarian cancer (EOC) is hampered by the limited clinical activity against BRCA wild-type or homologous recombination-proficient EOC. In order to decrease the resistance and increase the efficacy of PARPis, combination treatments of pharmacological ascorbate and PARPis in preclinical BRCA wild-type EOC models were investigated. The cytotoxicity of pharmacological ascorbate, olaparib and veliparib in a panel of BRCA1/2 wild-type EOC cell lines were measured using MTT assays. Poly(ADP-ribose) levels were quantified using chemiluminescent ELISA. The expression of proteins involved in DNA damage and DNA double-strand breaks (DSBs) repair pathways were assessed by western blotting. The in vivo efficacy of pharmacological ascorbate, olaparib and their combination was evaluated in an intraperitoneal xenograft mouse model of BRCA1/2 wild-type EOC. Pharmacological ascorbate induced H 2 O 2 -dependent cytotoxicity in BRCA1/2 wild-type EOC cells. SHIN3 and OVCAR5 cells were resistant to olaparib and veliparib treatment; however, the combination of ascorbate with olaparib or veliparib significantly enhanced cell death. Pharmacological ascorbate enhanced the effects olaparib or veliparib by downregulating the expression of BRCA1, BRCA2 and RAD51. Consequently, the combination of pharmacological ascorbate and olaparib potently enhanced DNA DSBs and significantly decreased tumor burden, ascites volume and the number of tumor cells in ascites in mice bearing BRCA1/2 wild-type ovarian cancer xenografts. The combination of pharmacological ascorbate and PARPis may be a promising therapeutic approach worth clinical investigation in patients with BRCA wild-type or PARPi-resistant EOC.

Sperm redox biology challenges the role of antioxidants as a treatment for male factor infertility

“…This opens to the possibility that resveratrol was exerting PARP inhibition. More recently, ascorbate was effective in enhancing PARP inhibition in an intraperitoneal xenograft mouse model of BRCA1/2 WT epithelial ovarian cancer (83). Again, the enhanced lethality provided by ascorbate was associated with a massive increase in DNA fragmentation, and the effect was explained with the pro-oxidant effect of high doses of ascorbate in cancer cells.…”

Pharmacologic Induction of BRCAness in BRCA-Proficient Cancers: Expanding PARP Inhibitor Use

“…Cytotoxicity is mediated in part through DNA damage accumulation resulting from the generation of hydrogen peroxide, which activates PARP1 and subsequently depletes the PARP1 substrate nicotinamide adenine dinucleotide (NAD+) leading to ATP depletion and cell death [ 184 ]. Although PARPi treatment prevents NAD+/ATP depletion, cell death still ensues secondary to DSB accumulation linked to the ascorbate-induced downregulation of BRCA1, BRCA2, and RAD51 [ 185 ].…”

High-Dose Vitamin C: Preclinical Evidence for Tailoring Treatment in Cancer Patients

“…DNA damage induced by vitamin C can occur at in vitro pro-oxidant concentrations (>1 mM), as well as at concentrations capable of regulating αKGDDs enzymatic activity (0.25–1 mM) [ 102 , 108 , 112 , 135 , 136 ]. In the latter case, vitamin C-induced DNA damage derives from its ability to increase 5hmC levels.…”