Pharmacological ascorbate reduces radiation-induced normal tissue toxicity and enhances tumor radiosensitization in pancreatic cancer

Chemoradiation therapy is the mainstay for treatment of locally advanced, borderline resectable pancreatic cancer. Pharmacological ascorbate (P-AscH-, i.e., intravenous infusions of ascorbic acid, vitamin C), but not oral ascorbate, produces high plasma concentrations capable of selective cytotoxicity to tumor cells. In doses achievable in humans, P-AscH- decreases the viability and proliferative capacity of pancreatic cancer via a hydrogen peroxide (H2O2)-mediated mechanism. In this study, we demonstrate that P-AscH- radiosensitizes pancreatic cancer cells but inhibits radiation-induced damage to normal cells. Specifically, radiation-induced decreases in clonogenic survival and double-stranded DNA breaks in tumor cells, but not in normal cells, were enhanced by P-AscH-, while radiation-induced intestinal damage, collagen deposition, and oxidative stress were also reduced with P-AscH- in normal tissue. We also report on our first-in-human phase 1 trial that infused P-AscH- during the radiation therapy 'beam on.' Specifically, treatment with P-AscH- increased median overall survival compared to our institutional average (21.7 vs. 12.7 mo, p = 0.08) and the E4201 trial (21.7 vs. 11.1 mo). Progression-free survival in P-AscH--treated subjects was also greater than our institutional average (13.7 vs. 4.6 mo, p < 0.05) and the E4201 trial (6.0 months). Results indicated that P-AscH- in combination with gemcitabine and radiation therapy for locally advanced pancreatic adenocarcinoma is safe and well tolerated with suggestions of efficacy. Because of the potential effect size and minimal toxicity, our findings suggest that investigation of P-AscH- efficacy is warranted in a phase 2 clinical trial.

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