Ascorbate (AscH−) functions as a versatile reducing agent. At pharmacological doses (P-AscH−; [plasma AscH−] ≥≈20 mM), achievable through intravenous delivery, oxidation of P-AscH− can produce a high flux of H2O2 in tumors. Catalase is the major enzyme for detoxifying high concentrations of H2O2. We hypothesize that sensitivity of tumor cells to P-AscH− compared to normal cells is due to their lower capacity to metabolize H2O2. Rate constants for removal of H2O2 (kcell) and catalase activities were determined for 15 tumor and 10 normal cell lines of various tissue types. A differential in the capacity of cells to remove H2O2 was revealed, with the average kcell for normal cells being twice that of tumor cells. The ED50 (50% clonogenic survival) of P-AscH− correlated directly with kcell and catalase activity. Catalase activity could present a promising indicator of which tumors may respond to P-AscH−.

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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HIF-1α is a transcriptional regulator that functions in the adaptation of cells to hypoxic conditions; it strongly impacts the prognosis of patients with cancer. High-dose, intravenous, pharmacological ascorbate (P-AscH−), induces cytotoxicity and oxidative stress selectively in cancer cells by acting as a pro-drug for the delivery of hydrogen peroxide (H2O2); early clinical data suggest improved survival and inhibition of metastasis in patients being actively treated with P-AscH−. Previous studies have demonstrated that activation of HIF-1α is necessary for P-AscH− sensitivity. We hypothesized that pancreatic cancer (PDAC) progression and metastasis could be be targeted by P-AscH− via H2O2-mediated inhibition of HIF-1α stabilization. Our study demonstrates an oxygen- and prolyl hydroxylase-independent regulation of HIF-1α by P-AscH−. Additionally, P-AscH− decreased VEGF secretion in a dose-dependent manner that was reversible with catalase, consistent with an H2O2-mediated mechanism. Pharmacological and genetic manipulations of HIF-1α did not alter P-AscH−-induced cytotoxicity. In vivo, P-AscH− inhibited tumor growth and VEGF expression. We conclude that P-AscH− suppresses the levels of HIF-1α protein in hypoxic conditions through a post-translational mechanism. These findings suggest potential new therapies specifically designed to inhibit the mechanisms that drive metastases as a part of PDAC treatment.

Pharmacologic ascorbate (P-AscH–) is emerging as a promising adjuvant for advanced pancreatic cancer. P-AscH–generates hydrogen peroxide (H2O2), leading to selective cancer cell cytotoxicity. Catalytic manganoporphyrins, such as MnT4MPyP, can increase the rate of oxidation of P-AscH–, thereby increasing the flux of H2O2, resulting in increased cytotoxicity. We hypothesized that a multimodal treatment approach, utilizing a combination of P-AscH–, ionizing radiation and MnT4MPyP, would result in significant flux of H2O2 and pancreatic cancer cytotoxicity. P-AscH– with MnT4MPyP increased the rate of oxidation of P-AscH–and produced radiosensitization in all pancreatic cancer cell lines tested. Three-dimensional (3D) cell cultures demonstrated resistance to P-AscH–, radiation or MnT4MPyP treatments alone; however, combined treatment with P-AscH– and MnT4MPyP resulted in the inhibition of tumor growth, particularly when also combined with radiation. In vivo experiments using a murine model demonstrated an increased rate of ascorbate oxidation when combinations of P-AscH– with MnT4MPyP were given, thus acting as a radiosensitizer. The translational potential was demonstrated by measuring increased ascorbate oxidation ex vivo, whereby MnT4MPyP was added exogenously to plasma samples from patients treated with P-AscH– and radiation. Combination treatment utilizing P-AscH–, manganoporphyrin and radiation results in significant cytotoxicity secondary to enhanced ascorbate oxidation and an increased flux of H2O2. This multimodal approach has the potential to be an effective treatment for pancreatic ductal adenocarcinoma.