The toxicity of pharmacological ascorbate is mediated by the generation of H2O2 via the oxidation of ascorbate. Since pancreatic cancer cells are sensitive to H2O2 generated by ascorbate they would also be expected to become sensitized to agents that increase oxidative damage such as ionizing radiation. The current study demonstrates that pharmacological ascorbate enhances the cytotoxic effects of ionizing radiation as seen by decreased cell viability and clonogenic survival in all pancreatic cancer cell lines examined, but not in non-tumorigenic pancreatic ductal epithelial cells. Ascorbate radiosensitization was associated with an increase in oxidative stress-induced DNA damage, which was reversed by catalase. In mice with established heterotopic and orthotopic pancreatic tumor xenografts, pharmacological ascorbate combined with ionizing radiation decreased tumor growth and increased survival, without damaging the gastrointestinal tract or increasing systemic changes in parameters indicative of oxidative stress. Our results demonstrate the potential clinical utility of pharmacological ascorbate as a radiosensitizer in the treatment of pancreatic cancer.

Patients surviving acute stages of sepsis often display impaired adaptive immune responses. Using the cecal ligation and puncture (CLP) model, we demonstrated that sepsis leads to substantial and long-lasting changes in the naïve CD8 T-cell repertoire affecting the capacity of the host to respond to new infections. However, the identity of CD8 T-cell extrinsic factor(s) and mechanism(s) that contribute to impaired CD8 T-cell responses after sepsis is currently unknown. Priming of naïve CD8 T-cells is critically dependent on the ability of dendritic cells (DCs) to provide Ag, co-stimulation, and inflammatory “signal 3” cytokines, therefore the sepsis-induced changes in the DC compartment might represent a contributing factor leading to diminished CD8 T-cell immunity in septic hosts. In a direct test of this hypothesis we show that in addition to numerical decline, sepsis leads to functional impairments in DCs diminishing their capacity to produce cytokines upon TLR stimulation in vitro or after infection in vivo. Importantly, we demonstrated a direct link between DC dysfunction and impairments in CD8 T-cell immunity after sepsis by directly targeting Ag to DCs. Finally, post-sepsis Flt3 ligand (Flt3L) treatment increased the number of DCs and improved DC function, including the ability to sense inflammation and produce IL-12 leading to improved primary CD8 T-cell responses to newly encountered antigens. Thus, sepsis-induced numerical and functional loss of DCs contributes to the observed defects in CD8 T-cell immunity, and therapeutic approaches designed to improve the status of the DC compartment after sepsis might facilitate the recovery of CD8 T-cell immunity.

Septic patients experience chronic immunosuppression resulting in enhanced susceptibility to infections normally controlled by T cells. Clinical research on septic patients has shown increased apoptosis and reduced total numbers of CD4 and CD8 T cells, suggesting contributing mechanism driving immunosuppression. Experimental models of sepsis, including cecal ligation and puncture, reverse translated this clinical observation to facilitate hypothesis-driven research and allow the use of an array of experimental tools to probe the impact of sepsis on T-cell immunity. In addition to numerical loss, sepsis functionally impairs the antigen-driven proliferative capacity and effector functions of CD4 and CD8 T cells. Sepsis-induced impairments in both the quantity and quality of T cells results in reduced protective capacity and increased susceptibility of mice to new or previously encountered infections. Therefore, the combined efforts of clinical and experimental sepsis research have begun to elucidate the impact of sepsis on T-cell-mediated immunity and potential T-cell-intrinsic and -extrinsic mechanisms driving chronic immunosuppression. Future work will explore the impact of sepsis on the recently appreciated tissue-resident memory (TRM) T cells, which provide robust protection against localized infections, and dendritic cells, which are needed to activate T cells and promote effective T-cell responses.

Pharmacological ascorbate (AscH−) selectively induces cytotoxicity in pancreatic cancer cells vs. normal cells via the generation of extracellular hydrogen peroxide (H2O2), producing double-stranded DNA breaks and ultimately cell death. Catalytic manganoporphyrins (MnPs) can enhance ascorbate-induced cytotoxicity by increasing the rate of AscH− oxidation and therefore the rate of generation of H2O2. We hypothesized that combining MnPs and AscH− with the chemotherapeutic agent gemcitabine would further enhance pancreatic cancer cell cytotoxicity without increasing toxicity in normal pancreatic cells or other organs. Redox active MnPs were combined with AscH− and administered with or without gemcitabine to human pancreatic cancer cell lines, as well as immortalized normal pancreatic ductal epithelial cells. The MnPs MnT2EPyP (Mn(III)meso-tetrakis(N-ethylpyridinium-2-yl) porphyrin pentachloride) and MnT4MPyP (Mn(III)tetrakis(N-methylpyridinium-4-yl) porphyrin pentachloride) were investigated. Clonogenic survival was significantly decreased in all pancreatic cancer cell lines studied when treated with MnP + AscH− + gemcitabine, whereas non-tumorigenic cells were resistant. The concentration of ascorbate radical (Asc•−, an indicator of oxidative flux) was significantly increased in treatment groups containing MnP and AscH−. Furthermore, MnP + AscH− increased double stranded DNA breaks in gemcitabine treated cells. These results were abrogated by extracellular catalase, further supporting the role of the flux of H2O2. In vivo growth was inhibited and survival increased in mice treated with MnT2EPyP, AscH−, and gemcitabine without a concomitant increase in systemic oxidative stress. These data suggest a promising role for the use of MnPs in combination with pharmacologic AscH− and chemotherapeutics in pancreatic cancer.

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<p>Supplemental Figure S5. Bioluminescence imaging microscopy.</p>

<div>Abstract<p>The toxicity of pharmacologic ascorbate is mediated by the generation of H₂O₂ via the oxidation of ascorbate. Because pancreatic cancer cells are sensitive to H₂O₂ generated by ascorbate, they would also be expected to become sensitized to agents that increase oxidative damage such as ionizing radiation. The current study demonstrates that pharmacologic ascorbate enhances the cytotoxic effects of ionizing radiation as seen by decreased cell viability and clonogenic survival in all pancreatic cancer cell lines examined, but not in nontumorigenic pancreatic ductal epithelial cells. Ascorbate radiosensitization was associated with an increase in oxidative stress–induced DNA damage, which was reversed by catalase. In mice with established heterotopic and orthotopic pancreatic tumor xenografts, pharmacologic ascorbate combined with ionizing radiation decreased tumor growth and increased survival, without damaging the gastrointestinal tract or increasing systemic changes in parameters indicative of oxidative stress. Our results demonstrate the potential clinical utility of pharmacologic ascorbate as a radiosensitizer in the treatment of pancreatic cancer. <i>Cancer Res; 75(16); 3314–26. ©2015 AACR</i>.</p></div>

<p>Supplemental Figure Legends. Legend for Supplemental Figures S1-S5.</p>