Effects of MnSOD-Plasmid Liposome Gene Therapy on Antioxidant Levels in Irradiated Murine Oral Cavity Orthotopic Tumors

Abstract

Intraoral manganese superoxide dismutase (SOD2)-plasmid liposome (PL) radioprotective gene therapy prolongs the survival of mice with orthotopic oral cavity tumors within the irradiated field. To determine whether the mechanism involved effects in antioxidant pool, C57BL/6J mice bearing orthotopic oral cavity squamous cell carcinoma SCC-VII tumors received intraoral or intravenous MnSOD-PL gene therapy 24 h prior to 18 Gy irradiation to the head and neck region. Glutathione (GSH) levels and levels of radiation-generated nitric oxide and peroxynitrite were measured in orthotopic tumors and in adjacent oral mucosa. MnSOD-PL transfection of the SCC-VII tumor cells, but not normal embryo fibroblasts, produced acute radiosensitization. Furthermore, SCC-VII tumor cells demonstrated increased relative hydrogen peroxide (the product of MnSOD superoxide dismutation)-induced apoptosis in vitro. Radiation decreased levels of GSH and increased GPX in both tumor and normal cells in vitro, effects that were blunted by MnSOD-PL treatment. In vivo irradiation decreased GSH and GPX more effectively in tumors, and the decrease was not reversed by MnSOD-PL therapy. Intravenous but not intraoral administration of epitope-tagged hemagglutinin MnSOD-PL resulted in significant uptake in orthotopic tumors and decreased the levels of radiation-induced nitric oxide and peroxynitrite. Thus normal tissue radioprotective MnSOD-PL gene therapy radiosensitizes tumor cell lines in vitro and has a therapeutic effect on orthotopic tumors in part through its effects on tumor antioxidants.

Differential Effects of Irradiation with Carbon Ions and X-Rays on Macrophage Function

“…36) In addition, over-expression of the MnSOD transgene resulted in an unexpected increase in tumor cell toxicity and radiosensitization, apparently due to the production of H2O2 by the action of MnSOD. 37) Our present study clearly showed that irradiation of RAW 264.7 macrophages alone with either X-rays or carbon ions up to doses of 32 Gy did not induce the production of the proinflammatory cytokines TNFα and IL-1β or the reactive nitrogen species NO. Production of these substances could only be detected in macrophages after LPS activation.…”

Manganese Superoxide Dismutase Enhances the Invasive and Migratory Activity of Tumor Cells

“…We refer the reader to comprehensive reviews on this topic (39,40). In addition, Sod2-plasmid liposomes have been shown to be effective in enhancing the killing of orthotopic lung and oral tumors in response to ionizing radiation while protecting normal tissue (41,42). Epperly et al (41) have shown that squamous cell carcinomas are much more susceptible to toxicity of H 2 O 2 than are primary fibroblast cultures.…”

“…In addition, Sod2-plasmid liposomes have been shown to be effective in enhancing the killing of orthotopic lung and oral tumors in response to ionizing radiation while protecting normal tissue (41,42). Epperly et al (41) have shown that squamous cell carcinomas are much more susceptible to toxicity of H 2 O 2 than are primary fibroblast cultures. The authors also show that the antioxidant scavenging pool is more severely depleted in tumor tissue relative to normal tissue in response to Sod2-plasmid liposome treatment and irradiation.…”

Gene therapy for radioprotection

“…17,23 Radioprotection experiments with SOD gene therapy have also been carried out using oral administration of plasmid liposome vectors. 24,25 Finally, plasmid liposomes have been administered in a manner making use of naturally occurring anatomical isolation such as inhalation via nebulizers 16 and intravesicular instillation. 15 …”