Intraoral Manganese Superoxide Dismutase-Plasmid/Liposome (MnSOD-PL) Radioprotective Gene Therapy Decreases Ionizing Irradiation-induced Murine Mucosal Cell Cycling and Apoptosis

Abstract

Background: Single or multiple intraoral administrations of manganese superoxide dismutase-plasmid/liposomes (MnSOD-PL) to C3H/HeNHsd mice receiving single fraction or fractionated ionizing irradiation to the head and neck region have been shown to significantly decrease mucosal ulceration, weight loss and to improve survival. Materials and Methods: To elucidate the mechanism of irradiation protection by MnSOD-PL and explore possible additive or synergistic protective effects with Amifostine (WR2721), mice received a single fraction of 19, 22.5, 25 or 30 Gy, or 24 fractions of 3 Gy irradiation to the oral cavity and oropharynx. Multiple parameters of irradiation-induced toxicity were quantitated in subgroups of each irradiated group of mice treated with single or multiple administrations of intraoral MnSOD-PL and/or intravenous WR2721. Results: In 19 Gy single fraction irradiated mice, MnSOD-PL treatment the day before irradiation alone or in combination with intravenous WR2721 significantly decreased the irradiation induction of mucosal cell cycling as measured by 5-bromo-2-deoxyuridine (BuDR) uptake in oral cavity mucosal cells at 48 hours and decreased ulceration of the tongue at nine days after irradiation compared to control, irradiated or irradiated, WR2721-treated mice. Mice treated in single fractions of 22.5, 25 or 30 Gy showed MnSOD-PL protection against irradiation-induced oral mucosal apoptosis and xerostomia measured in decreased saliva output. In fractionated irradiated mice, twice weekly hemagglutinin (HA) epitope-tagged MnSOD uptake in oral cavity and tongue mucosal cells was not detectably altered by daily WR2721 intravenous administration. Mice treated with both radioprotective agents (MnSOD-PL and WR2721) demonstrated a significant decrease in irradiation-induced xerostomia (measured as reduced salivary gland output volume), mucosal ulceration and improved survival. Conclusion: Enhanced salivary gland function in WR2721-treated mice in the absence of detectable mucosal protection, coupled with relatively low uptake of HA-MnSOD in the salivary glands of intraorally-treated mice, suggests that a combination of both radioprotective agents may prove optimally effective for the prevention of the acute and late normal tissue toxicities of fractionated radiotherapy for head and neck cancer.