513. Prevention of Irradiation-Induced Organizing Alveolitis by Inhalation Delivery of Manganese Superoxide Dismutase-Plasmid/ Liposome (MnSOD-PL) Complexes to Mouse Lung

Intratracheal injection of MnSOD-PL has been shown to protect the murine lung from irradiation-induced damage. To translate this modality to fractionated radiotherapy in the clinic, an inhalation model for the delivery of MnSOD-PL was developed. To demonstrate that MnSOD-PL can be delivered to the lungs, an ultrasonic nebulizer was used to deliver either 1 mg of alkaline phosphatase-PL (Alk-PL) complex or hemagglutinin epitope-tagged MnSOD (HA-MnSOD) to C57BL/6J mice. Other mice were intratracheally-injected with Alk-PL or HA-MnSOD-PL (500 μg plasmid DNA). All mice were sacrificed 24 hours after MnSOD-PL administration with the lungs assayed for increased MnSOD biochemical activity or DNA expression. An increase was observed in MnSOD biochemical activity from levels of 2.23 ± 0.15 U/mg protein in control mice to 5.0 ± 0.21 U/mg protein in mice that inhaled MnSOD-PL (p= 0.024). Real time PCR (RT-PCR) using primers specific for the human MnSOD gene detected a significant increase in MnSOD mRNA expression in mice that inhaled MnSOD-PL compared to control, C57BL/6J mice. In a second experiment, subgroups of mice inhaled 0, 250, 500, 1000, or 2000 μg of HA-MnSOD plasmid DNA over 5 minutes. MnSOD biochemical activity was significantly increased with maximal activity of 5.0 ± 0.4 U/mg protein at 500 μg plasmid DNA compared to 2.3 ± 0.1 in control, non-treated lungs (p= 0.0241). To demonstrate that inhalation of MnSOD-PL protected against irradiation-induced lung damage, C57BL/6J mice inhaled 1.0 mg of MnSOD-PL over 10 minutes or were intratracheally-injected with 0.5 mg of MnSOD-PL. Twenty-four hours later, control mice as well as MnSOD-PL-treated mice were irradiated to 20 Gy and followed for development of organizing alveolitis. Mice inhaling MnSOD or injected intratracheally with MnSOD-PL had significantly increased survival (p