Radiation and Endostatin Gene Therapy in a Lung Carcinoma Model: Pilot Data on Cells and Cytokines that Affect Angiogenesis and Immune Status

Abstract

The dose of radiation that can be safely delivered to cancers residing in sensitive areas such as the lungs is limited by concern for normal tissue damage. Therapies that target tumor vasculature have potential to enhance the efficacy of radiotherapy, with minimal risk for toxicity. We constructed a unique plasmid, pXLG-mEndo, containing the mouse endostatin gene. A significantly greater anti-tumor effect was obtained against Lewis lung carcinoma (LLC) in mice when pXLG-mEndo was combined with radiation compared to radiation alone. Here we report results of cellular and cytokine assessments performed one day after treatment. These analyses were done to obtain baseline data on leukocytes that affect angiogenesis, as well as anti-tumor immunity, and to detect possible treatment-related toxicities. White blood cell counts were dramatically elevated in blood and spleens of untreated tumor-bearing mice, primarily due to granulocytosis. Overall, the effect of radiation was more evident than that of the plasmids (pXLG-mEndo and parental pWS4); radiosensitivity of specific lymphocyte subsets was variable (B > T > NK; CD8⁺ Tc > CD4⁺ Th). Tumor presence resulted in dramatically elevated interleukin-2 (IL-2) and decreased tumor necrosis factor-α (TNF-α) in supernatants of activated splenocytes, but had no significant effect on interferon-γ (IFN-γ). Administration of pXLG-mEndo, radiation, or both modified the tumor-induced aberrations in IL-2 and TNF-α; IFN-γ production was decreased by radiation. Red blood cell counts, hemoglobin, and hematocrit were low in tumor-bearing mice, but there were no treatment-related differences among groups. Platelet counts were reduced, whereas their volumes were increased in tumor-bearing mice; both parameters were only slightly affected by either pXLG-mEndo or control plasmid injection, however. The data demonstrate in the Lewis lung carcinoma model that tumor-localized endostatin gene therapy and radiation had significant effects on cells and cytokines that can influence angiogenesis, tumor growth, and immune status.