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The dose of radiation that can be safely administered to cancers residing in sensitive areas such as the lungs is limited by normal tissue tolerance. However, gene therapies have potential to enhance the efficacy of radiotherapy, as well as other forms of cancer treatment. We have constructed a unique plasmid, pXLG-mEndo, containing the mouse version of the endostatin gene. Anti-tumor efficacy of pXLG-mEndo in combination with radiation was tested in the syngeneic Lewis lung carcinoma (LLC) - C57BL/6 mouse model. In one series of experiments, intratumoral injections of plasmid at 100 micrograms followed by 10 gray (Gy) irradiation 16 hr later were each delivered twice over an 8-day period. As previously reported, pXLG-mEndo significantly enhanced radiation-mediated control of LLC growth; reductions up to 50% in tumor volume were obtained. Here we present results from analyses that were performed on a subset of these animals one day after the last treatment (n = 56 mice). The goals were to assess immunological changes and identify toxicities that may occur due to combination therapy. Highly significant leukocytosis occurred in untreated groups with tumor (P<0.001); this was due primarily to increased number of granulocytes, an effect that was attenuated by radiation +/− pXLG-mEndo or empty vector. Two-way ANOVA revealed a main effect of radiation for white blood cell, lymphocyte, and monocyte counts in blood (P<0.001), whereas a radiation x plasmid interaction was noted for these cell types in the spleen. Flow cytometry analysis of specific lymphocyte populations demonstrated significant tumor-related increases in the numbers of CD3+ T, CD3+/CD4+ T helper, CD3+/CD8+ T cytotoxic, and NK1.1+ natural killer (NK) cells (P<0.05 or less), even in mice treated with radiation. In contrast, B220+ B cell counts were reduced to less than normal when radiation was applied. Red blood cell and platelet counts, hemoglobin concentration, and hematocrit were decreased in all tumor-bearing animals (p<0.05 or less), but there was no significant difference due to treatment. The results demonstrate that changes occurred in a number of measurements due to tumor presence, plasmids, and radiation in this mouse model of lung cancer. The apparent lack of toxicities due to combination treatment supports initiation of more aggressive regimens with pXLG-mEndo and radiation.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]