TNF-α gene and proton radiotherapy in an orthotopic brain tumor model

The major goal of this study was to evaluate the safety and efficacy of TNF-α gene therapy (pGL1-TNF-α) in combination with proton radiation in an orthotopic brain tumor model. C6 glioma cells were implanted into the left hemibrain of athymic rats (day 0). On day 5, pGL1-TNF-α (19 μg/10 μl) was injected into the same site; appropriate control groups were included. Proton irradiation (10 Gy, single fraction) was performed 18-20 h thereafter and, on day 10, a portion of animals from each group was assayed. Nearly all tumor-bearing groups had lower body mass compared to those without tumor; brain mass was somewhat increased with plasmid (pGL1-TNF-α or pWS4) injection (p<0.05). Histopathological analysis of brain sections revealed that rats receiving pGL1-TNF-α/proton irradiation had the smallest tumors and lowest number of mitotic tumor cells, although survival time for animals kept long-term was not significantly prolonged. A decline in leukocyte populations was noted with combination treatment compared to controls (p<0.05), but no differences were found compared to groups receiving each modality alone. Based on DNA synthesis, the pGL1-TNF-α/proton irradiated group had the highest levels of leukocyte activation. The highest percentage of lymphocytes expressing the CD71 activation marker occurred with pGL1-TNF-α, whereas the proton-irradiated group had the highest percentage of activated NK cells (NK1.1+/CD71+). No significant differences were found in erythrocyte and thrombocyte numbers, hemoglobin, and hematocrit. Overall, the data indicate that pGL1-TNF-α/proton treatment results in a measurable antitumor effect and is safe under the conditions used.