Formulated Poly IC Eliminates Intracranial GBM Models in Mice

These encouraging results led us to test the EGFR-targeted poly IC strategy in vivo. Ten thousand U87MGwtEGFR cells were implanted into the brains of nude mice as described (Methods) and the tumors left to grow for 10 d. During this period, visible tumors developed (Figure 5A). On day 10 after cell implantation, (poly IC)PEI-PEG-EGFþPEI-Mel complexes were delivered directly into the tumors at a constant rate for 3 d, using Alzet osmotic micropumps. On day 20 after cell implantation (7 d after the end of treatment), the tumors had disappeared completely from (poly IC)PEI-PEG-EGFþPEIMel- treated animals, while the tumors continued to grow in untreated animals until reaching 36.44 mm3 (Figure 5A).

Animals that were treated with PEI-PEG-EGFþPEI-Mel alone (no poly IC), survived for no longer than 32 d, as did untreated animals (Figure 5B). In contrast, the (poly IC)PEIPEG- EGFþPEI-Mel-treated animals are still alive on the day of submission of this manuscript (more than a year), and show no signs of increased intracranial pressure. When Melittin was omitted, the mice died from GBM 57–59 d after cell implantation (unpublished data). Histopathologic examination of the brains of the poly IC-treated mice at day 7 after the end of treatment did not reveal any residual tumors (Figures 5A and 6A), whereas the control animals had large tumors (Figures 5A and 6A). Pathological analysis of the brains at 24 h after treatment initiation showed increased gliosis in the brains of the animals of all experimental groups (Figure 6A). This was probably caused by the growing tumors in the brains. We also detected low infiltration of macrophages into the tumors in all groups (Figure 6A). None of the animals treated with poly IC showed any additional histopathological signs of toxicity or brain tissue damage either at 24 h after treatment initiation or at 7 d after the end of the treatment (Figures 5A and 6A). Similarly, we did not detect any significant increase in infiltration of immune cells into poly IC treated tumors as compared with the untreated tumors (Figure 6A).