ATPS-21MONITORING OF LOCAL TREATMENT EFFECTS WITH TEMOZOLOMIDE IN AN ORTHOTOPIC MURINE GLIOBLASTOMA MODEL

INTRODUCTION: Locally administered agents against malignant gliomas demand sophisticated metabolic imaging to monitor local and systemic treatment effects in animal models. The purpose of this feasibility study was to create an animal model suitable to represent the effect of locally delivered, soluble temozolomide in orthotopically implanted gliomas using micro-[18F] FLT-PET for high quality metabolic information with a distinct resolution for observation of treatment effects. METHODS: U87 glioma cells were stereotactically implanted in 48 female T-cell deficient athymic nude rats (RNU). Tumor existence and proliferation was proven by [18F] FLT-PET and microMRI. Rats were allocated to four treatment groups. Group one and two received a one-time intratumoral stereotactic injection of soluble temozolomide (TMZ) (group 1: 0.03mg; group 2: 0.015mg). Group three was administered systemic TMZ for 2 days (5mg). Group four served as untreated control group. Treatment was performed on day 15 post implantation. FLT-PET and MRI were performed 7 and 14 days after treatment. Animals showing signs of neurological impairment or reduced general health were immediately examined by MRI and sacrificed according to the animal ethical guidelines. RESULTS: The tumor take rate was 100 percent. Characteristically, U87 tumor cell formation was rather solid. Tumor size (MRI) and proliferation rate (PET) were congruent in all groups prior to treatment. Post treatment, FLT-PET was more specific for tumor growth compared to MRI. Tumor proliferation rates were significantly lower in the local treatment groups. MRI confirmed intratumoral TMZ fluid distribution which decreased within 7 days. CONCLUSION: Our orthotopic rat glioma model proved to be feasible and efficient for the performance of local therapy studies. Sophisticated Micro-PET offers distinct monitoring of tumor proliferation and supplements MR tumor imaging very well. The FLT-PET tracer is most suitable for the monitoring of local treatment effects of TMZ.