18F-Fluorothymidine-Pet Imaging of Glioblastoma Multiforme: Effects of Radiation Therapy on Radiotracer Uptake and Molecular Biomarker Patterns

Abstract

Introduction. PET imaging is a useful clinical tool for studying tumor progression and treatment effects. Conventional18F-FDG-PET imaging is of limited usefulness for imaging Glioblastoma Multiforme (GBM) due to high levels of glucose uptake by normal brain and the resultant signal-to-noise intensity.18F-Fluorothymidine (FLT) in contrast has shown promise for imaging GBM, as thymidine is taken up preferentially by proliferating cells. These studies were undertaken to investigate the effectiveness of18F-FLT-PET in a GBM mouse model, especially after radiation therapy (RT), and its correlation with useful biomarkers, including proliferation and DNA damage.Methods. Nude/athymic mice with human GBM orthografts were assessed by microPET imaging with18F-FDG and18F-FLT. Patterns of tumor PET imaging were then compared to immunohistochemistry and immunofluorescence for markers of proliferation (Ki-67), DNA damage and repair (γH2AX), hypoxia (HIF-1α), and angiogenesis (VEGF).Results. We confirmed that18F-FLT-PET uptake is limited in healthy mice but enhanced in the intracranial tumors. Our data further demonstrate that18F-FLT-PET imaging usefully reflects the inhibition of tumor by RT and correlates with changes in biomarker expression.Conclusions.18F-FLT-PET imaging is a promising tumor imaging modality for GBM, including assessing RT effects and biologically relevant biomarkers.