Longitudinal MicroPET Imaging of brain tumor growth with F-18-labeled RGD peptide

Purpose: EMD 121974, a potent cyclic RGD peptide inhibitor of a(v)-integrins, demonstrated effectiveness in suppressing brain tumor growth in both preclinical models and phases I/II clinical trials. The ability to non-invasively evaluate a(v)-integrin expression provides a novel and unique way to better understand brain tumor angiogenesis in relationship to a(v)-integrin expression, and allow for direct assessment of anti-integrin treatment efficacy. Procedures: We developed a F-18-labeled RGD peptide [F-18]FB-RGD and performed serial microPET imaging scans to follow brain tumor growth and angiogenesis as a function of time in an orthotopic U87MG glioblastoma xenograft model in athymic nude mice. Results: The tumor was barely visible on microPET at the size of <= 1.5 mm diameter at which time no angiogenesis was evident on histological examination. When tumor started to grow exponentially by day 35 the activity accumulation in the brain tumor also increased accordingly, with best tumor-to-brain contrast seven weeks after inoculation of 105 U87MG cells into the mice forebrain. Conclusions: Longitudinal microPET imaging and [F-18]FB-RGD provides the sensitivity and resolution to visualize and quantify anatomical variations during brain tumor growth and angiogenesis, most likely through interaction with a(v)-integrins expressed on tumor cells and angiogenic tumor vessels.