Monitoring Tumor Response to Antiangiogenic Sunitinib Therapy with 18F-Fluciclatide, an 18F-Labeled αvβ3-Integrin and αvβ5-Integrin Imaging Agent

Arginine-glycine-aspartate (RGD)-binding alpha(v)beta(3)-integrin and alpha(v)beta(5)-integrin play key roles in tumor angiogenesis. We examined an F-18-labeled small peptide (fluciclatide [United States Adopted Name (ASAN)-approved, International Nonproprietary Name (INN)-proposed name], previously referred to as AH111585) containing an RGD sequence. Fluciclatide binds with a high (nM) affinity to alpha(v)beta(3)-integrin and alpha(v)beta(5)-integrin, which are highly expressed on tumors and the tumor neovasculature. In this study, F-18-fluciclatide was used to examine the response of human glioblastoma xenografts to treatment with the antiangiogenic agent sunitinib. Methods: U87-MG tumor uptake of F-18-fluciclatide was determined by small-animal PET after longitudinal administration of the antiangiogenic agent sunitinib (a 2-wk dosing regimen). Tumor sizes were measured throughout the study, and tumor volumes were calculated. Tumor microvessel density (MVD) after therapy was also analyzed. Results: Dynamic small-animal PET of F-18-fluciclatide uptake after administration of the clinically relevant antiangiogenic agent sunitinib revealed a reduction in the tumor uptake of F-18-fluciclatide compared with that in vehicle-treated controls over the 2-wk dosing regimen. Skeletal muscle, used as a reference tissue, showed equivalent F-18-fluciclatide uptake in both therapy and control groups. A reduction in tumor MVD was also observed after treatment with the antiangiogenic agent. No significant changes in tumor volume were observed in the 2 groups. Conclusion: The data demonstrated that F-18-fluciclatide detected changes in tumor uptake after acute antiangiogenic therapy markedly earlier than any significant volumetric changes were observable. These results suggest that this imaging agent may provide clinically important information for guiding patient care and monitoring the response to antiangiogenic therapy.