Figure 3.

Monitoring of target inhibition by PET imaging. (A) Blockade of α_Vβ₃ integrin by the cyclic pentapeptide c(RGDfV). Mice were implanted with an α_Vβ₃-positive tumor on the left shoulder. Pretreatment with the α_Vβ₃ ligand c(RGDfV) leads to a dose-dependent decrease in the uptake of the radiolabeled imaging probe [¹⁸F]galacto-RGD. Permission obtained from the American Association for Cancer Research © Haubner R et al. (2001) Noninvasive imaging of α_Vβ₃ integrin expression using 18F–labeled RGD-containing glycopeptide and positron emission tomography. Cancer Res 61: 1781–1785. (B) Monitoring of Hsp90 inhibition by PET imaging with ⁶⁸Ga-labeled anti-HER2 antibody fragments. Mice were implanted on the left shoulder with a tumor that overexpressed HER2 (arrows). Treatment with the Hsp90 inhibitor 17-AAG leads, within 24 h, to a marked reduction of the uptake of anti-HER2 antibody fragments, indicating downregulation of HER2 expression. Downregulation of HER2 expression was confirmed by immunoblots of the tumor tissue. Permission obtained from Nature Publishing Group © Smith-Jones PM et al. (2004) Nat Biotechnol 22: 701–706. Abbreviations: 17-AAG, 17-allylaminogeldanamycin; HER2, human epidermal growth factor receptor 2; Hsp90, heat shock protein 90; RGD, arginine–glycine–aspartic acid.