Abstract
αv β6 Integrin is an epithelial transmembrane protein that recognizes latency-associated peptide (LAP) and primarily activates transforming growth factor beta (TGF-β). It is overexpressed in carcinomas (most notably, pancreatic) and other conditions associated with αv β6 integrin-dependent TGF-β dysregulation, such as fibrosis. We have designed a trimeric Ga-68-labeled TRAP conjugate of the αv β6 -specific cyclic pentapeptide SDM17 (cyclo[RGD-Chg-E]-CONH2 ) to enhance αv β6 integrin affinity as well as target-specific in-vivo uptake. Ga-68-TRAP(SDM17)3 showed a 28-fold higher αv β6 affinity than the corresponding monomer Ga-68-NOTA-SDM17 (IC50 of 0.26 vs. 7.4 nM, respectively), a 13-fold higher IC50 -based selectivity over the related integrin αv β8 (factors of 662 vs. 49), and a threefold higher tumor uptake (2.1 vs. 0.66 %ID/g) in biodistribution experiments with H2009 tumor-bearing SCID mice. The remarkably high tumor/organ ratios (tumor-to-blood 11.2; -to-liver 8.7; -to-pancreas 29.7) enabled high-contrast tumor delineation in PET images. We conclude that Ga-68-TRAP(SDM17)3 holds promise for improved clinical PET diagnostics of carcinomas and fibrosis.