@article {Hausner784, author = {Sven H. Hausner and Nadine Bauer and Lina Y. Hu and Leah M. Knight and Julie L. Sutcliffe}, title = {The Effect of Bi-Terminal PEGylation of an Integrin αvβ6{\textendash}Targeted 18F Peptide on Pharmacokinetics and Tumor Uptake}, volume = {56}, number = {5}, pages = {784--790}, year = {2015}, doi = {10.2967/jnumed.114.150680}, publisher = {Society of Nuclear Medicine}, abstract = {Radiotracers based on the peptide A20FMDV2 selectively target the cell surface receptor integrin αvβ6. This integrin has been identified as a prognostic indicator correlating with the severity of disease for several challenging malignancies. In previous studies of A20FMDV2 peptides labeled with 4-18F-fluorobenzoic acid (18F-FBA), we have shown that the introduction of poly(ethylene glycol) (PEG) improves pharmacokinetics, including increased uptake in αvβ6-expressing tumors. The present study evaluated the effect of site-specific C-terminal or dual (N- and C-terminal) PEGylation, yielding 18F-FBA-A20FMDV2-PEG28 (4) and 18F-FBA-PEG28-A20FMDV2-PEG28 (5), on αvβ6-targeted tumor uptake and pharmacokinetics. The results are compared with 18F-FBA{\textendash}labeled A20FMDV2 radiotracers (1{\textendash}3) bearing either no PEG or different PEG units at the N terminus. Methods: The radiotracers were prepared and radiolabeled on solid phase. Using 3 cell lines, DX3puroβ6 (αvβ6+), DX3puro (αvβ6-), and BxPC-3 (αvβ6+), we evaluated the radiotracers in vitro (serum stability; cell binding and internalization) and in vivo in mouse models bearing paired DX3puroβ6{\textendash}DX3puro and, for 5, BxPC-3 xenografts. Results: The size and location of the PEG units significantly affected αvβ6 targeting and pharmacokinetics. Although the C-terminally PEGylated 4 showed some improvements over the un-PEGylated 18F-FBA-A20FMDV2 (1), it was the bi-terminally PEGylated 5 that displayed the more favorable combination of high αvβ6 affinity, selectivity, and pharmacokinetic profile. In vitro, 5 bound to αvβ6-expressing DX3puroβ6 and BxPC-3 cells with 60.5\% {\textpm} 3.3\% and 48.8\% {\textpm} 8.3\%, respectively, with a significant fraction of internalization (37.2\% {\textpm} 4.0\% and 37.6\% {\textpm} 4.1\% of total radioactivity, respectively). By comparison, in the DX3puro control 5 showed only 3.0\% {\textpm} 0.5\% binding and 0.9\% {\textpm} 0.2\% internalization. In vivo, 5 maintained high, αvβ6-directed binding in the paired DX3puroβ6{\textendash}DX3puro model (1 h: DX3puroβ6, 2.3 {\textpm} 0.2 percentage injected dose per gram [\%ID/g]; DX3puroβ6/DX3puro ratio, 6.5:1; 4 h: 10.7:1). In the pancreatic BxPC-3 model, uptake was 4.7 {\textpm} 0.9 \%ID/g (1 h) despite small tumor sizes (20{\textendash}80 mg). Conclusion: The bi-PEGylated radiotracer 5 showed a greatly improved pharmacokinetic profile, beyond what was predicted from individual N- or C-terminal PEGylation. It appears that the 2 PEG units acted synergistically to result in an improved metabolic profile including high αvβ6+ tumor uptake and retention.}, issn = {0161-5505}, URL = {https://jnm.snmjournals.org/content/56/5/784}, eprint = {https://jnm.snmjournals.org/content/56/5/784.full.pdf}, journal = {Journal of Nuclear Medicine} }