Siglec-9 peptide specifically targets VAP-1 in tumors. (A) Mean time-activity curves of ⁶⁸Ga-DOTA peptide in a tumor xenograft obtained from PET imaging of wild-type mice (■) and after competition with excess of the unlabeled peptide (□). (B) A representative image of autoradiography (ie, distribution of radioactivity) in a tissue section and (C) H&E staining of the section. (D) Combined results from autoradiography analyses of ⁶⁸Ga-DOTA peptide distribution in melanoma xenografts of 4 mice at 15 minutes after intravenous injection presented as photo-stimulated luminescence (mean ± SD). Radioactivity was analyzed in VAP-1–negative and –positive areas. (E) Immunohistochemical staining of the section of the same tumor as in panels B and C with antimouse VAP-1 antibody and (F) with anti–PV-1 antibody showing the blood vessels. Scale bar represents 2.5 mm for the whole tumor sections. Insets: Individual VAP-1– and PV-1–positive tumor vessels (arrows). For the autoradiography in panel B, cryosections of the tumor were thaw-mounted onto microscope slides and apposed to a phosphor imaging plate (Fuji Imaging Plate BASTR2025, Fuji Photo Film Co Ltd). After the exposure, the imaging plates were scanned with the FLA-5000 analyzer (Fuji Tokyo, Japan) to produce digitalized images. The images were analyzed using TINA Version 2.10f, Raytest Isotopenmessgeräte GmbH. Images for panels C,E and F were taken with Zeiss Axiovert 200M microscope using 5×/0.25 objective and Hamamatsu 1394 ORCA-ER camera. The software was AxioVision Version 4.5.