Imaging of glioma with an integrin αvβ3 and neuropilin-1 dual-targeted PET probe 18F-FAl-NOTA-RGD-ATWLPPR

Abstract

Objective Arg-Gly-Asp(RGD) or Ala-Thr-Trp-Leu-Pro-Pro-Arg(ATWLPPR) peptide binds specifically to integrin αvβ3 or neuropilin-1 (NRP-1) receptor, respectively. In this study, a novel heterodimer peptide probe containing both RGD and ATWLPPR was designed in one molecule. The in vitro and in vivo biological behavior of the dual-targeted imaging probe RGD-ATWLPPR was compared with its corresponding counterparts. Methods 18F labeling was conducted through 18F-FAl approach. In the integrin αvβ3-positive U87MG human glioma cell line, the αvβ3/NRP-1 receptor binding affinity of RGD-ATWLPPR was tested and compared with its counterparts RGD and ATWLPPR. The tumor uptake and distribution pattern of 18F-labeled RGD-ATWLPPR through PET imaging was evaluated and compared with those of RGD and ATWLPPR. The means were compared using one-way ANOVA and t test. Results Both integrin αvβ3 and NRP-1 showed high expression in U87MG glioma cells and tumor tissues. RGD-ATWLPPR exhibited similar in vitro receptor binding affinity to those of RGD and ATWLPPR. Based on the PET imaging study, 18F-labeled RGD-ATWLPPR (denoted as 18F-FAl-NOTA-RGD-ATWLPPR) demonstrated significantly higher tumor uptake than RGD[(4.86±0.48)%ID/g vs. (3.33±0.15)%ID/g, t=10.21, P<0.05] and ATWLPPR [(4.86±0.48)%ID/g vs. (2.28±0.41)%ID/g, t=32.16, P<0.05]. In the blocking study, 18F-FAl-NOTA-RGD-ATWLPPR showed positive imaging result in the presence of excess unlabeled RGD or ATWLPPR. The tumor uptake decreased to the background level when unlabeled RGD and ATWLPPR were co-injected before administration of 18F-FAl-NOTA-RGD-ATWLPPR. Conclusions The dual-targeted PET probe 18F-FAl-NOTA-RGD-ATWLPPR specifically binds to either integrin αvβ3 or NRP-1 receptor and could be a promising PET imaging agent for NRP-1-/αvβ3+ and NRP-1+/αvβ3- tumors. The receptor-binding affinity of RGD-ATWLPPR must be further improved. Key words: Integrin αvβ3; Neuropilin-1; Positron-emission tomography; Molecular probes