Abstract
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Objectives: Pancreatic cancer is highly malignant, and has a five-year survival rate of 5% due to early lymph node, nerve and vascular metastasis. Very late antigen 3 (VLA-3, also called Integrin α3β1) is overexpressed in many tumors and plays a vital role in tumor formation, recurrence and metastasis. In this study, we developed a 68Ga-radiolabled peptide tracer targeting the α3 unit of VLA-3 and evaluated its potential application in positron emission computed tomography (PET) imaging of pancreatic cancer.
Methods: NOTA-CK11 was prepared by solid phase synthesis and radiolabeled with 68Ga. Human pancreatic cancer cells SW1990,BXPC-3 and PANC-1 were cultured and their VLA-3 expression levels were explored using western blot. To determine the specificity of the peptide, a fluorescence probe FITC-CK11 was also prepared. The in vitro specificity of the peptide to VLA-3 was evaluated by flow cytometry and immunofluorescence staining. In addition, cell uptake and blocking studies of 68Ga-NOTA-CK11 was also conducted. Static PET imaging and biodistribution were performed at 0.5 h and 1 h post-injecting of 68Ga-NOTA-CK11 to investigate its in vivo targeting specificity using subcutaneous pancreatic tumor-bearing mouse models.
Results: NOTA-CK11 was synthesized and identified using HPLC and mass spectrum. It was successfully radiolabeled with 68Ga with greater than 99% radiochemical purity and a specific activity of 37 ± 5 MBq/nmol (n = 5). The expression level of integrin α3 was SW1990, BXPC-3 and PANC-1 from high to low, while the expression level of integrin β1 was relatively close. When SW1990 cells with the highest expression levels of VLA-3 were stained with FITC-CK11, strong fluorescence was observed by flow cytometry and under a laser confocal microscope. However, no significant fluorescence was observed in the blocking group when treated with excessive CK11. 68Ga-NOTA-CK11 showed significant radioactivity accumulation in SW1990 cells and can be blocked by CK11 successfully. Subsequent small animal PET imaging and biodistribution studies in mice bearing SW1990 xenografts confirmed its high tumor uptake with a good tumor-to-blood ratio and tumor-to-muscle ratio (2.45 ± 0.31 and 3.65 ± 0.33, respectively) at 1 h postinjection of the probe.
Conclusions: We successfully developed a peptide-based imaging agent, 68Ga-NOTA-CK11, that showed strong binding affinity with VLA-3and good target specificity for SW1990 cells and xenografted pancreatic tumor. 68Ga-NOTA-CK11is a promising radionuclide molecular probe for early diagnosis pancreatic cancer. Acknowledgments: This work was supported by the National Natural Science Foundation of China (No. 81801738 and 81630049).
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