A Radiofluorinated Divalent Cystine Knot Peptide for Tumor PET Imaging

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• 作者：Lei Jiang ; Richard H. Kimura ; Xiaowei Ma ; Yingfeng Tu ; Zheng Miao ; Bin Shen ; Frederick T. Chin ; Hongcheng Shi ; Sanjiv Sam Gambhir ; Zhen Cheng
• 刊名：Molecular Pharmaceutics
• 出版年：2014
• 出版时间：November 3, 2014
• 年：2014
• 卷：11
• 期：11
• 页码：3885-3892
• 全文大小：333K
• ISSN：1543-8392

文摘

A divalent knottin containing two separate integrin binding epitopes (RGD) in the adjacent loops, 3-4A, was recently developed and reported in our previous publication. In the current study, 3-4A was radiofluorinated with a 4-nitrophenyl 2-¹⁸F-fluoropropinate (¹⁸F-NFP) group and the resulting divalent positron emission tomography (PET) probe, ¹⁸F-FP鈥?-4A, was evaluated as a novel imaging probe to detect integrin 伪v尾3 positive tumors in living animals. Knottin 3-4A was synthesized by solid phase peptide synthesis, folded, and site-specifically conjugated with ^18/19F-NFP to produce the fluorinated peptide ^18/19F-fluoropropinate-3-4A (^18/19F-FP鈥?-4A). The stability of ¹⁸F-FP鈥?-4A was tested in both phosphate buffered saline (PBS) buffer and mouse serum. Cell uptake assays of the radiolabeled peptides were performed using U87MG cells. In addition, small animal PET imaging and biodistribution studies of ¹⁸F-FP鈥?-4A were performed in U87MG tumor-bearing mice. The receptor targeting specificity of the radiolabeled peptide was also verified by coinjecting the probe with a blocking peptide cyclo(RGDyK). Our study showed that ¹⁸F-FP鈥?-4A exhibited excellent stability in PBS buffer (pH 7.4) and mouse serum. Small animal PET imaging and biodistribution data revealed that ¹⁸F-FP鈥?-4A exhibited rapid and good tumor uptake (3.76 卤 0.59% ID/g and 2.22 卤 0.62% ID/g at 0.5 and 1 h, respectively). ¹⁸F-FP鈥?-4A was rapidly cleared from the normal tissues, resulting in excellent tumor-to-normal tissue contrasts. For example, liver uptake was only 0.39 卤 0.07% ID/g and the tumor to liver ratio was 5.69 at 1 h p.i. Furthermore, coinjection of cyclo(RGDyK) with ¹⁸F-FP鈥?-4A significantly inhibited tumor uptake (0.41 卤 0.12 vs 1.02 卤 0.19% ID/g at 2.5 h) in U87MG xenograft models, demonstrating specific accumulation of the probe in the tumor. In summary, the divalent probe ¹⁸F-FP鈥?-4A is characterized by rapid and high tumor uptake and excellent tumor-to-normal tissue ratios. ¹⁸F-FP鈥?-4A is a highly promising knottin based PET probe for translating into clinical imaging of tumor angiogenesis.

Keywords:

cystine-knot peptide; divalent; integrin 伪_v尾₃; ¹⁸F; PET