Site-Specific Labeling of scVEGF with Fluorine-18 for Positron Emission Tomography Imaging

• Main Author: Hui Wang, Haokao Gao, Ning Guo, Gang Niu, Ying Ma, Dale O. Kiesewetter, Xiaoyuan Chen
• Format: Article
• Language: English
• Published: Ivyspring International Publisher 2012-01-01
• Series: Theranostics
• Online Access: http://www.thno.org/v02p0607.htm

<p>Vascular endothelial growth factor (VEGF) is one of the most important mediators of angiogenesis. Single-chain (sc)-VEGF protein containing an N-terminal Cys-tag has been designed for site-specific modification with a variety of imaging and therapeutic moieties. Site-specific labeling of scVEGF with thiol-reactive prosthetic group, <i>N</i>-[2-(4-¹⁸F-fluorobenzamido) ethyl] maleimide ([¹⁸F]FBEM) for positron emission tomography (PET) imaging of VEFGR may provide a new tracer which has great potential for clinical translation.</p><p><b>Methods</b>: [¹⁸F]FBEM-scVEGF was synthesized by site-specific conjugation of ¹⁸F-FBEM to a thiol group in Cys-tag of scVEGF at room temperature. The functional activity after labeling was tested by immunofluorescence staining, cellular uptake and efflux<i>. </i>The tumor targeting and <i>in vivo</i> properties were evaluated by biodistribution and microPET studies in tumor-bearing mice.</p><p><b>Results</b>: The radiolabeling yield and specific activity of [¹⁸F]FBEM-scVEGF were 20.6 &#177; 15.1% (based on starting [¹⁸F]FBEM, uncorrected, n = 5) and 58.8 &#177; 12.4 GBq/&#181;mol, respectively. Noninvasive microPET and direct tissue sampling experiments demonstrated that [¹⁸F]FBEM-scVEGF had VEGFR specific tumor uptake in MDA-MB-435, U87MG and 4T1 xenograft models. The optimal tumor uptake was achieved at 2 h p.i., which can be partially, but significantly blocked by co-injection of non-labeled scVEGF protein. Overall, [¹⁸F]FBEM-scVEGF showed VEGFR specific tumor uptake.</p><p><b>Conclusion</b>: The scVEGF was site-specifically labeled with ¹⁸F via [¹⁸F]FBEM prosthetic group and the tracer [¹⁸F]FBEM-scVEGF exhibited high receptor binding affinity and tumor targeting efficacy. Further study of [¹⁸F] FBEM-scVEGF to evaluate angiogenesis in cancer and other disease types is warranted.</p>