Imaging Vascular Endothelial Growth Factor (VEGF) Receptors in Turpentine-Induced Sterile Thigh Abscesses with Radiolabeled Single-Chain VEGF

Abstract

Angiogenesis plays a central role in the pathogenesis of chronic inflammatory disorders. Vascular endothelial growth factor (VEGF) and its receptors are the most important regulators of angiogenesis. We wished to determine whether labeled forms of single-chain VEGF (scVEGF) could be used to image VEGF receptors in a well-characterized model of sterile soft-tissue inflammation induced by intramuscular injection of turpentine. Methods: Anesthetized adult male Swiss-Webster mice received a 20-mL intramuscular injection of turpentine into the right thigh. At 4, 7, or 10 d later, groups of 3-5 mice were injected via the tail vein with 50 mg of either scVEGF that had been site specifically labeled with Cy5.5 (scVEGF/Cy) or inactivated scVEGF/ Cy (inVEGF/Cy) and then examined by fluorescence imaging. At 3, 4, 6, 7, 9, 10, or 12 d, additional groups of 3-5 mice were injected via the tail vein with 74-111 MBq of 99m Tc-scVEGF (or 99m Tc-inVEGF) and then examined by SPECT imaging. Results: On days 3 through 10, both forms of scVEGF (scVEGF/Cy and 99m Tc-scVEGF) showed significantly higher uptake (P , 0.05) in the right (abscessed) thigh than in the contralateral thigh (and higher uptake than the inactivated tracer). Peak uptake occurred on day 7 (3.67 6 1.79 [ratio of uptake in abscessed thigh to uptake in normal thigh, mean 6 SD] and 0.72 6 0.01 for scVEGF/Cy and inVEGF/Cy, respectively, and 3.49 6 1.22 and 1.04 6 0.41 for 99m Tc-scVEGF and 99m Tc-inVEGF, respectively) and slowly decreased thereafter. Autoradiography revealed peak tracer uptake in the thick irregular angiogenic rim of the abscess cavity on day 9 (5.83 · 10 27 6 9.22 · 10 28 and 5.85 · 10 28 6 5.95 · 10 28 percentage injected dose per pixel for 99m TcscVEGF and 99m Tc-inVEGF, respectively); in comparison, a thin circumscribed rim of uptake was seen with 99m Tc-inVEGF. Immunostaining revealed that VEGFR-2 (VEGF receptor) colocalized with CD31 (endothelial cell marker) at all time points in the abscess rim, whereas F4/80 (macrophage) immunostaining reached a maximum at day 7 and decreased by day 10. Conclusion: The uptake of scVEGF in turpentine-induced abscesses was specific and directly related to VEGFR-2 expression in the neovasculature of the angiogenic rim. Peak tracer uptake coincided with maximum macrophage infiltration, suggesting that scVEGF imaging may be useful for the detection, localization, and monitoring of chronic inflammation in bone, joints, or soft tissues.

Theranostic Probes for Targeting Tumor Microenvironment: An Overview

“…123 I-L19(scFv)2 targeted towards fibronectin an imaged by SPECT/CT modality [64]. SPECT imaging modality is also useful for detecting angiogenesis markers with help of probes like 99mTc-scVEGF targeted towards VEGF receptor [65]. VEGF121-Avi-streptavdidn IRDye800scVEGF/Cy is a probe which uses optical imaging or NIRF for detecting VEGF receptor [66].…”

Theranostic Probes for Targeting Tumor Microenvironment: An Overview

“…124-L19-SIP monoclonal antibody was targeted against extra domain-B of fibronectin on xenograft nude mice [62] (as shown in Figure 3). SPECT imaging modality is also useful for detecting angiogenesis markers with the help of probes like 99mTc-scVEGF targeted towards the VEGF receptor of Male Swiss–Webster mice [63]. VEGF121-Avi-streptavdidn IRDye800scVEGF/Cy is a probe which uses optical imaging or NIRF for detecting VEGF receptor performed on Mice bearing VEGFR-2 expressing 67NR murine breast tumors [64].…”

‘In vivo’ optical approaches to angiogenesis imaging

“…The scVEGF-based family of probes has been validated to target the VEGF receptor in vitro and in vivo tumor angiogenesis [90, 91]. More recently, scVEGF labeled with the near infrared dye Cy5.5 has been used for fluorescence imaging of VEGF receptor in angiogenic vasculature, in regions of sterile inflammation and during tumor angiogenesis [92, 93]. …”