VEGF receptor specific imaging in atherosclerotic lesions in diabetic and non-diabetic ApoE -/- mice

1648 Objectives Value of selective VEGF receptors in atherosclerotic plaque vulnerability is unknown; therefore we developed VEGF receptor-1 and -2 specific imaging tracers as research tools and potential clinical applications. Receptor-specific versions of scVEGF (engineered single-chain version of pan-receptor VEGF A with N-terminal cysteine-containing tag for site-specific conjugation) with enhanced selective affinity to either VEGFR-1 (scVR1) or VEGFR-2 (scVR2) were engineered via site-directed mutagenesis and their functional activity and receptor-specificity validated in tissue culture assays. PEGylated DOTA chelator was conjugated to Cys-tag, and high specific affinity of the resulting targeting conjugates, scVR1 and scVR2 characterized by surface plasmon resonance. Conjugates were radiolabeled with 99mTc using pan-receptor scVEGF-PEG-DOTA conjugate protocol. Methods 34-40 week diabetic ApoE-/- mice (DM) and age-matched non-diabetic (NDM) ApoE-/- mice were studied. For specificity testing, scVR1 and scVR2 were co-injected with excess of “cold” proteins of the same or opposite receptor specificity. Equal numbers of DM and NDM mice were then injected with tracer, 2-3 h later injected with CT contrast and underwent hybrid SPECT/CT. Tracer uptake localized to proximal aorta and brachiocephalic vessels was quantified and expressed as %ID. Results Excess “cold” protein of the same receptor blocked 60-70% of plaque uptake, but uptake was unaffected by “cold” protein of the opposite receptor specificity. Plaque uptake in DM vs. NDM for scVR1/99mTc was 0.06 ± 0.01 vs.0.03 ± 0.01 %ID (P = 0.02) and for scVR2/99mTc was 0.06 ± 0.02 vs. 0.05 ± 0.02 (P = 0.42) while for NDM alone scVR2/99mTc was higher than scVR1/99mTc (P = 0.04). Conclusions Selective VEGFR receptor targeting for in-vivo imaging is feasible and may be useful to explore plaque biology and identify vulnerability. Further data on relative affinity, binding, and retention are needed to interpret the differences in lesion uptake of scVR1/99mTc vs. scVR2/99mTc .