Radiolabeled RGD uptake and alphav integrin expression is enhanced in ischemic murine hindlimbs.
Radiolabeled RGD peptides that target alpha(v)beta3 integrin are promising tracers for imaging tumor angiogenesis. Integrins and angiogenesis also play important roles in healing of ischemic lesions. Thus, we investigated the biodistribution of radiolabeled RGD and expression of alpha(v) integrin in a mouse model of hindlimb ischemia.


METHODS
125I-3-Iodo-D-Tyr4-cyclo(-Arg-Gly-Asp-D-Tyr-Val-) (125I-c(RGD(I)yV)) was synthesized and tested for endothelial binding. Hindlimb ischemia was induced in ICR mice through femoral artery ablation, and perfusion was measured with laser Doppler blood flowmetry. 125I-c(RGD(I)yV) biodistribution was evaluated in control animals (n = 7) and ischemic models on day 3, 8, or 14 (n = 6 each). Control experiments were performed using a radiolabeled peptide with a scrambled amino acid sequence (125I-GfVGV). Microsections of hindlimb tissue were immunostained for alpha(v) integrin expression and stained with alkaline phosphatase to localize vascular endothelial cells.


RESULTS
125I-c(RGD(I)yV) retained specific binding to human umbilical vein endothelial cells. Perfusion in ischemic hindlimbs immediately fell to 10% +/- 4% of contralateral levels and gradually recovered to 22% +/- 11% and 64% +/- 9% on days 8 and 14, respectively. 125I-c(RGD(I)yV) uptake in ischemic muscles significantly increased from a control level of 0.16 +/- 0.05 %ID/g (percentage injected dose per gram of tissue) to 0.85 +/- 0.76 %ID/g at day 3, 0.43 +/- 0.23 %ID/g at day 8, and 0.43 +/- 0.28 %ID/g at day 14 (all P < 0.05). Ischemic muscle-to-lung count ratios had a virtually identical trend: 0.42 +/- 0.25 for controls, 2.34 +/- 1.70 at day 3 (P < 0.02), 1.46 +/- 0.52 at day 8 (P < 0.001), and 1.39 +/- 0.94 at day 14 (P < 0.02). In contrast, uptake of the control peptide in ischemic hindlimbs was not different from that of controls. Immunohistochemistry revealed substantially increased alpha(v) integrin staining in ischemic hindlimb tissue.


CONCLUSIONS
Radioiodine RGD uptake is significantly enhanced in ischemic hindlimbs of a mouse model, and is accompanied by an increase in alpha(v) integrin expression. Further investigation is thus warranted to illuminate the potential role of radiolabeled RGD for noninvasive monitoring of peripheral ischemic lesions.
Lee
Kyung-Han
KH
Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. khnm.lee@samsung.com
Jung
Kyoung-Ho
KH
Song
Sung-Hee
SH
Kim
Dong Hyun
DH
Lee
Byung Chul
BC
Sung
Hyun Ju
HJ
Han
Yu-Mi
YM
Choe
Yearn Seong
YS
Chi
Dae Yoon
DY
Kim
Byung-Tae
BT
D000818:Animals; D006614:Hindlimb / Q000098:blood supply / Q000000981:diagnostic imaging* / Q000378:metabolism*; D039564:Integrin alphaV / Q000378:metabolism*; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics; D007511:Ischemia / Q000000981:diagnostic imaging* / Q000378:metabolism*; D008297:Male; D008657:Metabolic Clearance Rate; D051379:Mice; D008813:Mice, Inbred ICR; D009842:Oligopeptides / Q000493:pharmacokinetics*; D009928:Organ Specificity; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D014018:Tissue Distribution
D039564:Integrin alphaV; D007457:Iodine Radioisotopes; D009842:Oligopeptides; D019275:Radiopharmaceuticals; C047981:arginyl-glycyl-aspartic acid