Synthesis andin vivoevaluation of99mTc–Transferrin conjugate for detection of inflamed site

99mTc-labeled and gadolinium-chelated transferrin enhances the sensitivity and specificity of dual-modality SPECT/MR imaging of breast cancer

A dual-modal probe ^99mTc–Tf–DTPA–Gd could provide high spatial resolution and high sensitivity images of breast tumor.

Dextran-conjugated vascular endothelial growth factor receptor antibody for in vivo melanoma xenografted mouse imaging

Intact immunoglobulin G antibody has a relatively large molecule size of approximately 150 kDa that remains in the bloodstream for many weeks, which is a considerable disadvantage when it is used to carry radioactive materials for imaging. To lower background activity and increase the contrast of images, we investigated antivascular endothelial growth factor (VEGF) receptor 2 antibody (DC101) conjugated dextran for VEGF receptor 2 imaging in tumor xenografted mice. DTPA-conjugated aminodextran was synthesized, reacted with sulfo-LC-SPDP, and then reacted with DC101. The binding affinity of DTPA-dextran-DC101 to Flk-1 was measured. The gamma imaging and biodistributions of (99m)Tc-DTPA-dextran-DC101, (99m)Tc-DTPA-DC101, and (125)I-DC101 were studied in B16F10 melanoma xenografted mice. The dissociation values for DC101, DTPA-DC101, and DTPA-dextran-DC101 were 22.48, 3.05, and 14.74 pM, respectively. In gamma images, (99m)Tc-DTPA-dextran-DC101 showed weak liver uptake and rapid kidney elimination. In biodistribution results, the liver uptake of (99m)Tc-DTPA-dextran-DC101 was similar with that of (99m)Tc-DTPA-DC101 at each time point. However, the blood activity of (99m)Tc-DTPA-dextran-DC101 has shown significant differences, compared with (99m)Tc-DTPA-DC101 at all time points. The tumor accumulation of dextran-conjugated antibody was increased with time, whereas that of dextran nonconjugated antibody decreased. In particular, the pattern of tumor uptake of (99m)Tc-DTPA-dextran-DC101 was similar to that of (125)I-DC101, so this was thought to reflect the kinetics of DC101, unlike the nonconjugated form. The results of this study suggested that introduction of dextran moiety to make (99m)Tc-radiolabeled DC101 imaging agent could provide better images with the impaired background and the steady increasing binding to the receptor. However, further studies are necessary to improve clinical pharmacokinetics, such as enhancement of tumor uptake and impaired renal uptake.

Current status and future perspectives of in vivo small animal imaging using radiolabeled nanoparticles

Small animal molecular imaging is a rapidly expanding efficient tool to study biological processes non-invasively. The use of radiolabeled tracers provides non-destructive, imaging information, allowing time related phenomena to be repeatedly studied in a single animal. In the last decade there has been an enormous progress in related technologies and a number of dedicated imaging systems overcome the limitations that the size of small animal possesses. On the other hand, nanoparticles (NPs) gain increased interest, due to their unique properties, which make them perfect candidates for biological applications. Over the past 5 years the two fields seem to cross more and more often; radiolabeled NPs have been assessed in numerous pre-clinical studies that range from oncology, till HIV treatment. In this article the current status in the tools, applications and trends of radiolabeled NPs reviewed.

Targeted molecular imaging of VEGF receptors overexpressed in ischemic microvasculature using chitosan-DC101 conjugates

Expression of vascular endothelial growth factor receptors (VEGFRs) increases in ischemic muscles, and thus, VEGFR could potentially be used as marker to detect ischemia. Here, we investigated whether (99m)Tc or Cy5.5-labeled chitosan-DC101 conjugates could identify VEGFR-2 overexpressed in ischemia. To this end, chitosan was conjugated with the DC101 antibody and Cy5.5, FITC, or the HYNIC chelator for (99m)Tc-labeling. Targeting of the conjugate was evaluated in vitro and in vivo through cell-binding studies and gamma/optical imaging, respectively. A hindlimb ischemic mouse model was surgically created by femoral artery occlusion. The chitosan-DC101 conjugates exhibited VEGFR-selective cell binding properties as determined by both confocal microscopy and flow cytometry. At postoperative times of 2, 12, and 24 h, (99m)Tc or Cy5.5-labeled chitosan-DC101 conjugates were intravenously injected into the mice, and gamma/optical imaging studies were conducted at 1 or 3 h. Both the gamma and optical imaging results indicated a significantly higher uptake in ischemic muscles when compared with the contralateral nonischemic muscle. Further, semiquantitative analysis of scintigraphic imaging data revealed that the ischemic to contralateral limb ratio was 4.5 +/- 0.25 at 24 h postoperation. Western blotting analysis confirmed VEGFR expression in the ischemic muscle. In conclusion, we believe that (99m)Tc or Cy5.5-labeled chitosan-DC101 conjugates have the potential to be useful as VEGFR-2-targeted imaging agents for monitoring ischemia.

Molecular scintigraphic imaging using 99mTc-transferrin is useful for early detection of synovial inflammation of collagen-induced arthritis mouse

Transferrin receptor (TfR) is highly expressed on rapidly dividing inflammatory cells, but not in nonproliferating cells. We investigated whether scintigraphic imaging using 99mTechnetium-radiolabeled transferrin (99mTc-Tf) is useful for early detection of synovial inflammation of collagen-induced arthritis (CIA) mouse. 99mTc-Tf conjugate was synthesized to target the TfR in inflamed synovium. 99mTc-Tf scintigraphic images were obtained in nonarthritic normal mouse and advanced phase of CIA mouse. 99mTc-Tf and 99mTc-methylenediphosphonate (99mTc-MDP) bone scintigraphic images were obtained in same early phase of CIA mouse. Western blot analysis, hematoxylin & eosin (H&E), and immunohistochemical staining were performed to determine development of arthritis and expression of TfR. Image analyses revealed that the uptake of 99mTc-Tf in inflamed joints of advanced phase of CIA mouse was markedly higher than those by normal nonarthritic mouse. 99mTc-Tf scintigraphy also showed higher uptake in knee joint prior to significant joint swelling in early phase of CIA mouse but 99mTc-MDP bone scintigraphy does not. These scintigraphic findings are well correlated with the results of Western blot, H&E and immunohistochemical analysis. In conclusion, TfR can be used as a specific target for molecular imaging in CIA mouse, and 99mTc-Tf scintigraphy detects synovial inflammation prior to significant clinical findings in CIA mouse.