Biodistribution of (125)I-labeled anti-endoglin antibody using SPECT/CT imaging: Impact of in vivo deiodination on tumor accumulation in mice

Nucl Med Biol. 2016 Jul;43(7):415-23. doi: 10.1016/j.nucmedbio.2016.03.007. Epub 2016 Mar 29.


Introduction: Radiolabeled antibodies directed against endoglin (CD105) are promising tools for imaging and antiangiogenic cancer therapy. To validate iodinated antibodies as reliable tracers, we investigated the influence of the radiolabeling method (direct or indirect) on their in vivo stability.

Methods: Anti-CD105 mAbs were radioiodinated directly using chloramine-T ((125)I-anti-CD105-mAbs) or indirectly using D-KRYRR peptide as a linker ((125)I-KRYRR-anti-CD105-mAbs). The biodistribution was studied in B16 tumor-bearing mice via SPECT/CT imaging.

Results: Radioiodinated mAbs were stable in vitro. In vivo, thyroid showed the most important increase of uptake after 24h for (125)I-anti-CD105-mAbs (91.9±4.0%ID/ml) versus(125)I-KRYRR-anti-CD105-mAbs (4.4±0.6%ID/ml). Tumor uptake of (125)I-anti-CD105-mAbs (0.9±0.3%ID/ml) was significantly lower than that of (125)I-KRYRR-anti-CD105-mAbs (4.7±0.2%ID/ml).

Conclusions: An accurate characterization of the in vivo stability of radioiodinated mAbs and the choice of an appropriate method for the radioiodination are required, especially for novel targets. The indirect radioiodination of internalizing anti-CD105 mAbs leads to more stable tracer by decreasing in vivo deiodination and improves the tumor retention of radioiodinated mAbs.

Advances in knowledge and implications for patient care: To date, the only antiangiogenic antibody approved for clinical indications is bevacizumab. There is a need to develop more antibodies that have targets highly expressed on tumor endothelium. CD105 represents a promising marker of angiogenesis, but its therapeutic relevance in cancer needs to be further investigated. In this context, this study suggests the potential use of indirectly iodinated anti-CD105 mAbs for tumor imaging and for therapeutic purposes.

Keywords: Anti-endoglin antibody; CD105; Deiodination; KRYRR; SPECT/CT; Tumor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal / chemistry
  • Antibodies, Monoclonal / immunology
  • Cell Line, Tumor
  • Endoglin / immunology*
  • Gene Expression Regulation, Neoplastic
  • Immunoconjugates / chemistry*
  • Immunoconjugates / pharmacokinetics*
  • Iodine Radioisotopes*
  • Isotope Labeling
  • Melanoma, Experimental / diagnostic imaging*
  • Melanoma, Experimental / metabolism*
  • Melanoma, Experimental / pathology
  • Mice
  • Rats
  • Single Photon Emission Computed Tomography Computed Tomography / methods*
  • Tissue Distribution


  • Antibodies, Monoclonal
  • Endoglin
  • Immunoconjugates
  • Iodine Radioisotopes