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Evaluation of 68Ga-labeled iNGR peptide with tumor-penetrating motif for microPET imaging of CD13-positive tumor xenografts

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The aim of the study is to evaluate the efficacy of 68Ga-labeled iNGR, containing Asn-Gly-Arg (NGR) homing sequence and CendR (R/KXXR/K) penetrating motif, as a new molecular probe for microPET imaging of CD13-positive xenografts. The synthesized iNGR and NGR peptides were conjugated with DOTA and then labeled with 68Ga. 68Ga-iNGR and 68Ga-NGR were compared in the performance of the in vitro stability, partition coefficient, binding affinity, cell uptake analysis, in vivo microPET imaging, and biodistribution studies in CD13-positive HT-1080 and CD13-negative HT-29 cell lines. The in vitro results revealed that both probes exhibited high radiochemical purity and stability, and no significant difference between two probes was observed in terms of the binding affinity to CD13. In vivo microPET/CT imaging showed that the uptake of 68Ga-iNGR in HT-1080 tumor was significantly higher than that of 68Ga−NGR. Moreover, tumor 68Ga-iNGR uptake could be completely blocked by cold NGR and partially blocked by neutralizing NRP-1 antibody. We concluded that 68Ga-iNGR has a higher tumor uptake and better tumor retention than 68Ga-NGR through NRP-1, indicating that CendR motif modification is a promising method for improving NGR peptide performance.

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This work was supported by the National Natural Science Foundation of China (grant nos. 81230033, 81401442, 81227901, and 81371594), the Post-doctoral Science Foundation of China (grant no. 2015M582802), and the Key Science and Technology Program of Shaanxi Province, China (grant no. 2013K12-03-05). No other potential conflict of interest relevant to this article was reported. We would like to thank Prof. Fan Wang from Medical Isotopes Research Center of Peking University (Beijing, China) for her generous support and Guiyu Li and Changhao Liu for their technical assistance in conducting this research.

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Correspondence to Fei Kang or Jing Wang.

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Mingxuan Zhao, Weidong Yang, Mingru Zhang, Fei Kang and Jing Wang contributed equally to this work.

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Zhao, M., Yang, W., Zhang, M. et al. Evaluation of 68Ga-labeled iNGR peptide with tumor-penetrating motif for microPET imaging of CD13-positive tumor xenografts. Tumor Biol. 37, 12123–12131 (2016).

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  • iNGR peptide
  • NGR peptide
  • CendR motif
  • CD13
  • Neuropilin-1