TY - JOUR T1 - Evaluation of <sup>68</sup>Ga-labeled iNGR peptide with tumor penetrating motif for microPET imaging of CD13-positive tumor xenografts JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1157 LP - 1157 VL - 56 IS - supplement 3 AU - Mingxuan Zhao AU - Fei Kang AU - Mingru Zhang AU - Shengjun Wang AU - Weidong Yang AU - Jing Wang Y1 - 2015/05/01 UR - http://jnm.snmjournals.org/content/56/supplement_3/1157.abstract N2 - 1157 Objectives To evaluate the efficacy of 68Ga-labelled iNGR peptide containing CendR tumor penetrating motif as a new molecular probe for microPET imaging of CD13-positive tumor xenografts.Methods NGR and iNGR peptides both conjugated with NOTA were synthesised. CD13 of HT1080 and HT29 cells was confirmed by western blot and immunofluorescence. NGR and iNGR peptides were labeled by 68Ga and assayed by HPLC and stability tests. In vitro affinity to cancer cells of the two peptides was compared by competitive cell binding assays. In vivo imaging of 68Ga-NGR and 68Ga-iNGR was compared by mricoPET imaging of the same nude mouse bearing HT1080 and HT29 tumors. The in vivo CD13 affinity was verified by competitive PET imaging of the same mouse with or without cold NGR blocking. The mechanism of the theoretically improved performance of iNGR via NRP1 was verified by comparison imaging by using blockade NRP1 antibody. Tumor uptake was measured by ROI method and quantified by SUV.Results CD13 was overexpressed in HT1080 cells but not in HT29 cells. Both probes exhibited high radiochemical purity and high stability in mouse serum or saline. The CD13 binding affinity of iNGR was comparable to that of NGR.The uptake of 68Ga-iNGR in HT1080 cells increased with incubation time, and the maximum uptake ratio was about 1.78±0.04% in HT1080 cells after 2h incubation, about 2-fold higher than that of 68Ga-NGR. In vivo imaging showed that the HT-1080 tumors were of higher contrast to HT29 tumors at all time points after injection of 68Ga-iNGR or 68Ga-NGR. The HT1080 tumor uptake of 68Ga-iNGR was significantly higher than that of 68Ga−NGR. Moreover, tumor 68Ga-iNGR uptake could be completely blocked by cold NGR and partly blocked by NRP1 antibody. Immunohistochemistry confirmed CD13 and NRP1 overexpression in HT1080 tumor neovasculature.Conclusions 68Ga-iNGR demonstrated higher tumor uptake and better tumor retention than 68Ga-NGR through NRP1, indicating the CendR motif modification is a promising way for improving NGR peptides performance.Research Support This work was supported by the National Natural Science Foundation of China (Grant Nos. 81230033, 81227901, 81090270, 81371594, 81401442), the National Basic Research Program of China (973 Program) (Grant No. 2011CB707704). ER -