Basic research of I-131 labeled CendR for the treatment of neuropilin-1 positive tumor

Objectives Neuropilin-1 (NRP-1) is a multifunctional single-pass transmembrane protein, which is also described as a biomarker for tumor therapy. CendR sequence motif (R/KXXR/K) could efficiently and specially bind with NRP-1, and transport therapeutic molecules into tumor cell based on the transmembrane capability of NRP-1. This study aimed to investigate the uptake and diagnostic effect of one kind of 131I labeled CendR peptide, tLyp-1, in NRP-1 highly expressed NSCLC A549.

Methods NRP-1 expression in normal and NSCLC cells was detected using immunobloting. The binding affinity of FITC-tLyp-1 peptide between A549 and normal bronchial epithelium HBE135-E6E7 was confirmed by flow-cytometry. 131I labeled tLyp-1 peptide was injected into nude mice with A549 xenograft tumor via tail vein (n=5). At 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, and 24 h post injection, the 131I radioactive distribution in mice was imaged and recorded by SPECT and fused with mouse whole body CT images.

Results High level expression of NRP-1 was detected in NSCLC A549 compared with normal bronchial epithelium HBE135-E6E7. Fluorescence microscope and flow cytometry results indicated that the FITC-labeled tLyP-1 had about 8.1 times higher binding affinity with A549 than HBE135 - E6E7 (p < 0.05). 131I radioactive signal was able to be captured at 2h post injection, and reached peak at 6 to 8h. Semi-quantitative analysis indicated that radioactive count ratio of Tumor / Contralateral non-tumor soft tissue (T/NT) was 4.84 ± 1.47 (p < 0.05). In vivo biodistribution result revealed the peptide metablosim was mainly dependent on kidney.

Conclusions Binding affinity and radio-labeled tLyp-1 peptide investigation indicated that CendR peptides holds potential as a new imaging biomarker in NRP-1 positive cancer.

Research Support National Natural Science Foundation of China (81371585 to L.Li and 81301250 to H.Cai), and the Department of Nuclear Medicine, West China Hospital of Sichuan University, Chengdu, P.R.China.