Synthesis and Preclinical Evaluation of the Fibrin-Binding Cyclic Peptide F-iCREKA: Comparison with Its Contrasted Linear Peptide.

PURPOSE

Cys-Arg-Glu-Lys-Ala (CREKA) is a pentapeptide which can target fibrin-fibronectin complexes. Our previous study has built a probe called iCREKA which was based on CREKA and has proved the feasibility and specificity of iCREKA by the fluorescence experiment. The purpose of this study is to achieve the F-labeled iCREKA and make preclinical evaluation of the F-iCREKA with comparison of its contrasted linear peptide (LP).

METHODS

CREKA, LP, and iCREKA were labeled by the AlF labeling method, respectively. These F-labeled peptides were evaluated by the radiochemistry, binding affinity, in vitro stability, in vivo stability, micro-PET imaging, and biodistribution tests.

RESULTS

F-NOTA-iCREKA was stable both in vitro and in vivo. However, F-NOTA-CREKA and F-NOTA-LP were both unstable. The FITC or F-labeled iCREKA could be abundantly discovered only in matrix metalloproteinases- (MMPs-) 2/9 highly expressed U87MG cells, while the FITC or F-labeled LP could also be abundantly discovered in MMP-2/9 lowly expressed Caov3 cells. Biodistribution and micropositron emission tomography (PET) imaging revealed that the U87MG xenografts showed a higher uptake of F-NOTA-iCREKA than F-NOTA-LP while the Caov3 xenografts showed very low uptake of both F-NOTA-iCREKA and F-NOTA-LP. The tumor-to-muscle (T/M) ratio of F-NOTA-iCREKA (9.93 ± 0.42) was obviously higher than F-NOTA-LP (2.69 ± 0.35) in U87MG xenografts.

CONCLUSIONS

The novel CREKA-based probe F-NOTA-iCREKA could get a high uptake in U87MG cells and high T/M ratio in U87MG mice. It was more stable and specific than the F-NOTA-LP.