Abstract
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Objectives: The aim of this study was to prepare 68Ga-DOTA-RRL as a better specific and effective tumor imaging agent.
Methods: the precursor compound DOTA-RRL was obtained using bifunctional chelating agent DOTA-NHS ester to modify the prepared peptide RRL. The radionuclide 68Ga was labeled with DOTA-RRL to obtain 68Ga-DOTA-RRL. The labeling rate of 68Ga-DOTA-RRL was determined, radiochemical purity and radioactivity specific activity were analyzed by HPLC and ESI-MS. the stability of the probe was evaluated by measuring the change of radiochemical purity at room temperature and in serum. Cellular uptake of 68Ga-DOTA-RRL and binding of FITC conjugated RRL in HepG2 cells was evaluated using gamma counter, confocal microscopy and flow cytometry. PET images and biodistribution were acquired in HepG2 tumor bearing mice after injection of 68Ga-DOTA-RRL or 68GaCl3 at different time points. The tumor-to-non-tumor ratio in different organs was calculated. Further, blocking study was investigated after the injection of cold RRL. Result:.The labeling rate of the probe 68Ga-DOTA-RRL was above 80.6 ± 3.89%, and the radiochemical purity was more than 95%. Cell uptake experiments showed that the uptake of 68Ga-DOTA-RRL in HepG2 cells was significantly higher than that of 68GaCl3 solution. The uptake rate of 68Ga-DOTA-RRL cells was 63.5 ± 0.64%, while the uptake rate of 68GaCl3 cells was only 1.2 ± 0.15%. The distribution data showed that 68Ga-DOTA-RRL had a good blood retention effect, and the tumor uptake was high and persistent. The tumor uptake rate was about 3.95 ± 0.71 (n = 5) at 30 min after injection. In the blocking group, the radioactive uptake of 68Ga-DOTA-RRL at 30 min was 1.28 ± 0.04, which was much lower than that of the experimental group (P<0.05). Moreover, FITC conjugated RRL showed high fluorescent affinity in HepG2 cells by confocal microscopy and flow cytometry. The micro-PET imaging of 68Ga-DOTA-RRL in tumor-bearing nude mice showed good tumor images at all time points. While the control group of tumor site uptake is not obvious. Conclusion:The new probe 68Ga-DOTA-RRL labeling method has the following advantages: simple operation, high labeling rate, stable labeled compound, excellent physical and chemical properties, good biodistribution characteristics and good imaging effect. It is expected to become a new tumor targeting tumor neonatal small molecule peptide imaging agent. KEY WORDS: Arginine-arginine-leucine, Peptide, MolecμLartumor imaging, Gallium-68, Angiogenesis
