Study on biodistribution and imaging of radioiodinated arginine-arginine-leucine peptide in nude mice bearing human prostate carcinoma

To investigate the biodistribution and imaging of ¹³¹I-labeled arginine-arginine-leucine (RRL) peptide in human prostate carcinoma bearing nude mice.

The 10-mer cyclic peptide containing the RRL sequence (YCGGRRLGGC) was synthesized by the solid-phase method. Disulfide bonds between the cysteines maintain the cyclic structure. Radioiodination of the RRL peptide was performed by the chloramine-T method. ¹³¹I-labeled peptides were injected into the nude mice bearing human prostate carcinoma via a tail vein. Biodistribution and imaging results in vivo were obtained.

The ¹³¹I-labeling rate of RRL peptide was about 60%. The radiochemical purity was 96.5%. The radiochemical purity of the labeled compound remained 90.3% at 24 h in human blood serum at 37°C. In the biodistribution studies, radiolabeled RRL peptide probe accumulated in the tumor to a level of approximately 2.52 and 0.65% injected dose per gram of tissue at 6 and 24 h after administration. The data for the ¹³¹I-labeled control peptide were 0.73 and 0.06% ID/g at 6 and 24 h after administration. The ratios of radioactivity in tumors to radioactivity in blood at 1, 6, and 24 h after injection were about 0.32, 1.12, 1.30 for RRL peptide and 0.30, 0.37, 0.22 for control peptide. The ratios of radioactivity in tumors to radioactivity in muscle at 1, 6, 24 h after injection were about 1.40, 3.94, 9.08 for RRL peptide and 1.98, 2.89, 1.78 for control peptide. At 24 h after administration, the SPECT imaging obtained clearly showed a contrasting tumor on the right armpit of mice with high concentrations of radioactivity, and the surrounding background was very low.

The results suggest that radioiodination of RRL peptide is feasible and that the labeled compound is stable in human blood serum. The ¹³¹I-labeled RRL peptide shows high tumor uptake and good tumor-to-organ ratios that allow noninvasive visualization of tumors. The ¹³¹I-labeled compound is valuable to detect tumors as molecular probe.