Abstract

Objective To incorporate 131I i nto the fifth generation polyamidoamine(PAMAM(G5.0)) with the targeting peptide Ser-Arg-Glu-Ser-Pro-His-Pro(SRESPHP)(SR for short) and observe the in vitro properties for the targeting probe of medullary carcinoma cells (MTCs). Methods PAMAM (G5.0)-SR and PAMAM(G5.0) were radiolabeled with 131I by chloramine T. Labeling yield and stability were determined by thin layer chromatography. Lipid-water partition coefficients were also evaluated. The targeting of the two types of 131I-radiotracers(131I-PAMAM(G5.0)-SR and 131I-PAMAM(G5.0)) was determined in a blocking uptake study where TT tumor cells were used. The median lethal dose of the two probes was then calculated. GraphPad Prism 5.01 analysis software was used to conduct a t-test for the data that fit the normal distribution and homogeneity of variance. Results The labeling yields of the two types of 131I radiotracers all exceeded 70%, and the radiochemical purity levels were higher than 90% after purification. The stability of the two probes in the PBS system was satisfactory, and both probes showed excellent water solubility. The results of the blocking uptake study on the TT cells showed that the cell uptake rate decreased significantly (t=7.315, 22.590, 22.570, all P<0.01) after the PAMAM (G5.0)-SR blocked the 131I-PAMAM (G5.0)-SR. This result indicated that 131I-PAMAM (G5.0)-SR achieved excellent targeting and that its median lethal dose was only 513.6 kBq/mL. The cell uptake results showed that the cell uptake rate of 131I-PAMAM (G5.0)-SR with a median lethal dose gradually decreased with time. However, cell uptake rate increased for 48 h before it decreased again. Conclusion 131I-PAMAM (G5.0)-SR can target medullary thyroid carcinoma cells and thus inhibit cell proliferation. Key words: Iodine radioisotopes; Molecular probes; Medullary thyroid carcinoma; Polyami-doamine; Ser-Arg-Glu-Ser-Pro-His-Pro

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