Experimental Study On Molecular Targeted Probe⁹⁹Tc^m-DTPA-c（CGRRAGGSC） Of Breast Cancer

Objective:To explore independent synthesis of c(CGRRAGGSC)(referred to as: cyclicpeptide), and preparation of molecular targeted probe99Tcm-DTPA-c(CGRRAGGSC).Further to investigate the specific binding of99Tcm-DTPA-c(CGRRAGGSC) and MDA-MB-231cells of human breast cancer and bio-distribution in tumor-bearing nude mice.Methods:(1) DTPA-c(CGRRAGGSC) was synthesized and its HPLC and MS qualityanalysis report were obtained.99Tcm-DTPA-c(CGRRAGGSC) was prepared and itsradiochemical purity, stability and biocompatibility were detected.(2) The differentexpression of IL-11R in MDA-MB-231cells and normal mammary epithelial (MCF-10A) cells were examined by Western blotting. The specific binding of99Tcm-DTPA-c(CGRRAGGSC)and MDA-MB-231cells were observed by a fluorescencemicroscope.(3) Eighteen tumor-bearing nude mice were randomly divided into6groups(n=3). Biodistribution and SPECT imaging of the tumor-bearing nude mice wereobserved in different times after intravenous injection7.4MBq/0.1ml of the molecularprobe.Results:(1) Synthetic c(CGRRAGGSC) peptide motifs was DTPA-KCGRRAGGSC-NH2, which was formed a pair of two disulfide bonds, molecular weight was1367.47,the purity was96.8%. The instant radiolabeled rate of99Tcm-DTPA-c(CGRRAGGSC)was98.3%, its immediate radiochemical purity was (95.33±0.28)%. After3h,6h and12h placement at room temperature, the radiochemical purity were95.0%,92.7%and90.1%, respectively.It showed that99Tcm-DTPA-c(CGRRAGGSC) had highradiolabeled rate and good stability in vitro.After0,3h,6h and12h mixing with human fresh serum, its radiochemical purity were95.1%，94.6%，91.05%，90.3%,respectively. It showed that the serum biological compatibility and the stability in vitroof99Tcm-DTPA-c(CGRRAGGSC) were good.(2) The expression of IL-11R in MDA-MB-231cells was6.7times as MCF-10A cells.Fluorescent staining confirmed that99Tcm-DTPA-c(CGRRAGGSC)-FITC was located in the cell membrane and cytoplasmof MDA-MB-231. DTPA-c(CGRRAGGSC) had competitive inhibited the combinationof99Tcm-DTPA-c(CGRRAGGSC)-FITC and MDA-MB-231cells. The combinationbetween the molecular probe and the IL-11R of MDA-MB-231cells had possessedsaturability.(3) The radioactive molecular probe was rapidly, continually concentrated inthe tumor tissue in the mice, and peaked4h later (17.63±1.73%ID/g). But the probewas not obviously observed in other vital organs.The difference has statisticalsignificance (P <0.05).99Tcm-DTPA-c(CGRRAGGSC) SPECT imaging showed thatthe probe had continually concentrated in tumor tissues, Except for bladder, notobvious concentrated in other tissues.Conclusion:(1) It is a key step that prepared the fine properties99Tcm-DTPA-c(CGRRAGGSC) by independent synthesis of DTPA-c(CGRRAGGSC) in this research. Ithas laid a good foundation for the next related research to investigate binding of themolecular probe and breast cancer cells in vitro and in vivo.(2) The IL-11R is highlyexpressed in MDA-MB-231cells, and the receptor protein are located in the cellmembrane and cytoplasm, The binding of99Tcm-DTPA-c(CGRRAGGSC) and IL-11R arespecific and saturable.(3)99Tcm-DTPA-c(CGRRAGGSC) combines with MDA-MB-231cells in vitro and in vivo specifically, It has potential of specific diagnosis breast cancer,and it provides scientific basis for specific imaging and targeted therapy in tumors whichare highly expressed IL-11R.