Imaging Study With^99mTc-Polypeptide Derived From The N-terminus Of Viral Macrophage Inflammatory Protein â…¡ In Murine Breast Cancer

Objective: To study the applied value of^99mTc–CXCR4inhibitor Derived from viralmacrophage inflammatory proteinⅡ（NT21MP） as SPECT Imaging Agent in breastcancer; To explore the method of direct radiolabeling of NT21MP by^99mTc withrelatively high radiochemical purity and stability and screen the best labeling conditions;To establish a simple and reliable method of preparation of^99mTc-NT21MP;Establishing the animal model of breast cancer and discussing the feasibility of thebreast cancer scan with^99mTc-NT21MP by SPECT; To provide theoretical andexperimental basis for early diagnosis with^99mTc-NT21MP in breast cancer.Method:①Detecting the expression of CXCR4and the combination of NT21MP andCXCR4in4T-1cell by immunofluorescence staining;②NT21MP was directlyradiolabeled using prethinning method. the rate of labeled product and theradiochemical purity of labeled were measured by the paper chromatography andoptimal condition was selected. The radiochemical purity was measured in saline orhuman serum at room temperature and different time and its stability was observed invitro and vivo;③The receptor binding assay with NT21MP to CXCR4receptors andthe receptor bingding activity were used by saturation and inhibition experiments;④The model of breast cancer in mice was produced by subcutaneously4T-1breastcancer cell and experiment is divided into three groups with blank control group, salinegroup and NT21MP group.3.7MBq （0.1ml）^99mTc–NT21MP was intravenouslyinjected to each mouse after three weeks when there is a obvious tumor in localinjection site. The dynamic distribution was observed by the scintigraphy with SPECTand T/NT values were calculated by ROI analysis;⑤The expression of CXCR4in tumor tissue was detected by immunohistochemistry method;⑥The size of tumor inmurine was detected by weight.Result: The three breast cancer4T-1cell lines were stained positive for CXCR4;NT21MP was comblined with CXCR4receptor in the cell membrane withoutpenetrating agent and in cell nucleus and cytoplasm with penetrating agent;^99mTc-NT21MP mark was the highest with2μg peptide,25μg SnCl2and incubation for15min under100℃and free^99mTc was zero, marking the reaction gel content of lessthan5%and the radiochemical purity up to96%;^99mTc-NT21MP remained stable inplasma within2h under37℃and^99mTc-NT21MP mark was over85%. But the markdropped faster after2h; Great product receptor marker analysis showed that:^99mTc-NT21MP with saturable receptor binding characteristics and inhibition and highaffinity which RT=23.2174pmol, KD=0.4348nmol; The imaging by SPECT showed^99mTc-NT21MP could directly target the tumor’s tissue after injection and T/NT was upto4.65after2h in the saline group, howerve T/NT was1.38in the NT21MP group;The expression of CXCR4was lowed in NT21MP group than in salin group and thegrowth of tumor was inhibited.Conclude:^99mTc-NT21MP preparation is simple, rapid and has good radiochemicalpurity which can high affinity binding to CXCR4positive breast cancer cells;^99mTc-NT21MP in imaging by SPECT has high T/NT quality and has the character ofspecific binding and targeting to CXCR4receptor which indicate^99mTc-NT21MP is aideal CXCR4receptor imaging agent in CXCR4-positive tumor. Our research providestheoretical and experimental basis for receptor diagnosis in breast cancer.