| Objective:In patients with breast cancer, proto-oncogene of HER-2overexpression is anindependent predictor of survival. It is associated with poor prognosis, aggressivedisease, resistance to chemotherapy and hormone therapy. It is by far the first targetgene for breast cancer treatment for HER-2targeted diagnosis and targeted therapybecome the hotspot.Compared to the immunohistochemical assay,there are several advantages ofthe receptor imaging which is targeting at HER-2following:1) HER-2expression inthe tumor is heterogeneous, however molecular imaging can overcome the limitationsof immunohistochemistry which is localized only.2) In vivo imaging, it isconveniently observed and followed-up.3) It shows the biologically active expressionof HER-2which can more accurately reflect the real situation,of the body, howeverthe immunohistochemical expression only reveals the immune activity content ofHER-2.The mimetic constrained peptide B2-S22-AFA can specifically bind to thereceptor of the HER-2，blockade of receptor-receptor interaction，resulted in thesuppression growth of in breast cancer cells over expressing HER-2receptor. Thisresearch is designed to get the target peptide—TP1623, after modifying the elevenpeptide named B2-S22-AFA having two disulfide bonds with GAGG-Aba, and toexplore the best labeling condition, physicochemical properties, tracer kinetics anddistribution in animals, imaging results in normal and tumor-burdened animals inorder to pave the way for targeted receptor imaging research.Methods:1. Synthesize TP1623: Using stannous chloride as the reductant, TP1623synthesized by chemosynthesis is labeled with99Tcm. The labeling rate and specificactivity of the labeled mixture are measured by chromatography.2. Identify the physicochemical properties of99Tcm-TP1623: The stability test invitro, seralbumin binding test and oil-water distribution test are used. 3. Biodistribution experiment: Divide28healthy mice randomly into7groupsequally. Then inject labeled solution (100μl,3.7MBq) from the tail vein. Finally,collect samples (blood, heart, lung, liver, kidney, intestine, muscle, bone and brain) tocalculate the Percentage Injected Dose per gram (%ID/g).4. Rabbits imaging research: Fix nine rabbits at supine position respectively.After intravenous injection of labeled peptide (200μl,74MBq), SPECT imaging isapplied to observe the dynamic distribution in main organs of the rabbits. Obtainfollowing images:1frame/s×60s,1frame/min×59min,1frame at different timephases (1.0st,2.0nd,3.5thh)Results:1. Synthesize TP1623: The purity of TP1623is95%. The labeling rate is RCP is>95%. The specific activity is (24.35±0.06) TBq/mmol.2. Identify the physicochemical properties of99Tcm-TP1623: After beingconserved at room temperature for four hours, the radiochemical purity and RCP isstill (95.03±0.97)%. Sephadex G50column chromatography a small proportion ofserum protein binding peak appears (18.5%). The oil-water distribution coefficient is－(2.51±0.15).3. Biodistribution experiment: The biodistribution in normal mice shows that theradioactivity in hearts, livers and blood disappears fast over time. Meanwhile, boththe muscle and bone present low radioactive background, following with the brainbeing the lowest radioactive background.4. Rabbits imaging research: The SPECT images of rabbits show that the bloodradioactivity disappears fast, and most radioactivities are eliminated through kidneys,there is no obvious nuclide accumulation in thyroids or brains.Conclusions:1. TP1623can be labeled easily with a high labeling rate and stability and thereis no need for purification.2. The blood elimination through renal system reaches a fast speed. |
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