Preparation Of ^99mTc Labeled HER2 Affibody And Its Application In Tumor Imaging

OBJECTIVE Firstly we prepare the^99mTc-HER2 aff ibody to image it in laboratory breast cancer animal models. Secondly, we investigate the safety, bio-distribution and radiation dosimetry of ^99mTc-HER2 affibody in healthy volunteers. Finally, we assess the HER2 expression level in breast cancer patients.METHODS ^99mTc were used to label HER2 affibody with sodium glucoheptonate and SnCl2·2H2O. The labeling yield and radiochemical purity of ^99mTc-HER2 affibody were determined by thin layer chromatography. The stability of ^99mTc-HER2 affibody was tested in PBS and serum. The equilibrium disassociation constant （Kd） of ^99mTc-HER2 affibody was measured with MBA-MD-361 breast cancer cells expressing HER2. Nano-SPECT imaging was carried at 1.0 h and 4.5 h after injection of 37MBq of ^99mTc-HER2 affibody through tail vein of four nude mice xenografted with human breast cancer. The ratios of target tumor to nontarget organs （T/N） such as liver, brain, lung, heart, bone and muscle were deduced from Nano SPECT/CT acquired data. Two healthy volunteers underwent whole-body SPECT acquisitions at 1.0 and 4.5hours after intravenous injection of ^99mTc-HER2 affibody of 370±74MBq. Regions of interest （ROIs） were drawn manually over major organs. The ratios of breast to other mainly organs such as liver, brain, lung and heart were deduced from SPECT acquired data. Twenty-eight patients with suspicious breast cancer were enrolled for the study. ROIs were drawn manually over lesions and the normal tissues around. When the ration of lesion to background is three or more the status of HER2 is identified to be positive and if not will be identified negative. The biopsy is used to correct between the radioactivity counts and HER2 expression level.RESULTS After incubating ^99mTc-HER2 affibody with serum at 37℃ for 3h and 6. Oh the labeling yield of 99mc-HER2 affibody was ususlly above 99% yield within 20 minutes. The radiochemical purity of ^99mTc-HER2 affibody reached up to 99%. The Kd of ^99mTc-HER2 affibody was 1.7nM. The uptake of radioactivity in cancer was visualized at 1. Oh and 4.5h after injection of ^99mTc-HER2 affibody in HER2 positive MDA-MB-361 breast cancer.^99mTc-HER2 affibody bound HER2 positive tumor rapidly and cleared out mainly through urinary system after entering into blood. The administration of ^99mTc-HER2 affibody was well tolerated in the healthy volunteers and no adverse effects have been noticed or reported.^99mTc-HER2 affibody showed rapid clearance from the blood circulation and excreted mainly through the hepatic-biliary tract and kidneys-urinary tract. The sensitivity and specific of ^99mTc-HER2 affibody was 76.9%and 57.1%, the accuracy rate was 64.3% compared to biopsy resultsn in 28 breast cancer patients.CONCLUSIONS Our experiments indicate that ^99mTc-HER2 affibody can be made in room temperature with high purity and this new agent can be used to image HER2-positive breast cancer specifically. Besides,^99mTc-HER2 affibody is a SPECT tracer with favorable pharmacokinetics and dosimetry profile. It has potential to evaluate HER2 expression in breast cancer patients and provides imaging guidance for further HER2 targeted therapy of breast cancer.