Abstract
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Objectives 99mTc-EC-tyrosine has been developed as an amino acid-based radiotracer for breast cancer imaging. The aim of this study was to investigate its potential in assessing tumor response to anti-cancer drug melphalan.
Methods The breast tumor-bearing rats (n=9) were equally divided into three groups and treated with melphalan at day 0: high dose group (40mg/kg), low dose group (20mg/kg), and untreated control group. Planar scintigraphic imaging studies of 99mTc-EC-tyrosine in all rats were performed at day 0 and day 3 after treatment, and tumor-to-muscle ratios (T/Ms) were calculated. In addition, the tumor size of each rat was measured by calliper. The standard H&E staining and immunohistochemical analysis (IHC) were conducted to determine the expression of amino acid transporter LAT1, cellular proliferation marker Ki-67, vascular marker CD34, and hypoxia marker HIF1-α.
Results Tumor volume decreased in a dose-dependent manner upon melphalan treatment. Significant reduction of 99mTc-EC-tyrosine T/Ms was observed after melphalan treatment at both low and high dose groups. H&E staining and IHC data indicate that about 70% of the tumor cells in the melphalan-treated groups underwent apoptosis, and the changes in 99mTc-EC-tyrsoine T/Ms reflects the decreased percentage of viable cells in treated tumors.
Conclusions Our findings collectively suggest that 99mTc-EC-tyrosine has great potential in evaluating the tumor response to melphalan in breast tumor-bearing rats