Novel Amino Acid Transporter-Targeted Radiotracers For Breast Cancer Imaging

Author

FanLin Kong, The University of Texas Graduate School of Biomedical Sciences at HoustonFollow

Date of Graduation

12-2011

Document Type

Dissertation (PhD)

Program Affiliation

Biomedical Sciences

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

David J Yang, Ph.D.

Committee Member

Wei Hu, M.D., Ph.D.

Committee Member

Euishin Edmund Kim, M.D.

Committee Member

Osama R Mawlawi, Ph.D.

Committee Member

Firas Mourtada, M.S.E., Ph.D., DABR

Abstract

Breast cancer is the most common malignancy among women in the world. Its 5-year survival rate ranges from 23.4% in patients with stage IV to 98% in stage I disease, highlighting the importance of early detection and diagnosis. ¹⁸F-2-Fluoro-2-deoxy-glucose (¹⁸F-FDG), using positron emission tomography (PET), is the most common functional imaging tool for breast cancer diagnosis currently. Unfortunately, ¹⁸F-FDG-PET has several limitations such as poorly differentiating tumor tissues from inflammatory and normal brain tissues. Therefore, ¹⁸F-labeled amino acid-based radiotracers have been reported as an alternative, which is based on the fact that tumor cells uptake and consume more amino acids to sustain their uncontrolled growth. Among those radiotracers, ¹⁸F-labeled tyrosine and its derivatives have shown high tumor uptake and great ability to differentiate tumor tissue from inflammatory sites in brain tumors and squamous cell carcinoma. They enter the tumor cells via L-type amino acid transporters (LAT), which were reported to be highly expressed in many cancer cell lines and correlate positively with tumor growth. Nevertheless, the low radiosynthesis yield and demand of an on-site cyclotron limit the use of ¹⁸F-labeled tyrosine analogues.

In this study, four Technetium-99m (^99mTc) labeled tyrosine/ AMT (α-methyl tyrosine)-based radiotracers were successfully synthesized and evaluated for their potentials in breast cancer imaging. In order to radiolabel tyrosine and AMT, the chelators N,N’-ethylene-di-L-cysteine (EC) and 1,4,8,11-tetra-azacyclotetradecane (N4 cyclam) were selected to coordinate ^99mTc. These chelators have been reported to provide stable chelation ability with ^99mTc. By using the chelator technology, the same target ligand could be labeled with different radioisotopes for various imaging modalities for tumor diagnosis, or for internal radionuclide therapy in future.

Based on the in vitro and in vivo evaluation using the rat mammary tumor models, ^99mTc-EC-AMT is considered as the most suitable radiotracer for breast cancer imaging overall, however, ^99mTc-EC-Tyrosine will be more preferred for differential diagnosis of tumor from inflammation.

Keywords

breast cancer imaging, amino acid transporter, radiotracer