Synthesis of (99m)Tc-EC-AMT as an imaging probe for amino acid transporter systems in breast cancer.
OBJECTIVE
This study was to develop a (99m)Tc-labeled alpha-methyl tyrosine (AMT) using L,L-ethylenedicysteine (EC) as a chelator and to evaluate its potential in breast tumor imaging in rodents.


METHODS
EC-AMT was synthesized by reacting EC and 3-bromopropyl AMT (N-BOC, ethyl ester) in ethanol/potassium carbonate solution. EC-AMT was labeled with (99m)Tc in the presence of tin (II) chloride. Rhenium-EC-AMT (Re-EC-AMT) was synthesized as a reference standard for (99m)Tc-EC-AMT. To assess the cellular uptake kinetics of (99m)Tc-EC-AMT, 13 762 rat breast cancer cells were incubated with (99m)Tc-EC-AMT for 0-2 h. To investigate the transport mechanism, the same cell line was used to conduct the competitive inhibition study using L-tyrosine. Tissue distribution of (99m)Tc-EC-AMT was determined in normal rats at 0.5-4 h. Planar imaging of breast tumor-bearing rats was performed at 30 and 90 min. The data were compared with those of (18)F-2-fluoro-2-deoxy-glucose. Blocking uptake study using unlabeled AMT was conducted to investigate the transport mechanism of (99m)Tc-EC-AMT in vivo.


RESULTS
Structures of EC-AMT and Re-EC-AMT were confirmed by nuclear magnetic resonance, high performance liquid chromatography and mass spectra. In-vitro cellular uptake of (99m)Tc-EC-AMT in 13,762 cells was increased as compared with that of (99m)Tc-EC and could be inhibited by L-tyrosine. Biodistribution in normal rats showed high in-vivo stability of (99m)Tc-EC-AMT. Planar scintigraphy at 30 and 90 min showed that (99m)Tc-EC-AMT could clearly visualize tumors. (99m)Tc-EC-AMT uptake could be significantly blocked by unlabeled AMT in vivo.


CONCLUSIONS
The results indicate that (99m)Tc-EC-AMT, a new amino acid transporter-based radiotracer, is suitable for breast tumor imaging.
Kong
Fan-Lin
FL
Department of Experimental Diagnostic Imaging, The University of Texas M.D. Anderson Cancer Center, Holcombe Boulevard, Houston, Texas 77030, USA. fanlin.kong@mdanderson.org
Zhang
YinHan
Y
Ali
Mohammad S
MS
Oh
Chanksok
C
Mendez
Richard
R
Kohanim
Saady
S
Tsao
Ning
N
Chanda
Mithu
M
Huang
Wen-Chien
WC
Yang
David J
DJ
D026905:Amino Acid Transport Systems / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D002614:Chelating Agents / Q000737:chemistry; D003545:Cysteine / Q000031:analogs & derivatives* / Q000737:chemistry; D005260:Female; D057054:Molecular Imaging / Q000379:methods*; D015609:Organotechnetium Compounds / Q000138:chemical synthesis* / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics; D049268:Positron-Emission Tomography; D051381:Rats; D019805:alpha-Methyltyrosine / Q000737:chemistry* / Q000494:pharmacology
D026905:Amino Acid Transport Systems; D002614:Chelating Agents; D015609:Organotechnetium Compounds; C109063:ethylene dicysteine; D019805:alpha-Methyltyrosine; D003545:Cysteine