Noninvasive in vivo imaging to measure the expression of
EpCAM, a
biomarker overexpressed in the majority of
carcinoma tumors and metastatic lesions, is highly desirable for accurate
tumor staging and
therapy evaluation. Here, we report the use of an aptamer radiotracer to enable
tumor-specific
EpCAM-targeting PET imaging.
Oligonucleotide aptamers are small molecular
ligands that specifically bind with high affinity to their target molecules. For specific
tumor imaging, an aptamer radiotracer was formulated by chelating a 64Cu
isotope and
DOTA-PEGylated aptamer sequence to target
EpCAM. In vitro cell uptake assays demonstrated that the aptamer radiotracer specifically bound
EpCAM-expressing
breast cancer cells but did not react with off-target
tumor cells. For in vivo
tumor imaging, aptamer radiotracer was systemically administered into xenograft mice. MicroPET/CT scans revealed that the aptamer radiotracer rapidly highlighted xenograft
tumors derived from MDA-MB-231
breast cancer cells (
EpCAM positive) as early
as 2 h postadministration with a gradually increasing
tumor uptake signal that peaked at 24 h but not in
lymphoma 937
tumors (
EpCAM negative). In contrast, nonspecific background signals in the liver and kidneys were rapidly decreased postadministration. This proof-of-concept study demonstrates the utility of aptamer radiotracers for
tumor-specific PET imaging.