Initial evaluation of Tc-99m-labeled anti-carcinoembryonic antigen single-chain fragment variable for micro-single-photon emission computed tomography imaging in mice with colorectal cancer

Carcinoembryonic antigen (CEA) has emerged as an important molecular target for several neoplastic diseases, including colorectal cancer with CEA over-expression. In this study, we report the production and radiolabeling of a novel anti-CEA single-chain fragment variable (scFv-96NRT, concentration for 50% of maximal effect 46 ng/ml), and evaluation of [Tc-99m]Tc-scFv-96NRT in non-invasive detection of CEA expression. [Tc-99m]Tc-scFv-96NRT was synthesized by one step reduction in labeling yield of >95% with radiochemical purity of >98% and molar activity of 10-11 GBq/mu mol. [Tc-99m]Tc-scFv-96NRT showed high stability in 0.01 M phosphate-buffered saline (PBS) and 5% human serum albumin (HSA). It exhibited elevated uptake in CEA over-expressing cells. Biodistribution studies in BALB/c mice revealed that the probe was cleared from blood rapidly, and the highest retention was observed in the kidneys. The micro-single-photon emission computed tomography (micro-SPECT) imaging of [Tc-99m]Tc-scFv-96NRT showed a specific accumulation pattern, as blocking experiment with excess scFv-96NRT suppressed the tumor uptake. These preliminary results suggest that [Tc-99m]Tc-scFv-96NRT is a potential non-invasive molecular probe for imaging tumors with CEA over-expression.