Abstract: DNA aptamers are small single stranded DNA molecules that possess antibody-like characteristics; they bind with high affinity to specific antigens as a result of their three dimensional structure and chemical properties. Carcinoembryonic antigen (CEA) is expressed on the surface of 95% of adenocarcinomas. Anti-CEA antibodies have been used diagnostically in vitro to monitor possible metastases and clinically for the treatment of tumors in vivo. The aim of this research was to isolate aptamers against CEA for vivo imaging and treatment of cancer cells. Fluorescence polarization assay was used to measure affinity and specificity of the candidate aptamers sequences towards purified CEA and related proteins. The aptamers were labeled with fluorescein at their 5’ end during synthesis. The results read with a Pan Vera Beacon 2000 fluorescence polarization instrument. To detect the binding of our DNA aptamers to CEA on the surface of cells, fluorescence microscopy was used. Our results showed that in the fluorescence polarization assay, the K values of BSA, BGG and IgGs were found to be 100 respectively 1000-fold higher than those obtained d for CEA. The FP experiments revealed two disparate aptamer sequences (primer versus consensus). We showed that these aptamers bind specifically to CEA on the surface of cancerous cell line: MCF7 (human breast adenocarcinoma) by fluorescence microscopy. We also demonstrated that CEA specific DNA aptamer does not bind to the surface of a CEA negative cell line: COLO320DM (human colon adenocarcinoma).

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