To establish a method for directly labeling antisense oligonucleotide ( ASON ) with iodine and evaluate the stability and biodistribution of labeled ASON

15mer bcl-2 ASON to mRNA was labeled with iodine by Iodogen

purified with Sephadex G-25. Labelling efficiency and purity of labeled ASON were measured

and the stability was evaluated. Biodistribution of labeled ASON was studied in BALB/c nude mice and CNE2 bearing mice. Results showed that 1) The Labelling efficiency was 85% under suitable conditions and radiopurity was 90%

and specific radioactivity was 4.77 × 105Bq/ μ g ( ASON ) . 2) The labeled ASON was stable at room temperature

but disintegrated partly in fresh serum. 3) The radioactivity of labeled ASON decreased fast in most of organs

presenting a two-phase distribution. The uptakes of radioactivity in thyroid gland and gastrointestine were obvious

indicating labeled ASON were not stable. Tumor tissues had little ASON uptake

and immunohistological test confirmed that the expression of bcl-2 in CNE2 was very low. These findings indicated that directly iodine labeling ASON with Iodogen was simple and reliable

and it could provide high labelling efficiency

high specific activity and stable labeled ASON. But stability of labeled ASON was poor in vivo due to disintegration of nucleotidase.