5′-,3′-Inverted Thymidine-modified Antisense Oligodeoxynucleotide Targeting Midkine

Abstract

Oligodeoxynucleotides modified at both 5'- and 3'- ends with inverted thymidine (5'-,3'-inverted T) were introduced as new reagents for antisense strategies. These modifications were performed to make the oli- godeoxynucleotides resistant to nucleases. The effec- tiveness of these oligodeoxynucleotides was evaluated in terms of inhibition of synthesis of midkine (MK), a heparin-binding growth factor, and consequent inhibi- tion of growt of CMT-93 mouse rectal carcinoma cells. 5'-,3'-Inverted T antisense MK suppressed synthesis of MK by CMT-93 cells and their growth in culture. Fur- thermore, 5ⴕ-,3ⴕ-inverted T oligodeoxynucleotides exhib- ited less cytotoxicity and better stability than phospho- rothioate oligodeoxynucleotides. When 5'-,3'-inverted T antisense MK was mixed with atelocollagen, and in- jected into CMT-93 tumors pregrown in nude mice, tu- mor growth was markedly suppressed as compared with tumors injected with sense controls. The suppressive effect of 5ⴕ-,3ⴕ-inverted T antisense MK on tumor growth was stronger than that of phosphorothioate antisense MK. These findings indicated the usefulness of inverted thymidine-modified antisense oligodeoxynucleotides as a new reagent instead of phosphorothioate-modified oligodeoxynucleotides.