STUDY OF BINDING ABILITY OF PHOSPHOROTHIOATE OLIGONUCLEOTIDES WITH PROTEIN

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We've recognized that phosphorothioate oligonucleotides (S-ODN) showed potent anti-herpetic activities when target site was limited near the splicing site. It was implied that S-ODN interfered the conservative structure which could be essential for the splicing, thus showed potent anti-herpetic activities. This was one explanation why S-ODN targeted splicing site showed potent anti-herpetic activities. However, it has been reported that G rich sequences reveal sequence non-specific biological activities. S-ODN may reveal another mechanism which might be based on strong protein binding activities. S-ODN strongly bound to serum protein at the ratio of 86.6%, while 21.6% for phosphodiester oligonucleotides (D-ODN). Binding activities which directly bound to the virus was more than 50% for S-ODN, on the other hand it was less than 5% for D-ODN.Thirteen mer S-ODN showed inhibitory effect on virus entry into the cell at the early stage of infection, while D-ODN did not. CD spectrum of S-ODN implied G-quartet structure, however, the relation between biological activities and higher dimension structure could not be clear.Moreover, we tried to enhance the anti-herpetic activities of S-ODN by using cationic liposomes. Cationic liposomes is useful tool to enhance the anti-herpetic activities of D-ODN, while it was not the case for SOD.One of the reason might be strong protein binding activities of S-ODN.From this study, the caution is proposed when S-ODN containing G-rich sequences might involve another mechanism other than antisense manner. We should carefully select the drug delivery system to enhance the biological activities of S-ODN.