The ‘‘Janus face” of the thrombin binding aptamer: Investigating the anticoagulant and antiproliferative properties through straightforward chemical modifications

Background: The thrombin binding aptamer (TBA) is endowed with both anticoagulant and antiproliferative activities. Its chemico-physical and/or biological properties can be tuned by the site-specific replacement of selected residues. Methods: Four oligodeoxynucleotides (ODNs) based on the TBA sequence (50-GGTTGGTGTGGTTGG-30) and containing 20-deoxyuridine (U) or 5-bromo-20-deoxyuridine (B) residues at positions 4 or 13 have been investigated by NMR and CD techniques. Furthermore, their anticoagulant (PT assay) and antiproliferative properties (MTT assay) have been tested and compared with two further ODNs containing 5-hydroxymethyl-20-deoxyuridine (H) residues in the same positions, previously investigated. Results: The CD and NMR data suggest that all the investigated ODNs are able to form G-quadruplexes strictly resembling that of TBA. The introduction of B residues in positions 4 or 13 increases the melting temperature of the modified aptamers by 7 C. The replacement of thymidines with U in the same positions results in an enhanced anticoagulant activity compared to TBA, also at low ODN concentration. Although all ODNs show antiproliferative properties, only TBA derivatives containing H in the positions 4 and 13 lose the anticoagulant activity and remarkably preserve the antiproliferative one. Conclusions: All ODNs have shown antiproliferative activities against two cancer cell lines but only those with U and B are endowed with anticoagulant activities similar or improved compared to TBA. General significance: The appropriate site-specific replacement of the residues in the TT loops of TBA with commercially available thymine analogues is a useful strategy either to improve the anticoagulant activity or to preserve the antiproliferative properties by quenching the anticoagulant ones.