5‘-Modified G-Quadruplex Forming Oligonucleotides Endowed with Anti-HIV Activity:  Synthesis and Biophysical Properties

Abstract

Oligodeoxyribonucleotides of sequence d(5'TGGGAG3') carrying bulky aromatic groups at the 5' end were found to exhibit potent anti-HIV activity [Hotoda, H., et al. (1998) J. Med. Chem. 41, 3655-3663 and references therein]. Structure-activity relationship investigations indicated that G-quadruplex formation, as well as the presence of large aromatic substituents at the 5'-end, were both essential for their antiviral activity. In this work, we synthesized some representative examples of the anti-HIV active Hotoda's 6-mers and analyzed the resulting G-quadruplexes by CD, DSC, and molecular modeling studies, in comparison with the unmodified oligonucleotide. In the case of the sequence carrying the 3,4-dibenzyloxybenzyl (DBB) group, identified as the best candidate for further drug optimization, we developed an alternative protocol to synthesize the 5'-DBB-thymidine phosphoramidite building block in higher yields. The thermodynamic and kinetic parameters for the association/dissociation processes of the 5'-conjugated quadruplexes, determined with respect to the unmodified one, were discussed in light of the molecular modeling studies. The aromatic groups at the 5' position of d(5'TGGGAG3') dramatically enhance both the equilibrium and the rate of formation of the quadruplex complexes. The overall stability of the investigated quadruplexes was found to correlate with the reported IC50 values, thus furnishing quantitative evidence for the hypothesis that the G-quadruplex structures are the ultimate active species, effectively responsible for the biological activity.

DNA Duplexes with Hydrophobic Modifications Inhibit Fusion between HIV-1 and Cell Membranes

“…Structural-activity relationship analysis showed that the presence of a DNA duplex and hydrophobic groups was crucial for the anti-HIV-1 activity observed, although the locations of the hydrophobic groups in the duplex and the sequence composition seemed not to be critical to the activity of the respective DNA duplexes tested. The modified DNA duplexes showed anti-HIV-1 activity at low M concentrations comparable to those of a previously described G-quadruplex HIV-1 entry inhibitor (17)(18)(19)(20)(21)(22)(23)(24). These duplex inhibitors were found to be interacting with the HIV-1 gp41 NHR deep pocket to prevent 6HB formation between the gp41 NHR and CHR.…”

“…In contrast to Hotoda's quadruplex inhibitors d(TGGGAG) 4 (17)(18)(19)(20)(21)(22)(23)(24), the duplex inhibitors reported in this paper can be extensively modified based on the location of the hydrophobic groups and skeleton length, thereby presenting more opportunities for modification.…”

“…These aptamers fold into defined three-dimensional (3D) structures and interact with HIV-1-associated proteins, such as HIV-1 reverse transcriptases (6,7), RNase H (8), Tat proteins (9), integrase (10)(11)(12)(13), and surface glycoproteins (14,15). A subcategory of aptamers possess an additional intermolecular assembly feature such as the quadruplex d(TGGGAG) 4 described by Hotoda et al, which was assembled by four 6-mer G-rich sequences in parallel with the 5=-end attaching to aromatic substituents of adequate size, such as tert-butyldiphenylsilyl (TBDPS) and 4=4-dimethoxytriphenyl (DMT) (16)(17)(18)(19)(20)(21)(22)(23)(24). These quadruplexes are aptamer-like since they interact with the V3 loop or the CD4 binding site on viral gp120, preventing viral adhesion and fusion with target cells (17,25,26).…”

DNA Triplex-Based Complexes Display Anti-HIV-1-Cell Fusion Activity

“…T1 contained three hydrophobic groups (one TBDPS and two DMTs) at each end of the helix. The IC 50 for T1 was 1.8 -0.7 mM, comparable to the previously reported IC 50 values of duplex and quadruplex inhibitors [3][4][5][6][7][8][9][10][11][12][13][14][15]. T2 had no hydrophobic group modifications and did not show the anti-HIV-1 fusion activity.…”

“…Nearly 20 years ago, researchers discovered a category of DNA G-quadruplexbased inhibitors that display an anti-HIV-1 fusion activity [2]. Among these inhibitors, the most representative structure is Hotoda's sequence, d(TGGGAG), which interacts with the V3 loop or CD4-binding site of viral glycoprotein 120 (gp120) [3][4][5][6][7][8][9][10][11][12][13]. Recently, we designed a novel class of DNA duplex-based HIV-1 fusion inhibitors, which have hydrophobic groups at several selected positions [14,15].…”