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It has been shown in previous reports that a guanine-rich phosphodiester oligonucleotide bearing a dimethoxytrityl (DmTr) residue on its 5'-terminal. DmTr-TGGGAGGTGGGTCTG (SA-1042), is an inhibitor of HIV-1 infection in vitro. SA-1042 interfered with the attachment of gp120 to the CD4 receptor and the subsequent entry stage of viral infection. We investigated the structure-activity relationship of the DmTr-conjugated oligomer by using 15-mer oligonucleotides with various nucleotide sequences. Results show that location of guanine nucleosides at the 5'-terminal and modification of the 5'-terminal with DmTr are essential for anti-HIV-1 activity. First, substitution of the guanine nucleoside close to the 5'-terminal of SA-1042 with another nucleotide prevented antiviral activity. Second, the existence of at least three consecutive guanine nucleosides adjacent to the 5'-terminal was required for the activity. Finally, modification of the 5'-terminal was essential for the activity. Based on these findings, the hexanucleotide, DmTr-TGGGAG, was identified as a potent inhibitor of HIV-1 infection. The hexamer was found to be capable of inhibiting the binding of gp120 to its receptor CD4 molecule, and it was also capable of inhibiting accessibility of anti-V3 monoclonal antibody to its ligand V3 peptide.

Oligodeoxyribonucleotides (ODN) linked at their 5'-end with dimethoxytrityl (DmTr) residue were examined for antiviral activities against human immunodeficiency virus type 1 (HIV-1). We found that guanine-rich oligonucleotides exhibit anti-HIV activity upon 5'-end modification with DmTr. One oligonucleotide, DmTr-TGGGAGGTGGGTCTG (SA-1042), showed potent anti-HIV activity in vitro. A greater than 95% reduction of infectivity was observed if the cells were treated with 10 micrograms/ml of SA-1042 at the time of viral infection, PCR analysis confirmed that there was a significant reduction of provirus in the cells exposed to virus in the presence of SA-1042. By contrast, no inhibition was observed if the cells were treated with the oligomer 1 h after virus adsorption. SA-1042 prevented syncytium formation between chronically infected cells and CD4 positive uninfected cells. Furthermore, the oligomer interfered the interaction of purified gp120 to the CD4 receptor. By contrast, SA-1042 had no inhibitory effect on chronically HIV-infected cells. These results strongly suggest that the DMTr-ODNs with appropriate base sequences antagonize HIV-1 infection during the stage of virus-cell interaction.

Previous studies have shown that a guanine-rich oligonucleotide SA-1042, DmTr-TGGGAGGTGGGTCTG, neutralizes HIV-1 infectivity, blocks syncytium formation and inhibits the binding of recombinant gp120 to immobilized soluble CD4 in vitro (Furukawa et al., 1994). We have now investigated the precise mode of action of SA-1042. We show here that SA-1042 specifically antagonizes the binding of anti-V3 loop antibodies or anti-CD4 binding-site antibodies to recombinant gp120, and also blocks the binding of an anti-V3 loop antibody to the V3 peptide (gp120IIIB: aa302-324). In contrast, SA-1042 does not inhibit gp120 binding of monoclonal antibodies directed to other regions of gp120, such as the conserved N-terminal regions (gp120IIIB: aa35-108 or gp120IIIB: aa72-130) or the C-terminal region (gp120IIIB: aa481-496). Furthermore, SA-1042 does not interfere with the binding of monoclonal antibodies directed to other molecules, gp41, CD4, CD11a, CD18, CD26, CD44 or CD54. These data suggest that SA-1042 exerts its antiviral effects by targeting the V3 loop as well as the CD4 binding site on gp120.