Identification of a novel bisimidazoacridone that inhibits HIV-1 replication by prevention of formation of post-integrative full-length RNA transcripts

Because of the DNA interactive nature of Bisimidazoacridones (BIAs) type compounds, rational drug design efforts were undertaken to develop analogs that might inhibit the nucleic acid-dependent processes of HIV-1 replication. In this report we reveal the discovery of NSC 687025, a BIA-type compound that exerts in vitro antiviral activity in the picomolar to low nM range against various HIV-1 strains, HIV-2 and SIV, and the relative selectivity index was typically greater than 100. NSC 687025 inhibited the in vitro 3'-processing and strand transfer enzymatic activity of purified HIV-1 integrase, but not the in vitro activities of HIV-1 RT, PR, virus binding, or the nucleocapsid protein zinc fingers. However, NSC 687025 did not prevent intracellular integration of proviral DNA into the cellular DNA, as evaluated by a novel nested PCR procedure that discriminates integrated proviral DNA from non-integrated forms. Surprisingly, NSC 687025 inhibited the post-integrative replication of HIV-1 from TNF-alpha stimulated U1 cells in the 1-5 nM range. Western blot analysis of viral protein production revealed a complete blockage of Gag precursors and mature viral proteins. Inspection of the viral RNA transcripts by PCR and Northern blots showed selective depletion of single-spliced (approximately 4.5-5 kb) and unspliced (approximately 9.2 kb) transcripts (approximately 10-fold reduction), while levels of multi-spliced transcripts (approximately 2-3 kb) were unaffected. Thus, we have identified a novel and potent inhibitor of HIV-1 replication, having a post-transcriptional molecular target that is distinct from other classes of antiviral agents.

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