Synthesis and antiviral activity of ethidium-arginine conjugates directed against the TAR RNA of HIV-1.

Abstract

The regulatory protein Tat is essential for viral gene expression and replication of the human immunodeficiency virus type 1 (HIV-1). Tat transactivates the HIV-1 long terminal repeat (LTR) via its binding to the transactivation responsive element (TAR) and increases the viral transcription. Studies have shown that the binding of arginine and arginine derivatives induces a conformational change of the TAR RNA at the Tat-binding site. The unpaired A17 residue delimits a small cavity which constitutes a receptor site for small molecules, especially for ethidium bromide. These binding characteristics have prompted us to design a series of ethidium-arginine conjugates capable of interacting with the TAR RNA. Here we report the synthesis of six ethidium derivatives equipped with arginine side chains. These molecules were biologically evaluated, and two compounds (17 and 20) exhibited in vitro anti-HIV-1 activity at micromolar concentration, without toxicity (up to 100 microM concentration). Melting temperature studies indicated that the most active molecule (20) bound strongly to TAR in vitro. RNase protection experiments agreed with the molecular modeling studies which suggested that the ethidium moiety of 20 was inserted next to the A17 residue while the arginine side chain occupied the pyrimidine bulge.