4th International Workshop on HIV Drug Resistance & Treatment Strategies Sitges, Spain, 12–16 June 2000

FAVOURABLE ANTIVIRAL RESISTANCE PROPERTIES OF SP1093V, AN INHIBITOR OF THE RIBONUCLEASE H ACTIVITY OF HIV-1 REVERSE TRANSCRIPTASE

Antivir Ther. 2000 Jun 12-16; 5 (Suppl. 3):3 (Abstract 2

MA Parniak, D Arion and N Sluis-Cremer
Lady Davis Institute for Medical Research and McGill University AIDS Center, Montreal, Canada

While numerous inhibitors of the DNA polymerase activity of HIV-1 reverse transcriptase (RT) have been identified, few inhibitors of RT ribonuclease H (RNase H) activity are available. We were the first group to describe a potent inhibitor of HIV-1 RT RNase H, N( 4-t-butylbenzoyl)-2-hydroxy-1-naphthaldehyde hydrazone (BBNH). BBNH also inhibits HIV-1 RT DNA polymerase activity, including that of RT with mutations in the NNRTI binding pocket. BBNH is therefore a multi-target inhibitor of HIV-1 RT. Continued development of BBNH has resulted in SP1093V, a delivery formulation comprising the Fe(III) chelate of BBNH incorporated into a block copolymer. SP1093V has significantly improved aqueous solubility and decreased cytotoxicity compared to BBNH. SP1093V is equally potent against both HIV-1 and HIV-2 replication (EC₅₀≈1 μM). More importantly, SP1093V is fully active against a variety of NRTI and NNRTI-resistant HIV-1 isolates, including viral strains with multiple mutations in the NNRTI binding pocket that are resistant to nevirapine, delavirdine and efavirenz. We postulated that the multi-target inhibitory activity of BBNH [and Fe(III)BBNH] would make resistance to SP1093V difficult to develop. Our preliminary attempts appear to confirm this possibility, since we have been unable to develop virus with significant in vitro resistance to SP1093V, despite numerous passages in the presence of low concentrations of SP1093V. Molecular modelling and biochemical experiments suggest that the binding of BBNH (and Fe(III)BBNH) to the HIV-1 RT RNase H domain involves significant π–π overlap with Y501. We therefore carried out a series of site-specific mutagenesis experiments, substituting Y501 with a variety of other amino acids, in order to determine the significance of this residue in the inhibition of HIV-1 RT RNase H by BBNH. All amino acid substitutions tested, other than Y501F, eliminated the ability of BBNH to inhibit RT RNase H activity. However, these same substitutions also resulted in significant decreases in the RNase H and/or DNA polymerase activity of RT. Our results suggest that the development of HIV-1 resistance to SP1093V may be significantly prolonged compared to that of the current clinically-used therapeutics, since mutation of a residue crucial for BBNH binding to the RNase H domain would likely result in significant attenuation of viral reverse transcription.

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2000-06-12
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