17th International HIV Drug Resistance Workshop 10-14 June 2008, Sitges, Spain

NUCLEOSIDE ANALOGUES TARGETED AGAINST NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITOR-RESISTANT HIV-1 REVERSE TRANSCRIPTASE

Antivir Ther. 2008; 13(Suppl. 3):A37 (abstract no. 35)

BC Vu¹, PL Boyer, MA Siddiqui², Z Ambrose³, VE Marquez² and SH Hughes^1
1HIV Drug Resistance Program, NCI-Frederick, Frederick, MD, USA; ²Laboratory for Medicinal Chemistry, NCI-Frederick, Frederick, MD, USA; ³Division of Infectious Diseases, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA

Nucleoside reverse transcriptase inhibitors (NRTIs) are important for the treatment of HIV-1 infections. All of the approved non-NRTIs lack the 3′-OH that is required for extension of viral DNA and act as chain terminators when incorporated by HIV-1 reverse transcriptase (RT). NRTI resistance implies that resistant RTs have an enhanced ability to discriminate between normal dNTPs and the NRTITPs. There are two mechanisms of NRTI resistance. Either the enhanced discrimination takes place at the time the NRTITP is incorporated into DNA (exclusion) or the mutant RT has gained the ability to selectively remove the NRTI after it has been incorporated into DNA (excision). We are trying to develop nucleoside analogues that are effective against the known NRTI-resistant viruses. The excision mechanism used by RT depends on the fact that conventional NRTIs remain at the end of the DNA primer strand. We have been analyzing novel nucleoside analogues that contain a 3′-OH that allows additional normal nucleotides to be incorporated after the analogue has been incorporated, protecting the analogue from excision. We have found that these delayed and kinetic chain terminators are able to inhibit excision-proficient HIV-1 RT mutants in vitro and block the replication of HIV-1-based vectors carrying NRTI-resistant RTs in cultured cells. Recently we have analyzed the efficacy of C4′-methyl-2deoxyadenosine and C4′-ethyl-2-deoxyadenosine as inhibitors of wild-type and NRTI-resistant HIV-1 vectors. Screening of these compounds in cells infected with HIV-1based vectors indicates that the compounds have low cytotoxicity and inhibit replication at sub-micromolar concentrations. Both compounds are effective against most NRTI-resistant mutants, with the exception of the exclusion mutant M184V. Analysis of viral DNA isolated from infected cells by real-time PCR indicates the compounds are targeting early steps in viral DNA synthesis. In vitro studies with purified wild-type RT suggest incorporation of C4′-methyl-2-deoxyadenosine triphosphate is efficiently incorporated into viral DNA, but poorly extended. These C4′-modified nucleoside analogues warrant further studies to assess clinical potential.

2008-06-10
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