3rd International Workshop on HIV Drug Resistance & Treatment Strategies 23-26 June 1999, San Diego, California, USA

THE NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITOR DAPD IS ACTIVE AGAINST RESISTANT HIV-1 ISOLATES FROM PATIENTS FAILING STANDARD NUCLEOSIDE THERAPY

Antiviral Therapy 1999;4 (Suppl 1):4 (abstract no. 3)

K Borroto-Esoda, J Mewshaw, D Wakefield, B Hooper, J Jeffrey, P Furman and B McCreedy
Triangle Pharmaceuticals, Durham, North Carolina, USA

DAPD, (–)-β-D-2,6-diaminopurine dioxolane, is a nucleoside reverse transcriptase inhibitor (NRTI) with activity against HIV-1 and hepatitis B virus. DAPD is deaminated in vivo by adenosine deaminase to give (–)- β-D-dioxolane guanine (DXG). Biochemical analysis of the 5' triphosphates of DAPD and DXG demonstrated that DXG 5'-triphosphate is a potent inhibitor of the HIV RT with a K_i of 0.019 µM. In contrast, the 5'- triphosphate of DAPD is a weak inhibitor of the HIV RT with a K_i of 250 µM. EC₅₀ values determined for DXG in PBMCs against several wild-type laboratory and clinical isolates of HIV-1 ranged from 30 nM to 290 nM. In vitro selection by passage of HIV-1 in increasing concentrations of DXG resulted in selection of virus with a single L74V mutation that demonstrated a fourfold increase in EC₅₀ for DXG. Selection of a K65R mutant by passage in DXG, eightfold increase in EC₅₀ has also been described. Recombinant viruses and clinical isolates of HIV-1 from patients who have failed NRTI and/or NNRTI combination therapies remain sensitive to DXG. Recombinant viruses with mutations at positions 41L, 67N, 69D, 70R, 184V, 215Y and 219Q, alone or in combination, had wild-type or less than threefold decreased susceptibility to DXG. Recombinant viruses containing SS or SG insertions between codons 68/69 were sensitive to DXG. A virus containing mutations in the RT gene associated with multi-NRTI resistance (S68Q, Q151M, T215Y) remained sensitive to DXG. However, viruses with multiple mutations that included K65R, F116Y and Q151M demonstrated 40-to 54-fold increase in EC₅₀ for DXG. Interestingly, isolates with mutations associated with NNRTI resistance (Y181C, G190A, K103N, V106A, V108I) appear to be hypersensitive to DXG. Recombinant viruses containing multiple NRTI mutations in addition to NNRTI mutations had lower EC₅₀ values for DXG in comparison with wild-type virus. The in vitro data indicate that DAPD may be useful as a part of a combination antiviral therapy for HIV-infected patients who are antiviral therapy-naïve or experienced, including patients infected with drug-resistant strains of HIV.

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