Lamivudine Can Exert a Modest Antiviral Effect against Human Immunodeficiency Virus Type 1 Containing the M184V Mutation

Abstract

The M184V mutation in human immunodeficiency virus (HIV) reverse transcriptase is associated with high-level resistance to both (؊)2,3-dideoxy-3-thiacytidine (3TC) and (؊)2,3-dideoxy-5-fluoro-3-thiacytidine as well as low-level resistance to 2,3-dideoxyinosine, 2,3-dideoxycytidine, and abacavir. This mutation is also associated with diminished HIV replicative fitness as well as several functional changes in enzyme activity, including diminutions in polymerase processivity, pyrophosphorylysis, and nucleotide primer unblocking. Despite the fact that M184V encodes up to 1,000-fold resistance to 3TC, we asked whether this drug might still display some antiviral effect in regard to viruses containing this mutation. Cell-free assays revealed that high concentrations of 3TC triphosphate (i.e., >100 M) could affect chain termination and/or inhibit purified reverse transcriptase containing the M184V substitution. This effect became more pronounced with elongation of reverse transcriptase products. In newly infected cells (i.e., peripheral blood mononuclear cells), we found that the amount of full-length reverse transcriptase product was diminished in the presence of 2 to 10 M 3TC, although no decrease in the first product of the reverse transcriptase reaction, i.e., minus strong-stop DNA, was observed. In the presence of two other HIV inhibitors, e.g., nevirapine and indinavir, 3TC exerted additive effects in tissue culture at concentrations only marginally higher than the 50% inhibitory concentration (IC 50 ). Reverse transcriptases cloned from clinical isolates harboring M184V in the context of multidrug resistance had similar IC 50 values for 3TC triphosphate compared to reverse transcriptase containing only the M184V mutation. These results suggest that viruses containing M184V can retain a higher degree of sensitivity to 3TC than previously assumed.

Human Immunodeficiency Virus Type 1: Resistance to Nucleoside Analogues and Replicative Capacity in Primary Human Macrophages

“…3D and 4). This finding is in line with those of Quan et al in cell-free RT assays and in PBMC (58) and with those of Aquaro et al (5), who found that the emergence of 3TC resistance in culture through acquisition of the M184V mutation is significantly slower and more difficult in MDMs than in other cell types. Although this latter finding could be related to an intrinsic lower rate of viral replication in MDMs, it may pertain to the fact that in these cells the selective advantage conferred by the M184V mutation, even in the presence of 3TC, is smaller than in other cell types.…”

“…For d4T, the mean IC 50 to 0.359 M in MDMs pretreated for 16 h. For 3TC, the mean IC 50 was fivefold lower in MDMs than in P4 cells ( Fig. 2 and Table 1) in accordance with what has been previously described in a study performed in PBMC (58). Taken together, these data illustrate the impact of the cellular context on the antiviral activity of some NRTIs such as d4T, ddI, and 3TC.…”

Clinical Significance of Human Immunodeficiency Virus Type 1 Replication Fitness

“…Early observations of viral load rebound during lamivudine monotherapy and lamivudine-containing regimens demonstrated that plasma HIV-1 RNA concentrations remained lower than pretherapy levels despite the uniform presence of M184V in plasma viruses (132,153). However, other studies have shown that lamivudine does exert some antiretroviral effect on the M184V mutant, suggesting that the incomplete viral rebounds that occur may represent residual antiviral activity rather than selection for a mutant with reduced fitness (139). Studies of selective lamivudine treatment interruptions demonstrate increases in viral load before reversion of the M184V mutant, also supporting the hypothesis that lamivudine retains antiretroviral activity against M184V (28).…”

Phosphorothioate Di- and Trinucleotides as a Novel Class of Anti-Hepatitis B Virus Agents

“…An in vitro antiviral selectivity assay was conducted against human immunodeficiency virus (HIV) as follows (17). Cord blood mononuclear cells were infected with HIV type 1 IIIb (laboratory strain) for 2 h. The free virus was washed off, and the cells were transferred to plates.…”

“…The compounds were added as a solution in water. Following 7 days of incubation in culture, the reverse transcriptase (RT) activity of the supernatant was measured to determine antiviral activity as previously described (17). Selectivity assays against other viruses were performed using standard cytopathic effect assays as previously described (7).…”