Quantification of the effects on viral DNA synthesis of reverse transcriptase mutations conferring human immunodeficiency virus type 1 resistance to nucleoside analogues

Synergistic reduction of HIV-1 infectivity by 5-azacytidine and inhibitors of ribonucleotide reductase

Although many compounds have been approved for the treatment of human immunodeficiency type-1 (HIV-1) infection, additional anti-HIV-1 drugs (particularly those belonging to new drug classes) are still needed due to issues such as long-term drug-associated toxicities, transmission of drug-resistant variants, and development of multi-class resistance. Lethal mutagenesis represents an antiviral strategy that has not yet been clinically translated for HIV-1 and is based on the use of small molecules to induce excessive levels of deleterious mutations within the viral genome. Here, we show that 5-azacytidine (5-aza-C), a ribonucleoside analog that induces the lethal mutagenesis of HIV-1, and multiple inhibitors of the enzyme ribonucleotide reductase (RNR) interact in a synergistic fashion to more effectively reduce the infectivity of HIV-1. In these drug combinations, RNR inhibitors failed to significantly inhibit the conversion of 5-aza-C to 5-aza-2'-deoxycytidine, suggesting that 5-aza-C acts primarily as a deoxyribonucleoside even in the presence of RNR inhibitors. The mechanism of antiviral synergy was further investigated for the combination of 5-aza-C and one specific RNR inhibitor, resveratrol, as this combination improved the selectivity index of 5-aza-C to the greatest extent. Antiviral synergy was found to be primarily due to the reduced accumulation of reverse transcription products rather than the enhancement of viral mutagenesis. To our knowledge, these observations represent the first demonstration of antiretroviral synergy between a ribonucleoside analog and RNR inhibitors, and encourage the development of additional ribonucleoside analogs and RNR inhibitors with improved antiretroviral activity.

Delaying reverse transcription does not increase sensitivity of HIV-1 to human TRIM5α

Background

Because uncoating of the capsid is linked to reverse transcription, modifications that delay this process lead to the persistence in the cytoplasm of capsids susceptible to recognition by the human restriction factor TRIM5α (hTRIM5α). It is unknown, however, if increasing the time available for capsid-hTRIM5α interactions would actually render viruses more sensitive to hTRIM5α.

Results

Viral sensitivity to hTRIM5α was evaluated by comparing their replication in human U373-X4 cells in which hTRIM5α activity had or had not been inhibited by overexpression of human TRIM5γ. No differences were observed comparing wild-type HIV-1 and variants carrying mutations in reverse transcriptase or the central polypurine tract that delayed the completion of reverse transcription. In addition, the effect of delaying the onset of reverse transcription for several hours by treating target cells with nevirapine was evaluated using viral isolates with different sensitivities to hTRIM5α. Delaying reverse transcription led to a time-dependent loss in viral infectivity that was increased by inhibiting capsid-cyclophilin A interactions, but did not result in increased viral sensitivity to hTRIM5α, regardless of their intrinsic sensitivity to this restriction factor.

Conclusions

Consistent with prior studies, the HIV-1 capsid can be targeted for destruction by hTRIM5α, but different strains display considerable variability in their sensitivity to this restriction factor. Capsids can also be lost more slowly through a TRIM5α-independent process that is accelerated when capsid-cyclophilin A interactions are inhibited, an effect that may reflect changes in the intrinsic stability of the capsid. Blocking the onset or delaying reverse transcription does not, however, increase viral sensitivity to hTRIM5α, indicating that the recognition of the capsids by hTRIM5α is completed rapidly following entry into the cytoplasm, as previously observed for the simian restriction factors TRIM-Cyp and rhesus TRIM5α.

Selection and characterization of Autographa californica multiple nucleopolyhedrovirus DNA polymerase mutations

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) DNA polymerase (DNApol) is essential for viral DNA replication. AcMNPV mutants resistant to aphidicolin, a selective inhibitor of viral DNA replication, and abacavir, an efficacious nucleoside analogue with inhibitory activity against reverse transcriptase, were selected by the serial passage of the parental AcMNPV in the presence of increasing concentrations of aphidicolin or abacavir. These drug-resistant mutants had either a single (C543R) (aphidicolin) or a double (C543R and S611T) (abacavir) point mutation within conserved regions II and III. To confirm the role of these point mutations in AcMNPV DNA polymerase, a dnapol knockout virus was first generated, and several repair viruses were constructed by transposing the dnapol wild-type gene or ones containing a single or double point mutation into the polyhedrin locus of the dnapol knockout bacmid. The single C543R or double C543R/S611T mutation showed increased resistance to both aphidicolin and abacavir and, even in the absence of drug, decreased levels of virus and viral DNA replication compared to the wild-type repair virus. Surprisingly, the dnapol mutant repair viruses led to the generation of occlusion-derived viruses with mostly single and only a few multiple nucleocapsids in the ring zone and within polyhedra. Thus, these point mutations in AcMNPV DNA polymerase increased drug resistance, slightly compromised virus and viral DNA replication, and influenced the viral morphogenesis of occlusion-derived virus.

Treating HIV/AIDS by reducing immune system activation: the paradox of immune deficiency and immune hyperactivation

PURPOSE OF REVIEW

To collect published evidence in support of a novel immune therapeutic approach to reduce the excess of immune activation that ultimately turns into immune deficiency in HIV/AIDS.

RECENT FINDINGS

A large body of evidence has been collected in support of the pathogenetic interpretation that prolonged immune overactivation induced by HIV during the course of chronic infection exhausts the immune system and leads to AIDS. Some groups are exploring the possibility of therapeutic interventions to limit the immune system overload. Cytostatic drugs appear promising candidates to achieve the goal, as they restrain cell proliferation without blocking it. At the same time, they do not affect cellular response to antigenic stimulation, and at appropriate dosages are not immune suppressive.

SUMMARY

Presently available antiretrovirals only partially reduce immune system activation during chronic HIV infection. Further clinical research is warranted to test cytostatic drugs to avert immune overactivation and prevent progression to AIDS.

Long-term follow-up of 11 protease inhibitor (PI)-naïve and PI-treated HIV-infected patients harbouring virus with insertions in the HIV-1 protease gene

OBJECTIVES

Amino acid insertions in the protease gene have been reported rarely, and mainly in patients receiving protease inhibitors (PIs). The aim of the study was to assess the long-term viro-immunological follow-up of HIV-infected patients harbouring virus with protease insertions.

METHODS

Cases of virus exhibiting protease insertions were identified in routine resistance genotyping tests. Therapeutic, immunological and virological data were retrospectively collected.

RESULTS

Eleven patients harbouring virus with a protease gene insertion were detected (prevalence 0.24%), including three PI-naïve patients. The insertions were mainly located between codons 33 and 39 and associated with surrounding mutations (M36I/L and R41K). The three PI-naïve patients were infected with an HIV-1 non-B subtype. Follow-up of these PI-naïve patients showed that the insert-containing virus persisted for several years, was archived in HIV DNA, and displayed a reduced viral replicative capacity with no impact on resistance level. Of the eight PI-experienced patients, 63% were infected with HIV-1 subtype B; one had been antiretroviral-free for 5 years and seven were heavily PI-experienced (median duration of follow-up 24 months; range 10-62 months). The protease insertion was selected under lopinavir in four patients and under darunavir in one, in the context of major PI-resistance mutations, and following long-term exposure to PIs. The insert-containing virus persisted for a median of 32 months (range 12-62 months) and displayed no specific impact on phenotypic resistance level or viral replicative capacity.

CONCLUSION

Our data, obtained during long-term follow-up, show that insertions in the protease gene do not seem to have an impact on resistance level. This finding supports the recommendation of PI-based regimens, although further work is required to confirm it.

HIV-1 integration is inhibited by stimulation of the VPAC2 neuroendocrine receptor

Successful HIV-1 infection requires a number of specific stages leading to integration of the provirus. We previously suggested that members of the VPAC neuroendocrine receptor family may play a role in HIV-1 infection. We now show that stimulation of the VPAC2 receptor with specific agonists provides strong resistance to HIV-1 infection. Daily stimulation of VPAC2, but not VPAC1 or PAC1, resulted in up to 90% inhibition of X4 or R5 productive infections in either cell lines or PBMCs. VPAC2 agonist stimulation had no effect on cell surface co-receptors, the rate of apoptotic cells, or HIV-1 entry or reverse transcription of viral RNA. However, we provide evidence that VPAC2-specific agonists inhibit HIV-1 infection through an inhibitory effect on the ability of the HIV-1 cDNA to integrate into the host DNA. These data reveal that VPAC2 agonists are appropriate candidates for further study as possible treatments aimed at the amelioration of HIV/AIDS.

Long-Term Foscarnet Therapy Remodels Thymidine Analogue Mutations and Alters Resistance to Zidovudine and Lamivudine in HIV-1

Objective

To study the evolution of multi-drug-resistant HIV-1 in treatment-experienced patients receiving foscarnet (PFA) as part of salvage therapy and to investigate the virological consequences of emerging mutations.

Methods

Genotypic and phenotypic resistance tests were performed on plasma viruses from seven patients at baseline and during treatment with PFA. The phenotypic effects of mutations suspected to be associated with PFA resistance were evaluated by site-directed mutagenesis of wild-type or thymidine analogue mutations (TAM)-carrying pNL4–3. Reversion of single mutations was performed in a patient-derived recombinant clone.

Results

Baseline multi-drug-resistant isolates exhibited hypersusceptibility to PFA. In two patients who received >12 months of PFA treatment, a novel mutation pattern including K70G, V75T, K219R and L228R emerged. These viruses had 3–6-fold resistance to PFA, a 2–20-fold decrease in resistance to zidovudine compared to baseline, and 14–39-fold resistance to lamivudine, in the absence of M184V. In wild-type clones mutations K70G and V75T induced moderate PFA resistance. In the case of TAMs, combinations of ≥3 mutations (K70G+K219R+L228R±V75T) induced PFA resistance and decreased zidovudine resistance 3–13-fold. These mutants exhibited high-level lamivudine resistance (>20-fold) without mutation M184V. Reversion of K70G→R and K219R→E in a patient-derived clone confirmed the contribution of individual mutations and the negative association between PFA resistance and zidovudine resistance.

Conclusions

In the context of multiple TAMs, hypersusceptibility to PFA was observed and a novel pattern of resistance, including alternative amino acid substitutions at TAM loci, emerged. This mutational pattern was associated with decreases in zidovudine resistance and surprisingly high-level lamivudine resistance.

Human immunodeficiency virus type 1: resistance to nucleoside analogues and replicative capacity in primary human macrophages

Antiretroviral treatment failure is associated with the emergence of resistant human immunodeficiency virus type 1 (HIV-1) populations which often express altered replicative capacity (RC). The resistance and RC of clinical HIV-1 strains, however, are generally assayed using activated peripheral blood mononuclear cells (PBMC) or tumor cell lines. Because of their high proliferation rate and concurrent high deoxynucleoside triphosphate (dNTP) content, both resistance and RC alterations might be misestimated in these cell systems. We have evaluated the resistance of HIV-1 clones expressing a variety of RT resistance mutations in primary human macrophages using a single cycle system. Our experiments indicate that d4T, ddI, and 3TC are more potent in macrophages than in HeLa-derived P4 tumor cells. Mutant viruses bearing thymidine analogue mutations (TAMs) or the K65R mutation had similar resistance levels in the two cell types. Strikingly, however, the M184V mutant, although fully resistant to 3TC in P4 cells, maintained some susceptibility to 3TC in macrophages from 8 of 11 donors. Using the same system, we found that the impact of resistance mutations on HIV RC was minimal in activated PBMC and in P4 cells. In contrast, mutant viruses exhibited strongly impaired RC relative to the wild type (WT) in macrophages, with the following RC order: WT > two TAMs > four TAMs = M184V > K65R. In undifferentiated monocytes, WT virus replication could be detected in three of six donors, but replication of all mutant viruses remained undetectable. Altogether, our results confirm that nucleoside reverse transcriptase inhibitors (NRTIs) are powerful antiviral agents in differentiated macrophages, reveal that HIV resistance to some NRTIs may be less efficient in these cells, and indicate that resistance-associated loss of RC is more pronounced in macrophages than in high-dNTP content cell systems.

The emergence of HIV transmitted resistance in Botswana: "when will the WHO detection threshold be exceeded?"

Background

The Botswana antiretroviral program began in 2002 and currently treats 42,000 patients, with a goal of treating 85,000 by 2009. The World Health Organization (WHO) has begun to implement a surveillance system for detecting transmitted resistance that exceeds a threshold of 5%. However, the WHO has not determined when this threshold will be reached. Here we model the Botswana government's treatment plan and predict, to 2009, the likely stochastic evolution of transmitted resistance.

Methods

We developed a model of the stochastic evolution of drug-resistant strains and formulated a birth-death Master equation. We analyzed this equation to obtain an analytical solution of the probabilistic evolutionary trajectory for transmitted resistance, and used treatment and demographic data from Botswana. We determined the temporal dynamics of transmitted resistance as a function of: (i) the transmissibility (i.e., fitness) of the drug-resistant strains that may evolve and (ii) the rate of acquired resistance.

Results

Transmitted resistance in Botswana will be unlikely to exceed the WHO's threshold by 2009 even if the rate of acquired resistance is high and the strains that evolve are half as fit as the wild-type strains. However, we also found that transmission of drug-resistant strains in Botswana could increase to ∼15% by 2009 if the drug-resistant strains that evolve are as fit as the wild-type strains.

Conclusions

Transmitted resistance will only be detected by the WHO (by 2009) if the strains that evolve are extremely fit and acquired resistance is high. Initially after a treatment program is begun a threshold lower than 5% should be used; and we advise that predictions should be made before setting a threshold. Our results indicate that it may be several years before the WHO's surveillance system is likely to detect transmitted resistance in other resource-poor countries that have significantly less ambitious treatment programs than Botswana.

Functional central polypurine tract provides downstream protection of the human immunodeficiency virus type 1 genome from editing by APOBEC3G and APOBEC3B

Lentiviruses utilize two polypurine tracts for initiation of plus-strand viral DNA synthesis. We have examined to what extent human immunodeficiency virus type 1 plus-strand initiation at the central polypurine tract (cPPT) could protect the viral genome from DNA editing by APOBEC3G and APOBEC3B. The presence of a functional cPPT, but not of a mutated cPPT, extensively reduced editing by both APOBEC3G and APOBEC3B of sequences downstream, but not upstream, of the cPPT, with significant protection observed as far as 400 bp downstream. Thus, in addition to other potential functions, the cPPT could help protect lentiviruses from editing by cytidine deaminases of the APOBEC family.

Effect of cell cycle arrest on the activity of nucleoside analogues against human immunodeficiency virus type 1

Human immunodeficiency virus (HIV) reverse transcription can be notably affected by cellular activation, differentiation, and division. We hypothesized that changes in the cell cycle could also affect HIV susceptibility to nucleoside analogues, which compete with natural nucleotides for incorporation into viral DNA and inhibit viral replication through premature termination of reverse transcription. Proliferating HeLa-derived indicator cells were arrested in the S/G2 phase with etoposide, a topoisomerase II inhibitor, or in the G1/S phase with aphidicolin, a polymerase alpha inhibitor. Cell cycle arrest by both agents induced a remarkable decrease in HIV susceptibility to zidovudine (AZT). This decrease was seen both with a single-cycle infectivity assay and with a viral DNA quantitation assay, indicating that the effect of cell cycle arrest was exerted at the reverse transcription stage. The increase in the 50% inhibitory concentration (IC50) seen with arrested cells was strongest for AZT (23-fold) and stavudine (21-fold) but more modest for other drugs (lamivudine, 11-fold; dideoxyinosine, 7-fold; and nevirapine, 3-fold). In drug-resistant reverse transcriptase mutants, the increase in AZT IC50 (relative to that in dividing cells) was most prominent with a Q151M mutant and was comparable to the wild type in other drug-resistant mutants. Quantitation of intracellular pools of dTTP and AZT 5'-triphosphate (AZTTP) showed that etoposide treatment induced a significant increase in intracellular dTTP and consequently a decrease in AZTTP/dTTP ratios, suggesting that the decrease in viral susceptibility to AZT was caused by reduced incorporation of the analogue into nascent viral DNA. These results emphasize the importance of cellular proliferation and deoxynucleoside triphosphate metabolism in HIV susceptibility to nucleoside analogues and underscore the need to study the activities of drugs of this class with natural target cells under physiological conditions of activation and proliferation.