Nevirapine-resistant human immunodeficiency virus: kinetics of replication and estimated prevalence in untreated patients

The nonnucleoside reverse transcriptase inhibitor nevirapine rapidly selects for mutant human immunodeficiency virus (HIV) in vivo. The most common mutation occurs at amino acid residue 181 in patients receiving monotherapy. After the initiation of nevirapine therapy, plasma and peripheral blood mononuclear cell samples were collected at frequent intervals and assayed for HIV RNA levels and the proportion of virus containing a mutation at residue 181. HIV RNA levels remained stable for the first 24 h after initiation of therapy and rapidly declined between 1 and 7 days. There was a consistent maximum decrease of 2 log10 HIV RNA copies per ml of plasma (range, 1.96 to 2.43) from baseline after 2 weeks in all monotherapy subjects. The estimated median half-life of HIV RNA was 1.11 days (range, 0.63 to 1.61). After 14 days of therapy, HIV RNA levels began to increase and 181 mutant virus was detected. The estimated doubling time of the emerging virus population ranged from 1.80 to 5.73 days. Viral DNA in peripheral blood mononuclear cells turned over from wild type to the mutant with a mutation at residue 181 significantly more slowly than did HIV RNA in plasma. In two subjects, the calculated prevalence of the 181 mutant virus prior to treatment was 7 and 133 per 10,000 copies of plasma HIV RNA.

Prognostic value of plasma human immunodeficiency virus type 1 (HIV-1) RNA levels in patients with advanced HIV-1 disease and with little or no prior zidovudine therapy. AIDS Clinical Trials Group Protocol 116A/116B/117 Team

The association of plasma human immunodeficiency virus type 1 (HIV-1) RNA level at study entry and over time with clinical progression was evaluated in 187 patients from AIDS Clinical Trials Group protocol 116A who had little or no prior zidovudine treatment. Three-fold-higher HIV-1 RNA levels at study entry and 3-fold increases by week 8 were associated with progression (relative hazard [RH], 1.67; 95% confidence limits [CL], 1.20, 2.32; and RH, 1.45; CL, 1.02, 2.05, respectively). Having 3-fold-higher CD4 cell count at entry was independently associated with a 52% reduction in risk for progression (adjusted RH, 0.48; CL, 0.33, 0.70). When stratified by length of prior zidovudine therapy, RNA level was predictive in drug-naive patients (adjusted RH, 1.87; CL, 1.23, 2.85) but not predictive in patients with up to 16 weeks of prior therapy (adjusted RH, 1.11; CL, 0.70, 1.76). Analysis suggests that the acquisition of mutations at HIV-1 reverse transcriptase codons 215 and 74 is associated with subsequent increases in HIV-1 RNA level (relative risk, 7.00; CL, 0.86, 56.90).

Association of plasma human immunodeficiency virus type 1 RNA level with risk of clinical progression in patients with advanced infection. AIDS Clinical Trials Group (ACTG) 116B/117 Study Team. ACTG Virology Committee Resistance and HIV-1 RNA Working Groups

Human immunodeficiency virus (HIV)-1 RNA level in plasma was evaluated as a surrogate marker for disease progression in a clinical trial of advanced HIV-1 infection. Baseline HIV-1 RNA level was an independent predictor of disease progression (relative hazard [RH] for each doubling of HIV-1 RNA level, 1.26; 95% confidence interval [CI], 1.03-1.54; P = .02), after adjusting for the week 4 change in HIV-1 RNA level, baseline CD4 cell count, syncytium-inducing phenotype, clinical status at study entry, and therapy randomization. A 50% reduction in HIV-1 RNA level was associated with a 27% decrease in the adjusted risk of disease progression during the study (RH, 0.73; 95% CI, 0.52-1.02; P = .07). The partial validation of HIV-1 RNA as a predictor for clinical end points has implications for the use of HIV-1 RNA in clinical trials and practice.

New strategies to combat HIV drug resistance

Recent insights into HIV dynamics argue strongly for early intervention with antiretroviral combinations designed to block resistant mutations. By using more potent agents and taking advantage of drug selective pressure to force the emergence of strains with reduced evolutionary fitness, investigators are attempting to bring HIV replication to a halt. And in many cases, they appear to be succeeding.

Antiretroviral therapy for HIV infection in 1996. Recommendations of an international panel. International AIDS Society-USA

OBJECTIVE

To provide clinical recommendations for antiretroviral therapy for human immunodeficiency virus (HIV) disease with currently (mid 1996) available drugs. When to start therapy, what to start with, when to change, and what to change to were addressed.

PARTICIPANTS

A 13-member panel representing international expertise in antiretroviral research and HIV patient care was selected by the international AIDS Society-USA.

EVIDENCE

Available clinical and basic science data, including phase 3 controlled trials, clinical endpoint data, virologic and immunologic endpoint data, interim analyses, studies of HIV pathophysiology, and expert opinions of panel members were considered. Recommendations were limited to drugs available in mid 1996.

PROCESS

For each question posed, 1 or more member(s) reviewed and presented available data. Recommendations were determined by group consensus (January 1996); revisions as warranted by new data were incorporated by group consensus (February-May 1996).

CONCLUSIONS

Recent data on HIV pathogenesis, methods to determine plasma HIV RNA, clinical trial data, and availability of new drugs point to the need for new approaches to treatment. Therapy is recommended based on CD4+ cell count, plasma HIV RNA level, or clinical status. Preferred initial drug regimens include nucleoside combinations; at present protease inhibitors are probably best reserved for patients at higher progression risk. For treatment failure or drug intolerance, subsequent regimen considerations include reasons for changing therapy, available drug options, disease stage, underlying conditions, and concomitant medication(s). Therapy for primary (acute) infection, high-risk exposures to HIV, and maternal-to-fetal transmission are also addressed. Therapeutic approaches need to be updated as new data continue to emerge.

Extensive polymorphisms observed in HIV-1 clade B protease gene using high-density oligonucleotide arrays

Naturally occurring mutations in HIV-1-infected patients have important implications for therapy and the outcome of clinical studies. However, little is known about the prevalence of mutations that confer resistance to HIV-1 protease inhibitors in isolates derived from patients naive for such inhibitors. In the first clinical application of high-density oligonucleotide array sequencing, the sequences of 167 viral isolates from 102 patients have been determined. The DNA sequence of USA HIV-1 clade B proteases was found to be extremely variable and 47.5% of the 99 amino acid positions varied. This level of amino acid diversity is greater than that previously known for all worldwide HIV-1 clades combined (40%). Many of the amino acid changes that are known to contribute to drug resistance occurred as natural polymorphisms in isolates from patients who had never received protease inhibitors.

Producer-cell modification of human immunodeficiency virus type 1: Nef is a virion protein

Type 1 human immunodeficiency viruses encoding mutated nef reading frames are 10- to 30-fold less infectious than are isogenic viruses in which the nef gene is intact. This defect in infectivity causes nef-negative viruses to grow at an attenuated rate in vitro. To investigate the mechanism of Nef-mediated enhancement of viral growth rate and infectivity, a complementation analysis of nef mutant viruses was performed. To provide Nef in trans upon viral infection, a CEM derivative cell line (designated CLN) that expresses Nef under the control of the viral long terminal repeat was constructed. When nef-negative virus was grown in CLN cells, its growth rate was restored to wild-type levels. However, the output of nef-negative virus during the first 72 h after infection of CLN cells was not restored, suggesting that provision of Nef within the newly infected cell does not enhance the productivity of a nef-negative provirus. The genetically nef-negative virions produced by the CLN cells, however, were restored to wild-type levels of infectivity as measured in a syncytium formation assay in which CD4-expressing HeLa cells were targets. These trans-complemented, genetically nef-negative virions yielded wild-type levels of viral output following a single cycle of replication in primary CD4 T cells as well as in parental CEM cells. To define the determinants for producer cell modification of virions by Nef, the role of myristoylation was investigated. Virus that encodes a myristoylation-negative nef was as impaired in infectivity as was virus encoding a deleted nef gene. Because myristoylation is required for both membrane association of Nef and optimal viral infectivity, the possibility that Nef protein is included in the virion was investigated. Wild-type virions were purified by filtration and exclusion chromatography. A Western blot (immunoblot) of the eluate fractions revealed a correlation between peak Nef signal and peak levels of p24 antigen. Although virion-associated Nef was detected in part as the 27-kDa full-length protein, the majority of immunoreactive protein was detected as a 20-kDa isoform. nef-negative virus lacked both 27- and 20-kDa immunoreactive species. Production of wild-type virions in the presence of a specific inhibitor of the human immunodeficiency virus type 1 protease resulted in virions which contained only 27-kDa full-length Nef protein. These data indicate that Nef is a virion protein which is processed by the viral protease into a 20-kDa isoform within the virion particle.

Recombination leads to the rapid emergence of HIV-1 dually resistant mutants under selective drug pressure

The potential contribution of recombination to the development of HIV-1 resistance to multiple drugs was investigated. Two distinct viruses, one highly resistant to a protease inhibitor (SC-52151) and the other highly resistant to zidovudine, were used to coinfect T lymphoblastoid cells in culture. The viral genotypes could be distinguished by four mutations conferring drug resistance to each drug and by other sequence differences specific for each parental virus. Progeny virions recovered from mixed infection were passaged in the presence and absence of both zidovudine and SC-52151. Dually resistant mutants emerged rapidly under selective conditions, and these viruses were genetic recombinants. These results emphasize that genetic recombination could contribute to high-level multiple-drug resistance and that this process must be considered in chemotherapeutic strategies for HIV infection.

Viral dynamics of HIV: implications for drug development and therapeutic strategies

The ability to quantitate human immunodeficiency virus (HIV) in blood and tissues from patients at all stages of disease has provided new insights into the pathogenesis of HIV disease. There is a dynamic equilibrium between HIV production and clearance even during the period of clinical latency, which may permit resistant virus to emerge with the imposition of drug pressure. Disruption of the equilibrium with effective drugs reduces circulating levels of HIV within 1 week, thus allowing the rapid assessment of new candidate drugs. To maximize the magnitude and durability of HIV RNA suppression, therapeutic strategies must be implemented that are effective against high levels of rapidly replicating virus that consist of many genetic variants.

HIV viral load markers in clinical practice

Plasma HIV RNA determinations are an important prognostic marker of disease progression and, when used appropriately, provide a valuable tool for the management of individual patients. But what constitutes appropriate use?

Lipid prodrugs of phosphonoacids: greatly enhanced antiviral activity of 1-O-octadecyl-sn-glycero-3-phosphonoformate in HIV-1, HSV-1 and HCMV-infected cells, in vitro

Phosphonoformate (PFA) effectively inhibits viral polymerases but is relatively ineffective in virus-infected cells in tissue culture. A lipid prodrug of phosphonoformate was synthesized by coupling the phosphonate residue of phosphonoformate to the sn-3 hydroxyl of 1-O-octadecyl-sn-glycerol. This prodrug, 1-O-octadecyl-sn-glycero-3-phosphonoformate (ODG-PFA), was 93-fold more active than phosphonoformate in cells infected with the AD169 strain of cytomegalovirus (CMV), and 111-147-fold more active in cells infected with three human clinical isolates of CMV. The compound was also 44-fold more active in human immunodeficiency virus-1 (HIV-1) infected cells and 43-fold more active in cells infected with herpes simplex virus (HSV). Studies of the mechanisms of increased antiviral activity indicate that 1-O-octadecyl-sn-glycero-3-[14C]phosphonoformate is taken up more extensively than the free drug by the host MRC-5 human lung fibroblasts. Intracellular enzymes convert 1-O-octadecyl-sn-glycero-3-phosphonoformate to phosphonoformate. This conversion does not occur in the tissue culture medium containing fetal bovine serum (FBS) or in MRC-5-conditioned medium. In view of its greatly increased in vitro potency and selectivity, 1-O-octadecyl-sn-glycero-3-phosphonoformate may be useful in treating viral diseases.

The impact of zidovudine compared with didanosine on health status and functioning in persons with advanced HIV infection and a varying duration of prior zidovudine therapy. AIDS Clinical Trials Group 116/117 Study Group

The objective of this study was to compare the effects of zidovudine and didanosine on health-related quality of life in persons with advanced HIV infection and varying duration of prior zidovudine exposure. It was designed as a substudy nested in two similar placebo-controlled active-control-arm randomized trials, using sites of the AIDS Clinical Trials Group participating in the randomized trials of zidovudine versus didanosine (ACTG 116 and 117). The patients comprised 356 participants enrolled in ACTG 116 and 117. All had HIV infection and either a CD4 count of <200 cells/mm3, or a CD4 count of <300 cells/mm3 plus symptoms of HIV disease. Participants were randomized equally within strata defined by duration of prior zidovudine therapy, to receive didanosine sachets at a dose of 500 mg daily (334 mg in subjects weighing <60 kg) or 750 mg daily (500 mg in subjects weighting <60 kg) plus inactive capsules resembling zidovudine, or to receive zidovudine capsules at a dose of 600 mg daily plus inactive sachets resembling didanosine. The main outcome measures were self-reported health-related quality of life, healthcare utilization, disability, work and symptom impact. The results showed no differences in reported symptom impact or healthcare utilization, and most measures of disability were similar. In the group with more than 8 weeks of prior zidovudine therapy, several of the health status scale scores for ongoing participants were significantly better for didanosine recipients, but average differences were small. Use of several different approaches to combining health status and survival showed no differences in the overall quality-time experiences between the treatment groups. Individuals taking zidovudine, low-dose didanosine and high-dose didanosine experienced 33, 34 and 35 weeks, respectively, in at least the typical health state if they had fewer than 8 weeks of previous zidovudine therapy, and had 23, 23 and 26 weeks, respectively, if they had more than 8 weeks previous use of zidovudine. Results did not differ when data were analysed within strata ofpatients who had any versus no prior exposure to zidovudine, or AIDS versus non-AIDS status. In conclusion, functional status and health-related quality of life were substantially similar among persons receiving either zidovudine or didanosine, regardless of the duration of prior zidovudine treatment.

HIV-induced apoptosis requires the CD4 receptor cytoplasmic tail and is accelerated by interaction of CD4 with p56lck

The roles of the CD4 receptor and the src kinase p56lck were examined in the process of HIV-induced apoptosis of CD4+ T lymphocytes. The presence of the CD4 cytoplasmic tail was found to be essential in delivering an apoptotic signal, and interaction of CD4 with p56lck potentiated HIV-induced apoptosis. Apoptosis, but not HIV replication, was abrogated by deleting the NH2-terminal intracytoplasmic tail of CD4, or by mutating the two critical cysteines in this tail that are responsible for CD4-p56lck interaction. Introduction of p56lck in C8166-45 or MT-2 cells, CD4+ T cell lines deficient for this protein, greatly increased HIV-induced apoptosis and syncytium formation. The ability of p56lck to deliver an apoptotic signal did not depend on its kinase function, since a kinase-deficient mutant was as effective as its normal counterpart in inducing apoptosis, suggesting that p56lck may act as an adapter to anchor other proteins to transduce the death signal.

Antiretroviral drug resistance: mechanisms, pathogenesis, clinical significance

The contribution of HIV drug resistance to treatment failure, the relationship of drug resistance to pathogenesis and the impact of resistance in the role of the promising new class of protease inhibitors remain areas of active investigation. A more precise understanding of these aspects of antiretroviral drug resistance will permit the more effective use of available drugs and the design of new drugs and drug regimens.

Kinetic analysis of intravirion reverse transcription in the blood plasma of human immunodeficiency virus type 1-infected individuals: direct assessment of resistance to reverse transcriptase inhibitors in vivo

Intravirion reverse transcripts have been identified in the blood plasma of human immunodeficiency virus type 1 (HIV-1)-infected individuals. In the present studies, the kinetic processes of intravirion HIV-1 reverse transcription, in the blood plasma of HIV-1-infected persons treated with nevirapine, were investigated. Nevirapine is a nonnucleoside inhibitor of reverse transcriptase (RT) which decreases the level of HIV-1 viral particles in the blood plasma of infected individuals. By analyzing HIV-1 virions at different time points prior to and after initiation of nevirapine therapy in vivo, the levels of intravirion reverse transcripts have been demonstrated to be dramatically susceptible to this anti-RT agent, out of proportion to effects on plasma virion load. The intravirion reverse transcripts were also documented to rebound to the pretreatment levels, concomitant with the development of resistant viral mutants. In addition, the infectivity of HIV-1 virions dramatically decreased after nevirapine treatment, further indicating that the effects of this anti-RT agent begin within the cell-free virions. Since the levels of intravirion reverse transcripts were altered according to the susceptibility or resistance of the HIV-1 RT enzyme to this inhibitor, these data demonstrate that the formation of intravirion reverse transcripts is a dynamic process in vivo. Moreover, because the alteration in ratios between intravirion HIV-1 reverse transcripts and viral genomic RNA directly reflects the efficiency of reverse transcription, we propose that the determination of these ratios in the blood plasma of HIV-1-positive patients may be a useful and, most importantly, a direct assay to monitor the efficacy of anti-RT agents in vivo.

A randomized trial of the activity and safety of Ro 24-7429 (Tat antagonist) versus nucleoside for human immunodeficiency virus infection. The AIDS Clinical Trials Group 213 Team

Ro 24-7429, a Tat antagonist, dosed at 75, 150, or 300 mg/day, was compared with nucleoside analogue (zidovudine or didanosine) for 12 weeks in 96 human immunodeficiency virus (HIV)-infected patients to assess safety and activity. The primary adverse effect of Ro 24-7429 was rash, which necessitated treatment discontinuation in 6 of 71 patients. Nucleoside analogue treatment produced an average increase in CD4 cell count of 28 cells/mm3 at week 8 versus a decrease of 27 cells/mm3 in recipients of Ro 24-7429 (P < .001). Serum HIV p24 antigen levels decreased by an average of 111 pg/mL in nucleoside recipients at week 8 compared with an increase of 41 pg/mL in recipients of Ro 24-7429 (P = .007). Nucleoside-treated patients had a mean 0.66 log10 reduction in infectious peripheral blood mononuclear cells, while Ro 24-7429 recipients had a mean 0.02 log10 reduction (P = .02). No dose-response relationships were observed in the Ro 24-7429 groups. In this study, Ro 24-7429 treatment showed no evidence of antiviral activity.

A pilot study to evaluate the development of resistance to nevirapine in asymptomatic human immunodeficiency virus-infected patients with CD4 cell counts of > 500/mm3: AIDS Clinical Trials Group Protocol 208

Treatment of human immunodeficiency virus (HIV) infection with nevirapine in patients with < 400 CD4 cells/mm3 rapidly selects for virus with reduced susceptibility to nevirapine. To test whether resistance would develop less quickly in patients with a lower virus burden, nevirapine was studied in asymptomatic patients with > 500 CD4 cells/mm3. With 400 mg of nevirapine daily, the median reduction in HIV RNA was 0.51 log10 copies/mL, and all isolates recovered by 12 weeks were resistant to nevirapine. As in patients with lower CD4 cell counts, some patients experienced sustained reduction in plasma HIV RNA despite the presence of resistant virus. These results suggest that lower levels of HIV RNA and immunosuppression did not retard the rate of emergence of nevirapine-resistant virus; also, a polymerase chain reaction-based HIV RNA assay is sufficiently sensitive to evaluate the antiviral effect of a drug in patients with > 500 CD4 cells/mm3.

Cytomegalovirus infection induces high levels of cyclins, phosphorylated Rb, and p53, leading to cell cycle arrest

Human cytomegalovirus (HCMV) infection stimulates cellular DNA synthesis and causes chromosomal damage. Because such events likely affect cellular proliferation, we investigated the impact of HCMV infection on key components of the cell cycle. Early after infection, HCMV induced elevated levels of cyclin E, cyclin E-associated kinase activity, and two tumor suppressor proteins, p53 and the retinoblastoma gene product (Rb). The steady-state concentration of Rb continued to rise throughout the infection, with most of the protein remaining in the highly phosphorylated form. At early times, HCMV infection also induced cyclin B accumulation, which was associated with a significant increase in mitosis-promoting factor activity as the infection progresses. In contrast, the levels of cyclin A and cyclin A-associated kinase activity increased only at late times in the infection, and the kinetics were delayed relative to those for cyclins E and B. Analysis of the cellular DNA content in the infected cells by flow cytometry showed a progressive shift of the cells from the G1 to the S and G2/M phases of the cell cycle, leading to an accumulation of aneuploid cells at late times. We propose that these HCMV-mediated perturbations result in cell cycle arrest in G2/M.

Phosphatidyl-2',3'-dideoxy-3'-thiacytidine: synthesis and antiviral activity in hepatitis B-and HIV-1-infected cells

We recently found that phosphatidyl-2',3'-dideoxycytidine (phosphatidyl-ddC) had substantial anti-hepatitis B virus (HBV) activity in vitro compared to 2',3'-dideoxycytidine (ddC) (Hostetler et al. (1994) Antiviral Res. 24, 59-67). Upon administration of liposomal phosphatidyl-ddC to mice, a 40-fold higher drug area under curve was observed in the liver. To evaluate the possibility of using liver-targeted anti-HBV nucleosides to treat woodchuck hepatitis virus, we wanted to find the most potent and selective lipid conjugates. It has been shown that 2',3'-dideoxy-3'-thiacytidine as a racemic mixture of the cis-isomer (cis-(+/-)-BCH-189) has much greater activity against HBV viruses than ddC in vitro. Recently, it was shown that the (-)-beta-L-enantiomer (3TC) is more active and less toxic than the (+)-beta-D-form ((+)-BCH-189). To determine whether phospholipid conjugates of 3TC retain antiviral activity in 2.2.15 cells as demonstrated previously with ddC, we synthesized the 1,2-dipalmitoyl-sn-glycerol-3-phosphate conjugates of (+/-)-BCH-189 and 3TC and assessed their anti-HBV and anti-HIV activities, in vitro. Phosphatidyl-3TC and phosphatidyl-BCH-189 had antiviral activity comparable to the respective free drugs in 2.2.15 cells which chronically produce HBV. In HIV-1-infected human peripheral blood mononuclear cells and HT4-6C cells, phosphatidyl-3TC and phosphatidyl-(+/-)-BCH-189 exhibited significantly lower activity than the corresponding free nucleosides. In view of the documented ability of phosphatidyl-ddC to target drug to the liver, it seems reasonable to expect that phosphatidyl-3TC or phosphatidyl-(+/-)-BCH-189 could be employed to provide greatly enhanced hepatic antiviral activity in HBV infection in vivo.

Clinical significance of drug resistance in human immunodeficiency virus

Antiretroviral drugs exert only limited activity against viruses that replicate persistently to high levels. Thus, drug-resistant viruses readily emerge. It has been difficult to assess the contribution of such drug resistance to the failure of treatment with drugs that have only limited effectiveness in the first place. The emergence of zidovudine-resistant human immunodeficiency virus is predictive of clinical disease progression, although the relationship of this event to treatment failure is particularly complicated. The relationship between drug resistance and the loss of activity of non-nucleoside reverse transcriptase inhibitors and protease inhibitors appears to be more straightforward. The optimal use of antiretroviral drugs and combination regimens requires an appreciation of the impact of drug resistance.