Since the introduction of HAART there has been a substantial decline in morbidity and mortality in HIV-infected individuals. Unfortunately, due to the emergence of drug-resistant viruses in the HAART-treated population and the escalating transmission of these viruses to newly infected subjects, there is a need for further improvements to therapy [1–4]. Factors that influence the lack of success of current HAART strategies include incomplete adherence to some or all antiretroviral drugs in a regimen and the toxicities associated with these drugs. There is clearly a need for therapies that are well tolerated and convenient, factors that are critical for complete adherence and viral suppression, and in limiting the development of viral resistance .
During the last 4 years non-nucleoside reverse transcriptase inhibitors (NNRTI) have become important components of HAART due to their high potency and different toxicity profiles compared with protease inhibitors (PI) [3–5]. However, the use of current NNRTI has been hindered by the rapid emergence of viral strains which are resistant to all NNRTI as a class . Given the relatively small number of approved NNRTI and their advantageous clinical benefits, novel NNRTI with improved binding to HIV-1 reverse transcriptase (RT) and higher thresholds against cross-resistance are urgently required .
TMC278 is a diarylpyrimidine compound, developed by Tibotec, which has a higher genetic barrier to the development of resistance compared with all currently approved NNRTI. It is active against wild-type viruses and retains activity against NNRTI-resistant HIV-1 strains in vitro [6,7]. A possible explanation for this is the internal conformational flexibility of TMC278, and plasticity of the interaction between TMC278 and the highly flexible NNRTI-binding site of HIV-1 RT which allows the compound to bind in different modes and adjust in case of RT mutations [7,8]. TMC278 has a 50% effective concentration (EC50) against wild-type HIV-1 of 0.5 nM and has shown in vitro little or no loss of activity against a number of single NNRTI mutations including L100I, K103N, Y181C and Y188L . Moreover, TMC278 retains activity against the K103N+Y181C and the L100I+K103N double mutants which are completely resistant to other currently licensed NNRTI . Activity against K103N and Y181C mutants is particularly welcome as these are becoming more common in clinical practice .
TMC278 is being evaluated as a once-daily oral NNRTI for use in HIV-infected individuals including those infected with NNRTI-resistant viruses . The objective of the study (TMC278-C201) was to evaluate the short-term (7 day) antiviral effect, pharmacokinetics, safety and tolerability of once-daily treatment (q.d.) of 25, 50, 100 or 150 mg of TMC278 monotherapy compared with placebo in treatment-naive HIV-1-infected individuals. The genotypic and phenotypic patterns of the viruses were also assessed before and after the study.
Eligible patients were antiretroviral-naive, HIV-1-infected men of at least 18 years of age who had a plasma HIV-1 RNA viral load above 5000 copies/ml and a CD4 T-lymphocyte cell count between 75 and 500 cells/μl. To be eligible, subjects had to agree not to start antiretroviral therapy before the baseline visit and also agreed to start a standard HAART regimen on day 8 of the study. Exclusion criteria included: the use of concomitant medication containing any approved or investigational antiretroviral agent; a history of or currently active alcohol or drug abuse which, in the opinion of the investigator, would have compromised compliance; a life expectancy of < 6 months; acute HIV-1 infection, pre-existing antiretroviral drug resistance based on genotype; current active AIDS-defining illness (category C according to Centers of Disease Control and Prevention definition); any active clinically relevant disease (e.g., tuberculosis, or cardiac dysfunction); renal impairment; and coinfection with hepatitis A, B or C. The study was carried out in nine centres in the UK, Germany and Russia. The protocol was approved by local independent ethics committees and all subjects provided written informed consent before enrolling in the study, in line with the principles of the Declaration of Helsinki and principles of Good Clinical Practice.
The TMC278-C201 study was a phase IIa, randomized, double-blind, placebo-controlled, multiple-dose-escalating trial to compare the antiviral effect, tolerability and safety of a 7-day treatment with one of four doses of TMC278 given as monotherapy. Eligible subjects were randomised in a 3: 1 ratio to receive one of four doses (25, 50, 100 or 150 mg q.d.) of TMC278 or placebo (nine subjects receiving drug and three subjects receiving placebo per dose of TMC278) as an oral solution in polyethylene glycol (PEG)-400. The safety of each dose of TMC278 was assessed by a review panel at Tibotec before any subjects started treatment at the higher dose level. At the end of the 7-day treatment period patients were offered a standard antiretroviral combination regimen with approved agents, but without TMC278 according to local practice.
The primary endpoint of the study was change in log10 copies/ml viral load from baseline to day 8. Secondary endpoints included TMC278 pharmacokinetics, changes in CD4 and CD8 T-lymphocyte cell counts and percentages, evolution of genotypic and phenotypic patterns, and tolerability and safety. Special attention was paid to common adverse events observed in treatment with NNRTI including rashes, hepatitis, central nervous system and psychiatric abnormalities.
All clinical laboratory tests were performed by the central laboratory, Labcorp (Mechelen, Belgium). Plasma HIV-1 RNA viral load measurements were assessed at baseline, daily to day 8 and at the week 1 and week 4 follow-up visits, using the ultra sensitive Roche Amplicor HIV-1 Monitor™ test (version 1.5; Roche Diagnostics, Vilvoorde, Belgium). Samples with a value higher than the upper limit of detection of the ultra sensitive assay (> 75 000 copies/ml) were reassessed by the standard Roche Amplicor HIV-1 Monitor™ test (version 1.5). Phenotypic and genotypic resistance testing were performed at screening, on days 1 and 8 (or early withdrawal) and at the 4-week follow-up visit by Virco BVBA, Mechelen, Belgium, using the Antivirogram® and Virtual phenotype™, respectively. Resistance mutations were defined according to the International AIDS Society (IAS-USA) list of mutations .
Samples for pharmacokinetic analysis were collected just prior to drug intake and then hourly until 12 h post-dose, and at 16 and 24 h post-dose on day 1 and day 7. Further samples were collected on days 2 to 6, day 8 and at the 1-week follow-up visit. Plasma concentrations of TMC278 were determined using liquid chromatography/mass spectrometry.
Pharmacokinetic analysis was carried out using WinNonlin Professional™ version 3.3 (Pharsight Corporation, Mountain View, California, USA) and/or Microsoft Excel version 2000 (Microsoft Ltd, Redmond, Washington, USA). TMC278 plasma concentration–time data was evaluated using a non-compartmental analysis model. Steady state conditions were verified at the end of the dosing period by graphical comparison of plasma concentrations.
Data analysis and statistics
The primary population for efficacy and safety analysis was the intent-to-treat group which was defined as those subjects who received at least one dose of trial medication. All statistical tests were interpreted at the 5% significance level (two tailed). As this was an exploratory trial, there were no adjustments for multiple comparisons. Overall comparison by treatment groups of the change in log10 plasma viral load from baseline was analysed using the Kruskal–Wallis test. Pairwise comparisons were done with the Wilcoxon rank sum test.
HIV-1 RNA decay rate and change in plasma viral load from baseline during the treatment period were measured by a mixed effect model. The number and percentages of subjects with at least a 0.5, 1.0 and 2.0 log10 decrease in plasma viral load from baseline, and the number and percentage of subjects with plasma viral load below 50 copies/ml and below 400 copies/ml were compared between the groups, using Fisher's exact test. Any value below the assay detection limit (< 50 copies/ml) was assigned a value of 49 copies/ml for the purpose of analysis. An ANCOVA model was used to analyse viral nadir in the treatment groups with baseline plasma HIV-1 RNA viral load as a covariate. Changes from baseline CD4 and CD8 T-lymphocyte cell count and percentages were compared by the Kruskal–Wallis and Wilcoxon rank sum test.
The type and incidence of all adverse events were tabulated for all the groups over the entire trial period. Toxicity grades in the laboratory tests were computed according to the enhanced AIDS Clinical Trials Group severity grading list, the World Health Organization grading list or the Common Toxicity Criteria list.
Forty-seven subjects were included in the study. Nine subjects were randomized into each of the four dose levels of TMC278 and 11 subjects were randomized to receive placebo. All subjects completed a 7-day treatment period; one subject in the 25 mg TMC278 group was lost to follow-up (he did not attend his second follow-up visit at week 4). There were no relevant differences between the randomization groups with respect to any demographic or disease characteristics (Table 1). The median duration of HIV infection for the 47 subjects at screening was 1.65 years (range 0.4–18.8 years). Thirty-two of the 47 study subjects had clade B virus, but clades A, AE, AG, BF and F were also represented. IAS–USA resistance-associated mutations in RT were detected in 6/47 (12.8%) subjects (one from the 50, 100 and 150 mg TMC278 groups, respectively, and three from the placebo group) but no NNRTI resistance-associated mutations were detected at baseline. Overall, at baseline 46 subjects (97.9%) did not have phenotypic-resistant virus to any of the currently approved NNRTI. One subject in the placebo group had virus with phenotypic resistance to delavirdine, with a fold-change of 10.1 just above the biological cut-off of 10. This subject also had fold-change values of 2.7, 2.6 and 1.5 for nevirapine, efavirenz and TMC278, respectively (biological cut-offs for nevirapine and efavirenz are 8.0 and 6.0, respectively). Three more subjects had virus resistant to one or two antiretroviral drugs; one other subject in the placebo group had a fold-change value of 4.2 for atazanavir (cut-off 2.4). One subject in the 100 mg TMC278 group had fold-changes of 5.2 and 6.1 for the PI atazanavir and ritonavir, respectively (biological cut-offs 2.4 and 3.5, respectively). A further subject in the 150 mg TMC278 group had a fold-change of 4.3 for stavudine (biological cut-off 3.0).
The change in HIV-1 viral load from baseline to day 8 was significantly greater with all TMC278 doses than with placebo (P < 0.01 Wilcoxon rank sum test for pair-wise comparison; Table 2). There was no apparent dose relationship in antiviral activity and the median log10 viral load reduction on day 8 for the combined TMC278 groups was −1.199 compared with +0.002 in the placebo group. The viral load nadir was significant for all TMC278 treatment groups compared with placebo (P = 0.004 Fisher's exact test) but was not significant between treatment groups. The viral load decay rate was between −0.16 and −0.19 log10 copies/ml/day for the TMC278 treatment groups. A significantly greater proportion of subjects in the TMC278 treatment groups (25/36, 78%) obtained a viral load decrease of > 1.0 log10 compared with the placebo group (0/11; P < 0.01). Four out of thirty-six (12.1%) subjects in the TMC278 groups reached a viral load of < 400 copies/ml on day 8 compared with no subjects in the placebo group. No subject reached a viral load of < 50 copies/ml at any time point in the trial. No viral load rebounds were observed during the treatment period.
No changes in viral genotype or phenotype of the treated subjects were identified during the period of treatment with TMC278 in any of the four treatment groups.
The changes in the CD4 and CD8 lymphocyte cell count were highly variable. None of the median changes and between-group differences observed in this short-term study were considered clinically relevant.
The mean plasma concentration–time curves of TMC278 for day 1 and day 7 are shown in Fig. 1 and pharmacokinetic results for TMC278 on day 1 through to day 14 are shown in Table 3. The drug was rapidly absorbed after once-daily administration on day 1 and day 7. Cmax was generally reached 3.0–4.0 h after dosing. Within each dose level, plasma concentrations increased by a factor of two- to three-fold from day 1 to day 7, suggesting an effective half-life in the region of 2 days. Plasma concentrations were above the target concentration (13.5 ng/ml, the protein binding corrected EC50 for wild-type virus) at all time points after day 1. For most individuals TMC278 could be detected up to 168 h after last dosing. Plasma concentrations increased with increasing dose of TMC278, but these increases were less than dose-proportional. There was a trend towards greater inter-individual variability of pharmacokinetic parameters at higher dosages.
TMC278 was well tolerated over 7 days of treatment. At least one adverse event was reported by 61.1% of subjects in the TMC278 groups and 63.6% in the placebo group (Table 4). The most frequent adverse events were gastrointestinal disorders which were reported by 9/36 (25%) subjects in the TMC278 groups and 2/11 (18.2%) in the placebo group. In general the adverse events were mild with only 2/36 (5.6%) subjects in the TMC278 groups experiencing a gastrointestinal adverse event of grade 2 (one with abdominal pain and one with nausea). One grade 3 adverse event of nausea was considered possibly due to the medication. There were no grade 4 or serious adverse events in the treatment period. There were no adverse events for which the trial medication was permanently or temporarily discontinued.
Treatment-emergent grade-1 liver function parameters were detected in three TMC278-treated individuals (increased alanine amino transferase in one subject, increased hyperbilrubinaemia in one subject and decreased lactic dehydrogenase in one subject). Abnormal increases in indirect bilirubin were detected in three TMC278-treated subjects and two subjects in the placebo group. Treatment-emergent grade-2 increased cholesterol was observed in two TMC278-treated subjects, but both had cholesterol above the upper normal limit at baseline. Treatment-emergent grade-1 hyperglycaemia was detected in three TMC278-treated subjects versus two in the placebo group. With the exception of cholesterol the abnormal changes in liver function, lipid/glucose and general biochemistry parameters occurring in subjects with normal baseline and screening values were isolated incidents and resolved by the next assessment time point. Eight treated subjects experienced decreased white blood cell counts (one subject grade 3) during the trial but the abnormal changes in haematology were isolated incidents and resolved by the next assessment timepoint. None of the observed abnormalities were considered clinically relevant and no dose relationship with TMC278 was observed in the incidence of any abnormal change.
The TMC278-C201 trial was a phase IIa double-blind, placebo-controlled, dose-escalating ‘proof-of-principle’ trial designed to assess virological and immunological responses, changes in resistance patterns, and pharmacokinetic and safety profiles of once-daily TMC278. The study was limited to 7 days to reduce the potential for early emergence of resistance to TMC278 while allowing adequate time to evaluate short-term antiviral activity . Despite the short course of therapy, TMC278 achieved a statistically significant median viral load reduction of 1.199 log10 copies/ml from baseline compared with no change in the placebo group. There was no dose-associated relationship in viral reduction with TMC278. The lowest doses of TMC278 administered in the study produced minimal exposures well above the protein binding corrected EC50 for wild-type virus possibly explaining the lack of dose–response relationship.
No newly acquired resistance mutations were detected in RT between baseline and end of the study in any TMC278-treated group. Further clinical trials with longer duration are required to confirm this observation.
Overall, 7-day, once-daily treatment with TMC278 monotherapy was well tolerated and safe with no dose-related adverse events. The most common adverse events in the TMC278-treated group were associated with the gastrointestinal tract. A number of abnormal changes in liver function, lipids, glucose, general biochemistry and haematological parameters were observed in some subjects during the study but these were generally transient and quickly resolved by the next assessment time point.
The antiviral effect of 7-day TMC278 monotherapy was significant in all TMC278 groups and did not result in NNRTI resistance. This novel NNRTI is being developed as a component of once-daily dosing in combination therapy with other antiretroviral drugs. Trials of longer treatment duration with TMC278, in combination with other antiretroviral drugs, are underway in treatment-naive subjects, to assess the long-term durability of the antiviral effect, the rate of emergence of resistant viruses and the time of onset, and the frequency and severity of adverse events, including those common to currently approved NNRTI.
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Keywords:© 2006 Lippincott Williams & Wilkins, Inc.
TMC278; non-nucleoside reverse transcriptase inhibitor; monotherapy; phase IIa clinical trial; antiviral response; pharmacokinetics; safety and tolerability; proof of principle