John A. Bilello

A 24-week open-label phase I/II evaluation of the HIV protease inhibitor MK-639 (indinavir).

Objective:To investigate the safety, pharmacokinetics, and activity of the orally bioavailable protease inhibitor MK-639. Design:An open-label Phase I/II trial of medically stable subjects with screening CD4 lymphocyte counts ≤ 300×106/l and ≥ 20 000 HIV RNA copies/ml. Pharmacokinetics were performed at days 1 and 15. In order to better understand the relationships between drug exposure, baseline activity markers, and their changes during the study, mathematical modeling was performed using the traditional sigmoid-Emax relationship of pharmacologic effect and first order inhomogeneous differential equations for a two compartment system. Results:The five men enrolled had extensive prior nucleoside therapy (mean, 32.6 ± 25.6 months), a low mean CD4 lymphocyte cell count (CD4 count, 66.1 ± 61×106/l and CD4 percentage, 4.4 ± 3.1%), high soluble tumor necrosis factor-α type II (sTNFII) receptor concentration (6.23 ± 2.76 ng/ml) and high viral load (5.13 ± 0.46 log10 RNA copies/ml; geometric mean, 133 941 copies/ml). The drug was well tolerated at a dose of 600 mg every 6 h. The steady state concentrations Cmax and Cmin were 4.94 ± 2.16 μM and 0.28 ± 0.1 μM, respectively, which are ≈50 and 3 times the 95% inhibitory concentration (IC95) for clinical isolates, respectively. The mean increase in CD4 cell count was 143×106/l (217% increase), the mean increase in CD4 percentage was 5.2 percentage points (118%), mean decrease in HIV RNA was 1.55 log10 RNA copies/ml (a geometric mean difference of 130 120 copies/ml or 97% decrease) with a slow upward drift on continued therapy to a mean 0.64 log10 RNA copies/ml decrease by week 24 (a geometric mean difference of 103 084 copies/ml or 77% decrease), and a mean decrease in sTNFII receptors of 2.78 ng/ml (45% decrease). The mean CD4 counts per week as a function of the starting CD4 counts fit a sigmoid-Emax relationship (r2 = 0.998, P < 0.0001) with the return of CD4 cells being strongly related to the number of CD4 cells at baseline. Drug exposure as measured by either the total exposure (area under the concentration/time curve) or as the Cmin gave similar significant relationships to the fractional inhibition of HIV generation (r2 = 0.999, P < 0.0001, and r2 = 0.996, P < 0.0001, respectively). Conclusions:MK-639 appears to have significant dose-related antiviral activity and is well tolerated.

Predicting Clinical Progression or Death in Subjects with Early-Stage Human Immunodeficiency Virus (HIV) Infection: A Comparative Analysis of Quantification of HIV RNA, Soluble Tumor Necrosis Factor Type II Receptors, Neopterin, and β2-Microglobulin

Quantification of human immunodeficiency virus (HIV) RNA by branched-chain DNA signal amplification, measurement of soluble tumor necrosis factor type II receptors (sTNFR-II), neopterin, beta2-microglobulin, or CD4 cell counts can be used to predict the risk of clinical progression or death in HIV infection but have not been compared in the same study. Ninety subjects were categorized into progression groups by their rate of CD4 cell decline and matched into triplets by initial CD4 cell count, age, race, and calendar time. By matched logistic regression, only the sTNFR-II and HIV RNA values were predictive of outcome across the progression groups. Categorization of baseline HIV RNA and sTNFR-II resulted in differences in progression to several clinical outcomes. sTNFR-II concentrations were the only immune marker examined that increased the prognostic utility of HIV RNA determination in early-stage subjects. Further studies in later stages of disease or after therapy are indicated.

Hollow-Fiber Unit Evaluation of a New Human Immunodeficiency Virus Type 1 Protease Inhibitor, BMS-232632, for Determination of the Linked Pharmacodynamic Variable

BMS-232632 is a potent human immunodeficiency type 1 (HIV-1) protease inhibitor with a half-life that allows for once-daily dosing. A concentration of 4 times the viral 50% effective concentration (EC(50) [i.e., approximately EC(95)]) administered as a continuous infusion in vitro provides virtually complete suppression of viral replication. This exposure, modeled in vitro as once-daily administration with oral absorption, allows ongoing viral replication. An exposure 4 times as large was calculated to be necessary to provide virus suppression equivalent to the continuous-infusion exposure. These experiments demonstrated that concentration above a threshold (time > 4xEC50) is the pharmacodynamically linked variable for this HIV-1 protease inhibitor. Protein-binding experiments demonstrated that the EC(50) was increased 13.4 times by the addition of human binding proteins. Monte Carlo simulation of protein binding-adjusted pharmacokinetic data from volunteers demonstrated that 64%-70% of a simulated population (n = 3000) would achieve virus suppression with 400-600 mg of BMS-232632 given once daily, if the viral EC(50) were < or = 1 nM.

Pharmacodynamics of Abacavir in an In Vitro Hollow-Fiber Model System

ABSTRACT Abacavir is a potent new carbocyclic nucleoside analogue. We employed our hollow-fiber pharmacodynamic modeling system to examine the antiretroviral effects of different abacavir exposures, as well as the impact of the schedule of drug administration on efficacy. Dose ranging of abacavir revealed that a concentration of four times the 50% effective concentration (EC50) (approximately the EC95) was required to inhibit the replication of human immunodeficiency virus type 1 (HIV-1) (strain MN) either in a continuous-infusion hollow-fiber experiment or in a classical tissue culture flask experiment. In contrast to earlier work with another drug class (HIV-1 protease inhibitors), addition of physiological amounts of the human drug binding proteins albumin and α1 acid glycoprotein revealed that there was little impact on the antiviral effect of the drug. Comparison of equivalent exposures (an area under the concentration-time curve [AUC] developed by approximately 500 mg per day of orally administered abacavir), either in a continuous-infusion mode or as a single oral dose of abacavir, demonstrated no difference in the ability to suppress either strain IIIB or strain MN. Comparison of administration of 250 mg every 12 h (q12h) versus once-daily administration of 500 mg for strain MN again showed no significant difference in suppressive effect. These experiments were carried out over 8 to 15 days. Because of these promising initial results, we extended the experiment to 30 days and examined three different schedules of administration that generated the same AUC at 24 h (AUC24): 300 mg q12h, 600 mg q24h, and 1,200 mg q48h. The aim of the last of these regimens was to definitively demonstrate schedule failure. There was little difference between the 1,200-mg q48h treatment group and the untreated control at 30 days. Likewise, there was little difference between the 600-mg q24h and 300-mg q12h treatment groups. However, at circa day 18 of the experiment, there was a small increase in viral output of p24 in the once-daily dosing unit. Examination of virus from all groups demonstrated no phenotypic or genotypic differences. The small difference in hollow-fiber unit p24 in the once-daily dosing group was not due to emergence of resistance over the 30-day single-drug exposure. We conclude that the dose of abacavir currently being studied in clinical trials (300 mg orally q12h) will be efficacious for the majority of sensitive clinical isolates of HIV-1. These in vitro data also suggest that this drug may be able to be administered to patients on a once-daily basis at a dose of 600 mg.

The Safety and Efficacy of Granulocyte-Macrophage Colony-Stimulating Factor (Sargramostim) Added to Indinavir- or Ritonavir-Based Antiretroviral Therapy: A Randomized Double-Blind, Placebo-Controlled Trial

Sargramostim is a yeast-derived, recombinant human granulocyte-macrophage colony-stimulating factor with therapeutic potential in human immunodeficiency virus (HIV) infection. Its safety and activity when used in combination with protease inhibitors were evaluated in a randomized, double-blind trial in which 20 HIV-infected subjects on stable antiretroviral regimens, including indinavir or ritonavir, received sargramostim or placebo 3 times a week for 8 weeks. Analysis of HIV virus load excluded any 0. 5 log10 increase due to sargramostim (95% confidence interval, -0.68 to 0.44). Sargramostim was well tolerated, and inflammatory cytokines and surrogate markers of disease progression, such as serum levels of interleukin-10 and soluble tumor necrosis factor receptors types Iota and IotaIota, remained stable in subjects receiving sargramostim. Sargramostim treatment was associated with a trend toward decreased HIV RNA (>0.5 log10) and increased CD4+ cell count (>30%). These results became statistically significant only when subjects with baseline virus loads within the limits of detection or baseline CD4 cell count >50 were analyzed. No difference in indinavir pharmacokinetics was observed before or after sargramostim therapy.

In vitro-in vivo model for evaluating the antiviral activity of amprenavir in combination with ritonavir administered at 600 and 100 milligrams, respectively, every 12 hours

ABSTRACT The study objective was to evaluate the pharmacodynamics of amprenavir in an in vitro system, develop an exposure target for maximal viral suppression, and determine the likelihood of target attainment based on the pharmacokinetics of amprenavir and ritonavir in human immunodeficiency virus (HIV)-infected patients. Population pharmacokinetic data were obtained from 13 HIV-infected patients receiving amprenavir and ritonavir in doses of 600 and 100 mg, respectively, every 12 h. A 2,500-subject Monte Carlo simulation was performed. Target attainment was also estimated for a target derived from clinical data. Maximal viral suppression (in vitro) was achieved when amprenavir free-drug concentrations remained greater than four times the 50% effective concentration (EC50) for 80% of the dosing interval. At an amprenavir EC50 of 0.03 μM, the likelihood of target attainment is 97.4%. For reduced-susceptibility isolates for which the EC50s are 0.05 and 0.08 μM, target attainment is 91.0 and 75.8%, respectively. For the clinical target of a trough concentration/EC50 ratio of 5, the target attainment rates were similar. Treatment with amprenavir and ritonavir at doses of 600 and 100 mg, respectively, twice a day provides excellent suppression of wild-type isolates and reduced-susceptibility isolates up to an EC50 of 0.05 μM. Even at 0.12 μM, target attainment likelihood exceeds 50%, making this an option for patients with extensive exposure to protease inhibitors when this treatment is used with additional active antiretroviral agents.

Efficacy of constant infusion of A-77003, an inhibitor of the human immunodeficiency virus type 1 (HIV-1) protease, in limiting acute HIV-1 infection in vitro.

A-77003, a human immunodeficiency virus type 1 (HIV-1) protease inhibitor, is effective for both acute and chronic infection in vitro and was evaluated clinically by continuous intravenous infusion administration. The minimum effective dose (the concentration required to completely inhibit viral replication) was determined in vitro in a population of uninfected (99%) and HIV-infected (1%) cells exposed to A-77003 by continuous infusion in hollow-fiber bioreactors. The production of infectious HIV and release of p24 antigen from infected cells were completely inhibited in cultures exposed to A-77003 at or above a concentration of 0.5 microM. Measurement of unintegrated HIV-1 DNA synthesis and flow cytometric analysis for cells expressing HIV p24 antigen demonstrated that the spread of HIV to uninfected cells was also blocked at 0.5 microM A-77003. Dose deescalation to 0.25 microM or removal of A-77003 resulted in the limited spread of the virus throughout the culture, the resumption of viral DNA synthesis, and release of p24. HIV produced after exposure to 0.5 microM A-77003 was noninfectious for a period of 72 h after the removal of the drug. Addition of 1 mg of alpha 1-acid glycoprotein per ml to this in vitro system completely ablated the anti-HIV effect of 0.5 microM A-77003. These data suggest that determination of the minimum effective dose under conditions which simulate human pharmacodynamic patterns may be useful in determining the initial dose and schedule for clinical trials. However, other factors, such as serum protein binding, may influence the selection of a therapeutic regimen.