Nucleoside analog 1592U89 and human immunodeficiency virus protease inhibitor 141W94 are synergistic in vitro

Abstract

The use of combinations of anti-human immunodeficiency virus (anti-HIV) agents targeted to different molecular targets will most likely result in increased viral suppression and may also delay or prevent the emergence of resistant HIV strains. The purpose of the present study was to develop information on the in vitro anti-HIV activities of combinations of the reverse transcriptase inhibitor 1592U89 and the protease inhibitor 141W94 to help guide the choice of dosages in clinical trials. Triplicate in vitro dose-response matrices were prepared with MT-2 cells infected with HIV type 1 (HIV-1) strain IIIB. In order to account for the effects of protein binding, tissue culture medium with 10% fetal bovine serum was supplemented with the human serum proteins alpha1 acid glycoprotein (1 mg/ml) and albumin (40 mg/ml). The three-dimensional drug interaction surface for 1592U89 and 141W94 was constructed with the program MacSynergy II. As analyzed relative to a Bliss Independence null reference model, this combination was synergistic, with volumes of synergy exceeding 100 (99% confidence). Analysis of the data set with a fully parametric form of an equation for the quantitation of drug interaction developed by Greco et al. (W. R. Greco, G. Bravo, and J. C. Parsons, Pharmacol. Rev. 47:331-385, 1995) resulted in an interaction term statistically significantly greater than 0.0, indicating true synergy. Both methods concur that this combination is significantly synergistic. These data, with favorable findings from phase I/II trials for each drug alone, suggest that the combination of 1592U89 plus 141W94 should be further evaluated in clinical trials.

FIG. 1

1592U89 and 141W94 combination study with no plasma protein addition. A three-dimensional response surface of 1592U89 and 141W94 combination matrix is shown. Percent inhibition data are from an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay with HIV-1_IIIB and MT-2 cells. No human serum proteins were added to the media.

FIG. 2

Synergy plot of 1592U89 and 141W94 with no plasma addition. MacSynergy II analysis of the data from Fig. 1 is shown. The synergy plot is at the 95% confidence level.

FIG. 3

1592U89 and 141W94 combination study with albumin and α₁ acid glycoprotein. A three-dimensional response surface of 1592U89 and 141W94 combination matrix is shown. Percent inhibition data from an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay with HIV-1_IIIB and MT-2 cells. Human serum proteins α₁ acid glycoprotein (1 mg/ml) and albumin (40 mg/ml) were added to the media.

FIG. 4

Synergy plot of 1592U89 and 141W94 with 4% albumin and α₁ acid glycoprotein at 1 mg/ml. MacSynergy II analysis of the data from Fig. 3 is shown. Synergy plot is at the 95% confidence level.

FIG. 5

Weighted residuals in 1592U89-141W94 synergy plot. In order to evaluate whether there was a systematic misprediction of the antiviral effect by the fully parametric model, the weighted difference of the model prediction from the observed data is presented. The residuals are scattered about the zero line without bias, and the errors are quite trivial.