Kinetics of antiviral activity and intracellular pharmacokinetics of humanimmunodeficiency virus type 1 protease inhibitors in tissue culture

We have examined the kinetics of the inhibition of human immunodeficiency v irus type 1 (HIV-1) particle infectivity by protease inhibitors (PIs) in ce ll culture, using either transfected HeLa cells or infected peripheral bloo d mononuclear cells (PBMCs) as producers of infectious virions. Both the ki netics of the initiation of antiviral activity after addition of the PIs to these cultures and the kinetics of restoration of virion infectivity after removal of the PIs from the treated cultures were examined. We found that the kinetics of initiation of particle infectivity inhibition produced by a high extracellular concentration (5 mu M) of the inhibitors were similar f or all five inhibitors tested: loss of particle infectivity was perceptible as early as 1 h after the initiation of PI treatment and increased gradual ly thereafter. By contrast, the durability of this antiviral effect followi ng removal of the drug from the culture varied dramatically according to th e drug studied. In transfected HeLa cells, saquinavir and nelfinavir exerte d the most prolonged inhibition, with the half-lives of their antiviral act ivities being greater than 24 h, while ritonavir exerted an intermediate le ngth of inhibition (18 h) and indinavir and amprenavir exerted a reproducib ly shorter length of inhibition (5 h). For all five tested PIs, these kinet ics were significantly faster in PBMCs than in HeLa cells. The striking dif ferences in antiviral kinetics observed among the different PIs appear most ly due to differences in their intracellular concentrations and/or rates of cellular clearance. Our observations, although limited to tissue culture c onditions, may help delineate the cellular parameters of the antiviral acti vities of HIV-1 PIs and further optimize the efficiencies of these antiretr ovirals in vivo.