In vitro combination of PNU-140690, a human immunodeficiency virus type 1 protease inhibitor, with ritonavir against ritonavir-sensitive and -resistant clinical isolates.

PNU-140690 (sulfonamide-containing 5,6-dihydro-4-hydroxy-2-pyrone) is a potent, nonpeptidic inhibitor of the human immunodeficiency virus type 1 (HIV-1) protease currently under clinical evaluation. PNU-140690 and ritonavir were studied in two-drug combinations against the replication of HIV-1 clinical isolates in peripheral blood mononuclear cells. A ritonavir-sensitive (301-1x) and -resistant (301-6x) isolate pair derived from an individual before and after monotherapy with ritonavir were used. These isolates showed no significant difference in sensitivity to PNU-140690, but isolate 301-6x was more than 50-fold less sensitive to ritonavir than isolate 301-1x. Mathematical analysis showed that the combination of various concentrations of PNU-140690 with ritonavir yielded additive to moderately synergistic antiviral effects against the ritonavir-sensitive isolate and stronger synergy against the ritonavir-resistant isolate. The mechanism of synergy was not investigated, but the results suggested that both the virological and the observed in vitro pharmacological effects may have contributed to the observed synergy. Importantly, no significant antagonism was observed with the drug combinations studied. These data suggest that PNU-140690 may be useful in combination regimens with a structurally unrelated protease inhibitor such as ritonavir.