The P236L delavirdine-resistant human immunodeficiency virus type 1 mutantis replication defective and demonstrates alterations in both RNA 5 '-end-and DNA 3 '-end-directed RNase H activities

The nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) delavirdine (DLV) selects in vitro for the human immunodeficiency virus type 1 (HIV-1) RT mutation P236L, which confers high-level resistance to DLV but not other NNRTIs. Unexpectedly, P236L has developed infrequently in HIV-1 isolates o btained from patients receiving DLV; K103N is the predominant resistance mu tation observed in that setting. We characterized the replication fitness o f viruses derived from pNL4-3 containing P236L or K103N in both H9 and prim ary human peripheral blood mononuclear cell cultures infected in parallel w ith the two mutants. In the absence of DLV, p24 production by wild-type vir us occurred more rapidly and to higher levels than with either mutant; P236 L consistently demonstrated a two- to threefold decrease in p24 relative to K103N. At low levels of DLV, growth of wild-type virus was severely inhibi ted, and K103N replicated two- to threefold more efficiently than P236L. At high concentrations of DLV, P236L replication and K103N replication were b oth inhibited. Recombinant RTs containing K103N or P236L were analyzed for DNA polymerization on heteropolymeric RNA templates and RNase H degradation of RNA-DNA hybrids. Neither mutant demonstrated defects in polymerization. K103N demonstrated normal RNA 5'-end-directed RNase H cleavage and slowed DNA 3'-end-directed RNase H cleavage compared to wild-type RT. P236L demons trated slowing of both DNA 3'-end- and RNA 5'-end-directed RNase H cleavage , consistent with its reduced replication efficiency relative to K103N. The se data suggest that NNRTI resistance mutations can lead to reductions in t he efficiency of RNase H cleavage, which may contribute to a reduction in t he replication fitness of HIV-1.