Search

The nonnucleoside reverse transcriptase (RT) inhibitors comprise a class of structurally diverse compounds that are functionally related and specific for the human immunodeficiency virus type 1 RT. Viral variants resistant to these compounds arise readily in cell culture and in treated, infected human. Therefore, the eventual clinical usefulness of the nonnucleoside inhibitors will rely on a thorough understanding of the genetic and biochemical bases for resistance. A study was performed to assess the effects of substitutions at each RT amino acid residue that influences the enzyme's susceptibility to the various nonnucleoside compounds. Single substitutions were introduced into both purified enzyme and virus. The resulting patterns of resistance were markedly distinct for each of the tested inhibitors. For instance, a > 50-fold loss of enzyme susceptibility to BI-RG-587 was engendered by any of four individual substitutions, while the same level of relative resistance to the pyridinone derivatives was mediated only by substitution at residue 181. Similarly, substitution at residue 181. Similarly, substitution at residue 106 had a noted effect on virus resistance to BI-RG-587 but not to the pyridinones. The opposite effect was mediated by a substitution at residue 179. Such knowledge of nonucleoside inhibitor resistance profiles may help in understanding the basis for resistant virus selection during clinical studies of these compounds.

The reverse transcriptase (RT) of human immunodeficiency virus type 1 (HIV-1) is potently inhibited by a structurally diverse group of nonnucleoside compounds. These include pyridinone derivatives, tetrahydroimadazo[4,5,1-j,k][1,4]-benzodiazepin-2(1H)-one and -thione, and BI-RG-587 (nevirapine). The compounds act noncompetitively, by an unknown mechanism, with respect to template-primer and nucleotide substrates. Despite a high degree of similarity between the HIV-1 and HIV-2 RTs, the HIV-2 enzyme is totally insensitive to these inhibitors. Using a novel method for joining DNA sequences, we have exploited this difference between the two enzymes to identify the regions of the RT that contribute to the compounds' inhibitory activities. The relative in vitro sensitivities of HIV-1/HIV-2 chimeric and site-specific mutant enzymes were determined. Sensitivity to inhibition was largely, though not exclusively, dependent upon the RT region defined by amino acid residues 176 to 190, with specific contributions by residues 181 and 188. The region defined by residues 101 to 106 was found to functionally interact with the domain from 155 to 217. In addition, the functional equivalence of the three inhibitor groups was shown.