A NOVEL MUTATION (F227L) ARISES IN THE REVERSE-TRANSCRIPTASE OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 ON DOSE-ESCALATING TREATMENT OF HIV TYPE 1-INFECTED CELL-CULTURES WITH THE NONNUCLEOSIDE REVERSE-TRANSCRIPTASE INHIBITOR THIOCARBOXANILIDE UC-781

Treatment of wild-type human immunodeficiency virus [HIV-1(HIB)]-infec ted cell cultures with the thiocarboxanilide UC-781 under low selectiv e pressure (i.e., 0.01 mu g/ml) resulted in the emergence of V106A RT mutant virus, On increasing drug concentrations (stepwise up to 30 mu g/ml) the virus retained the V106A RT mutation but acquired the novel F227L mutation in the RT genome in addition to the L100I, K101I, and Y 181C mutations, This multiple-mutant virus proved highly resistant to virtually all nonnucleoside RT inhibitors (NNRTIs) (e.g., nevirapine, delavirdine, and loviride), but retained full sensitivity to nucleosid e analogs such as AZT, ddI, (-)FTC, and 3TC. The F227 amino acid is hi ghly conserved in HIV-1 strains and forms part of the NNRTI-binding po cket, Our model suggests a hydrophobic interaction between F227 and th e chloro atom of UC-781.