3rd International Workshop on HIV Drug Resistance 2-5 August 1994, Kauai, Hawaii, USA

MOLECULAR CHARACTERIZATION OF HIV-1 VARIANTS RESISTANT TO SPECIFIC VIRAL PROTEASE INHIBITORS

Int Wkshop HIV Drug Res 1994 Aug 2-5;3:10 (abstract no. 9)

D, Lamarre, G, Croteau, L. Pilote, P. Rousseau and L. Doyon
Bio-Méga/Boehringer Ingelheim Research Inc., Canada

Inhibitors of the HIV-1 protease are a promising new class of antiviral compounds under development for the treatment of AIDS. Numerous studies of HIV reverse transcriptase inhibitors, the only clinically approved drugs for treatment of HIV-1 infections, have indicated that drug resistant viral variants can be selected in cell culture or arise during antiviral therapy in the clinical setting. The potential appearance of variants with resistance to HIV protease inhibitors is therefore of great concern in the development of these compounds as effective antiviral agents. HIV-1 IIIB was serially passaged in the highly permissive human T-cell line, C8166, in the presence of increasing concentrations of antiviral drug, in order to select variants with a drug resistance phenotype. With this protocol we have selected HIV-1 variants with reduced sensitivity to two potent (EC₅₀ ~ 1-2 nM; TC₅₀ >10 µM) HIV-1 protease inhibitors (BILA 1906 BS and BILA 2185 BS), and to the reverse transcriptase inhibitors, AZT and nevirapine. HIV-1 variants were obtained with highly reduced sensitivity (1000 fold increase in the EC₅₀) with both protease inhibitors, although these appear to arise less readily than with RT inhibitors. Virus breakthroughs were systematically observed with both protease inhibitors but a long period of selection (33-37 passages) was required to generate highly resistant virus. Cross-resistance analysis demonstrated a variable degree of resistance with different classes of protease inhibitor but the sensitivity of these variants to AZT and nevirapine was maintained. Sequence analysis of the protease gene from variants emerging at different passages revealed the progressive appearance of mutations involving position 23, 32, 46, 71 and 84. With both protease inhibitors, a substitution at position 84 (Ile→Ala) involving a double point mutation was observed in highly resistant virus. Furthermore, substitution in the protease cleavage site of the nucleocapsid (p7/p6) was observed. Passage of the highly resistant virus population in the absence of selective pressure resulted in reversion to a moderately resistant phenotype. The relevance of the different mutations to the resistance phenotype will be discussed. These data suggest that emergence of resistance may occur in vivo with HIV-1 protease inhibitors but the relevance of these observations to the clinical setting remains to be established.

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1994-08-02
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