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1st International Workshop on HIV Drug Resistance & Treatment Strategies25-28 June 1997, St. Petersburg, Florida, USA |
TWO DISTINCT MUTATIONAL PATHWAYS IN HIV-1 RT CONFER ZIDOVUDINE/LAMIVUDINE DUAL RESISTANCE
Antiviral Therapy 1997;2 (Suppl 5):7 (abstract no. 11)
SD Kemp and S Bloor for the FASP Resistance Study Group
Glaxo Wellcome, Stevenage, UK
We have previously reported that zidovudine/lamivudine dual resistance can occur in HIV-1 isolates from antiretroviral-experienced patients with extensive zidovudine/lamivudine therapy. Phenotypic assays showed that a significant percentage of the viral isolates from patients failing therapy were resistant to both zidovudine and lamivudine (defined as having a 50-fold or greater increase in IC50 for both drugs). Genetic mapping, using RT deletion clones of three different sizes, mapped the RT mutations responsible for dual resistance within distinct 5´ and 3´ regions of the RT. The objective of this study was to define those polymorphisms in either of these regions that facilitate zidovudine/lamivudine dual resistance. Sequence analysis of the HIV-1 RT of the doubly resistant recombinant viruses revealed complex patterns of RT mutations. Site-directed mutants modelled on these sequence data have been generated to further elucidate the molecular basis of this dual resistance. Mutants generated within the 5´ region of RT with two to six of the known zidovudine resistance mutations and M184V did not confer resistance to both zidovudine and lamivudine. However, the addition of the known polymorphisms R211K and L214F conferred high-level resistance to both drugs in some of the resistance backgrounds described above. A novel change in the 3´ region of RT (G333E) in a variant derived by in vitro selection has previously been shown to facilitate dual resistance to zidovudine and lamivudine. Sequence variation at codon 333 (including G333E/D) was seen in some of the clinical isolates where dual resistance mapped to the 3´ region. Phenotypic resistance was confirmed on an individual clonal basis using the RT cassette cloning vector xxHIVLAI-np. Other unidentified polymorphisms in the 3´ region also facilitated dual resistance. From this work it is clear that a number of distinct molecular mechanisms of zidovudine/lamivudine dual resistance can occur and that the genetic background is very important. Polymorphisms other than those responsible for zidovudine or lamivudine resistance are required for dual resistance. This study clearly identifies two possible routes to zidovudine/lamivudine dual resistance via a complex series of multiple mutations in the 5´ and 3´ regions of RT.
The FASP Resistance Study Group are V Miller, S Staszewski, R Pauwels, M-P de Bethune, K Hertogs, BA Larder, PR Harrigan, M Tisdale, SD Kemp, S Bloor, C Stone, A Kohli, R Myers, J Mellors and C Shi.
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1997-06-25
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