XI International HIV Drug Resistance Workshop: Basic Principles and Clinical Implications Seville, Spain, 2–5 July 2002

BACKGROUND: Tipranavir is the first in a new class of non-peptidic HIV protease inhibitors (NPPIs). It retains broad and impressive in vitro antiviral activity for a wide range of patient-derived HIV isolates resistant to multiple protease inhibitors (PIs). The mutational pattern conferring resistance to tipranavir is poorly understood, in part due to the limited number of available clinical isolates exhibiting reduced susceptibility to the drug and to the diverse and complex genotypic changes present in such isolates. In addition, attempts to select viruses in culture with reduced susceptibility to tipranavir, by cultivating the wild-type virus under escalating concentrations of drug have met with limited success. Here we report the selection in vitro of such viruses with reduced susceptibility, and we describe a mutational pattern leading to reduced sensitivity to tipranavir.

METHODS: Wild-type HIV-1 was passaged in C8166 cells in culture for 8 months in the presence of increasing concentrations of tipranavir. Following each viral breakthrough the protease gene and adjacent regions of the genome of replicating viruses were PCR-amplified, cloned and sequenced to identify mutations. Formal proof for the role of these mutational changes in decreased tipranavir susceptibility was obtained by their re-introduction into viral molecular clones. The reconstructed mutant viruses were tested for their susceptibility to tipranavir and to marketed PIs.

RESULTS: Viruses selected to grow in the presence of tipranavir acquired multiple mutations in the protease gene. In successive breakthroughs the following mutations accumulated in the replicating virus population: L33F, I84V, K45I, I13V/V32I and V82L. Five of these six mutations are within or in very close proximity to the protease active site. None of these mutations individually conferred significant decreased susceptibility to tipranavir, although a combination of five or more of these mutations caused a significant decrease in susceptibility to the drug, as well as to other marketed protease inhibitors. Three of these mutations, at positions 33, 84 and 82 have been reported to be associated with reduced susceptibility to tipranavir (4- to 10-fold) in virus from patients enrolled in clinical studies with tipranavir (Conf Retroviruses Opportunistic Infect. 2002 Feb 24-28;9th: Abstract No. 562-T). It is of particular note, however, that in these clinical isolates, the mutations appeared in the context of complex baseline genotypes containing at least 16 PI resistance mutations.

CONCLUSION: The development of decreased susceptibility to tipranavir in vitro is slow and complex, involving the sequential accumulation of multiple mutations in the viral protease. Acquisition of a similar constellation of mutations appears to influence susceptibility to tipranavir in the context of both the wild-type and multi-PI resistant protease.

PRESENTING AUTHOR: L Doyon

Download PDF of this abstract.

2002-07-02
10

Copyright © 2002 - International Medical Press Ltd. Reproduction of this abstract (other than one copy for personal reference) must be cleared through the International Medical Press Ltd. 2-4 Idol Lane, London EC3R 5DD UK.