HIV-1 resistance to fusion inhibitors

Abstract

Fusion inhibitors, such as T-20 and T-1249, block HIV-1 entry by preventing 6-helix-bundle formation of gp41 and represent a new class of antiretroviral drugs. The present study analyzed the susceptibility of highly divergent HIV-1 strains to T-20 and T-1249 inhibition and the mechanism(s) mediating resistance to these fusion inhibitors. The first aim of this thesis was to assess the effect of naturally-occurring sequence variations in the gp41 Heptad Repeat-1 (HR-1) region on HIV-1 susceptibility to fusion inhibitors. The results demonstrated that some naturally occurring sequence variations in the gp41 HR-1 region reduce the sensitivity of HIV-1 to T-20 but not T-1249 inhibition. The second aim was to clarify whether fusion inhibitors are not only active against HIV-1 group M strains but also against highly diverse group O clinical isolates. The results showed that HIV-1 O isolates were as sensitive as group M viruses to inhibition by T-20 but frequently less susceptible to T-1249. The third aim of the thesis was to understand the HIV-1 resistance mechanism(s) to T-1249. Site-specific random PCR mutagenesis was used as a tool to select T-1249 resistant forms and to evaluate where changes in HR-1 might be tolerated or not. Infectivity assays demonstrated that only changes at positions 37I, 38V and 40Q near the N-terminus of HR-1 were tolerated. Moreover, the data demonstrate that the "GIV" motif in the gp41 HR-1 region also plays a key role in resistance to T-1249 similar to T-20. This suggests that T-1249 should not be used in combination with T-20 or as salvage therapy in pretreated patients. Altogether, the results of the present thesis further emphasize that fusion inhibitors hold great promise for antiretroviral therapy because they are effective against highly divergent HIV-1 strains and resistance usually comes at the cost of reduced viral fitness.