Changes in darunavir/r resistance score after previous failure to tipranavir/r in HIV-1-infected multidrug-resistant patients

The L33F darunavir resistance mutation acts as a molecular anchor reducing the flexibility of the HIV-1 protease 30s and 80s loops

HIV-1 protease (PR) is a 99 amino acid protein responsible for proteolytic processing of the viral polyprotein - an essential step in the HIV-1 life cycle. Drug resistance mutations in PR that are selected during antiretroviral therapy lead to reduced efficacy of protease inhibitors (PI) including darunavir (DRV). To identify the structural mechanisms associated with the DRV resistance mutation L33F, we performed X-ray crystallographic studies with a multi-drug resistant HIV-1 protease isolate that contains the L33F mutation (MDR769 L33F). In contrast to other PR L33F DRV complexes, the structure of MDR769 L33F complexed with DRV reported here displays the protease flaps in an open conformation. The L33F mutation increases noncovalent interactions in the hydrophobic pocket of the PR compared to the wild-type (WT) structure. As a result, L33F appears to act as a molecular anchor, reducing the flexibility of the 30s loop (residues 29-35) and the 80s loop (residues 79-84). Molecular anchoring of the 30s and 80s loops leaves an open S1/S1' subsite and distorts the conserved hydrogen-bonding network of DRV. These findings are consistent with previous reports despite structural differences with regards to flap conformation.

The role of mutations at codons 32, 47, 54, and 90 in HIV-1 protease flap dynamics

Treatment of Human Immunodeficiency Virus remains challenging due to the emergence of drug resistant strains under the selective pressure produced by standard anti-retroviral therapy. To explore the structural mechanisms of drug resistance, we performed 40 ns molecular dynamics simulations on three multi-drug resistant HIV-1 protease clinical isolates from patients attending an infectious diseases clinic in Detroit, MI. We identify a novel structural role for the I47V, V32I, I54M and L90M major resistance mutations in flap opening and closure of MDR-PR isolates. Our studies suggest I47V is involved in flap opening and the interaction between I47V and V32I tethers the flaps to the active site. Also, I54M and L90M may be responsible for asymmetric movement of the protease flaps. These findings can be utilized to improve drug design strategies against MDR HIV-1 PR variants.

Drug resistance mutations in HIV-infected patients in the Spanish drug resistance database failing tipranavir and darunavir therapy

The presence of resistance mutations in patients failing tipranavir or darunavir was examined at the national drug resistance database of the Spanish AIDS Research Network. Although mutations emerging during tipranavir and darunavir failures differed considerably, cross-resistance was found in up to half of the patients tested. Interestingly, mutation 54L, which is associated with tipranavir hypersusceptibility, was selected in half of the darunavir failures. Thus, resistance testing seems mandatory to ensure the benefit of the sequential use of these drugs.

HAART for children with treatment failure

Even as pediatric rollout programs are struggling to meet global need, increasing numbers of children are failing first-line antiretroviral therapy in low- and middle-income countries. Without better access to viral load monitoring, second-line antiretrovirals and research to guide optimal regimen selection, it will be difficult to ensure that HIV-infected children will survive into adulthood. Data available on pediatric drug resistance demonstrate that failure occurs early in childhood. Studies of salvage drug options have been promising, but are primarily conducted in adults. Evidence-based approaches to regimen selection, pediatric antiretroviral formulations and expanded access to novel drugs are now required to prepare for the future.

Managing treatment-experienced pediatric and adolescent HIV patients: role of darunavir

Darunavir is currently the most recently approved HIV-1 protease inhibitor. It is approved for twice-daily dosing with ritonavir in treatment-experienced patients as young as 6 years of age and is available in numerous pill strengths. Emergence of darunavir-specific mutations is generally slow; therefore it can retain activity against viral strains that are resistant to other protease inhibitors, including tipranavir. Darunavir pharmacokinetics, clinical efficacy, resistance mutations and pharmacodynamics, and adverse effects are reviewed here. Substantial data support its use as a potent, well-tolerated option for salvage therapy in highly treatment-experienced children and adolescents.