16th International HIV Drug Resistance Workshop 12-16 June 2007, Barbados

CCR5 BINDING PROPERTIES OF A CCR5 SMALL-MOLECULE INHIBITOR WITH HIGH ANTIVIRAL POTENCY AGAINST A MARAVIROC-RESISTANT HIV-1 STRAIN

Antivir Ther. 2007; 12:S13 (abstract no. 11)

A Jekle, R Kondru, C Ji, K-T Chuang, DC Swinney, D Rotstein, S Sankuratri, N Cammack and G Heilek
Viral Diseases, Roche Palo Alto LLC, Palo Alto, CA, USA

BACKGROUND: CCR5 inhibitors are in clinical development as promising treatment options for HIV-1 infection. We studied whether the antiviral potency of a CCR5 inhibitor against a maraviroc-resistant virus can be explained by subtle differences in the ligand-receptor interactions.

METHODS: A maraviroc-resistant virus was selected by in vitro passaging of the CCR5-tropic virus CC1/85 in peripheral blood mononuclear cells (PBMC). The resulting maraviroc-resistant virus was analysed for susceptibility to inhibitors in a PBMC infection assay. Specific binding interactions and kinetics were determined with wild-type and mutant CCR5 receptors using competitive binding methods with ³H-maraviroc as radioligand.

RESULTS: Passaging of CC1/85 in presence of maraviroc resulted in a maraviroc- and vicriviroc-resistant virus (CC1/85_MVRres). The maraviroc and vicriviroc IC₅₀ for CC1/85_MVRres was shifted more than 8,000- and 12,000-fold compared to a control virus. In contrast, fusion inhibitors, CCR5 antibodies as well as the CCR5 small-molecule inhibitor RO1752 retained potent antiviral activity. Receptor mutation data to model receptor–ligand interactions suggest that maraviroc and RO1752 share the same binding site. However, the nature of specific interactions within the site is different. Specific interactions of antagonists within the site stabilize conformations of the receptor that are not recognized by wild-type HIV-1. The conformational changes are associated with slower binding kinetics due to the energy barriers associated with the conformational changes. We observed that the dynamics of maraviroc binding are distinct from RO1752. Mutation of residues Y108 on helix III and Y251 on helix VI to alanine eliminated the time-dependent binding for maraviroc, but not for RO1752.

CONCLUSION: 1) A maraviroc-resistant virus was selected by in vitro passaging. 2) This virus is highly resistant to maraviroc and vicriviroc. 3) CCR5 small-molecule inhibitors with good antiviral potency against the maraviroc-resistant virus can be engineered. 4) Based on kinetic data from mutant receptor-binding-experiments, we propose that binding of inhibitors to CCR5 changes the receptor conformation. Distinct differences in the binding dynamics of individual inhibitors translate into differences in the receptor conformation. Inhibitors with antiviral potency cause conformations that can are not recognized by wildtype HIV-1. Resistant viruses learned to bind to conformations of inhibitor-bound receptors.

2007-06-12
11

Copyright © 2006 - 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.