Abstract Background Maraviroc (MVC) and other CCR5 antagonists are HIV-1 entry inhibitors that bind to- and alter the conformation of CCR5, such that CCR5 is no longer recognized by the viral gp120 envelope (Env) glycoproteins. Resistance to CCR5 antagonists results from HIV-1 Env acquiring the ability to utilize the drug-bound conformation of CCR5. Selecting for HIV-1 resistance to CCR5-antagonists in vitro is relatively difficult. However, the CCR5-using CC1/85 strain appears to be uniquely predisposed to acquiring resistance to several CCR5 antagonists in vitro including MVC, vicriviroc and AD101. Findings Here, we show that Env derived from the parental CC1/85 strain is inherently capable of a low affinity interaction with MVC-bound CCR5. However, this phenotype was only revealed in 293-Affinofile cells and NP2-CD4/CCR5 cells that express very high levels of CCR5, and was masked in TZM-bl, JC53 and U87-CD4/CCR5 cells as well as PBMC, which express comparatively lower levels of CCR5 and which are more commonly used to detect resistance to CCR5 antagonists. Conclusions Env derived from the CC1/85 strain of HIV-1 is inherently capable of a low-affinity interaction with MVC-bound CCR5, which helps explain the relative ease in which CC1/85 can acquire resistance to CCR5 antagonists in vitro. The detection of similar phenotypes in patients may identify those who could be at higher risk of virological failure on MVC.

Abstract Background The CCR5 antagonist maraviroc (MVC) inhibits human immunodeficiency virus type 1 (HIV-1) entry by altering the CCR5 extracellular loops (ECL), such that the gp120 envelope glycoproteins (Env) no longer recognize CCR5. The mechanisms of HIV-1 resistance to MVC, the only CCR5 antagonist licensed for clinical use are poorly understood, with insights into MVC resistance almost exclusively limited to knowledge obtained from in vitro studies or from studies of resistance to other CCR5 antagonists. To more precisely understand mechanisms of resistance to MVC in vivo, we characterized Envs isolated from 2 subjects who experienced virologic failure on MVC. Results Envs were cloned from subjects 17 and 24 before commencement of MVC (17-Sens and 24-Sens) and after virologic failure (17-Res and 24-Res). The Envs cloned during virologic failure showed broad divergence in resistance levels, with 17-Res Env exhibiting a relatively high maximal percent inhibition (MPI) of ~90% in NP2-CD4/CCR5 cells and peripheral blood mononuclear cells (PBMC), and 24-Res Env exhibiting a very low MPI of ~0 to 12% in both cell types, indicating relatively “weak” and “strong” resistance, respectively. Resistance mutations were strain-specific and mapped to the gp120 V3 loop. Affinity profiling by the 293-Affinofile assay and mathematical modeling using VERSA (Viral Entry Receptor Sensitivity Analysis) metrics revealed that 17-Res and 24-Res Envs engaged MVC-bound CCR5 inefficiently or very efficiently, respectively. Despite highly divergent phenotypes, and a lack of common gp120 resistance mutations, both resistant Envs exhibited an almost superimposable pattern of dramatically increased reliance on sulfated tyrosine residues in the CCR5 N-terminus, and on histidine residues in the CCR5 ECLs. This altered mechanism of CCR5 engagement rendered both the resistant Envs susceptible to neutralization by a sulfated peptide fragment of the CCR5 N-terminus. Conclusions Clinical resistance to MVC may involve divergent Env phenotypes and different genetic alterations in gp120, but the molecular mechanism of resistance of the Envs studied here appears to be related. The increased reliance on sulfated CCR5 N-terminus residues suggests a new avenue to block HIV-1 entry by CCR5 N-terminus sulfopeptidomimetic drugs.