Antiviral synergy between the CCR5 mAb PRO 140 and small-molecule CCR5 antagonists
Introduction: PRO 140 is a humanized monoclonal antibody (mAb) to CCR5, which serves as the major fusion coreceptor for HIV-1. Currently in Phase 1 human testing, PRO 140 broadly and potently inhibits R5 HIV-1 without CCR5 antagonism. In the present studies, we examined the in vitro inhibitory interactions between PRO 140 and small-molecule CCR5 antagonists, including SCH-C, SCH-D and TAK-779, as well as with the only approved entry inhibitor, T-20 (Fuzeon). The studies could have utility in the design of clinical trials that examine combinations of entry inhibitors.
Methods: In order to study the combination effects of inhibitors on HIV-1 entry, we have utilized a fluorescence resonance energy transfer (RET) assay that measures the fusion of effector HeLa cells expressing HIV-1 JR-FL env glycoproteins to target HeLa cells expressing CD4 and CCR5 (Litwin et al., J. Virol. 70:6437). This assay faithfully recapitulates each stage of the HIV-1 entry process. Confirmatory assays examined inhibition of single-cycle, luciferase-encoding HIV-1 pseudoviruses complemented with env from additional HIV-1 isolates. Inhibition data were analyzed for cooperativity using the Combination Index method.
Results: PRO 140 exhibited potent and reproducible synergy with small-molecule CCR5 antagonists and with T-20. Synergies routinely translated into 5- to 10-fold dose reductions, suggesting significant improvement in inhibitory potency for the drug combinations. In contrast, purely additive effects were observed for combinations of small-molecule CCR5 antagonists. The findings may reflect the patterns of CCR5 recognition: Whereas small-molecule CCR5 antagonists bind a common hydrophobic pocket defined by the transmembrane regions of CCR5, PRO 140 recognizes an extracellular epitope that spans multiple hydrophilic domains.
Conclusions: PRO 140 inhibits HIV-1 entry synergistically with small-molecule CCR5 antagonists and with T-20. The findings support the use of PRO 140 in combination with other HIV-1 entry inhibitors and suggest that PRO 140 represents a distinct CCR5 inhibitor subclass.
The 3rd IAS Conference on HIV Pathogenesis and Treatment
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Antiviral synergy between the CCR5 mAb PRO 140 and small-molecule CCR5 antagonists.
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