Improvement of HIV fusion inhibitor C34 efficacy by membrane anchoring and enhanced exposure

The aim of the present work was to evaluate the interaction of two new HIV fusion inhibitors {HIVP3 [C34polyethylene glycol (PEG)(4)cholesterol] and HIVP4 [(C34PEG(4))(2)cholesterol]} with membrane model systems and human blood cells in order to clarify where and how the fusion inhibitors locate, allowing us to understand their mechanism of action at the molecular level, and which strategies may be followed to increase efficacy. Lipid vesicles with defined compositions were used for peptide partition and localization studies, based on the intrinsic fluorescence of HIVP3 and HIVP4. Lipid monolayers were employed in surface pressure studies. Finally, human erythrocytes and peripheral blood mononuclear cells (PBMCs) isolated from blood samples were used in dipole potential assays. Membrane partition, dipole potential and surface pressure assays indicate that the new fusion inhibitors interact preferentially with cholesterol-rich liquid-ordered membranes, mimicking biological membrane microdomains known as lipid rafts. HIVP3 and HIVP4 are able to interact with human erythrocytes and PBMCs to a similar degree as a previously described simpler drug with monomeric C34 and lacking the PEG spacer, C34cholesterol. However, the pocket-binding domain (PBD) of both HIVP3 and HIVP4 is more exposed to the aqueous environment than in C34cholesterol. The present data allow us to conclude that more efficient blocking of HIV entry results from the synergism between the membranotropic behaviour and the enhanced exposure of the PBD.