Cooperative membrane retention: How does β-CMCD coating enhance cationic liposome association with cells?

Associationof cationic liposomes to cells is not governed by their mean surface charge alone. Using flow cytometry and confocal microscopy, we show that coating DOTAP/DOPC liposomes with anionic carboxymethyl-β-cyclodextrin (β-CMCD) increases cell association: the fraction of liposome-associated cells rises from 35% to 45% for MSC and from 59% to 65% for MDA-MB-231 cells, with a shift from peripheral to more volume-coupled accumulation in cancer cells. Based on an energy-based model, we attribute this enhancement to the formation of a rough, patchy, multivalent β-CMCD shell. Despite partial screening of the average positive charge, local contact amplification by protrusions, charge-patch matching, cooperative surface accumulation and secondary cyclodextrin-lipid contacts outweigh the electrostatic loss. This resolves the apparent paradox: β-CMCD-coated liposomes show greater association with model membranes and cells than bare cationic liposomes despite their lower electrophoretic mobility.