Intracellular Fates of Cell-Penetrating Block Copolypeptide Vesicles

The block copolypeptide poly(L-homoarginine)(60)-b-poly(L-leucine)(20) (R60L20) was previously found to self-assemble into versatile vesicles with controllable size and encapsulate hydrophilic cargo. These R60L20 vesicles also demonstrated ability to cross the cell membrane and transport encapsulated cargo into different cell lines. To assess the potential for using the R60L20 vesicles as drug delivery vehicles further, we have investigated their endocytosis and intracellular trafficking behavior. Using drugs that inhibit different endocytosis pathways, we identified macropinocytosis to be a major process by which the R60L20 vesicles enter HeLa cells. Subsequent immunostaining experiments demonstrated that the vesicles entered the early endosomes but not the lysosomes, suggesting that they recycle back to the cell surface. Overall, our studies indicate that the R60L20 vesicles are able to enter cells intact with their cargos, and although some manage to escape from early endosomes, most are trapped within these intracellular compartments.