TAT peptide on the surface of liposomes affords their efficient intracellular delivery even at low temperature and in the presence of metabolic inhibitors

To achieve an efficient intracellular drug and DNA delivery, attempts were made to target microparticulate drug carriers into cytoplasm bypassing the endocytotic pathway. TAT peptides derived from the HIV-1 TAT protein facili tate intracellular delivery of proteins and small colloidal particles. We d emonstrated that relatively large drug carriers, such as 200-nm liposomes, can also be delivered into cells by TAT peptide attached to the liposome su rface. Liposomes were fluorescently labeled with membranotropic rhodamine-p hosphatidylethanolamine or by entrapping FITC-dextran. Incubation of fluore scent TAT liposomes with mouse Lewis lung carcinoma cells, human breast tum or BT20 cells, and rat cardiac myocyte H9C2 results in intracellular locali zation of certain liposomes. Steric hindrances for TAT peptide-cell interac tion (attachment of TAT directly to the liposome surface without spacer or the presence of a high MW polyethylene glycol on the liposome surface) abol ish liposome internalization, evidencing the importance of direct contact o f TAT peptide with the cell surface. Low temperature or metabolic inhibitor s, sodium azide or iodoacetamide, have little influence on the translocatio n of TAT liposomes into cells, confirming the energy-independent character of this process. The approach may have important implications for drug deli very directly into cell cytoplasm.