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FRET-CR9. The efficiency of FRET-CDR9may be due to improved resistance againstdegradative enzymes. Figure 2 shows theconfocal microscope images of cells treatedwith FRET-CDR9. The time-course resultscoincided well with that of cellular uptake(Figure 1).When cellular uptake was examined byFACS using FRET-CDR9 at 4°C, a slightintracellular fluorescence was detected.Interestingly, when cells were incubated at20°C or hyperthermia-treated cells (42°C for1 h) were used, uptake of FRET-CDR9increased linearly, and the decrease offluorescence intensity was not observed.From these results, it is most likely that thedecrease of intracellular fluorescence after aprolonged time (~90 min) is attributable toelimination by exclusion processes such asexocytosis or metabolism.The cellular uptake of FRET-CDR9 waseffectively inhibited by the macropinocytosisinhibitor, EPIA (50 µM), but not bychlorpromazine (30 µM) which is aninhibitor of clathrin-mediated endocytosis.Fluorescence intensity14001200100080060040020000 15 30 45 60 75 90incubation time (min)Fig. 1. Cellular uptake of FRET-peptides inJurkat cells. Cells were incubated at 37°Cwith FRET-CR9 (▲), rev-FRET-CR9 ()and FRET-CDR9 (•).Under conditions of 10% FBS (but not FBS free conditions), methyl-β-cyclodextrin(2 mM) inhibited the cellular uptake. These results suggest that the FRET-peptide wasdelivered into cells mainly via a macropinocytosis mechanism, and partially via caveolaemediatedendocytosis. Under the FBS-free conditions, non-endocytic direct translocationwould partially participate in cellular uptake of the FRET-peptide.5 min 10 min 20 minFig. 2. Confocal microscopic appearance of FRET-CDR9 (5 µM) internalization at 37°C.Jurkat cells were incubated in 10% FBS/RPMI-1640 under 5% CO 2 . The fluorescencesignals were detected by excitation at 499 nm using a 519 nm emission filter.ConclusionIn conclusion, the present study demonstrated the utility of FRET-nonaarginine peptides,especially FRET-CDR9, to investigate mechanisms of cellular uptake of oligoargininepeptides. The FRET-peptide was delivered into Jurkat cells efficiently. Kinetic studiesusing FRET-CDR9 revealed that fluorescein-labeled cargo peptide was delivered mainly bymacropinocytosis into the cells. The intracellularly delivered peptides are probablyexcluded from cells or metabolized after prolonged periods.References1. Fonseca, S.B., Pereira, M.P., Kelley, S.O. Adv. Deliv. Rev. 61, 953-964 (2009).2. Schmidt, N., Mishra, A., Lai, G.H., Wong, G.C. FEBS Lett. 584, 1806-1813 (2010).521