title: Kinetic uptake profiles of cell penetrating peptides in lymphocytes and monocytes.
abstract: BACKGROUND
  Nucleolar targeting peptides (NrTPs), resulting from structural minimization of the rattlesnake toxin crotamine, are a novel family of cell-penetrating peptides (CPPs) shown to internalize and deliver cargos into different cell types.
  
  
  METHODS
  In this study, we address NrTP kinetics of translocation into primary cells. We used flow cytometry to measure the intracellular uptake of rhodamine B-labeled NrTPs in peripheral blood mononucleated cells (PBMCs).
  
  
  RESULTS
  The kinetic profiles for each peptide are concentration-independent but significantly different among NrTPs, pointing out for the amino acid sequence importance. Arginine-containing peptides (NrTP7 and Tat48-60, used for comparison) were found to be more toxic than lysine-containing ones, as expected. On the other hand, one same peptide behaves differently in each of the lymphocyte and monocyte cell populations, suggesting differences in entry mechanism that in turn reflect diversity in cell functionality. Uptake results obtained at 4°C or using chemical endocytosis inhibitors support the importance of non-endocytic mechanisms in the cellular internalization of NrTP1 and NrTP5, while confirming endocytosis as the main mechanism of NrTPs entry.
  
  
  CONCLUSIONS
  Overall, both direct translocation and endocytosis mechanisms play a role in NrTP entry. Yet, there is predominance of endocytosis-mediated mechanisms. NrTPs (especially NrTP6) are an excellent intracellular delivery tool, with efficient internalization and no toxicity.
  
  
  CONCLUSIONS
  This work validates NrTPs as potential therapeutic tools for, e.g., cancer or inhibition of viral replication and establishes a new comparative and quantitative method to test CPP efficiency.
authors.affiliation: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisbon, Portugal.
authors.forename: Margarida
authors.initials: M
authors.lastname: Rodrigues
authors.forename: Beatriz G
authors.initials: BG
authors.lastname: de la Torre
authors.forename: David
authors.initials: D
authors.lastname: Andreu
authors.forename: Nuno C
authors.initials: NC
authors.lastname: Santos
mesh_terms: D057846:Cell-Penetrating Peptides / Q000378:metabolism*; D004705:Endocytosis; D006801:Humans; D007700:Kinetics; D008214:Lymphocytes / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism*
chemical_list: D057846:Cell-Penetrating Peptides
keywords: 6-aminohexanoic acid; AMP; Ahx; CPPs; CPZ; Cell penetrating peptide; FITC; FSC; HPLC; Kinetics; Lymphocyte; Monocyte; NrTPs; Nucleolar targeting peptide; PBMCs; RhB; SSC; Uptake; antimicrobial peptide; cell penetrating peptides; chlorpromazine; fluorescein isothiocyanate; forward scatter; high-performance liquid chromatography; nucleolar-targeting peptides; peripheral blood mononucleated cells; rhodamine B; side scatter