title: The use of inhibitors to study endocytic pathways of gene carriers: optimization and pitfalls.
abstract: Nonviral gene complexes can enter mammalian cells through different endocytic pathways. For efficient optimization of the gene carrier it is important to profile its cellular uptake, because this largely determines its intracellular processing and subsequent transfection efficiency. Most of the current information on uptake of these gene-delivery vehicles is based on data following the use of chemical inhibitors of endocytic pathways. Here, we have performed a detailed characterization of four commonly used endocytosis inhibitors [chlorpromazine, genistein, methyl-beta-cyclodextrin (MbetaCD), and potassium depletion] on cell viability and endocytosis in five well-described cell lines. We found that chlorpromazine and to a lesser extent MbetaCD significantly decreased cell viability of some cell lines even after short incubation periods and at concentrations that are routinely used to inhibit endocytosis. Through analyzing the uptake and subcellular distribution of two fluorescent endocytic probes transferrin and lactosylceramide (LacCer) that are reported to enter cells via clathrin-dependent (CDE) and clathrin-independent (CIE) mechanisms, respectively, we showed poor specificity of these agents for inhibiting distinct endocytic pathways. Finally, we demonstrate that any inhibitory effects are highly cell line dependent. Overall, the data question the significance of performing endocytosis studies with these agents in the absence of very stringent controls.
authors.affiliation: Laboratory of General Biochemistry and Physical Pharmacy, Department of Pharmaceutics, Ghent University, Ghent, Belgium.
authors.forename: Dries
authors.initials: D
authors.lastname: Vercauteren
authors.forename: Roosmarijn E
authors.initials: RE
authors.lastname: Vandenbroucke
authors.forename: Arwyn T
authors.initials: AT
authors.lastname: Jones
authors.forename: Joanna
authors.initials: J
authors.lastname: Rejman
authors.forename: Joseph
authors.initials: J
authors.lastname: Demeester
authors.forename: Stefaan C
authors.initials: SC
authors.lastname: De Smedt
authors.forename: Niek N
authors.initials: NN
authors.lastname: Sanders
authors.forename: Kevin
authors.initials: K
authors.lastname: Braeckmans
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000737:chemistry; D019556:COS Cells; D002470:Cell Survival; D002522:Chlorocebus aethiops; D002966:Clathrin / Q000737:chemistry; D004705:Endocytosis; D005456:Fluorescent Dyes / Q000494:pharmacology; D018014:Gene Transfer Techniques; D005822:Genetic Vectors; D006801:Humans; D007790:Lactosylceramides / Q000737:chemistry; D008856:Microscopy, Fluorescence / Q000379:methods; D008957:Models, Genetic; D014168:Transferrin / Q000737:chemistry; D047392:beta-Cyclodextrins / Q000737:chemistry
chemical_list: D015703:Antigens, CD; D002966:Clathrin; D005456:Fluorescent Dyes; D007790:Lactosylceramides; D014168:Transferrin; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; C009744:CDw17 antigen