title: Uptake of ricinB-quantum dot nanoparticles by a macropinocytosis-like mechanism.
abstract: BACKGROUND
  There is a huge effort in developing ligand-mediated targeting of nanoparticles to diseased cells and tissue. The plant toxin ricin has been shown to enter cells by utilizing both dynamin-dependent and -independent endocytic pathways. Thus, it is a representative ligand for addressing the important issue of whether even a relatively small ligand-nanoparticle conjugate can gain access to the same endocytic pathways as the free ligand.
  
  
  RESULTS
  Here we present a systematic study concerning the internalization mechanism of ricinB:Quantum dot (QD) nanoparticle conjugates in HeLa cells. Contrary to uptake of ricin itself, we found that internalization of ricinB:QDs was inhibited in HeLa cells expressing dominant-negative dynamin. Both clathrin-, Rho-dependent uptake as well as a specific form of macropinocytosis involve dynamin. However, the ricinB:QD uptake was not affected by siRNA-mediated knockdown of clathrin or inhibition of Rho-dependent uptake caused by treating cells with the Clostridium C3 transferase. RicinB:QD uptake was significantly reduced by cholesterol depletion with methyl-β-cyclodextrin and by inhibitors of actin polymerization such as cytochalasin D. Finally, we found that uptake of ricinB:QDs was blocked by the amiloride analog EIPA, an inhibitor of macropinocytosis. Upon entry, the ricinB:QDs co-localized with dextran, a marker for fluid-phase uptake. Thus, internalization of ricinB:QDs in HeLa cells critically relies on a dynamin-dependent macropinocytosis-like mechanism.
  
  
  CONCLUSIONS
  Our results demonstrate that internalization of a ligand-nanoparticle conjugate can be dependent on other endocytic mechanisms than those used by the free ligand, highlighting the challenges of using ligand-mediated targeting of nanoparticles-based drug delivery vehicles to cells of diseased tissues.
authors: Centre for Cancer Biomedicine, Faculty Division Norwegian Radium Hospital, University of Oslo, Oslo, Norway. toregi@rr-research.no
authors: Tore Geir
authors: TG
authors: Iversen
authors: Nadine
authors: N
authors: Frerker
authors: Kirsten
authors: K
authors: Sandvig
mesh_terms: D000199:Actins / Q000378:metabolism; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D002784:Cholesterol / Q000172:deficiency / Q000378:metabolism; D002966:Clathrin / Q000378:metabolism; D034281:Dynamins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D053758:Nanoparticles / Q000737:chemistry*; D010873:Pinocytosis / Q000187:drug effects; D045663:Quantum Dots; D012276:Ricin / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D000199:Actins; D002966:Clathrin; D000584:Amiloride; D012276:Ricin; D002784:Cholesterol; D020742:rhoA GTP-Binding Protein; D034281:Dynamins; C039614:ethylisopropylamiloride