title: Cellular uptake and intracellular degradation of poly(alkyl cyanoacrylate) nanoparticles.
abstract: BACKGROUND
  Poly(alkyl cyanoacrylate) (PACA) nanoparticles have shown promise as drug carriers both to solid tumors and across the blood-brain barrier. Efficient drug delivery requires both high cellular uptake of the nanoparticles and release of the drug from the nanoparticles. Release of hydrophobic drugs from PACA nanoparticles is primarily governed by nanoparticle degradation, and this process has been poorly studied at the cellular level. Here we use the hydrophobic model drug Nile Red 668 (NR668) to investigate intracellular degradation of PACA nanoparticles by measuring changes in NR668 fluorescence emission and lifetime, as the spectral properties of NR668 depend on the hydrophobicity of the dye environment. We also assess the potential of poly(butyl cyanoacrylate) (PBCA) and poly(octyl cyanoacrylate) (POCA) nanoparticles for intracellular drug delivery in the prostate cancer cell line PC3 and rat brain endothelial cell line RBE4 and the role of endocytosis pathways in PACA nanoparticle uptake in those cell lines.
  
  
  RESULTS
  Fluorescence lifetime imaging, emission spectra analysis and Förster resonance energy transfer indicated that the intracellular degradation was in line with the degradation found by direct methods such as gas chromatography and scanning electron microscopy, showing that PBCA has a faster degradation rate compared to POCA. The combined P(BCA/OCA) nanoparticles had an intermediate degradation rate. The uptake of POCA and PBCA nanoparticles was much higher in RBE4 than in PC3 cells. Endocytosis inhibition studies showed that both clathrin- and caveolin-mediated endocytosis were involved in PACA nanoparticle uptake, and that the former played a predominant role, particularly in PC3 cells.
  
  
  CONCLUSIONS
  In the present study, we used three different optical techniques to show that within a 24-hour period PBCA nanoparticles degraded significantly inside cells, releasing their payload into the cytosol, while POCA nanoparticles remained intact. This indicates that it is possible to tune the intracellular drug release rate by choosing appropriate monomers from the PACA family or by using hybrid PACA nanoparticles containing different monomers. In addition, we showed that the uptake of PACA nanoparticles depends not only on the monomer material, but also on the cell type, and that different cell lines can use different internalization pathways.
authors.affiliation: Department of Physics, The Norwegian University of Science and Technology, NTNU, Høgskoleringen 5, 7491, Trondheim, Norway. einar.sulheim@ntnu.no.
authors.forename: Einar
authors.initials: E
authors.lastname: Sulheim
authors.affiliation: Department of Physics, The Norwegian University of Science and Technology, NTNU, Høgskoleringen 5, 7491, Trondheim, Norway. habib.baghirov@ntnu.no.
authors.forename: Habib
authors.initials: H
authors.lastname: Baghirov
authors.affiliation: Department of Physics, The Norwegian University of Science and Technology, NTNU, Høgskoleringen 5, 7491, Trondheim, Norway. eva.hartman@abo.fi.|Pharmaceutical Sciences Laboratory, Faculty of Natural Sciences and Technology, Åbo Akademi University, Turku, Finland. eva.hartman@abo.fi.
authors.forename: Eva
authors.initials: E
authors.lastname: von Haartman
authors.affiliation: Department of Physics, The Norwegian University of Science and Technology, NTNU, Høgskoleringen 5, 7491, Trondheim, Norway. andreas.boe@spfr.no.
authors.forename: Andreas
authors.initials: A
authors.lastname: Bøe
authors.affiliation: Department of Physics, The Norwegian University of Science and Technology, NTNU, Høgskoleringen 5, 7491, Trondheim, Norway. Andreas.aslund@ntnu.no.
authors.forename: Andreas K O
authors.initials: AK
authors.lastname: Åslund
authors.affiliation: SINTEF Materials and Chemistry, Trondheim, Norway. yrr.morch@sintef.no.
authors.forename: Yrr
authors.initials: Y
authors.lastname: Mørch
authors.affiliation: Department of Physics, The Norwegian University of Science and Technology, NTNU, Høgskoleringen 5, 7491, Trondheim, Norway. catharina.davies@ntnu.no.
authors.forename: Catharina de Lange
authors.initials: Cde L
authors.lastname: Davies
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D045744:Cell Line, Tumor; D003487:Cyanoacrylates / Q000378:metabolism*; D004337:Drug Carriers / Q000378:metabolism; D016503:Drug Delivery Systems / Q000379:methods; D065546:Drug Liberation / Q000502:physiology; D004705:Endocytosis / Q000502:physiology; D005453:Fluorescence; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008297:Male; D053758:Nanoparticles / Q000378:metabolism*; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism; D051381:Rats
chemical_list: D003487:Cyanoacrylates; D004337:Drug Carriers; D004364:Pharmaceutical Preparations