title: Deep-penetrating photodynamic therapy with KillerRed mediated by upconversion nanoparticles.
abstract: The fluorescent protein KillerRed, a new type of biological photosensitizer, is considered as a promising substitute for current synthetic photosensitizes used in photodynamic therapy (PDT). However, broad application of this photosensitiser in treating deep-seated lesions is challenging due to the limited tissue penetration of the excitation light with the wavelength falling in the visible spectral range. To overcome this challenge, we employ upconversion nanoparticles (UCNPs) that are able to convert deep-penetrating near infrared (NIR) light to green light to excite KillerRed locally, followed by the generation of reactive oxygen species (ROS) to kill tumour cells under centimetre-thick tissue. The photosensitizing bio-nanohybrids, KillerRed-UCNPs, are fabricated through covalent conjugation of KillerRed and UCNPs. The resulting KillerRed-UCNPs exhibit excellent colloidal stability in biological buffers and low cytotoxicity in the dark. Cross-comparison between the conventional KillerRed and UCNP-mediated KillerRed PDT demonstrated superiority of KillerRed-UCNPs photosensitizing by NIR irradiation, manifested by the fact that ∼70% PDT efficacy was achieved at 1-cm tissue depth, whereas that of the conventional KillerRed dropped to ∼7%.
  
  
  
  KillerRed is a protein photosensitizer that holds promise as an alternative for the existing hydrophobic photosensitizers that are widely used in clinical photodynamic therapy (PDT). However, applications of KillerRed to deep-seated tumours are limited by the insufficient penetration depth of the excitation light in highly scattering and absorbing biological tissues. Herein, we reported the deployment of upconversion nanoparticles (UCNPs) to enhance the treatment depth of KillerRed by converting the deep-penetrating near-infrared (NIR) light to upconversion photoluminescence and activating the PDT effect of KillerRed under deep tissues. This work demonstrated clear potential of UCNPs as the NIR-to-visible light converter to overcome the light penetration limit that has plagued PDT application for many years.
authors.affiliation: ARC Centre of Excellence for Nanoscale BioPhotonics, Macquarie University, North Ryde, Sydney, NSW 2109, Australia; Department of Biomedical Sciences, Macquarie University, North Ryde, Sydney, NSW 2109, Australia.
authors.forename: Liuen
authors.initials: L
authors.lastname: Liang
authors.affiliation: ARC Centre of Excellence for Nanoscale BioPhotonics, Macquarie University, North Ryde, Sydney, NSW 2109, Australia; Department of Physics and Astronomy, Macquarie University, North Ryde, Sydney, NSW 2109, Australia.
authors.forename: Yiqing
authors.initials: Y
authors.lastname: Lu
authors.affiliation: ARC Centre of Excellence for Nanoscale BioPhotonics, Macquarie University, North Ryde, Sydney, NSW 2109, Australia. Electronic address: run.zhang@mq.edu.au.
authors.forename: Run
authors.initials: R
authors.lastname: Zhang
authors.affiliation: ARC Centre of Excellence for Nanoscale BioPhotonics, Macquarie University, North Ryde, Sydney, NSW 2109, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Care
authors.affiliation: Department of Physics and Astronomy, Macquarie University, North Ryde, Sydney, NSW 2109, Australia.
authors.forename: Tiago A
authors.initials: TA
authors.lastname: Ortega
authors.affiliation: Shemyakin & Ovchinnikov Institute of Bioorganic Chemistry of the Russian Academy of Sciences, Moscow 117997, Russia; National Research Tomsk Polytechnic University, Tomsk 634050, Russia.
authors.forename: Sergey M
authors.initials: SM
authors.lastname: Deyev
authors.affiliation: Department of Biomedical Sciences, Macquarie University, North Ryde, Sydney, NSW 2109, Australia.
authors.forename: Yi
authors.initials: Y
authors.lastname: Qian
authors.affiliation: ARC Centre of Excellence for Nanoscale BioPhotonics, Macquarie University, North Ryde, Sydney, NSW 2109, Australia; Department of Physics and Astronomy, Macquarie University, North Ryde, Sydney, NSW 2109, Australia; Laboratory of Optical Theranostics, N. I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod 603950, Russia; Institute for Regenerative Medicine, Sechenov First Moscow State Medical University, Moscow 119991, Russia. Electronic address: andrei.zvyagin@mq.edu.au.
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Zvyagin
mesh_terms: D045744:Cell Line, Tumor; D002470:Cell Survival; D004705:Endocytosis; D004735:Energy Transfer; D049452:Green Fluorescent Proteins / Q000627:therapeutic use*; D006801:Humans; D018613:Microscopy, Confocal; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D010778:Photochemotherapy; D017382:Reactive Oxygen Species / Q000378:metabolism; D019265:Spectroscopy, Near-Infrared
chemical_list: D017382:Reactive Oxygen Species; C508771:killer red protein, Anthomedusae; D049452:Green Fluorescent Proteins
keywords: Energy transfer; Photodynamic therapy; Photosensitizing protein; Reactive oxygen species; Upconversion nanoparticles