title: Photobleaching kinetics of optically trapped multilamellar vesicles containing verteporfin using two-photon excitation section sign.
abstract: Two-photon excitation photodynamic therapy (TPE-PDT) is being developed as an improved treatment for retinal diseases. TPE-PDT has advantages over one-photon PDT, including lower collateral damage to healthy tissue and more precise delivery of PDT. As with one-photon PDT, there can be local photochemical depletion of oxygen during TPE-PDT. Here, we investigate model systems and live cells to measure local photosensitizer photobleaching and through it, infer local oxygen consumption in therapeutic volumes of the order 1 microm3. Multilamellar vesicles (MLV) and African green monkey kidney (CV-1) cells were used to study the TPE photobleaching dynamics of the photosensitizer, Verteporfin. It was found that in an oxygen-rich environment, photobleaching kinetics could not be modeled using a mono-exponential function, whereas in hypoxic conditions a mono-exponential decay was adequate to represent photobleaching. A biexponential was found to adequately model the oxygen-rich conditions and it is hypothesized that the fast part of the decay is oxygen-dependent, whereas the slower rate constant is largely oxygen-independent. Photobleaching recovery studies in the CV-1 cells support this hypothesis.
authors.affiliation: Department of Chemistry, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Kimberley S
authors.initials: KS
authors.lastname: Samkoe
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Fecica
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Goyan
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Buchholz
authors.forename: Chantel
authors.initials: C
authors.lastname: Campbell
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Kelly
authors.forename: David T
authors.initials: DT
authors.lastname: Cramb
mesh_terms: D006801:Humans; D007700:Kinetics; D008081:Liposomes; D010100:Oxygen; D010778:Photochemotherapy; D017785:Photons; D011166:Porphyrins / Q000737:chemistry*; D012164:Retinal Diseases / Q000628:therapy; D000077362:Verteporfin
chemical_list: D008081:Liposomes; D011166:Porphyrins; D000077362:Verteporfin; D010100:Oxygen