title: Effects of combined photodynamic therapy and ionizing radiation on human glioma spheroids.
abstract: The effects of combined photodynamic therapy (PDT) and ionizing radiation are studied in a human glioma spheroid model. The degree of interaction between the two modalities depends in a complex manner on factors such as PDT irradiation fluence, fluence rate and dose of ionizing radiation. It is shown that gamma radiation and PDT interact in a synergistic manner only if both light fluence and gamma radiation dose exceed approximately 25 J cm(-2) and 8 Gy, respectively. Synergistic interactions are observed only for the lower fluence rate (25 mW cm(-2)) investigated. The degree of interaction appears to be independent of both sequence and the PDT or ionizing radiation time intervals investigated (1 and 24 h). Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assays show that low-fluence rate PDT is very efficient at inducing apoptotic cell death, whereas neither high-fluence rate PDT nor ionizing radiation produces significant apoptosis. Although the mechanisms remain to be elucidated, the data imply that the observed synergism is likely not due to gamma-induced cell cycle arrest or to PDT-induced inhibition of DNA repair.
authors.affiliation: steenm@ccmail.nevada.edu
authors.forename: Steen J
authors.initials: SJ
authors.lastname: Madsen
authors.forename: Chung-Ho
authors.initials: CH
authors.lastname: Sun
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Tromberg
authors.forename: Alvin T
authors.initials: AT
authors.lastname: Yeh
authors.forename: Rogelio
authors.initials: R
authors.lastname: Sanchez
authors.forename: Henry
authors.initials: H
authors.lastname: Hirschberg
mesh_terms: D001932:Brain Neoplasms / Q000473:pathology*; D005720:Gamma Rays; D005909:Glioblastoma / Q000473:pathology*; D006801:Humans; D008954:Models, Biological; D010778:Photochemotherapy; D014407:Tumor Cells, Cultured