title: Effect of photodynamic therapy in combination with ionizing radiation on human squamous cell carcinoma cell lines of the head and neck.
abstract: Photodynamic therapy (PDT) is a promising treatment modality for head and neck, and other tumours, using drugs activated by light. A second generation drug, 5-aminolaevulinic acid (5-ALA), is a precursor of the active photosensitizer protoporphyrin IX (PpIX) and has fewer side-effects and much more transient phototoxicity than previous photosensitizers. We have investigated the effect of 5-ALA mediated PDT in combination with gamma-irradiation on the colony forming ability of several human head and neck tumour cell lines. The effect of treatments on the DNA cell cycle kinetics was also investigated. Our results indicate that the combination of 5-ALA mediated PDT and gamma-irradiation results in a level of cytotoxicity which is additive and not synergistic. 5-ALA mediated PDT had no discernible effect on DNA cell cycle distributions. gamma-irradiation-induced cell cycle arrest in G2 did not enhance the phototoxicity of 5-ALA.
authors.affiliation: Research Department, Velindre Hospital, Whitchurch, Cardiff, CF14 2TL, Wales, UK.
authors.forename: R
authors.initials: R
authors.lastname: Allman
authors.forename: P
authors.initials: P
authors.lastname: Cowburn
authors.forename: M
authors.initials: M
authors.lastname: Mason
mesh_terms: D000622:Aminolevulinic Acid / Q000494:pharmacology; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000532:radiotherapy*; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D003131:Combined Modality Therapy; D004247:DNA / Q000187:drug effects / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D006258:Head and Neck Neoplasms / Q000188:drug therapy* / Q000532:radiotherapy*; D006801:Humans; D007700:Kinetics; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology; D011524:Protoporphyrins / Q000378:metabolism; D011839:Radiation, Ionizing; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: D017319:Photosensitizing Agents; D011524:Protoporphyrins; D000622:Aminolevulinic Acid; D004247:DNA; C028025:protoporphyrin IX