title: Different cell death mechanisms are induced by a hydrophobic flavin in human tumor cells after visible light irradiation.
abstract: Riboflavin (RF) is an endogenous cell component and an efficient photosensitizer that can act by both types I and II photochemical mechanisms. Human tumor cells lines cultured in vitro, were used as model to study the effect of a photosensitizer synthesized from riboflavin, the 2',3',4',5'-riboflavin-tetrabutyrate (RTB), to increase the flavin concentration in the human promyelocytic leukemia cell line HL-60 and the human epithelial cervical cancer cell line HeLa. We demonstrate that this compound, alone or with Trp, has a toxic dose-response effect evidenced by abnormal cell morphology and a decrease in the cell proliferation rate. The mechanism of cell death was investigated and the experimental evidence indicates that it proceeds primarily via apoptosis; however, autophagy cannot be discarded. Nuclear fluorescent staining with Hoechst 33258 and transmission electron microscopy of the cells showed condensed chromatin margination at the nuclear periphery and the formation of apoptotic bodies. Furthermore, Caspase-3 activity was demonstrated in both cell lines. In addition, the characteristic apoptotic DNA ladder was observed in HL-60 cells. On the other hand, a high cytoplasmic vacuolization was observed by electron transmission and confocal microscopy. LysoTraker-red localization in the vacuoles was observed by fluorescence microscopy, and a significant decrease in the number of vacuoles and in the cell proliferation rate diminution was observed when irradiation was performed in the presence of the autophagy inhibitor 3-methyladenine. Considering that both cell death mechanisms have a dual role in the killing of tumor cells in vivo, a harmful effect that does not cause inflammation leading to tumor prophylaxis, we conclude that RTB could have potential clinical applications.
authors.affiliation: Facultad de Química, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 6094411, Chile.
authors.forename: Marcelo A
authors.initials: MA
authors.lastname: Muñoz
authors.forename: Ariadna
authors.initials: A
authors.lastname: Pacheco
authors.forename: María Inés
authors.initials: MI
authors.lastname: Becker
authors.forename: Eduardo
authors.initials: E
authors.lastname: Silva
authors.forename: Roberto
authors.initials: R
authors.lastname: Ebensperger
authors.forename: Angélica M
authors.initials: AM
authors.lastname: Garcia
authors.forename: Alfredo E
authors.initials: AE
authors.lastname: De Ioannes
authors.forename: Ana M
authors.initials: AM
authors.lastname: Edwards
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D001343:Autophagy / Q000187:drug effects / Q000528:radiation effects; D016923:Cell Death / Q000187:drug effects* / Q000528:radiation effects*; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D018922:HL-60 Cells; D006367:HeLa Cells; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008027:Light; D017319:Photosensitizing Agents / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use; D012256:Riboflavin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use; D012871:Skin Diseases / Q000188:drug therapy / Q000473:pathology
chemical_list: D017319:Photosensitizing Agents; C009175:riboflavin tetrabutyrate; D012256:Riboflavin