title: Inhibition of autophagosome formation by the benzoporphyrin derivative verteporfin.
abstract: Autophagy enables cells to degrade and recycle cytoplasmic materials both as a housekeeping mechanism and in response to extracellular stress such as nutrient deprivation. Recent studies indicate that autophagy also functions as a protective mechanism in response to several cancer therapy agents, making it a prospective therapeutic target. Few pharmacological inhibitors suitable for testing the therapeutic potential of autophagy inhibition in vivo are known. An automated microscopy assay was used to screen >3,500 drugs and pharmacological agents and identified one drug, verteporfin, as an inhibitor of autophagosome accumulation. Verteporfin is a benzoporphyrin derivative used in photodynamic therapy, but it inhibits autophagy without light activation. Verteporfin did not inhibit LC3/Atg8 processing or membrane recruitment in response to autophagic stimuli, but it inhibited drug- and starvation-induced autophagic degradation and the sequestration of cytoplasmic materials into autophagosomes. Transient exposure to verteporfin in starvation conditions reduced cell viability whereas cells in nutrient-rich medium were unaffected by drug treatment. Analysis of structural analogs indicated that the activity of verteporfin requires the presence of a substituted cyclohexadiene at ring A of the porphyrin core but that it can tolerate a number of large substituents at rings C and D. The existence of an autophagy inhibitor among FDA-approved drugs should facilitate the investigation of the therapeutic potential of autophagy inhibition in vivo.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Donohue
authors.forename: Andrew
authors.initials: A
authors.lastname: Tovey
authors.forename: A Wayne
authors.initials: AW
authors.lastname: Vogl
authors.forename: Steve
authors.initials: S
authors.lastname: Arns
authors.forename: Ethan
authors.initials: E
authors.lastname: Sternberg
authors.forename: Robert N
authors.initials: RN
authors.lastname: Young
authors.forename: Michel
authors.initials: M
authors.lastname: Roberge
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology*; D001343:Autophagy / Q000187:drug effects* / Q000502:physiology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D003911:Dextrans / Q000493:pharmacokinetics; D015195:Drug Design; D005260:Female; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D049452:Green Fluorescent Proteins / Q000493:pharmacokinetics; D006801:Humans; D008854:Microscopy, Electron; D010588:Phagosomes / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D011166:Porphyrins / Q000737:chemistry / Q000494:pharmacology*; D000077362:Verteporfin
chemical_list: D000970:Antineoplastic Agents; D003911:Dextrans; D011166:Porphyrins; C485184:enhanced green fluorescent protein; C015219:fluorescein isothiocyanate dextran; D000077362:Verteporfin; D049452:Green Fluorescent Proteins; D016650:Fluorescein-5-isothiocyanate