title: Pharmacokinetics, Safety, and Efficacy of Intravitreal Digoxin in Preclinical Models for Retinoblastoma.
abstract: OBJECTIVE
  To assess in vitro cytotoxic activity and antiangiogenic effect, ocular and systemic disposition, and toxicity of digoxin in rabbits after intravitreal injection as a potential candidate for retinoblastoma treatment.
  
  
  METHODS
  A panel of two retinoblastoma and three endothelial cell types were exposed to increasing concentrations of digoxin in a conventional (72-hour exposure) and metronomic (daily exposure) treatment scheme. Cytotoxicity was defined as the digoxin concentration that killed 50% of the cells (IC50) and was assessed with a vital dye in all cell types. Induction of apoptosis and cell-cycle status were evaluated by flow cytometry after both treatment schemes. Ocular and systemic disposition after intravitreal injection as well as toxicity was assessed in rabbits. Electroretinograms (ERGs) were recorded before and after digoxin doses and histopathological examinations were performed after enucleation.
  
  
  RESULTS
  Digoxin was cytotoxic to retinoblastoma and endothelial cells under conventional and metronomic treatment. IC50 was comparable between both schedules and induced apoptosis in all cell lines. Calculated vitreous digoxin Cmax was 8.5 μg/mL and the levels remained above the IC50 for at least 24 hours after intravitreal injection. Plasma digoxin concentration was below 0.5 ng/ml. Retinal toxicity was evident after the third intravitreal dose with considerable changes in the ERG and histologic damage to the retina.
  
  
  CONCLUSIONS
  Digoxin has antitumor activity for retinoblastoma while exerting antiangiogenic activity in vitro at similar concentrations. Metronomic treatment showed no advantage in terms of dose for cytotoxic effect. Four biweekly injections of digoxin led to local toxicity to the retina but no systemic toxicity in rabbits.
authors.affiliation: Clinical Pharmacokinetics Unit, Hospital de Pediatría J.P. Garrahan, Ciudad Autonoma de Buenos Aires (CABA), Buenos Aires, Argentina 2Consejo Nacional de Investigaciones Cientificas y Tecnicas, Consejo Nacional de Investigaciones Científicas y Técnicas (C.
authors.forename: Ursula
authors.initials: U
authors.lastname: Winter
authors.affiliation: Clinical Pharmacokinetics Unit, Hospital de Pediatría J.P. Garrahan, Ciudad Autonoma de Buenos Aires (CABA), Buenos Aires, Argentina.
authors.forename: Emiliano
authors.initials: E
authors.lastname: Buitrago
authors.affiliation: Experimental Thrombosis Laboratory, Instituto de Medicina Experimental (IMEX), National Academy of Medicine, CABA, Buenos Aires, Argentina.
authors.forename: Hebe A
authors.initials: HA
authors.lastname: Mena
authors.affiliation: Pharmacology Laboratory, Faculty of Veterinary, National University of the Center of Buenos Aires, Tandil, Buenos Aires, Argentina.
authors.forename: Maria José
authors.initials: MJ
authors.lastname: Del Sole
authors.affiliation: Clinical Pharmacokinetics Unit, Hospital de Pediatría J.P. Garrahan, Ciudad Autonoma de Buenos Aires (CABA), Buenos Aires, Argentina.
authors.forename: Viviana
authors.initials: V
authors.lastname: Laurent
authors.affiliation: Consejo Nacional de Investigaciones Cientificas y Tecnicas, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), CABA, Buenos Aires, Argentina 3Experimental Thrombosis Laboratory, Instituto de Medicina Experimental (IMEX), National Academ.
authors.forename: Soledad
authors.initials: S
authors.lastname: Negrotto
authors.affiliation: Ophthalmic Oncology Service, Memorial Sloan-Kettering Cancer Center, New York, New York, United States.
authors.forename: Jasmine
authors.initials: J
authors.lastname: Francis
authors.affiliation: Inmunogenetics Laboratory, Instituto de Inmunologia, Genetica y Metabolismo (INIGEM), University of Buenos Aires, CABA, Buenos Aires, Argentina.
authors.forename: Eloisa
authors.initials: E
authors.lastname: Arana
authors.affiliation: Service of Ophthalmology, Hospital de Pediatría J.P. Garrahan, CABA, Buenos Aires, Argentina.
authors.forename: Mariana
authors.initials: M
authors.lastname: Sgroi
authors.affiliation: Consejo Nacional de Investigaciones Cientificas y Tecnicas, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), CABA, Buenos Aires, Argentina 8Argentinean Foundation of Ophthalmology Jorge Malbrán, CABA, Buenos Aires, Argentina.
authors.forename: Juan O
authors.initials: JO
authors.lastname: Croxatto
authors.affiliation: High-Throughput Drug Screening Facility (HTS) Core Facility Memorial Sloan-Kettering Cancer Center, New York, New York, United States.
authors.forename: Hakim
authors.initials: H
authors.lastname: Djaballah
authors.affiliation: Service of Hematology-Oncology, Hospital de Pediatría JP Garrahan, CABA, Buenos Aires, Argentina.
authors.forename: Guillermo L
authors.initials: GL
authors.lastname: Chantada
authors.affiliation: Ophthalmic Oncology Service, Memorial Sloan-Kettering Cancer Center, New York, New York, United States.
authors.forename: David
authors.initials: D
authors.lastname: Abramson
authors.affiliation: Clinical Pharmacokinetics Unit, Hospital de Pediatría J.P. Garrahan, Ciudad Autonoma de Buenos Aires (CABA), Buenos Aires, Argentina 2Consejo Nacional de Investigaciones Cientificas y Tecnicas, Consejo Nacional de Investigaciones Científicas y Técnicas (C.
authors.forename: Paula
authors.initials: P
authors.lastname: Schaiquevich
mesh_terms: D000818:Animals; D017209:Apoptosis; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D004077:Digoxin / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004305:Dose-Response Relationship, Drug; D004596:Electroretinography; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D005434:Flow Cytometry; D005500:Follow-Up Studies; D006801:Humans; D058449:Intravitreal Injections; D009374:Neoplasms, Experimental; D011817:Rabbits; D012160:Retina / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D019572:Retinal Neoplasms / Q000188:drug therapy* / Q000473:pathology / Q000503:physiopathology; D012175:Retinoblastoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D016896:Treatment Outcome
chemical_list: D004791:Enzyme Inhibitors; D004077:Digoxin