title: Biphosphinic palladacycle complex mediates lysosomal-membrane permeabilization and cell death in K562 leukaemia cells.
abstract: The cell death mechanism of cytotoxicity induced by the Biphosphinic Palladacycle Complex (BPC) was studied using a K562 leukaemia cell line. The IC50 values obtained for K562 cells post-72 h of BPC were less than 5.0 microM by using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) and trypan blue assays. Using the Acridine Orange vital staining combining fluorescence microscopy it was observed that the complex triggers apoptosis in K562 cells, inducing DNA fragmentation, as analysed through electrophoresis. Lysosomal-membrane permeabilization was also observed in K562 cells post-5 h of BPC, which suggests intralysosomal accumulation by proton-trapping, since its pKa value ranged from 5.1 to 6.5. Caspase-3, and -6 activity induced by BPC in K562 cells was prevented by the cathepsin-B inhibitor [N-(L-3-trans-propylcarbamoyl-oxirane-2-carbonyl)-L-isoleucyl-L-proline] (CA074). These events occurred in the presence of endogenous bcl-2 and bax expression. Acute toxicological studies demonstrated that BPC produces no lesions for liver and kidney fourteen-days after drug administration (100 mg/kg--i.p.). White and red blood cells of BPC-treated mice presented normal morphological characteristics. Taken together, these data suggest a novel lysosomal pathway for BPC-induced apoptosis, in which lysosomes are the primary target and cathepsin B acts as death mediator.
authors.affiliation: Centro Interdisciplinar de Investigação Bioquímica, Universidade de Mogi das Cruzes, Mogi das Cruzes, SP, Brazil.
authors.forename: Christiano M V
authors.initials: CM
authors.lastname: Barbosa
authors.forename: Carlos R
authors.initials: CR
authors.lastname: Oliveira
authors.forename: Fábio D
authors.initials: FD
authors.lastname: Nascimento
authors.forename: Mickaela C M
authors.initials: MC
authors.lastname: Smith
authors.forename: Daniela M
authors.initials: DM
authors.lastname: Fausto
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Soufen
authors.forename: Eliana
authors.initials: E
authors.lastname: Sena
authors.forename: Ronaldo C
authors.initials: RC
authors.lastname: Araújo
authors.forename: Ivarne L S
authors.initials: IL
authors.lastname: Tersariol
authors.forename: Claudia
authors.initials: C
authors.lastname: Bincoletto
authors.forename: Antonio C F
authors.initials: AC
authors.lastname: Caires
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D053178:Caspase 6 / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D004164:Diphosphonates; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D015870:Gene Expression / Q000235:genetics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism*; D020014:K562 Cells; D007668:Kidney / Q000187:drug effects / Q000473:pathology; D007938:Leukemia / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008099:Liver / Q000187:drug effects / Q000473:pathology; D008247:Lysosomes / Q000378:metabolism*; D051379:Mice; D018613:Microscopy, Confocal; D009942:Organometallic Compounds / Q000737:chemistry / Q000494:pharmacology* / Q000633:toxicity; D063065:Organophosphonates / Q000737:chemistry; D010165:Palladium / Q000737:chemistry; D010539:Permeability / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D013055:Spectrophotometry, Infrared; D051028:bcl-2-Associated X Protein / Q000235:genetics
chemical_list: C434766:2-sulfonato-1,1-ethylidene bisphosphonic acid; D004164:Diphosphonates; D009942:Organometallic Compounds; D063065:Organophosphonates; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D010165:Palladium; D053148:Caspase 3; D053178:Caspase 6