title: Release of toxic Gd3+ ions to tumour cells by vitamin B12 bioconjugates.
abstract: Two probes consisting of vitamin B(12) (CNCbl) conjugated to Gd chelates by esterification of the ribose 5'-OH moiety, Gd-DTPA-CNCbl (1; DTPA = diethylenetriamine-N,N,N',N'',N''-pentaacetic acid) and Gd-TTHA-CNCbl (2; TTHA = triethylenetetramine-N,N,N',N'',N''',N'''-hexaacetic acid), have been synthesised and characterised. The crystal structure of a dimeric form of 1, obtained by crystallisation with an excess of GdCl(3), has been determined. The kinetics of binding to and dissociation from transcobalamin II show that 1 and 2 maintain high-affinity binding to the vitamin B(12) transport protein. Complex 2 is very stable with respect to Gd(3+) release owing to the saturated co-ordination of the Gd(3+) ion by four amino and five carboxylate groups. Hydrolysis of the ester functionality occurs on the time scale of several hours. The lack of saturation and the possible involvement of the ester functionality in co-ordination result in lower stability of 1 towards hydrolysis and in a considerable release of Gd(3+) in vitro. Gd(3+) ions released from 1 are avidly taken up by the K562 tumour cells to an extent corresponding to approximately 10(10) Gd(3+) per cell. The internalisation of toxic Gd(3+) ions causes a marked decrease in cell viability as assessed by Trypan blue and WST-1 tests. On the contrary, the experiments with the more stable 2 did not show any significant cell internalisation of Gd(3+) ions and any influence on cell viability. The results point to new avenues of in situ generation of cytotoxic pathways based on the release of toxic Gd(3+) ions by vitamin B(12) bioconjugates.
authors: Department of Chemical Sciences, Centre of Excellence in Biocrystallography, University of Trieste, Via Licio Giorgieri 1, 32127 Trieste (Italy), Fax: (+39) 040-558-3903.
authors: Patrizia
authors: P
authors: Siega
authors: Department of Chemical Sciences, Centre of Excellence in Biocrystallography, University of Trieste, Via Licio Giorgieri 1, 32127 Trieste (Italy), Fax: (+39) 040-558-3903.
authors: Jochen
authors: J
authors: Wuerges
authors: Department of Chemistry, IFM and Center of Molecular Imaging, University of Turin, Via Nizza 52, 10127 Turin (Italy), Fax: (+39) 011-670-7855.
authors: Francesca
authors: F
authors: Arena
authors: Department of Chemistry, IFM and Center of Molecular Imaging, University of Turin, Via Nizza 52, 10127 Turin (Italy), Fax: (+39) 011-670-7855.
authors: Eliana
authors: E
authors: Gianolio
authors: Protein Chemistry Laboratory, Department of Molecular Biology, University of Aarhus, Science Park, Gustav Wieds Vey 10, 8000 Aarhus C (Denmark).
authors: Sergey N
authors: SN
authors: Fedosov
authors: Department of Chemical Sciences, Centre of Excellence in Biocrystallography, University of Trieste, Via Licio Giorgieri 1, 32127 Trieste (Italy), Fax: (+39) 040-558-3903.
authors: Renata
authors: R
authors: Dreos
authors: Department of Chemical Sciences, Centre of Excellence in Biocrystallography, University of Trieste, Via Licio Giorgieri 1, 32127 Trieste (Italy), Fax: (+39) 040-558-3903.
authors: Silvano
authors: S
authors: Geremia
authors: Department of Chemistry, IFM and Center of Molecular Imaging, University of Turin, Via Nizza 52, 10127 Turin (Italy), Fax: (+39) 011-670-7855.
authors: Silvio
authors: S
authors: Aime
authors: Department of Chemical Sciences, Centre of Excellence in Biocrystallography, University of Trieste, Via Licio Giorgieri 1, 32127 Trieste (Italy), Fax: (+39) 040-558-3903.
authors: Lucio
authors: L
authors: Randaccio
mesh_terms: D002412:Cations; D018360:Crystallography, X-Ray; D005682:Gadolinium / Q000737:chemistry / Q000633:toxicity*; D019786:Gadolinium DTPA / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D020014:K562 Cells; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D013778:Tetrazolium Salts; D014343:Trypan Blue; D014407:Tumor Cells, Cultured; D014805:Vitamin B 12 / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology
chemical_list: C110656:2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium; D002412:Cations; C543391:Gd-DTPA-CNCbl; C543392:Gd-TTHA-CNCbl; D009942:Organometallic Compounds; D013778:Tetrazolium Salts; D005682:Gadolinium; D014343:Trypan Blue; D019786:Gadolinium DTPA; D014805:Vitamin B 12