title: Structure-activity studies of Ti(IV) complexes: aqueous stability and cytotoxic properties in colon cancer HT-29 cells.
abstract: As part of our research efforts in the area of titanium-based antitumor agents, we have investigated the cytotoxic activity of [Ti(4)(maltolato)(8)(mu-O)(4)], (Cp-R)(2)TiCl(2) and (Cp-R)CpTiCl(2) (R = CO(2)CH(3) and CO(2)CH(2)CH(3)), and three water-soluble titanocene-amino acid complexes-[Cp(2)Ti(aa)(2)]Cl(2) (aa = L: -cysteine, L: -methionine, and D: -penicillamine)-on the human colon adenocarcinoma cell line, HT-29. The capacity of [Ti(4)(maltolato)(8)(mu-O)(4)] to donate Ti(IV) to human apo-transferrin and its hydrolytic stability have been investigated and compared to the previously reported data on modified titanocenes with either hydrophilic ancillary ligands or the functionalized cyclopentadienyl ligands. Notably, the titanium-maltolato complex does not transfer Ti(VI) to human apo-transferrin at any time within the first seven days of its interaction, demonstrating the inert character of this species. Stability studies on these complexes have shown that titanocene complexes decompose at physiological pH while the [Ti(4)(maltolato)(8)(mu-O)(4)] complex is stable at this pH without any notable decomposition for a period of ten days. The antitumor activity of these complexes against colon cancer HT-29 cells was determined using an MTT cell viability assay at 72 and 96 h. The titanocene-amino acid and the (Cp-R)(2)TiCl(2)/(Cp-R)CpTiCl(2) (R = CO(2)CH(3)) complexes were not biologically active when human transferrin was absent; they also were inactive when human transferrin was present at dose-equivalent concentrations. (Cp-R)(2)TiCl(2) and (Cp-R)CpTiCl(2) (R = CO(2)CH(2)CH(3)) showed cytotoxic activity in HT-29 cells comparable to that which is displayed by titanocene dichloride. The titanium-maltolato complex had higher levels of cytotoxic activity than any other titanocene complex investigated. Transferrin may be important in protecting the titanium center from hydrolysis, but this may be achieved by selecting ligands that could result in hydrolytically stable, yet active, complexes.
authors.affiliation: Department of Chemistry, University of Puerto Rico, Mayaguez, PR, 00681, USA.
authors.forename: Ramón
authors.initials: R
authors.lastname: Hernández
authors.forename: José
authors.initials: J
authors.lastname: Lamboy
authors.forename: Li Ming
authors.initials: LM
authors.lastname: Gao
authors.forename: Jaime
authors.initials: J
authors.lastname: Matta
authors.forename: Félix R
authors.initials: FR
authors.lastname: Román
authors.forename: Enrique
authors.initials: E
authors.lastname: Meléndez
mesh_terms: D000970:Antineoplastic Agents; D001059:Apoproteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004355:Drug Stability; D019073:HT29 Cells; D006801:Humans; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000494:pharmacology*; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship; D013778:Tetrazolium Salts; D013844:Thiazoles; D014025:Titanium / Q000494:pharmacology*; D014168:Transferrin / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D001059:Apoproteins; D008024:Ligands; D009942:Organometallic Compounds; D012996:Solutions; D013778:Tetrazolium Salts; D013844:Thiazoles; D014168:Transferrin; C028284:apotransferrin; D014025:Titanium; C022616:thiazolyl blue; C020528:titanocene dichloride