title: Differential cytotoxicity induced by the Titanium(IV)Salan complex Tc52 in G2-phase independent of DNA damage.
abstract: Chemotherapy is one of the major treatment modalities for cancer. Metal-based compounds such as derivatives of cisplatin are in the front line of therapy against a subset of cancers, but their use is restricted by severe side-effects and the induction of resistance in treated tumors. Subsequent research focused on development of cytotoxic metal-complexes without cross-resistance to cisplatin and reduced side-effects. This led to the discovery of first-generation titanium(IV)salan complexes, which reached clinical trials but lacked efficacy. New-generation titanium (IV)salan-complexes show promising anti-tumor activity in mice, but their molecular mechanism of cytotoxicity is completely unknown.
  
  
  
  Four different human cell lines were analyzed in their responses to a toxic (Tc52) and a structurally highly related but non-toxic (Tc53) titanium(IV)salan complex. Viability assays were used to reveal a suitable treatment range, flow-cytometry analysis was performed to monitor the impact of dosage and treatment time on cell-cycle distribution and cell death. Potential DNA strand break induction and crosslinking was investigated by immunostaining of damage markers as well as automated fluorometric analysis of DNA unwinding. Changes in nuclear morphology were analyzed by DAPI staining. Acidic beta-galactosidase activity together with morphological changes was monitored to detect cellular senescence. Western blotting was used to analyze induction of pro-apoptotic markers such as activated caspase7 and cleavage of PARP1, and general stress kinase p38.
  
  
  
  Here we show that the titanium(IV)salan Tc52 is effective in inducing cell death in the lower micromolar range. Surprisingly, Tc52 does not target DNA contrary to expectations deduced from the reported activity of other titanium complexes. Instead, Tc52 application interferes with progression from G2-phase into mitosis and induces apoptotic cell death in tested tumor cells. Contrarily, human fibroblasts undergo senescence in a time and dose-dependent manner. As deduced from fluorescence studies, the potential cellular target seems to be the cytoskeleton.
  
  
  
  In summary, we could demonstrate in four different human cell lines that tumor cells were specifically killed without induction of major cytotoxicity in non-tumorigenic cells. Absence of DNA damaging activity and the cell-cycle block in G2 instead of mitosis makes Tc52 an attractive compound for further investigations in cancer treatment.
authors.affiliation: University of Zurich, Institute of Veterinary Pharmacology and Toxicology, 8057, Zurich, Switzerland.
authors.forename: Theresa
authors.initials: T
authors.lastname: Pesch
authors.affiliation: University of Konstanz, Molecular Toxicology Group, 78457, Konstanz, Germany.|Present address: Leibniz Institute for Age Research: FLI, Beutenbergstr. 11, 07745, Jena, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Schuhwerk
authors.affiliation: University of Zurich, Institute of Veterinary Pharmacology and Toxicology, 8057, Zurich, Switzerland.
authors.forename: Philippe
authors.initials: P
authors.lastname: Wyrsch
authors.affiliation: Department of Chemistry, University of Konstanz, 78457, Konstanz, Germany.|Present address: Lanxess, 41539, Dormagen, Germany.
authors.forename: Timo
authors.initials: T
authors.lastname: Immel
authors.affiliation: Leibniz Institute DSMZ, Molecular Biology Group, 38124, Braunschweig, Germany.
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Dirks
authors.affiliation: University of Konstanz, Molecular Toxicology Group, 78457, Konstanz, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Bürkle
authors.affiliation: Department of Chemistry, University of Konstanz, 78457, Konstanz, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Huhn
authors.affiliation: University of Zurich, Institute of Veterinary Pharmacology and Toxicology, 8057, Zurich, Switzerland. sascha.beneke@uni-konstanz.de.|Present address: Department of Biology, University of Konstanz, Ecotoxicology Group, 78457, Konstanz, Germany. sascha.beneke@uni-konstanz.de.
authors.forename: Sascha
authors.identifier: 0000-0002-1998-7373
authors.initials: S
authors.lastname: Beneke
mesh_terms: D000970:Antineoplastic Agents; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D053179:Caspase 7 / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D016922:Cellular Senescence / Q000187:drug effects; D056831:Coordination Complexes / Q000737:chemistry / Q000494:pharmacology*; D003599:Cytoskeleton / Q000187:drug effects; D004249:DNA Damage / Q000187:drug effects; D005434:Flow Cytometry; D016195:G2 Phase / Q000187:drug effects*; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D000071137:Poly (ADP-Ribose) Polymerase-1 / Q000378:metabolism; D011868:Radioisotopes / Q000737:chemistry / Q000494:pharmacology*; D014025:Titanium / Q000737:chemistry / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D056831:Coordination Complexes; D011868:Radioisotopes; D014025:Titanium; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D048051:p38 Mitogen-Activated Protein Kinases; C505520:CASP7 protein, human; D053179:Caspase 7
keywords: Apoptosis; Cell-cycle; Senescence; Titanium(IV)salan complex; Tumorigenicity