A Glimpse Into Molecular Mechanism of Phenolato Titanium(IV) Anicancer Complexes

Maya Miller, Chemistry, HUJI, Jerusalem, Israel
Ori Braitbard, Alexander Silberman Institute of Life Science, HUJI, Jerusalem, Israel
Yoav Smith, Genomic Data Analysis Unit, HUJI, Jerusalem, Israel
Jacob Hochman, Alexander Silberman Institute of Life Science, HUJI, Jerusalem, Israel
Edit Y. Tshuva, Chemistry, HUJI, Jerusalem, Israel

In the past decades titanium complexes have emerged as potential anticancer drugs. We  have developed a class of titanium compounds based on aminophenolato ligands. This group of complexes exhibits high cytotoxicity towards various cancer cell lines, negligible toxicity towards primary murine cells, high hydrolytic stability, and identified hydrolysis products that are both stable and biologically active.

This study aims to probe into the mechanism(s) of action of the phenolato titanium(IV) complexes. Since these complexes exhibit C₂ or C₁ symmetry, rendering them chiral, the examination of isolated enantiomers is essential both for medicinal use and for gaining mechanistic insights. We found that for complexes based on bipyrrolidine chiral moiety, generally the racemic mixtures were inactive whereas the pure enantiomers exhibited similarly high cytotoxic activity. This observation supports the assumption on the involvement of polynuclear hydrolysis product as the active species as well as the premise that the biological target is chiral.

To further explore possible molecular mechanism(s) of action for this class of compounds, gene chip array, western blotting, ELISA and FACS methods were applied on leading salan complexes. Gene chip array studies suggested involvement of the following pathways: 1) Systemic Lupus Erythematosus; 2) Disruption to cell cycle; 3) p53 signaling; 4) ECM receptor interaction. Studies of flow cytommetry revealed growth arrest in G-1 of the cell cycle within 24 hours. ELISA and western blotting revealed increasing levels of apoptotic related proteins, p53 and p21, throughout exposure for 48hr, as well as the expression of caspase3, caspase9 and MDM2 proteins.

Collectively, the present findings are consistent with interaction of phenolato Ti(IV) complexes with DNA and initiation of a DNA damage response culminating in cell cycle arrest and apoptosis. This pathway resembles those of chemotherapeutic drugs that exert their effect through DNA interstrand crosslinking and double strand breaks. 

References
Miller M., Tshuva E.Y. (2014) Eur. J. Inorg. Chem. 9: 1485-1491