Cytotoxic dinuclear titanium-salan complexes: structural and biological characterization

Bioactive O^N^O^ Schiff base appended homoleptic titanium(iv) complexes: DFT, BSA/CT-DNA interactions, molecular docking and antitumor activity against HeLa and A549 cell lines

Five new homoleptic derivatives of titanium(iv) have been developed and characterized by physicochemical techniques. Metal complexes, TiH2L1 [(C38H26N6O4)Ti], TiH2L2 [(C38H24F2N6O4)Ti], TiH2L3 [(C38H24Cl2N6O4)Ti], TiH2L4 [(C38H24Br2N6O4)Ti] and TiH2L5 [(C38H24N8O8)Ti], were obtained by treating Ti(OPri)4 with appropriate ONO ligands (H2L1-H2L5) in anhydrous THF as solvent. The electronic structures and properties of titanium(iv) complexes (TiH2L1-TiH2L5) and ligands (H2L1-H2L5) were examined by DFT studies. The stability of all synthesized derivatives was assessed by a UV-visible technique using 10% DMSO, GSH medium and n-octanol/water systems. The binding interactions of BSA and CT-DNA with respective titanium(iv) complexes were successfully evaluated by employing UV-visible absorption, fluorescence, circular dichroism (CD) techniques and docking studies. The in vitro cytotoxicity of TiH2L2, TiH2L3 and TiH2L4 complexes was assessed against HeLa (human epithelioid cervical cancer cells) and A549 (lung carcinoma) cell lines. The IC50 values of TiH2L2, TiH2L3 and TiH2L4 were observed to be 28.8, 14.7 and 31.2 μg mL-1 for the HeLa cell line and 38.2, 32.9 and 67.78 μg mL-1 for A549 cells, respectively. Complex TiH2L3 exhibited remarkably induced cell cycle arrest in the G1 phase and 77.99% ROS production selectivity in the HeLa cell line.

Structural Characterization and Bioactivity of a Titanium(IV)-Oxo Complex Stabilized by Mandelate Ligands

Research on titanium-oxo complexes (TOCs) is usually focused on their structure and photocatalytic properties. Findings from these investigations further sparked our interest in exploring their potential biological activities. In this study, we focused on the synthesis and structure of a compound with the general formula [Ti8O2(OiPr)20(man)4] (1), which was isolated from the reaction mixture of titanium(IV) isopropoxide with mandelic acid (Hman) in a molar ratio of 4:1. The structure (1) was determined using single-crystal X-ray diffraction, while spectroscopic studies provided insights into its physicochemical properties. To assess the potential practical applications of (1), its microcrystals were incorporated into a polymethyl methacrylate (PMMA) matrix, yielding composite materials of the type PMMA + (1) (2 wt.%, 5 wt.%, 10 wt.%, and 20 wt.%). The next stage of our research involved the evaluation of the antimicrobial activity of the obtained materials. The investigations performed demonstrated the antimicrobial activity of pure (1) and its composites (PMMA + (1)) against both Gram-positive and Gram-negative strains. Furthermore, MTT tests conducted on the L929 murine fibroblast cell line confirmed the lack of cytotoxicity of these composites. Our study identified (1) as a promising antimicrobial agent, which is also may be use for producing composite coatings.

A metal-free salalen ligand with anti-tumor and synergistic activity in resistant leukemia and solid tumor cells via mitochondrial pathway

PURPOSE

Since the discovery of the well-known cis-platin, transition metal complexes are highly recognized as cytostatic agents. However, toxic side effects of the metal ions present in the complexes may pose significant problems for their future development. Therefore, we investigated the metal-free salalen ligand WQF 044.

METHODS

DNA fragmentations in leukemia (Nalm6) and solid tumor cells (BJAB, MelHO, MCF-7, RM82) proved the apoptotic effects of WQF 044, its overcoming of resistances and the cellular pathways that are affected by the substance. The apoptotic mechanisms finding were supported by western blot analysis, measurement of the mitochondrial membrane potential and polymerase chain reactions.

RESULTS

A complex intervention in the mitochondrial pathway of apoptosis with a Bcl-2 and caspase dependence was observed. Additionally, a wide range of tumors were affected by the ligand in a low micromolar range in-vitro. The compound overcame multidrug resistances in P-gp over-expressed acute lymphoblastic leukemia and CD95-downregulated Ewing's sarcoma cells. Quite remarkable synergistic effects with vincristine were observed in Burkitt-like lymphoma cells.

CONCLUSION

The investigation of a metal-free salalen ligand as a potential anti-cancer drug revealed in promising results for a future clinical use.

Synthesis, structure and cytotoxicity of a series of Dioxidomolybdenum(VI) complexes featuring Salan ligands

Seven hexacoordinated cis-dioxidomolybdenum(VI) complexes [MoO₂L^1-7] (1-7) derived from various tetradentate diamino bis(phenolato) "salan" ligands, N,N'-dimethyl-N,N'-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminoethane {(X=Br, Y=Me, Z=H (H₂L¹); X=Me, YCl, Z=H (H₂L²); X=ⁱPr, Y=Cl, Z=Me (H₂L³)} and N,N'-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminopropane {(X=Y=^tBu, Z=H (H₂L⁴); X=Y=Me, Z=H (H₂L⁵); X=ⁱPr, YCl, Z=Me (H₂L⁶); X=Y=Br, Z=H (H₂L⁷)} containing O-N donor atoms, have been isolated and structurally characterized. The formation of cis-dioxidomolybdenum(VI) complexes was confirmed by elemental analysis, IR, UV-vis and NMR spectroscopy, ESI-MS and cyclic voltammetry. X-ray crystallography showed the O₂N₂ donor set to define an octahedral geometry in each case. The complexes (1-7) were tested for their in vitro antiproliferative activity against HT-29 and HeLa cancer cell line. IC₅₀ values of the complexes in HT-29 follow the order 6<7<<1<2<5<<3<4 while the order was 6<7<5<1<<3<4<2 in HeLa cells. Some of the complexes proved to be as active as the clinical referred drugs, and the greater potency of 6 and 7 (IC₅₀ values of 6 are 2.62 and 10.74μM and that of 7 is 11.79 and 30.48μM in HT-29 and HeLa cells, respectively) may be dependent on the substituents in the salan ligand environment coordinated to the metal.

A Straightforward Electrochemical Approach to Imine- and Amine-bisphenolate Metal Complexes with Facile Control Over Metal Oxidation State

Synthetic methods to prepare organometallic and coordination compounds such as Schiff-base complexes are diverse, with the route chosen being dependent upon many factors such as metal-ligand combination and metal oxidation state. In this work we have shown that electrochemical methodology can be employed to synthesize a variety of metal-salen/salan complexes which comprise diverse metal-ligand combinations and oxidation states. Broad application has been demonstrated through the preparation of 34 complexes under mild and ambient conditions. Unprecedented control over metal oxidation state (M(II/III/IV) where M=Fe, Mn) is presented by simple modification of reaction conditions. Along this route, a general protocol-switch is described which allows access to analytically pure Fe(II/III)-salen complexes. Tuning electrochemical potential, selective metalation of a Mn/Ni alloy is also presented which exclusively delivers Mn(II/IV)-salen complexes in high yield.

Insights into molecular mechanism of action of salan titanium(IV) complex with in vitro and in vivo anticancer activity

Titanium compounds, in particular, Ti(IV) based diaminobis(phenolato) "salan" complexes demonstrate high cytotoxicity towards a wide range of cancer cell lines in vitro, and still, very little is known on their mode of action. A representative salan Ti(IV) complex was tested both in vitro and in vivo on human HT-29 colorectal adenocarcinoma and A2780 ovarian carcinoma cells. Both cell lines were sensitive in vitro with A2780 demonstrating an enhanced rate of uptake and intracellular accumulation and thus an earlier response to the drug. HT-29 cells responded in vivo by impaired tumor development in nude mice. Both cell lines responded in vitro (but to a different extent) by upregulation of p53 with no apparent effect on p21 followed by cell cycle arrest, apoptosis and necrosis as demonstrated by sub-G1 cell accumulation and staining by Annexin-V and propidium iodide. Furthermore, time dependent activation of cysteine-aspartic proteases9 (caspase9) as well as some minor activation of cysteine-aspartic proteases3 (caspase3) support a direct effect on the apoptotic pathway. The differential response of the two cell lines to the salan titanium(IV) complex suggests that more than one pathway is involved in their growth regulation and thus could inhibit development of drug resistant variants.

Titanium Salan/Salalen Complexes: The Twofaced Janus of Asymmetric Oxidation Catalysis

Optically pure chiral epoxides and sulfoxides are ubiquitous building blocks in fine organic synthesis, employed in the pharmaceutical, agrochemical, and cosmetic industries. On the road to chiral epoxides and sulfoxides, efficient and stereoselective transition metal-based catalysts are the most promising guides. Among transition metals, we favor titanium for its cheapness and availability, nontoxicity, and well-known ability to catalyze a variety of stereoselective transformations, including oxidations with environmentally benign H2O2. In this personal account, we summarize the state-of-the-art of rational design of chiral titanium(IV) salan and salalen catalysts, and investigations of their catalytic reactivities and stereoselectivities in the epoxidations of olefins and oxidations of thioethers, unraveling the peculiarities and mechanisms of their catalytic action.

Observed hydrolysis of fluorine substituted bis(β-diketonato)-dichlorotitanium(IV) complexes

Novel fluorine substituted mononuclear Ti(β-diketonato)2Cl2 complexes have been synthesised and shown to be involved in a partial hydrolysis reaction in solution, in which the hydrolyzed dinuclear {Ti(β-diketonato)2Cl}2(μ-O) is in equilibrium with the monomer. This is in contrast to the solution behaviour of the non CF3-containing Ti(CH3COCHCOCH3)2Cl2, Ti(PhCOCHCOCH3)2Cl2 and Ti(PhCOCHCOPh)2Cl2 complexes, under the same conditions. Variable temperature ((1)H and (19)F) NMR spectra and X-ray structure analyses reveal that the partially hydrolyzed dinuclear complex exists both in solution and in solid state, bridging through a single μ-oxo bridge and having one labile chloro-ligand per titanium center. Inclusion of electron-withdrawing CF3 groups into the already electron-deficient Ti complexes, led to the formation of {Ti(CF3COCHCOCF3)2Cl}2(μ-O) (dinuclear) and [Ti(CF3COCHCOCF3)2(μ-O)]4 (tetranuclear) complexes in CDCl3 containing trace amounts of water. DFT calculated free energies of hydrolysis support the existence of Ti(CH3COCHCOCH3)2Cl2 as a monomer and Ti(CF3COCHCOCF3)2Cl2 as a equilibrium mixture of the monomer and partially hydrolyzed dinuclear {Ti(β-diketonato)2Cl}2(μ-O) in CDCl3 solution.

Heptacoordinate Heteroleptic Salan (ONNO) and Thiosalan (OSSO) Titanium(IV) Complexes: Investigation of Stability and Cytotoxicity

Seven heptacoordinate titanium(IV) complexes were synthesized based on the concept of hetero-bis-chelate stabilization of salan (ONNO) and thiosalan (OSSO) titanium(IV)alkoxides with 2,6-pyridinedicarboxylic acid (dipic) and derivatives thereof. The resulting compounds were investigated in a solid by X-ray diffraction and in solution by NMR spectroscopy. A thiosalan (OSSO) titanium(IV) complex could be isolated and its conformational stabilization by dipic was shown by (1)H NMR spectroscopy to lead to nonfluxional behavior even at room temperature. The stability of selected complexes was assessed at pH 1.9, 6.8, and 12.1 by an UV-vis monitored hydrolysis study with >5 Mio. equivalents of water. Even at pH 12.1 [L(1)Ti(dipic)(1)] showed t1/2 of more than 2 days. The cytotoxicity of all compounds was investigated in two human carcinoma cell lines. IC50-values in the range of cisplatin were achieved by all tested compounds except for [L(4)Ti(dipic)(1)], which was proven to be nontoxic. The functionalization of dipic was thus well tolerated and did neither interfere with the stability nor the cytotoxicity of the heteroleptic complexes.

Anti-proliferative activity of nano-formulated phenolato titanium(IV) complexes against cancer cells

Nanoparticles of titanium(IV) complexes of phenolato ligands were formed and evaluated for cytotoxicity toward human HT-29 colon cancer, murine T-25 lymphoma, and murine HU-2 multidrug-resistant (MDR) cells. The nano-formulation, besides increasing the complexes' shelf lives, is particularly efficient in overcoming limitations in solubility and cell-penetration, thus enhancing biological accessibility; large complexes that were inactive when measured in a non-formulated form showed marked activity when nano-formulated. For active and accessible small complexes, the effect of the formulation was negligible. Most complexes showed similar activity toward MDR cells and their drug-sensitive analogues, further increasing their therapeutic potential. An exception is a particularly hydrophobic complex, which is presumably more accessible to interaction with the membrane ABCB1 (MDR1) transporter active in the multidrug resistance of HU-2 cells. The most efficient compound is a mononuclear complex of a single hexadentate ligand, combining particularly high activity and hydrolytic stability with accessibility aided by the nano-formulation.

Heteroleptic titanium(IV) catecholato/piperazine systems and their anti-cancer properties

In this paper we report the synthesis and full characterisation of a range of Ti(IV)-catecholato systems complexed to piperazine or homopiperazine salan ligands. The steric/electronic environment of the catecholate moiety has been varied and the effect this has on cytotoxicity discussed. It was observed that the 7-membered homopiperazine complexes are more stable to hydrolysis than their piperazine cousins in biological media. In general the homopiperazine complexes show higher cytotoxicity than the piperazine complexes, with the most cytotoxic complex exhibiting IC50 (μM) values of 3 ± 0.5 μM (HT-29) and 4 ± 1 μM (OVCAR).