Complexes of cytotoxic chelators from the dipyridyl ketone isonicotinoyl hydrazone (HPKIH) analogues

[3-Hydr-oxy-N'-(2-oxidobenzyl-idene)-2-naphthohydrazidato-κO,N,O']tris-(pyridine-κN)nickel(II) pyridine tris-olvate

The asymmetric unit of the crystal structure of the title complex, [Ni(C₁₈H₁₂N₂O₃)(C₅H₅N)₃]·3C₅H₅N, contains two independent Ni^II complex mol­ecules and six uncoordinated pyridine mol­ecules. Each Ni^II atom is coordinated by two O and four N atoms, from three pyridine and a chelating 3-hydr­oxy-N′-(2-oxidobenzyl­idene)-2-naphthohydrazide dianionic ligand, with a distorted octa­hedral geometry. Intra­molecular O—H⋯N hydrogen bonding exists in both complex mol­ecules but no inter­molecular hydrogen bonding is observed in the crystal structure.

Synthesis, Characterization, and Antibacterial and Cytotoxic Study of Metal Complexes with Schiff Base Ligands

The synthesis of 16 metal complexes from four Schiff bases prepared from 5-chloro-2-hydroxybenzaldehyde and primary amines has been described. The synthesized Schiff base ligands and their complexes were characterized by elemental analyses, spectroscopic (UV, IR, 1H and 13C NMR, electrospray ionization-mass spectrometry) methods, and magnetic and conductance measurements. Furthermore, complexes 1a, 1b, 3d, 4a, and 4d were characterized by X-ray diffraction analysis. After the structural characterization, all the compounds were tested in vitro for their antibacterial (Bacillus subtilis, Escherichia coli, Pseudomonas fluorescens, and Staphylococcus aureus) activities. The cytotoxic activities of the synthesized compounds were evaluated in vitro against human chronic myeloid leukaemia cells (K562) and a human nasopharyngeal epidermoid tumour cell line. The results indicated that most of the complexes showed good cytotoxic activity against human cancer cell lines but weak cytotoxic activity against a human normal cell line (L02). Among the compounds tested, the cobalt complexes 1a, 2a, 3a, and 4a showed the most favourable antibacterial and cytotoxic activities.

Tuning the antiproliferative activity of biologically active iron chelators: characterization of the coordination chemistry and biological efficacy of 2-acetylpyridine and 2-benzoylpyridine hydrazone ligands

2-Pyridinecarbaldehyde isonicotinoyl hydrazone (HPCIH) and di-2-pyridylketone isonicotinoyl hydrazone (HPKIH) are two Fe chelators with contrasting biological behavior. HPCIH is a well-tolerated Fe chelator with limited antiproliferative activity that has potential applications in the treatment of Fe-overload disease. In contrast, the structurally related HPKIH ligand possesses significant antiproliferative activity against cancer cells. The current work has focused on understanding the mechanisms of the Fe mobilization and antiproliferative activity of these hydrazone chelators by synthesizing new analogs (based on 2-acetylpyridine and 2-benzoylpyridine) that resemble both series and examining their Fe coordination and redox chemistry. The Fe mobilization activity of these compounds is strongly dependent on the hydrophobicity and solution isomeric form of the hydrazone (E or Z). Also, the antiproliferative activity of the hydrazone ligands was shown to be influenced by the redox properties of the Fe complexes. This indicated that toxic Fenton-derived free radicals are important for the antiproliferative activity for some hydrazone chelators. In fact, we show that any substitution of the H atom present at the imine C atom of the parent HPCIH analogs leads to an increase in antiproliferative efficacy owing to an increase in redox activity. These substituents may deactivate the imine R-C=N-Fe (R is Me, Ph, pyridyl) bond relative to when a H atom is present at this position preventing nucleophilic attack of hydroxide anion, leading to a reversible redox couple. This investigation describes novel structure-activity relationships of aroylhydrazone chelators that will be useful in designing new ligands or fine-tuning the activity of others.

Development of Gallium Compounds for Treatment of Lymphoma: Gallium Maltolate, a Novel Hydroxypyrone Gallium Compound, Induces Apoptosis and Circumvents Lymphoma Cell Resistance to Gallium Nitrate

Clinical studies have shown gallium nitrate to have significant antitumor activity against non-Hodgkin's lymphoma and bladder cancer, thus indicating that gallium-based drugs have potential for further development as antineoplastic agents. In this study, we compared the cytotoxicity of gallium maltolate, a novel gallium compound, with gallium nitrate in lymphoma cell lines, including p53 variant and unique gallium nitrate-resistant cells. We found that gallium maltolate inhibited cell proliferation and induced apoptosis through the mitochondrial pathway at lower concentrations and more rapidly than gallium nitrate. Gallium maltolate produced an increase in intracellular reactive oxygen species (ROS) within 2 h of incubation with cells; this effect could be blocked by mitoquinone, a mitochondria-targeted antioxidant. The role of the transferrin receptor (TfR) in gallium maltolate's action was examined using monoclonal antibody (MoAb) 42/6 to block TfR function. However, although MoAb 42/6 reduced gallium maltolate-induced caspase-3 activity, it had only a minor effect on cell growth inhibition. Importantly, gallium maltolate induced apoptosis in cells resistant to gallium nitrate, and, unlike gallium nitrate, its cytotoxicity was not affected by cellular p53 status. Cellular gallium uptake was greater with gallium maltolate than with gallium nitrate. We conclude that gallium maltolate inhibits cell proliferation and induces apoptosis more efficiently than gallium nitrate. Gallium maltolate is incorporated into lymphoma cells to a greater extent than gallium nitrate via both TfR-independent and -dependent pathways; it has significant activity against gallium nitrate-resistant cells and acts independently of p53. Further studies to evaluate its antineoplastic activity in vivo are warranted.