An Insight into the Effect of Schiff Base and their d and f Block Metal Complexes on Various Cancer Cell Lines as Anticancer Agents: A Review

Over the last few decades, an alarming rise in the percentage of individuals with cancer and those with multi-resistant illnesses has forced researchers to explore possibilities for novel therapeutic approaches. Numerous medications currently exist to treat various disorders, and the development of small molecules as anticancer agents has considerable potential. However, the widespread prevalence of resistance to multiple drugs in cancer indicates that it is necessary to discover novel and promising compounds with ideal characteristics that could overcome the multidrug resistance issue. The utilisation of metallo-drugs has served as a productive anticancer chemotherapeutic method, and this approach may be implemented for combating multi-resistant tumours more successfully. Schiff bases have been receiving a lot of attention as a group of compounds due to their adaptable metal chelating abilities, innate biologic properties, and versatility to tweak the structure to optimise it for a specific biological purpose. The biological relevance of Schiff base and related complexes, notably their anticancer effects, has increased in their popularity as bio-inorganic chemistry has progressed. As a result of learning about Schiff bases antitumor efficacy against multiple cancer cell lines and their complexes, researchers are motivated to develop novel, side-effect-free anticancer treatments. According to study reports from the past ten years, we are still seeking a powerful anticancer contender. This study highlights the potential of Schiff bases, a broad class of chemical molecules, as potent anticancer agents. In combination with other anticancer strategies, they enhance the efficacy of treatment by elevating the cytotoxicity of chemotherapy, surmounting drug resistance, and promoting targeted therapy. Schiff bases also cause cancer cell DNA repair, improve immunotherapy, prevent angiogenesis, cause apoptosis, and lessen the side effects of chemotherapy. The present review explores the development of potential Schiff base and their d and f block metal complexes as anticancer agents against various cancer cell lines.

Depicting the DNA Binding and Cytotoxicity Studies against Human Colorectal Cancer of Aquabis (1-Formyl-2-Naphtholato-k2O,O′) Copper(II): A Biophysical and Molecular Docking Perspective

In this study, we attempted to examine the biological activity of the copper(II)–based small molecule aquabis (1-formyl-2-naphtholato-k2O,O′)copper(II) (1) against colon cancer. The characterization of complex 1 was established by analytical and spectral methods in accordance with the single-crystal X-ray results. A monomeric unit of complex 1 exists in an O4 (H2O) coordination environment with slightly distorted square pyramidal geometry (τ = ~0.1). The interaction of complex 1 with calf thymus DNA (ctDNA) was determined by employing various biophysical techniques, which revealed that complex 1 binds to ctDNA at the minor groove with a binding constant of 2.38 × 105 M–1. The cytotoxicity of complex 1 towards human colorectal cell line (HCT116) was evaluated by the MTT assay, which showed an IC50 value of 11.6 μM after treatment with complex 1 for 24 h. Furthermore, the apoptotic effect induced by complex 1 was validated by DNA fragmentation pattern, which clarified that apoptosis might be regulated through the mitochondrial-mediated production of reactive oxygen species (ROS) causing DNA damage pathway. Additionally, molecular docking was also carried out to confirm the recognition of complex 1 at the minor groove.

From solid state to in vitro anticancer activity of copper(II) compounds with electronically-modulated NNO Schiff base ligands

The copper(ii) complexes of general formula [Cu(GL)(Cl)] (1-3, G = OMe, H and NO2, respectively), bearing tridentate Schiff base ligands (GL-) and a chloride as a fourth labile one, are here reported. The Schiff bases derive from the monocondensation of ethylenediamine and substituted salicylaldehyde, where the electronic properties are modulated by the releasing or withdrawing power of the G group. The compounds were structurally characterized through single crystal Synchrotron X-ray diffraction experiments in the solid state, revealing that 1 (OMe) and 2 (H) adopt a dimeric assembly [Cu(μ-Cl)(GL)]2 through apical interaction of the chloride ions of two monomeric units, while 3 embraces a 1D polymeric chain structure [Cu(μ-Cl)(NO2L)]n with a similar bridging fashion, all supported by extended intramolecular or intrachain hydrogen bonds. The redox properties of the complexes were also studied by cyclic voltammetry with no marked effect of the substituent on the potential of the CuII/CuI redox system. UV/Vis spectroscopic studies in mimicked physiological conditions highlighted the intactness and stability of the coordinated NNO tridentate ligand in 1-3 and the lability of the coordinated chloride ion with the formation of the aquo-complexes [Cu(GL)(H2O)]+ in aqueous solution, as confirmed by conductance measurements with a 1 : 1 electrolyte molar conductivity. In vitro tests on cell viability were conducted on malignant cell lines typical for their poor prognosis and curability, revealing time-dependent and differential cytotoxicity given by the substituent G. All compounds were capable of formation of intracellular reactive oxygen species and DNA intercalation, acting as nuclease and producing double-strand DNA breaks. This is especially effective for 3 (NO2), which revealed the highest anticancer activity against malignant triple-negative breast cancer MDA-MB-231 cells, with a two-to-four-fold cytotoxicity enhancement with respect to 1 (OMe) and 2 (H), and, most important, substantial differentiation of cytotoxicity with respect to healthy endothelial HUVEC cell line.

Copper(II) N,N,O-Chelating Complexes as Potential Anticancer Agents

Three novel dinuclear Cu(II) complexes based on a N,N,O-chelating salphen-like ligand scaffold and bearing varying aromatic substituents (−H, −Cl, and −Br) have been synthesized and characterized. The experimental and computational data obtained suggest that all three complexes exist in the dimeric form in the solid state and adopt the same conformation. The mass spectrometry and electron paramagnetic resonance results indicate that the dimeric structure coexists with the monomeric form in solution upon solvent (dimethyl sulfoxide and water) coordination. The three synthesized Cu(II) complexes exhibit high potentiality as ROS generators, with the Cu(II)/Cu(I) redox potential inside the biological redox window, and thus being able to biologically undergo Cu(II)/Cu(I) redox cycling. The formation of ROS is one of the most promising reported cell death mechanisms for metal complexes to offer an inherent selectivity to cancer cells. In vitro cytotoxic studies in two different cancer cell lines (HeLa and MCF7) and in a normal fibroblast cell line show promising selective cytotoxicity for cancer cells (IC₅₀ about 25 μM in HeLa cells, which is in the range of cisplatin and improved with respect to carboplatin), hence placing this N,N,O-chelating salphen-like metallic core as a promising scaffold to be explored in the design of future tailor-made Cu(II) cytotoxic compounds.

Three novel dinuclear Cu(II) complexes based on a N,N,O-chelating salphen-like ligand scaffold and bearing varying aromatic substituents (−H, −Cl, and −Br) have been synthesized and characterized. They three exhibit high potentiality as reactive oxygen species (ROS) generators, with the Cu(II)/Cu(I) redox potential inside the biological redox window. In vitro studies in two different cancer cell lines (HeLa and MCF7) and in a normal fibroblast cell line show promising selective cytotoxicity for cancer cells.

DNA-binding and in vitro cytotoxic activity of platinum(II) complexes of curcumin and caffeine

Three Pt(II) complexes containing the natural ligands curcumin and caffeine, namely [Pt(curc)(PPh₃)₂]Cl (1), [PtCl(curc)(DMSO)] (2) (curc = deprotonated curcumin) and trans-[Pt(caffeine)Cl₂(DMSO)] (3), were synthesized and fully characterized. The data obtained suggest that, for both 1 and 2, the anion of curcumin is coordinated to the platinum ion via the oxygen atoms of the β-diketonate moiety. Spectroscopic features reveal that in 2 and 3, a DMSO molecule is S-bonded to the metal centre. For 3, all data indicate a square-planar geometry formed by a 9-N bonded caffeine, two trans chloride anions and a DMSO. The three complexes undergo changes in solution upon incubation for 24 h; 1 and 2 release curcumin while 3 isomerizes from trans to cis configuration. The DNA-binding and cytotoxic properties of 1-3 were evaluated in vitro. Despite their structural similarity, curcuminate-containing 1 and 2 exhibit distinct DNA interactions. While 1 appears to intercalate between nucleobase pairs, inducing the oxidative degradation of the biomolecule, 2 behaves as a groove binder, by means of electrostatic forces. Caffeine-containing 3 exhibits a behaviour that is comparable to that of 2. Complexes 1 and 2 showed moderate to high cytotoxicity and selectivity against several cancer cell lines, while 3 is inactive. Compounds 1 and 2 can be further activated by visible-light irradiation.

Designing antiferromagnetically coupled mono-, di- and tri-bridged copper(ii)-based catecholase models by varying the ‘Auxiliary Parts’ of the ligand and anionic co-ligand

The role of the auxiliary part of ligands towards the architecture of copper(ii)-based catecholase models were unveiled with the help of DFT study.

A vanillin-based copper(ii) metal complex with a DNA-mediated apoptotic activity

Vanillin (vanH) is the major component of vanilla and one of the most widely used flavoring agents. In this work the complex [Cu(phen)(van)2] was prepared and characterized by structural (X-ray), spectroscopic (IR, UV-Vis, EPR) and electrochemical techniques. This compound showed an octahedral geometry with an unusual arrangement of the vanillin ligands, where the methoxy groups of the vanillinate ions are coordinated opposite to each other. The compound promoted DNA cleavage in the presence of glutathione (GSH) and H2O2. At 40 μmol L-1 of complex with GSH (10 mmol L-1), there is a complete cleavage of DNA to nicked form II, while only at 10 μmol L-1 of this complex with H2O2 (1 mmol L-1) an extensive cleavage leading to form III took place. Additionally, we have evidences of superoxide generation upon reaction with GSH. Therefore, DNA fragmentation occurs likely through an oxidative pathway. MTT assays indicated that the complex is highly cytotoxic against three distinct cell lines: B16-F10 (IC50 = 3.39 ± 0.61 μmol L-1), HUH-7 (IC50 = 4.22 ± 0.31 μmol L-1) and 786-0 (IC50 = 10.38 ± 0.91 μmol L-1). Flow cytometry studies conducted with 786-0 cell line indicated cell death might occur by apoptosis. Cell cycle progression evaluated at 5 and 10 μmol L-1 resulted in a clear increase of 786-0 cells at G1 phase and depletion of G2/M, while higher doses showed an expressive increase of sub-G1 phase. Altogether, these results pointed out to a promising biological activity and potential as an anti-cancer agent.

Evaluation of the metal-dependent cytotoxic behaviour of coordination compounds

The [Cu(L)Cl2]2 and [Pt(L)Cl2] complexes were prepared from the simple Schiff-base ligand (E)-phenyl-N-((pyridin-2-yl)methylene)methanamine (L) and respectively, CuCl₂ and cis-[PtCl₂(DMSO)₂].

DNA interactions of non-chelating tinidazole-based coordination compounds and their structural, redox and cytotoxic properties

DNA interactions of novel tinidazole Cu^II complexes.

Electrochemical studies of DNA interaction and antimicrobial activities of MnII, FeIII, CoII and NiII Schiff base tetraazamacrocyclic complexes

Tetraazamacrocyclic complexes of Mn^II, Fe^III, Co^II and Ni^II have been synthesized by template method. These tetraazamacrocycles have been analyzed with various techniques like molar conductance, IR, UV-vis, mass spectral and cyclic voltammetric studies. On the basis of all these studies, octahedral geometry has been assigned to these tetraazamacrocyclic complexes. The DNA binding properties of these macrocyclic complexes have been investigated by electronic absorption spectra, fluorescence spectra, cyclic voltammetric and differential pulse voltammetric studies. The cyclic voltammetric data showed that i_pc and i_pa were effectively decreased in the presence of calf thymus DNA, which is a strong evidence for the interaction of these macrocyclic complexes with the calf thymus DNA (ct-DNA). The heterogeneous electron transfer rate constant found in the order: K_Co^II>K_Ni^II>K_Mn^II which indicates that Co^II macrocyclic complex has formed a strong intercalated intermediate. The Stern-Volmer quenching constant (K_SV) and voltammetric binding constant were found in the order K_SV(Co^II)>K_SV(Ni^II)>K_SV(Mn^II) and K⁺(Co^II)>K⁺(Ni^II)>K⁺(Mn^II) which shows that Co^II macrocyclic complex exhibits the high interaction affinity towards ct-DNA by the intercalation binding. Biological studies of the macrocyclic complexes compared with the standard drug like Gentamycin, have shown antibacterial activities against E. coli, P. aeruginosa, B. cereus, S. aureus and antifungal activity against C. albicans.

Multisensitive drug-loaded polyurethane/polyurea nanocapsules with pH-synchronized shell cationization and redox-triggered release

A one-pot versatile method for the preparation of sub-30 nm multisensitive polyurethane/polyurea nanocapsules with pH-synchronized shell cationization is presented. The nanocapsules have been loaded with different drugs which are released through a redox-triggered mechanism.

Novel bio-essential metal based complexes linked by heterocyclic ligand: Synthesis, structural elucidation, biological investigation and docking analysis

New series of bio-essential metal based complexes linked by Schiff base ligand (L) and 2,2'-bipyridine (bpy) have been synthesized and characterized by diverse spectral techniques such as elemental analysis, magnetic susceptibility, molar conductivity measurements, FT-IR, UV-Vis., (1)H NMR, (13)C NMR, EPR and Mass. The spectral data suggest that the metal complexes espouse octahedral geometry around the metal ions. Interactions of the complexes with CT DNA have been explored by electronic absorption, ethidium bromide displacement assay, viscosity measurements, cyclic voltammetry and differential pulse voltammetry in order to evaluate the possible DNA-binding mode and to calculate the corresponding DNA-binding constants. The DNA interaction studies propose that the intercalative mode of interaction and the complexes exhibit oxidative cleavage of pUC19 DNA in the presence of hydrogen peroxide as activator. The synthesized Schiff base ligand and its metal complexes have been screened for anti-microbial activity by micro dilution method against two Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), two Gram-negative bacteria (Escherichia coli and Salmonella typhi) and three fungi strains (Fusarium solani, Aspergillus niger and Candida albicans) revealing that the complexes are good anti-pathogenic agents than the ligand. Moreover, molecular docking analysis has been performed to confirm the nature of binding of the complexes with DNA.

The effect of potential supramolecular-bond promoters on the DNA-interacting abilities of copper–terpyridine compounds

Supramolecular interactions prevail over DNA-cleaving abilities in the cytotoxicity behaviour of terpyridine-based copper(ii) complexes.

Synthesis and antitumor mechanisms of a copper(ii) complex of anthracene-9-imidazoline hydrazone (9-AIH)

A copper(ii) complex of anthracene-9-imidazoline hydrazone induced cell apoptosis by suppressing mutant p53 expression and activating caspase cascade pathway.