Chemical and Biological Evaluation of Thiosemicarbazone-Bearing Heterocyclic Metal Complexes

Bio-molecular Fe(III) and Zn(II) complexes stimulate the interplay between PI3K/AKT1/EGFR inhibition and induce autophagy and apoptosis in epidermal skin cell cancer

This study investigated the effectiveness and safety of a hybrid thiosemicarbazone ligand (HL) and its metal complexes (MnII-L, FeIII-L, NiII-HL, and ZnII-HL) against epidermoid carcinoma (A-431). The results indicated that FeIII-L is the most effective, with a high selectivity index of 8.01 and an IC50 of 17.49 ± 2.12 μM for FeIII-L. The study also revealed that the synthesized complexes effectively inhibited gene expression of the Phosphoinositide 3-kinases (PI3K), alpha serine/threonine-protein kinase (AKT1), epidermal growth factor receptor (EGFR2) axis mechanism (P < 0.0001). Additionally, these complexes trigger a chain of events that include the inhibition of proliferating cell nuclear antigen (PCNA), transforming growth factor β1 (TGF β1), and topoisomerase II, and leading to a decrease in epidermoid cell proliferation. Furthermore, the inhibitory activity also resulted in the upregulation of caspases 3 and 9, indicating the acceleration of apoptotic markers, and the down regulation of miRNA221, suggesting a decrease in epidermoid proliferation. Molecular modeling of FeIII-L revealed that it had the best binding energy -8.02 kcal/mol and interacted with five hydrophobic π-interactions with Val270, Gln79, Leu210, and Trp80 against AKT1. Furthermore, the binding orientation of FeIII-L with Topoisomerase II was found to be the most stable, with a binding energy -8.25 kcal/mol. This stability was attributed to the presence of five hydrophobic π-interactions with His759, Guanin13, Cytosin8, and Ala465, and numerous ionic interactions, which were more favorable than those of doxorubicin and etoposide for new regimens of chemotherapeutic activities against skin cancer.

Recent progress in thiocarbazone metal complexes for cancer therapy via mitochondrial signalling pathway

Mitochondria are the energy factories of cells and are important targets for the development of novel tumour treatment strategies owing to their involvement in processes such as apoptosis, oxidative stress, and metabolic programming. Thiosemicarbazone metal complexes target mitochondria and reduce mitochondrial membrane potential. The breakdown of mitochondrial membrane potential is a key event in the early stage of apoptosis, which releases cytochrome C and other pro-apoptotic factors, activates the intracellular apoptotic enzyme cascade, and eventually causes irreversible apoptosis of tumour cells. Thiosemicarbazone metal complexes targeting the mitochondria have recently emerged as potential antitumour agents; therefore, this review describes the structural diversity of thiosemicarbazone metal [Fe(III), Cu(II), Ni(II), Zn(II), Ga(III), Pb(II), Au(III), and Ir(III)] complexes and explores their anti-tumour mechanisms that target mitochondrial pathways.

Desulfurization of thiosemicarbazones: the role of metal ions and biological implications

Thiosemicarbazones are biologically active substances whose structural formula is formed by an azomethine, an hydrazine, and a thioamide fragments, to generate a R2C=N-NR-C(=S)-NR2 backbone. These compounds often act as ligands to generate highly stable metal-organic complexes. In certain experimental conditions, however, thiosemicarbazones undergo reactions leading to the cleavage of the chain. Sometimes, the breakage involves desulfurization processes. The present work summarizes the different chemical factors that influence the desulfurization reactions of thiosemicarbazones, such as pH, the presence of oxidant reactants or the establishment of redox processes as those electrochemically induced, the effects of the solvent, the temperature, and the electromagnetic radiation. Many of these reactions require coordination of thiosemicarbazones to metal ions, even those present in the intracellular environment. The nature of the products generated in these reactions, their detection in vivo and in vitro, together with the relevance for the biological activity of these compounds, mainly as antineoplastic agents, is discussed.

Novel mono-, bi-, tri- and tetra-nuclear copper complexes that inhibit tumor growth through apoptosis and anti-angiogenesis

To develop the next-generation metal agents for efficiently inhibiting tumor growth, a series of novel mononuclear, binuclear and trinuclear copper (Cu) thiophene-2-formaldehyde thiosemicarbazone complexes and a tetranuclear Cu 1,2,4-triazole-derived complex have been synthesized and their structure-activity relationships have been studied. The trinucleated Cu complex showed the strongest inhibitory activity against T24 cells among all the Cu complexes. Its antitumor effect in vivo was superior to that of cisplatin, with reduced side effects. Further studies on the antitumor mechanism have showed that Cu complexes not only induced apoptosis of cancer cells but also inhibited tumor angiogenesis by inhibiting the migration and invasion of vascular endothelial cells, blocking the cell cycle in the G1 phase, and inducing autophagy.

Dithiobiureas Palladium(II) complexes' studies: From their synthesis to their biological action

Dithiobiureas coordination chemistry towards palladium (II) ions and their possible application is presented and discussed. 1,6-(4-Methoxyphenyl)-2,5-dithiobiurea and 1,6-(4-chlorophenyl)-2,5-dithiobiurea afford two Pd(II) complexes with the general formula [Pd2(H2L)Cl2(PPh3)2]. The metal ion forms one chelate ring with the dithiobiurea, and binds to a triphenylphosphine and an additional leaving group cisplatin like. One of the complexes (1) is endowed not only with stability in DMSO and aqua solutions containing a biological buffer but also with cytotoxicity versus gastric cancer cell lines. Complex 1 does not interact covalently to DNA models, neither activates p53 or Checkpoint Kinase 1 key proteins for DNA damage response. Thus, we propose that complex 1 exerts its action by activating Mitogen-Activated Protein Kinases [p38, Extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs)] as cell death inductors.

Inhibition of Topoisomerases by Metal Thiosemicarbazone Complexes

Topoisomerases, common targets for anti-cancer therapeutics, are crucial enzymes for DNA replication, transcription, and many other aspects of DNA metabolism. The potential anti-cancer effects of thiosemicarbazones (TSC) and metal-TSC complexes have been demonstrated to target several biological processes, including DNA metabolism. Human topoisomerases were discovered among the molecular targets for TSCs, and metal-chelated TSCs specifically displayed significant inhibition of topoisomerase II. The processes by which metal-TSCs or TSCs inhibit topoisomerases are still being studied. In this brief review, we summarize the TSCs and metal-TSCs that inhibit various types of human topoisomerases, and we note some of the key unanswered questions regarding this interesting class of diverse compounds.

Modulation of Transcription Profile Induced by Antiproliferative Thiosemicarbazone Metal Complexes in U937 Cancer Cells

Since the discovery of cisplatin, the search for metal-based compounds with therapeutic potential has been a challenge for the scientific community. In this landscape, thiosemicarbazones and their metal derivatives represent a good starting point for the development of anticancer agents with high selectivity and low toxicity. Here, we focused on the action mechanism of three metal thiosemicarbazones [Ni(tcitr)₂], [Pt(tcitr)₂], and [Cu(tcitr)₂], derived from citronellal. The complexes were already synthesized, characterized, and screened for their antiproliferative activity against different cancer cells and for genotoxic/mutagenic potential. In this work, we deepened the understanding of their molecular action mechanism using an in vitro model of a leukemia cell line (U937) and an approach of transcriptional expression profile analysis. U937 cells showed a significant sensitivity to the tested molecules. To better understand DNA damage induced by our complexes, the modulation of a panel of genes involved in the DNA damage response pathway was evaluated. We analyzed whether our compounds affected cell cycle progression to determine a possible correlation between proliferation inhibition and cell cycle arrest. Our results demonstrate that metal complexes target different cellular processes and could be promising candidates in the design of antiproliferative thiosemicarbazones, although their overall molecular mechanism is still to be understood.

Developing an Anticancer Platinum(II) Compound Based on the Uniqueness of Human Serum Albumin

To develop the next-generation Pt drug with remarkable activity and low toxicity to maximally inhibit tumor growth, we optimized a Pt(II) thiosemicarbazone compound (C4) with remarkable cytotoxicity to SK-N-MC cells and then constructed a new human serum albumin-C4 (HSA-C4) complex delivery system. The in vivo results showed that C4 and the HSA-C4 complex have remarkable therapeutic efficiency and almost no toxicity; they induced apoptosis and inhibited tumor angiogenesis. This system showed potential as a practical Pt drug. This study could pave the way for developing next-generation dual-targeted Pt drugs and achieving their targeting therapy for cancer.

Tuning the nuclearity of [Mo2O2S2]2+-based assemblies by playing with the degree of flexibility of bis-thiosemicarbazone ligands

[MoV2O₂S₂]²⁺-based thiosemicarbazone complexes appear as very promising molecules for biological applications due to the intrinsic properties of their components. This paper deals with the synthesis and characterization of six coordination complexes obtained by the reaction of [MoV2O₂S₂]²⁺ clusters with bis-thiosemicarbazone ligands that contain flexible or rigid spacers between the two thiosemicarbazone units. Interestingly, structural characterization by single-crystal X-ray diffraction, MALDI-TOF MS technique and NMR spectroscopy revealed that the nuclearity of the complex is controlled by the nature of the spacer between the thiosemicarbazone units. Binuclear complexes, namely [MoV2O₂S₂(L^1-3)], are isolated with flexible spacers while tetranuclear complexes [(MoV2O₂S₂)₂(L^4-6)₂] are formed when the bis-thiosemicarbazone ligands are built on rigid spacers.

Advances in thiosemicarbazone metal complexes as anti-lung cancer agents

The great success of cisplatin as a chemotherapeutic agent considerably increased research efforts in inorganic biochemistry to identify more metallic drugs having the potential of treating lung cancer. Metal coordination centres, which exhibit a wide range of coordination numbers and geometries, various oxidised and reduced states and the inherent ligand properties offer pharmaceutical chemists a plethora of drug structures. Owing to the presence of C=N and C=S bonds in a thiosemicarbazone Schiff base, N and S atoms in its hybrid orbital has lone pair of electrons, which can generate metal complexes with different stabilities with most metal elements under certain conditions. Such ligands and complexes play key roles in the treatment of anti-lung cancer. Research regarding metallic anti-lung cancer has advanced considerably, but there remain several challenges. In this review, we discuss the potential of thiosemicarbazone Schiff base complexes as anti-lung cancer drugs, their anti-cancer activities and the most likely action mechanisms involving the recent families of copper, nickel, platinum, ruthenium and other complexes.

Thiosemicarbazone Derivatives Developed to Overcome COTI-2 Resistance

COTI-2 is currently being evaluated in a phase I clinical trial for the treatment of gynecological and other solid cancers. As a thiosemicarbazone, this compound contains an N,N,S-chelating moiety and is, therefore, expected to bind endogenous metal ions. However, besides zinc, the metal interaction properties of COTI-2 have not been investigated in detail so far. This is unexpected, as we have recently shown that COTI-2 forms stable ternary complexes with copper and glutathione, which renders this drug a substrate for the resistance efflux transporter ABCC1. Herein, the complex formation of COTI-2, two novel terminal N-disubstituted derivatives (COTI-NMe2 and COTI-NMeCy), and the non-substituted analogue (COTI-NH2) with iron, copper, and zinc ions was characterized in detail. Furthermore, their activities against drug-resistant cancer cells was investigated in comparison to COTI-2 and Triapine. These data revealed that, besides zinc, also iron and copper ions need to be considered to play a role in the mode of action and resistance development of these thiosemicarbazones. Moreover, we identified COTI-NMe2 as an interesting new drug candidate with improved anticancer activity and resistance profile.

Synthesis, Structures, and Solution Studies of a New Class of [Mo2O2S2]-Based Thiosemicarbazone Coordination Complexes

This paper deals with the synthesis, structural studies, and behavior in solution of unprecedented coordination complexes built by the association of a panel of 14 representative thiosemicarbazone ligands with the cluster [Mo₂O₂S₂]²⁺. These complexes have been thoroughly characterized both in the solid state and in solution by XRD and by NMR, respectively. In particular, HMBC ¹H{¹⁵N} and ¹H DOSY NMR experiments bring important elements for understanding the complexes' behavior in solution. These studies demonstrate that playing on the nature and the position of various substituents on the ligands strongly influences the coordination modes of the ligands as well as the numbers of isomers in solution, mainly 2 products for the majority of complexes and up to 5 for some of them.

Conformational Properties of New Thiosemicarbazone and Thiocarbohydrazone Derivatives and Their Possible Targets

The structure assignment and conformational analysis of thiosemicarbazone KKI15 and thiocarbohydrazone KKI18 were performed through homonuclear and heteronuclear 2D Nuclear Magnetic Resonance (NMR) spectroscopy (2D-COSY, 2D-NOESY, 2D-HSQC, and 2D-HMBC) and quantum mechanics (QM) calculations using Functional Density Theory (DFT). After the structure identification of the compounds, various conformations of the two compounds were calculated using DFT. The two molecules showed the most energy-favorable values when their two double bonds adopted the E configuration. These configurations were compatible with the spatial correlations observed in the 2D-NOESY spectrum. In addition, due to the various isomers that occurred, the energy of the transition states from one isomer to another was calculated. Finally, molecular binding experiments were performed to detect potential targets for KKI15 and KKI18 derived from SwissAdme. In silico molecular binding experiments showed favorable binding energy values for all four enzymes studied. The strongest binding energy was observed in the enzyme butyrylcholinesterase. ADMET calculations using the preADMET and pKCSm software showed that the two molecules appear as possible drug leads.

Distinct Mechanisms of Cytotoxicity in Novel Nitrogenous Heterocycles: Future Directions for a New Anti-Cancer Agent

Electron-rich, nitrogenous heteroaromatic compounds interact more with biological/cellular components than their non-nitrogenous counterparts. The strong intermolecular interactions with proteins, enzymes, and receptors confer significant biological and therapeutic properties to the imidazole derivatives, giving rise to a well-known and extensively used range of therapeutic drugs used for infections, inflammation, and cancer, to name a few. The current study investigates the anti-cancer properties of fourteen previously synthesized nitrogenous heterocycles, derivatives of imidazole and oxazolone, on a panel of cancer cell lines and, in addition, predicts the molecular interactions, pharmacokinetic and safety profiles of these compounds. Method: The MTT and CellTiter-Glo® assays were used to screen the imidazole and oxazolone derivatives on six cancer cell lines: HL60, MDA-MB-321, KAIMRC1, KMIRC2, MCF-10A, and HCT8. Subsequently, in vitro tubulin staining and imaging were performed, and the level of apoptosis was measured using the Promega ApoTox-Glo® triplex assay. Furthermore, several computational tools were utilized to investigate the pharmacokinetics and safety profile, including PASS Online, SEA Search, the QikProp tool, SwissADME, ProTox-II, and an in silico molecular docking study on tubulin to identify the critical molecular interactions. Results: In vitro analysis identified compounds 8 and 9 to possess the most significant potent cytotoxic activity on the HL60 and MDA-MB-231 cell lines, supported by PASS Online anti-cancer predictions with pa scores of 0.413 and 0.434, respectively. In addition, compound 9 induced caspase 3/7 dependent-apoptosis and interfered with tubulin polymerization in the MDA-MB-231 cell line, consistent with in silico docking results, identifying binding similarity to the native ligand colchicine. All the derivatives, including compounds 8 and 9, had acceptable pharmacokinetics; however, the safety profile was suboptimal for all the tested derivates except compound 4. Conclusion: The imidazole derivative compound 9 is a promising anti-cancer agent that switches on caspase-dependent apoptotic cell death and modulates microtubule function. Therefore, it could be a lead compound for further drug optimization and development.

Albumin Conjugates of Thiosemicarbazone and Imidazole-2-thione Prochelators: Iron Coordination and Antiproliferative Activity

The central role of iron in tumor progression and metastasis motivates the development of iron-binding approaches in cancer chemotherapy. Disulfide-based prochelators are reductively activated upon cellular uptake to liberate thiol chelators responsible for iron sequestration. Herein, a trimethyl thiosemicarbazone moiety and the imidazole-2-thione heterocycle are incorporated in this prochelator design. Iron binding of the corresponding tridentate chelators leads to the stabilization of a low-spin ferric center in 2 : 1 ligand-to-metal complexes. Native mass spectrometry experiments show that the prochelators form stable disulfide conjugates with bovine serum albumin, thus affording novel bioconjugate prochelator systems. Antiproliferative activities at sub-micromolar levels are recorded in a panel of breast, ovarian and colorectal cancer cells, along with significantly lower activity in normal fibroblasts.