Anticancer Applications and Recent Investigations of Metallodrugs Based on Gallium, Tin and Titanium

Computational and experimental examinations of new antitumor palladium(II) complex: CT-DNA-/BSA-binding, in-silico prediction, DFT perspective, docking, molecular dynamics simulation and ONIOM

Since the design of metal complexes with better biological activities is important, herein a new palladium(II) complex bearing en and acac (en and acac stand for ethylenediamine and acetylacetonato, respectively) as its ligands, [Pd(en)(acac)]NO3 complex, was synthesized and fully characterized. Quantum chemical computations of the palladium(II) complex were done via DFT/B3LYP method. Cytotoxicity activity of the new compound on leukemia cell line (K562) was assessed via MTT method. The findings indicated that the metal complex has remarkable cytotoxic effect than cisplatin. OSIRIS DataWarrior software was employed to calculate in-silico physicochemical and toxicity parameters of the synthesized complex which rendered significant results. To comprehend the interaction type of new metal compound with macromolecules, the in depth investigation of interaction of mentioned complex with CT-DNA and BSA was accomplished by fluorescence, UV-Visible absorption spectroscopy, viscosity measurement, gel electrophoresis, FRET analysis and circular dichroism (CD) spectroscopy. On the other hand, computational molecular docking was carried out and the obtained data demonstrated that H-bond and van der Waals forces are the dominant forces for the binding of the compound to the mentioned biomolecules. Molecular dynamics simulation was also done and confirmed the stability of best docked pose of palladium(II) complex inside DNA or BSA over the time and in presence of water solvent. Also, Our own N-layered Integrated molecular Orbital and molecular Mechanics (ONIOM) methodology based on the hybridization of quantum mechanics and molecular mechanics (QM/MM) methodology was accomplished to inquire about binding of Pd(II) complex with DNA or BSA.HIGHLIGHTSNew biologically active Pd(II) complex was synthesized and characterized.The in silico studies of the designed complex and its ligands were accomplished by OSIRIS DataWarrior softwareInteraction with CT-DNA and BSA was assessed by various spectroscopic methods.Molecular docking simulation supported the interaction with both macromolecules.Based on ONIOM analysis, the structures of the complex and biomolecules are altered after binding. Communicated by Ramaswamy H. Sarma.

Titanium-45 (45Ti) Radiochemistry and Applications in Molecular Imaging

Molecular imaging is an important part of modern medicine which enables the non-invasive identification and characterization of diseases. With the advancement of radiochemistry and scanner technology, nuclear medicine is providing insight into efficient treatment options for individual patients. Titanium-45 (45Ti) is a lesser-explored radionuclide that is garnering increasing interest for the development of positron emission tomography (PET) radiopharmaceuticals. This review discusses aspects of this radionuclide including production, purification, radiochemistry development, and molecular imaging studies.

Vanadocene-functionalized mesoporous silica nanoparticles: platforms for the development of theranostic materials against breast cancer

Nanoscale materials have demonstrated a very high potential in anticancer therapy by properly adjusting their functionalization and physicochemical properties. Herein, we report the synthesis of some novel vanadocene-loaded silica-based nanomaterials incorporating four different S-containing amino acids (penicillamine, methionine, captopril, and cysteine) and different fluorophores (rhodamine B, coumarin 343 or Alexa Fluor™ 647), which have been characterized by diverse solid-state spectroscopic techniques viz; FTIR, diffuse reflectance spectroscopies,13C and51V solid-state NMR spectroscopy, thermogravimetry and TEM. The analysis of the biological activity of the novel vanadocene-based nanostructured silicas showed that the materials containing cysteine and captopril aminoacids demonstrated high cytotoxicity and selectivity against triple negative breast cancer cells, making them very promising antineoplastic drug candidates. According to the biological results it seems that vanadium activity is connected to its incorporation through the amino acid, resulting in synergy that increases the cytotoxic activity against cancer cells of the studied materials presumably by increasing cell internalization. The results presented herein hold significant potential for future developments in mesoporous silica-supported metallodrugs, which exhibit strong cytotoxicity while maintaining low metal loading. They also show potential for theranostic applications highlighted by the analysis of the optical properties of the studied systems after incorporating rhodamine B, coumarin 343 (possible)in vitroanticancer analysis, or Alexa Fluor™ 647 (in vivostudies of cancer models).

Organotin(IV)-Decorated Graphene Quantum Dots as Dual Platform for Molecular Imaging and Treatment of Triple Negative Breast Cancer

The pharmacological activity of organotin(IV) complexes in cancer therapy is well recognized but their large applicability is hampered by their poor water solubility. Hence, carbon dots, in particular nitrogen-doped graphene quantum dots (NGQDs), may be a promising alternative for the efficient delivery of organotin(IV) compounds as they have a substantial aqueous solubility, a good chemical stability, and non-toxicity as well as a bright photoluminescence that make them ideal for theranostic applications against cancer. Two different multifunctional nanosystems have been synthesized and fully characterized based on two fragments of organotin-based cytotoxic compounds and 4-formylbenzoic acid (FBA), covalently grafted onto the NGQDs surface. Subsequently, an in vitro determination of the therapeutic and theranostic potential of the achieved multifunctional systems was carried out. The results showed a high cytotoxic potential of the NGQDs-FBA-Sn materials against breast cancer cell line (MDA-MB-231) and a lower effect on a non-cancer cell line (kidney cells, HEK293T). Besides, thanks to their optical properties, the dots enabled their fluorescence molecular imaging in the cytoplasmatic region of the cells pointing towards a successful cellular uptake and a release of the metallodrug inside cancer cells (NGQDs-FBA-Sn).

Effect of the extra-nuclear cation on the cytotoxicity and mechanism of action of pyridine-2,6-dicarboxylate Ga(III) complexes

Two Ga(III) complexes (C1) and (C2) were prepared by the one-pot reaction of pyridine-2,6-dicarboxylic acid and aminopyridine derivatives with gallium(III) nitrate octahydrate. The compounds were characterized by single-crystal X-ray diffraction. The distorted octahedral geometry was confirmed by crystallographic data for both complexes. The study of the in vitro cytotoxicity of the compounds showed that the presence of different extra-nuclear cations can affect the cytotoxicity of the same anionic complexes. The most significant antiproliferative activity was observed for C1 (IC50 = 0.69 μM, MAE = 73.96%) and C2 (IC50 = 3.78 μM, MAE = 60.35%) (where MAE represents the maximal antiproliferative effect) against A431 cell line. The mechanistic study evidenced the same pathway for the death of A431 cells treated with the complexes, although the results for C2 were obtained at approximately five times the concentration of C1. According to the study, both complexes induced cell cycle arrest in G2/M phase in A431 cells by upregulating the levels of p21, p27, p-cdc25C, and p-cdc2 and downregulating the levels of cdc25C, cdc2, and cyclin B1. In addition, apoptosis via a caspase-dependent mitochondrial pathway was confirmed by a decrease in Bcl-2 family proteins and an increase in the expression of procaspase-9 and 3. Also, the complexes induced autophagic cell death by activating the RAGE /PI3KC3/Beclin 1 pathway in A431 cells. DATA AVAILABILITY: CCDC 874052 and 874055 contain the supplementary crystallographic data for C1 and C2, respectively. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/services/structures?pid=ccdc:874052,874055&sid=CCDCManual, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.

Bioinorganic Modulators of Ferroptosis: A Review of Recent Findings

Ferroptosis was first reported as a separate modality of regulated cell death in 2008 and distinguished under its current name in 2012 after it was first induced with erastin. In the following decade, multiple other chemical agents were researched for their pro- or anti-ferroptotic properties. Complex organic structures with numerous aromatic moieties make up the majority of this list. This review fills a more overlooked niche by gathering, outlining and setting out conclusions regarding less prominent cases of ferroptosis induced by bioinorganic compounds and reported on within the last few years. The article contains a short summary of the application of bioinorganic chemicals based on gallium, several chalcogens, transition metals and elements known as human toxicants used for the purpose of evoking ferroptotic cell death in vitro or in vivo. These are used in the form of free ions, salts, chelates, gaseous and solid oxides or nanoparticles. Knowledge of how exactly these modulators promote or inhibit ferroptosis could be beneficial in the context of future therapies aimed against cancer or neurodegenerative diseases, respectively.

Dual Anticancer and Antibacterial Properties of Silica-Based Theranostic Nanomaterials Functionalized with Coumarin343, Folic Acid and a Cytotoxic Organotin(IV) Metallodrug

Five different silica nanoparticles functionalized with vitamin B12, a derivative of coumarin found in green plants and a minimum content of an organotin(IV) fragment (1-MSN-Sn, 2-MSN-Sn, 2-SBA-Sn, 2-FSPm-Sn and 2-FSPs-Sn), were identified as excellent anticancer agents against triple negative breast cancer, one of the most diagnosed and aggressive cancerous tumors, with very poor prognosis. Notably, compound 2-MSN-Sn shows selectivity for cancer cells and excellent luminescent properties detectable by imaging techniques once internalized. The same compound is also able to interact with and nearly eradicate biofilms of Staphylococcus aureus, the most common bacteria isolated from chronic wounds and burns, whose treatment is a clinical challenge. 2-MSN-Sn is efficiently internalized by bacteria in a biofilm state and destroys the latter through reactive oxygen species (ROS) generation. Its internalization by bacteria was also efficiently monitored by fluorescence imaging. Since silica nanoparticles are particularly suitable for oral or topical administration, and considering both its anticancer and antibacterial activity, 2-MSN-Sn represents a new dual-condition theranostic agent, based primarily on natural products or their derivatives and with only a minimum amount of a novel metallodrug.

Biological Use of Nanostructured Silica-Based Materials Functionalized with Metallodrugs: The Spanish Perspective

Since the pioneering work of Vallet-Regí's group on the design and synthesis of mesoporous silica-based materials with therapeutic applications, during the last 15 years, the potential use of mesoporous silica nanostructured materials as drug delivery vehicles has been extensively explored. The versatility of these materials allows the design of a wide variety of platforms that can incorporate numerous agents of interest (fluorophores, proteins, drugs, etc.) in a single scaffold. However, the use of these systems loaded with metallodrugs as cytotoxic agents against different diseases and with distinct therapeutic targets has been studied to a much lesser extent. This review will focus on the work carried out in this field, highlighting both the pioneering and recent contributions of Spanish groups that have synthesized a wide variety of systems based on titanium, tin, ruthenium, copper and silver complexes supported onto nanostructured silica. In addition, this article will also discuss the importance of the structural features of the systems for evaluating and modulating their therapeutic properties. Finally, the most interesting results obtained in the study of the potential therapeutic application of these metallodrug-functionalized silica-based materials against cancer and bacteria will be described, paying special attention to preclinical trials in vivo.

Gold(III) Complexes with Phenanthroline-derivatives Ligands Induce Apoptosis in Human Colorectal and Breast Cancer Cell Lines

Due to their promising effects, gold(III) complexes recently drew increasing attention in the design of new metal-based anticancer therapeutics. Two gold(III) complexes, square-planar [Au(DPP)Cl2]+ - Complex 1 and distorted square-pyramidal [Au(DMP)Cl3] - Complex 2 (where DPP=4,7-diphenyl-1,10-phenanthroline and DMP=2,9-dimethyl-1,10-phenanthroline) were previously synthetized, described and approved as complexes with pronounced cytotoxic effects on colorectal HCT-116 and breast MDA-MB-231 cancer cells. This study investigated the type of cell death by AO/EB double staining, and identification of possible targets responsible for their cytotoxicity, monitored by immunofluorescence and qPCR methods. Both complexes induced apoptosis in all applied concentrations. In the HCT-116 cells apoptosis was activated by external apoptotic pathway, via increase of Fas receptor protein expression and Caspase 8 gene expression. Also, the mitochondrial pathway was triggered by affecting the Bcl-2 members of regulatory proteins and increased caspase 9 protein expression. In MDA-MB-231 cells, apoptosis was initiated from the mitochondria, due to disbalance between expressions of pro- and anti-apoptotic Bcl-2 family members and caspase 9 activation. Complex 1 shows better activity compared to Complex 2, which is in accordance with its structural characteristics. The results deal weighty data about proapoptotic activity of gold(III) complexes and highlighted potential targets for cancer therapy.

Cytotoxic effects of halogenated tin phosphinoyldithioformate complexes against several cancer cell lines

Organotin complexes are studied as promising alternatives to the anticancer drug cisplatin. We report two monoorganotin(IV) complexes based on a dibenzyl phosphinoyldithioformate (H-DBPTF) ligand, containing either bromide (Sn-DBPTF-1) or chloride (Sn-DBPTF-2) anions. The complexes were characterized by standard analytical techniques and the structural details of these complexes were elucidated by single crystal X-ray diffraction. Sn-DBPTF-1 was cytotoxic at IC50 <10 μg mL-1 against cancer cell lines A549 (lung cancer), Aspc-1 (pancreatic cancer), OVCAR-3 (ovarian cancer), T-47D (breast cancer) and HCT116 (colon cancer), and breast epithelial stem cell line D492. The non-tumorigenic breast epithelial cell line MCF-10 was less sensitive at IC50 = 22 μg mL-1. Sn-DBPTF-2 had limited cytotoxic effect at IC50 13-37 μg mL-1. Sn-DBPTF-1 induced apoptosis and double-strand DNA breaks. Cell cycle arrest in G2 occurred in HCT116 and accumulation in G1 in Aspc-1. The results indicate that the basic effect of Sn-DBPTF-1 is to induce DNA damage, leading to apoptosis and cell cycle arrest depending on the cell line.

Curcumin-Based β-Diketo Ligands for Ga3+: Thermodynamic Investigation of Potential Metal-Based Drugs

Curcumin is known for its therapeutic properties; among these, antioxidant, anti-inflammatory and anti-cancer ones stand out. Besides, curcumin metal complexes have shown widespread application in medicine and can be exploited as lead structures for developing metal-based drugs. Unfortunately, curcumin is poorly bioavailable, mainly due to its instability in physiological conditions; this weakness is tightly connected to the presence of the β-diketo moiety undergoing tautomeric equilibrium. Stability and metal-chelating ability can be tuned by modulating the electronic effects and steric hindrance close to the β-diketo moiety; in addition, formation of a metal complex shifts the tautomeric equilibrium towards the β-keto–enol form and increases stability in biological media. Among the metals used in clinical therapy, gallium nitrate has shown to have significant antitumor activity against non-Hodgkin lymphoma and bladder cancer, thus indicating that gallium-based drugs have potential for further development as antineoplastic agents with improved therapeutic activity. Curcuminoids have demonstrated high affinity for gallium(III), allowing the formation of stable positively charged M:L 1:2 β-diketonate complexes that benefit from the therapeutic activity of both the metal and the ligand. Seven new curcumin derivatives were synthesized and completely characterized. The new derivatives retain the solvent-dependent keto–enol tautomerism, with the prevalence of the diketo form in aqueous solution. Enhanced stability in simulated physiological conditions was observed in comparison to the lead compound curcumin. The presence of Ga3+ anticipates the dissociation of the enolic proton, allowing chelate complex formation, and simultaneously it shifts the tautomeric equilibrium towards the keto–enol form. A complete 1H/13C NMR and UV–Vis study was performed to define the metal-to-ligand stoichiometry ratio and the overall stability constants. In addition, we demonstrated that some of the derivatives have increased antiproliferative activity on colon cancer cells compared to curcumin and antioxidant properties. On the whole, the synthesized curcumin-based molecules may act as new gallium(III) chelators with improved stability with respect to curcumin and could open interesting perspectives for the development of novel therapeutic agents for cancer.

Medicinal Hypervalent Tellurium Prodrugs Bearing Different Ligands: A Comparative Study of the Chemical Profiles of AS101 and Its Halido Replaced Analogues

Ammonium trichloro (dioxoethylene-O,O′) tellurate (AS101) is a potent immunomodulator prodrug that, in recent years, entered various clinical trials and was tested for a variety of potential therapeutic applications. It has been demonstrated that AS101 quickly activates in aqueous milieu, producing TeOCl3−, which likely represents the pharmacologically active species. Here we report on the study of the activation process of AS101 and of two its analogues. After the synthesis and characterization of AS101 and its derivatives, we have carried out a comparative study through a combined experimental and computational analysis. Based on the obtained results, we describe here, for the first time, the detailed reaction that AS101 and its bromido- and iodido-replaced analogues undergo in presence of water, allowing the conversion of the original molecule to the likely true pharmacophore. Interestingly, moving down in the halogens’ group we observed a higher tendency to react, attributable to the ligands’ effect. The chemical and mechanistic implications of these meaningful differences are discussed.

Gallium(III) Complex with Cloxyquin Ligands Induces Ferroptosis in Cancer Cells and Is a Potent Agent against Both Differentiated and Tumorigenic Cancer Stem Rhabdomyosarcoma Cells

In this work, gallium(III) complex with cloxyquin (5-chloro-8-quinolinol, HClQ) ligands is shown to effectively inhibit proliferation of rhabdomyosarcoma cells, the frequent, aggressive, and poorly treatable cancer of children. It offers striking selectivity to cancer cells compared to noncancerous human fibroblasts. The data reveal that the complex induces ferroptosis in rhabdomyosarcoma cells, likely due to interfering with iron metabolism. Importantly, it can kill both bulk and stem rhabdomyosarcoma cells. To the best of our knowledge, this is the first compound based on metal other than Fe capable of inducing ferroptosis in cancer cells.

OUP accepted manuscript

Fourteen new organotin(IV) complexes were successfully synthesized and characterized by elemental analyses, Fourier transform infrared spectroscopy (FT-IR), multinuclear (1H, 13C, and 119Sn) NMR spectroscopy, high-resolution mass spectrometry (HRMS), and X-ray single-crystal techniques. Crystallographic data showed that the complexes 1b, 2b, 3b, and 5b were macrocyclic compounds, 4b exhibited a one-dimensional spiral chain structure with distorted trigonal bipyramidal geometry, other complexes were centrosymmetric dimers, and there was an Sn2O2 four-membered ring in the middle of the molecule. In-vitro anticancer activity against the three human tumor cell lines NCI-H460, MCF-7, and HepG2 was studied, and the dibutyltin complex 5a is a more potent antitumor agent than other complexes and cisplatin. Cell apoptosis study of 5a with the highest activity on HepG2 cancer cell lines was done by flow cytometry; it was shown that the antitumor activity of 5a was related to apoptosis, and it inhibited proliferation by blocking cells in the G2/M phase. The single-cell gel electrophoresis assay results show that 5a induces DNA damage. 5a interacts with ct-DNA by intercalating the mode of interaction. UV-visible absorption spectrometry, fluorescence competitive, viscosity measurements, and gel electrophoresis results also support the intercalative mode of interaction for 5a with DNA.

In Vitro Anti-SARS-CoV-2 Activity of Selected Metal Compounds and Potential Molecular Basis for Their Actions Based on Computational Study

Metal-based drugs represent a rich source of chemical substances of potential interest for the treatment of COVID-19. To this end, we have developed a small but representative panel of nine metal compounds, including both synthesized and commercially available complexes, suitable for medical application and tested them in vitro against the SARS-CoV-2 virus. The screening revealed that three compounds from the panel, i.e., the organogold(III) compound Aubipyc, the ruthenium(III) complex KP1019, and antimony trichloride (SbCl₃), are endowed with notable antiviral properties and an acceptable cytotoxicity profile. These initial findings prompted us to perform a computational study to unveil the likely molecular basis of their antiviral actions. Calculations evidenced that the metalation of nucleophile sites in SARS-CoV-2 proteins or nucleobase strands, induced by Aubipyc, SbCl₃, and KP1019, is likely to occur. Remarkably, we found that only the deprotonated forms of Cys and Sec residues can react favorably with these metallodrugs. The mechanistic implications of these findings are discussed.

Pt(II)-Thiocarbohydrazone Complex as Cytotoxic Agent and Apoptosis Inducer in Caov-3 and HT-29 Cells through the P53 and Caspase-8 Pathways

In this study, a platinum(II) complex ([Pt(H₂L)(PPh₃)] complex) containing a thiocarbohydrazone as the ligand was tested as an anti-proliferative agent against ovarian adenocarcinoma (Caov-3) and human colorectal adenocarcinoma (HT-29) through MTT assays. Apoptotic markers were tested by the AO/PI double staining assay and DNA fragmentation test. Flow cytometry was conducted to measure cell cycle distribution, while the p53 and caspase-8 pathways were tested via immunofluorescence assay. Results demonstrated that the cytotoxic effect of the Pt(II)-thiocarbohydrazone complexes against Caov-3 and HT-29 cells was highly significant, and this effect triggered the activation of the p53 and caspase-8 pathways. Besides, apoptosis stimulated by the Pt(II)-thiocarbohydrazone complex was associated with cell cycle arrest at the G0/G1 phase. These findings suggest that the target complex inhibited the proliferation of Caov-3 and HT-29 cells, resulting in the arrest of the cell cycle and induction of apoptosis via the stimulation of the p53 and caspase-8 pathways. The present data suggests that the Pt(II)-thiocarbohydrazone complex could also be a promising chemotherapeutic agent for other types of cancer cells.

Synthesis of asymmetrical diaminobis(alkoxo)-bisphenol compounds and their C1-symmetrical mono-ligated titanium(iv) complexes as highly stable highly active antitumor compounds

Asymmetrical 2,2'-((ethane-1,2-diylbis((2-hydroxyethyl)azanediyl))bis(methylene))diphenol substituted compounds and their C1-symmetrical diaminobis(phenolato)-bis(alkoxo) titanium(iv) complexes were synthesized, with one symmetrical analogue. X-ray crystallography corroborated tight ligand binding. Different substitutions on the two aromatic rings enabled fine-tuning of the complex properties, giving enhanced solubility, high anticancer activity (IC50 < 4 μM), and significant hydrolytic stability.

In Vitro Interaction of 5-Aminoorotic Acid and Its Gallium(III) Complex with Superoxide Radical, Generated by Two Model Systems

Increased levels of the superoxide radical are associated with oxidative damage to healthy tissues and with elimination of malignant cells in a living body. It is desirable that a chemotherapeutic combines pro-oxidant behavior around and inside tumors with antioxidant action near healthy cells. A complex consisting of a pro-oxidant cation and antioxidant ligands could be a potential anticancer agent. Ga(III) salts are known anticancer substances, and 5-aminoorotic acid (HAOA) is a ligand with antioxidant properties. The in vitro effects of HAOA and its complex with Ga(III) (gallium(III) 5-aminoorotate (GaAOA)) on the in vitro accumulation of superoxide and other free radicals were estimated. Model systems such as potassium superoxide (KO2), xanthine/xanthine oxidase (X/XO), and rat blood serum were utilized. Data suggested better antioxidant effect of GaAOA compared to HAOA. Evidently, all three ligands of GaAOA participated in the scavenging of superoxide. The effects in rat blood serum were more nuanced, considering the chemical and biochemical complexity of this model system. It was observed that the free-radical-scavenging action of both compounds investigated may be manifested via both hydrogen donation and electron transfer pathways. It was proposed that the radical-scavenging activities (RSAs) of HAOA and its complex with Ga(III) may be due to a complex process, depending on the concentration, and on the environment, nature, and size of the free radical. The electron transfer pathway was considered as more probable in comparison to hydrogen donation in the scavenging of superoxide by 5-aminoorotic acid and its gallium(III) complex.

Titanium Tackles the Endoplasmic Reticulum: A First Genomic Study on a Titanium Anticancer Metallodrug

PhenolaTi is an advanced non-toxic anticancer chemotherapy; this inert bis(phenolato)bis(alkoxo) Ti(IV) complex demonstrates the intriguing combination of high and wide efficacy with no detected toxicity in animals. Here we unravel the cellular pathways involved in its mechanism of action by a first genome study on Ti(IV)-treated cells, using an attuned RNA sequencing-based available technology. First, phenolaTi induced apoptosis and cell-cycle arrest at the G2/M phase in MCF7 cells. Second, the transcriptome of the treated cells was analyzed, identifying alterations in pathways relating to protein translation, DNA damage, and mitochondrial eruption. Unlike for common metallodrugs, electrophoresis assay showed no inhibition of DNA polymerase activity. Reduced in vitro cytotoxicity with added endoplasmic reticulum (ER) stress inhibitor supported the ER as a putative cellular target. Altogether, this paper reveals a distinct ER-related mechanism by the Ti(IV) anticancer coordination complex, paving the way for wider applicability of related techniques in mechanistic analyses of metallodrugs.

Five new complexes with deferiprone and N,N-donor ligands: evaluation of cytotoxicity against breast cancer MCF-7 cell line and HSA-binding determination

In this study, five new complexes containing deferiprone (dfp) and N,N-donor ligands [bipyridine (bpy), 1,10-phenanthroline (phen) and ethylenediamine (en)] were synthesized: [Fe(dfp)₂(bpy)](PF₆) (1), [Fe(dfp)₂(phen)](PF₆) (2), [Cu₂(dfp)₂(bpy)₂](PF₆)₂ (3), [Ga(dfp)₂(bpy)](PF₆) (4), and [Fe(dfp)₂(en)](PF₆) (5). Characterization of these complexes was carried out through elemental analysis and FT-IR, and single-crystal X-ray crystallography was used to determine their structures. Whilst the polyhedron has a distorted octahedral geometry in 1, 2, 4, and 5, it adopts a distorted square-pyramidal geometry in 3. Interaction of these compounds with human serum albumin (HSA) has been investigated through electronic absorption and fluorescence titration techniques. Emission quenching was performed separately for each complex at three different temperatures and thermodynamic parameters were calculated using binding constants to better understand the power of different binding forces with the HSA. Results demonstrated that compounds interact strongly with the HSA with a static quenching mechanism. Our evaluation of the cytotoxicity of complexes against the breast cancer MCF-7 cell line showed that complex 2 presents a better cytotoxicity than the standard cis-Pt. Finally, using the AutoDock 4.2 program, simulations to analyze the mechanism of complex-HSA interactions and their binding mode were carried out. Results showed that the best binding mode is located in subdomain IB for 1, 2, and 4, in I/II for 3, and in IA/IIA for 5. Communicated by Ramaswamy H. Sarma.

Role of Folic Acid in the Therapeutic Action of Nanostructured Porous Silica Functionalized with Organotin(IV) Compounds Against Different Cancer Cell Lines

The synthesis, characterization and cytotoxic activity against different cancer cell lines of various mesoporous silica-based materials containing folate targeting moieties and a cytotoxic fragment based on a triphenyltin(IV) derivative have been studied. Two different mesoporous nanostructured silica systems have been used: firstly, micronic silica particles of the MSU-2 type and, secondly, mesoporous silica nanoparticles (MSNs) of about 80 nm. Both series of materials have been characterized by different methods, such as powder X-ray diffraction, X-ray fluorescence, absorption spectroscopy and microscopy. In addition, these systems have been tested against four different cancer cell lines, namely, OVCAR-3, DLD-1, A2780 and A431, in order to observe if the size of the silica-based systems and the quantity of incorporated folic acid influence their cytotoxic action. The results show that the materials are more active when the quantity of folic acid is higher, especially in those cells that overexpress folate receptors such as OVCAR-3 and DLD-1. In addition, the study of the potential modulation of the soluble folate receptor alpha (FOLR1) by treatment with the synthesized materials has been carried out using OVCAR-3, DLD-1, A2780 and A431 tumour cell lines. The results show that a relatively high concentration of folic acid functionalization of the nanostructured silica together with the incorporation of the cytotoxic tin fragment leads to an increase in the quantity of the soluble FOLR1 secreted by the tumour cells. In addition, the studies reported here show that this increase of the soluble FOLR1 occurs presumably by cutting the glycosyl-phosphatidylinositol anchor of membrane FR-α and by the release of intracellular FR-α. This study validates the potential use of a combination of mesoporous silica materials co-functionalized with folate targeting molecules and an organotin(IV) drug as a strategy for the therapeutic treatment of several cancer cells overexpressing folate receptors.

Evaluating Ligand Modifications of the Titanocene and Auranofin Moieties for the Development of More Potent Anticancer Drugs

Over time platinum-based anticancer drugs have dominated the market, but their side effects significantly impact the quality of life of patients. Alternative treatments are being developed all over the world. The titanocene and auranofin families of compounds, discovered through an empirical search for other metal-based therapeutics, hold tremendous promise to improve the outcomes of cancer treatment. Herein we present a historical perspective of these compounds and review current efforts focused on the evolution of their ligands to improve their physiological solution stability, cancer selectivity, and antiproliferative performance, guided by a clear understanding of the coordination chemistry and aqueous speciation of the metal ions, of the cytotoxic mechanism of action of the compounds, and the external factors that limit their therapeutic potential. Newer members of these families of compounds and their combination in novel bimetallic complexes are the result of years of scientific research. We believe that this review can have a positive impact in the development and understanding of the metal-based drugs of gold, titanium, and beyond.

Multifunctional Silica-Based Nanoparticles with Controlled Release of Organotin Metallodrug for Targeted Theranosis of Breast Cancer

Three different multifunctional nanosystems based on the tethering onto mesoporous silica nanoparticles (MSN) of different fragments such as an organotin-based cytotoxic compound Ph3Sn{SCH2CH2CH2Si(OMe)3} (MSN-AP-Sn), a folate fragment (MSN-AP-FA-Sn), and an enzyme-responsive peptide able to release the metallodrug only inside cancer cells (MSN-AP-FA-PEP-S-Sn), have been synthesized and fully characterized by applying physico-chemical techniques. After that, an in vitro deep determination of the therapeutic potential of the achieved multifunctional nanovectors was carried out. The results showed a high cytotoxic potential of the MSN-AP-FA-PEP-S-Sn material against triple negative breast cancer cell line (MDA-MB-231). Moreover, a dose-dependent metallodrug-related inhibitory effect on the migration mechanism of MDA-MB-231 tumor cells was shown. Subsequently, the organotin-functionalized nanosystems have been further modified with the NIR imaging agent Alexa Fluor 647 to give three different theranostic silica-based nanoplatforms, namely, MSN-AP-Sn-AX (AX-1), MSN-AP-FA-Sn-AX (AX-2), and MSN-AP-FA-PEP-S-Sn-AX (AX-3). Their in vivo potential as theranostic markers was further evaluated in a xenograft mouse model of human breast adenocarcinoma. Owing to the combination of the receptor-mediated site targeting and the specific fine-tuned release mechanism of the organotin metallodrug, the nanotheranostic drug MSN-AP-FA-PEP-S-Sn-AX (AX-3) has shown targeted diagnostic ability in combination with enhanced therapeutic activity by promoting the inhibition of tumor growth with reduced hepatic and renal toxicity upon the repeated administration of the multifunctional nanodrug.

Designing of novel zinc(ii) Schiff base complexes having acyl hydrazone linkage: study of phosphatase and anti-cancer activities

The phosphatase and anti-cancer activities of three novel acyl hydrazone based zinc(ii) Schiff base complexes have been unveiled.

Developments in Platinum-Group Metals as Dual Antibacterial and Anticancer Agents

Platinum-group (PG) complexes have been used as antibacterial and anticancer agents since the discovery of cisplatin. The science world still requires improvement on these complexes because of multidrug and antineoplastic resistances. This review observes discoverers and history of these platinum-group metals (PGMs), as well as their beneficial applications. The focus of this study was biological applications of PGMs in relation to human health. Sandwich and half-sandwich PGM coordination compounds and their metal nanoparticles give improved results for biological activities by enhancing efficient delivery of both antibacterial and anticancer drugs, as well as luminescent bioimaging (biomarkers) for biological identifications.

Structure and bonding in triorganotin chlorides: a perspective from energy decomposition analysis

The Sn-Cl chemical bond of four organotin halides (Me₃SnCl, Et₃SnCl, Bu₃SnCl, and Ph₃SnCl) was studied by using relativistic density functional theory in combination with a quantitative energy decomposition analysis to explain the formation of charged species. The σ orbital is the dominant contributor to the stabilization of the Sn-Cl bond, and the π-orbital interactions also have a significant contribution to the stabilization of Ph₃Sn⁺ cation when the aromatic groups are bonded to the tin atom. The aromaticity of the phenyl groups delocalizes the positive charge, donating electrons to tin atom by conjugation. Although Me₃SnCl and Ph₃SnCl are constituted by groups which the size of the substituents is different, the interaction energies obtained with the energy decomposition analysis present similar values, which also occur with the thermodynamic parameters. Graphical abstract Organotin compounds have widely studied as a potential antitumoral agent. The mechanism in triorganotin compounds includes the formation of cation species, R₃Sn⁺. This article studies the influence of the R groups on the rupture of Sn-Cl bond using the fragment analysis and quantitative energy decomposition analysis.

Insight into the antitumor activity of carbosilane Cu(ii)-metallodendrimers through their interaction with biological membrane models

Current cancer therapies present serious drawbacks including severe side-effects and development of drug resistance. Strategies based on nanosized metallodrugs combine the structural diversity and non-classical modes of action of metal complexes with the selectivity arising from the unique interaction of nanoparticles with biological membranes. A new family of water-soluble copper(ii) carbosilane metallodendrimers was synthesized and characterized as a nanotechnological alternative to current therapies. The interactions occurring over time between the dendrimers, at different generations (G₀ to G₂) and with different Cu(ii) counter-ions (nitrate vs. chloride), and cell-membrane models (cethyl-trimethylammonium bromide (CTAB) micelles and lecithin liposomes) were investigated using a computer-aided analysis of the electron paramagnetic resonance (EPR) spectra. The EPR analysis provided structural and dynamical information on the systems indicating that the increase in generation and the change of the Cu(ii) contra-ion - from nitrate to chloride - produce an increased relative amount and strength of interaction of the dendrimer with the model membranes. Interestingly, the stabilization effect produced a lower toxicity towards cancer cells. The cytotoxic effect of Cu(ii) metallodendrimers was verified by an in vitro screening in a selection of tumor cell lines, revealing the impact of multivalency on the effectivity and selectivity of the metallodrugs. As a proof-of-concept, first-generation dendrimer G₁-Cu(ONO₂)₂ was selected for in-depth in vitro and in vivo antitumor evaluation towards resistant prostate cancer. The Cu(ii)-metallodendrimers produced a significant tumor size reduction with no signs of toxicity during the experiment, confirming their promising potential as anticancer metallodrugs.

Challenges and Chances in the Preclinical to Clinical Translation of Anticancer Metallodrugs

Despite being “sentenced to death” for quite some time, anticancer platinum compounds are still the most frequently prescribed cancer therapies in the oncological routine and recent exciting news from late-stage clinical studies on combinations of metallodrugs with immunotherapies suggest that this situation will not change soon. It is perhaps surprising that relatively simple molecules like cisplatin, discovered over 50 years ago, are still widely used clinically, while none of the highly sophisticated metal compounds developed over the last decade, including complexes with targeting ligands and multifunctional (nano)formulations, have managed to obtain clinical approval. In this book chapter, we summarize the current status of ongoing clinical trials for anticancer metal compounds and discuss the reasons for previous failures, as well as new opportunities for the clinical translation of metal complexes.

Copper(ii) complexes with 2,2′:6′,2′′-terpyridine, 2,6-di(thiazol-2-yl)pyridine and 2,6-di(pyrazin-2-yl)pyridine substituted with quinolines. Synthesis, structure, antiproliferative activity, and catalytic activity in the oxidation of alkanes and alcohols with peroxides

The toxicity of six new Cu(ii) complexes was evaluated in cancer derived cell lines. A model of competitive interaction of hydroxyl radicals with CH₃CN and RH in the catalyst cavity has been proposed.

Modulation of the mechanism of apoptosis in cancer cell lines by treatment with silica-based nanostructured materials functionalized with different metallodrugs

The mesoporous silica-based material SBA-15 (Santa Barbara Amorphous-15) has been modified with the aminodiol ligand 3-[bis(2-hydroxyethyl)amino]propyltriethoxysilane (PADOH) to give the corresponding material SBA-PADOH. Subsequent functionalization with a diorganotin(iv) compound, SnPh2Cl2 (1), and with two titanocene derivatives, TiCp2Cl2 ([Ti(η5-C5H5)2Cl2] (2)) and TiCpCpPhNfCl2 ([Ti(η5-C5H5)(η5-C5H4CHPhNf)Cl2] (3) (Ph = C6H5; Nf = C10H7)), gave the materials SBA-PADO-SnPh2 (M1), SBA-PADO-TiCp2 (M2) and SBA-PADO-TiCpCp* (M3), respectively. SBA-PADOH and M1-M3 have been characterized by various techniques such as FT-IR, XRD, XRF, solid-state NMR, nitrogen adsorption-desorption isotherms, electrochemical methods, SEM and TEM, observing that the functionalization has mainly taken place inside the pores of the corresponding porous system. In addition, mechanistic aspects of the apoptosis triggered by the synthesized materials have been studied in vitro in tumour cell lines derived from three distinct types of cancer in order to elucidate their growth inhibition and interference with the expression of tumour necrosis factor alfa (TNF-α) and the first apoptosis signal receptor (Fas or tumour necrosis factor receptor 6). It was observed that the antiproliferative and proapoptotic capacity of the materials depends on their functionalization with the different cytotoxic prodrugs (organotin or titanocene derivatives). The study shows that M1-M3 influence the metabolic activity of the tumour cells and modulate the apoptotic pathways by different mechanisms, according to the active compound inside the material.

In Vivo Anticancer Activity of a Nontoxic Inert Phenolato Titanium Complex: High Efficacy on Solid Tumors Alone and Combined with Platinum Drugs

Due to the toxicity of platinum compounds used in the clinic as anticancer chemotherapies, titanium serves as a safe and attractive alternative. Lately, we introduced a new family of Ti complexes based on readily available phenolato ligands, demonstrating incredibly high hydrolytic stability, with the lead compound phenolaTi demonstrating wide cytotoxic activity toward the NCI‐60 panel of human cancer cell lines, with an average GI₅₀ value of 4.7±2 μm. Herein, we evaluated in vivo: a) the safety, and b) the growth inhibitory capacity (efficacy) of this compound. PhenolaTi was found to be effective in vivo against colon (CT‐26) and lung (LLC‐1) murine cell lines in syngeneic hosts and toward a human colon cancer (HT‐29) cell line in immune‐deficient (Nude) mice, with an efficacy similar to that of known chemotherapy. Notably, no clinical signs of toxicity were observed in the treated mice, namely, no effect on body weight, spleen weight or kidney function, unlike the effects observed with the positive control Pt drugs. Studies of combinations of phenolaTi and Pt drugs provided evidence that similar efficacy with decreased toxicity may be achieved, which is highly valuable for medicinal applications.

Mesoporous SBA-15 modified with titanocene complexes and ionic liquids: interactions with DNA and other molecules of biological interest studied by solid state electrochemical techniques

The immobilization of two titanocene complexes on SBA-15 has been accomplished following post-synthetic procedures. The ionic liquid, 1-methyl-3-[(triethoxysilyl)propyl]imidazolium chloride, has also been incorporated into the titanium containing materials to determine its influence on the interaction with molecules of biological interest. Cyclic voltammetry has been used to study the influence of the ionic liquid on the mechanism of reduction of titanocene derivatives. The interaction of titanocene and titanocene/ionic liquid-containing mesoporous silica SBA-15 materials, with molecules of biological interest associated with important processes of metallodrug action against cancer cells, has been studied. Thus, we have carried out hydrolysis experiments on the materials functionalized with titanocene derivatives in physiological media to determine their stability and the interaction with serum/transport proteins such as transferrin and BSA and with target molecules such as guanosine, single-stranded DNA and double-stranded DNA by means of solid state voltammetry techniques. A qualitative analysis of the data based on peak current and reduction potential value changes of the couple Ti(iv)/Ti(iii) in the presence of biomolecules at physiological pH, has revealed that grafted titanocene complexes show higher affinity for serum/transport proteins than for nucleic acids, indicating that the transport steps to the cells may be easier than the subsequent attack on DNA.

Metalation Studies on Titanocene Dithiolates

Titanocene bis-arylthiolates [(C5H4X)(C5H4Y)Ti(SC6H4R)2] (X,Y = H, Cl; R = H, Me) can be prepared from the corresponding titanocene dichlorides by reacting with the thiols in the presence of DABCO as a base. They react with n-butyl lithium to give unstable Ti(III) radical anions. While the unsubstituted thiolates (X = Y = R = H) react with lithium Di-isopropylamide by decomposing to dimeric fulvalene-bridged and thiolate-bridged Ti(III) compounds, the ring-chlorinated compounds can be deprotonated with LDA and give appropriate electrophiles di-substituted and tri-substituted titanocene dithiolates.