Ferrocenes as new anticancer drug candidates: Determination of the mechanism of action

CuAAC-Based Synthesis, Copper-Catalyzed Aldehyde-Forming Hydrolytic Fission and Antiproliferative Evaluation of Novel Ferrocenoylamino-Substituted Triazole-Tethered Quinine-Chalcone Hybrids

A series of novel triazole-tethered ferrocenoylamino-substituted cinchona-chalcone hybrids along with two representative benzoylamino-substituted reference compounds were prepared by three methods of CuAAC chemistry. In line with the limited success or complete failure of attempted conversions with low catalyst loadings, by means of DFT modeling studies, we demonstrated that a substantial part of the Cu(I) ions can be chelated and thus trapped in the aroylamino-substituted cinchona fragment and all of the accessible coordinating sites of the chalcone residues. Accordingly, increased amounts of catalysts were used to achieve acceptable yields; however, the cycloadditions with para-azidochalcones were accompanied by partial or complete aldehyde-forming hydrolytic fission of the enone C=C bond in a substituent-, solvent- and copper load-dependent manner. The experienced hydrolytic stability of the hybrids obtained by cycloadditions with ortho-azidochalcones was interpreted in terms of relative energetics, DFT reactivity indices and MO analysis of simplified models of two isomer copper-enone complexes. The novel hybrids were evaluated on HeLa, MDA-MB-231 and A2780 cell lines and showed substantial activity at low-to-submicromolar concentrations. An organometallic model carrying 3,4,5-trimethoxyphenyl residue in the enone part with a para-disubstituted benzene ring in the central skeletal region was identified as the most potent antiproliferative lead, characterized by submicromolar IC50 values measured on the three investigated cells. The biological assays also disclosed that this ferrocenoylamino-containing lead compound displays a ca. two- to five-fold more substantial antiproliferative effect than its benzoylamino-substituted counterpart.

Electrochemically Controlled Release from a Thin Hydrogel Layer

In this study, we present a thermoresponsive thin hydrogel layer based on poly(N-isopropylacrylamide), functionalized with β-cyclodextrin groups (p(NIPA-βCD)), as a novel electrochemically controlled release system. This thin hydrogel layer was synthesized and simultaneously attached to the surface of a Au quartz crystal microbalance (QCM) electrode using electrochemically induced free radical polymerization. The process was induced and monitored using cyclic voltammetry and a quartz crystal microbalance with dissipation monitoring (QCM-D), respectively. The properties of the thin layer were investigated by using QCM-D and scanning electron microscopy (SEM). The incorporation of β-cyclodextrin moieties within the polymer network allowed rhodamine B dye modified with ferrocene (RdFc), serving as a model metallodrug, to accumulate in the p(NIPA-βCD) layer through host-guest inclusion complex formation. The redox properties of the electroactive p(NIPA-βCD/RdFc) layer and the dissociation of the host-guest complex triggered by changes in the oxidation state of the ferrocene groups were investigated. It was found that oxidation of the ferrocene moieties led to the release of RdFc. It was crucial to achieve precise control over the release of RdFc by applying the appropriate electrochemical signal, specifically, by applying the appropriate potential to the electrode. Importantly, the electrochemically controlled RdFc release process was performed at a temperature similar to that of the human body and monitored using a spectrofluorimetric technique. The presented system appears to be particularly suitable for transdermal delivery and delivery from intrabody implants.

Small change - big consequence: The impact of C15-C16 double bond in a D‑ring of estrone on estrogen receptor activity

Estrogen receptor alpha (ER) is a key biomarker for breast cancer, and the presence or absence of ER in breast and other hormone-dependent cancers decides treatment regimens and patient prognosis. ER is activated after ligand binding - typically by steroid. 2682 steroid compounds were used in a molecular docking study to identify novel ligands for ER and to predict compounds that may show anticancer activity. The effect of the most promising compounds was determined by a novel luciferase reporter assay. Two compounds, 7 and 12, showing ER inhibitory activity comparable to clinical inhibitors such as tamoxifen or fulvestrant were selected. We propose that the inhibitory effect of compounds 7 and 12 on ER is related to the presence of a double bond in their D-ring, which may protect against ER activation by reducing the electron density of the keto group, or may undergo metabolism leading to an active compound. Western blotting revealed that compound 12 decreased the level of ER in the breast cancer cell line MCF7, which was associated with reduced expression of both isoforms of the progesterone receptor, a well-known downstream target of ER. However, compound 12 has a different mechanism of action from fulvestrant. Furthermore, we found that compound 12 interferes with mitochondrial functions, probably by disrupting the electron transport chain, leading to induction of the intrinsic apoptotic pathway even in ER-negative breast cancer cells. In conclusion, the combination of computational and experimental methods shown here represents a rapid approach to determine the activity of compounds towards ER. Our data will not only contribute to research focused on the regulation of ER activity but may also be useful for the further development of novel steroid receptor-targeted drugs applicable in clinical practice.

Construction of N-Ferrocene Substituted Benzodihydrooxazoles via a Catalyst-Free Aza-Michael Addition/C(sp3)-O Bond Formation Tandem Reaction

A catalyst-free aza-Michael addition/C(sp³)-O bond formation tandem reaction of substituted amino ferrocenes with quinone esters was developed, which provided a green and efficient strategy for the construction of a C(sp³)-O bond from C(sp³)-H, and a series of N-ferrocene-substituted benzodihydrooxazoles were smoothly produced in moderate to excellent yields (up to >99% yield). The mechanism experiments showed that quinone esters performed as both substrate and oxidant. The salient features of this transformation include good functional group tolerance, broad substrate scope and mild conditions.

Ferrocene modified analogues of imatinib and nilotinib as potent anti-cancer agents

The unique features of ferrocene and the need for development of targeted anticancer drugs inspired the design, synthesis and biological evaluation of ferrocenyl modified tyrosine kinase inhibitors by replacing the pyridyl moiety in imatinib and nilotinib generalized structures with a ferrocenyl group. A series of seven new ferrocene analogues were synthesized and evaluated for their anticancer activity in a panel of bcr-abl positive human malignant cell lines using imatinib as a reference drug. The metallocenes exhibited a dose-dependent inhibition on malignant cell growth with varying antileukemic activity. The most potent analogues were compounds 9 and 15a showing comparable or even superior efficacy to the reference. Their cancer selectivity indices suggest a favorable selectivity profile, indicating a 250 times higher preferential activity of 15a towards malignantly transformed K-562 cells and an even twice greater one (500) of 9 in the LAMA-84 leukemic model as compared to the normal murine fibroblast cell line.

Mitochondrial targeting half-sandwich iridium(III) and ruthenium(II) dppf complexes and in vitro anticancer assay

Considering the potential application of half-sandwich and ferrocenyl-containing organometallic complexes in the area of anticancer, four half-sandwich iridium(III) (Ir^III) and ruthenium(II) (Ru^II) diphenylphosphino ferrocene (dppf) complexes were prepared in this study. Complexes showed favorable anti-proliferation activity towards A549 cell lines compared to cisplatin, meanwhile, which could effectively inhibit cell migration. These complexes followed an energy dependence uptake mechanism, effectively accumulated in mitochondria with a Pearson's Colocalization Coefficient (PCC) of 0.77, decreased the mitochondrial membrane potential, induced a surge of reactive oxygen species, disturbed cell cycle, and eventually led to apoptosis. Western blot assay further confirmed that these complexes induced apoptosis following a mitochondrial pathway. Above all, half-sandwich Ir^III and Ru^II dppf complexes show the prospect of becoming a new multifunctional therapeutic platform for mitochondrial targeted imaging and anticancer drugs.

Synthesis and bioactivity evaluation of ferrocene-based hydroxamic acids as selective histone deacetylase 6 inhibitors

Histone deacetylase 6 (HDAC6) is involved in multiple regulatory processes and emerges as a promising target for treating cancer and neurodegenerative diseases. Benefited from the unique sandwich conformation of ferrocene, a series of ferrocene-based hydroxamic acids have been developed as novel HDAC6 inhibitors in this paper, especially the two ansa-ferrocenyl complexes with IC₅₀s at the nanomolar level. [3]-Ferrocenophane hydroxamic acid analog II-5 displays the most potent inhibitory activity on HDAC6 and establishes remarkable selectivity towards other HDAC isoforms. Compound II-5 dose-dependently induces accumulation of acetylated α-tubulin while having a negligible effect on the level of acetylated Histone H3, confirming its isoform selectivity. Further biological evaluation of II-5 on cancer cells corroborates its antiproliferative effect, which mainly contributed to the induction of cellular apoptosis. It is worth noting that compound II-5 demonstrates an optimal profile on human plasma stability. These results strengthen ferrocene's unique role in developing selective protein inhibitors and indicate that compound II-5 may be a suitable lead for further evaluation and development for treating HDAC6-associated disorders and diseases.

Modern Trends in Bio-Organometallic Ferrocene Chemistry

Organometallic sandwich compounds, especially ferrocenes, possess a wide variety of pharmacological activities and therefore are attracting more and more attention from chemists, biologists, biochemists, etc. Excellent reviews concerning biological aspects and design of ferrocene-modified compounds appear regularly in scientific journals. This brief overview highlights recent achievements in the field of bio-organometallic ferrocene chemistry from 2017 to 2022. During this period, new ferrocene-modified analogues of various bio-structures were synthesized, namely, betulin, artemisinin, steroids, and alkaloids. In addition, studies of the biological potential of ferrocenes have been expanded. Since ferrocene is 70 years old this year, a brief historical background is also given. It seemed to me useful to sketch the ‘ferrocene picture’ in broad strokes.

Succinimido–Ferrocidiphenol Complexed with Cyclodextrins Inhibits Glioblastoma Tumor Growth In Vitro and In Vivo without Noticeable Adverse Toxicity

SuccFerr (N-[4-ferrocenyl,5-5-bis (4-hydroxyphenyl)-pent-4-enyl]-succinimide) has remarkable antiproliferative effects in vitro, attributed to the formation of a stabilized quinone methide. The present article reports in vivo results for a possible preclinical study. SuccFerr is lipophilic and insoluble in water, so the development of a formulation to obviate this inconvenience was necessary. This was achieved by complexation with randomly methylated cyclodextrins (RAMEßCDs). This supramolecular water-soluble system allowed the in vivo experiments below to proceed. Application of SuccFerr on the glioblastoma cancer cell line U87 indicates that it affects the cellular cycle by inducing a blockade at G0/G1 phase, linked to apoptosis, and another one at the S phase, associated with senescence. Using healthy Fischer rats, we show that both intravenous and subcutaneous SuccFerr: RAMEßCD administration at 5 mg/kg lacks toxic effects on several organs. To reach lethality, doses higher than 200 mg/kg need to be administered. These results prompted us to perform an ectopic in vivo study at 1 mg/kg i.v. ferrocidiphenol SuccFerr using F98 cells xenografted in rats. Halting of cancer progression was observed after six days of injection, associated with an immunological defense response linked to the active principle. These results demonstrate that the properties of the selected ferrocidiphenol SuccFerr transfer successfully to in vivo conditions, leading to interesting therapeutic perspectives based on this chemistry.

Synthesis, structural characterization, DFT calculations, molecular docking, and molecular dynamics simulations of a novel ferrocene derivative to unravel its potential antitumor activity

In this article, we describe a set of subsequent five-steps chemical reactions to synthesize a ferrocene derivative named 1-(5-(diphenylphosphaneyl)cyclopenta-1,3-dien-1-yl)ethyl)imino)-1,3-dihydroisobenzofuran-5-yl)methanol (compound 10). Structural characterization of 10 and its intermediate products was also performed and reported to attest to their formation. A molecular docking study was performed to propose the novel synthesized ferrocene derivative (10) as a potential antitumor candidate targeting the mitogen-activated protein (MAP) kinases interacting kinase (Mnk) 1. The computed docking score of (10) at -9.50 kcal/mol compared to the native anticancer staurosporine at -8.72 kcal/mol postulated a promising anticancer activity. Also, molecular dynamics (MD) simulations were carried out for 500 ns followed by MM-GBSA-binding free energy calculations for both the docked complexes of ferrocene and staurosporine to give more deep insights into their dynamic behavior in physiological conditions. Furthermore, DFT calculations were performed to unravel some of the physiochemical characteristics of the ferrocene derivative (10). The quantum mechanics calculations shed the light on some of the structural and electrochemical configurations of (10) which would open the horizon for further investigation. HighlightsThe synthesis of a ferrocene derivative named 1-(5-(diphenylphosphaneyl)cyclopenta-1,3-dien-1-yl)ethyl)imino)-1,3-dihydroisobenzofuran-5-yl)methanol (compound 10) was described.Structural characterizations of ferrocene derivative (10) and its intermediate products were also performed.DFT calculations, molecular docking, molecular dynamics, and MM-GBSA calculations were carried out.Computational studies revealed the antitumor potential of ferrocene derivative (10) through targeting and inhibiting mitogen-activated protein (MAP) kinases interacting kinase (Mnk) 1.Communicated by Ramaswamy H. Sarma.

Coordination compounds of biogenic metals as cytotoxic agents in cancer therapy

The review summarizes the data on the structures and methods for the synthesis of compounds with anticancer activity based on biogenic metals, which can replace platinum drugs prevailing in cytotoxic therapy. The main focus is given to the comparison of the mechanisms of the cytotoxic action of these complexes, their efficacy and prospects of their use in clinical practice. This is the first systematic review of cytotoxic zinc, iron, cobalt and copper compounds. The structure – activity relationships and the mechanisms of antitumour action are formulated for each type of metal complexes.

The bibliography includes 181 references.

Expedition of sulfur-containing heterocyclic derivatives as cytotoxic agents in medicinal chemistry: A decade update

This review article proposes a comprehensive report of the design strategies engaged in the development of various sulfur-bearing cytotoxic agents. The outcomes of various studies depict that the sulfur heterocyclic framework is a fundamental structure in diverse synthetic analogs representing a myriad scope of therapeutic activities. A number of five-, six- and seven-membered sulfur-containing heterocyclic scaffolds, such as thiazoles, thiadiazoles, thiazolidinediones, thiophenes, thiopyrans, benzothiazoles, benzothiophenes, thienopyrimidines, simple and modified phenothiazines, and thiazepines have been discussed. The subsequent studies of the derivatives unveiled their cytotoxic effects through multiple mechanisms (viz. inhibition of tyrosine kinases, topoisomerase I and II, tubulin, COX, DNA synthesis, and PI3K/Akt and Raf/MEK/ERK signaling pathways), and several others. Thus, our concise illustration explains the design strategy and anticancer potential of these five- and six-membered sulfur-containing heterocyclic molecules along with a brief outline on seven-membered sulfur heterocycles. The thorough assessment of antiproliferative activities with the reference drug allows a proficient assessment of the structure-activity relationships (SARs) of the diversely synthesized molecules of the series.

Redox-dependent cytotoxicity of ferrocene derivatives and ROS-activated prodrugs based on ferrocenyliminoboronates

Four ferrocene derivatives - ferrocenecarboxylic acid, ferrocenium salt, ferroceneboronic acid, and aminoferrocene - were characterized electrochemically, and their cytotoxicity was probed using cancer cells (line MG-63). We related the observed cytotoxicity with the determined redox potentials of these four ferrocenes - aminoferrocene with its lowest redox potential exhibited the highest cytotoxicity. Thus, we synthesized four derivatives consisting of aminoferrocene and phenylboronic acid residue with the intent to employ them as ROS-activated prodrugs (ROS - reactive oxygen species). We characterized them and studied their time-dependent stability in aqueous environments. Then, we performed electrochemical measurements at oxidative conditions to confirm ROS-responsivity of the synthesized molecules. Finally, the cytotoxicity of the synthesized molecules was tested using cancer MG-63 cells and noncancerous NIH-3T3 cells. The experiments revealed sought behaviour, especially for para-regioisomers of synthesized ferrocenyliminoboronates.

Recent advances in iron-complexes as drug candidates for cancer therapy: reactivity, mechanism of action and metabolites

In this perspective, we discuss iron-complexes as drug candidates that are promising alternatives to conventional platinum-based chemotherapies owing to their broad range of reactivities and to the targeting of different biological systems. Breakthroughs in the comprehension of iron complexes' structure-activity relationship contributed to the clarification of their metabolization pathways, sub-cellular localization and influence on iron homeostasis, while enlightening the primary molecular targets of theses likely multi-target metallodrugs. Both the antiproliferative activity and elevated safety index observed among the family of iron complexes showed encouraging results as per their therapeutic potential and selectivity also with the aim of reducing chemotherapy side-effects, and facilitated more pre-clinical investigations. The purpose of this perspective is to summarize the recent advances that contributed in unveiling the intricate relationships between the structural modifications on iron-complexes and their reactivity, cellular trafficking and global mechanisms of action to broaden their use as anticancer drugs and advance to clinical evaluation.

The Cytotoxic Effect of Newly Synthesized Ferrocenes against Cervical Carcinoma Cells Alone and in Combination with Radiotherapy

Cervical cancer is one of the most common types of cancer in women, with approximately 500,000 new cases and 250,000 deaths every year. Radiotherapy combined with chemotherapy represents the treatment of choice for advanced cervical carcinomas. The role of the chemotherapy is to increase the sensitivity of the cancer cells to irradiation. Cisplatin, the most commonly used drug for this purpose, has its limitations. Thus, we used a family of ferrocene derivatives (in addition, one new species was prepared using standard Schlenk techniques) and studied their effects on cervical cancer cells alone and in combination with irradiation. We applied colorimetric assay to determine the cytotoxicity of the compounds; flow cytometry to analyze the production of reactive oxygen species (ROS), cell cycle, and mitochondrial membrane potential (MMP); immunochemistry to study protein expression; and colony forming assay to evaluate changes in radiosensitivity. Treatment with ferrocenes exhibited significant cytotoxicity against cervical cancer cells, associated with increasing ROS production and MMP changes, suggesting the induction of apoptosis. The combined activity of ferrocenes and ionizing radiation highlighted ferrocenes as potential radiosensitizing drugs, while their higher single-agent toxicity in comparison with routinely used cisplatin could also be promising. Our results demonstrate antitumor activity of several tested ferrocenes both alone and in combination with radiotherapy.

Purine and Purine Isostere Derivatives of Ferrocene: An Evaluation of ADME, Antitumor and Electrochemical Properties

Novel purine and purine isosteres containing a ferrocene motif and 4,1-disubstituted (11a-11c, 12a-12c, 13a-13c, 14a-14c, 15a-15c, 16a, 23a-23c, 24a-24c, 25a-25c) and 1,4-disubstituted (34a-34c and 35a-35c) 1,2,3-triazole rings were synthesized. The most potent cytotoxic effect on colorectal adenocarcinoma (SW620) was exerted by the 6-chloro-7-deazapurine 11c (IC₅₀ = 9.07 µM), 6-chloropurine 13a (IC₅₀ = 14.38 µM) and 15b (IC₅₀ = 15.50 µM) ferrocenylalkyl derivatives. The N-9 isomer of 6-chloropurine 13a containing ferrocenylmethylene unit showed a favourable in vitro physicochemical and ADME properties including high solubility, moderate permeability and good metabolic stability in human liver microsomes.