A New Series of Succinimido-ferrociphenols and Related Heterocyclic Species Induce Strong Antiproliferative Effects, Especially against Ovarian Cancer Cells Resistant to Cisplatin

Deciphering the Diversified Metabolic Behavior of Hydroxyalkyl Ferrocidiphenols as Anticancer Complexes

Ferrocidiphenols possessing appropriate substituents in the aliphatic chain have very promising anticancer properties, but a systematic approach to deciphering their diversified metabolic behavior has so far been lacking. Herein, we show that a series of novel ferrocidiphenols bearing different hydroxyalkyl substituents exhibit strong anticancer activity as revealed in a range of in vitro and in vivo experiments. Moreover, they display diversified oxidative transformation profiles very distinct from those of previous complexes, shown by the use of chemical and enzymatic methods and in cellulo and in vivo metabolism studies. In view of this phenomenon, unprecedented chemo-evolutionary sequences that connect all the ferrocidiphenol-related intermediates and analogues have been established. In addition, a comprehensive density functional theory (DFT) study has been performed to decipher the metabolic diversification profiles of these complexes and demonstrate the delicate modulation of carbenium ions by the ferrocenyl moiety, via either α- or β-positional participation.

Is it still worth renewing nucleoside anticancer drugs nowadays?

Nucleoside has situated the convergence point in the discovery of novel drugs for decades, and a large number of nucleoside derivatives have been constructed for screening novel pharmacological properties at various experimental platforms. Notably, nearly 20 nucleosides are approved to be used in the clinic treatment of various cancers. Nevertheless, the blossom of synthetic nucleoside analogs in comparison with the scarcity of nucleoside anticancer drugs leads to a question: Is it still worth insisting on the screening of novel anticancer drugs from nucleoside derivatives? Hence, this review attempts to emphasize the importance of nucleoside analogs in the discovery of novel anticancer drugs. Firstly, we introduce the metabolic procedures of nucleoside anticancer drug (such as 5-fluorouracil) and summarize the designing of novel nucleoside anticancer candidates based on clinically used nucleoside anticancer drugs (such as gemcitabine). Furthermore, we collect anticancer properties of some recently synthesized nucleoside analogs, aiming at emphasizing the availability of nucleoside analogs in the discovery of anticancer drugs. Finally, a variety of synthetic strategies including the linkage of sugar moiety with nucleobase scaffold, modifications on the sugar moiety, and variations on the nucleobase structure are collected to exhibit the abundant protocols in the achievement of nucleoside analogs. Taken the above discussions collectively, nucleoside still advantages for the finding of novel anticancer drugs because of the clearly metabolic procedures, successfully clinic applications, and abundantly synthetic routines.

Design, Synthesis, and Evaluation of Biological Activity of Ferrocene-Ispinesib Hybrids: Impact of a Ferrocenyl Group on the Antiproliferative and Kinesin Spindle Protein Inhibitory Activity

With the aim to combine more than one biologically-active component in a single molecule, derivatives of ispinesib and its (S) analogue were prepared that featured ferrocenyl moieties or bulky organic substituents. Inspired by the strong kinesin spindle protein (KSP) inhibitory activity of ispinesib, the compounds were investigated for their antiproliferative activity. Among these compounds, several derivatives demonstrated significantly higher antiproliferative activity than ispinesib with nanomolar IC50 values against cell lines. Further evaluation indicated that the antiproliferative activity is not directly correlated with their KSP inhibitory activity while docking suggested that several of the derivatives may bind in a manner similar to ispinesib. In order to investigate the mode of action further, cell cycle analysis and reactive oxygen species formation were investigated. The improved antiproliferative activity of the most active compounds may be assigned to synergic effects of various factors such as KSP inhibitory activity due to the ispinesib core and ability to generate ROS and induce mitotic arrest.

Unravelling the Role of Uncommon Hydrogen Bonds in Cyclodextrin Ferrociphenol Supramolecular Complexes: A Computational Modelling and Experimental Study

We sought to determine the cyclodextrins (CDs) best suited to solubilize a patented succinimido-ferrocidiphenol (SuccFerr), a compound from the ferrociphenol family having powerful anticancer activity but low water solubility. Phase solubility experiments and computational modelling were carried out on various CDs. For the latter, several CD-SuccFerr complexes were built starting from combinations of one or two CD(s) where the methylation of CD oxygen atoms was systematically changed to end up with a database of ca. 13 k models. Modelling and phase solubility experiments seem to indicate the predominance of supramolecular assemblies of SuccFerr with two CDs and the superiority of randomly methylated β-cyclodextrins (RAMEβCDs). In addition, modelling shows that there are several competing combinations of inserted moieties of SuccFerr. Furthermore, the models show that ferrocene can contribute to high stabilization by making atypical hydrogen bonds between Fe and the hydroxyl groups of CDs (single bond with one OH or clamp with two OH of the same glucose unit).

Ferrocene-Based Drugs, Delivery Nanomaterials and Fenton Mechanism: State of the Art, Recent Developments and Prospects

Ferrocene has been the most used organometallic moiety introduced in organic and bioinorganic drugs to cure cancers and various other diseases. Following several pioneering studies, two real breakthroughs occurred in 1996 and 1997. In 1996, Jaouen et al. reported ferrocifens, ferrocene analogs of tamoxifen, the chemotherapeutic for hormone-dependent breast cancer. Several ferrocifens are now in preclinical evaluation. Independently, in 1997, ferroquine, an analog of the antimalarial drug chloroquine upon the introduction of a ferrocenyl substituent in the carbon chain, was reported by the Biot-Brocard group and found to be active against both chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum. Ferroquine, in combination with artefenomel, completed phase IIb clinical evaluation in 2019. More than 1000 studies have been published on ferrocenyl-containing pharmacophores against infectious diseases, including parasitic, bacterial, fungal, and viral infections, but the relationship between structure and biological activity has been scarcely demonstrated, unlike for ferrocifens and ferroquines. In a majority of ferrocene-containing drugs, however, the production of reactive oxygen species (ROS), in particular the OH. radical, produced by Fenton catalysis, plays a key role and is scrutinized in this mini-review, together with the supramolecular approach utilizing drug delivery nanosystems, such as micelles, metal-organic frameworks (MOFs), polymers, and dendrimers.

Physicochemical Characterization of Ferrocifen Lipid Nanocapsules: Customized Drug Delivery Systems Guided by the Molecular Structure

Ferrocifens, lipophilic organometallic complexes, comprise a biologically active redox motif [ferrocenyl-ene-p-phenol] which confers very interesting cytotoxic properties to this family. However, because of their highly lipophilic nature, a formulation stage is required before being administered in vivo. In recent decades, ferrocifen lipid nanocapsules (LNCs) have been successfully formulated and have demonstrated anticancer activity on multidrug-resistant cancers in several mice and rat models (glioblastoma, breast cancer, and metastatic melanoma). A recent family of ferrocifens (succinimidoalkyl-ferrociphenols, including P722) appears to be most efficacious on several resistant cancer cell lines, with IC₅₀ values in the nanomolar range together with promising in vivo results on murine ovarian cancer models. As LNCs are composed of an oily core (caprylic/capric triglycerides), modulation of the succinimido-ferrociphenol lipophilicity could be a valuable approach toward improving the drug loading in LNCs. As the drug loading of the diphenol P722 in LNCs was low, it was structurally modified to increase its lipophilicity and thereby the payload in LNCs. Chemical modification led to a series of five succinimido-ferrocifens. Results confirmed that these slight structural modifications led to increased drug loading in LNCs for all ferrocifens, with no reduction of their cytotoxicity on the SKOV3 ovarian cancer cell line. Interestingly, encapsulation of two of the ferrocifens, diester P769 and monophenolic ester (E)-P998, led to the formation of a gel. This was unprecedented behavior, a phenomenon that could be rationalized in terms of the positioning of ferrocifens in LNCs as shown by the decrease of interfacial tension measurements at the water/oil interface. Moreover, these results highlighted the importance of obtaining a gel of this particular motif, in which the acetylated phenolic ring and the succinimidoalkyl moieties are mutually cis relative to the central double bond. Promising perspectives to use these ferrocifen-loaded LNCs to treat glioblastoma could be readily envisaged by local application of the gel in the cavity after tumor resection.

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.

Ferrocifen stealth LNCs and conventional chemotherapy: A promising combination against multidrug-resistant ovarian adenocarcinoma

Ovarian cancer is one of the deadliest epithelial malignancies in women, owing to the multidrug resistance that restricts the success of conventional chemotherapy, carboplatin and paclitaxel. High grade serous ovarian carcinoma can be classified into two subtypes, the chemosensitive High OXPHOS and the Low OXPHOS tumour, less sensitive to chemotherapy. This difference of treatment efficacy could be explained by the redox status of these tumours, High OXPHOS exhibiting a chronic oxidative stress and an accumulation of reactive oxygen species. Ferrocifens, bio-organometallic compounds, are believed to be ROS producers with a good cytotoxicity on ovarian cancer cell lines. The aim of this study was to evaluate the in vivo efficacy of ferrocifen stealth lipid nanocapsules on High and Low OXPHOS ovarian Patient-Derived Xenograft models, alone or in combination to standard chemotherapy. Accordingly, two ferrocifens, P53 and P722, were encapsulated in stealth LNCs. The treatment by stealth P722-LNCs in combination with standard chemotherapy induced, with a concentration eight time lower than in stealth P53-LNCs, similar tumour reduction on a Low OXPHOS model, allowing us to conclude that P722 could be a leading ferrocifen to treat ovarian cancer. This combination of treatments may represent a promising synergistic approach to treat resistant ovarian adenocarcinoma.

Synthesis and SAR Analysis of Novel 4-Hydroxytamoxifen Analogues Based on Their Cytotoxic Activity and Electron-Donor Character

Utilizing McMurry reactions of 4,4′-dihydroxybenzophenone with appropriate carbonyl compounds, a series of 4-Hydroxytamoxifen analogues were synthesized. Their cytotoxic activity was evaluated in vitro on four human malignant cell lines (MCF-7, MDA-MB 231, A2058, HT-29). It was found that some of these novel Tamoxifen analogues show marked cytotoxicity in a dose-dependent manner. The relative ROS-generating capability of the synthetized analogues was evaluated by cyclic voltammetry (CV) and DFT modeling studies. The results of cell-viability assays, CV measurements and DFT calculations suggest that the cytotoxicity of the majority of the novel compounds is mainly elicited by their interactions with cellular targets including estrogen receptors rather than triggered by redox processes. However, three novel compounds could be involved in ROS-production and subsequent formation of quinone-methide preventing proliferation and disrupting the redox balance of the treated cells. Among the cell lines studied, HT-29 proved to be the most susceptible to the treatment with compounds having ROS-generating potency.

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.

α-Hydroxylactams as Efficient Entries to Diversely Functionalized Ferrociphenols: Synthesis and Antiproliferative Activity Studies

The [ferrocene-ene-phenol] motif has been identified as the pharmacophore responsible for the anticancer activity of the family of ferrocene-based molecules coined ferrocifens, owing to its unique redox properties. The addition of imide entities to the historical ferrociphenol scaffold tremendously enhanced the cytotoxic activity of a large panel of cancer cell cultures and preliminary studies showed that the reduction of one of the carbonyl groups of the imide groups to the corresponding α-hydroxylactams only slightly affected the antiproliferative activity. As a continuation to these studies, we took advantage of the facile conversion of α-hydroxylactams to highly electrophilic N-acyliminium ions to graft various substituents to the imide motif of phthalimido ferrocidiphenol. Cell viability studies showed that the newly synthesized compounds showed diverse cytotoxic activities on two breast cancer cell lines, while only one compound was significantly less active on the non-tumorigenic cell line hTERT-RPE1.

Heterogeneity of Response to Iron-Based Metallodrugs in Glioblastoma Is Associated with Differences in Chemical Structures and Driven by FAS Expression Dynamics and Transcriptomic Subtypes

Glioblastoma (GBM) is the most frequent and deadliest primary brain cancer in adults, justifying the search for new treatments. Some members of the iron-based ferrocifen family have demonstrated a high cytotoxic effect on various cancer cell lines via innovative mechanisms of action. Here, we evaluated the antiproliferative activity by wst-1 assay of six ferrocifens in 15 molecularly diverse GBM patient-derived cell lines (PDCLs). In five out of six compounds, the half maximal inhibitory concentration (IC₅₀) values varied significantly (10 nM < IC₅₀ < 29.8 µM) while the remaining one (the tamoxifen-like complex) was highly cytotoxic against all PDCLs (mean IC₅₀ = 1.28 µM). The pattern of response was comparable for the four ferrocifens bearing at least one phenol group and differed widely from those of the tamoxifen-like complex and the complex with no phenol group. An RNA sequencing differential analysis showed that response to the diphenol ferrocifen relied on the activation of the Death Receptor signaling pathway and the modulation of FAS expression. Response to this complex was greater in PDCLs from the Mesenchymal or Proneural transcriptomic subtypes compared to the ones from the Classical subtype. These results provide new information on the mechanisms of action of ferrocifens and highlight a broader diversity of behavior than previously suspected among members of this family. They also support the case for a molecular-based personalized approach to future use of ferrocifens in the treatment of GBM.

Synthesis, structure and in vitro antiproliferative effects of alkyne-linked 1,2,4-thiadiazole hybrids including erlotinib- and ferrocene-containing derivatives

Chemotherapy is an indispensable tool to treat cancer, therefore, the development of new drugs that can treat cancer with minimal side effects and lead to more favorable prognoses is of crucial importance. A series of eleven novel 1,2,4-thiadiazoles bearing erlotinib (a known anticancer agent), phenylethynyl, ferrocenyl, and/or ferrocenethynyl moieties were synthesized in this work and characterized by NMR, IR and mass spectroscopies. The solid-phase structures were determined by single-crystal X-ray diffraction. Partial isomerisation of bis(erlotinib)-1,2,4-thiadiazole into its 1,3,4-thiadiazole isomer, leading to the isolation of a 3 : 2 isomer mixture, was observed and a plausible mechanism for isomerisation is suggested. The in vitro cytostatic effect and the long-term cytotoxicity of these thiadiazole-hybrids, as well as that of erlotinib, 3,5-dichloro-1,2,4-thiadiazole and 3,5-diiodo-1,2,4-thiadiazole were investigated against A2058 human melanoma, HepG2 human hepatocellular carcinoma, U87 human glioma, A431 human epidermoid carcinoma, and PC-3 human prostatic adenocarcinoma cell lines. Interestingly, erlotinib did not exhibit a significant cytostatic effect against these cancer cell lines. 1,2,4-Thiadiazole hybrids bearing one erlotinib moiety or both an iodine and a ferrocenethynyl group, as well as 3,5-diiodo-1,2,4-thiadiazole demonstrated good to moderate cytostatic effects. Among the synthesized 1,2,4-thiadiazole hybrids, the isomer mixture of bis-erlotinib substituted 1,2,4- and 1,3,4-thiadiazoles showed the most potent activity. This isomer mixture was proven to be the most effective in long-term cytotoxicity, too. 3,5-Diiodo-1,2,4-thiadiazole and its hybrid with one erlotinib fragment were also highly active against A431 and PC-3 proliferation. These novel compounds may serve as new leads for further study of their antiproliferative properties.

Synthesis, electrochemistry, DNA binding and in vitro cytotoxic activity of tripodal ferrocenyl bis-naphthalimide derivatives

A series of tripodal ferrocenyl bis-naphthalimide derivatives were synthesized and characterized. All of the bis-naphthalimide derivatives exhibited good DNA binding ability which was confirmed by ethidium bromide (EB) displacement experiment and ultraviolet (UV)-visible absorption titration. And the binding mode of these compounds was proved to be a hybrid binding mode by experiments. The cytotoxicity of synthesized compounds against 4 different human cancer cell lines (EC109, BGC823, SGC7901 and HEPG2) was evaluated by thiazolyl blue tetrazolium bromide (MTT) assay. All of the bis-naphthalimide derivatives exhibited good anticancer activity than the positive control drug (amonafide), which was due to the promotion of reactive oxygen species (ROS) level in test cancer cells by the reversible one-electron redox process of ferrocenyl bis-naphthalimide derivatives. Although there was no obvious relationship between the binding constants and the chain length, the structure cytotoxicity relationship revealed that the linker of n = 3, m = 1 was the best choice for the tested tripodol bis-naphthalimide derivatives. SYNOPSIS: A series of tripodal ferrocenyl bis-naphthalimide derivatives were synthesized to study the DNA binding ability and the cytotoxicity induced by reactive oxygen species. All of the compounds exhibited good DNA binding ability. And the structure cytotoxicity relationship revealed that the structure of 5h was the best choice.

Have molecular hybrids delivered effective anti-cancer treatments and what should future drug discovery focus on?

INTRODUCTION

Cancer continues to be a big threat and its treatment is a huge challenge among the medical fraternity. Conventional anti-cancer agents are losing their efficiency which highlights the need to introduce new anti-cancer entities for treating this complex disease. A hybrid molecule has a tendency to act through varied modes of action on multiple targets at a given time. Thus, there is the significant scope with hybrid compounds to tackle the existing limitations of cancer chemotherapy.

AREA COVERED

This perspective describes the most significant hybrids that spring hope in the field of cancer chemotherapy. Several hybrids with anti-proliferative/anti-tumor properties currently approved or in clinical development are outlined, along with a description of their mechanism of action and identified drug targets.

EXPERT OPINION

The success of molecular hybridization in cancer chemotherapy is quite evident by the number of molecules entering into clinical trials and/or have entered the drug market over the past decade. Indeed, the recent advancements and co-ordinations in the interface between chemistry, biology, and pharmacology will help further the advancement of hybrid chemotherapeutics in the future.List of abbreviations: Deoxyribonucleic acid, DNA; national cancer institute, NCI; peripheral blood mononuclear cells, PBMC; food and drug administration, FDA; histone deacetylase, HDAC; epidermal growth factor receptor, EGFR; vascular endothelial growth factor receptor, VEGFR; suberoylanilide hydroxamic acid, SAHA; farnesyltransferase inhibitor, FTI; adenosine triphosphate, ATP; Tamoxifen, TAM; selective estrogen receptor modulator, SERM; structure activity relationship, SAR; estrogen receptor, ER; lethal dose, LD; half maximal growth inhibitory concentration, GI₅₀; half maximal inhibitory concentration, IC₅₀.

p722 ferrocifen loaded lipid nanocapsules improve survival of murine xenografted-melanoma via a potentiation of apoptosis and an activation of CD8+ T lymphocytes

Metastatic melanoma is a malignant tumor with a poor prognosis. Recent new therapeutics improved the survival of patients at a metastatic stage. However, the low response rate to immunotherapy, explained in part by resistance to apoptosis, needs to develop new strategies. The ferrocifen family represents promising bioorganometallic molecules for melanoma treatment since they show potent anticancer properties. The aim of this study is (i) to evaluate the benefits of a strategy involving encapsulated p722 in lipid nanocapsules (LNC) in B16F10 melanoma mice models and (ii) to compare the beneficial effects with an existing therapy such as anti-CTLA4 mAb. Interestingly, LNC-p722 induces a significant decrease of melanoma cell viability. In vivo data shows a significant improvement in the survival rate and a slower tumor growth with p722-loaded LNC in comparison with anti-CTLA4 mAb. Western blots confirm that LNC-p722 potentiates intrinsic apoptotic pathway. Treatment with LNC-p722 significantly activates CD8⁺ T lymphocytes compared to treatment with anti-CTLA4 mAb. This study uncovers a new therapeutic strategy with encapsulated p722 to prevent B16F10 melanoma growth and to improve survival of treated mice.

Enantioselective Synthesis of Planar Chiral Ferrocifens that Show Chiral Discrimination in Antiproliferative Activity on Breast Cancer Cells

The design and first enantioselective synthesis of a series of chiral ferrocifens and ferrociphenols was realised by enantioselective palladium-catalysed intramolecular direct C-H bond activation followed by McMurry coupling. Biological evaluation revealed moderate anticancer activities on breast cancer cells and evidence of chiral discrimination between enantiomers. Treatment of the novel ferrocifens with Ag₂ O revealed that these systems are unable to form a neutral quinone methide, yet still demonstrate marked antiproliferative properties against both the hormone-dependent MCF-7 and hormone-independent MDA-MB-231 cell lines. This bioactivity arises from two mechanisms: Fenton-type chemistry and the anti-estrogenic activity associated with the tamoxifen-like structure.

Nanomedicine to target multidrug resistant tumors

Nanomedicine employs nanotechnologies to develop innovative applications, and more specifically nano-objects in the field of human health, through exploitation of the physical, chemical and biological properties of materials at the nanoscale. The use of nanovehicles capable of transporting and releasing the active therapeutic payload into target cells, particularly in the case of cancer or inflammatory diseases, can also enhance diagnosis. Therefore, nanomedicines improve the benefit/risk ratio of drugs by increasing their bioavailability, selectivity, and efficacy in the target tissue, while reducing the necessary doses and hence diminishing untoward toxicity to healthy tissues. Overcoming multidrug resistance (MDR) to antitumor agents is a central goal of cancer research and therapeutics, making it possible to treat these diseases more accurately and effectively. The adaptability of nanomedicines e.g. modulation of their components, surface functionalization, encapsulation of various active therapeutics as well as the possibility of combining several treatments using a single nanoparticle platform, are characteristics which are perfectly poised to address classical chemoresistance, a major obstacle towards curative cancer therapy. In this review, we discuss an assortment of nanomedicines along with those that should be developed in order to surmount cancer MDR; these include exosomes, natural compounds, lipid nanocapsules, prodrug self-assemblies, and gold nanoparticles.

Ferrocene-containing hybrids as potential anticancer agents: Current developments, mechanisms of action and structure-activity relationships

Cancer is one of the most fatal threatens to human health throughout the world. The major challenges in the control and eradication of cancers are the continuous emergency of drug-resistant cancer and the low specificity of anticancer agents, creating an urgent need to develop novel anticancer agents. Organometallic compounds especially ferrocene derivatives possess remarkable structural and mechanistic diversity, inherent stability towards air, heat and light, low toxicity, low cost, reversible redox, ligand exchange, and catalytic properties, making them promising drug candidates for cancer therapy. Ferrocifen, a ferrocene-phenol hybrid, has demonstrated promising anticancer properties on drug-resistant cancers. Currently, Ferrocifen is in pre-clinical trial against cancers. Obviously, ferrocene moiety is a useful template for the development of novel anticancer agents. This review will provide an overview of ferrocene-containing hybrids with potential application in the treatment of cancers covering articles published between 2010 and 2020. The mechanisms of action, the critical aspects of design and structure-activity relationships are also discussed.

Ferrocene-Based Compounds with Antimalaria/Anticancer Activity

Malaria and cancer are chronic diseases. The challenge with drugs available for the treatment of these diseases is drug toxicity and resistance. Ferrocene is a potent organometallic which have been hybridized with other compounds resulting in compounds with enhanced biological activity such as antimalarial and anticancer. Drugs such as ferroquine were developed from ferrocene and chloroquine. It was tested in the 1990s as an antimalarial and is still an effective antimalarial. Many researchers have reported ferrocene compounds as potent compounds useful as anticancer and antimalarial agents when hybridized with other pharmaceutical scaffolds. This review will be focused on compounds with ferrocene moieties that exhibit either an anticancer or antimalarial activity.

Atypical Lone Pair-π Interaction with Quinone Methides in a Series of Imido-Ferrociphenol Anticancer Drug Candidates

Ferrociphenols, especially those possessing a heterocycle at the terminus of an aliphatic chain, display strong anticancer activity through a novel redox mechanism that generates active metabolites such as quinone methides (QMs). X-ray crystallography and UV/Vis spectroscopy reveal that the specific lone pair (lp)-π interaction between a carbonyl group of the imide and the quinone motif of the QM plays an important role in the exceptional cytotoxic behaviour of their imido-ferrociphenol precursors. This intramolecular lp-π interaction markedly enhanced the stability of the QMs and lowered the pK_a values of the corresponding phenol/phenolate couples. As the first example of such a non-covalent interaction that stabilizes QMs remotely, it not only expands the scope of the lp-π interaction in supramolecular chemistry, but also represents a new mode of stabilization of a QM. This unprecedented application of lp-π interactions in imido-ferrociphenol anticancer drug candidates may also have great potential in drug discovery and organocatalyst design.

Efficient synthesis of ferrocifens and other ferrocenyl-substituted ethylenes via a 'sulfur approach'

Stable and non-odorous alkyl ferrocenyl thioketones react with bis(4-methoxyphenyl)diazomethane according to the 'two-fold extrusion' reaction principles, and tetrasubstituted ethylenes obtained thereby can be demethylated to give (Fc,2OH)-ferrocifens in good yields. The method offers an alternative approach to this class of medically relevant compounds. A similar protocol with alkyl ferrocenyl thioketones and selected diaryldiazomethanes leads to ferrocenyl-substituted ethylenes including dibenzofulvenes. These products are of potential interest for electrochemical and photophysical studies.

Metal-based antitumor compounds: beyond cisplatin

Despite improvements in the 5-year survival rate to over 80% in cancers, such as Hodgkin lymphoma and testicular cancer, more aggressive tumors including pancreatic and brain cancer still have extremely low survival rates. The establishment of chemoresistance, responsible for the reduction in treatment efficiency and cancer relapse, is one possible explanation for this setback. Metal-based compounds, a class of anticancer drugs, are largely used in the treatment of cancer. Herein, we will review the use of metal-based small molecules in chemotherapy, focusing on recent studies, and we will discuss how new nonplatinum-based agents are prompting scientists to increase drug specificity to overcome chemoresistance in cancer cells.

Ferrocene-appended pharmacophores: an exciting approach for modulating the biological potential of organic scaffolds

The present review article describes the recent developments (2014–18) on the synthesis of ferrocene-based pharmacophores with the specific benefits of introducing/replacing organic pharmacophores with the ferrocene core for desired bioactivities.

Application of organocatalysis in bioorganometallic chemistry: asymmetric synthesis of multifunctionalized spirocyclic pyrazolone–ferrocene hybrids as novel RalA inhibitors

Asymmetric construction of chiral spirocyclic pyrazolone–ferrocene hybrids has been developed. The lead compound displayed potent RalA inhibition.