Enhancing the Activity of Drugs by Conjugation to Organometallic Fragments

The effect of a varying pyridine ligand on the anticancer activity of Diiron(I) bis-cyclopentadienyl complexes

The new diiron complexes [Fe2Cp2(CO)(L)(μ-CO){μ-CN(Me)(Cy)}]CF3SO3 (L = pyridine, 3a; 4-aminopyridine, 3b; 4-dimethylaminopyridine, 3c; 4-trifluoromethylpyridine, 3d; nicotinic acid, 4; Cp = η5-C5H5, Cy = C6H11 = cyclohexyl) were synthesized in moderate to high yields using two distinct synthetic routes from the precursors 1 (L = CO, for 4) and 2 (L = NCMe, for 3a-d), respectively. All products were characterized by IR and multinuclear NMR spectroscopy, and the structures of 3b and 3d were ascertained by X-ray diffraction studies. The behavior of the complexes in aqueous solutions (solubility, Log Pow, stability) was assessed using NMR and UV-Vis methods. The in vitro antiproliferative activity of 3a-c and 4 was evaluated against seven human cancer cell lines (A2780, A2780R, A549, MCF-7, PC3, HOS and HT-29) and one normal cell line (MRC-5), following 24 h of incubation (MTT test). Overall, 3-4 demonstrated stronger cytotoxicity than cisplatin, with 3c emerging as the most potent compound. The activity seems primarily linked to the inhibition of metabolic processes in the cancer cells, including depletion of reactive oxygen species (ROS) levels. However, subtle differences have been observed between the complexes, with 4 exerting its cytotoxicity through a distinct multimodal mechanism.

Two bis-maltol-polyamines: Synthesis, characterization and studies of their palladium(II) complexes exploring their potential anticancer activity

The interest in the antineoplastic and binding properties shown by the bis-maltol polyamine family, particularly Malten and Maltonis, prompted us to study the Pd2+ complexes of these latter from both a biological and metallo-receptor point of view. The Malten-Pd2+ complex can lodge hard species such as Sr2+ in its coordination-driven preorganized pocket, as confirmed by X-ray diffraction. UV-Vis and NMR data showed that Malten-Pd2+ forms even at acidic pH and exists in aqueous solution in a wide range of pH. The mononuclear complex is stable enough not to release Pd2+ in solution for a long period of time (at least one week), thus Malten-Pd2+, similarly to Maltonis-Pd2+, is suitable to be tested in biological analyses. Studies on the U937 cell line revealed that the effect on cell survival reduction induced by Malten is partially lost in Malten-Pd2+, while no differences where monitored between the effects of Maltonis-Pd2+ and Maltonis, suggesting that the availability of free maltol moieties, that is retained in Maltonis-Pd2+, but not in Malten-Pd2+, is crucial to guarantee the biological activity of these compounds.

Quinoline- and coumarin-based ligands and their rhenium(I) tricarbonyl complexes: synthesis, spectral characterization and antiproliferative activity on T-cell lymphoma

Novel 6-substituted 2-(trifluoromethyl)quinoline 5a-5e and coumarin 6a-6d ligands with aldoxime ether linked pyridine moiety were synthesized by O-alkylation of quinoline and coumarin with (E)-picolinaldehyde oxime and subsequently with [Re(CO)5Cl] gave rhenium(I) tricarbonyl complexes 5aRe-5eRe and 6aRe-6dRe that were fully characterized by NMR, single-crystal X-ray diffraction, IR and UV-Vis spectroscopy. The results of antiproliferative evaluation of quinoline and coumarin ligands and their rhenium(I) tricarbonyl complexes on various human tumor cell lines, including acute lymphoblastic leukemia (CCRF-CEM), acute monocytic leukemia (THP1), cervical adenocarcinoma (HeLa), colon adenocarcinoma (CaCo-2), T-cell lymphoma (HuT78), and non-tumor human fibroblasts (BJ) showed that the quinoline complexes 5aRe-5eRe had higher inhibitory activity than coumarin complexes 6aRe-6dRe, particularly against T-cell lymphoma (HuT78) cells. 6-Methoxy-2-(trifluoromethyl)quinoline 5e and 6-methylcoumarin 6d, and their rhenium(I) tricarbonyl complexes 5eRe and 6dRe were found to arrest the cell cycle of HuT78 cells by causing a significant accumulation of cells in the G0/G1 phase and a marked decrease in the number of cells in the G2/M phase. These rhenium(I) tricarbonyl complexes also slightly increased ROS production and significantly decreased the mitochondrial membrane potential by 50 % (5eRe) and 45 % (6dRe) compared to untreated cells and cells treated with 5e and 6d. These results suggest that the cytotoxic effects of these compounds are mediated by their effects on mitochondrial membrane potential and the subsequent increase in ROS production.

Chemistry of organometallic nucleic acid components: personal perspectives and prospects for the future

Organometallic modifications of biologically important compounds such as drugs, secondary natural products, peptides, and nucleic acids, to name just a few, represent a well-established strategy for the development of new anticancer and antimicrobial agents. Supported by these reasons, over 12 years ago, we initiated a research program into organometallic modifications of nucleic acid components. This account summarizes key results regarding the synthetic chemistry and biological activities of the obtained compounds. As synthetic chemists, our main goal over the last 12 years has been to develop new strategies that allow for the exploration of the chemical space of organometallic nucleic acid components. Accordingly, we have developed a Michael addition reaction-based methodology that enabled the synthesis of an entirely new class of glycol nucleic acid (GNA) constituents. Concerning GNA chemistry, we also reported the synthesis of the first-ever ferrocenyl GNA-RNA "mixed" dinucleoside phosphate analog. Recently, we developed a Cu(I)-catalyzed Huisgen azide-alkyne 1,3-dipolar cycloaddition reaction-based approach for the synthesis of novel 1,2,3-triazole-linked ("click") nucleosides. The high value of this approach is because it allows for the introduction of functional (e.g., luminescent and redox-active) groups that protrude from the main oligomer sequence. With respect to biological activity studies, we identified several promising anticancer and antimicrobial compounds. Furthermore, we found that simple ferrocenyl-nucleobase conjugates have potential as modulators of Aβ21-40 amyloid aggregation. The final section of this article serves as a guide for future studies, as it presents some challenging goals yet to be achieved within the rapidly growing field of nucleic acid chemistry.

Enhanced DNA damage and anti-proliferative activity of a novel ruthenium complex with a chlorambucil-decorated ligand

Triphenylphosphine substitution reactions of [RuCl(PPh3)2(tpm)]Cl, 1, featuring tris(pyrazolyl)methane (tpm) as ligand, with the chlorambucil-decorated pyridine ligand PyCA, 3-aminopyridine (PyNH2) and 4-pyridinemethanol (PyOH) afforded the corresponding pyridine complexes 2-4 in high yields. PyCA was preliminarily obtained via esterification of 4-pyridinemethanol with chlorambucil. The new compounds PyCA and 2-3 were characterized by IR and multinuclear NMR spectroscopy. Additionally, the structure of 3 was ascertained by single crystal X-ray diffraction. The in vitro anti-proliferative activity of 2-4 and PyCA was determined against a panel of cancer cell lines, outlining 2 as the most performing compound. Targeted studies were subsequently undertaken using 2 to elucidate mechanistic aspects, including the assessment of ruthenium cellular uptake, cell cycle arrest, production of reactive oxygen species (ROS), western blotting and DNA damage (comet test). Overall, data highlight that the anticancer activity provided by 2 primarily affects the mitochondria pathway with a potential additional contribution from DNA damage.

Recent trends in the design and delivery strategies of ruthenium complexes for breast cancer therapy

As the most frequent and deadly type of cancer in women, breast cancer has a high propensity to spread to the brain, bones, lymph nodes, and lungs. The discovery of cisplatin marked the beginning of the development of anticancer metal-based medications, although the drug's severe side effects have limited its usage in clinical settings. The remarkable antimetastatic and anticancer activity of different ruthenium complexes such as NAMI-A, KP1019, KP1339, etc. reported in the 1980s has bolstered the discovery of ruthenium complexes with various types of ligands for anticancer applications. The review meticulously elucidates the cytotoxic and antimetastatic potential of reported ruthenium complexes against breast cancer cells. Notably, arene-based and cyclometalated ruthenium complexes emerge as standout candidates, showcasing remarkable potency with notably low IC50 values. These findings underscore the promising therapeutic avenues offered by ruthenium-based compounds, particularly in addressing the challenges posed by conventional treatments in refractory or aggressive breast cancer subtypes. Moreover, the review comprehensively integrates a spectrum of ruthenium complexes, spanning traditional metal complexes to nano-based formulations and light-activated variants, underscoring the versatility and adaptability of ruthenium chemistry in breast cancer therapy.

Coumarin-modified ruthenium complexes: Synthesis, characterization, and antiproliferative activity against human cancer cells

Among ruthenium complexes studied as anticancer metallodrugs, NKP-1339, NAMI-A, RM175, and RAPTA-C have already entered clinical trials due to their potent antitumor activity demonstrated in preclinical studies and reduced toxicity in comparison with platinum drugs. Considering the advantages of ruthenium-based anticancer drugs and the cytostatic activity of organometallic complexes with triazole- and coumarin-derived ligands, we set out to synthesize Ru(II) complexes of coumarin-1,2,3,-triazole hybrids (L) with the general formula [Ru(L)(p-cymene)(Cl)]ClO4. The molecular structure of the complex [Ru(2a)(p-cymene)(Cl)]ClO4 (2aRu) was determined by single-crystal X-ray diffraction, which confirmed the coordination of the ligand to the central ruthenium(II) cation by bidentate mode of coordination. Coordination with Ru(II) resulted in the enhancement of cytostatic activity in HepG2 hepatocellular carcinoma cells and PANC-1 pancreatic cancer cells. Coumarin derivative 2a positively regulated the expression and activity of c-Myc and NPM1 in RKO colon carcinoma cells, while the Ru(II) half-sandwich complex 2cRu induced downregulation of AKT and ERK signaling in PANC-1 cells concomitant with reduced intracellular levels of reactive oxygen species. Altogether, our findings indicated that coumarin-modified half-sandwich Ru(II) complexes held potential as anticancer agents against gastrointestinal malignancies.

A combined solid state, solution and DFT study of a dimethyl-cyclen-Pd(II) complex

A new palladium(II) complex containing the previously synthesized 4,10-bis[(3-hydroxy-4-pyron-2-yl)methyl]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane ligand maltonis was prepared and characterized both in solution and in the solid state. Hirshfeld surface and energy framework analyses were also performed. Because maltonis already showed antineoplastic activity, the complexation of Pd(II), chosen as an alternative to Pt(II), was investigated to study its possible biological activity. UV-vis and NMR studies confirmed the formation and stability of the complex in aqueous solution at physiological pH. X-ray diffraction data revealed a structure where the Pd(II) ion is lodged in the dimethyl-cyclen cavity, with maltol rings facing each other (closed shape) even if they are not involved in the coordination. DFT analysis was performed in order to understand the most stable shape of the complex. In view of evaluating its possible bioactive conformation, the DFT study suggested a slight energetic preference for the closed one. The resulting closed complex was stabilized in the X-ray structure by intermolecular interactions that replace the intramolecular interactions present in the optimized complex. According to the DFT calculated formation energies, notwithstanding its rarity, the Pd(II) complex of maltonis is the thermodynamically preferred one among analogous complexes containing different metal ions (Pt(II), Co(II), and Cu(II)). Finally, to study its possible biological activity, the interaction between the Pd(II) complex of maltonis and nucleosides was evaluated through NMR and DFT calculations, revealing a possible interaction with purines via the maltol moieties.

Exploring antimalarial potential: Conjugating organometallic moieties with organic fragments for enhanced efficacy

In the search for novel ligands with efficacy against various diseases, particularly parasitic diseases, molecular hybridization of organometallic units into biologically active scaffolds has been hailed as an appealing strategy in medicinal chemistry. The conjugation to organometallic fragments can be achieved by an appropriate linker or by directly coordinating the existing drugs to a metal. The success of Ferroquine (FQ, SR97193), an effective chloroquine-ferrocene conjugate currently undergoing the patient-exploratory phase as a combination therapy with the novel triaminopyrimidine ZY-19489 for malaria, has sparked intense interest in organometallic compound drug discovery. We present the evolution of organometallic antimalarial agents over the last decade, focusing on the parent moiety's class and the type of organometallics involved. Four main organometallic antimalarial compounds have been chosen based on conjugated organic moieties: existing antimalarial drugs, other clinical drugs, hybrid drugs, and promising scaffolds of thiosemicarbazones, benzimidazoles, and chalcones, in particular. The presented insights contribute to the ongoing discourse on organometallic compound drug development for malaria diseases.

Copper(II) and Zinc(II) Complexes with Bacterial Prodigiosin Are Targeting Site III of Bovine Serum Albumin and Acting as DNA Minor Groove Binders

The negative environmental and social impacts of food waste accumulation can be mitigated by utilizing bio-refineries' approach where food waste is revalorized into high-value products, such as prodigiosin (PG), using microbial bioprocesses. The diverse biological activities of PG position it as a promising compound, but its high production cost and promiscuous bioactivity hinder its wide application. Metal ions can modulate the electronic properties of organic molecules, leading to novel mechanisms of action and increased target potency, while metal complex formation can improve the stability, solubility and bioavailability of the parent compound. The objectives of this study were optimizing PG production through bacterial fermentation using food waste, allowing good quantities of the pure natural product for further synthesizing and evaluating copper(II) and zinc(II) complexes with it. Their antimicrobial and anticancer activities were assessed, and their binding affinity toward biologically important molecules, bovine serum albumin (BSA) and DNA was investigated by fluorescence emission spectroscopy and molecular docking. The yield of 83.1 mg/L of pure PG was obtained when processed meat waste at 18 g/L was utilized as the sole fermentation substrate. The obtained complexes CuPG and ZnPG showed high binding affinity towards target site III of BSA, and molecular docking simulations highlighted the affinity of the compounds for DNA minor grooves.

Anticancer potential of NSAID-derived tris(pyrazolyl)methane ligands in iron(II) sandwich complexes

Tris(pyrazolyl)methane (tpm), 2,2,2-tris(pyrazolyl)ethanol (tpmOH) and its esterification derivatives with ibuprofen and flurbiprofen (tpmIBU and tpmFLU) were used as ligands to obtain complexes of the type [Fe(tpmX)2]Cl2 (1-4). The tpmIBU and tpmFLU ligands and corresponding complexes 3 and 4 were characterized by IR and multinuclear NMR spectroscopy, and the structure of tpmIBU was elucidated by single crystal X-ray diffraction. Complexes 1-4 were also assessed for their behaviour in aqueous media (solubility in D2O, octanol/water partition coefficient, stability in physiological-like conditions). The antiproliferative activity of ligands and complexes was determined on A2780, A2780cis and A549 cancer cell lines and the non-cancerous HEK 293T and BJ cell lines. The ligands and complexes were investigated for their ability to inhibit COX-2 (cyclooxygenase) and HNE (4-hydroxynonenal) enzymes. Complexes 3 and 4 exhibited cytotoxicity that may be attributed predominantly to their bioactive fragments, while DNA binding and enhancement of ROS production do not appear to play any significant role.

1,3,5-Triaza-7-phosphaadamantane and Cyclohexyl Groups Impart to Di-Iron(I) Complex Aqueous Solubility and Stability, and Prominent Anticancer Activity in Cellular and Animal Models

Using a multigram-scalable synthesis, we obtained nine dinuclear complexes based on nonendogenous iron(I) centers and featuring variable aminocarbyne and P-ligands. One compound from the series (FEACYP) emerged for its strong cytotoxicity in vitro against four human cancer cell lines, surpassing the activity of cisplatin by 3-6 times in three cell lines, with an average selectivity index of 6.2 compared to noncancerous HEK293 cells. FEACYP demonstrated outstanding water solubility (15 g/L) and stability in physiological-like solutions. It confirmed its superior antiproliferative activity when tested in 3D spheroids of human pancreatic cancer cells and showed a capacity to inhibit thioredoxin reductase (TrxR) similar to auranofin. In vivo treatment of murine LLC carcinoma with FEACYP (8 mg kg-1 dose) led to excellent tumor growth suppression (88%) on day 15, with no signs of systemic toxicity and only limited body weight loss.

Multifunctional Organometallic Compounds Active against Infective Trypanosomes: Ru(II) Ferrocenyl Derivatives with Two Different Bioactive Ligands

Human African trypanosomiasis (HAT, sleeping sickness) and American trypanosomiasis (Chagas disease) are endemic zoonotic diseases caused by genomically related trypanosomatid protozoan parasites (Trypanosoma brucei and Trypanosoma cruzi, respectively). Just a few old drugs are available for their treatment, with most of them sharing poor safety, efficacy, and pharmacokinetic profiles. Only fexinidazole has been recently incorporated into the arsenal for the treatment of HAT. In this work, new multifunctional Ru(II) ferrocenyl compounds were rationally designed as potential agents against these pathogens by including in a single molecule 1,1'-bis(diphenylphosphino)ferrocene (dppf) and two bioactive bidentate ligands: pyridine-2-thiolato-1-oxide ligand (mpo) and polypyridyl ligands (NN). Three [Ru(mpo)(dppf)(NN)](PF6) compounds and their derivatives with chloride as a counterion were synthesized and fully characterized in solid state and solution. They showed in vitro activity on bloodstream T. brucei (EC50 = 31-160 nM) and on T. cruzi trypomastigotes (EC50 = 190-410 nM). Compounds showed the lowest EC50 values on T. brucei when compared to the whole set of metal-based compounds previously developed by us. In addition, several of the Ru compounds showed good selectivity toward the parasites, particularly against the highly proliferative bloodstream form of T. brucei. Interaction with DNA and generation of reactive oxygen species (ROS) were ruled out as potential targets and modes of action of the Ru compounds. Biochemical assays and in silico analysis led to the insight that they are able to inhibit the NADH-dependent fumarate reductase from T. cruzi. One representative hit induced a mild oxidation of low molecular weight thiols in T. brucei. The compounds were stable for at least 72 h in two different media and more lipophilic than both bioactive ligands, mpo and NN. An initial assessment of the therapeutic efficacy of one of the most potent and selective candidates, [Ru(mpo)(dppf)(bipy)]Cl, was performed using a murine infection model of acute African trypanosomiasis. This hit compound lacks acute toxicity when applied to animals in the dose/regimen described, but was unable to control parasite proliferation in vivo, probably because of its rapid clearance or low biodistribution in the extracellular fluids. Future studies should investigate the pharmacokinetics of this compound in vivo and involve further research to gain deeper insight into the mechanism of action of the compounds.

Tuning the photoactivated anticancer activity of Pt(iv) compounds via distant ferrocene conjugation

Photoactive prodrugs offer potential for spatially-selective antitumour activity with minimal effects on normal tissues. Excited-state chemistry can induce novel effects on biochemical pathways and combat resistance to conventional drugs. Photoactive metal complexes in particular, have a rich and relatively unexplored photochemistry, especially an ability to undergo facile intersystem crossing and populate triplet states. We have conjugated the photoactive octahedral Pt(iv) complex trans, trans, trans-[Pt(N3)2(OH)2(py)2] to ferrocene to introduce novel features into a candidate photochemotherapeutic drug. The X-ray crystal structure of the conjugate Pt-Fe confirmed the axial coordination of a ferrocene carboxylate, with Pt(iv) and Fe(ii) 6.07 Å apart. The conjugation of ferrocene red-shifted the absorption spectrum and ferrocene behaves as a light antenna allowing charge transfer from iron to platinum, promoting the photoactivation of Pt-Fe with light of longer wavelength. Cancer cellular accumulation is enhanced, and generation of reactive species is catalysed after photoirradiation, introducing ferroptosis as a contribution towards the cell-death mechanism. TDDFT calculations were performed to shed light on the behaviour of Pt-Fe when it is irradiated. Intersystem spin-crossing allows the formation of triplet states centred on both metal atoms. The dissociative nature of triplet states confirms that they can be involved in ligand detachment due to irradiation. The Pt(ii) photoproducts mainly retain the trans-{Pt(py)2}2+fragment. Visible light irradiation gives rise to micromolar activity for Pt-Fe towards ovarian, lung, prostate and bladder cancer cells under both normoxia and hypoxia, and some photoproducts appear to retain Pt(iv)-Fe(ii) conjugation.

Antifungal and Antiparasitic Activities of Metallocene-Containing Fluconazole Derivatives

The search for new anti-infectives based on metal complexes is gaining momentum. Among the different options taken by researchers, the one involving the use of organometallic complexes is probably the most successful one with a compound, namely, ferroquine, already in clinical trials against malaria. In this study, we describe the preparation and in-depth characterization of 10 new (organometallic) derivatives of the approved antifungal drug fluconazole. Our rationale is that the sterol 14α-demethylase is an enzyme part of the ergosterol biosynthesis route in Trypanosoma and is similar to the one in pathogenic fungi. To demonstrate our postulate, docking experiments to assess the binding of our compounds with the enzyme were also performed. Our compounds were then tested on a range of fungal strains and parasitic organisms, including the protozoan parasite Trypanosoma cruzi (T. cruzi) responsible for Chagas disease, an endemic disease in Latin America that ranks among some of the most prevalent parasitic diseases worldwide. Of high interest, the two most potent compounds of the study on T. cruzi that contain a ferrocene or cobaltocenium were found to be harmless for an invertebrate animal model, namely, Caenorhabditis elegans (C. elegans), without affecting motility, viability, or development.

Mitochondria-targeted iridium(III) complexes encapsulated in liposome induce cell death through ferroptosis and gasdermin-mediated pyroptosis

This paper unveils a novel perspective on synthesis and characterization of the ligand 5-bromo-2-amino-2'-(phenyl-1H-imidazo[4,5-f][1,10]phenanthroline) (BAPIP), and its iridium(III) complexes [Ir(PPY-)2(BAPIP)](PF6) (1a, with PPY- as deprotonated 2-phenylpyridine), [Ir(PIQ-)2(BAPIP)](PF6) (1b, piq- denoting deprotonated 1-phenylisoquinoline), and [Ir(BZQ-)2(BAPIP)](PF6) (1c, bzq- signifying deprotonated benzo[h]quinoline). Systematic evaluation of the cytotoxicity of 1a, 1b, and 1c across diverse cell lines encompassing B16, HCT116, HepG2, A549, HeLa, and LO2 using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Unexpectedly, compounds 1b and 1c demonstrated no cytotoxicity against the above cell lines. Motivated by the pursuit of heightened anti-proliferative potential, a strategic encapsulation approach yielded liposomes 1alip, 1blip, and 1clip. As expectation, 1alip, 1blip, and 1clip displayed remarkable anti-proliferative efficacy, particularly noteworthy in A549 cells, exhibiting IC50 values of 4.9 ± 1.0, 5.9 ± 0.1, and 7.6 ± 0.2 μM, respectively. Moreover, our investigation illuminated the mitochondrial accumulation of these liposomal entities, 1alip, 1blip, and 1clip, evoking apoptosis through the mitochondrial dysfunction mediated by reactive oxygen species (ROS). The ferroptosis was confirmed by decrease in glutathione (GSH) concentrations, the downregulation of glutathione peroxidase 4 (GPX4), increase of high mobility group protein 1 (HMGB1), and lipid peroxidation. Simultaneously, pyroptosis as another mode of cell death was undertaken. RNA-sequencing was employed to investigate intricate signalling pathways. In vivo examination provided tangible evidence of 1alip in effectively curbing tumor growth. Collectively, this study provides a multifaceted mode of cellular demise orchestrated by 1a, 1alip, 1blip, and 1clip, involving pathways encompassing apoptosis, ferroptosis, and pyroptosis.

Ciprofloxacin and Norfloxacin Hybrid Compounds: Potential Anticancer Agents

BACKGROUND

The concept of utilizing drug repurposing/repositioning in the development of hybrid molecules is an important strategy in drug discovery. Fluoroquinolones, a class of antibiotics, have been reported to exhibit anticancer activities. Although anticancer drug development is achieving some positive outcomes, there is still a need to develop new and effective anticancer drugs. Some limitations associated with most of the available anticancer drugs are drug resistance and toxicity, poor bio-distribution, poor solubility, and lack of specificity, thereby reducing their therapeutic outcomes.

OBJECTIVES

Fluoroquinolones, a known class of antibiotics, have been explored by hybridizing them with other pharmacophores and evaluating their anticancer activity in silico and in vitro. Hence, this review provides an update on new anticancer drugs containing fluoroquinolones moiety, Ciprofloxacin and Norfloxacin between 2020 and 2023, their structural relationship activity, and the future strategies to develop potent chemotherapeutic agents.

METHODS

Fluoroquinolones were mostly hybridized via the N-4 of the piperazine ring on position C-7 with known pharmacophores characterized, followed by biological studies to evaluate their anticancer activity.

RESULTS

The hybrid molecules displayed promising and interesting anticancer activities. Factors such as the nature of the linker, the presence of electron-withdrawing groups, nature, and position of the substituents influenced the anticancer activity of the synthesized compounds.

CONCLUSION

The hybrids were selective towards some cancer cells. However, further in vivo studies are needed to fully understand their mode of action.

Utilizing coordination chemistry through formation of a CuII-quinalizarin complex to manipulate cell biology: An in vitro, in silico approach

Quinalizarin, an analogue of anthracycline anticancer agents, is an anticancer agent itself. A CuII complex was prepared and characterized by elemental analysis, UV-Vis & IR spectroscopy, mass spectrometry, EPR and DFT. The intention behind the preparation of the complex was to increase cellular uptake, compare its binding with DNA against that of quinalizarin, modulation of semiquinone formation, realization of human DNA topoisomerase I & human DNA topoisomerase II inhibition and observation of anticancer activity. While the first two attributes of complex formation lead to increased efficacy, decrease in semiquinone generation could results in a compromise with efficacy. Inhibition of human DNA topoisomerase makes up this envisaged compromise in free radical activity since the complex shows remarkable ability to disrupt activities of human DNA topoisomerase I and II. The complex unlike quinalizarin, does not catalyze flow of electrons from NADH to O2 to the extent known for quinalizarin. Hence, decrease in semiquinone or superoxide radical anion could make modified quinalizarin [as CuII complex] less efficient in free radical pathway. However, it would be less cardiotoxic and that would be advantageous to qualify it as a better anticancer agent. Although binding to calf thymus DNA was comparable to quinalizarin, it was weaker than anthracyclines. Low cost of quinalizarin could justify consideration as a substitute for anthracyclines but the study revealed IC50 of quinalizarin/CuII-quinalizarin was much higher than anthracyclines or their complexes. Even then, there is a possibility that CuII-quinalizarin could be an improved and less costly form of quinalizarin as anticancer agent.

Resurgence and Repurposing of Antifungal Azoles by Transition Metal Coordination for Drug Discovery

Coordination compounds featuring one or more antifungal azole (AA) ligands constitute an interesting family of candidate molecules, given their medicinal polyvalence and the viability of drug complexation as a strategy to improve and repurpose available medications. This review reports the work performed in the field of coordination derivatives of AAs synthesized for medical purposes by discussing the corresponding publications and emphasizing the most promising compounds discovered so far. The resulting overview highlights the efficiency of AAs and their metallic species, as well as the potential still lying in this research area.

Synthesis of Novel Heterocyclic Ferrocenyl Chalcones and Their Biological Evaluation

Breast cancer is currently the most commonly diagnosed cancer, with 287,850 new cases estimated for 2022 as reported by the American Cancer Society. Therefore, finding an effective treatment for this disease is imperative. Chalcones are α,β-unsaturated systems found in nature. These compounds have shown a wide array of biological activities, making them popular synthetic targets. Chalcones consist of two aromatic substituents connected by an enone bridge; this arrangement allows for a large number of derivatives. Given the biological relevance of these compounds, novel ferrocene-heterocycle-containing chalcones were synthesized and characterized based on a hybrid drug design approach. These heterocycles included thiophene, pyrimidine, thiazolyl, and indole groups. Fourteen novel heterocyclic ferrocenyl chalcones were synthesized and characterized. Herein, we also report their cytotoxicity against triple-negative breast cancer cell lines MDA-MB-231 and 4T1 and the noncancer lung cell line MRC-5. System 3 ferrocenyl chalcones displayed superior anticancer properties compared to their system 1 analogues. System 3 chalcones bearing five-membered heterocyclic substituents (thiophene, pyrazole, pyrrole, and pyrimidine) were the most active toward the MDA-MB-231 cancer cell line with IC50 values from 6.59 to 12.51 μM. Cytotoxicity of the evaluated compounds in the 4T1 cell line exhibited IC50 values from 13.23 to 213.7 μM. System 3 pyrazole chalcone had consistent toxicity toward both cell lines (IC50 ∼ 13 μM) as well as promising selectivity relative to the noncancer MRC-5 control. Antioxidant activity was also evaluated, where, contrary to anticancer capabilities, system 1 ferrocenyl chalcones were superior to their system 3 analogues. Antioxidant activity comparable to that of ascorbic acid was observed for thiophene-bearing ferrocenyl chalcone with EC50 = 31 μM.

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.

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.

Computer-Aided Drug Design and Synthesis of Rhenium Clotrimazole Antimicrobial Agents

In the context of the global health issue caused by the growing occurrence of antimicrobial resistance (AMR), the need for novel antimicrobial agents is becoming alarming. Inorganic and organometallic complexes represent a relatively untapped source of antibiotics. Here, we report a computer-aided drug design (CADD) based on a 'scaffold-hopping' approach for the synthesis and antibacterial evaluation of fac-Re(I) tricarbonyl complexes bearing clotrimazole (ctz) as a monodentate ligand. The prepared molecules were selected following a pre-screening in silico analysis according to modification of the 2,2'-bipyridine (bpy) ligand in the coordination sphere of the complexes. CADD pointed to chiral 4,5-pinene and 5,6-pinene bipyridine derivatives as the most promising candidates. The corresponding complexes were synthesized, tested toward methicillin-sensitive and -resistant S. aureus strains, and the obtained results evaluated with regard to their binding affinity with a homology model of the S. aureus MurG enzyme. Overall, the title species revealed very similar minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values as those of the reference compound used as the scaffold in our approach. The obtained docking scores advocate the viability of 'scaffold-hopping' for de novo design, a potential strategy for more cost- and time-efficient discovery of new antibiotics.

Copper(ii) and silver(i) complexes with dimethyl 6-(pyrazine-2-yl)pyridine-3,4-dicarboxylate (py-2pz): the influence of the metal ion on the antimicrobial potential of the complex

Dimethyl 6-(pyrazine-2-yl)pyridine-3,4-dicarboxylate (py-2pz) was used as a ligand for the synthesis of new copper(ii) and silver(i) complexes, [CuCl2(py-2pz)]2 (1), [Cu(CF3SO3)(H2O)(py-2pz)2]CF3SO3·2H2O (2), [Ag(py-2pz)2]PF6 (3) and {[Ag(NO3)(py-2pz)]·0.5H2O} n (4). The complexes were characterized by spectroscopic and electrochemical methods, while their structures were determined by single crystal X-ray diffraction analysis. The X-ray analysis revealed the bidentate coordination mode of py-2pz to the corresponding metal ion via its pyridine and pyrazine nitrogen atoms in all complexes, while in polynuclear complex 4, the heterocyclic pyrazine ring of one py-2pz additionally behaves as a bridging ligand between two Ag(i) ions. DFT calculations were performed to elucidate the structures of the investigated complexes in solution. The antimicrobial potential of the complexes 1-4 was evaluated against two bacterial (Pseudomonas aeruginosa and Staphylococcus aureus) and two Candida (C. albicans and C. parapsilosis) species. Silver(i) complexes 3 and 4 have shown good antibacterial and antifungal properties with minimal inhibitory concentration (MIC) values ranging from 4.9 to 39.0 μM (3.9-31.2 μg mL-1). All complexes inhibited the filamentation of C. albicans and hyphae formation, while silver(i) complexes 3 and 4 had also the ability to inhibit the biofilm formation process of this fungus. The binding affinity of the complexes 1-4 with calf thymus DNA (ct-DNA) and bovine serum albumin (BSA) was studied by fluorescence emission spectroscopy to clarify the mode of their antimicrobial activity. Catechol oxidase biomimetic catalytic activity of copper(ii) complexes 1 and 2 was additionally investigated by using 3,5-di-tert-butylcatechol (3,5-DTBC) and o-aminophenol (OAP) as substrates.

New multifunctional Ru(II) organometallic compounds show activity against Trypanosoma brucei and Leishmania infantum

Human African trypanosomiasis (sleeping sickness) and leishmaniasis are prevalent zoonotic diseases caused by genomically related trypanosomatid protozoan parasites (Trypanosoma brucei and Leishmania spp). Additionally, both are co-endemic in certain regions of the world. Only a small number of old drugs exist for their treatment, with most of them sharing poor safety, efficacy, and pharmacokinetic profiles. In this work, new multifunctional Ru(II) ferrocenyl compounds were rationally designed as potential agents against these trypanosomatid parasites by including in a single molecule 1,1'-bis(diphenylphosphino)ferrocene (dppf) and two bioactive bidentate ligands: 8-hydroxyquinoline derivatives (8HQs) and polypyridyl ligands (NN). Three [Ru(8HQs)(dppf)(NN)](PF₆) compounds were synthesized and fully characterized. They showed in vitro activity on bloodstream Trypanosoma brucei (IC₅₀ 140-310 nM) and on Leishmania infantum promastigotes (IC₅₀ 3.0-4.8 μM). The compounds showed good selectivity towards T. brucei in respect to J774 murine macrophages as mammalian cell model (SI 15-38). Changing hexafluorophosphate counterion by chloride led to a three-fold increase in activity on both parasites and to a two to three-fold increase in selectivity towards the pathogens. The compounds affect in vitro at least the targets of the individual bioactive moieties included in the new chemical entities: DNA and generation of ROS. The compounds are stable in solution and are more lipophilic than the free bioactive ligands. No clear correlation between lipophilicity, interaction with DNA or generation of ROS and activity was detected, which agrees with their overall similar anti-trypanosoma potency and selectivity. These compounds are promising candidates for further drug development.

Self-Amplifying Iridium(III) Photosensitizer for Ferroptosis-Mediated Immunotherapy Against Transferrin Receptor-Overexpressing Cancer

Photoimmunotherapy is attractive for cancer treatment due to its spatial controllability and sustained responses. This work presents a ferrocene-containing Ir(III) photosensitizer (IrFc1) that can bind with transferrin and be transported into triple-negative breast cancer (TNBC) cells via a transferrin receptor-mediated pathway. When the ferrocene in IrFc1 is oxidized by reactive oxygen species, its capability to photosensitize both type I (electron transfer) and type II (energy transfer) pathways is activated through a self-amplifying process. Upon irradiation, IrFc1 induces the generation of lipid oxidation to cause ferroptosis in TNBC cells, which promotes immunogenic cell death (ICD) under both normoxia and hypoxia. In vivo, IrFc1 treatment elicits a CD8⁺ T-cell response, which activates ICD in TNBC resulting in enhanced anticancer immunity. In summary, this work reports a small molecule-based photosensitizer with enhanced cancer immunotherapeutic properties by eliciting ferroptosis through a self-amplifying process.

Molecular Hybridization Strategy on the Design, Synthesis, and Structural Characterization of Ferrocene-N-acyl Hydrazones as Immunomodulatory Agents

Immunomodulatory agents are widely used for the treatment of immune-mediated diseases, but the range of side effects of the available drugs makes necessary the search for new immunomodulatory drugs. Here, we investigated the immunomodulatory activity of new ferrocenyl-N-acyl hydrazones derivatives (SintMed(141−156). The evaluated N-acyl hydrazones did not show cytotoxicity at the tested concentrations, presenting CC50 values greater than 50 µM. In addition, all ferrocenyl-N-acyl hydrazones modulated nitrite production in immortalized macrophages, showing inhibition values between 14.4% and 74.2%. By presenting a better activity profile, the ferrocenyl-N-acyl hydrazones SintMed149 and SintMed150 also had their cytotoxicity and anti-inflammatory effect evaluated in cultures of peritoneal macrophages. The molecules were not cytotoxic at any of the concentrations tested in peritoneal macrophages and were able to significantly reduce (p < 0.05) the production of nitrite, TNF-α, and IL-1β. Interestingly, both molecules significantly reduced the production of IL-2 and IFN-γ in cultured splenocytes activated with concanavalin A. Moreover, SintMed150 did not show signs of acute toxicity in animals treated with 50 or 100 mg/kg. Finally, we observed that ferrocenyl-N-acyl hydrazone SintMed150 at 100 mg/kg reduced the migration of neutrophils (44.6%) in an acute peritonitis model and increased animal survival by 20% in an LPS-induced endotoxic shock model. These findings suggest that such compounds have therapeutic potential to be used to treat diseases of inflammatory origin.

Synthesis of Novel Ferrocene-Benzofuran Hybrids via Palladium- and Copper-Catalyzed Reactions

The combination of the ferrocene skeleton with pharmacophores often leads to molecules with interesting biological properties. Five ferrocene-benzofuran hybrids of different structures were synthesized by transition metal catalyzed reactions. The efficiency of both homogeneous and heterogeneous catalytic methods was tested. The products were characterized using 1H, 13C NMR and FTIR spectroscopy, HRMS and cyclic voltammetry. The structure of one of the new compounds was also proved with X-ray crystallography. The new hybrids showed moderate cytotoxicity on MCF-7 and MDA-MB-231 cell lines. It is remarkable that the less curable MDA-MB-231 cell line was more sensitive to treatment with three ferrocene derivatives.

Rhenium(I) derivatives of aminoquinoline and imidazolopiperidine-based ligands: Synthesis, in vitro and in silico biological evaluation against Plasmodium falciparum

A small library of aminoquinoline and imidazolopiperidine (IMP)-based ligands, containing the 1,2,3-triazole moiety, and their corresponding tricarbonyl rhenium complexes were synthesised and their inhibitory activities evaluated against the chloroquine-sensitive (CQS) and multidrug-resistant (MDR) strains (NF54 and K1, respectively) of P. falciparum. The quinoline-based compounds (L1, L2, ReL1, and ReL2) were at least six-fold more potent than their IMP-based counterparts (L3, L4, ReL3, and ReL4) against both strains of P. falciparum, with the most promising compound (L1) displaying activity comparable to chloroquine diphosphate (CQDP) in the MDR strain. Additionally, all of the synthesised compounds have resistance indices less than CQDP. To gain insight into a possible mechanism of action, in silico hemozoin docking simulations were performed. These studies proposed that the tested compounds may act via hemozoin inhibition, as the new aminoquinoline-derivatives, with the exception of complex ReL2 (binding affinity: -12.62 kcal/mol), showed higher binding affinities than the reference drug chloroquine (CQ, -13.56 kcal/mol). Furthermore, the ligands exhibited superior binding affinity relative to their corresponding Re(I) complexes, which is reflected in their antiplasmodial activity.

Harmicens, Novel Harmine and Ferrocene Hybrids: Design, Synthesis and Biological Activity

Cancer and malaria are both global health threats. Due to the increase in the resistance to the known drugs, research on new active substances is a priority. Here, we present the design, synthesis, and evaluation of the biological activity of harmicens, hybrids composed of covalently bound harmine/β-carboline and ferrocene scaffolds. Structural diversity was achieved by varying the type and length of the linker between the β-carboline ring and ferrocene, as well as its position on the β-carboline ring. Triazole-type harmicens were prepared using Cu(I)-catalyzed azide-alkyne cycloaddition, while the synthesis of amide-type harmicens was carried out by applying a standard coupling reaction. The results of in vitro biological assays showed that the harmicens exerted moderate antiplasmodial activity against the erythrocytic stage of P. falciparum (IC50 in submicromolar and low micromolar range) and significant and selective antiproliferative activity against the MCF-7 and HCT116 cell lines (IC50 in the single-digit micromolar range, SI > 5.9). Cell localization experiments showed different localizations of nonselective harmicene 36 and HCT116-selective compound 28, which clearly entered the nucleus. A cell cycle analysis revealed that selective harmicene 28 had already induced G1 cell cycle arrest after 24 h, followed by G2/M arrest with a concomitant drastic reduction in the percentage of cells in the S phase, whereas the effect of nonselective compound 36 on the cell cycle was much less pronounced, which agreed with their different localizations within the cell.

Ferrocene-appended anthraquinone and coumarin as redox-active cytotoxins

Appending of ferrocene (Fc) to biologically-active organic backbones can generate novel multi-functional species for targeting bacteria and cancer. In this work Fc was linked to coumarin and anthraquinone with the goal of harnessing the redox-active Fc centre to generate new compounds that exhibit cytoxicity through the generation of toxic reactive oxygen species (ROS). A Cu(I)-catalyzed azide-alkyne cycloaddition "click" reaction was used to connect the organic and Fc components via a triazole linker. Cyclic voltammetry shows that the Fc potentials are suitable for oxidation by biological hydrogen peroxide to give reactive ferrocenium (Fc⁺) species, which can then generate hydroxyl radicals. The ability of the compounds to generate hydroxyl radicals in the presence of hydrogen peroxide was shown directly using EPR spin-trapping experiments. Furthermore, in vitro studies in MCF-7 breast cancer cells show significant increases in ROS following incubation with the Fc-functionalized compounds. Screening for antibacterial activity produced negative results for all of the Fc compounds, consitent with low levels of hydrogen peroxide typically found in bacteria. By contrast, Fc-coumarin showed cytotoxicity against A549 lung cancer and SKOV3 ovarian cancer cell lines, whereas the parent compound was inactive. This is consistent both with the cytoxic potential of the Fc group and the elevated hydrogen peroxide levels found in many cancers. Interestingly, the anthraquinone compounds showed the opposite effect with the parent compounds showing modest activity against A549 cells, but the Fc compounds being inactive. This demonstrates other potential negative impacts of including Fc, such as significantly increased lipophilicity.

Light Triggers the Antiproliferative Activity of Naphthalimide-Conjugated (η6-arene)ruthenium(II) Complexes

We report the synthesis and characterization of three half-sandwich Ru(II) arene complexes [(η⁶-arene)Ru(N,N')L][PF₆]₂ containing arene = p-cymene, N,N' = bipyridine, and L = pyridine meta- with methylenenaphthalimide (C1), methylene(nitro)naphthalimide (C2), or methylene(piperidinyl)naphthalimide (C3). The naphthalimide acts as an antenna for photoactivation. After 3 h of irradiation with blue light, the monodentate pyridyl ligand had almost completely dissociated from complex C3, which contains an electron donor on the naphthalimide ring, whereas only 50% dissociation was observed for C1 and C2. This correlates with the lower wavelength and strong absorption of C3 in this region of the spectrum (λ_max = 418 nm) compared with C1 and C2 (λ_max = 324 and 323 nm, respectively). All the complexes were relatively non-toxic towards A549 human lung cancer cells in the dark, but only complex C3 exhibited good photocytoxicity towards these cancer cells upon irradiation with blue light (IC₅₀ = 10.55 ± 0.30 μM). Complex C3 has the potential for use in photoactivated chemotherapy (PACT).

Electronic Coupling in 1,2,3-Triazole Bridged Ferrocenes and Its Impact on Reactive Oxygen Species Generation and Deleterious Activity in Cancer Cells

Mixed-valence (MV) binuclear ferrocenyl compounds have long been studied as models for testing theories of electron transfer and in attempts to design molecular-scale electronic devices (e.g., molecular wires). In contrary to that, far less attention has been paid to MV binuclear ferrocenes as anticancer agents. Herein, we discuss the synthesis of six 1,2,3-triazole ferrocenyl compounds for combined (spectro)electrochemical, electron paramagnetic resonance (EPR), computational, and anticancer activity studies. Our synthetic approach was based on the copper-catalyzed 1,3-dipolar azide–alkyne cycloaddition reaction and enabled us to obtain in one step compounds bearing either one, two, or three ferrocenyl entities linked to the common 1,2,3-triazole core. Thus, two series of complexes were obtained, which pertain to derivatives of 3′-azido-3′-deoxythymidine (AZT) and 3-azidopropionylferrocene, respectively. Based on the experimental and theoretical data, the two mono-oxidized species corresponding to binuclear AZT and trinuclear 3-azidopropionylferrocene complexes have been categorized as class II mixed-valence according to the classification proposed by Robin and Day. Of importance is the observation that these two compounds are more active against human A549 and H1975 non-small-cell lung cancer cells than their congeners, which do not show MV characteristics. Moreover, the anticancer activity of MV species competes or surpasses, dependent on the cell line, the activity of reference anticancer drugs such as cisplatin, tamoxifen, and 5-fluorouracil. The most active from the entire series of compounds was the binuclear thymidine derivative with the lowest IC₅₀ value of 5 ± 2 μM against lung H1975 cancer cells. The major mechanism of antiproliferative activity for the investigated MV compounds is based on reactive oxygen species generation in cancer cells. This hypothesis was substantiated by EPR spin-trapping experiments and the observation of decreased anticancer activity in the presence of N-acetyl cysteine (NAC) free-radical scavenger.

The 1,2,3-triazole bridged bi- and triferrocenyl compounds were prepared via a “click” reaction. Their corresponding mono-oxidized forms have been categorized as class II MV species. The biferrocenyl thymidine derivative showed remarkable anticancer activity against human A549 and H1975 cancer cells and negligible activity against nonmalignant human BEAS-2B cells. The anticancer activity mechanism is mainly due to ROS generation, and it originates from the combination of electronic coupling and the thymidine moiety, combined all together in one molecular scaffold.

Metalloimmunotherapy with Rhodium and Ruthenium Complexes: Targeting Tumor-Associated Macrophages

Tumor associated macrophages (TAMs) suppress the cancer immune response and are a key target for immunotherapy. The effects of ruthenium and rhodium complexes on TAMs have not been well characterized. To address this gap in the field, a panel of 22 dirhodium and ruthenium complexes were screened against three subtypes of macrophages, triple-negative breast cancer and normal breast tissue cells. Experiments were carried out in 2D and biomimetic 3D co-culture experiments with and without irradiation with blue light. Leads were identified with cell-type-specific toxicity toward macrophage subtypes, cancer cells, or both. Experiments with 3D spheroids revealed complexes that sensitized the tumor models to the chemotherapeutic doxorubicin. Cell surface exposure of calreticulin, a known facilitator of immunogenic cell death (ICD), was increased upon treatment, along with a concomitant reduction in the M2-subtype classifier arginase. Our findings lay a strong foundation for the future development of ruthenium- and rhodium-based chemotherapies targeting TAMs.

Facing Diseases Caused by Trypanosomatid Parasites: Rational Design of Pd and Pt Complexes With Bioactive Ligands

Human African Trypanosomiasis (HAT), Chagas disease or American Trypanosomiasis (CD), and leishmaniases are protozoan infections produced by trypanosomatid parasites belonging to the kinetoplastid order and they constitute an urgent global health problem. In fact, there is an urgent need of more efficient and less toxic chemotherapy for these diseases. Medicinal inorganic chemistry currently offers an attractive option for the rational design of new drugs and, in particular, antiparasitic ones. In this sense, one of the main strategies for the design of metal-based antiparasitic compounds has been the coordination of an organic ligand with known or potential biological activity, to a metal centre or an organometallic core. Classical metal coordination complexes or organometallic compounds could be designed as multifunctional agents joining, in a single molecule, different chemical species that could affect different parasitic targets. This review is focused on the rational design of palladium(II) and platinum(II) compounds with bioactive ligands as prospective drugs against trypanosomatid parasites that has been conducted by our group during the last 20 years.

Forever young: the first seventy years of ferrocene

The discovery of ferrocene, [Fe(η5-C5H5)2], seventy years ago has significantly influenced chemical research and provided a key impetus for establishing and rapidly expanding organometallic chemistry, which has continued at a...

Ferroptosis-Enhanced Cancer Immunity by a Ferrocene-Appended Iridium(III) Diphosphine Complex

Ferroptosis is a programmed cell death pathway discovered in recent years, and ferroptosis-inducing agents have great potential as new antitumor candidates. Here, we report a Ir(III) complex (Ir1) containing a ferrocene-modified diphosphine ligand that localizes in lysosomes. Under the acidic environments of lysosomes, Ir1 can effectively catalyze Fenton reaction, produce hydroxyl radicals, induce lipid peroxidation, down-regulate glutathione peroxidase 4, and induce ferroptosis. RNA sequencing analysis shows that Ir1 can significantly affect pathways related to ferroptosis and cancer immunity. Accordingly, Ir1 can induce immunogenic cells death and suppress tumor growth in vitro, regulate T cell activity and immune microenvironments in vivo. In conclusion, we show the potential of small molecules with ferroptosis-inducing capabilities for effective cancer immunotherapy.

4-Amino-1,8-naphthalimide-ferrocene conjugates as potential multi-targeted anticancer and fluorescent cellular imaging agents

Herein we present eight ferrocenyl 4-amino-1,8-naphthalimides. Designed as fluorescent logic gates for acidity and oxidisability, the molecules have been repurposed as anti-proliferation and cellular imaging agents. The compounds were studied in vitro against MCF-7 and K562 cancer cell lines by the MTT method. Compounds with protonable secondary amines tended to exhibit greater cytotoxicity than those with tertiary amines. Compounds with no measurable GI₅₀ values within a 24 hour time window, as well as at shorter exposure times, may be suitable as fluorescent cellular imaging probes.

Has Ferrocene Really Delivered Its Role in Accentuating the Bioactivity of Organic Scaffolds?

Ferrocene is an important structural core in bioorganometallic chemistry because of its inherent stability, excellent redox properties, and low toxicity. Ferroquine and ferrocifen are two of the most notable contributions of ferrocene to medicinal chemistry with remarkable antimalarial and anticancer properties. The improved medicinal properties of these drug candidates highlight the impact that ferrocene can have on the molecular and biological properties of the bioactive compounds. In this Perspective, we investigate the scope and limitations of ferrocene incorporation into organic compounds/natural products on their mode of action and biological activities. We have also discussed the detailed role of ferrocene modifications in influencing the anticancer, antimalarial, and antimicrobial properties of various bioactive moieties to design safer and promising ferrocene-based drugs.