Anticancer Activity of Metallodrugs and Metallizing Host Defense Peptides-Current Developments in Structure-Activity Relationship

This article provides an overview of the development, structure and activity of various metal complexes with anti-cancer activity. Chemical researchers continue to work on the development and synthesis of new molecules that could act as anti-tumor drugs to achieve more favorable therapies. It is therefore important to have information about the various chemotherapeutic substances and their mode of action. This review focuses on metallodrugs that contain a metal as a key structural fragment, with cisplatin paving the way for their chemotherapeutic application. The text also looks at ruthenium complexes, including the therapeutic applications of phosphorescent ruthenium(II) complexes, emphasizing their dual role in therapy and diagnostics. In addition, the antitumor activities of titanium and gold derivatives, their side effects, and ongoing research to improve their efficacy and reduce adverse effects are discussed. Metallization of host defense peptides (HDPs) with various metal ions is also highlighted as a strategy that significantly enhances their anticancer activity by broadening their mechanisms of action.

Strategies for the Nuclear Delivery of Metal Complexes to Cancer Cells

The nucleus is an essential organelle for the function of cells. It holds most of the genetic material and plays a crucial role in the regulation of cell growth and proliferation. Since many antitumoral therapies target nucleic acids to induce cell death, tumor-specific nuclear drug delivery could potentiate therapeutic effects and prevent potential off-target side effects on healthy tissue. Due to their great structural variety, good biocompatibility, and unique physico-chemical properties, organometallic complexes and other metal-based compounds have sparked great interest as promising anticancer agents. In this review, strategies for specific nuclear delivery of metal complexes are summarized and discussed to highlight crucial parameters to consider for the design of new metal complexes as anticancer drug candidates. Moreover, the existing opportunities and challenges of tumor-specific, nucleus-targeting metal complexes are emphasized to outline some new perspectives and help in the design of new cancer treatments.

Linkage of the Dinuclear Gold(I) Complex Luminescence and Origin of Endocyclic Amino Group of Cyclic P2N2-Bridging Ligands

Gold(I) complexes of LAu2Cl2 composition based on P2N2 ligands, namely 1,5-diaza-3,7-diphosphacyclooctanes, containing ethylpyridyl substituents at the phosphorus atoms and sp2- or sp3-hybridized endocyclic nitrogen atoms were synthesized. The SCXRD analysis indicated the strong impact of the geometry of the nitrogen atom on the structure and conformational flexibility of the complexes. The N-aryl substituted ligand with the planar endocyclic nitrogen atom provides higher flexibility of the complex and an ability to bind the solvent molecules in the "host-guest" mode, whereas that kind of behavior is forbidden for the complex with an N-alkyl substituted ligand with a pyramidal nitrogen atom. The substituents at nitrogen atoms also control the origin of the emission, which is phosphorescence for the N-aryl substituted complex and fluorescence for the N-alkylaryl substituted complex. The phosphorescent gold(I) complex displays high cytotoxicity without selectivity toward the m-HeLa and normal cells, but the core-shell nanoparticles formed on the base of the complex demonstrate reduced cytotoxicity. The luminescence of the NPs allows tracking the complexes in the cell samples.

5-Nitrofuryl-Containing Thiosemicarbazone Gold(I) Compounds: Synthesis, Stability Studies, and Anticancer Activity

This work describes the synthesis of four gold(I) [AuClL] compounds containing chloro and biologically active protonated thiosemicarbazones based on 5-nitrofuryl (L=HSTC). The stability of the compounds in dichloromethane, DMSO, and DMSO/culture media solutions was investigated by spectroscopy, cyclic voltammetry, and conductimetry, indicating the formation overtime of cationic monometallic [Au(HTSC)(DMSO)]± or [Au(HTSC)2 ]± , and/or dimeric species. Neutral [{Au(TSC)}2 ] species were obtained from one of the compounds in dichlomethane/n-hexane solution and characterized by X-ray crystallography revealing a Au-Au bond, and deprotonated thiosemicarbazone (TSC). The cytotoxicity of the gold compounds and thiosemicarbazone ligands was evaluated against selected cancer cell lines and compared to that of Auranofin. Studies of the most stable, cytotoxic, and selective compound on a renal cancer cell line (Caki-1) demonstrated its relevant antimigratory and anti-angiogenic properties, and preferential accumulation in the cell nuclei. Its mode of action seems to involve interaction with DNA, and subsequent cell death via apoptosis.

Next Generation Gold Drugs and Probes: Chemistry and Biomedical Applications

The gold drugs, gold sodium thiomalate (Myocrisin), aurothioglucose (Solganal), and the orally administered auranofin (Ridaura), are utilized in modern medicine for the treatment of inflammatory arthritis including rheumatoid and juvenile arthritis; however, new gold agents have been slow to enter the clinic. Repurposing of auranofin in different disease indications such as cancer, parasitic, and microbial infections in the clinic has provided impetus for the development of new gold complexes for biomedical applications based on unique mechanistic insights differentiated from auranofin. Various chemical methods for the preparation of physiologically stable gold complexes and associated mechanisms have been explored in biomedicine such as therapeutics or chemical probes. In this Review, we discuss the chemistry of next generation gold drugs, which encompasses oxidation states, geometry, ligands, coordination, and organometallic compounds for infectious diseases, cancer, inflammation, and as tools for chemical biology via gold-protein interactions. We will focus on the development of gold agents in biomedicine within the past decade. The Review provides readers with an accessible overview of the utility, development, and mechanism of action of gold-based small molecules to establish context and basis for the thriving resurgence of gold in medicine.

DNA binding properties and cytotoxic effects of two double rollover cycloplatinated (II) complexes on cancer cell lines

In this study, the DNA binding capacity and cytotoxic effects of two double rollovers cycloplatinated complexes, [Pt₂(μ-bpy-2H)(CF₃COO)₂(PPh₃)₂] and [Pt₂(μ-bpy-2H)(I)₂(PPh₃)₂] denoted as C1 and C2, respectively, were evaluated. By using UV-Visible spectroscopy the intrinsic binding constant (K_b) of C1 and C2 to DNA were determined as 2.9 × 10⁵ M^-1, and 5.4 × 10⁵ M^-1, respectively. Both the compounds were able to quench the fluorescence of ethidium bromide as a well known DNA intercalator. The calculated Stern-Volmer quenching constants (K_sv) for C1 and C2 were 3.5 × 10³ M^-1, and 1.2 × 10⁴ M^-1, respectively. Upon interaction of both the compounds with DNA, increase in viscosity of DNA solution were observed, further confiming the involvement of intercalative interactions between the complexes and DNA. The cytotoxic effects of complexes in compare to cisplatin were evaluated on different cancer cell lines by MTT assay. Interestingly, C2 showed the highest cytotoxicity on A2780R, a cisplatin resistant-cell line. Induction of apoptosis by the complexes was proved by flowcytometry. In all the studied cell lines, the extent of apoptosis induced by C2 was comparable or higher than cisplatin. Cisplatin induced more necrosis in all the cancer cell lines in the tested concentration.

N, Kumara K, Lokanath NK, Butcher RJ, Kumbar V, Bhat K. Copper(i) complexes with quinolone appended 1,8-naphthalimide conjugates: structural characterization, DNA and protein binding and cytotoxicity studies

Cytotoxicity, cellular uptake of copper(i) complexes containing 1,8-naphthalimide conjugates have been investigated.

Structure impact on photodynamic therapy and cellular contrasting functions of colloids constructed from dimeric Au(I) complex and hexamolybdenum clusters

Electrostatically driven self-assembly of [Au₂L₂]²⁺ (L is cyclic PNNP ligand) with [{Mo₆I₈}(L')₆]^2- (L' = I^-, CH₃COO^-) in aqueous solutions is introduced as facile route for combination of therapeutic and cellular contrasting functions within heterometallic colloids (Mo₆-Au₂). The nature of L' affects the size and aggregation behavior of crystalline Mo₆-Au₂ aggregates, which in turn affect the luminescence of the cluster units incorporated into Mo₆-Au₂ colloids. The spin trap facilitated electron spin resonance spectroscopy technique indicates that the level of ROS generated by Mo₆-Au₂ colloids is also affected by their size. Both (L' = I^-, CH₃COO^-) Mo₆-Au₂ colloids undergo cell internalization, which is enhanced by their assembly with poly-DL-lysine (PL) for L' = CH₃COO^-, but remains unchanged for L' = I^-. The colloids PL-Mo₆-Au₂ (L' = CH₃COO^-) are visualized as huge crystalline aggregates both outside and inside the cell cytoplasm by confocal microscopy imaging of the incubated cells, while the smaller sized (30-50 nm) PL-Mo₆-Au₂ (L' = I^-) efficiently stain the cell nuclei. Quantitative colocalization analysis of PL-Mo₆-Au₂ (L' = CH₃COO^-) in lysosomal compartments points to the fast endo-lysosomal escape of the colloids followed by their intracellular aggregation. The cytotoxicity of PL-Mo₆-Au₂ differs from that of Mo₆ and Au₂ blocks, predominantly acting through apoptotic pathway. The photodynamic therapeutic effect of the PL-Mo₆-Au₂ colloids on the cancer cells correlates with their intracellular trafficking and aggregation.

Bis-N-Heterocyclic Carbene Complexes of Coinage Metals Containing Four Naphthalimide Units: A Structure-Emission Properties Relationship Study

Naphthalimide derivatives provide highly versatile self-assembled systems and aggregated forms with fascinating emission properties that make them potential candidates for many applications such as bioimaging and sensing. Although various aggregated species of naphthalimide derivatives have been well documented, little is known about the correlation between their structure and photophysical properties. Here the preparation of a series of tetrameric naphthalimide molecules in which naphthalimide units are linked by bis-N-heterocyclic carbene complexes of coinage metals is described. An in-depth structural investigation into these tetramers has been carried out in solution and the solid state using spectroscopic methods, X-ray crystallography, and computational methods. The experimental and calculated data indicate that the magnitude of the intramolecular interchromophoric π-interactions increases either by an increase in the metal ionic radius or on going from the solid to the solution state. These tetrameric naphthalimide compounds show intramolecular excimeric emissions in the solid and solution phases. However, the quantum yield efficiencies of these excimeric emissions show a trend similar to that for the intramolecular π-interactions either by going from the solution to the solid state or with an increase in the metal ionic radius. Surprisingly, the amine derivative analogues of the silver(I) compound showed an unusual increase in the emission quantum yield efficiency to 92% in solution due to intramolecular hydrogen bonds between amine substituents on adjacent naphthalimde units.

DNA-Binding and Anticancer Activity of Binuclear Gold(I) Alkynyl Complexes with a Phenanthrenyl Bridging Ligand

3,6-Diethynyl-9,10-diethoxyphenanthrene (4) was synthesized from phenanthrene and employed in the synthesis of the binuclear gold(I) alkynyl complexes (R3P)Au(C≡C-3-[C14H6-9,10-diethoxy]-6-C≡C)Au(PR3) (R = Ph (5a), Cy (5b)). The diyne 4 and complexes 5a and 5b were characterized by NMR spectroscopy, mass spectrometry, and elemental analysis. UV-Vis spectroscopy studies of the metal complexes and precursor diyne show strong p à p* transitions in the near UV region that red shift by ca. 50 nm upon coordination at the gold centers. The emission spectrum of 4 shows an intense fluorescence band centered at 420 nm which red shifts, slightly upon coordination of 4 to gold. Binding studies of 4, 5a, and 5b against calf thymus DNA were carried out, revealing that 4, 5a, and 5b have >40% stronger binding affinities than the commonly used intercalating agent ethidium bromide. The molecular docking scores of 4, 5a, and 5b with B-DNA suggest a similar trend in behavior to that observed in the DNA-binding study. Unlike the ligand 4, promising anticancer properties for 5a and 5b were observed against several cell lines; the DNA binding capability of the precursor alkyne was maintained, and its anticancer efficacy enhanced by the gold centers. Such phenanthrenyl complexes could be promising candidates in certain biological applications because the two components (phenanthrenyl bridge and metal centers) can be altered independently to improve the targeting of the complex, as well as the biological and physicochemical properties.

Gold as a Possible Alternative to Platinum-Based Chemotherapy for Colon Cancer Treatment

Due to the increasing incidence and high mortality associated with colorectal cancer (CRC), novel therapeutic strategies are urgently needed. Classic chemotherapy against CRC is based on oxaliplatin and other cisplatin analogues; however, platinum-based therapy lacks selectivity to cancer cells and leads to deleterious side effects. In addition, tumor resistance to oxaliplatin is related to chemotherapy failure. Gold(I) derivatives are a promising alternative to platinum complexes, since instead of interacting with DNA, they target proteins overexpressed on tumor cells, thus leading to less side effects than, but a comparable antitumor effect to, platinum derivatives. Moreover, given the huge potential of gold nanoparticles, the role of gold in CRC chemotherapy is not limited to gold(I) complexes. Gold nanoparticles have been found to be able to overcome multidrug resistance along with reduced side effects due to a more efficient uptake of classic drugs. Moreover, the use of gold nanoparticles has enhanced the effect of traditional therapies such as radiotherapy, photothermal therapy, or photodynamic therapy, and has displayed a potential role in diagnosis as a consequence of their optic properties. Herein, we have reviewed the most recent advances in the use of gold(I) derivatives and gold nanoparticles in CRC therapy.

A Ruthenium(II) N-Heterocyclic Carbene (NHC) Complex with Naphthalimide Ligand Triggers Apoptosis in Colorectal Cancer Cells via Activating the ROS-p38 MAPK Pathway

The p38 MAPK pathway is known to influence the anti-tumor effects of several chemotherapeutics, including that of organometallic drugs. Previous studies have demonstrated the important role of p38 both as a regulator and a sensor of cellular reactive oxygen species (ROS) levels. Investigating the anti-cancer properties of novel 1,8-naphthalimide derivatives containing Rh(I) and Ru(II) N-heterocyclic carbene (NHC) ligands, we observed a profound induction of ROS by the complexes, which is most likely generated from mitochondria (mtROS). Further analyses revealed a rapid and consistent activation of p38 signaling by the naphthalimide-NHC conjugates, with the Ru(II) analogue—termed MC6—showing the strongest effect. In view of this, genetic as well as pharmacological inhibition of p38α, attenuated the anti-proliferative and pro-apoptotic effects of MC6 in HCT116 colon cancer cells, highlighting the involvement of this signaling molecule in the compound’s toxicity. Furthermore, the influence of MC6 on p38 signaling appeared to be dependent on ROS levels as treatment with general- and mitochondria-targeted anti-oxidants abrogated p38 activation in response to MC6 as well as the molecule’s cytotoxic- and apoptogenic response in HCT116 cells. Altogether, our results provide new insight into the molecular mechanisms of naphthalimide-metal NHC analogues via the ROS-induced activation of p38 MAPK, which may have therapeutic interest for the treatment of various cancer types.

Fluorescent organometallic rhodium(I) and ruthenium(II) metallodrugs with 4-ethylthio-1,8-naphthalimide ligands: Antiproliferative effects, cellular uptake and DNA-interaction

Fluorescent 4-ethylthio-1,8-naphthalimides containing rhodium(I) N-heterocyclic carbene (NHC) and ruthenium (II) NHC fragments were synthesised and evaluated for their antiproliferative effects, cellular uptake and DNA-binding activity. Both types of organometallics triggered ligand dependent efficient cytotoxic effects against tumor cells with the rhodium(I) NHC derivatives causing stronger effects than the ruthenium (II) NHC analogues. Antiproliferative effects could also be observed against several pathogenic Gram-positive bacterial strains, whereas the growth of Gram-negative bacteria was not substantially affected. Cellular uptake was confirmed by atomic absorption spectroscopy as well as by fluorescence microscopy indicating a general ligand dependent accumulation in the cells. An in-depth study on the interaction with DNA confirmed insertion of the naphthalimide moiety between the planar bases of B-DNA via an intercalation mechanism, as well as its stacking on top of the quartets of G-quadruplex structures. Furthermore, additional coordinative binding of the organometallic complexes to the model DNA base 9-ethylguanine could be detected. The studied compounds thus represent promising bioorganometallics featuring strong pharmacological effects in combination with excellent cellular imaging properties.

Metal NHC Complexes with Naphthalimide Ligands as DNA-Interacting Antiproliferative Agents

Naphthalimide-based N-heterocyclic carbene (NHC) complexes of the type [(1,5-cyclooctadiene)(NHC)RhCl)] (4 a-c), [(p-cymene)(NHC)RuCl₂ )] (5 a-c), and [(NHC)CuBr] (6 a-c) were synthesized and investigated as antiproliferative agents that target DNA. The cytotoxic effects were largely driven by the naphthalimide structure, which is a DNA-intercalating moiety. Regarding the metal center, the highest activities were observed with the rhodium complexes, and cytotoxic activity was significantly lower for the ruthenium derivatives. The stable coordination of the NHC ligands of selected complexes 4 b and 5 b in solution was confirmed, and their DNA binding properties were studied by UV/Vis spectroscopy, mass spectrometry, and circular dichroism. Stable intercalative binding into the DNA for all selected naphthalimide-based complexes is indicated by high DNA binding constants. Particularly efficient binding was observed in the case of the rhodium complex 4 b. More detailed biological studies on 4 b showed promising activities against multidrug-resistant Nalm-6 cells and confirmed an important role for mitochondrial pathways in 4 b-induced apoptosis.

Photophysical, G-quadruplex DNA binding and cytotoxic properties of terpyridine complexes with a naphthalimide ligand

The complex3inhibits A549 cells selectively over non-cancerous NIH3T3 cells, which may correlate with its selective G-quadruplex binding and nuclear location.

Development of trackable metal-based drugs: new generation of therapeutic agents

Today, it is not sufficient to conceive an efficient drug, its mechanism of action have to be understood. To tackle this issue, trackable therapeutic agents are an interesting solution.

Anticancer and Antibacterial Activity Studies of Gold(I)-Alkynyl Chromones

Three gold(I) complexes of alkynyl chromones were synthesized and characterized. The single-crystal X-ray structure analysis of a dinuclear compound and of a flavone derivative exhibit a typical d10 gold(I)-alkynyl linear arrangement. All complexes were evaluated as anticancer and antibacterial agents against four human cancer cell lines and four pathogenic bacterial strains. All compounds show antiproliferative activity at lower micromolar range concentrations. Complex 4 showed a broad activity profile, being more active than the reference drug auranofin against HepG2, MCF-7 and CCRF-CEM cancer cells. The cellular uptake into MCF-7 cells of the investigated complexes was measured by atomic absorption spectroscopy (AAS). These measurements showed a positive correlation between an increased cellular gold content and the incubation time of the complexes. Unexpectedly an opposite effect was observed for the most active compound. Biological assays revealed various molecular mechanisms for these compounds, comprising: (i) thioredoxin reductase (TrxR) inhibition, (ii) caspases-9 and -3 activation; (iii) DNA damaging activity and (iv) cell cycle disturbance. The gold(I) complexes were also bactericidal against Gram-positive methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) bacterial strains, while showing no activity against the Gram-negative Escherichia coli bacterial strain.

Gold(i) thiotetrazolates as thioredoxin reductase inhibitors and antiproliferative agents

Gold(i) complexes with thiotetrazolate ligands are potent TrxR inhibitors with activity in drug resistant Nalm-6 cells.

Fluorescence sensing systems for gold and silver species

Here, we provide an overview of the reported fluorescent detection systems for gold and silver species, and discuss their sensing properties with promising features.

Antiangiogenic ruthenium(ii) benzimidazole complexes, structure-based activation of distinct signaling pathways

A series of ruthenium(ii) benzimidazole complexes has been synthesized and identified as antiangiogenic agents with distinct structure-based action mechanisms.

Gold(I) N-heterocyclic carbene complexes with naphthalimide ligands as combined thioredoxin reductase inhibitors and DNA intercalators

Organometallic conjugates consisting of a gold(I) N-heterocyclic carbene (NHC) moiety and a naphthalimide were prepared and investigated as cytotoxic agents that interact with both DNA and the disulfide reductase enzyme thioredoxin reductase (TrxR). The complexes were potent DNA intercalators related to their naphthalimide partial structure, inhibited TrxR as a consequence of the incorporation of the gold(I) moiety, and triggered efficient cytotoxic effects in MCF-7 breast and HT-29 colon adenocarcinoma cells. Strong effects on tumor cell metabolism were noted for the most cytotoxic complex, chlorido[1-(3'-(4''-ethylthio-1'',8''-naphthalimid-N''-yl))-propyl-3-methyl-imidazol-2-ylidene]gold(I) (4 d). In conclusion, the conjugation of naphthalimides with gold(I) NHC moieties provided a useful strategy for the design of bioorganometallic anticancer agents with multiple modes of action.

Fluorescent silver(I) and gold(I)-N-heterocyclic carbene complexes with cytotoxic properties: mechanistic insights

Silver(I) and gold(I)-N-heterocyclic carbene (NHC) complexes bearing a fluorescent anthracenyl ligand were examined for cytotoxicity in normal and tumor cells. The silver(I) complex exhibits greater cytotoxicity in tumor cells compared with normal cells. Notably, in cell extracts, this complex determines a more pronounced inhibition of thioredoxin reductase (TrxR), but it is ineffective towards glutathione reductase (GR). Both gold and silver complexes lead to oxidation of the thioredoxin system, the silver(I) derivative being particularly effective. In addition, the dimerization of peroxiredoxin 3 (Prx3) was also observed, demonstrating the ability of these compounds to reach the mitochondrial target. The fluorescence microscopy visualization of the subcellular distribution of the complexes shows a larger diffusion of these molecules in tumor cells with respect to normal cells.

Fine-tuning solid-state luminescence in NPIs (1,8-naphthalimides): impact of the molecular environment and cumulative interactions

A series of solid-state emissive NPIs (1,8-naphthalimides) are reported and their solution and solid-state emissive properties are correlated with their solid-state packing interactions.