Silver(I)-N-heterocyclic carbene complexes challenge cancer; evaluation of their anticancer properties and in silico studies

Advancing cancer therapy: the role of silver(I) phosphine complexes in overcoming resistance and toxicity

Silver(I) phosphine complexes have attracted significant attention recently due to their structural versatility and promising anticancer properties. These complexes exhibit diverse coordination geometries-ranging from tetrahedral and trigonal planar to linear-depending on the ligand environment and metal-to-ligand ratio, directly influencing their biological activity. Notably, they demonstrate substantial cytotoxicity against various cancer cell lines, including oesophageal (SNO), breast (MCF-7), and lung (A549) cancers, with IC₅₀ values in the low micromolar range. A key advantage of these complexes is their selective toxicity toward malignant cells while sparing healthy ones, positioning them as potential alternatives to traditional chemotherapeutics like cisplatin, often associated with severe side effects and drug resistance. The anticancer mechanism of silver(I) phosphine complexes primarily involves apoptosis induction through mitochondrial disruption, phosphatidylserine externalisation, and caspase activation. Additionally, these complexes can overcome common resistance mechanisms encountered in conventional cancer treatments by targeting alternative cellular pathways. This review critically evaluates the structural chemistry, synthesis, and characterisation of silver(I) phosphine complexes and recent advancements in their biological applications. Furthermore, we discuss their potential to address critical limitations in cancer therapies, particularly in overcoming drug resistance and toxicity, while exploring opportunities for ligand optimisation and progress toward clinical applications.

Cytotoxicity, Cell Line Selectivity and Proapoptotic Activity of New Anticancer Agents Derived From N,N'-Functionalised Benzimidazolium Salts and Their Silver(I)-N-Heterocyclic Carbene Complexes

A new series of N-decyl-N'-benzylbenzimidazolium N-heterocyclic carbene (NHC) precursors and their mononuclear silver(I)-NHC complexes were synthesised and characterised. The benzyl group was functionalised with various para substituents (H, CH3, F, Cl, Br, CN, NO2). The effect of these substituents on cytotoxicity and cell line selectivity against human cervical cancer (HeLa), oestrogen-positive human breast cancer (MCF-7), and normal skin fibroblasts (Hs-27) was investigated. All compounds exhibited significant growth inhibition against the tested cell lines. The activity and selectivity of the compounds were influenced by the para substituents and the type of cell line. The electron-donating methylated NHC precursor and its silver complex generally demonstrated higher growth inhibition potentials than the analogues with electron-withdrawing groups, except in two cases where the fluorinated compounds were more potent against Hs-27 and HeLa, while the chlorinated NHC precursor was more active against MCF-7. Notably, all compounds, particularly the silver(I)-NHC complexes, were more active towards MCF-7 but less toxic towards Hs-27. The methyl-, bromo-, and cyano-containing silver(I)-NHC complexes broadened the safety windows against MCF-7 (selectivity indices ≥ 3). The most selective (against MCF-7) chlorinated NHC precursor and its silver(I)-NHC exhibited ROS-mediated proapoptotic activity, which indicated that these compounds promoted cell death by inducing intracellular ROS formation and accumulation. Our findings highlight the potential use of silver(I)-NHC complexes in the design and development of safe and selective anticancer agents.

Silver N-Heterocyclic Carbene (NHC) Complexes as Antimicrobial and/or Anticancer Agents

The strict connections/interactions between microbial infections and cancer are nowadays widely accepted. Hence, the dual (or multiple) targeting of microbial infections and cancer is an essential issue to be addressed. In this context, metal complexes have gained considerable importance and effectiveness in medicinal chemistry. Particularly, N-heterocyclic carbene (NHC) complexes with transition metals have emerged as very promising compounds. Among the myriad of NHC-metal complexes, those bearing silver will be the subject of this review. Numerous Ag(I)-NHC complexes have revealed high antibacterial and/or anticancer properties, even higher than those of reference drugs. Herein, we summarize the most recent studies while also discussing the proposed mechanism of action and offering an interesting remark about the research in this field. Literature databases (PubMed/MEDLINE, Scopus, and Google Scholar) were used as sources to search the literature, referring to the last five years.

Fluorinated N-Heterocyclic Carbene Silver(I) Complexes with High Cancer Cell Selectivity

This work presents the synthesis of five new functionalized (benz)imidazolium N-heterocyclic (NHC) ligands (L) and four new (benz)imidazole silver(I) NHC (Ag(I)-NHC) complexes of mononuclear [Ag(L)2](PF6) or binuclear [Ag2(L)2](PF6)2 type. The complexes have been fully characterized, including single crystal X-ray diffraction of three new structures. The complexes and their corresponding free NHC ligands have been screened against breast cancer and noncancerous cell lines, showing the mononuclear benzimidazole complex has the highest activity, while the binuclear benzimidazole complex has the highest cancer cell selectivity. The silver uptake was measured by ICP-MS and highlights a strong link between cytotoxicity and cellular uptake. DNA interaction studies, molecular docking, and evaluation of reactive oxygen species (ROS) have been conducted for the most promising complexes to identify modes of action. Overall, the binuclear benzimidazole complex is the most selective and promising candidate against the MDA-MD-231 (breast cancer) cell line and has potential to be developed for treatment of late-stage breast cancers.

Cadmium and silver complexes of a pyridine containing ligand: syntheses, structural studies, biological activity and docking studies

The current study aimed to synthesize seven new metal coordination complexes (Q1-Q7) with potential biomedical applications. Novel mononuclear, polynuclear and mixed-ligand coordination compounds of the elements, cadmium(ii) and silver(i) derived from a pyridine containing ligand (2,4,6-tris-(2-pyridyl)-1,3,5-triazine (TPT)) have been synthesized successfully with the general formulae [Cd(TPT)Cl6]·H2O and [Ag x (TPT) y (L)2(ClO4)](ClO4) z (x = 1,2,3, y = 1,2,3, L = PPh3 or phen, z = 1,2). The structural features were fully characterized using various spectroscopic techniques, such as infrared, ultraviolet-visible spectroscopy, 1D and 2D-NMR (1H, 13C, 31P, 1H-1H COSY and 1H-13C HSQCAD), CHN analysis, molar conductance (Λ), thermogravimetric analysis (TGA), and powder X-ray diffraction analysis. The structure of complex Q6 was also confirmed by single-crystal X-ray analysis. The luminescence and electrochemical properties of complexes, in solution, have been studied. X-ray crystallographic determination of the [Ag(TPT)(PPh3)2]ClO4·EtOH (Q6) complex shows that the Ag+ cation is bonded to one tridentate TPT ligand through NNN set of donor atoms and two triphenylphosphine ligands, giving the Ag+ a distorted trigonal bipyramidal geometry. X-ray powder diffraction analysis showed that metal complexes Q3, Q6 and Q7 display crystalline peaks. The complexes were evaluated for their in vitro antibacterial efficacy against various bacterial and fungal species. The in vitro efficacy against the MCF-7 human breast cancer cell line was assessed to determine the anticancer activities. The tri-nuclear silver complex Q3 shows great potential as a therapeutic candidate for treating breast cancer, since it exhibits a half-maximal inhibition concentration (IC50) of 13.45 ± 0.9 μM. Molecular docking simulations were also carried out to evaluate the interaction strength and properties of the metal complexes with selected cancer and bacteria relevant proteins namely cyclin-dependent kinase 2 (CDK2), cyclin-dependent kinase 6 (CDK6), signal transducer and activator of transcription 3 (STAT3), and beta-lactamases from Escherichia coli and Staphylococcus aureus.

Silver(I) Complexes Based on Oxadiazole-Functionalized α-Aminophosphonate: Synthesis, Structural Study, and Biological Activities

Two silver(I) complexes, bis{diethyl[(5-phenyl-1,3,4-oxadiazol-2-yl-κN3:κN4-amino) (4-trifluoromethylphenyl)methyl]phosphonate-(tetrafluoroborato-κF)}-di-silver(I) and tetrakis-{diethyl[(5-phenyl-1,3,4-oxadiazol-2-yl-κN3-amino)(4-trifluoromethylphenyl)methyl]phosphonate} silver(I) tetrafluoroborate, were prepared starting from the diethyl[(5-phenyl-1,3,4-oxadiazol-2-yl-amino)(4-trifluoromethylphenyl)methyl]phosphonate (1) ligand and AgBF4 salt in Ag/ligand ratios of 1/1 and 1/4, respectively. The structure, stoichiometry, and geometry of the silver complexes were fully characterized by elemental analyses, infrared, single-crystal X-ray diffraction studies, multinuclear NMR, and mass spectroscopies. The binuclear complex ([Ag2(1)2(BF4)2]; 2) crystallizes in the monoclinic asymmetric space group P21/c and contains two silver atoms adopting a {AgN2F} planar trigonal geometry, which are simultaneously bridged by two oxadiazole rings of two ligands, while the mononuclear complex ([Ag(1)4]BF4; 3) crystallizes in the non-usual cubic space group Fd-3c in which the silver atom binds to four distinct electronically enriched nitrogen atoms of the oxadiazole ring, in a slightly distorted {AgN4} tetrahedral geometry. The α-aminophosphonate and the monomeric silver complex were evaluated in vitro against MCF-7 and PANC-1 cell lines. The silver complex is promising as a drug candidate for breast cancer and the pancreatic duct with half-maximal inhibitory concentration (IC50) values of 8.3 ± 1.0 and 14.4 ± 0.6 μM, respectively. Additionally, the interactions of the ligand and the mononuclear complex with Vascular Endothelial Growth Factor Receptor-2 and DNA were evaluated by molecular docking methods.