Lapachol in the Design of a New Ruthenium(II)-Diphosphine Complex as a Promising Anticancer Metallodrug

Unlocking the potential of 1,4-naphthoquinones: A comprehensive review of their anticancer properties

Cancer encompasses a group of pathologies with common characteristics, high incidence, and prevalence in all countries. Although there are treatments available for this disease, they are not always effective or safe, often failing to achieve the desired results. This is why it is necessary to continue the search for new therapies. One of the strategies for obtaining new antitumor drugs is the use of 1,4-naphthoquinone as a scaffold in synthetic or natural products with antitumor activity. This review focuses on compiling studies related to the antitumor activity of 1,4-naphthoquinone and its natural and synthetic derivatives over the last 10 years. The work describes the main natural naphthoquinones with antitumor activity and classifies the synthetic naphthoquinones based on the structural modifications made to the scaffold. Additionally, the formation of metal complexes using naphthoquinones as a ligand is considered. After a thorough review, 197 synthetic compounds with potent biological activity against cancer have been classified according to their chemical structures and their mechanisms of action have been described.

Recent Trends in the Development of Novel Metal-Based Antineoplastic Drugs

Since the accidental discovery of the anticancer properties of cisplatin more than half a century ago, significant efforts by the broad scientific community have been and are currently being invested into the search for metal complexes with antitumor activity. Coordination compounds of transition metals such as platinum (Pt), ruthenium (Ru) and gold (Au) have proven their effectiveness as diagnostic and/or antiproliferative agents. In recent years, experimental work on the potential applications of elements including lanthanum (La) and the post-transition metal gallium (Ga) in the field of oncology has been gaining traction. The authors of the present review article aim to help the reader "catch up" with some of the latest developments in the vast subject of coordination compounds in oncology. Herewith is offered a review of the published scientific literature on anticancer coordination compounds of Pt, Ru, Au, Ga and La that has been released over the past three years with the hope readers find the following article informative and helpful.

Novel Ru(II)-bipyridine/phenanthroline-lapachol complexes as potential anti-cancer agents

For the first time, we herein report on the syntheses of two new Ru(II)/bipyridine/phenanthroline complexes containing lapachol as ligand: complex (1), [Ru (bipy)₂(Lap)]PF₆ and complex (2), [Ru(Lap)(phen)₂]PF₆, where bipy = 2,2'-bipyridine and ph en = 1,10-phenanthroline; Lap = lapachol (2-hydroxy-3-(3-methylbut-2-en-1- yl)naphthalene-1,4-dione). The complexes were synthesized and characterized by elemental analyses, molar conductivity, mass spectrometry, ultraviolet-visible and infrared spectroscopies, nuclear magnetic resonance (¹H, ¹³C), and single crystal X-ray diffraction, for complex (2). In addition, in vitro cytotoxicity was tested against six cancer cells: A549 (lung carcinoma); DU-145 (human prostate carcinoma); HepG2 (human hepatocellular carcinoma), PC-3 (human prostate adenocarcinoma); MDA-MB-231 (human breast adenocarcinoma); Caco-2 (human colorectal adenocarcinoma), and against two non-cancer cells, FGH (human gingival normal fibroblasts) and PNT-2 (prostate epithelial cells). Complex (1) was slightly more toxic and selective than complex (2) for all cell lines, except against the A549 cells, where (2) was more potent than complex (1). The complexes induced an increase in the reactive oxygen species, and the co-treatment with N-acetyl-L-cysteine remarkably suppressed the ROS generation and prevented the reduction of cell viability, suggesting that the cytotoxicity of the complexes is related to the ROS-mediated pathway. Further studies indicated that the complexes may bind to DNA via minor groove interaction. Our studies also revealed that free Lap induces gene mutations in Salmonella Typhimurium, nevertheless, the complexes demonstrated the absence of genotoxicity by the Ames test. The present study provides a relevant contribution to understanding the anti-cancer potential and genetic toxicological events of new ruthenium complexes containing the lapachol molecule as a ligand.

Three water-soluble acylhydrazone tetranuclear transition metal complexes: Crystal structures, DNA/BSA interactions and cytotoxicity studies

2-acetylpyridine-4-chloropyridine-2‑carbonyl hydrazone (C₁₃H₁₁ClN₄O, HL) and its three water-soluble tetranuclear complexes [Cu₄(NO₃)₂(L)₄]·(NO₃)₂ (1), [Co₄(NO₃)₂(H₂O)(C₂H₅OH)(L)₄]·(NO₃)₂ (2) and [Zn₄(NO₃)₂(H₂O)(C₂H₅OH)(L)₄]·(NO₃)₂ (3) were synthesized and characterized showing that 1-3 were all tetranuclear complexes. The interactions of HL, 1-3 with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) were explored using ultraviolet-visible (UV-Vis) titration, fluorescence spectroscopy, microcalorimetry and molecular docking techniques. The UV-Vis spectroscopy measurements showed that complexes 1-3 could strongly bind to CT-DNA by the intercalation mode, while HL interacted with CT-DNA through groove binding. From the fluorescence spectroscopy results, the interaction between HL, 1-3 and BSA was a static quenching procedure, in which complexes 1-3 had two binding sites near Trp residues of BSA while HL only had one. The microcalorimetric studies revealed that the interactions of HL and 1-3 to CT-DNA/BSA were all endothermic and the duration of each interaction was all less than 30 min. The in silico molecular docking illustrated intermolecular interactions of 1-3 binding with DNA/BSA included hydrogen bond, halogen bond, hydrophobic and electrostatic interactions. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay indicated that complex 1 possessed better cytotoxicity against HeLa, A549, MCF7 and HCT-116 than cisplatin and could be used as an alternative anticancer drug.

Organometallic gold(I) and gold(III) complexes for lung cancer treatment

Metal compounds, especially gold complexes, have recently gained increasing attention as possible lung cancer therapeutics. Some gold complexes display not only excellent activity in cisplatin-sensitive lung cancer but also in cisplatin-resistant lung cancer, revealing promising prospects in the development of novel treatments for lung cancer. This review summarizes examples of anticancer gold(I) and gold (III) complexes for lung cancer treatment, including mechanisms of action and approaches adopted to improve their efficiency. Several excellent examples of gold complexes against lung cancer are highlighted.

Metallodrugs, an approach against invasion and metastasis in cancer treatment

Cancer is a heterogeneous and multifactorial disease that causes high mortality throughout the world; therefore, finding the most effective therapies is a major research challenge. Currently, most anticancer drugs present a limited number of well‐established targets, such as cell proliferation or death; however, it is important to consider that the worse progression of cancer toward pathological stages implies invasion and metastasis processes. Medicinal Inorganic Chemistry (MIC) is a young area that deals with the design, synthesis, characterization, preclinical evaluation, and mechanism of action of new inorganic compounds, called metallodrugs. The properties of metallic ions allow enriching of strategies for the design of new drugs, enabling the adjustment of physicochemical and stereochemical properties. Metallodrugs can adopt geometries, such as tetrahedral, octahedral, square planar, and square planar pyramid, which adjusts their arrangement and facilitates binding with a wide variety of targets. The redox properties of some metal ions can be modulated by the presence of the bound ligands to adjust their interaction, thereby opening a range of mechanisms of action. In this regard, the mechanisms of action that trigger the biological activity of metallodrugs have been generally identified by: (a) coordination of the metal to biomolecules (for instance, cisplatin binds to the N7 in DNA guanine, as Pt‐N via coordination of the inhibition of enzymes); (b) redox‐active; and (c) ROS production. For this reason, a series of metallodrugs can interact with several specific targets in the anti‐invasive processes of cancer and can prevent metastasis. The structural base of several metal compounds shows great anticancer potential by inhibiting the signaling pathways related to cancer progression. In this minireview, we present the advances in the field of antimetastatic effects of metallodrugs.

Ruthenium(II)-diphosphine complexes containing acylthiourea ligands are effective against lung and breast cancers

We have synthesized and characterized three new ruthenium(II) diphosphine complexes containing an acylthiourea ligand, with the general formula [Ru(DPEPhos)(O,S)(bipy)]PF₆, where DPEPhos = bis(2-(diphenylphosphino)phenyl)ether, bipy = 2,2'-bipyridine, and O,S = N,N-dimethyl-N'-(benzoyl)thiourea (1), N,N-dimethyl-N'-(furoyl)thiourea (2), and N,N-dimethyl-N'-(thiophenyl)thiourea (3), by several physicochemical techniques. We evaluated the ruthenium complexes for their cytotoxicity against two human cancer cell lines, A549 (lung) and MDA-MB-231 (breast), and two corresponding lines of non-cancer cells, MRC-5 (lung) and MCF-10A (breast). All the complexes are cytotoxic against the cancer cell lines; the IC₅₀ values lie in the micromolar range (0.07-0.70 μM). Ruthenium complex 1 is more selective (7 times more active) toward lung cancer cells (A549) than toward non-cancer cells (MRC-5) and is 160 times more cytotoxic than cisplatin against A549 cells. Investigations of the mechanism of action of complex 1 in A549 cells demonstrated that it inhibits colony formation and promotes cell cycle arrest in the G1 phase and apoptotic cell death. DNA binding studies revealed that complexes 1-3 interact with the biomolecule via minor grooves. These complexes also interact with human serum albumin (HSA) and have affinity for site I by hydrophobic forces. Therefore, this new class of ruthenium complexes can act as cytotoxic agents, mainly for lung cancer treatment.

A binuclear Fe(iii)/quinizarin complex as a structural model for anthracycline drugs binding to iron

Quinizarin, an anthracyclin-like compound, was used to prepare a binuclear complex, [(Fe(cyclam))2Qz]Cl(PF6)3, which showed damage to DNA with glutathione. This mimic of anthracyclin drugs might explain undesired side effects of these compounds.

Intracellular Localization Studies of the Luminescent Analogue of an Anticancer Ruthenium Iminophosphorane with High Efficacy in a Triple-Negative Breast Cancer Mouse Model

The potential of ruthenium(II) compounds as an alternative to platinum-based clinical anticancer agents has been unveiled after extensive research for over 2 decades. As opposed to cisplatin, ruthenium(II) compounds have distinct mechanisms of action that do not rely solely on interactions with DNA. In a previous report from our group, we described the synthesis, characterization, and biological evaluation of a cationic, water-soluble, organometallic ruthenium(II) iminophosphorane (IM) complex of p-cymene, ([(η⁶-p-cymene)Ru{(Ph₃P═N-CO-2N-C₅H₄)-κ-N,O}Cl]Cl (1 or Ru-IM), that was found to be highly cytotoxic against a panel of cell lines resistant to cisplatin, including triple-negative breast cancer (TNBC) MDA-MB-231, through canonical or caspase-dependent apoptosis. Studies on a MDA-MB-231 xenograft mice model (after 28 days of treatment) afforded an excellent tumor reduction of 56%, with almost negligible systemic toxicity, and a favored ruthenium tumor accumulation compared to other organs. 1 is known to only interact weakly with DNA, but its intracellular distribution and ultimate targets remain unknown. To gain insight on potential mechanisms for this highly efficacious ruthenium compound, we have developed two luminescent analogues containing the BOPIPY fluorophore (or a modification) in the IM scaffold with the general structure of [(η⁶-p-cymene)Ru{(BODIPY-Ph₂P═N-CO-2-NC₅H₄)-κ-N,O}Cl]Cl {BODIPY-Ph₂P = 8-[(4-diphenylphosphino)phenyl]-4,4-dimethyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (3a) and 4,4-difluoro-8-[4-[[2-[4-(diphenylphosphino)benzamido]ethyl]carbamoyl]phenyl]-1,3,5,7-tetramethyl,2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (3b)}. We report on the synthesis, characterization, lipophilicity, stability, luminescence properties, and cell viability studies in the TNBC cell line MDA-MB-231, nonmalignant breast cells (MCF10a), and lung fibroblasts (IMR-90) of the new compounds. The ruthenium derivative 3b was studied by fluorescence confocal microscopy. These studies point to a preferential accumulation of the compound in the endoplasmic reticulum, mitochondria, and lysosomes. Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis also confirms a greater ruthenium accumulation in the cytoplasmic fraction, including endoplasmic reticulum and lysosomes, and a smaller percentage of accumulation in mitochondria and the nucleus. ICP-OES analysis of the parent compound 1 indicates that it accumulates preferentially in the mitochondria and cytoplasm. Subsequent experiments in 1-treated MDA-MB-231 cells demonstrate significant reactive oxygen species generation.

Anti-melanoma effect of ruthenium(II)-diphosphine complexes containing naphthoquinone ligand

The use of natural products as potential ligands has been explored as a strategy in the development of metal-based chemotherapy. Since ruthenium complexes are promising alternatives to traditional antitumor agents, this study evaluated the anti-melanoma potential of two ruthenium(II) complexes containing the naphthoquinone ligands lapachol (lap), [Ru(lap)(dppm)2]PF6, and lawsone (law), [Ru(law)(dppm)2]PF6, in addition to the bis(diphenylphosphino)methane (dppm) ligand, referred to as complexes (1) and (2), respectively, using a syngeneic murine melanoma model. Activation of the apoptotic pathway by the treatments was assessed by immunohistochemistry in tumor tissue. Additionally, toxicity of the treatments was evaluated by variation in body and organ weight, quantification of biochemical indicators of renal damage, and genotoxicity in bone marrow and hepatocytes. First, the antiproliferative activity of (1) and (2) was observed in B16F10 cells, with IC50 values of 2.78 and 1.68 μM, respectively. The results obtained in mice showed that, unlike complex (1), (2) possesses significant anti-melanoma activity demonstrated by a reduction in tumor volume and mass (88.42%), as well as in mitosis frequency (83.86%). Additionally, complex (2) increased the levels of cleaved caspase-3, inducing tumor cell apoptosis. When compared to the metallodrug cisplatin, complex (2) exhibited similar anti-melanoma activity and lower toxicity considering all parameters evaluated. In silico studies demonstrated no difference in the binding energy of the naphthoquinone complex between complexes (1) and (2). However, the complex containing the lawsone ligand has a lower molar volume, which may be important for interactions with minor DNA grooves. The present results demonstrate the antitumor efficiency of complex (2) and a significantly lower systemic toxicity compared to cisplatin.

Binding mode transformation and biological activity on the Ru(II)-DMSO complexes bearing heterocyclic pyrazolyl ligands

Three Ru(II)-DMSO complexes (1-3) containing 2-(3-pyrazolyl)pyridine (PzPy), 2-pyrazol-3-ylfuran (PzO), or 2-pyrazol-3-ylthiophene (PzS) ligand, were synthesized and characterized. The monodentate coordination of the heterocyclic pyrazolyl ligand (Pz^Py) with Ru(II) ion via N atom was confirmed by single crystal X-ray diffraction. Complex 1 could be converted to the known η²-bidentate Pz^Py complex cis(Cl), cis(S)-[RuCl₂(Pz^Py)(DMSO)₂] (4) under reflux conditions. The mechanism underlying binding mode transformation was studied by ¹H NMR spectroscopy and density functional theory (DFT) calculations. The binding abilities of the complexes (1-4) with calf-thymus (CT) DNA and bovine serum albumin (BSA) were investigated using spectroscopic and molecular docking techniques. Among the four Ru(II) complexes, complexes 1 and 3 inhibited the long-term proliferation of human breast cancer cells, whereas complexes 2 and 4 did not inhibit their proliferation to a considerable extent. Interestingly, complexes 1 and 3 did not induce significant cell death but rather attenuated the clonogenicity of breast cancer cells by upregulating reactive oxygen species (ROS), endoplasmic reticulum (ER) and autophagic stress.

Tridentate 3-Substituted Naphthoquinone Ruthenium Arene Complexes: Synthesis, Characterization, Aqueous Behavior, and Theoretical and Biological Studies

A series of nine Ru^II arene complexes bearing tridentate naphthoquinone-based N,O,O-ligands was synthesized and characterized. Aqueous stability and their hydrolysis mechanism were investigated via UV/vis photometry, HPLC-MS, and density functional theory calculations. Substituents with a positive inductive effect improved their stability at physiological pH (7.4) intensely, whereas substituents such as halogens accelerated hydrolysis and formation of dimeric pyrazolate and hydroxido bridged dimers. The observed cytotoxic profile is unusual, as complexes exhibited much higher cytotoxicity in SW480 colon cancer cells than in the broadly chemo- (incl. platinum-) sensitive CH1/PA-1 teratocarcinoma cells. This activity pattern as well as reduced or slightly enhanced ROS generation and the lack of DNA interactions indicate a mode of action different from established or previously investigated classes of metallodrugs.