Research paperIn vitro and in vivo anticancer activity of tridentate thiosemicarbazone copper complexes: Unravelling an unexplored pharmacological target
Introduction
Bioinorganic chemistry can offer an innovative approach to many issues in the biomedical arena, allowing to exploit the characteristics of metal ions (redox activity, interaction with cellular proteins, alteration of homeostatic equilibria) in synergy with organic ligands [1,2]. The cisplatin milestone is an epitome in this field. It is in fact one of the most used anticancer agents in several therapeutic regimens, in combination with other drugs, including topoisomerase II inhibitors (like doxorubicin or bleomycin), antimetabolites (e.g. gentamicin, 5-fluorouracil, methotrexate), and taxol [3,4]. However, its strong activity is accompanied by a poor selectivity, with consequent important side effects such as neurotoxicity, nephrotoxicity and ototoxicity, that limit its efficacy. In addition, the use of cisplatin can be undermined by innate or acquired drug resistance [5,6]. Therefore, extensive research is on-going in order to develop other metal-based anti-tumor compounds with improved pharmacological profiles. Researchers have been extensively investigating the possibility of using endogenous metals, since they could be less toxic and more selective than platinum [7].
In this scenario, copper has attracted considerable interest, also due to the different response of tumor cells to the presence of this metal when compared to healthy ones. It has been verified that in cancerous tissues the concentration of Cu2+ is much higher than that found in healthy tissues [[10], [8], [9]]. This fact has been related to the crucial role of copper in the angiogenesis processes and, consequently, in tumor growth and metastasis formation [11]. The “tumor-specific” high copper level could represent a key target to develop novel selective anticancer drugs. Two different approaches [12] have been pursued so far: the use of chelating compounds able to sequester copper ions and the development of copper(I/II)-based antitumor drugs. If, schematically, the mode of action of cisplatin is ascribable to its ability to crosslink the purine bases of DNA, causing DNA damages, and subsequently inducing apoptosis in cancer cells, the questions about the mechanism of action of anticancer copper complexes are mainly still unanswered [[12], [13], [14]].
The role of the ligands in the activity of the metal complexes is obviously crucial, since they can modulate important aspects such as lipophilicity, solubility, stability versus sequestration by serum or cellular proteins. A very interesting class of ligands studied so far for their anticancer activity is constituted by thiosemicarbazones (TSCs) [[15], [16], [17]]. The most outstanding representative of this class of compounds is Triapine (3-AP, Fig. 1), that has already entered a number of clinical trials [18,19]. Moreover, very recently, other promising TSCs, like di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC) and (E)-N′-(6,7-dihydroquinolin-8(5H)-ylidene)-4-(pyridin-2-yl)piperazine-1-carbothiohydrazide (COTI-2) (Fig. 1), have also entered clinical trials [20,21].
TSCs represent a very diversified class, in which structural variations can have different mechanisms of action and modulate different pathways, also as a function of their coordinating properties, since the role of metal chelation seems to be crucial in relation to their anticancer activity [[22], [23], [24]]. TSCs can form a great variety of coordination compounds with biologically-relevant transition metal ions, like iron(II/III), copper (I/II) and zinc(II) [16,25,26]. Interestingly, metal complexes very often show enhanced cytotoxic profiles and alternative modes of action when compared with the parent ligands. Many investigations highlighted the ability of TSCs metal complexes to inhibit enzymatic pathways related to DNA synthesis and polymerization (i.e. to inhibit ribonucleotide reductase or DNA polymerase) [[27], [28], [29]]. TSCs can also chelate intracellular iron and, by establishing redox cycling, produce oxygen reactive species (ROS) within the cytoplasm [15,30,31]. The chelation properties of TSCs can be exploited also to target copper(II) and its homeostasis [12,32]. Copper, as well as iron, can be involved in the Haber-Weiss reaction and in the production of ROS, the activation of redox cycles and the reduction of GSH, inducing oxidative stress [12,33]; in addition, other pathways are probably also to be taken into account [12,34,35].
With these considerations in mind and looking at encouraging previous results that we obtained with salicylaldehyde-TSCs [[36], [37], [38]], we focused our attention on the 2,3-dihydroxy- and 2-hydroxy-3-methoxy-benzaldehyde thiosemicarbazone derivatives HL1-HL6, with different substituents at the N4 nitrogen (Fig. 2). Salicylaldehyde thiosemicarbazones behave essentially as tridentate ligands, but they can also be involved in the formation of polynuclear species [39]. The copper(II) complexes 1–6 (Fig. 2) with HL1-HL6 were characterized in solution by means of UV–visible spectrophotometric titrations, and in the solid state, also by means of X-ray diffraction analysis. The antitumor properties of HL1-HL6 and 1–6 were assayed in vitro on a panel of cell lines (HCT-15, LoVo and LoVo oxaliplatin resistant colon carcinoma, A375 melanoma, BxPC3 and PSN1 pancreatic adenocarcinoma, BCPAP thyroid carcinoma, 2008 ovarian carcinoma, HEK293 non-transformed embryonic kidney). The in vivo antitumor activity of 1, the most promising copper(II) complex, was finally evaluated. Detailed investigations on the mechanism of action of the copper(II) complexes 1–6 are also reported, unveiling new possible biological targets so far unexplored.
Section snippets
Synthesis
The thiosemicarbazone ligands HL1-HL6 (Fig. 2) were synthesized in high yields by condensation of thiosemicarbazide or 4-N-substituted-3-thiosemicarbazide with 2-hydroxy-3-methoxybenzaldehyde or 2,3-dihydroxybenzaldehyde. They were satisfactorily characterized by standard spectroscopic and spectrometric techniques and experimental data are in accordance with the literature data [36,57]. The ligands are in the E form in DMSO‑d6 solution at room temperature, as evidenced by the chemical shift
Conclusions
In the last years, the “old story” of TSCs as anticancer compounds seems to find new perspectives [15]. TSCs and, in particular, their metal complexes could have cellular targets different from cisplatin, opening the expectation to widen the spectrum of action and obtain better selectivity. Until now, TSCs with the 2-pyridyl group (Fig. 1) have attracted more attention, but here we would like to suggest that also salicylaldehyde derivatives can offer interesting opportunities. In fact, if the
Materials and methods. Chemistry
Commercial reagents were purchased from Sigma-Aldrich. The purity of the synthesized compounds was determined by elemental analysis and verified to be ≥ 95%. 1H NMR spectra were recorded at 25 °C on a Bruker Avance 400 FT spectrophotometer. The ATR-IR spectra were recorded by means of a Nicolet-Nexus (Thermo Fisher) spectrophotometer by using a diamond crystal plate in the range of 4000–400 cm−1. Elemental analyses were performed by using a FlashEA 1112 series CHNS/O analyzer (Thermo Fisher)
Author contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
Declaration of competing interest
The authors declare no competing financial interest.
Acknowledgments
The authors thank “Centro Interfacoltà Misure Giuseppe Casnati” of the University of Parma for facilities. This work has benefited from the equipment and framework of the COMP-HUB Initiative, funded by the ‘Departments of Excellence’ program of the Italian Ministry for Education, University and Research(MIUR, 2018–2022).
References (77)
The inorganic side of chemical biology
Nat. Chem. Biol.
(2006)- et al.
Exploration of the medical periodic table: towards new targets
Chem. Commun.
(2013) - et al.
Cellular processing of platinum anticancer drugs
Nat. Rev. Drug Discov.
(2005) Potential and cytotoxicity of cis-platinum complex with anti-tumor activity in combination therapy
Recent Pat. Anti-Cancer Drug Discov.
(2006)- et al.
Modifications of DNA by platinum complexes
Drug Resist. Updates
(2005) - et al.
J. Am. Chem. Soc.
(2005) - et al.
Novel metals and metal complexes as platforms for cancer therapy
Curr. Pharmaceut. Des.
(2010) - et al.
Serum and tissue trace metal levels in lung cancer
Oncology
(1989) - et al.
Concentrations of Fe, Cu and Zn in breast tissue: a synchrotron XRF study
Phys. Med. Biol.
(2002) - et al.
Quantitative analysis of copper, zinc and copper/zinc ratio in selected human brain tumors
J. Neuro-Oncol.
(1993)
Role of copper in angiogenesis and its medicinal implications
Curr. Med. Chem.
Advances in copper complexes as anticancer agents
Chem. Rev.
Copper complexes as anticancer agents
Anticancer Agents Med. Chem.
Copper compounds in anticancer strategies
Curr. Med. Chem.
Thiosemicarbazones from the old to new: iron chelators that are more than just ribonucleotide reductase inhibitors
J. Med. Chem.
Thiosemicarbazone metal complexes: from structure to activity
Open Crystallogr. J.
Thiosemicarbazones: the new wave in cancer treatment
Future Med. Chem.
Phase I trial of daily triapine in combination with cisplatin chemotherapy for advanced-stage malignancies
Canc. Chemother. Pharmacol.
A phase II trial of sequential ribonucleotide reductase inhibition in aggressive myeloproliferative neoplasms
Haematologica
The renaissance of polypharmacology in the development of anti-cancer therapeutics: inhibition of the "Triad of Death" in cancer by Di-2-pyridylketone thiosemicarbazones
Pharmacol. Res.
COTI-2, a novel small molecule that is active against multiple human cancer cell lines in vitro and in vivo
Oncotarget
The iron chelator Dp44mT causes DNA damage and selective inhibition of topoisomerase II alpha in breast cancer cells
Canc. Res.
The role of oxidative stress in activity of anticancer thiosemicarbazones
Oncotarget
Anticancer activity of the thiosemicarbazones that are based on di-2-pyridine ketone and quinoline moiety
Eur. J. Med. Chem.
Pyridine-2-carbaldehyde thiosemicarbazone copper system: extending some findings to other thiosemicarbazone and coordination compounds
Curr. Inorg. Chem.
Complex-formation ability of salicylaldehyde thiosemicarbazone towards ZnII, CuII, FeII, FeIII and GaIII Ions
Eur. J. Inorg. Chem.
The wide pharmacological versatility of semicarbazones, thiosemicarbazones and their metal complexes
Mini Rev. Med. Chem.
Ribonucleotide reductase inhibition by metal complexes of Triapine (3-aminopyridine-2-carboxaldehyde thiosemicarbazone): a combined experimental and theoretical study
J. Inorg. Biochem.
The potent and novel thiosemicarbazone chelators di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone and 2-benzoylpyridine-4,4-dimethyl-3-thiosemicarbazone affect crucial thiol systems required for ribonucleotide reductase activity
Mol. Pharmacol.
Novel thiosemicarbazones of the ApT and DpT series and their copper complexes: identification of pronounced redox activity and characterization of their antitumor activity
J. Med. Chem.
Iron chelators of the dipyridylketone thiosemicarbazone class: precomplexation and transmetallation effects on anticancer activity
J. Med. Chem.
Targeting copper in cancer therapy: “Copper that Cancer”
Metallomics
Increased generation of intracellular reactive oxygen species initiates selective cytotoxicity against the MCF-7 cell line resultant from redox active combination therapy using copper-thiosemicarbazone complexes
J. Biol. Inorg. Chem.
Mechanisms underlying reductant-induced reactive oxygen species formation by anticancer copper(II) compounds
J. Biol. Inorg. Chem.
Inhibition of human copper trafficking by a small molecule significantly attenuates cancer cell proliferation
Nat. Chem.
Novel thiosemicarbazone derivatives as potential antitumor agents: synthesis, physicochemical and structural properties, DNA interactions and antiproliferative activity
Bioorg. Med. Chem.
Developing anticancer ferric prodrugs based on the N-donor residues of human serum albumin carrier IIA subdomain
J. Med. Chem.
Half-sandwich arene ruthenium(II) and osmium(II) thiosemicarbazone complexes: solution behavior and antiproliferative activity
Organometallics
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These authors contributed equally to the work.