Synthesis, characterization, in vivo antitumor properties of the cluster rhenium compound with GABA ligands and its synergism with cisplatin

DNA-Targeted Complexes of Tc and Re for Biomedical Applications

Due to their favorable chemical features, Re and Tc complexes have been widely used for the development of new therapeutic agents and imaging probes to solve problems of biomedical relevance. This review provides an update of the most relevant research efforts towards the development of novel cancer theranostic agents using Re and Tc-based compounds interacting with specific DNA structures. This includes a variety of homometallic complexes, namely those containing M(CO)3 (M=Re, Tc) moieties, that exhibit different modes of interaction with DNA, such as covalent binding, intercalation, groove binding or G-quadruplex DNA binding. Additionally, heterometallic complexes, designed to potentiate synergistic effects of different metal centers to improve DNA-targeting, cytotoxicity and fluorescence properties, are also reviewed. Particular attention is also given to 99m Tc- and 188 Re-labeled oligonucleotides that have been widely explored to develop imaging and therapeutic radiopharmaceuticals through the in vivo hybridization with a specific complementary DNA or RNA target sequence to provide useful molecular tools in precision medicine for cancer diagnosis and treatment. Finally, the need for further improvement of DNA-targeted Re and Tc-based compounds as potential therapeutic and diagnostic agents is highlighted, and future directions are discussed.

Diastereomeric Separation of Chiral fac-Tricarbonyl(iminopyridine) Rhenium(I) Complexes and Their Cytotoxicity Studies: Approach toward an Action Mechanism against Glioblastoma

A series of new (tricarbonyl)rhenium(I) complexes were synthesized using chiral bidentate ligands (+)/(-)-iminopyridines (L_R/L_S). The reaction yielded a mixture of mononuclear Re(I) diastereoisomers, formulated as fac-[Br(CO)₃Re_(S/R)L_(S/R)]. Each single diastereoisomer was isolated and fully characterized. X-ray crystallography and circular dichroism spectra verified their enantiomeric nature. The cytotoxicity of each complex was evaluated against six cancer cell lines. The effect of the two complexes on viability, proliferation, and migration was analyzed on glioblastoma cell lines (U251 and LN229). Changes in the expression of histones, apoptotic, and key signaling proteins, as well as alterations in DNA structure, were also observed. These experiments showed that the chirality associated with both metal and ligand has a strong influence on cytotoxicity.

Cluster dirhenium(III) cis-dicarboxylates with α-amino acids ligands as mighty selective G4s binders

The synthesis of four dirhenium(III) cis-dicarboxylates with the α-amino acids residues Asp (I), Glu (II), Phe (III) and Tyr (IV) is presented. The G-quadruplex stabilization potential was evaluated by fluorescence resonance energy transfer - melting analysis. All derivatives show specific binding to c-kit1 quadruplex, while II and IV have also strong stabilization activity to HTelo21 quadruplex. At the same time, the compounds do not show any stabilization activity for ds26 DNA, which suggests unique mechanisms of molecular DNA recognition for these complexes.

Rhenium-Based Complexes and in Vivo Testing: A Brief History

The success of metal-based anticancer therapeutics in the treatment of cancer is best exemplified by cisplatin. Currently used in 32/78 cancer regimens, metal-based drugs have a clear role in cancer therapy. Despite this, metal-based anticancer therapeutics are not without drawbacks, with issues such as toxic side effects and the development of resistance mechanisms. This has led to investigations of other metal-based drug candidates such as auranofin, a gold-based drug candidate as well as ruthenium-based candidates, NAMI-A, NKP-1339 and TLD-1433. All are currently undergoing clinical trials. Another class of complexes under study are rhenium-based; such complexes have undergone extensive in vitro testing but only nine have been reported to display antitumour in vivo activity, which is a necessary step before entering clinical trials. This review will document, chronologically, the rhenium-based drug candidates that have undergone in vivo testing and the outlook for such complexes.

X-Ray fluorescence microscopy reveals that rhenium(i) tricarbonyl isonitrile complexes remain intact in vitro

An endoplasmic reticulum stress-inducing rhenium isonitrile complex was investigated for its axial ligand stability in living cells using X-ray fluorescence microscopy.

The first examples of triply bonded dirhenium(II,II) complexes that contain bis(diphenylphosphino)methane and dithiocarbamato ligands: spectroscopic, structural, cytotoxicity and computational studies

The synthesis, structure and properties of the hitherto unreported triply bonded dirhenium(II,II) dithiocarbamato complexes have been reported.

Design of Rhenium Compounds in Targeted Anticancer Therapeutics

Background:

Many rhenium (Re) complexes with potential anticancer properties have been synthesized in the recent years with the aim to overcome the clinical limitations of platinum agents. Re(I) tricarbonyl complexes are the most common but Re compounds with higher oxidation states have also been investigated, as well as hetero-metallic complexes and Re-loaded self-assembling devices. Many of these compounds display promising cytotoxic and phototoxic properties against malignant cells but all Re compounds are still at the stage of preclinical studies.

Methods:

The present review focused on the rhenium based cancer drugs that were in preclinical and clinical trials were examined critically. The detailed targeted interactions and experimental evidences of Re compounds reported by the patentable and non-patentable research findings used to write this review.

Results:

In the present review, we described the most recent and promising rhenium compounds focusing on their potential mechanism of action including, phototoxicity, DNA binding, mitochondrial effects, oxidative stress regulation or enzyme inhibition. Many ligands have been described that modulating the lipophilicity, the luminescent properties, the cellular uptake, the biodistribution, and the cytotoxicity, the pharmacological and toxicological profile.

Conclusion:

Re-based anticancer drugs can also be used in targeted therapies by coupling to a variety of biologically relevant targeting molecules. On the other hand, combination with conventional cytotoxic molecules, such as doxorubicin, allowed to take into profit the targeting properties of Re for example toward mitochondria. Through the example of the diseleno-Re complex, we showed that the main target could be the oxidative status, with a down-stream regulation of signaling pathways, and further on selective cell death of cancer cells versus normal cells.

In Vivo Anticancer Activity of a Rhenium(I) Tricarbonyl Complex

The rhenium(I) complex fac-[Re(CO)₃(2,9-dimethyl-1,10-phenanthroline)(OH₂)]⁺ (1) was previously shown to exhibit potent in vitro anticancer activity in a manner distinct from conventional platinum-based drugs (J. Am. Chem. Soc. 2017, 139, 14302-14314). In this study, we report further efforts to explore its aqueous speciation and antitumor activity. The cellular uptake of 1 was measured in A2780 and cisplatin-resistant A2780CP70 ovarian cancer cells by inductively coupled plasma mass spectrometry, revealing similar uptake efficiency in both cell lines. High accumulation in the mitochondria was observed, contradicting prior fluorescence microscopy studies. The luminescence of 1 is highly dependent on pH and coordination environment, making fluorescence microscopy somewhat unreliable for determining compound localization. The in vivo anticancer activity of 1 was evaluated in mice bearing patient-derived ovarian cancer tumor xenografts. These studies conclusively show that 1 is capable of inhibiting tumor growth, providing further credibility for the use of these compounds as anticancer agents.

The first examples of multiply bonded dirhenium(iii,ii) paramagnetic complexes containing nitrobenzoate ligands: spectroscopic, structural, cytotoxicity and computational studies

4-Nitrobenzoic acid, 3-nitrobenzoic acid and 4'-nitro[1,1'-biphenyl]-4-carboxylic acid react with the multiply bonded paramagnetic dirhenium(iii,ii) complex Re₂(μ-O₂CCH₃)Cl₄(μ-Ph₂PCH₂PPh₂)₂ (1) in refluxing ethanol to afford the paramagnetic substitution products of the type Re₂(μ-L)Cl₄(μ-Ph₂PCH₂PPh₂)₂, where L represents the nitrobenzoate ligands [L = 4-nitrobenzoate, 2; 3-nitrobenzoate, 3; 4'-nitro[1,1'-biphenyl]-4-carboxylate, 4]. These are the first examples of paramagnetic dirhenium complexes containing nitrobenzoate ligands. The spectral (UV-vis, IR, and EPR) and electrochemical properties of the complexes are described. The identity of 4 has been established by single-crystal X-ray structure determination (Re-Re distance of 2.2967(4) Å). The electronic structures of the complexes were scrutinized by density functional theory (DFT) calculations. X-band EPR spectral measurements along with the DFT analysis show that the unpaired electron resides in the metal-metal δ* antibonding orbital. The complexes were also screened in vitro for their antiproliferative properties against the human breast cancer cell line MCF-7 by the MTT assay. Flow cytometry analysis showed that the complexes arrested the sub-G0/G1 phase.

Crystal structure of di-μ-isobutyrato-κ(4) O:O'-bis-[cis-di-chlorido-(dimethyl sulfoxide-κS)rhenium(III)]

The title compound, [Re2(C3H7COO)2Cl4{(CH3)2SO}2], comprises binuclear complex mol-ecules [Re-Re = 2.24502 (13) Å] involving cis-oriented double carboxyl-ate bridges, four equatorial chloride ions and two weakly bonded O atoms from dimethyl sulfoxide ligands in the axial positions at the Re(III) atoms. In the crystal, mol-ecules are linked into corrugated layers parallel to (101) by very weak C-H⋯Cl and C-H⋯O hydrogen-bonding inter-actions. C-H⋯Cl hydrogen bonding provides the links between layers to consolidate a three-dimensional framework.

Antitumor activity of a rhenium (I)-diselenoether complex in experimental models of human breast cancer

Rhenium (I)-diselenother (Re-diselenoether) is a water soluble metal-based compound, combining one atom of rhenium and two atoms of selenium. This compound has been reported to exhibit marked activities against several solid tumor cell lines. We now disclose an improved synthesis of this complex. The Re-diselenoether showed a potent inhibitory effect on MDA-MB231 cell division in vitro, which lasted when the complex was no longer present in the culture. Re-diselenoether induced a remarkable reduction of the volume of the primitive breast tumors and of the pulmonary metastases without clinical signs of toxicity, in mice-bearing a MDA-MB231 Luc+ tumor, orthotopically transplanted, after a daily oral administration at the dose of 10 mg/kg/d. Interestingly, an antagonism was observed when cisplatin was administered as a single i.p. injection 1 week after the end of the Re-diselenoether administration. In an effort to gain insight of the mechanisms of action of Re-diselenoether complex, interaction with 9-methylguanine as a nucleic acid base model was studied. We have shown that Re-diselenoether gave both mono- and bis-guanine Re adducts, the species assumed to be responsible for the DNA intrastrand lesions.

Necroptosis-inducing rhenium(V) oxo complexes

Rhenium(V) oxo complexes of general formula [ReO(OMe)(N^N)Cl2], where N^N = 4,7-diphenyl-1,10-phenanthroline, 1, or 3,4,7,8-tetramethyl-1,10-phenanthroline, 2, effectively kill cancer cells by triggering necroptosis, a non-apoptotic form of cell death. Both complexes evoke necrosome (RIP1-RIP3)-dependent intracellular reactive oxygen species (ROS) production and propidium iodide uptake. The complexes also induce mitochondrial membrane potential depletion, a possible downstream effect of ROS production. Apparently, 1 and 2 are the first rhenium complexes to evoke cellular events consistent with programmed necrosis in cancer cells. Furthermore, 1 and 2 display low acute toxicity in C57BL/6 mice and reasonable stability in fresh human blood.

Synthesis, crystal structure and magnetic properties of the complex [ReCl3(tppz)]·MeCN

The paper reports the synthesis, X-ray structure and a deep analysis of the variable-temperature magnetic data of the new complex [ReCl₃(tppz)]·MeCN being a very scarce example of mononuclear Re(iii) complexes incorporating nitrogen donor ligands.

Crystal structure ofcis-bis(μ-β-alanine-κ2O:O′)bis[trichloridorhenium(III)](Re–Re) sesquihydrate

A dirhenium(III) cis-di­carboxyl­ate complex is reported, which is representative of a small class of zwitterionic ammonia­carboxyl­ato complexes involving a quadruple metal–metal bond.

The structure of the title compound, [Re₂Cl₆(C₃H₇NO₂)₂]·1.5H₂O, comprises a dinuclear complex cation [Re—Re = 2.2494 (3) Å] involving cis-oriented double carboxyl­ate bridges, four equatorial chloride ions and two weakly bonded chloride ligands in the axial positions at the two rhenium(III) atoms. In the crystal, two complex mol­ecules and two water mol­ecules constitute hydrogen-bonded dimers, while an extensive hydrogen-bonding network involving the groups of the zwitterionic ligand is important for generation of the framework. An additional partially occupied water molecule is disordered over two sets of sites about a symmetry centre with a site-occupancy ratio of 0.3:0.2.

Underestimated potential of organometallic rhenium complexes as anticancer agents

In the recent years, organometallic compounds have become recognized as promising anti-cancer drug candidates. While radioactive (186/188)Re compounds are already used in clinics for cancer treatment, cold Re organometallic compounds have mostly been explored as luminescent probes for cell imaging and photosensitizers in photocatalysis. However, a growing number of studies have recently revealed the potential of Re organometallic complexes as anti-cancer agents. Several compounds have displayed cytotoxicity equaling or exceeding that of the well-established anti-cancer drug cisplatin. In this review, we present the currently known Re organometallic complexes that have shown anti-proliferative activity on cancer cell lines. A particular emphasis is placed on their cellular uptake and localization as well as their potential mechanism of action.

Rhenium(IV) compounds inducing apoptosis in cancer cells

The anticancer properties of a series of mononuclear Re(IV) compounds of formula ReCl(4)L (where L is bpy = 2,2'-bipyridine; bpym = 2,2'-bipyrimidine; dmbpy = 4,4'-dimethyl-2,2'-bipyridine; phen = 1,10-phenanthroline) were investigated for the first time. All compounds displayed potent in vitro antiproliferative activity against selected cancer cells.