The impact of biomolecule interactions on the cytotoxic effects of rhenium(I) tricarbonyl complexes

Rhenium complexes show great promise as anticancer drug candidates. Specifically, compounds with a Re(CO)3(NN)(py)+ core in their architecture have shown cytotoxicity equal to or greater than that of well-established anticancer drugs based on platinum or organic molecules. This study aimed to evaluate how the strength of the interaction between rhenium(I) tricarbonyl complexes fac-[Re(CO)3(NN)(py)]+, NN = 1,10-phenanthroline (phen), dipyrido[3,2-f:2',3'-h]quinoxaline (dpq) or dipyrido[3,2-a:2'3'-c]phenazine (dppz) and biomolecules (protein, lipid and DNA) impacted the corresponding cytotoxic effect in cells. Results showed that fac-[Re(CO)3(dppz)(py)]+ has higher Log Po/w and binding constant (Kb) with biomolecules (protein, lipid and DNA) compared to complexes of fac-[Re(CO)3(phen)(py)]+ and fac-[Re(CO)3(dpq)(py)]+. As consequence, fac-[Re(CO)3(dppz)(py)]+ exhibited the highest cytotoxicity (IC50 = 8.5 μM for HeLa cells) for fac-[Re(CO)3(dppz)(py)]+ among the studied compounds (IC50 > 15 μM). This highest cytotoxicity of fac-[Re(CO)3(dppz)(py)]+ are probably related to its lipophilicity, higher permeation of the lipid bilayers of cells, and a more potent interaction of the dppz ligand with biomolecules (protein and DNA). Our findings open novel avenues for rational drug design and highlight the importance of considering the chemical structures of rhenium complexes that strongly interact with biomolecules (proteins, lipids, and DNA).

Necrosis-Inducing High-Valent Oxo-Rhenium(V) Complexes with Potent Antitumor Activity: Synthesis, Aquation Chemistry, Cisplatin Cross-Resistance Profile, and Mechanism of Action

Chemotherapy with the cytotoxic platinum (Pt) drugs cisplatin, carboplatin, and oxaliplatin is the mainstay of anticancer therapy in the clinic. The antitumor activity of Pt drugs originates from their ability to induce apoptosis via covalent adduct formation with nuclear DNA. While the phenomenal clinical success is highly encouraging, resistance and adverse toxic side effects limit the wider applicability of Pt drugs. To circumvent these limitations, we embarked on an effort to explore the antitumor potential of a new class of oxo-rhenium(V) complexes of the type [(N∧N)(EG)Re(O)Cl] (where EG = ethylene glycolate and N∧N = bipyridine, Bpy (1); phenanthroline, Phen (2); 3,4,7,8-tetramethyl-phenanthroline, Me4Phen (3)). Investigation of speciation chemistry in aqueous media revealed the formation of [(N∧N)Re(O)(OH)3] as the biologically active species. Complex 3 was found to be the most potent among the three, with IC50 values ranging from 0.1 to 0.4 μM against a panel of cancer cells, which is 5-70-fold lower when compared with cisplatin. The higher potency of 3 is attributed to its higher lipophilicity, which enhanced cellular uptake. Importantly, complex 3 efficiently overcomes cisplatin resistance in ovarian, lung, and prostate cancer cells. In addition to reporting the aquation chemistry and identifying the active species in aqueous media, we performed in-depth in vitro mechanistic studies, which revealed that complex 3 preferentially accumulates in mitochondria, depletes mitochondrial membrane potential, and upregulates intracellular reactive oxygen species (ROS), leading to ER stress-mediated necrosis-mediated cancer cell death.

Trinuclear rhenium(I)-based metallocages as anticancer agents towards human cervical cancer cells

The first examples of spherical-shaped trinuclear rhenium(I) organometallic cages displaying cytotoxic, antimetastatic, antiproliferative and DNA-damaging behavior towards a human cervical (HeLa) cancer cell line are reported. The compact design of the metallocages facilitates their interactions with biosystems leading to comparable efficiency to that of the commonly used anticancer drug cisplatin.

Half-sandwich Ru(II) N-heterocyclic carbene complexes in anticancer drug design

The ruthenium arene fragment is a rich source for the design of anticancer drugs; in this design, the co-ligand is a critical factor for obtaining effective anticancer complexes. In comparison with other types of ligands, N-heterocyclic carbenes (NHCs) have been less explored, despite the versatility in structural modifications and the marked stabilization of metal ions, being these characteristics important for the design of metal drugs. However, notable advances have been made in the development of NHC Ruthenium arene as anticancer agents. These advances include high antitumor activities, proven both in in vitro and in in vivo models and, in some cases, with marked selectivity against tumorigenic cells. The versatility of the structure has played a fundamental role, since they have allowed a selective interaction with their molecular targets through, for example, bio-conjugation with known anticancer molecules. For this reason, the structure-activity relationship of the imidazole, benzimidazole, and abnormal NHC ruthenium (II) η6-arene complexes have been studied. Taking into account this study, several synthetic aspects are provided to contribute to the next generations of this kind of complexes. Moreover, in recent years nanotechnology has provided innovative nanomedicines, where half-sandwich Ruthenium(II) complexes are paving their way. In this review, the recent developments in nanomaterials functionalized with Ruthenium complexes for targeted drug delivery to tumors will also be highlighted.

Comprehensive Insights into Medicinal Research on Imidazole-Based Supramolecular Complexes

The electron-rich five-membered aromatic aza-heterocyclic imidazole, which contains two nitrogen atoms, is an important functional fragment widely present in a large number of biomolecules and medicinal drugs; its unique structure is beneficial to easily bind with various inorganic or organic ions and molecules through noncovalent interactions to form a variety of supramolecular complexes with broad medicinal potential, which is being paid an increasing amount of attention regarding more and more contributions to imidazole-based supramolecular complexes for possible medicinal application. This work gives systematical and comprehensive insights into medicinal research on imidazole-based supramolecular complexes, including anticancer, antibacterial, antifungal, antiparasitic, antidiabetic, antihypertensive, and anti-inflammatory aspects as well as ion receptors, imaging agents, and pathologic probes. The new trend of the foreseeable research in the near future toward imidazole-based supramolecular medicinal chemistry is also prospected. It is hoped that this work provides beneficial help for the rational design of imidazole-based drug molecules and supramolecular medicinal agents and more effective diagnostic agents and pathological probes.

Synthesis and the photophysical and biological properties of tricarbonyl Re(I) diimine complexes bound to thiotetrazolato ligands

Twelve Re(I) tricarbonyl diimine (2,2'-bipyridine and 1,10-phenanthroline) complexes with thiotetrazolato ligands have been synthesised and fully characterised. Structural characterisation revealed the capacity of the tetrazolato ligand to bind to the Re(I) centre through either the S atom or the N atom with crystallography revealing most complexes being bound to the N atom. However, an example where the Re(I) centre is linked via the S atom has been identified. In solution, the complexes exist as an equilibrating mixture of linkage isomers, as suggested by comparison of their NMR spectra at room temperature and 373 K, as well as 2D exchange spectroscopy. The complexes are photoluminescent in fluid solution at room temperature, with emission either at 625 or 640 nm from the metal-to-ligand charge transfer excited states of triplet multiplicity, which seems to be exclusively dependent on the nature of the diimine ligand. The oxygen-sensitive excited state lifetime decay ranges between 12.5 and 27.5 ns for the complexes bound to 2,2'-bipyrdine, or between 130.6 and 155.2 ns for those bound to 1.10-phenanthroline. Quantum yields were measured within 0.4 and 1.5%. The complexes were incubated with human lung (A549), brain (T98g), and breast (MDA-MB-231) cancer cells, as well as with normal human skin fibroblasts (HFF-1), revealing low to moderate cytotoxicity, which for some compounds exceeded that of a standard anti-cancer drug, cisplatin. Low cytotoxicity combined with significant cellular uptake and photoluminescence properties provides potential for their use as cellular imaging agents. Furthermore, the complexes were assessed in disc diffusion and broth microdilution assays against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Escherichia coli (E. coli), and Pseudomonas aeruginosa (P. aeruginosa) bacterial strains, which revealed negligible antibacterial activity in the dark or after irradiation.

Recent Development of Rhenium-Based Materials in the Application of Diagnosis and Tumor Therapy

Rhenium (Re) is widely used in the diagnosis and treatment of cancer due to its unique physical and chemical properties. Re has more valence electrons in its outer shell, allowing it to exist in a variety of oxidation states and to form different geometric configurations with many different ligands. The luminescence properties, lipophilicity, and cytotoxicity of complexes can be adjusted by changing the ligand of Re. This article mainly reviews the development of radionuclide 188Re in radiotherapy and some innovative applications of Re as well as the different therapeutic approaches and imaging techniques used in cancer therapy. In addition, the current application and future challenges and opportunities of Re are also discussed.

Synthesis, characterization, and in vivo evaluation of the anticancer activity of a series of 5- and 6-(halomethyl)-2,2'-bipyridine rhenium tricarbonyl complexes

We report the synthesis, characterization, and in vivo evaluation of the anticancer activity of a series of 5- and 6-(halomethyl)-2,2'-bipyridine rhenium tricarbonyl complexes. The study was promoted in order to understand if the presence and position of a reactive halomethyl substituent on the diimine ligand system of fac-[Re(CO)₃]⁺ species may be a key molecular feature for the design of active and non-toxic anticancer agents. Only compounds potentially able to undergo ligand-based alkylating reactions show significant antiproliferative activity against colorectal and pancreatic cell lines. Of the new species presented in this study, one compound (5-(chloromethyl)-2,2'-bipyridine derivative) shows significant inhibition of pancreatic tumour growth in vivo in zebrafish-Panc-1 xenografts. The complex is noticeably effective at 8 μM concentration, lower than its in vitro IC₅₀ values, being also capable of inhibiting in vivo cancer cells dissemination.

Heteronuclear Ru(II)-Re(I) complexes as potential photodynamic anticancer agents with anti-metastatic and anti-angiogenic activities

Herein, three heterometallic Ru(II)-Re(I) complexes, [Ru(NN)₂(tpphz)Re(CO)₃Cl](PF₆)₂ (N-N = 2,2'-bipyridine (bpy, in RuRe1), 1,10-phenanthroline (phen, in RuRe2), 4,7-diphenyl-1,10-phenanthroline (DIP, in RuRe3), tpphz = tetrapyrido[3,2-a:2',3'-c:3″,2″-h:2″',3″'-j]phenazine), using tpphz as a bridging ligand to connect Ru(II) polypyridyl moiety and Re(I) tricarbonyl moiety were designed and synthesized. Cytotoxicity tests revealed that RuRe1-3 exhibited high phototoxicities against several cancer cell lines tested, with IC₅₀ values ranging from 0.8 to 6.8 μM. Notably, RuRe2 exhibited the most significant increase in cytotoxicity against human prostate cancer (PC3) cells under light (450 nm) irradiation, with phototoxicity index (PI) value increasing by >112.3-fold. Further mechanistic studies of RuRe2 revealed that RuRe2-mediated PDT could induce tumor cell apoptosis through the mitochondrial pathway. Moreover, RuRe2-mediated PDT could inhibit PC3 cell scratch healing and reduce the expression levels of matrix metalloproteinases 2 (MMP-2), matrix metalloproteinases 9 (MMP-9) and vascular endothelial growth factor receptor VEGFR2. Finally, angiogenic activity assays performed in human umbilical vein endothelial cells (HUVECs) showed that RuRe2 exerted an anti-angiogenesis effect. Our study demonstrated that RuRe1-3 were promising PDT antitumor agents with potential anti-metastatic and anti-angiogenic activities.

Evaluation of cytotoxic properties of two fluorescent fac-Re(CO)3 complexes bearing an N,N-bidentate benzimidazole coligand

The reaction between 1H-benzimidazol-2-ylmethyl-(N-aryl)amine derivatives (L^R) and [ReBr(CO)₅] afforded octahedral Re(i) complexes of the general formula of [ReBr(CO)₃L^R] (R = 4-Cl and 4-COOCH₃). The Re(i) complexes were screened for their potential cytotoxicity against three malignant cell lines and one normal cell line of different origins. The solvatochromic characteristics of the complexes were examined by UV/vis. spectroscopy with the aid of time-dependent density functional theory calculations. Strong autofluorescence emission can be seen in the two Re(i) complexes between 460 and 488 nm. They appeared to accumulate inside intercellular connections and surrounding cellular membranes. The substances gathered also, along the cell membrane, waiting for their entry. The mode of cell death staining and the DNA fragmentation analysis revealed that the 4-Cl complex showed increased apoptotic changes in the MCF-7, and the Caco-2 cell line, while the HepG2 cell line showed little apoptotic changes.

An Anticancer Rhenium Tricarbonyl Targets Fe-S Cluster Biogenesis in Ovarian Cancer Cells

Target identification remains a critical challenge in inorganic drug discovery to deconvolute potential polypharmacology. Herein, we describe an improved approach to prioritize candidate protein targets based on a combination of dose-dependent chemoproteomics and treatment effects in living cancer cells for the rhenium tricarbonyl compound TRIP. Chemoproteomics revealed 89 distinct dose-dependent targets with concentrations of competitive saturation between 0.1 and 32 μM despite the broad proteotoxic effects of TRIP. Target-response networks revealed two highly probable targets of which the Fe-S cluster biogenesis factor NUBP2 was competitively saturated by free TRIP at nanomolar concentrations. Importantly, TRIP treatment led to a down-regulation of Fe-S cluster containing proteins and upregulated ferritin. Fe-S cluster depletion was further verified by assessing mitochondrial bioenergetics. Consequently, TRIP emerges as a first-in-class modulator of the scaffold protein NUBP2, which disturbs Fe-S cluster biogenesis at sub-cytotoxic concentrations in ovarian cancer cells.

Rhenium Perrhenate (188ReO4) Induced Apoptosis and Reduced Cancerous Phenotype in Liver Cancer Cells

Recurrence in hepatocellular carcinoma (HCC) after conventional treatments is a crucial challenge. Despite the promising progress in advanced targeted therapies, HCC is the fourth leading cause of cancer death worldwide. Radionuclide therapy can potentially be a practical targeted approach to address this concern. Rhenium-188 (188Re) is a β-emitting radionuclide used in the clinic to induce apoptosis and inhibit cell proliferation. Although adherent cell cultures are efficient and reliable, appropriate cell-cell and cell-extracellular matrix (ECM) contact is still lacking. Thus, we herein aimed to assess 188Re as a potential therapeutic component for HCC in 2D and 3D models. The death rate in treated Huh7 and HepG2 lines was significantly higher than in untreated control groups using viability assay. After treatment with 188ReO4, Annexin/PI data indicated considerable apoptosis induction in HepG2 cells after 48 h but not Huh7 cells. Quantitative RT-PCR and western blotting data also showed increased apoptosis in response to 188ReO4 treatment. In Huh7 cells, exposure to an effective dose of 188ReO4 led to cell cycle arrest in the G2 phase. Moreover, colony formation assay confirmed post-exposure growth suppression in Huh7 and HepG2 cells. Then, the immunostaining displayed proliferation inhibition in the 188ReO4-treated cells on 3D scaffolds of liver ECM. The PI3-AKT signaling pathway was activated in 3D culture but not in 2D culture. In nude mice, Huh7 cells treated with an effective dose of 188ReO4 lost their tumor formation ability compared to the control group. These findings suggest that 188ReO4 can be a potential new therapeutic agent against HCC through induction of apoptosis and cell cycle arrest and inhibition of tumor formation. This approach can be effectively combined with antibodies and peptides for more selective and personalized therapy.

Anticancer and Antibiotic Rhenium Tri- and Dicarbonyl Complexes: Current Research and Future Perspectives

Organometallic compounds are increasingly recognized as promising anticancer and antibiotic drug candidates. Among the transition metal ions investigated for these purposes, rhenium occupies a special role. Its tri- and dicarbonyl complexes, in particular, attract continuous attention due to their relative ease of preparation, stability and unique photophysical and luminescent properties that allow the combination of diagnostic and therapeutic purposes, thereby permitting, e.g., molecules to be tracked within cells. In this review, we discuss the anticancer and antibiotic properties of rhenium tri- and dicarbonyl complexes described in the last seven years, mainly in terms of their structural variations and in vitro efficacy. Given the abundant literature available, the focus is initially directed on tricarbonyl complexes of rhenium. Dicarbonyl species of the metal ion, which are slowly gaining momentum, are discussed in the second part in terms of future perspective for the possible developments in the field.

Anticancer Properties of Rhenium(I) Tricarbonyl Complexes of N-Heterocyclic Carbene Ligands

A family of eight rhenium(I) tricarbonyl complexes bearing pyridyl-imidazolylidene or bis-imidazolylidene ligand in combination with a series of N-acetyl amino acids ligands (glycine, isoleucine, proline) and acetate have been synthesised...

V, Kar B, Das U, Paira P. Target-specific mononuclear and binuclear rhenium(i) tricarbonyl complexes as upcoming anticancer drugs

Metal complexes have gradually been attracting interest from researchers worldwide as potential cancer therapeutics. Driven by the many side effects of the popular platinum-based anticancer drug cisplatin, the tireless endeavours of researchers have afforded strategies for the design of appropriate metal complexes with minimal side effects compared to cisplatin and its congeners to limit the unrestricted propagation of cancer. In this regard, transition metal complexes, especially rhenium-based complexes are being identified and highlighted as promising cancer theranostics, which are endowed with the ability to detect and annihilate cancer cells in the body. This is attributed the amazing photophysical properties of rhenium complexes together with their ability to selectively attack different organelles in cancer cells. Therefore, this review presents the properties of different rhenium-based complexes to highlight their recent advances as anticancer agents based on their cytotoxicity results.

In this review, rhenium-based complexes are highlighted as promising cancer theranostics, which are endowed with the ability to detect and annihilate cancer cells in the body.

Real-time tracking of ER turnover during ERLAD by a rhenium complex via lifetime imaging

Endoplasmic reticulum (ER) degradation by autophagy (ER-phagy) is a recently revealed selective autophagy pathway that plays important roles in organelle turnover and protein degradation, but the biological functions of ER-phagy are largely unknown. Here, we present an ER-targeting Re(I) tricarbonyl complex (Re-ERLAD) that can accumulate in the ER, induce ER-to-lysosome-associated degradation (ERLAD) upon visible light irradiation, and label ER buds and track their morphological alterations during ER-phagy. The emission of Re-ERLAD is sensitive to viscosity, which is a key parameter reflecting the amount of unfolded protein in the ER. Quantitative detection using two-photon fluorescence lifetime imaging microscopy shows that ER viscosity initially increases and then decreases during ERLAD, which reveals that ERLAD is a pathway for alleviating ER stress caused by unfolded proteins. In conclusion, our work presents the first specific photoinducer and tracker of ERLAD, which can be used in studying the regulatory mechanism and function of this process.

Photochemistry and in vitro anticancer activity of Pt(IV)Re(I) conjugates

The photophysical and photochemical properties of two Pt(IV)Re(I) conjugates were studied via both experimental and computational methods. Both conjugates exhibit modest photocytotoxicity against ovarian cancer cells. X-ray fluorescence microscopy showed that Pt and Re colocalize in cells whether they had been irradiated or not. This work demonstrates the potential of photoactivated multilimetallic agents for combating cancer.

Phosphorescent rhenium(I) complexes conjugated with artesunate: Mitochondrial targeting and apoptosis-ferroptosis dual induction

Cell death is essential for cancer, which can be induced through multiple mechanisms. Ferroptosis, a newly emerging form of non-apoptotic cell death, involves the generation of iron-dependent reactive oxygen species (ROS). In this study, we designed and synthesized two artesunate (ART) conjugated phosphorescent rhenium(I) complexes (Re(I)-ART conjugates), [Re(N^N)(CO)₃(PyCH₂OART)](PF₆) (Re-ART-1 and Re-ART-2) (Py = pyridine, N^N = 1,10-phenanthroline (phen, in Re-ART-1) and 4,7-diphenyl-1,10-phenanthroline (DIP, in Re-ART-2)) that can specifically locate in the mitochondria of human cervical carcinoma (HeLa). Mechanism studies show that Re-ART-1 and Re-ART-2 exhibit high cytotoxicity against cancer cells lines and can induce both apoptosis and ferroptosis in HeLa cells through mitochondrial damage, caspase cascade, glutathione (GSH) depletion, glutathione peroxidase 4 (GPX4) inactivation and lipid peroxidation accumulation. As a result, this work presents the rational design of Re(I)-ART conjugates as a promising strategy to induce both apoptosis and ferroptosis and improve therapeutic efficiency of cancer treatment.

Rhenium N-heterocyclic carbene complexes block growth of aggressive cancers by inhibiting FGFR- and SRC-mediated signalling

BACKGROUND

Platinum-based anticancer drugs have been at the frontline of cancer therapy for the last 40 years, and are used in more than half of all treatments for different cancer types. However, they are not universally effective, and patients often suffer severe side effects because of their lack of cellular selectivity. There is therefore a compelling need to investigate the anticancer activity of alternative metal complexes. Here we describe the potential anticancer activity of rhenium-based complexes with preclinical efficacy in different types of solid malignancies.

METHODS

Kinase profile assay of rhenium complexes. Toxicology studies using zebrafish. Analysis of the growth of pancreatic cancer cell line-derived xenografts generated in zebrafish and in mice upon exposure to rhenium compounds.

RESULTS

We describe rhenium complexes which block cancer proliferation in vitro by inhibiting the signalling cascade induced by FGFR and Src. Initially, we tested the toxicity of rhenium complexes in vivo using a zebrafish model and identified one compound that displays anticancer activity with low toxicity even in the high micromolar range. Notably, the rhenium complex has anticancer activity in very aggressive cancers such as pancreatic ductal adenocarcinoma and neuroblastoma. We demonstrate the potential efficacy of this complex via a significant reduction in cancer growth in mouse xenografts.

CONCLUSIONS

Our findings provide a basis for the development of rhenium-based chemotherapy agents with enhanced selectivity and limited side effects compared to standard platinum-based drugs.

Identification and characterization of deschloro-chlorothricin obtained from a large natural product library targeting aurora A kinase in multiple myeloma

Multiple myeloma (MM) is a devastating disease with low survival rates worldwide. The mean lifetime of patients may be extendable with new drug alternatives. Aurora A kinase (AURKA) is crucial in oncogenesis, because its overexpression or amplification may incline the development of various types of cancer, including MM. Therefore, inhibitors of AURKA are innovative and promising targets. Natural compounds always represented a valuable resource for anticancer drug development. In the present study, based on virtual drug screening of more than 48,000 natural compounds, the antibiotic deschloro-chlorotricin (DCCT) has been identified to bind to AURKA with even higher binding affinity (free bindung energy: −12.25 kcal/mol) than the known AURKA inhibitor, alisertib (free binding energy: −11.25 kcal/mol). The in silico studies have been verified in vitro by using microscale thermophoresis. DCCT inhibited MM cell lines (KMS-11, L-363, RPMI-8226, MOLP-8, OPM-2, NCI-H929) with IC₅₀ values in a range from 0.01 to 0.12 μM. Furthermore, DCCT downregulated AURKA protein expression, induced G2/M cell cycle arrest and disturbed the cellular microtubule network as determined by Western blotting, flow cytometry, and fluorescence microscopy. Thus, DCCT may be a promising lead structure for further derivatization and the development of specific AURKA inhibitors in MM therapy.

Exploring the In Vivo and In Vitro Anticancer Activity of Rhenium Isonitrile Complexes

The established platinum-based drugs form covalent DNA adducts to elicit their cytotoxic response. Although they are widely employed, these agents cause toxic side-effects and are susceptible to cancer-resistance mechanisms. To overcome these limitations, alternative metal complexes containing the rhenium(I) tricarbonyl core have been explored as anticancer agents. Based on a previous study ( Chem. Eur. J. 2019, 25, 9206), a series of highly active tricarbonyl rhenium isonitrile polypyridyl (TRIP) complexes of the general formula fac-[Re(CO)3(NN)(ICN)]+, where NN is a chelating diimine and ICN is an isonitrile ligand, that induce endoplasmic reticulum (ER) stress via activation of the unfolded protein response (UPR) pathway are investigated. A total of 11 of these TRIP complexes were synthesized, modifying both the equatorial polypyridyl and axial isonitrile ligands. Complexes with more electron-donating equatorial ligands were found to have greater anticancer activity, whereas the axial ICN ligands had a smaller effect on their overall potency. All 11 TRIP derivatives trigger a similar phenotype that is characterized by their abilities to induce ER stress and activate the UPR. Lastly, we explored the in vivo efficacy of one of the most potent complexes, fac-[Re(CO)3(dmphen)(ptolICN)]+ (TRIP-1a), where dmphen = 2,9-dimethyl-1,10-phenanthroline and ptolICN = para-tolyl isonitrile, in mice. The 99mTc congener of TRIP-1a was synthesized, and its biodistribution in BALB/c mice was investigated in comparison to the parent Re complex. The results illustrate that both complexes have similar biodistribution patterns, suggesting that 99mTc analogues of these TRIP complexes can be used as diagnostic partner agents. The in vivo antitumor activity of TRIP-1a was then investigated in NSG mice bearing A2780 ovarian cancer xenografts. When administered at a dose of 20 mg/kg twice weekly, this complex was able to inhibit tumor growth and prolong mouse survival by 150% compared to the vehicle control cohort.

β-radiating radionuclides in cancer treatment, novel insight into promising approach

Targeted radionuclide therapy, known as molecular radiotherapy is a novel therapeutic module in cancer medicine. β-radiating radionuclides have definite impact on target cells via interference in cell cycle and particular signalings that can lead to tumor regression with minimal off-target effects on the surrounding tissues. Radionuclides play a remarkable role not only in apoptosis induction and cell cycle arrest, but also in the amelioration of other characteristics of cancer cells. Recently, application of novel β-radiating radionuclides in cancer therapy has been emerged as a promising therapeutic modality. Several investigations are ongoing to understand the underlying molecular mechanisms of β-radiating elements in cancer medicine. Based on the radiation dose, exposure time and type of the β-radiating element, different results could be achieved in cancer cells. It has been shown that β-radiating radioisotopes block cancer cell proliferation by inducing apoptosis and cell cycle arrest. However, physical characteristics of the β-radiating element (half-life, tissue penetration range, and maximum energy) and treatment protocol determine whether tumor cells undergo cell cycle arrest, apoptosis or both and to which extent. In this review, we highlighted novel therapeutic effects of β-radiating radionuclides on cancer cells, particularly apoptosis induction and cell cycle arrest.

Dinuclear phosphorescent rhenium(i) complexes as potential anticancer and photodynamic therapy agents

Two dinuclear organometallic Re(i) complexes increase intracellular ROS levels, causing lysosomal dysfunction and cell apoptosis.

Red-emitting neutral rhenium(i) complexes bearing a pyridyl pyridoannelated N-heterocyclic carbene

Two novel neutral rhenium(i) tricarbonyl complexes bearing a pyridoannelated N-heterocyclic carbene are synthetized and fully characterized, which display red photoluminescence arising from a triplet excited state with ligand centered character.

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.

A Rhenium Isonitrile Complex Induces Unfolded Protein Response-Mediated Apoptosis in Cancer Cells

Complexes of the element Re have recently been shown to possess promising anticancer activity through mechanisms of action that are distinct from the conventional metal-based drug cisplatin. In this study, we report our investigations on the anticancer activity of the complex [Re(CO)₃ (dmphen)(p-tol-ICN)]⁺ (TRIP) in which dmphen=2,9-dimethyl-1,10-phenanthroline and p-tol-ICN=para-tolyl isonitrile. TRIP was synthesized by literature methods and exhaustively characterized. This compound exhibited potent in vitro anticancer activity in a wide variety of cell lines. Flow cytometry and immunostaining experiments indicated that TRIP induces intrinsic apoptosis. Comprehensive biological mechanistic studies demonstrated that this compound triggers the accumulation of misfolded proteins, which causes endoplasmic reticulum (ER) stress, the unfolded protein response, and apoptotic cell death. Furthermore, TRIP induced hyperphosphorylation of eIF2α, translation inhibition, mitochondrial fission, and expression of proapoptotic ATF4 and CHOP. These results establish TRIP as a promising anticancer agent based on its potent cytotoxic activity and ability to induce ER stress.

Metal-based antitumor compounds: beyond cisplatin

Despite improvements in the 5-year survival rate to over 80% in cancers, such as Hodgkin lymphoma and testicular cancer, more aggressive tumors including pancreatic and brain cancer still have extremely low survival rates. The establishment of chemoresistance, responsible for the reduction in treatment efficiency and cancer relapse, is one possible explanation for this setback. Metal-based compounds, a class of anticancer drugs, are largely used in the treatment of cancer. Herein, we will review the use of metal-based small molecules in chemotherapy, focusing on recent studies, and we will discuss how new nonplatinum-based agents are prompting scientists to increase drug specificity to overcome chemoresistance in cancer cells.

Impairment of the autophagy-related lysosomal degradation pathway by an anticancer rhenium(i) complex

A Re(i) complex induces autophagy, which is arrested at the lysosomal stage due to lysosomal dysfunction, and inhibits tumor growth in vivo.

Tricarbonyl rhenium(i) tetrazolato and N-heterocyclic carbene complexes: versatile visible-light-mediated photoredox catalysts

This study demonstrates that structurally-diverse, photoactive rhenium(i) tricarbonyl complexes can mediate representative atom-transfer radical addition, hydrodehalogenation, and α-amino C–H functionalisation reactions.

New organometallic imines of rhenium(i) as potential ligands of GSK-3β: synthesis, characterization and biological studies

Substituted amino-piperazine derivatives were synthesized and used as precursors for the preparation of a series of new organometallic Re(i) imine complexes with the general formula [(η⁵-C₅H₄CH[double bond, length as m-dash]N-(CH₂)₅-Pz-R)Re(CO)₃] (Pz-R: -alkyl or aryl piperazine). The piperazine-based ligands were designed to be potential inhibitors of GSK-3β kinase. All the ligands and complexes were fully characterized and evaluated against the HT-29 and PT-45 cancer cell lines, in which GSK-3β plays a crucial role. In this context, we carried out biological evaluation using the MTT colorimetric assay. In terms of structure activity relationship, our findings indicated improved biological activity when aromaticity increased in the organic ligands (3d). In addition, the presence of the rhenium fragment in the imines (5a-d) leads to better activity with IC₅₀ values in the range of 25-100 μM. In addition, our experimental studies were complemented by computational studies, where the volume and electrostatic surface of the organic ligands and organometallic compounds as well as their binding to the kinase protein are calculated.

Properties and prospects for rhenium(i) tricarbonyl N-heterocyclic carbene complexes

Rhenium tricarbonyl complexes bound to N-heterocyclic carbene ligands are emerging as a new class of complexes with promising applications in a wide variety of areas.

Rhenium tricarbonyl complexes with arenethiolate axial ligands

Pyta and Tapy-based [Re(N^N)(CO)₃X] complexes with para-substituted benzenethiolates as axial ligand are reported along with their electrochemical and photophysical properties.

Anticancer activity of complexes of the third row transition metals, rhenium, osmium, and iridium

A summary of recent developments on the anticancer activity of complexes of rhenium, osmium, and iridium is described.

In Vitro Anticancer Activity and in Vivo Biodistribution of Rhenium(I) Tricarbonyl Aqua Complexes

Seven rhenium(I) complexes of the general formula fac-[Re(CO)3(NN)(OH2)]+ where NN = 2,2'-bipyridine (8), 4,4'-dimethyl-2,2'-bipyridine (9), 4,4'-dimethoxy-2,2'-bipyridine (10), dimethyl 2,2'-bipyridine-4,4'-dicarboxylate (11), 1,10-phenanthroline (12), 2,9-dimethyl-1,10-phenanthroline (13), or 4,7-diphenyl-1,10-phenanthroline (14), were synthesized and characterized by 1H NMR spectroscopy, IR spectroscopy, mass spectrometry, and X-ray crystallography. With the exception of 11, all complexes exhibited 50% growth inhibitory concentration (IC50) values that were less than 20 μM in HeLa cells, indicating that these compounds represent a new potential class of anticancer agents. Complexes 9, 10, and 13 were as effective in cisplatin-resistant cells as wild-type cells, signifying that they circumvent cisplatin resistance. The mechanism of action of the most potent complex, 13, was explored further by leveraging its intrinsic luminescence properties to determine its intracellular localization. These studies indicated that 13 induces cytoplasmic vacuolization that is lysosomal in nature. Additional in vitro assays indicated that 13 induces cell death without causing an increase in intracellular reactive oxygen species or depolarization of the mitochondrial membrane potential. Further studies revealed that the mode of cell death does not fall into one of the canonical categories such as apoptosis, necrosis, paraptosis, and autophagy, suggesting that a novel mode of action may be operative for this class of rhenium compounds. The in vivo biodistribution and metabolism of complex 13 and its 99mTc analogue 13* were also evaluated in naı̈ve mice. Complexes 13 and 13* exhibited comparable biodistribution profiles with both hepatic and renal excretion. High-performance liquid chromatography inductively coupled plasma mass-spectrometry (HPLC-ICP-MS) analysis of mouse blood plasma and urine postadministration showed considerable metabolic stability of 13, rendering this potent complex suitable for in vivo applications. These studies have shown the biological properties of this class of compounds and demonstrated their potential as promising theranostic anticancer agents that can circumvent cisplatin resistance.

Benzannulated Re(i)–NHC complexes: synthesis, photophysical properties and antimicrobial activity

A series of novel Re(i)(CO)₃–NHC complexes bearing unsubstituted benzimidazol-2-ylidene ligands is presented which provide strong luminescence as well as high antibacterial activity.