N-Heterocyclic Carbene-Polyethylenimine Platinum Complexes with Potent in Vitro and in Vivo Antitumor Efficacy

N-Heterocyclic carbene platinum complexes encapsulated in lipid particles: a novel strategy to target cancer cells and cancer stem cells in glioblastoma

The properties against cancer cells and glioblastoma stem cells of a series of platinum NHC complexes in lipid formulations are reported. As these organometallic compounds show very promising biological activities using conventional formulations, i.e. by solubilization in a DMSO/water system, the challenge for a therapeutic application is to be able to make them biocompatible while retaining this activity. Herein with the aim of eradicating cancer cells and cancer stem cells from glioblastoma, a disease in need of new therapies, we studied the encapsulation of platinum compounds in either liposome or lipid nanocapsule formulations and investigated the physical and chemical stability of the resulting nano-objects. It was then demonstrated that in these lipid formulations, platinum complexes retained their cytotoxic activity on both cancer cells and cancer stem cells. The best candidate, i.e. triphenylphosphonium-functionalized platinum-based complex, was then used for in vivo studies on mice using a U87-MG glioblastoma model, with significant results in slowing tumor growth, in particular when comparing to oxaliplatin. Another key strength of this study is the preservation of the compound's anti-cancer activity within a lipid-based formulation, eliminating the need for DMSO as a solvent. The findings of this study signify a major advance in the field, particularly in light of the expanding body of research on organometallic complexes conducted under conditions that preclude direct clinical applicability.

Multiproperty Polyethylenimine-Caged Platinum Nanoclusters Promote Apoptosis of Osteosarcoma Cells via Regulating the BAX-Bcl-2/Caspase-3/PARP Axis

Osteosarcoma, a prevalent primary bone cancer in children, exhibits a poor prognosis due to the high prevalence of drug resistance. The objective of this study was to investigate the potential of fluorescent ultrafine polyethylenimine-coated caged platinum nanoclusters (PEI-Pt NCs) as an antitumor agent in osteosarcoma. The primary focus of this study involved the utilization of osteosarcoma cells (U2-OS and MG-63) and normal control cells (hBMSC) as the primary subjects of investigation. The capacity of PEI-Pt NCs to enter osteosarcoma cells was observed through the implementation of confocal microscopy. The impact of PEI-Pt NCs on migration and proliferation was assessed through the utilization of various methodologies, including the CCK8 assay, Ki-67 immunofluorescence, clone formation assay, transwell assay, and wound healing assay. Furthermore, the influence of PEI-Pt NCs on apoptosis and its underlying mechanism was explored through the implementation of flow cytometry and Western blotting techniques. The PEI-Pt NCs demonstrated the capability to enter osteosarcoma cells, including the nucleus, while also exhibiting fluorescent labeling properties. Furthermore, the PEI-Pt NCs effectively impeded the migration and proliferation of osteosarcoma cells. Additionally, the PEI-Pt NCs facilitated apoptosis by modulating the BAX-Bcl-2/Caspase 3/PARP axis. The novel nanomaterial PEI-Pt NCs possess diverse advantageous capabilities, including the ability to impede cell proliferation and migration, as well as the capacity to modulate the BAX-Bcl-2/Caspase 3/PARP axis, thereby promoting cell apoptosis. Consequently, this nanomaterial exhibits promising potential in addressing the issue of inadequate platinum-based treatment for osteosarcoma.

Triphenylphosphonium-functionalized N-heterocyclic carbene platinum complexes [(NHC-TPP+)Pt] induce cell death of human glioblastoma cancer stem cells

A growing body of experimental and clinical evidence suggests that rare cell populations, known as cancer stem cells (CSCs), play an important role in the development and therapeutic resistance of several cancers, including glioblastoma. Elimination of these cells is therefore of paramount importance. Interestingly, recent results have shown that the use of drugs that specifically disrupt mitochondria or induce mitochondria-dependent apoptosis can efficiently kill cancer stem cells. In this context, a novel series of platinum(II) complexes bearing N-heterocyclic carbene (NHC) of the type [(NHC)PtI2(L)] modified with the mitochondria targeting group triphenylphosphonium were synthesized. After a complete characterization of the platinum complexes, the cytotoxicity against two different cancer cell lines, including a cancer stem cell line, was investigated. The best compound reduced the cell viability of both cell lines by 50% in the mM range, with an approximately 300-fold higher anticancer activity on the CSC line compared to oxaliplatin. Finally, mechanistic studies showed that the triphenylphosphonium functionalized platinum complexes significantly altered mitochondrial function and also induced atypical cell death.

Evaluation of the Cytotoxicity of Cationic Polymers on Glioblastoma Cancer Stem Cells

Cationic polymers such as polyethylenimine (PEI) have found a pervasive place in laboratories across the world as gene delivery agents. However, their applications are not limited to this role, having found a place as delivery agents for drugs, in complexes known as polymer-drug conjugates (PDCs). Yet a potentially underexplored domain of research is in their inherent potential as anti-cancer therapeutic agents, which has been indicated by several studies. Even more interesting is the recent observation that certain polycations may present a significantly greater toxicity towards the clinically important cancer stem cell (CSC) niche than towards more differentiated bulk tumour cells. These cells, which possess the stem-like characteristics of self-renewal and differentiation, are highly implicated in cancer drug resistance, tumour recurrence and poor clinical prognosis. The search for compounds which may target and eliminate these cells is thus of great research interest. As such, the observation in our previous study on a PEI-based PDC which showed a considerably higher toxicity of PEI towards glioblastoma CSCs (GSCs) than on more differentiated glioma (U87) cells led us to investigate other cationic polymers for a similar effect. The evaluation of the toxicity of a range of different types of polycations, and an investigation into the potential source of GSC's sensitivity to such compounds is thus described.

Polyethylenimine, an Autophagy-Inducing Platinum-Carbene-Based Drug Carrier with Potent Toxicity towards Glioblastoma Cancer Stem Cells

The difficulty involved in the treatment of many tumours due to their recurrence and resistance to chemotherapy is tightly linked to the presence of cancer stem cells (CSCs). This CSC sub-population is distinct from the majority of cancer cells of the tumour bulk. Indeed, CSCs have increased mitochondrial mass that has been linked to increased sensitivity to mitochondrial targeting compounds. Thus, a platinum-based polyethylenimine (PEI) polymer-drug conjugate (PDC) was assessed as a potential anti-CSC therapeutic since it has previously displayed mitochondrial accumulation. Our results show that CSCs have increased specific sensitivity to the PEI carrier and to the PDC. The mechanism of cell death seems to be necrotic in nature, with an absence of apoptotic markers. Cell death is accompanied by the induction of a protective autophagy. The interference in the balance of this pathway, which is highly important for CSCs, may be responsible for a partial reversion of the stem-like phenotype observed with prolonged PEI and PDC treatment. Several markers also indicate the cell death mode to be capable of inducing an anti-cancer immune response. This study thus indicates the potential therapeutic perspectives of polycations against CSCs.

An N-heterocyclic carbene iridium(III) complex as a potent anti-cancer stem cell therapeutic

Cancer stem cells (CSCs) represent a difficult to treat cellular niche within tumours due to their unique characteristics, which give them a high propensity for resistance to classical anti-cancer treatments and the ability to repopulate the tumour mass. An attribute that may be implicated in the high rates of recurrence of certain tumours. However, other characteristics specific to these cells, such as their high dependence on mitochondria, may be exploited for the development of new therapeutic agents that are effective against the niche. As such, a previously described phosphorescent N-heterocyclic carbene iridium(III) compound which showed a high level of cytotoxicity against classical tumour cell lines with mitochondria-specific effects was studied for its potential against CSCs. The results showed a significantly higher level of activity against several CSC lines compared to non-CSCs. Mitochondrial localisation and superoxide production were confirmed. Although the cell death involved caspase activation, their role in cell death was not definitive, with a potential implication of other, non-apoptotic pathways shown. A cytostatic effect of the compound was also displayed at low mortality doses. This study thus provides important insights into the mechanisms and the potential for this class of molecule in the domain of anti-CSC therapeutics.

Biomarking and Induction of Apoptosis in Ovarian Cancer Using Bifunctional Polyethyleneimine-Caged Platinum Nanoclusters

According to the 2020 GLOBOCAN Global Cancer Women's Cancer Data, ovarian cancer is the eighth most common tumor in humans. Still, its mortality rate ranks first among all gynecological tumors, with a 5-year survival rate of 30% to 50%. Widespread clinical use of platinum-based drugs has improved survival outcomes in patients with ovarian cancer, but organ toxicity and drug resistance hinder their anticancer effects. In particular, the resistance to platinum drugs is an important reason for ovarian cancer's high recurrence rate and mortality. With the development of chemotherapeutic drugs synthesized by nanomaterials in the biomedical field, we developed bifunctional ultrafine polyethyleneimine caged platinum nanoclusters (PEI-Pt NCs) to improve the dilemma of platinum drugs. This study aimed to elucidate the antitumor effect of PEI-Pt NCs in OC. First, as observed by confocal microscopy, Pt NCs entered OC cells in a dose-dependent manner and accumulated on the surface of the nuclear membrane and in the nucleus. Subsequently, through cck8, ki-67 immunofluorescence, wound healing assay, transwell assay, clone formation assay, flow cytometry, tunel staining, and western blotting assay, it was confirmed that PEI-Pt NCs could inhibit the proliferation and migration and induce the apoptosis of ovarian cancer cells. PEI-Pt NCs can be used as fluorescent markers for systemic bioimaging of ovarian cancer, showing great potential in diagnosing and treating ovarian cancer, and making a specific contribution to solving the dilemma of platinum-based drug therapy for OC.

N-Heterocyclic Carbene-Platinum Complexes Featuring an Anthracenyl Moiety: Anti-Cancer Activity and DNA Interaction

A platinum (II) complex stabilized by a pyridine and an N-heterocyclic carbene ligand featuring an anthracenyl moiety was prepared. The compound was fully characterized and its molecular structure was determined by single-crystal X-ray diffraction. The compound demonstrated high in vitro antiproliferative activities against cancer cell lines with IC50 ranging from 10 to 80 nM. The presence of the anthracenyl moiety on the N-heterocyclic carbene (NHC) Pt complex was used as a luminescent tag to probe the metal interaction with the nucleobases of the DNA through a pyridine-nucleobase ligand exchange. Such interaction of the platinum complex with DNA was corroborated by optical tweezers techniques and liquid phase atomic force microscopy (AFM). The results revealed a two-state interaction between the platinum complex and the DNA strands. This two-state behavior was quantified from the different experiments due to contour length variations. At 24 h incubation, the stretching curves revealed multiple structural breakages, and AFM imaging revealed a highly compact and dense structure of platinum complexes bridging the DNA strands.

Exploring diversity in platinum(iv) N-heterocyclic carbene complexes: synthesis, characterization, reactivity and biological evaluation

Platinum(iv) complexes stabilized by N-heterocyclic carbene ligands of the type [(NHC)PtX4L], where L is a neutral nitrogen-based ligand and X is a halide anion (Br, Cl), were prepared by using straightforward and high-yielding synthetic routes and the scope was extended to amphiphilic derivatives. The complexes were fully characterized and the molecular structure of the three derivatives was determined by single-crystal X-ray analyses. The complexes demonstrated in vitro antiproliferative activities against several cancer cell lines. In particular, a representative Pt(iv) complex, namely, [(NHC)PtCl4(pyridine)], displayed efficient antiproliferative activity against cisplatin-resistant cancer cells. These results were correlated with their physicochemical properties, namely, solubility, stability and redox behavior by means of UV-vis spectroscopy, NMR or cyclic voltammetry, whereas in DMSO/water, these Pt(iv) complexes transform into biologically less active cis[(NHC)PtX2(DMSO)] species, in the presence of a bioreductant such as glutathione which quickly leads to the formation of a biologically active trans[(NHC)PtX2L] complex. Overall, these data show that NHC-Pt(iv) compounds are good candidates as anti-cancer prodrugs.

N-Heterocyclic Carbene-Polyethyleneimine (PEI) Platinum Complexes Inducing Human Cancer Cell Death: Polymer Carrier Impact

The high interest in N-Heterocyclic platinum carbene complexes in cancer research stems from their high cytotoxicity to human cancer cells, their stability, as well as their ease of functionalization. However, the development of these new molecules as anticancer agents still faces multiple challenges, in particular solubility in aqueous media. Here, we synthesized platinum-NHC bioconjugates that combine water-solubility and cytotoxicity by using polyethyleneimine as polymer carrier. We showed on 8 different types of cells that the activity of these conjugates is modulated by the size of the polymer and the overall density of metal ions onto polymer chains. Using HCT116 cells, the conjugates displayed an effective activity after only 45 min of exposure in vitro correlated with a quick uptake by the cells as shown by the use of various fluorescent-tagged derivatives.

Combining imaging and anticancer properties with new heterobimetallic Pt(ii)/M(i) (M = Re, 99mTc) complexes

In this article, we report on the development of new metal-based anticancer agents with imaging, chemotherapeutic and photosensitizing properties. Hence, a new heterobimetallic complex (Pt-LQ-Re) was prepared by connecting a non-conventional trans-chlorido Pt(ii) complex to a photoactive Re tricarbonyl unit (LQ-Re), which can be replaced by ^99mTc to allow for in vivo imaging. We describe the photophysical and biological properties of the new complexes, in the dark and upon light irradiation (DNA interaction, cellular localization and uptake, and cytotoxicity). Furthermore, planar scintigraphic images of mice injected with Pt-LQ-Tc clearly showed that the radioactive compound is taken up by the excretory system organs, namely liver and kidneys, without significant retention in other tissues. All in all, the strategy of conjugating a chemotherapeutic compound with a PDT photosensitizer endows the resulting complexes with an intrinsic cytotoxic activity in the dark, driven by the non-classical platinum core, and a selective activity upon light irradiation. Most importantly, the possibility of integrating a SPECT imaging radiometal (^99mTc) in the structure of these new heterobimetallic complexes might allow for in vivo non-invasive visualization of their tumoral accumulation, a crucial issue to predict therapeutic outcomes.

Palladium(ii) and palladium(ii)-silver(i) complexes with N-heterocyclic carbene and zwitterionic thiolate mixed ligands: synthesis, structural characterization and catalytic properties

The integration of a geometrically rigid Pd(ii), a coordinatively monotonous N-heterocyclic carbene 1,3-dimethylimidazoline-2-ylidene (IMe), and a flexible zwitterionic thiolate 4-(trimethylammonio)benzenethiolate (Tab) affords a class of Pd-IMe-Tab complexes with various nuclearities, namely, trans-[Pd(IMe)₂(Tab)₂](OTf)₂ (2, mononuclear), cis-[Pd(IMe)₂(Tab)₂](OTf)(Cl) (3a, mononuclear), cis-[Pd(IMe)₂(Tab)₂](PF₆)₂·MeCN (3b·MeCN, mononuclear), [Pd₂(IMe)₄(Tab)₂](PF₆)₄·2MeCN (4·2MeCN, dinuclear) and [Pd₄(IMe)₄(Tab)₆](OTf)₆(Cl)₂ (5, tetranuclear). Further presence of Ag(i) in the assembly provides a heterometallic octanuclear cluster of [Pd₄Ag₄(IMe)₈(Tab)₁₀](PF₆)₁₂ (6). Compounds 2-6 are formed by the reaction of trans-Pd(IMe)₂Cl₂ (1) with various additional reagents via different reaction pathways. These compounds are characterized by means of FT-IR, ¹H and ¹³C NMR, ESI-MS, elemental analysis and X-ray crystallography. Notably, the skeleton of compound 5 features a [Pd₄S₄] parallelogram wherein each of the four Pd(ii) centers bisects the edge defined by the S atoms. The main skeleton of compound 6 is an oval-shaped Pd₄Ag₄S₁₀ unit, featuring an edge-fused norbornane-like (Pd₂Ag₄S₆) framework appended by two additional PdS₂ motifs at the polar positions. Compounds 5 and 6 also feature PdPd (5), PdAg and AgAg (6) interactions. Compound 5 as a representative example is highly effective at catalyzing Suzuki-Miyaura couplings in water, highlighting the potential of applying these types of homo- and heterometallic clusters as catalysts for organic transformations in environmentally benign media.

On the binding modes of metal NHC complexes with DNA secondary structures: implications for therapy and imaging

This perspective review aims at providing an overview of the most representative examples of bioactive metal NHC complexes reacting with nucleic acidsviadifferent binding modes.