Pt(II) versus Pt(IV) in Carbene Glycoconjugate Antitumor Agents: Minimal Structural Variations and Great Performance Changes

Exploring the effect of the axial ligands on the anticancer activity of [C,N,N'] Pt(IV) cyclometallated compounds

The synthesis of three novel [C,N,N'] Pt(IV) cyclometallated compounds containing hydroxo, dichloroacetato or trifluoroacetato axial ligands is reported. Compound [PtCl(OH)2{(CH3)2N(CH2)2NCH(4-FC6H3)}] (3) was prepared by the oxidative addition of hydrogen peroxide to [C,N,N'] Pt(II) cyclometallated compound [PtCl{(CH3)2N(CH2)2NCH(4-FC6H3)}] (1) and further the reaction of compound 3 with dichloroacetate or trifluoroacetate anhydrides led to the formation of the corresponding compounds [PtCl(CHCl2COO)2{(CH3)2N(CH2)2NCH(4-FC6H3)}] (4) and [PtCl(CF3COO)2{(CH3)2N(CH2)2NCH(4-FC6H3)}] (5). The properties of the new compounds along with those of the compound [PtCl3{(CH3)2N(CH2)2NCH(4-FC6H3)}] (2), including stability in aqueous media, reduction potential using cyclic voltammetry, cytotoxic activity against the HCT116 CRC cell line, DNA interaction, topoisomerase I and cathepsin inhibition, and computational studies involving reduction of the Pt(IV) compounds and molecular docking studies, are presented. Interestingly, the antiproliferative activity of these compounds against the HCT116 CRC cell line, which is in all cases higher than that of cisplatin, follows the same trend as the reduction potentials so that the most easily reduced compound 2 is the most potent. In contrast, according to the electrophoretic mobility and molecular docking studies, the efficacy of these compounds in binding to DNA is not related to their cytotoxicity. The most active compound 2 does not modify the DNA electrophoretic mobility while the less potent compound 3 is the most efficient in binding to DNA. Although compounds 2 and 3 have only a slight effect on cell cycle distribution and apoptosis induction, generation of ROS to a higher extent for the most easily reduced compound 2 was observed.

Synthesis, Structure and Anticancer Activity of a Dinuclear Organoplatinum(IV) Complex Stabilized by Adenine

The dinuclear organoplatinum(IV) compound {Pt(CH3)3}2(μ-I)2(μ-adenine) (abbreviated Pt2ad), obtained by treating cubic [Pt(CH3)3(μ3-I)]4 with two equivalents of adenine, was isolated and structurally characterized by single crystal X-ray diffraction. The National Cancer Institute Developmental Therapeutics Program's in vitro sulforhodamine B assays showed Pt2ad to be particularly cytotoxic against central nervous system cancer cell line SF-539, and human renal carcinoma cell line RXF-393. Furthermore, Pt2ad displayed some degree of cytotoxicity against non-small cell lung cancer (NCI-H522), colon cancer (HCC-2998, HCT-116, HT29, and SW-620), melanoma (LOX-IMVI, MALME-3M, M14, MDA-MB-435, SK-MEL-28, and UACC-62), ovarian cancer (OVCAR-5), renal carcinoma (A498), breast cancer (BT-549 and MDA-MB-468), and triple-negative breast cancer (MDA-MB-231).

Cytotoxic Pt(II) complexes containing alizarin: a selective carrier for DNA metalation

Many efforts have been made in the last few decades to selectively transport antitumor agents to their potential target sites with the aim to improve efficacy and selectivity. Indeed, this aspect could greatly improve the beneficial effects of a specific anticancer agent especially in the case of orphan tumors like the triple negative breast cancer. A possible strategy relies on utilizing a protective leaving group like alizarin as the Pt(II) ligand to reduce the deactivation processes of the pharmacophore enacted by Pt resistant cancer cells. In this study a new series of neutral mixed-ligand Pt(II) complexes bearing alizarin and a variety of diamine ligands were synthesized and spectroscopically characterized by FT-IR, NMR and UV-Vis analyses. Three Pt(II) compounds, i.e., 2b, 6b and 7b, emerging as different both in terms of structural properties and cytotoxic effects (not effective, 10.49 ± 1.21 μM and 24.5 ± 1.5 μM, respectively), were chosen for a deeper investigation of the ability of alizarin to work as a selective carrier. The study comprises the in vitro cytotoxicity evaluation against triple negative breast cancer cell lines and ESI-MS interaction studies relative to the reaction of the selected Pt(II) complexes with model proteins and DNA fragments, mimicking potential biological targets. The results allow us to suggest the use of complex 6b as a prospective anticancer agent worthy of further investigations.

Rational design of galactopyranoside-substituted N-heterocyclic carbene palladium(ii) complexes. Stable and efficient catalyst for C-C coupling in aqueous media

Following a rational design, three novel palladium(ii) complexes bearing galactopyranoside-based N-heterocyclic carbene ligands have been synthesized via transmetalation of the corresponding Ag(i) complexes. Palladium(ii) complexes have been characterized by NMR, FT-IR and elemental analysis. Catalytic studies, using the Stille and Suzuki-Miyaura cross-coupling reactions as model C-C coupling, reveal that the complexes are active and reusable. The best results in terms of TON values were achieved in aqueous medium using either the in situ deacetylation of the catalyst or the previously deacetylated catalyst. The catalytic condition using in situ deacetylation was more efficient because it avoids an additional deprotection step.

Einbau von (Bioaktiven) Äquatorialen Liganden in Platin(IV)-Komplexe

Platin(IV)‐Prodrugs sind aufgrund ihrer erhöhten Tumorselektivität und geringeren Nebenwirkungen äußerst interessante Alternativen zu Platin(II)‐Antitumortherapeutika. Im Gegensatz zur gängigen Theorie haben wir kürzlich beobachtet, dass äquatoriale Liganden von z. B. Oxaliplatin(IV)‐Komplexen unter Bildung von [(DACH)Pt(OHeq)2(OAcax)2] hydrolysiert werden können. In der hier vorgestellten Arbeit untersuchten wir die Reaktivität und synthetische Verwendbarkeit dieses Komplexes, als Vorstufe für die Entwicklung neuartiger Platin(IV)‐Komplexe, welche mit herkömmlichen Methoden nicht zugänglich sind. Tatsächlich war es möglich die äquatorialen Hydroxidoliganden z. B. durch ein oder zwei monodentate Biotin‐Liganden, die unter Standardmethoden oxidiert werden würden, zu ersetzen. Die gebildeten Komplexe erwiesen sich als sehr stabil und zeigten auch nach der Reduktion eine langsame Ligandenfreisetzung, eine ideale Eigenschaft für lang zirkulierende zielgerichtete Strategien. Daraufhin wurden zwei Platin(IV)‐Komplexe mit äquatorialen Maleimiden, für die Bindung an Serumalbumin als natürlichen Nanocarrier, synthetisiert. Die Komplexe zeigten im Vergleich zu Oxaliplatin eine stark verlängerte Plasmahalbwertszeit und eine deutlich verbesserte Antitumoraktivität in vivo. Zusammenfassend ermöglicht diese neu entwickelte Syntheseplattform den einfachen und gezielten Einbau äquatorialer Liganden in Platin(IV)‐Komplexe. Des Weiteren können verschiedene (bioaktive) Einheiten koordiniert werden, wodurch sogar zielgerichtete dreifach‐wirksame Platin(IV)‐Prodrugs mit nur einem Platinzentrum möglich wären.

Insertion of (Bioactive) Equatorial Ligands into Platinum(IV) Complexes

Platinum(IV) prodrugs are highly interesting alternatives to platinum(II) anticancer therapeutics due to their increased tumor selectivity and reduced side effects. In contrast to the established theory, we recently observed that the equatorial ligand(s) of e.g. oxaliplatin(IV) complexes can be hydrolyzed with formation of [(DACH)Pt(OHeq )2 (OAcax )2 ]. In the work presented here, we investigated the reactivity and synthetic usability of this complex to be exploited as a precursor for the development of novel platinum(IV) complexes, not able to be synthesized by conventional protocols. Indeed, we could substitute the equatorial hydroxido ligand(s) e.g. by one or two monodentate biotin ligands (which would be oxidized under standard methods). The formed complexes turned out to be very stable with slow ligand release after reduction, ideal for long-circulating tumor-targeting strategies. Therefore, two platinum(IV) complexes with equatorial maleimides, capable of exploiting serum albumin as a natural nanocarrier, were synthesized as well. The complexes showed massively prolonged plasma half-life and distinctly improved anticancer activity in vivo compared to oxaliplatin. Taken together, the newly developed synthetic platform allows the simple and specific insertion of equatorial ligands into platinum(IV) complexes. This will enable the attachment of three different (bioactive) moieties generating targeted triple-action platinum(IV) prodrugs within one single platinum complex.

The Role of Inverted Ligand Field in the Electronic Structure and Reactivity of Octahedral Formal Platinum (IV) Complexes

Platinum complexes are ubiquitous in chemistry and largely used as catalysts or as precursors in drug chemistry, thus a deep knowledge of their electronic properties may help in planning new synthetic strategies or exploring new potential applications. Herein, the electronic structure of many octahedral platinum complexes is drastically revised especially when they feature electronegative elements such as halogens and chalcogens. The investigation revealed that in most cases the five d platinum orbitals are invariably full, thus the empty antibonding orbitals, usually localized on the metal, are mainly centered on the ligands, suggesting a questionable assignment of formal oxidation state IV. The analysis supports the occurrence of the inverted ligand field theory in all cases with the only exceptions of the Pt-F and Pt-O bonding. The trends for the molecular complexes are mirrored also by the density of states plots of extended structures featuring octahedral platinum moieties in association with chalcogens atoms. Finally, the oxidative addition of a Se-Cl linkage to a square platinum complex to achieve an octahedral moiety has been revised in the framework of the inverted ligand field.

Anticancer Activity of Nonpolar Pt(CH3)2I2{bipy} is Found to be Superior among Four Similar Organoplatinum(IV) Complexes

The anticancer properties of well-defined molecules serve to bolster the field of metals in medicine. Such compounds, particularly those of platinum and their closely related structural analogs, continue to be potentially highly interesting to researchers and clinicians alike. The four octahedral organoplatinum(IV) compounds [Pt(CH3)2X2{bipy-R 2 }] (X = Br, I; bipy-R 2 = 2,2'-bipyridine, 2,2'-bipyridine-4,4'-dicarboxylic acid) have been isolated and structurally characterized by single-crystal X-ray diffraction. Nuclear magnetic resonance and infrared spectroscopic data are also tabulated as useful reference values. The anticancer potential of each compound was assessed via in vitro MTT assays, using human breast cancer cells (cell line ZR-75-1). EC50 values were determined as 11.5 μM for Pt(CH3)2Br2{bipy}; 3020 μM, for Pt(CH3)2Br2{bipy-(CO 2 H) 2 }; 6.1 μM, for Pt(CH3)2I2{bipy}; and 86.0 μM, for Pt(CH3)2I2{bipy-(CO 2 H) 2 }; for comparison, the EC50 value for cisplatin against the ZR-75-1 cells was 16.4 μM. The most cytotoxic of the four compounds Pt(CH3)2I2{bipy} undergoes reaction with glutathione in a THF/water mixture at 68°C very slowly.

Halo complexes of gold(i) containing glycoconjugate carbene ligands: synthesis, characterization, cytotoxicity and interaction with proteins and DNA model systems

New neutral Au(i) glycoconjugate carbene complexes show stability in aqueous solutions and interact with both DNA and protein model systems. Cytotoxicity studies demonstrate that the activity depends on the halide ancillary ligand.

Enhancing cisplatin anticancer effectivity and migrastatic potential by modulation of molecular weight of oxidized dextran carrier

The molecular weight (M_w) of dextran derivatives, such as regioselectively oxidized dicarboxydextran (DXA), is greatly influencing their faith in an organism, which could be possibly used to improve anticancer drug delivery. Here we present a modified method of sulfonation-induced chain scission allowing direct and accurate control over the M_w of DXA without increasing its polydispersity. Prepared DXA derivatives (M_w = 10-185 kDa) have been conjugated to cisplatin and the M_w of the carrier found to have a significant impact on cisplatin release rates, in vitro cytotoxicity, and migrastatic potential. Conjugates with the high-M_w DXA showed particularly increased anticancer efficacy. The best conjugate was four times more effective against malignant prostatic cell lines than free cisplatin and significantly inhibited the ovarian cancer cell migration. This was traced to the characteristics of spontaneously formed cisplatin-crosslinked DXA nanogels influenced by M_w of DXA and amount of loaded cisplatin.

Synthesis and evaluation of the anticancer activity of [Pt(diimine)(N,N-dibutyl-N'-acylthiourea)]+ complexes

Despite the concerted efforts to develop targeted cancer treatments, these therapies are plagued by the rapid development of resistance and serious adverse drug reactions. Based on the wide clinical use and successes of the platinum drugs like cisplatin and oxaliplatin, we investigated the synthesis and potential anticancer efficacy of alternative platinum complexes. A series of nine cationic square planar platinum(ii) complexes were synthesized and characterized and then evaluated for their anticancer activity. The complexes were of the type [Pt(diimine)(Ln-κO,S)]+ where diimine is either 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (dmp) or dipyrido[3,2-f:2',3'-h]quinoxaline (dpq) and Ln-κO,S representing various N,N-dibutyl-N'-acylthiourea ligands. The anticancer activity of the synthesised complexes was evaluated against two lung cancer cell lines (A549 and H1975) and a colorectal cancer cell line, HT-29. The 50% inhibitory concentrations (IC50) for the most cytotoxic compounds were determined and the mode of cell death evaluated. The structure-activity relationships indicated that complexes with the 5,6-dimethyl-1,10-phenanthroline variation of the diimine ligand were the most active against the cell lines tested, while the activity of complexes based on the acylthiourea ligand varied between the cell lines. IC50 values for the three active platinum complexes were in the low micromolar range for the three cell lines and ranged between 0.68 μM and 2.28 μM. Changes to cell morphology indicate that the active platinum complexes induce cell death by both apoptosis and paraptosis. The complexes were able to induce the nuclear expression of the cyclin-dependent kinase inhibitor, p21, which is an indicator of DNA damage. The collective data indicate that these platinum complexes are valuable lead compounds for further analysis and cancer drug discovery.

Role of ferroptosis in cisplatin-induced acute nephrotoxicity in mice

BACKGROUND

Cisplatin is widely used as an antitumor drug for the treatment of solid tumors. However, its use has been limited owing to nephrotoxicity, a major side effect. The mechanism of cisplatin-induced nephrotoxicity (CIN) has long been investigated in order to develop preventive/therapeutic drugs. Ferroptosis is a newly identified form of non-apoptotic regulated cell death induced by iron-mediated lipid peroxidation and is involved in the pathophysiology of various diseases. In this study, we examined the role of ferroptosis in CIN.

METHODS

We evaluated the role of ferroptosis in CIN by in vivo experiments in a mouse model.

RESULTS

Cisplatin increased the protein expressions of transferrin receptor-1 and ferritin, and iron content in the kidney of mice. In addition, treatment with cisplatin augmented renal ferrous iron and hydroxyl radical levels with co-localization. Mice administered cisplatin demonstrated kidney injury, with renal dysfunction and increased inflammatory cytokine expression; these changes were ameliorated by Ferrostatin-1 (Fer-1), an inhibitor of ferroptosis. The expression of the ferroptosis markers, COX2 and 4-hydroxynonenal (4-HNE), increased with cisplatin administration, and decreased with the administration of Fer-1. By contrast, cisplatin-induced apoptosis and necroptosis were inhibited by treatment with Fer-1. Moreover, deferoxamine, an iron chelator, also inhibited CIN, with a decrease in the expression of COX-2 and 4-HNE.

CONCLUSION

Ferroptosis is involved in the pathogenesis of CIN and might be used as a new preventive target for CIN.

Square-Planar vs. Trigonal Bipyramidal Geometry in Pt(II) Complexes Containing Triazole-Based Glucose Ligands as Potential Anticancer Agents

This article describes the synthesis, characterization, and biological activity of novel square-planar cationic platinum(II) complexes containing glucoconjugated triazole ligands and a comparison with the results obtained from the corresponding five-coordinate complexes bearing the same triazole ligands. Stability in solution, reactivity with DNA and small molecules of the new compounds were evaluated by NMR, fluorescence, and UV–vis absorption spectroscopy, together with their cytotoxic action against pairs of immortalized and tumorigenic cell lines. The results show that the square-planar species exhibit greater stability than the corresponding five-coordinate ones. Furthermore, although the square-planar complexes are less cytotoxic than the latter ones, they exhibit a certain selectivity. These results simultaneously demonstrate that overall stability is a fundamental prerequisite for preserving the performance of the agents and that coordinative saturation constitutes a point in favor of their biological action.

Synthesis and characterization of new Pd(ii) and Pt(ii) complexes with 3-substituted 1-(2-pyridyl)imidazo[1,5-a]pyridine ligands

Several palladium(ii) and platinum(ii) complexes (1-20) of general formula [M(Lⁿ)(X)(Y)] [M = Pd, X = Y = Cl (1-Cl-4-Cl), X = Y = OAc (1-OAc-4-OAc); M = Pt: X = Y = Cl (5-8); M = Pd, X = Cl, Y = CH₃ (9-12); M = Pt, X = Cl, Y = CH₃ (13-16) or X = Y = CH₃ (17-20); n = 1-4] have been synthesized by reaction of different Pd(ii) and Pt(ii) derivatives with various 3-substituted 1-(2-pyridyl)-imidazo[1,5-a]pyridines; i.e.Lⁿ = 1-(2-pyridyl)-3-arylimidazo[1,5-a]pyridine (aryl = Phenyl, L¹; 2-o-Tolyl, L²; Mesityl, L³) and 1-(2-pyridyl)-3-benzylimidazo[1,5-a]pyridine (L⁴). Detailed spectroscopic investigation (including IR, mono- and bi-dimensional ¹H NMR) and elemental analysis has been performed for all these species, allowing their complete characterization. Lⁿ act as N,N-bidentate ligands and coordinate the metal centers in a chelate fashion through the pyridyl (N_py) and the pyridine-like nitrogen atom of the imidazo[1,5-a]pyridine group (N_im). The X-ray structural analysis performed on two of Pd(ii) and three Pt(ii) complexes, namely [Pd(L²)(CH₃)Cl] (10), [Pd(L³)(CH₃)Cl] (11) and [Pt(L¹)Cl₂] (5), [Pt(L⁴)Cl₂] (8), [Pt(L²)(CH₃)Cl] (14) confirmed the spectroscopic and analytical data. Finally DFT studies unveiled the structural reasons behind the inertia of the synthesised compounds toward metalation, identified as the higher angle steric strain in comparison with the analogous bipyridine complexes.

Arsenoplatin-Ferritin Nanocage: Structure and Cytotoxicity

Arsenoplatin-1 (AP-1), the prototype of a novel class of metallodrugs containing a PtAs(OH)₂ core, was encapsulated within the apoferritin (AFt) nanocage. UV-Vis absorption spectroscopy and inductively coupled plasma-atomic emission spectroscopy measurements confirmed metallodrug encapsulation and allowed us to determine the average amount of AP-1 trapped inside the cage. The X-ray structure of AP-1-encapsulated AFt was solved at 1.50 Å. Diffraction data revealed that an AP-1 fragment coordinates the side chain of a His residue. The biological activity of AP-1-loaded AFt was comparatively tested on a few representative cancer and non-cancer cell lines. Even though the presence of the cage reduces the overall cytotoxicity of AP-1, it improves its selectivity towards cancer cells.

On the hydrolytic stability of unsymmetric platinum(iv) anticancer prodrugs containing axial halogens

The hydrolytic stability of Pt(iv) complexes is determined by all the six ligands that coordinate to the Pt(iv) center. By appropriately choosing all the ligands during the design of Pt(iv) prodrugs, the stability of Pt(iv) prodrugs can be improved.

Synthesis and Biological Studies on Dinuclear Gold(I) Complexes with Di-(N-Heterocyclic Carbene) Ligands Functionalized with Carbohydrates

The design of novel metal complexes with N-heterocyclic carbene (NHC) ligands that display biological activity is an active research field in organometallic chemistry. One of the possible approaches consists of the use of NHC ligands functionalized with a carbohydrate moiety. Two novel Au(I)–Au(I) dinuclear complexes were synthesized; they present a neutral structure with one bridging diNHC ligand, having one or both heterocyclic rings decorated with a carbohydrate functionality. With the symmetric diNHC ligand, the dicationic dinuclear complex bearing two bridging diNHC ligands was also synthesized. The study was completed by analyzing the antiproliferative properties of these complexes, which were compared to the activity displayed by similar mononuclear Au(I) complexes and by the analogous bimetallic Au(I)–Au(I) complex not functionalized with carbohydrates.