A positively charged trinuclear 3N-chelated monofunctional platinum complex with high DNA affinity and potent cytotoxicity

A novel benzothiazole-based mononuclear platinum(II) complex displaying potent antiproliferative activity in HepG-2 cells via mitochondrial-mediated apoptosis

A novel mononuclear platinum(II) complex, [Pt(L-H)Cl] (1, where L= N-(4-(benzo[d]thiazol-2-yl)phenyl)-2-((2-pyridylmethyl)(2-hydroxyethyl)-amino)acetamide), was obtained by covalently tethering a benzothiazole derivative 2-(4-aminophenyl)benzothiazole to the 2-pyridylmethyl-2-hydroxyethylamine chelating PtII center. In vitro tests indicated that complex 1 displayed excellent antiproliferative activity against the tested cancer cell lines, especially liver cancer HepG-2 and SMMC-7221 cells. Importantly, the complex possessed 4.33-fold higher antiproliferative activity as compared with cisplatin against HepG-2 cells, but was less toxic to the normal cell line L02 with the selectivity index (SI = IC50(L02)/IC50(HepG-2)) value of 8.36 compared to cisplatin (SI, 1.40). The results suggested that 1 might have the potential to act as a candidate for the treatment of hepatocellular carcinoma (HCC). Cellular uptake and distribution studies showed that 1 could effectively pass through the membrane of cells, enter the nuclei and mitochondria, induce the platination of cellular DNA. The interaction of 1 with CT-DNA demonstrated that 1 could effectively bind to DNA in a dual binding mode, i.e., the intercalation of the 2-(4-aminophenyl)benzothiazole unit plus monofunctional platination of the platinum(II) moiety. In addition, Hoechst 33342 staining and flow cytometry analysis illustrated that 1 arrested the cell cycle in HepG-2 cancer cells at G2/M phases, induced mitochondrial membrane depolarization, increased ROS generation, and caused obvious cell apoptosis. Further cellular mechanism studies elucidated that 1 triggered HepG-2 cell apoptosis via the mitochondrial-mediated pathway by upregulating the gene and protein expression levels of Bax, downregulating the gene and protein expression levels of Bcl-2, and activating the caspase cascade.

A novel star-shaped trinuclear platinum(II) complex based on a 1,3,5-triazine core displaying potent antiproliferative activity against TNBC by the mitochondrial injury and DNA damage mechanism

Polynuclear platinum(II) complexes represent a class of great prospective Pt-based antitumor drugs that may expand the antitumor spectrum and overcome the clinical problems of drug resistance and side effects of platinum-based drugs. Herein, a novel star-shaped trinuclear platinum(II) complex [Pt₃(L-3H)Cl₃] (1, L = 2,4,6-tris[(2-hydroxybenzyl)(2-pyridylmethyl)amine]-1,3,5-triazine) and its monomer [Pt(L'-H)Cl] (2, L' = (2-hydroxybenzyl)(2-pyridylmethyl)amine) were synthesized and characterized. The in vitro antiproliferative activities of complexes 1 and 2 against a panel of human cancer cell lines including MDA-MB-231 (triple-negative breast cancer, TNBC), MCF-7 (breast), HepG-2 (liver), and A549 (lung) were investigated. The results revealed that 1 exhibited much higher antiproliferative properties than its monomer 2 against the tested cell lines. Importantly, 1 possessed 3.3-fold higher antiproliferative activity as compared with cisplatin against the TNBC cell line MDA-MB-231. Another TNBC cell line MDA-MB-468 is also sensitive to 1. The results indicated that 1 might have the potential to act as a candidate for the treatment of TNBC. Cellular uptake and distribution studies showed that 1 could pass through the membrane of cells and enter into cells and mainly accumulate in the nuclei and mitochondria. 1 could bind to DNA in a cooperative groove-electrostatic-platinating binding mode and induce stronger DNA double-strand breaks (DSBs) and damaging effects on MDA-MB-231 than cisplatin (upregulation of γ-H2AX). Moreover, the DNA damage could not be easily repaired (upregulation of p53), which would exert a much positive influence on the overcoming of drug resistance. Additionally, flow cytometry studies showed that 1 arrested the cell cycle in the G0/G1 phase, induced mitochondrial membrane depolarization, increased ROS generation, and induced cell apoptosis. The results demonstrated that 1 could target simultaneously mitochondria and nuclei that gave rise to mitochondrial injury and DNA damage and ultimately efficiently promote the apoptotic death of tumor cells. Further mechanistic studies showed that 1 induced MDA-MB-231 cell apoptosis via the p53-mediated mitochondrial pathway by upregulating Bax and cytochrome c and downregulating Bcl-2 proteins, leading to the activation of caspase-3 and upregulation of the cleaved-PARP level. Taken together, 1 with such a synergic mechanism has great potential to be an effective anticancer agent that can overcome treatment resistance in TNBC.

Linear Bidentate Ligands (L) with Two Terminal Pyridyl N-Donor Groups Forming Pt(II)LCl2 Complexes with Rare Eight-Membered Chelate Rings

NMR and X-ray diffraction studies were conducted on Pt(II)LCl₂ complexes prepared with the new N-donor ligands N(SO₂R)Me _ndpa (R = Me, Tol; n = 2, 4). These ligands differ from N(H)dpa (di-2-picolylamine) in having the central N within a tertiary sulfonamide group instead of a secondary amine group and having Me groups at the 6,6'-positions ( n = 2) or 3,3',5,5'-positions ( n = 4) of the pyridyl rings. The N(SO₂R)3,3',5,5'-Me₄dpa ligands are coordinated in a bidentate fashion in Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes, forming a rare eight-membered chelate ring. The sulfonamide N atom did not bind to Pt(II), consistent with indications in the literature that tertiary sulfonamides are unlikely to anchor two meridionally coordinated five-membered chelate rings in solutions of coordinating solvents. The N(SO₂R)6,6'-Me₂dpa ligands coordinate in a monodentate fashion to form the binuclear complexes [ trans-Pt(DMSO)Cl₂]₂( N(SO₂R)6,6'-Me₂dpa). The monodentate instead of bidentate N(SO₂R)6,6'-Me₂dpa coordination is attributed to 6,6'-Me steric bulk. These binuclear complexes are indefinitely stable in DMF- d₇, but in DMSO- d₆ the N(SO₂R)6,6'-Me₂dpa ligands dissociate completely. In DMSO- d₆, the bidentate ligands in Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes also dissociate, but incompletely; these complexes provide rare examples of association-dissociation equilibria of N,N bidentate ligands in Pt(II) chemistry. Like typical cis-PtLCl₂ complexes, the Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes undergo monosolvolysis in DMSO- d₆ to form the [Pt( N(SO₂R)3,3',5,5'-Me₄dpa)(DMSO- d₆)Cl]⁺ cations. However, unlike typical cis-PtLCl₂ complexes, the Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes surprisingly do not react readily with the excellent N-donor bioligand guanosine. A comparison of the structural features of over 50 known relevant Pt(II) complexes having smaller chelate rings with those of the very few relevant Pt(II) complexes having eight-membered chelate rings indicates that the pyridyl rings in Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes are well positioned to form strong Pt-N bonds. Therefore, the dissociation of the bidentate ligand and the poor biomolecule reactivity of the Pt( N(SO₂R)3,3',5,5'-Me₄dpa)Cl₂ complexes arise from steric consequences imposed by the -CH₂-N(SO₂R)-CH₂- chain in the eight-membered chelate ring.

A new class of platinum(ii) complexes with the phosphine ligand pta which show potent anticancer activity

A series of 16 Pt(ii) complexes with 8-hydroxyquinolines and sulfoxide/phosphine ligands were synthetized, characterized and evaluated for cytotoxic and embryotoxic activity.

Bifunctional Platinum(II) Complexes with Bisphosphonates Substituted Diamine Derivatives: Synthesis and In vitro Cytotoxicity

A series of N,N'-dibisphosphonate-containing 1,3-propanediamine derivatives (L1 - L6) and their corresponding dichloridoplatinum(II) complexes (1 - 6) have been synthesized and characterized by elemental analysis, ¹ H-NMR, ¹³ C-NMR, ³¹ P-NMR and HR-MS spectra. The in vitro antitumor activities of compounds L1 - L6 and 1 - 6 were tested by WST-8 assay with Cell Counting Kit-8, indicating that platinum-based complexes 1 - 6 showed higher cytotoxicity than corresponding ligands L1 - L6 against A549 and MG-63, especially complex 2 which displayed comparable cytotoxicity to those of cisplatin and zoledronate after 48 h incubation. In addition, complexes 1 - 6 were more active in vitro on osteosarcoma cell line MG-63 than normal osteoblast cell line hFOB 1.19. The structure-activity relationship has been summarized based on the in vitro cytotoxicity of three series of platinum complexes from this and our previous studies. The in vitro bone affinity of platinum complexes was also tested by hydroxyapatite (HAP) chromatography in terms of capacity factor K'. Besides, in this paper, representative complex 2, which has been proved to be a promising antitumor agent with high cytotoxicity and bone HAP binding property, was investigated for its mechanism of action producing cell death against MG-63.

Research progress in modern structure of platinum complexes

Since the antitumor activity of cisplatin was discovered in 1967 by Rosenberg, platinum-based anticancer drugs have played an important role in chemotherapy in clinic. Nevertheless, platinum anticancer drugs also have caused severe side effects and cross drug resistance which limited their applications. Therefore, a significant amount of efforts have been devoted to developing new platinum-based anticancer agents with equal or higher antitumor activity but lower toxicity. Until now, a large number of platinum-based complexes have been prepared and extensively investigated in vitro and in vivo. Among them, some platinum-based complexes revealing excellent anticancer activity showed the potential to be developed as novel type of anticancer agents. In this account, we present such platinum-based anticancer complexes which owning various types of ligands, such as, amine carrier ligands, leaving groups, reactive molecule, steric hindrance groups, non-covalently binding platinum (II) complexes, Platinum(IV) complexes and polynuclear platinum complexes. Overall, platinum-based anticancer complexes reported recently years upon modern structure are emphasized.

Enhanced anti-cancer efficacy to cancer cells by a novel monofunctional mononuclear platinum(ii) complex containing a mixed S,N,S-donor ligand

A novel platinum–intercalator hybrid complex (1) exhibits a cytotoxicity comparable to that of cisplatin against MCF-7 cell lines, and more potent activities against HeLa and A-549 cell lines, especially against the former.

Preparation and Biological Evaluation of Two Novel Platinum(II) Complexes Based on the Ligands of Dipicolyamine Bisphosphonate Esters

Two new platinum(II)-based complexes bearing a bone-targeting group were synthesized and characterized. They both have excellent affinity for hydroxyapatite (HA), which is abundant in human bone tissues. Their antitumor activities against five human cancer cell lines (U2OS, A549, HCT116, MDA-MB-231 and HepG2) were evaluated and compared with cisplatin (CDDP). Though the antitumor efficacies of new complexes are lower than that of CDDP, they show higher selectivity against the HepG2 hepatoma cell line than the L02 normal liver cell line. Morphology studies exhibited typical characteristics of cell apoptosis and the cell cycle distribution analysis indicated that the complexes can inhibit cancer cells by inducing cell cycle arrest at the G2/M phase, a similar mechanism of action to CDDP.

Affinity of a mononuclear monofunctional anticancer Pt(II) complex to human serum albumin: a spectroscopic approach

The interaction of a mononuclear monofunctional anticancer Pt(II) complex, [PtLCl]Cl (L = 4′-bis(pyridine-2-ylmethyl)amino-2-phenylbenzothiazole) (1), and human serum albumin (HSA) was investigated under physiological conditions using UV–Vis absorption, circular dichroism, fluorescence, and synchronous fluorescence. The experimental results suggested that the Pt(II) complex could bind to HSA, induce conformation and microenvironmental changes of HSA with a moderate binding affinity, and quench the intrinsic fluorescence of HSA through a static quenching mechanism. The thermodynamic parameters, ΔG°, ΔH°, and ΔS°, calculated at different temperatures, indicated that the binding reaction was spontaneous and hydrophobic forces and π–π stacking played major roles in the association. Based on the number of binding sites, it was considered that one molecule of complex 1 could bind to a single site of HSA. In view of the results of site marker competition experiments, the reactive site of HSA to complex 1 mainly located in subdomain IIA (site I). Moreover, the binding distance, r, between donor (HSA) and acceptor (complex 1) was 4.69 nm according to Förster nonradiation energy transfer theory. The present study provides relevant and useful information that can be used for the design and application of mononuclear monofuctional Pt(II) complexes in biomedical sciences.

Synthesis and evaluation of series of diazine-bridged dinuclear platinum(II) complexes through in vitro toxicity and molecular modeling: correlation between structure and activity of Pt(II) complexes

Polynuclear Pt(II) complexes are a novel class of promising anticancer agents with potential clinical significance. A series of pyrazine (pz) bridged dinuclear Pt(II) complexes with general formulas {[Pt(L)Cl]2(μ-pz)}(2+) (L, ethylenediamine, en; (±)-1,2-propylenediamine, 1,2-pn; isobutylenediamine, ibn; trans-(±)-1,2-diaminocyclohexane, dach; 1,3-propylenediamine, 1,3-pd; 2,2-dimethyl-1,3-propylenediamine, 2,2-diMe-1,3-pd) and one pyridazine (pydz) bridged {[Pt(en)Cl]2(μ-pydz)}(2+) complex were prepared. The anticancer potential of these complexes were determined through in vitro cytotoxicity assay in human fibroblasts (MRC5) and two carcinoma cell lines (A375 and HCT116), interaction with double stranded DNA through in vitro assay, and molecular docking study. All complexes inhibited cell proliferation with inhibitory concentrations in the 0.5-120 μM range. While {[Pt(1,3-pd)Cl]2(μ-pz)}(2+) showed improved activity and {[Pt(en)Cl]2(μ-pydz)}(2+) showed comparable activity to that of clinically relevant cisplatin, {[Pt(en)Cl]2(μ-pydz)}(2+) was less toxic in an assay with zebrafish (Danio rerio) embryos, causing no adverse developmental effects. The in vitro cytotoxicity of all diazine-bridged dinuclear Pt(II) complexes is discussed in correlation to their structural characteristics.

Syntheses, crystal structures and antimicrobial activities of Cu(ii), Ru(ii), and Pt(ii) compounds with an anthracene-containing tripodal ligand

Three new Cu(ii), Ru(ii), and Pt(ii) compounds of an anthracene-containing tripodal ligand were synthesized. Their crystal structures was determined by a single-crystal X-ray diffraction method and their antimicrobial activities were investigated.

New heteronuclear gold(I)-platinum(II) complexes with cytotoxic properties: are two metals better than one?

A series of mono- and heterodinuclear gold(I) and platinum(II) complexes with a new bipyridylamine-phosphine ligand have been synthesized and characterized. The X-ray structures of the ligand precursor 4-iodo-N,N-di(pyridin-2-yl)benzamide, and of one gold derivative are reported. All the complexes display antiproliferative properties in vitro in human cancer cells in the range of cisplatin or higher, which appear to correlate with compounds' uptake. Interestingly, studies of the interactions of the compounds with models of DNA indicate different mechanisms of actions with respect to cisplatin. The biological activity study of these complexes provides useful information about the interest of designing multimetallic complexes for enhanced cytotoxic properties.

Metal-based anticancer chemotherapeutic agents

Since the discovery of the cisplatin antitumor activity, great efforts have focused on the rational design of metal-based anticancer agents that can be potentially used in cancer chemotherapy. Over the last four decades, a large number of metal complexes have been extensively investigated and evaluated in vitro and in vivo, and some of them were at different stages of clinical studies. Amongst these complexes, platinum (Pt(II) and Pt(IV)), ruthenium (Ru(II) and Ru(III)), gold (Au(I) and Au(III)) and titanium (Ti(IV)) complexes are the most studied metals. We describe here some most recent progresses on Pt(IV) prodrugs which can be activated once enter tumor cells, polynuclear Pt(II) complexes which have unique DNA binding ability and mode, anti-metastatic Ru(II)/Ru(III) complexes, and Au(I)/Au(III) and Ti(IV) antitumor active complexes. The key focuses of these studies lie in finding novel metal complexes which could potentially overcome the hurdles of current clinical drugs including toxicity, resistance and other pharmacological deficiencies.

Toxicity in tumor cells, DNA binding mode, and resistance to decomposition by sulfur nucleophiles of new dinuclear bifunctional trans-PtII complexes containing long alkane linkers

In an effort to design dinuclear PtII compounds that maintain the target (DNA) binding profile of the trans-oriented dinuclear bifunctional PtII complexes containing aliphatic linker chains but are less susceptible to metabolic decomposition, the new, long-chain dinuclear PtII complexes—[{trans-PtCl(dien)}2-μ-(CH2)n]2+ (n = 7,10,12, dien = diethylenetriamine)—were synthesized. The toxicity of these metallodrugs was examined in ovarian tumor cell lines. The results showed that the activity of these complexes increased with growing length of the linker; the activity of complex containing the longest linker (n = 12) was comparable with that of cis-diamminedichloridoplatinum(II) (cisplatin). This observation correlated with the results of DNA binding studies performed in cell-free media. The results of these studies demonstrated that the growing length of the aliphatic bridge promoted more distorting conformational alterations induced in DNA. Attention was also paid to the reactivity of {[Pt(dien)Cl]2-alkane} compounds with glutathione (GSH). The results of these experiments support the thesis that the dinuclear structure of {[Pt(dien)Cl]2-alkane} complexes remains stable in the presence of S-containing compounds without undergoing chemical degradation as previously observed for some di/trinuclear bifunctional PtII complexes. This enhanced stability represents a favorable property which may contribute to reduce side effects and increase therapeutic efficacy of the dinuclear {[Pt(dien)Cl]2-alkane} compounds.

Platinum(II) compounds bearing bone-targeting group: synthesis, crystal structure and antitumor activity

Platinum(II) complexes bearing geminal bisphosphonate moieties have excellent solubility in both organic and aqueous solutions and show considerable cytotoxicity against human osteosarcoma (MG-63) and ovarian cancer (COC1) cell lines with different apoptotic pathways from that of cisplatin.

Non-traditional platinum compounds for improved accumulation, oral bioavailability, and tumor targeting

The five platinum anticancer compounds currently in clinical use conform to structure-activity relationships formulated (M. J. Cleare and J. D. Hoeschele, Bioinorg. Chem., 1973, 2, 187-210) shortly after the discovery that cis-diamminedichloroplatinum(II), cisplatin, has antitumor activity in mice. These compounds are neutral platinum(II) species with two am(m)ine ligands or one bidentate chelating diamine and two additional ligands that can be replaced by water through aquation reactions. The resulting cations ultimately form bifunctional adducts on DNA. Information about the chemistry of these platinum compounds and correlations of their structures with anticancer activity have provided guidance for the design of novel anticancer drug candidates based on the proposed mechanisms of action. This article discusses advances in the synthesis and evaluation of such non-traditional platinum compounds, including cationic and tumor-targeting constructs.

Differences in conformational dynamics of [Pt3(HPTAB)]6+-DNA adducts with various cross-linking modes

We present here molecular dynamics simulations and DNA conformational dynamics for a series of trinuclear platinum [Pt₃(HPTAB)]⁶⁺-DNA adducts [HPTAB = N,N,N′,N′,N′′,N′′-hexakis (2-pyridyl-methyl)-1,3,5-tris(aminomethyl) benzene], including three types of bifunctional crosslinks and four types of trifunctional crosslinks. Our simulation results reveal that binding of the trinuclear platinum compound to a DNA duplex induces the duplex unwinding in the vicinity of the platination sites, and causes the DNA to bend toward the major groove. As a consequence, this produces a DNA molecule whose minor groove is more widened and shallow compared to that of an undamaged bare-DNA molecule. Notably, for trifunctional crosslinks, we have observed extensive DNA conformational distortions, which is rarely seen for normal platinum–DNA adducts. Our findings, in this study, thus provide further support for the idea that platinum compounds with trifunctional intra-strand or long-range-inter-strand cross-linking modes can generate larger DNA conformational distortions than other types of cross-linking modes.

Mixed-Ligand Copper(II)-phenolate Complexes: Effect of Coligand on Enhanced DNA and Protein Binding, DNA Cleavage, and Anticancer Activity

The copper(II) complex [Cu(tdp)(ClO4)].0.5H2O (1), where H(tdp) is the tetradentate ligand 2-[(2-(2-hydroxyethylamino)ethylimino)methyl]phenol, and the mixed ligand complexes [Cu(tdp)(diimine)]+ (2-5), where diimine is 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp) (4), and dipyrido-[3,2-d:2',3'-f]-quinoxaline (dpq) (5), have been isolated and characterized by analytical and spectral methods. Complexes 1 and [Cu(tdp)(phen)]ClO4 (3) have been structurally characterized, and their coordination geometries around copper(II) are described as distorted octahedral. The equatorially coordinated ethanolic oxygen in 1 is displaced to an axial position upon incorporating the strongly chelating phen, as in 3. The solution structures of all the complexes have been assessed to be square-based using electronic absorption and electron paramagnetic resonance (EPR) spectroscopy. The interaction of the complexes with calf thymus DNA (CT DNA) has been explored by using absorption, emission, and circular dichroic spectral and viscometric studies, and modes of DNA binding for the complexes have been proposed. Absorption spectral (Kb = 0.071 +/- 0.005 (2), 0.90 +/- 0.03 (3), 7.0 +/- 0.2 (4), 9.0 +/- 0.1 x 10(5) M(-1) (5)), emission spectral (Kapp = 4.6 (1), 7.8 (2), 10.0 (3), 12.5 (4), 25.0 x 10(5) M(-1) (5)), and viscosity measurements reveal that 5 interacts with DNA more strongly than the other complexes through partial intercalation of the extended planar ring of the coordinated dpq with the DNA base stack. Interestingly, only complex 4 causes a B to A conformational change upon binding DNA. All the complexes hydrolytically cleave pBR322 supercoiled DNA in 10% DMF/5 mM Tris-HCl/50 mM NaCl buffer at pH 7.1 in the absence of an activating agent, and the cleavage efficiency varies in the order 5 > 3 > 2 > 4 > 1 with 5 displaying the highest Kcat value (5.47 +/- 0.10 h(-1)). The same order of cleavage is observed for the oxidative cleavage of DNA in the presence of ascorbic acid as a reducing agent. Interestingly, of all the complexes, only 5 displays efficient photonuclease activity through double-strand DNA breaks upon irradiation with 365 nm light through a mechanistic pathway involving hydroxyl radicals. The protein binding ability of 1-5 has been also monitored by using the plasma protein bovine serum albumin (BSA), and 4 exhibits a protein binding higher than that of the other complexes. Further, the anticancer activity of the complexes on human cervical epidermoid carcinoma cell line (ME180) has been examined. Interestingly, the observed IC50 values reveal that complex 4, which effects conformational change on DNA and binds to BSA more strongly, exhibits a cytotoxicity higher than the other complexes. It also exhibits approximately 100 and 6 times more potency than cisplatin and mitomycin C for 24 and 48 h incubation times, respectively, suggesting that 4 can be explored further as a potential anticancer drug. Complexes 4 and 5 mediate the arrest of S and G2/M phases in the cell cycle progression at 24 h harvesting time, which progress into apoptosis.