Chiral cyclopalladated complexes derived from N,N-dimethyl-1-phenethylamine with bridging bis(diphenylphosphine)ferrocene ligand as inhibitors of the cathepsin B activity and as antitumoral agents

Palladium (II) compounds containing oximes as promising antitumor agents for the treatment of osteosarcoma: An in vitro and in vivo comparative study with cisplatin

Drug resistance, evasion of cell death and metastasis are factors that contribute to the low cure rate and disease-free survival in osteosarcomas (OS). In this study, we demonstrated that a new class of oxime-containing organometallic complexes called Pd-BPO (O3) and Pd-BMO (O4) are more cytotoxic than cisplatin (CDDP) for SaOS-2 and U2OS cells using the MTT assay. Annexin-FITC/7-AAD staining demonstrated a greater potential for palladium-oxime complexes to induce death in SaOS-2 cells than CDDP, an event confirmed using the pan-caspase inhibitor Z-VAD-FMK. Compared to CDDP, only palladium-oxime complexes eradicated the clonogenicity of SaOS-2 cells after 7 days of treatment. The involvement of the lysosome-mitochondria axis in the cell death-inducing properties of the complexes was also evaluated. Using LysoTracker Red to label the acidic organelles of SaOS-2 cells treated with the O3 and O4 complexes, a decrease in the fluorescence intensity of this probe was observed in relation to CDDP and the control. Lysosomal membrane permeabilization (LMP) was also induced by the O3 and O4 complexes in an assay using acridine orange (A/O). The greater efficiency of the complexes in depolarizing the mitochondrial membrane compared to SaOS-2 cells treated with CDDP was also observed using TMRE (tetramethyl rhodamine, ethyl ester). For in vivo studies, C. elegans was used and demonstrated that both complexes reduce body bends and pharyngeal pumping after 24 h of treatment to the same extent as CDDP. We conclude that both palladium-oxime complexes are more effective than CDDP in inducing tumor cell death. The toxicity of these complexes to C. elegans was like that induced by CDDP. These results encourage preclinical studies aimed at developing more effective drugs for the treatment of osteosarcoma (OS). Furthermore, we propose palladium-oxime complexes as a new class of antineoplastic agents.

Dimeric Drugs

This review intends to summarize the structures of an extensive number of symmetrical-dimeric drugs, having two monomers linked via a bridging entity while emphasizing the large versatility of biologically active substances reported to possess dimeric structures. The largest number of classes of these compounds consist of anticancer agents, antibiotics/antimicrobials, and anti-AIDS drugs. Other symmetrical-dimeric drugs include antidiabetics, antidepressants, analgesics, anti-inflammatories, drugs for the treatment of Alzheimer's disease, anticholesterolemics, estrogenics, antioxidants, enzyme inhibitors, anti-Parkisonians, laxatives, antiallergy compounds, cannabinoids, etc. Most of the articles reviewed do not compare the activity/potency of the dimers to that of their corresponding monomers. Only in limited cases, various suggestions have been made to justify unexpected higher activity of the dimers vs. the corresponding monomers. These suggestions include statistical effects, the presence of dimeric receptors, binding of a dimer to two receptors simultaneously, and others. It is virtually impossible to predict which dimers will be preferable to their respective monomers, or which linking bridges will lead to the most active compounds. It is expected that the extensive number of articles summarized, and the large variety of substances mentioned, which display various biological activities, should be of interest to many academic and industrial medicinal chemists.

Experimental and theoretical studies of Palladium-hydrazide complexes' interaction with DNA and BSA, in vitro cytotoxicity activity and plasmid cleavage ability

New palladium complexes with general formula trans-[Pd(L)₂(OAc)₂] (1,2), (L = Benzhydrazide and 2-Furoic hydrazide) have been synthesized and characterized with various methods including elemental analysis, FT-IR, ¹HNMR and mass spectroscopy. Afterward their interactions with bovine serum albumin and calf thymus deoxyribonucleic acid have been investigated by UV-vis absorption, fluorescence emission and circular dichroism spectroscopy. Also, site-selective replacement experiments with site probes have been carried out. Analysis of fluorescence spectrum indicated static quenching mechanism. Spectroscopic measurements for DNA binding showed the groove binding to DNA for both complexes. Furthermore, cytotoxicity studies of complexes and cis-platin have been done against colon carcinoma (CT26) and breast cancer (4T1) cell lines. Evaluation of complexes (1) and (2) on induction of apoptosis in CT26 cells has been done. Finally, plasmid cleavage ability of (1) and (2) was investigated by gel electrophoresis that indicate the more activity of (1) than (2).

Novel P,C-orthopalladated complexes containing histidine and phenylalanine amino acids: synthesis, DNA and BSA interactions, in vitro antitumoral activity and molecular docking approach

Novel [Pd(o-CH₂C₆H₄P(o-tolyl)₂)(histidine)] (1) and [Pd(o-CH₂C₆H₄P(o tolyl)₂)(phenylalanine)] (2) P,C-orthopalladated complexes have been prepared and characterized by elemental analysis, IR and NMR spectroscopy. To study the stability of the compounds in biological media, the complexes were incubated in Tris buffer during 10 days. The absorbance of the compounds remained constant, which confirmed the stability of the complexes in biological media. UV-Vis absorption spectrophotometry, fluorescence spectroscopy and viscosity studies were used to investigate the binding of the complexes with native calf thymus DNA (CT-DNA). These methods along with competitive binding of methylene blue (MB) DNA show that the complexes interact with DNA via groove mode. The UV-Vis absorption spectrophotometry of BSA with complexes has shown an α-helix perturbation induced by a particular interaction between the metal complexes and BSA. In addition, the fluorescence quenching mechanism of BSA with the complexes is a static process, according to the fluorescence spectrometry of bovine serum albumin (BSA). The experimental results of site competitive replacement with specific site markers are clear indications that the complexes bind to site I of BSA. Furthermore, both complexes showed significant selective cytotoxic activity against melanoma B16F0 and colon carcinoma C26 cancer cells as well as normal fibroblast NIH cell line. Ultimately, the binding of Pd(II) complexes to DNA and BSA was verified by molecular docking experiment.Communicated by Ramaswamy H. Sarma.

Palladium(ii) complexes bearing 1-iminothiolate-3,5-dimethylpyrazoles: synthesis, cytotoxicity, DNA binding and enzymatic inhibition studies

This work describes the enzymatic inhibitory activity of four novel Pd(ii) complexes towards topoisomerase IIα and cathepsins B and L.In silicostudies agree well with the enhancedin vitrocathepsin B inhibition induced by compound4(58% at 10 μM).

Cyclopalladated compounds containing 2,6-lutidine: Synthesis, spectral and biological studies

Bridge splitting reactions between [Pd(C²,N-dmba)(μ-X)]₂ (dmba = N,N-dimethylbenzylamine; X = Cl, I, N₃, NCO) and 2,6-lutidine (lut) in the 1:2 molar ratio at room temperature afforded cyclopalladated compounds of general formulae [Pd(C²,N-dmba)(X)(lut)] {X = Cl^- (1), I^-(2), NNN^-(3), NCO^-(4)}, which were characterized by elemental analyses and infrared (IR), ¹H NMR spectroscopy. The molecular structures of all synthesized palladacycles have been solved by single-crystal X-ray crystallography. The cytotoxicity of the cyclopalladated compounds has been evaluated against a panel of murine {mammary carcinoma (4T1) and melanoma (B16F10-Nex2)} and human {melanoma (A2058, SK-MEL-110 and SK-MEL-5) tumor cell lines. All complexes were about 10 to 100-fold more active than cisplatin, depending on the tested tumor cell line. For comparison purposes, the cytotoxic effects of 1-4 towards human lung fibroblasts (MRC-5) have also been tested. The late apoptosis-inducing properties of 1-4 compounds in SK-MEL-5 cells were verified 24 h incubation using annexin V-Fluorescein isothiocyanate (FITC)/propidium iodide (PI). The binding properties of the model compound 1 on human serum albumin (HSA) and calf thymus DNA (ct-DNA) have been studied using circular dichroism and fluorescence spectroscopy. Docking simulations have been carried out to gain more information about the interaction of the palladacycle and HSA. The ability of compounds 1-4 to inhibit the activity of cathepsin B and L has also been investigated in this work.

Synthesis, anti-proliferative and apoptosis-inducing studies of palladacycles containing a diphosphine and a Sn,As-based chelate ligand

Cleavage of the bromide bridges in [Pd2(μ-Br)2{κ2(Sn,As)-2-MeBrSnC6F4AsPh2}2] (1) by diphosphine ligands gave the mono- and dinuclear palladacycles [Pd(L)Br{κ2(Sn,As)-2-MeBrSnC6F4AsPh2}] [L = dppe (2) dppm (3), ortho-dppBz (4)] and [Pd2Br2(para-dppBz){κ2(Sn,As)-2-MeBrSnC6F4AsPh2}2] (5). The interactions of these complexes with DNA (CT-DNA) and proteins (human serum albumin) were studied by UV-Vis and fluorescence spectroscopy, respectively. The results confirmed the interaction of these palladium complexes with CT-DNA through groove binding, and their strong binding affinity to HSA. The anti-proliferative activities of complexes 1-5 were tested against four human cancer cell lines (HeLa, A549, PC-3, and HT1080) and normal keratinocytes (HaCaT). Among the series, the palladium(ii) complex containing the 1,2-bis(diphenylphosphino)benzene ligand (4) showed the highest cytotoxicity against HeLa, PC-3 and HT1080 cells, with IC50 values of 0.25 ± 0.08, 0.85 ± 0.11, and 0.66 ± 0.15 μM, respectively. Interestingly, compound 4 exhibited lower cytotoxic activity toward normal HaCaT cells (IC50 = 4.65 ± 0.16 μM). Additionally, this complex exhibited lower toxicity and better anti-cancer activity than cisplatin. Further mechanistic studies, including Hoechst staining and flow cytometry, confirmed that complex 4 induced G2/M phase cell cycle arrest and apoptotic cell death in HeLa cells.

Leishmanicidal and Immunomodulatory Activities of the Palladacycle Complex DPPE 1.1, a Potential Candidate for Treatment of Cutaneous Leishmaniasis

The present study focused on the activity of the palladacycle complex DPPE 1.1 on Leishmania (Leishmania) amazonensis. Promastigotes of L. (L.) amazonensis were destroyed in vitro by nanomolar concentrations of DPPE 1.1, whereas intracellular amastigotes were killed at drug concentrations fivefold less toxic than those harmful to macrophages. L. (L.) amazonensis-infected BALB/c mice were treated by intralesional injection of DPPE 1.1. Animals treated with 3.5 and 7.0 mg/kg of DPPE 1.1 showed a significant decrease of foot lesion sizes and a parasite load reduction of 93 and 99%, respectively, when compared to untreated controls. Furthermore, DPPE 1.1 was non-toxic to treated animals. The cathepsin B activity of L. (L.) amazonensis amastigotes was inhibited by DPPE 1.1 as demonstrated spectrofluorometrically by use of a specific fluorogenic substrate. Analysis of T-cells populations in mice treated with DPPE 1.1 and untreated controls was performed by fluorescence-activated cell sorter (FACS). IFN-γ was measured in supernatants of lymphocytes from popliteal and inguinal lymph nodes isolated from treated and untreated mice and stimulated with L. (L.) amazonensis amastigotes extract and active TGF-β was evaluated in supernatants of foot lesions; both dosages were carried out by means of a double-sandwich ELISA assay. A significant increase of TCD4+ and TCD8+ lymphocytes and IFN-γ secretion was displayed in mice treated with DPPE 1.1 compared to untreated animals, whereas a significant reduction of active TGF-β was observed in treated mice. These findings open perspectives for further investment in DPPE 1.1 as an alternative option for the chemotherapy of cutaneous leishmaniasis.

Affinity-Enhanced Luminescent Re(I)- and Ru(II)-Based Inhibitors of the Cysteine Protease Cathepsin L

Two new Re(I)- and Ru(II)-based inhibitors were synthesized with the formulas [Re(phen)(CO)₃(1)](OTf) (7; phen = 1,10-phenanthroline, OTf = trifluoromethanesulfonate) and [Ru(bpy)₂(2)](Cl)₂ (8; bpy = 2,2'-bipyridine), where 1 and 2 are the analogues of CLIK-148, an epoxysuccinyl-based cysteine cathepsin L inhibitor (CTSL). Compounds 7 and 8 were characterized using various spectroscopic techniques and elemental analysis; 7 and 8 both show exceptionally long excited state lifetimes. Re(I)-based complex 7 inhibits CTSL in the low nanomolar range, affording a greater than 16-fold enhancement of potency relative to the free inhibitor 1 with a second-order rate constant of 211000 ± 42000 M^-1 s^-1. Irreversible ligation of 7 to papain, a model of CTSL, was analyzed with mass spectroscopy, and the major peak shown at 24283 au corresponds to that of papain-1-Re(CO)₃(phen). Compound 7 was well tolerated by DU-145 prostate cancer cells, with toxicity evident only at high concentrations. Treatment of DU-145 cells with 7 followed by imaging via confocal microscopy showed substantial intracellular fluorescence that can be blocked by the known CTSL inhibitor CLIK-148, consistent with the ability of 7 to label CTSL in living cells. Overall this study reveals that a Re(I) complex can be attached to an enzyme inhibitor and enhance potency and selectivity for a medicinally important target, while at the same time allowing new avenues for tracking and quantification due to long excited state lifetimes and non-native element composition.

New RuII pincer complexes: synthesis, characterization and biological evaluation for photodynamic therapy

Three new ruthenium(ii) complexes of NCN pincer and phenylcyanamide derivative ligands of the formula [Ru(L)(Ph₂phen)(3,5-(NO₂)₂pcyd)], 1, [Ru(L)(Me₂phen)(3,5-(NO₂)₂pcyd)], 2, and [Ru(L)(Cl₂phen)(3,5-(NO₂)₂pcyd)], 3 (HL: 5-methoxy-1,3-bis(1-methyl-1H-benzo[d]imidazol-2-yl)benzene, 3,5-(NO₂)₂pcyd: 3,5-(NO₂)₂pcyd, Ph₂phen: 4,7-diphenyl-1,10-phenanthroline, Me₂phen: 4,7-dimethyl-1,10-phenanthroline, Cl₂phen: 4,7-dichloro-1,10-phenanthroline) have been synthesized and studied as potential photosensitizers (PSs) in photodynamic therapy (PDT). The complexes exhibited promising ¹O₂ production quantum yields comparable with PSs available on the market. The DNA-binding interactions of the complexes with calf thymus DNA have been studied by absorption, emission, and viscosity measurements. All complexes cleave SC-DNA efficiently on photoactivation at 350 nm with the formation of singlet oxygen (¹O₂) and hydroxyl radicals (˙OH) in type-II and photoredox pathways. Complexes 1-3 showed very good uptake in cervical cancer cells (HeLa). The compounds studied were found to exhibit low toxicity against HeLa cells (IC₅₀ > 300 μM) and, remarkably, on non-cancerous MRC-5 cells (IC₅₀ > 100 μM) in the dark. However, 1 showed very promising behavior with an increment of about 90 times, in its cytotoxicity upon light illumination at 420 nm in addition to very good human plasma stability.

Synthesis and spectroscopic characterization study of new palladium complexes containing bioactive O,O-chelated ligands: evaluation of the DNA/protein BSA interaction, in vitro antitumoural activity and molecular docking

[Pd{(C,N)-C₆H₄CH₂NH(Et) (Qu)] (2) and [Pd{(C,N)-C₆H₄CH₂NH(Et) (Nar)] (3) (Qu = Quercetin, Nar = Naringin) mononuclear palladium (II) complexes have been synthesized and characterized using elemental analysis, IR and electronic spectroscopy. The interaction of the prepared complexes with calf thymus DNA and bovine serum albumin (BSA), monitored by UV-visible and fluorescence titrations, respectively, have been carried out to better understand the mode of their action under biological conditions. Intercalative binding mode between the complexes and DNA is suggested by the binding constant (K_b) values of 2.5 × 10⁶ and 3.2 × 10⁶ for complexes 2 and 3, respectively. In particular, the in vitro cytotoxicity of the complexes on two cancer cells lines (bladder carcinoma TCC and breast cancer MCF7) showed that the compounds had broad spectrum, anti-cancer activity with low IC₅₀ values and the order of in vitro anticancer activities is consistent with the DNA-binding affinities. In the meantime, the quenching of tryptophan emission with the addition of complexes using BSA as a model protein indicated the protein binding ability. The quenching mechanisms of BSA by the complexes were static processes, according to the results obtained. The competitive binding using Warfarin, Digoxin and Ibuprofen site markers, which contain definite biding sites, demonstrated that the complexes bind to site I on BSA. Ultimately, the binding sites of DNA and BSA with the complexes have been determined by molecular modelling studies.

Linking the future of anticancer metal-complexes to the therapy of tumour metastases

Cancer chemotherapy is almost always applied to patients with one or more diagnosed metastases and is expected to impact these lesions, thus providing significant benefits to the patient.

The current stage of cathepsin B inhibitors as potential anticancer agents

Cathepsin B is a lysosomal cysteine peptidase, with an important role in the development and progression of cancer. It is involved in the degradation of extracellular matrix proteins, a process promoting invasion and metastasis of tumor cells and tumor angiogenesis. Cathepsin B is unique among cathepsins in possessing both carboxypeptidase and endopeptidase activities. While the former is associated with its physiological role, the latter is involved in pathological degradation of the extracellular matrix. Its activities are regulated by different means, the most important being its endogenous inhibitors, the cystatins. In cancer this peptidase/inhibitor balance is altered, leading to harmful cathepsin B activity. The latter can be prevented by exogenous inhibitors. They differ in modes of inhibition, size, structure, binding affinity, selectivity, toxicity and bioavailability. In this article, we review the properties and function of endogenous and exogenous cathepsin B inhibitors and indicate their application as possible anticancer agents.

Anti-cancer palladium complexes: a focus on PdX2L2, palladacycles and related complexes

Much success has been achieved with platinum-based chemotherapeutic agents, i.e. through interactions with DNA. The long-term application of Pt complexes is thwarted by issues, leading scientists to examine other metals such as palladium which could exhibit complementary modes of action (given emphasis wherever known). Over the last 10 years several research groups have focused on the application of an eclectic array of palladium complexes (of the type PdX2L2, palladacycles and related structures) as potential anti-cancer agents. This review therefore provides readers with an up to date account of the advances that have taken place over the past several decades.

Palladacycle (BPC) antitumour activity against resistant and metastatic cell lines: the relationship with cytosolic calcium mobilisation and cathepsin B activity

The search for new compounds that induce p53-independent apoptosis is the focus of many studies in cancer biology because these compounds could be more specific and would overcome chemotherapy resistance. In this study, we evaluated the in vitro antitumour activity of a Biphosphinic Palladacycle Complex (BPC) and extended preclinical studies to an in vivo model. Saos-2 cells, a p53-null human osteosarcoma drug-resistant cell line, were treated with BPC in the presence or absence of a cathepsin B inhibitor and a calcium chelator (CA074 and BAPTA-AM, respectively), and several parameters related to apoptosis were evaluated. Preclinical studies were performed with mice that were intravenously inoculated with murine melanoma B16F10-Nex2 cells and treated intraperitoneally (i.p.) with BPC (8 mg/kg/day) for ten consecutive days, when lung metastatic nodules were counted. In vitro data show that BPC induces cell death in Saos-2 cells mainly by apoptosis, which was accompanied by the effector caspase-3 activation. These events are most likely related to Bax translocation and increased cytosolic calcium mobilisation, mainly from intracellular compartments. Lysosomal Membrane Permeabilisation (LMP) was also observed after 12 h of BPC exposure. Interestingly, BAPTA-AM and CA074 significantly decreased BPC cytotoxicity, suggesting that both calcium and cathepsin B are required for BPC antitumour activity. In vivo studies demonstrated that BPC protects mice against murine metastatic melanoma. In conclusion, BPC complex is an effective anticancer compound against metastatic murine melanoma. This complex is cytotoxic to the drug-resistant osteosarcoma Saos-2 human tumour cells by inducing apoptosis triggered by calcium signalling and a lysosomal-dependent pathway.

Stepwise cyclopalladation of 2-phenacylthiopyridine to give C,C,N-pincer complexes

The synthesis of a family of palladium C,C,N-pincer complexes derived from 2-phenacylthiopyridine, obtained by an unprecedented stepwise double cyclopalladation process, is reported. The pincer moiety behaves as a metallaligand.

Potential anticancer heterometallic Fe-Au and Fe-Pd agents: initial mechanistic insights

A series of gold(III) and palladium(II) heterometallic complexes with new iminophosphorane ligands derived from ferrocenylphosphanes [{Cp-P(Ph2)═N-Ph}2Fe] (1), [{Cp-P(Ph2)═N-CH2-2-NC5H4}2Fe] (2), and [{Cp-P(Ph2)═N-CH2-2-NC5H4}Fe(Cp)] (3) have been synthesized and structurally characterized. Ligands 2 and 3 afford stable coordination complexes [AuCl2(3)]ClO4, [{AuCl2}2(2)](ClO4)2, [PdCl2(3)], and [{PdCl2}2(2)]. The complexes have been evaluated for their antiproliferative properties in human ovarian cancer cells sensitive and resistant to cisplatin (A2780S/R), in human breast cancer cells (MCF7) and in a nontumorigenic human embryonic kidney cell line (HEK-293T). The highly cytotoxic trimetallic derivatives M2Fe (M = Au, Pd) are more cytotoxic to cancer cells than their corresponding monometallic fragments. Moreover, these complexes were significantly more cytotoxic than cisplatin in the resistant A2780R and the MCF7 cell lines. Studies of the interactions of the trimetallic compounds with DNA and the zinc-finger protein PARP-1 indicate that they exert anticancer effects in vitro based on different mechanisms of actions with respect to cisplatin.

Cancer cell cytotoxicity of cyclometalated compounds obtained with osmium(II) complexes

A library of 29 organoosmium compounds has been built up with known and novel cyclometalated compounds obtained with C-N, N(∧)C(∧)N, and C(∧)N(∧)N ligands. All compounds have been tested for their in vitro cytotoxic properties against A172, a tumor cell line derived from a human glioblastoma, this affording a contrasted picture of the activities of the compounds gathered in this study. Some compounds displayed good to excellent activities, some of them showing IC50 in the nanomolar range. The level of activity was tentatively correlated to several physicochemical properties of the compounds such as their E(0)1/2(Os(III/II)) redox potential and their lipophilicity (log Po/w). A parallel with related ruthenium derivatives was tentatively proposed.