Promising anticancer mono- and dinuclear ruthenium(III) dithiocarbamato complexes: systematic solution studies.

During the last decade, our research group has prepared a number of metal dithiocarbamato derivatives of Pt, Pd and Au that were expected to resemble the main features of cisplatin together with higher activity, improved selectivity and bioavailability, and lower side-effects. Furthermore, we have already published the synthesis, characterization and in vitro cytotoxicity studies of novel ruthenium(III) dithiocarbamato complexes such as [RuL(3)] monomers (11) and α-[Ru(2)L(5)]Cl dimers (12) with five different dithiocarbamate ligands. As both the monomer and the dinuclear complexes have shown significant antitumor activity in different human tumor cell lines, we decided to widen the characterization studies and to analyse thoroughly their behavior in physiological-like medium by UV-visible and CD spectroscopy. In the present paper we report on the crystal structure of [Ru(DMDT)(3)], [Ru(PDT)(3)] and [Ru(ESDT)(3)] complexes and we determine the spin state of the paramagnetic Ru(III) by means of Evans' method. Then, we discuss in detail the UV-visible spectral data of the complexes in different medium. All the studied complexes are stable in dimethyl sulfoxide, and show low solubility in phosphate buffered saline solution, particularly the monomer species, even at low concentration, while increased solubility for both types of complexes have been found in the presence of bovine serum albumin (BSA). Moreover, no changes on the coordination sphere of the metal, as well as no direct interaction between the BSA protein and the complex have been identified by UV-visible spectroscopy. However, some conformational changes on the BSA structure, induced by the ruthenium(III) complexes have been confirmed by CD spectroscopy, indicating a probable secondary electrostatic interaction between the metal complex and the peptide. In addition, no significant interaction has been demonstrated with the components of Dulbecco's Modified Eagle's Medium, used for the in vitro assays.

Antiproliferative and apoptotic effects of two new Pd(II) methylsarcosinedithiocarbamate derivatives on human acute myeloid leukemia cells in vitro.

[Pd(MSDT)Cl]n palladium, chloro[methyl N-(dithiocarboxy-kS,kS')-N-methylglycinate], and [Pd(MSDT) Br]n palladium, bromo[methyl N-(dithiocarboxy-kS,kS')-N-methylglycinate], palladium (Pd)(II) derivatives are two newly synthesized Pd(II) derivatives of methylsarcosinedithiocarbamate (MSDT), containing a sulfur chelating ligand that is able to strongly bind the metal center, so preventing interactions with sulfur-containing enzymes. In fact, these reactions are believed to be responsible for the nephrotoxicity induced by platinum (II)-based drugs. Their activity has been evaluated in a panel of acute myeloid leukemia (AML) cell lines representing different French-American-British (FAB) subtypes and in the Philadelphia (Ph)-positive cell line K-562 and compared to cisplatin. Both compounds suppressed, in a dose-dependent manner, colony formation in methylcellulose with ID50 values comparable to those of the reference drug cisplatin, excluding the ML-3 cell line (ID50 10-fold lower than cisplatin). Exposure of HL-60, ML-3, NB-4, and THP-1 cell lines to a cytotoxic concentration of [Pd(MSDT)Br]n (5 microM) determined: downregulation of the antiapoptotic molecule Bcl-2, upregulation of the proapoptotic molecule Bax; apoptosis induction, as evaluated by APO2.7 and annexin V staining; mitochondrial membrane permeabilization; and DNA fragmentation. In ML-3 cells the Pd(II) complexes were more active than cisplatin in apoptosis induction. Finally, [Pd(MSDT)Br]n showed an inhibitory effect on clonogenic growth of hematopoietic progenitors (CFU-GM, CFU-GEMM, and BFU-E) with both ID50 and ID90 comparable to those of cisplatin. Remarkably, the Pd(II) complex was more potent in inhibiting the clonogenic growth of the less differentiated AML cell lines KG-1a, HL-60, NB-4, ML-3, and THP-1 (ID50 ranging from 0.02 +/- 0.001 to 0.52 +/- 0.04 microM), compared to normal hematopoietic progenitors (ID50 of 2.1 +/- 0.1, 3.8 +/- 0.4, and 2.5 +/- 0.2 microM) for CFU-GEMM, BFU-E, and CFU-GM, respectively). These data suggest that leukemic cells of myelomonoblast lineage might represent a preferential target for its cytotoxic activity compared to normal committed hemopoietic progenitor cells. Altogether, our results indicate that these new Pd(II) dithiocarbamate derivatives might represent novel potentially active drugs for the management of some selected myeloid leukemia strains, able to conjugate cytostatic and apoptotic activity with reduced toxicity.

Chemical and biological profiles of novel copper(II) complexes containing S-donor ligands for the treatment of cancer.

In the last years, we have synthesized some new platinum(II), palladium(II), gold(I/III) complexes with dithiocarbamato derivatives as potential anticancer drugs, to obtain compounds with superior chemotherapeutic index in terms of increased bioavailability, higher cytotoxicity, and lower side effects than cisplatin. On the basis of the obtained encouraging results, we have been studying the interaction of CuCl2 with methyl-/ethyl-/tert-butylsarcosine-dithiocarbamato moieties in a 1:2 molar ratio; we also synthesized and studied the N,N-dimethyl- and pyrrolidine-dithiocarbamato copper complexes for comparison purposes. The reported compounds have been successfully isolated, purified, and fully characterized by means of several spectroscopic techniques. Moreover, the electrochemical properties of the designed compounds have been studied through cyclic voltammetry. In addition, the behavior in solution was followed by means of UV-vis technique to check the stability with time in physiological conditions. To evaluate their in vitro cytotoxic properties, preliminary biological assays (MTT test) have been carried out on a panel of human tumor cell lines. The results show that cytotoxicity levels of all of the tested complexes are comparable or even greater than that of the reference drug (cisplatin).

Pyrrolidine dithiocarbamate-zinc(II) and -copper(II) complexes induce apoptosis in tumor cells by inhibiting the proteasomal activity.

Zinc and copper are trace elements essential for proper folding, stabilization and catalytic activity of many metalloenzymes in living organisms. However, disturbed zinc and copper homeostasis is reported in many types of cancer. We have previously demonstrated that copper complexes induced proteasome inhibition and apoptosis in cultured human cancer cells. In the current study we hypothesized that zinc complexes could also inhibit the proteasomal chymotrypsin-like activity responsible for subsequent apoptosis induction. We first showed that zinc(II) chloride was able to inhibit the chymotrypsin-like activity of a purified 20S proteasome with an IC(50) value of 13.8 microM, which was less potent than copper(II) chloride (IC(50) 5.3 microM). We then compared the potencies of a pyrrolidine dithiocarbamate (PyDT)-zinc(II) complex and a PyDT-copper(II) complex to inhibit cellular proteasomal activity, suppress proliferation and induce apoptosis in various human breast and prostate cancer cell lines. Consistently, zinc complex was less potent than copper complex in inhibiting the proteasome and inducing apoptosis. Additionally, zinc and copper complexes appear to use somewhat different mechanisms to kill tumor cells. Zinc complexes were able to activate calpain-, but not caspase-3-dependent pathway, while copper complexes were able to induce activation of both proteases. Furthermore, the potencies of these PyDT-metal complexes depend on the nature of metals and also on the ratio of PyDT to the metal ion within the complex, which probably affects their stability and availability for interacting with and inhibiting the proteasome in tumor cells.

Ru(III)-based compounds with sulfur donor ligands: synthesis, characterization, electrochemical behaviour and anticancer activity.

In recent years, Ru(iii) complexes have emerged as a new class of effective anticancer agents against tumors that proved to be resistant to all other chemotherapeutic drugs currently in clinical use. To extend our previous studies on metal complexes containing sulfur-donor ligands, we report here on the synthesis and characterization, by means of several spectroscopic and analytical techniques, some [Ru(RSDT)(3)] and [Ru(2)(RSDT)(5)]Cl complexes with dithiocarbamato ligands derived from methyl/ethyl/tert-butyl esters of sarcosine. Their electrochemical behaviour was also studied by cyclic voltammetry. All the complexes were tested for their cytotoxicity on a panel of human tumor cell lines showing highly significant antitumor activity. The chemical and biological properties of the newly synthesized complexes, were compared with those of [Ru(DMDT)(3)] and [Ru(2)(DMDT)(5)]Cl species (DMDT = N,N-dimethyldithiocarbamate) whose chemical (not biological) characterization has been already reported in literature.

Antiproliferative and apoptotic effects of two new gold(III) methylsarcosinedithiocarbamate derivatives on human acute myeloid leukemia cells in vitro.

[Au(MSDT)Cl2] (dichloro[methyl N-(dithiocarboxy-kS,kS')-N-methylglicinato]gold(III)) and [Au(MSDT)Br2] (dibromo[methyl N-(dithiocarboxy-kS,kS')-N-methylglicinato]gold(III)) gold(III) dithiocarbamate derivatives are two newly synthesized gold(III) derivatives of methylsarcosinedithiocarbamate, containing a sulfur chelating ligand that is able to bind the metal center strongly, so preventing interactions with sulfur-containing enzymes; in fact these reactions are believed to be responsible for the nephrotoxicity induced by the platinum(II)-based drugs. Their activity has been compared with the well-known platinum-based anticancer agent cisplatin on a panel of acute myelogenous leukemia cell lines representing different French-American-British subtypes and in the Philadelphia-positive cell line K562. Both compounds suppressed, in a dose-dependent manner, colony formation in methylcellulose with ID50 values of about 10-fold lower than that of the reference drug. After a short exposure (18 h), our compounds, but not cisplatin, were able to: downregulate the antiapoptotic molecule Bcl-2, upregulate the proapoptotic molecule Bax and induce apoptosis, as determined by a strong induction of APO2.7 and phosphatidylserine exposure. Finally, after a 72-h exposure, both gold(III) dithiocarbamate derivatives determined modest cell cycle modifications, but induced DNA fragmentation in all myeloid cell lines tested. Altogether, our results indicate that these new gold(III) dithiocarbamate derivatives might represent novel potentially active drugs for the management of myeloid leukemia, able to combine cytostatic and apoptotic activity with reduced nephrotoxicity.

Gold dithiocarbamate derivatives as potential antineoplastic agents: design, spectroscopic properties, and in vitro antitumor activity.

At present, cisplatin (cis-diamminodichloroplatinum(II)) is one of the most largely employed anticancer drugs as it is effective in the treatment of 70-90% of testicular and, in combination with other drugs, of ovarian, small cell lung, bladder, brain, and breast tumors. Anyway, despite its high effectiveness, it exhibits some clinical problems related to its use in the curative therapy, such as a severe normal tissue toxicity (in particular, nephrotoxicity) and the frequent occurrence of initial and acquired resistance to the treatment. To obtain compounds with superior chemotherapeutic index in terms of increased bioavailability, higher cytotoxicity, and lower side effects than cisplatin, we report here on some gold(I) and gold(III) complexes with dithiocarbamate ligands (DMDT = N,N-dimethyldithiocarbamate; DMDTM = S-methyl-N,N-dimethyldithiocarbamate; ESDT = ethylsarcosinedithiocarbamate), which have been synthesized, purified, and characterized by means of elemental analyses, conductivity measurements, mono- and bidimensional NMR, FT-IR, and UV-vis spectroscopy, and thermal analyses. Moreover, the electrochemical properties of the designed compounds have been studied through cyclic voltammetry. All the synthesized gold complexes have been tested for their in vitro cytotoxic activity. Remarkably, most of them, in particular gold(III) derivatives of N,N-dimethyldithiocarbamate and ethylsarcosinedithiocarbamate, have been proved to be much more cytotoxic in vitro than cisplatin, with IC50 values about 1- to 4-fold lower than that of the reference drug, even toward human tumor cell lines intrinsically resistant to cisplatin itself. Moreover, they appeared to be much more cytotoxic also on the cisplatin-resistant cell lines, with activity levels comparable to those on the corresponding cisplatin-sensitive cell lines, ruling out the occurrence of cross-resistance phenomena and supporting the hypothesis of a different antitumor activity mechanism of action.

Synthesis, characterization, and comparative in vitro cytotoxicity studies of platinum(II), palladium(II), and gold(III) methylsarcosinedithiocarbamate complexes.

This work reports on the synthesis, characterization, and in vitro cytotoxic activity of some new platinum(II), palladium(II), and gold(III) derivatives of methylsarcosinedithiocarbamate and its S-methyl ester, to study their behavior as potential antitumor agents. The biological activity of these compounds, as determined by growth inhibition and apoptosis induction, has been investigated in both human leukemic promyelocites HL60 and human squamous cervical adenocarcinoma HeLa cell lines, and their activity has been compared to the well-known platinum-based anticancer agent cisplatin. On the basis of these experimental results, [Pd(MSDT)X]n (MSDT = methylsarcosinedithiocarbamate; X = Cl, Br) complexes show a strong dose-dependent growth inhibition of both HL60 and HeLa cells, with IC(50) values slightly higher than those recorded for cisplatin; moreover, [Au(MSDT)X(2)] activity appears significantly higher or, at least, comparable to that of the reference drug. Exposure of both cell lines to [Pd(MSDT)X]n and [Au(MSDT)X(2)] complexes induces apoptosis, as determined by an Apo2.7 assay.

Antitumor activity of a new platinum(II) complex with low nephrotoxicity and genotoxicity.

Cisplatin is an important antineoplastic agent, but dose-limiting nephrotoxicity and the occurrence of cellular resistance prevent its potential efficacy. Moreover, cisplatin is known to be carcinogenic and genotoxic in mammalian cells and this feature is of a special interest due to the risk of inducing secondary malignancies. There is a great interest in developing new platinum agents that have broad spectrum of antitumor activity and reduced toxicity. We have recently synthesized a novel platinum(II) coordination complex containing a pyridine nucleus and a dithiocarbamate moiety as ligands, [Pt(ESDT)(Py)Cl], in order to obtain an agent with more favorable therapeutic indices than cisplatin. In this study, the new platinum(II) complex was tested for its cytotoxicity, by MTT assay, on various human cancer cell lines also including different cisplatin-resistant cells endowed with different mechanisms of resistance. On human peripheral blood lymphocytes we evaluated the genotoxic potential of [Pt(ESDT)(Py)Cl] via micronuclei and SCE detection. We also performed in vivo experiments with the purpose of investigating the antitumor and nephrotoxic effects of the new platinum(II) complex. The antitumor activity was studied in ascitic or solid Ehrlich carcinoma bearing mice while nephrotoxicity was monitored in male Wistar rats by means of histopathological findings of renal specimens and of biochemical investigation on urinary parameters (GS and NAG activities and of TUP excretion) of urine samples. The results reported here indicate that [Pt(ESDT)(Py)Cl] showed a remarkable in vitro antitumor activity (with IC50 values about twofold as low as those of cisplatin), moreover, it markedly circumvented the acquired cisplatin resistance in selected human cancer cells. The analysis of the cytogenetic damage in normal cells clearly attested that the new dithiocarbamate complex, tested at equitoxic concentrations, is less genotoxic than cisplatin. Chemotherapy in Ehrlich carcinoma bearing mice with [Pt(ESDT)(Py)Cl] was significantly better tolerated than that with cisplatin. Against the ascitic tumor, [Pt(ESDT)(Py)Cl], showed an activity noticeably higher than that of cisplatin in increasing the life span of treated animals (% T/C = 190 and 129, respectively). In solid-tumor-bearing mice, [Pt(ESDT)(Py)Cl] induced a tumor size reduction very close to that observed with the reference compound. Finally, our findings obtained from the nephrotoxicity studies demonstrated [Pt(ESDT)(Py)Cl] was not nephrotoxic, contrary to cisplatin which caused a notorious acute proximal tubular damage. In summary, [Pt(ESDT)(Py)Cl] may be considered as a new platinum(II) complex with remarkable antitumor activity and low nephrotoxicity and genotoxicity compared with cisplatin.

Cytotoxicity and DNA damage induced by a new platinum(II) complex with pyridine and dithiocarbamate.

A new platinum(II) complex containing a pyridine nucleus and a dithiocarbamate moiety as ligands ([Pt(ESDT)(Py)Cl]) was evaluated for in vitro cytotoxicity in the cisplatin-sensitive human ovarian 2008 and in the isogenic-resistant C13* cell lines. In both cell types, a tumor cell growth inhibition greater than cisplatin and a complete lack of cross-resistance in C13* cells were found. Despite its molecular size, [Pt(ESDT)(Py)Cl] accumulation was much higher than cisplatin both in parent and resistant cells. Studying the mechanism of action in cell-free media, we established that [Pt(ESDT)(Py)Cl] more efficiently interacts with DNA in vitro compared to cisplatin maintaining a binding preference for GG rich sequences of DNA. On the contrary, DNA platination in vivo by [Pt(ESDT)(Py)Cl] was found lower than cisplatin. An analysis of the type of DNA lesions induced by [Pt(ESDT)(Py)Cl] suggests that the cytotoxic efficacy and the ability to overcome cisplatin resistance seem to be related to a different mechanism of interaction with DNA and/or with other key cellular components.

Synthesis of a palladium(II)-dithiocarbamate complex: biological assay and nephrotoxicity in rats.

A new palladium(II)-dithiocarbamate complex, [Pd(ESDT)Cl](n), was synthesised and its chemical characteristics are discussed. This complex was examined for its cytotoxic properties in human tumour cell lines; for comparison, the cytotoxicity of cisplatin was evaluated under the same experimental conditions. In particular, Pd(II)-complex cytotoxicity on ovarian carcinoma C13 cells, resistant to cisplatin, showed that there seemed to be no cross-resistance between [Pd(ESDT)Cl](n) and cisplatin. The effects on the kidney were also studied. Biochemical investigation on urinary parameters showed that the effects after a single injection are similar to those of cisplatin, with an increase of urinary proteins and enzyme excretion in urine, and a significant decrease of glutamine synthetase activity in the renal tissue. In addition, the Pd(II)-complex caused a significant decrease of p-aminohippuric acid uptake in renal cortical slices relative to cisplatin. On the other hand, histopathological findings showed that the effects of the Pd(II)-complex are more severe and diffuse than the damage caused by cisplatin. Biochemical and histopathological findings show that the Pd(II)-complex affects the pars recta and pars convoluta, in contrast to cisplatin, which only affects the pars recta.