Chemoresistance in rat ovarian tumours

Synthesis, characterization, and DNA binding study of ruthenium(II/III) complexes containing ONS donor Schiff base

A chelating ligand of thioether with ONS donor Schiff base HL [(E)-2-(((2-(benzylthio)phenyl)imino)methyl)napthalen-1-ol] and its metal complexes (RuL₁ and RuL₂) have been synthesized. They have been characterized by UV-Vis, FTIR, ¹H NMR, ¹³C NMR, mass spectrometry methods. The formulas of the synthesized compounds have been confirmed by elemental analysis and magnetic susceptibility measurements. The binding ability studies of the ligand (HL) and its Ru complexes (RuL₁ and RuL₂), with calf-thymus DNA have been explored by the absorption titration method. The binding interaction study reveals that the ligand (HL) and the complex RuL₁ interact with CT-DNA through an intercalative mode of binding whereas the complex RuL₂ does not show any interaction with CT-DNA due to steric effect.

Recent Advances in Schiff Base Ruthenium Metal Complexes: Synthesis and Applications

This review concentrates on recent developments in ruthenium Schiff bases, whose steric and electronic characteristics can be manipulated easily by selecting suitable condensing aldehydes or ketones and primary amines, and their metal complexes. Ruthenium metal-based complexes and Schiff base ligands are rapidly becoming conventionally considered for biological applications (antioxidant, anticancer, antimicrobial), in catalysis, in functional materials, in sensors, and as pigments for dyes. Ruthenium complexes exhibit a broad variety of activities concerning simple Schiff base ligands. This may be due to the octahedral bonding of both Ru(II) and Ru(III) complexes, which acquire an extended reservoir of a three-dimensional framework, providing the potential for an elevated degree of site selectivity for binding to their biological targets. This review provides an overview of this field, and intends to highlight both ligand design and synthetic methodology development, as well as significant applications of these metal complexes. In this review, we summarize our work on the development of ruthenium complexes, which was performed over the last few years.

Important cytotoxicity of novel iron(II) cyclopentadienyl complexes with imidazole based ligands

Four new compounds of general formula [FeCp(dppe)L][CF3SO3] with L=imidazole substituted ligands, and dppe=ethylenebis(diphenylphosphane) have been synthesized and characterized with the aim to evaluate their anticancer properties. The new compounds were fully characterized by spectroscopic and electrochemical methods and the structure of [Fe(η(5)-C5H5)(dppe)(1-BuIm)] [CF3SO3] (1), [Fe(η(5)-C5H5)(dppe) (ImH)][CF3SO3] (3) and [Fe(η(5)-C5H5)(dppe)(1HmIm)][CF3SO3] (4) (where 1-BuIm=1-butylimidazole, and 1HmIm=N-hydroxymethylimidazole) was determined by X-ray diffraction studies. Apparently, these compounds are the first reported 'Fe(η(5)-C5H5)' half sandwich derivatives presenting high cytotoxic activity against a set a human tumor cell lines predicting their potential value as antitumor drugs.

Biological activity and cellular uptake of [Ru(η5-C5H5)(PPh3)(Me2bpy)][CF3SO3] complex

Anticancer activity of the new [Ru(η(5)-C5H5)(PPh3)(Me2bpy)][CF3SO3] (Me2bpy = 4,4'-dimethyl-2,2'-bipyridine) complex was evaluated in vitro against several human cancer cell lines, namely A2780, A2780CisR, HT29, MCF7, MDAMB231 and PC3. Remarkably, the IC50 values, placed in the nanomolar and sub-micromolar range, largely exceeded the activity of cisplatin. Binding to human serum albumin, either HSA (human serum albumin) or HSA(faf) (fatty acid-free human serum albumin) does not affect the complex activity. Fluorescence studies revealed that the present ruthenium complex strongly quench the intrinsic fluorescence of albumin. Cell death by the [Ru(η(5)-C5H5)(PPh3)(Me2bpy)][CF3SO3] complex was reduced in the presence of endocytosis modulators and at low temperature, suggesting an energy-dependent mechanism consistent with endocytosis. On the whole, the biological activity evaluated herein suggests that the complex could be a promising anticancer agent.

Anticancer activity of metal complexes: involvement of redox processes

Cells require tight regulation of the intracellular redox balance and consequently of reactive oxygen species for proper redox signaling and maintenance of metal (e.g., of iron and copper) homeostasis. In several diseases, including cancer, this balance is disturbed. Therefore, anticancer drugs targeting the redox systems, for example, glutathione and thioredoxin, have entered focus of interest. Anticancer metal complexes (platinum, gold, arsenic, ruthenium, rhodium, copper, vanadium, cobalt, manganese, gadolinium, and molybdenum) have been shown to strongly interact with or even disturb cellular redox homeostasis. In this context, especially the hypothesis of "activation by reduction" as well as the "hard and soft acids and bases" theory with respect to coordination of metal ions to cellular ligands represent important concepts to understand the molecular modes of action of anticancer metal drugs. The aim of this review is to highlight specific interactions of metal-based anticancer drugs with the cellular redox homeostasis and to explain this behavior by considering chemical properties of the respective anticancer metal complexes currently either in (pre)clinical development or in daily clinical routine in oncology.

Cytotoxic and genotoxic effects of cis-tetraammine(oxalato)ruthenium(III) dithionate on the root meristem cells of Allium cepa

Ruthenium complexes have attracted much attention as possible building blocks for new transition-metal-based antitumor agents. The present study examines the mitotoxic and clastogenic effects induced in the root tips of Allium cepa by cis-tetraammine(oxalato)ruthenium(III) dithionate {cis-[Ru(C(2)O(2))(NH(3))(4)](2)(S(2)O(6))} at different exposure durations and concentrations. Correlation tests were performed to determine the effects of the time of exposure and concentration of ruthenium complex on mitotic index (MI) and mitotic aberration index. A comparison of MI results of cis-[Ru(C(2)O(2))(NH(3))(4)](2)(S(2)O(6)) to those of lead nitrate reveals that the ruthenium complex demonstrates an average mitotic inhibition eightfold higher than lead, with the frequency of cellular abnormalities almost fourfold lower and mitotic aberration threefold lower. A. cepa root cells exposed to a range of ruthenium complex concentrations did not display significant clastogenic effects. Cis-tetraammine(oxalato)ruthenium(III) dithionate therefore exhibits a remarkable capacity to inhibit mitosis, perhaps by inhibiting DNA synthesis or blocking the cell cycle in the G2 phase. Further investigation of the mechanisms of action of this ruthenium complex will be important to define its clinical potential and to contribute to a novel and rational approach to developing a new metal-based drug with antitumor properties complementary to those exhibited by the drugs already in clinical use.

In vitro and in vivo activity and cross resistance profiles of novel ruthenium (II) organometallic arene complexes in human ovarian cancer

Ruthenium complexes offer the potential of reduced toxicity, a novel mechanism of action, non-cross resistance and a different spectrum of activity compared to platinum containing compounds. Thirteen novel ruthenium(II) organometallic arene complexes have been evaluated for activity (in vitro and in vivo) in models of human ovarian cancer, and cross-resistance profiles established in cisplatin and multi-drug-resistant variants. A broad range of IC50 values was obtained (0.5 to >100 microM) in A2780 parental cells with two compounds (RM175 and HC29) equipotent to carboplatin (6 microM), and the most active compound (HC11) equipotent to cisplatin (0.6 microM). Stable bi-dentate chelating ligands (ethylenediamine), a more hydrophobic arene ligand (tetrahydroanthracene) and a single ligand exchange centre (chloride) were associated with increased activity. None of the six active ruthenium(II) compounds were cross-resistant in the A2780cis cell line, demonstrated to be 10-fold resistant to cisplatin/carboplatin by a mechanism involving, at least in part, silencing of MLH1 protein expression via methylation. Varying degrees of cross-resistance were observed in the P-170 glycoprotein overexpressing multi-drug-resistant cell line 2780AD that could be reversed by co-treatment with verapamil. In vivo activity was established with RM175 in the A2780 xenograft together with non-cross-resistance in the A2780cis xenograft and a lack of activity in the 2780AD xenograft. High activity coupled to non cross-resistance in cisplatin resistant models merit further development of this novel group of anticancer compounds.

Growth inhibition of subcutaneously transplanted hepatomas without cachexia by alteration of the dietary arginine-methionine balance

Previous studies have shown that alteration of the dietary arginine-methionine balance by use of synthetic L-amino acids inhibits tumor growth of a subcutaneously transplanted Morris hepatoma at the expense of maintaining body weight. However, L-methionine is susceptible to degradation and, therefore, may contribute to a deficiency state. The present studies were performed to determine whether growth of subcutaneous hepatoma transplants is inhibited, and body growth maintained, when rats are fed diets containing L-methionine in replacement of N-acetyl-L-methionine (NALM) for 28 days. Tumor-free and tumor-bearing rats fed a control diet, with amino acids replacing protein, had gains in body weight: 31.3 +/- 1.0 and 19.1 +/- 0.5 g (12% and 7%), respectively. Rats fed six experimental diets, with varying L-arginine-NALM balances, had body weight gains ranging from 18.4 +/- 0.3 to 26.7 +/- 0.9 g (7-10%). Tumor weight of control rats was 10.65 +/- 0.24% of body weight. Diets supplemented with L-arginine in combination with normal and deficient NALM decreased tumor weights by 35% and 38%, respectively, It is concluded that dietary replacement of L-methionine with NALM and supplementation with L-arginine inhibits growth of a subcutaneously transplanted Morris hepatoma in the absence of cachexia.

Inhibition of O6-alkylguanine-DNA alkyltransferase in animal and human ovarian tumor cell lines by O6-benzylguanine and sensitization to BCNU

O6-Alkylguanine-DNA alkyltransferase (O6-AGT) activity in rat ovarian tumor lines O-342 and O 342/DDP was 103.4 +/- 18.4 and 240.9 +/- 40.2 fmol/mg protein, respectively; thus, cisplatin (DDP) resistance was paralleled by an increase in O6-AGT activity by a factor of approximately 2.3. The DDP-resistant line expressed a collateral resistance to BCNU. Both lines could be sensitized to BCNU by O6-BG, with sensitization factors of 6.0 and 2.1, respectively. In neither line did depletion of O6-AGT have any sensitizing effect towards DDP. In the human ovarian cancer lines SK-OV-3 and OAW 42, O6-AGT activity was 337.6 +/- 18.2 and 180.0 +/- 39.9 fmol/mg protein, respectively; in these lines depletion of O6-AGT activity by O6-BG treatment resulted in sensitization factors of 3.0 and 4.1, respectively. The increase in sensitivity of ovarian tumor cell lines against a chloroethylating agent by O6-AGT depletion and possible pharmacological advantages of regional (i.p.) administration of this combination might be beneficial in advanced ovarian cancer.

Reversal of acquired cisplatin resistance by nicotinamide in vitro and in vivo

At a concentration of 2.5 mM, nicotinamide (NA), an inhibitor of poly(ADP-ribose) polymerase (PARP), significantly potentiated the cytotoxicity of cisplatin (DDP) in a DDP-resistant rat ovarian tumor cell line (O-342/DDP) in vitro, whereas the same treatment had no substantial effect on DDP's cytotoxic activity against the DDP-sensitive parental line (O-342). Furthermore, in a nude mouse model where the O-342/DDP tumor grew intraperitoneally, whereas DDP given alone at 1 mg/kg x 3 exhibited no antitumor activity as compared with control values due to the resistance, NA given at a nontoxic dose (5 mmol/kg x3) significantly increased the mean survival time (MST) of the tumor-bearing NMRI nude mice from 20.7 days in the DDP-treated group to 29.0 days in the combination group. Mechanism studies showed that endogenous PARP activity (incorporation of tritiated nicotinamide adenine dinucleotide, [3H]-NAD) was 2.6 times higher in O-342/DDP than in O-342 cells and that the presence of 2.5 mM NA during the incubation with the isotope resulted in 73.3% inhibition of the enzyme activity in O-342/DDP cells but in only about 30% inhibition in the sensitive line. However, treatment with NA during and after DDP exposure failed to produce any significant effect on the formation of DNA single-strand breaks (SSB) but decreased the induction of DNA interstrand cross-links (ISCL) by DDP in the sensitive and resistant cell lines. These results suggest that NA might have some clinical potential in reversing DDP resistance, and further studies are therefore warranted to confirm the resistance-reversing effect of NA in other DDP-resistant cell lines.

Acquisition of platinum drug resistance and platinum cross resistance patterns in a panel of human ovarian carcinoma xenografts

In vivo models of acquired resistance to the platinum-based agents cisplatin (CDDP), carboplatin (CBDCA), iproplatin (CHIP) and tetraplatin have been established using a panel of six parent human ovarian carcinoma lines, two (HX/110 and PXN/87) being derived from previously untreated patients. Resistance has been generated to CDDP (three lines), CBDCA (one line), CHIP (three lines) and tetraplatin (one line) either by treatment in vivo or (for one line to CDDP) through exposure in vitro and subsequent transfer to mice. With the four tumours where resistance was generated using CDDP or CBDCA, a complete cross-resistance to the remaining platinum agents studied was observed. In contrast, in one of three lines with derived resistance to the platinum (IV) agent, CHIP, (PXN/951) a retention in sensitivity was observed with CDDP and CBDCA. Only one of the six parent tumour lines (PXN/100) was markedly sensitive to tetraplatin. Where resistance was generated to tetraplatin (PXN/100T) there was some retention of activity by CDDP. For the CDDP-resistant line established in vitro, there was a close agreement between the cross-resistance profile obtained in vitro vs that obtained in vivo. This tumour panel may be useful in the elucidation of cellular and molecular resistance mechanisms to platinum drugs operative in vivo. Moreover, as they appear to mimic the clinical observations of shared cross-resistance between CDDP, CBDCA and CHIP, they may represent valuable preclinical evaluation models for the discovery of drugs capable of conferring responses in CDDP-refractory ovarian cancer.

Modulation of cis-diamminedichloroplatinum(II) resistance: a review

In this review an inventory is made of agents used to circumvent cis-diamminedichloroplatinum(II) (CDDP) resistance in vitro and in vivo. Agents that affect CDDP accumulation and membrane related systems, cytoplasmic defense mechanisms, as well as DNA accessibility and repair are reviewed. In resistant cell lines that have decreased accumulation, this can be restored by hyperthermic treatment. With or without effects on accumulation compounds that affect cell signal transduction often increase CDDP cytotoxicity. Calcium channel blockers and calmodulin inhibitors do not seem to be uniformly good modulators of CDDP resistance. For transduction modulators as well as cellular calcium affecting agents mechanisms are mainly unclear or controversial. Glutathione appears, with the now available agents, to be the most promising target for modulation of cytoplasmic defense mechanisms. At the nuclear level the inhibition of DNA repair related enzymes as well as the use of modified nucleosides to interfere with repair is studied in various cell lines. Results with these agents suggest opportunities for clinically feasible cytotoxicity modulation. DNA accessibility could in vitro be affected, but seems to be an unreliable target for modulation. Whenever possible the resistance mechanism affected and the mode of action of the modulator are discussed. As an alternative for modulation another method of overcoming CDDP resistance namely the application of CDDP analogues is considered.

In vitro evaluation of platinum, titanium and ruthenium metal complexes in cisplatin-sensitive and -resistant rat ovarian tumors

The antitumor activity of eight new metal complexes (three platinum, one titanium, four ruthenium derivatives) was investigated in a cisplatin (DDP)--sensitive (O-342) and a DDP-resistant (O-342/DDP) ovarian tumor line using the bilayer soft-agar assay. A continuous exposure set up at logarithmically spaced concentrations was used to test the drugs; to uncover possible pharmacokinetic features, a short-term exposure was additionally included for selected compounds. DDP served as the reference drug. The following compounds were investigated: 18-crown-6-tetracarboxybis-diammineplatinum(II) (CTDP), cis-aminotrismethylenephosphonato-diammine-platinum(II) (ADP), cis-diamminecyclohexano-aminotrismethylenephosphonato-platin um(II) (DAP), diethoxybis(1-phenylbutane-1,3-dionato)titanium(IV) (DBT, budotitane), trans-imidazolium-bisimidazoletetrachlororuthenate(III) (ICR), trans-indazolium-tetrachlorobisindazoleruthenate(III) (IndCR), cis-triazolium-tetrachlorobis-triazoleruthenate(III) (TCR) and trans-pyrazolium-tetrachlorobispyrazoleruthenate(III) (PCR). Of the new metal complexes, CTDP was the most active compound in O-342, resulting in a percentage of control plating efficiency (+/- SE) of 1 +/- 1, 12 +/- 8 and 40 +/- 21 following continuous exposure to 10, 1 and 0.1 microM, respectively, and was thus comparable to DDP at equimolar concentrations. In the resistant line, 10 microM CTDP reduced colony growth to 18% +/- 8%, whereas an equimolar concentration of DDP effected a reduction to 26% +/- 9%. During short-term exposure. CTDP was inferior to DDP, which may be ascribed to the stability of the bis-dicarboxylate platinum ring system. The titanium compound DBT, in contrast, showed promising effects at its highest concentration (100 microM) during short-term exposure in both lines; at this concentration the activity in O-342/DDP was higher than that in O-342 (7% +/- 7% vs 34% +/- 17% of control plating efficiency at 100 microM). All ruthenium complexes showed higher activity in the resistant line O-342/DDP than in the sensitive counterpart. ICR was the most active compound. Following continuous exposure of O-342/DDP cells to 10 microM ICR, colony growth was reduced to 18% +/- 4% that of controls. Further studies should concentrate on CTDP and ICR for the following reasons; the activity of CTDP was equal to that of DDP at equimolar concentrations during continuous exposure; considering that the in vivo toxicity of DDP was 3-fold that of CTDP, an increase in the therapeutic index of CTDP would be expected. ICR showed the best effect of all ruthenium complexes; it was superior to DDP in the resistant line.