Structure-toxicity relationships for different types of dinuclear platinum complexes

Nine structurally distinct dinuclear platinum complexes have been evaluated in a novel model system for the investigation of renal epithelial toxicity of platinum drugs. The results showed that these compounds are toxic when applied at the basolateral side of renal epithelia, whereas their toxic effects on the apical side are negligible. Such a difference in toxicity of the complexes has been found to result from their poor uptake through the apical membrane, as compared to the basolateral membrane. Toxicity of the compounds on the basolateral side varies depending on their structure. Structure-toxicity relationships for the group of complexes with rigid ligands and for the group of complexes with flexible ligands are discussed. Among the dinuclear complexes with rigid ligands, sterically hindered complexes are less toxic, due to their poor uptake and low reactivity towards glutathione. Within the group of complexes with flexible ligands, cis-configured isomers are more toxic than their trans-counterparts.     

DNA-protein cross-linking by chromium salts

DNA-protein cross-links were detected in several types of mammalian cells in culture when they were exposed to chromate salts. The cell types included human bronchial epithelial cells — the apparent cell type of origin of the malignancies reported in chromate workers. The level of cross-linking was proportional to the concentration of chromate used. These cross-links appeared to be persistent since no removal was seen after 12 h of repair incubation. A low level of DNA single strand breaks (SSB) were also induced after exposure of the cells to chromate but were rejoined after 4 h of repair incubation. The active form of chromium appears to be the trivalent since chromic but not chromate salts induced DNA-protein cross-links in isolated nuclei. Chromic salts also produced cross-linking between DNA and protein in solution while the hexavalent form was inactive. These data imply that chromate crosses the cell membrane, is reduced to the trivalent form and induces stable linkages of DNA to protein.     

DNA-protein cross-linking by trans-[PtCl(2)(E-iminoether)(2)]. A concept for activation of the trans geometry in platinum antitumor complexes

The structure-pharmacological activity relationships generally accepted for antitumor platinum compounds stressed the necessity for the cis-[PtX(2)(amine)(2)] structure while the trans-[PtX(2)(amine)(2)] structure was considered inactive. However, more recently, several trans-platinum complexes have been identified which are potently toxic, antitumor-active and demonstrate activity distinct from that of conventional cisplatin (cis-[PtCl(2)(NH(3))(2)]). We have shown in the previous report that the replacement of ammine ligands by iminoether in transplatin (trans-[PtCl(2)(NH(3))(2)]) results in a marked enhancement of its cytotoxicity so that it is more cytotoxic than its cis congener and exhibits significant antitumor activity, including activity in cisplatin-resistant tumor cells. In addition, we have also shown previously that this new trans compound (trans-[PtCl(2)(E-iminoether)(2)]) forms mainly monofunctional adducts at guanine residues on DNA, which is generally accepted to be the cellular target of platinum drugs. In order to shed light on the mechanism underlying the antitumor activity of trans-[PtCl(2)(E-iminoether)(2)] we examined oligodeoxyribonucleotide duplexes containing a single, site-specific, monofunctional adduct of this transplatin analog by the methods of molecular biophysics. The results indicate that major monofunctional adducts of trans-[PtCl(2)(E-iminoether)(2)] locally distort DNA, bend the DNA axis by 21 degrees toward the minor groove, are not recognized by HMGB1 proteins and are readily removed from DNA by nucleotide excision repair (NER). In addition, the monofunctional adducts of trans-[PtCl(2)(E-iminoether)(2)] readily cross-link proteins, which markedly enhances the efficiency of this adduct to terminate DNA polymerization by DNA polymerases in vitro and to inhibit removal of this adduct from DNA by NER. It is suggested that DNA-protein ternary cross-links produced by trans-[PtCl(2)(E-iminoether)(2)] could persist considerably longer than the non-cross-linked monofunctional adducts, which would potentiate toxicity of this antitumor platinum compound toward tumor cells sensitive to this drug. Thus, trans-[PtCl(2)(E-iminoether)(2)] represents a quite new class of platinum antitumor drugs in which activation of trans geometry is associated with an increased efficiency to form DNA-protein ternary cross-links thereby acting by a different mechanism from 'classical' cisplatin and its analogs.     

Antitumor dinuclear platinum(II) complexes derived from a novel chiral ligand

A new chiral ligand, 2-(((1R,2R)-2-aminocyclohexyl)amino)acetic acid (HL), was designed and synthesized to prepare a series of novel dinuclear platinum(II) complexes with dicarboxylates or sulfate as bridges. The evaluation of these metal complexes in vitro cytotoxicity against human HCT-116, MCF-7 and HepG-2 cell lines were made. All compounds showed antitumor activity to HCT-116 and MCF-7. Particularly, compounds M3 and M5 not only exhibited better activity than carboplatin against MCF-7 and HepG-2, but also showed very close activity to oxaliplatin against HCT-116.     

Solid-phase synthesis and pharmacological evaluation of novel nucleoside-tethered dinuclear platinum(II) complexes

Three novel inosine-based dinuclear platinum complexes have been synthesized via a solid-phase strategy. In these compounds, the metal is linked both to the N-7 of the purine nucleus and to the terminal amine group of a hexylamine side chain installed on N-1. Cis- or trans- diamine as well as ethylenediamine ligands are coordinated to platinum along with a chloride. The synthesised complexes were tested against four different human tumor cell lines. One of these complexes proved to be more cytotoxic than cisplatin against the MCF7 cancer cell line in a short-term exposure assay.     

Design,synthesis and biological evaluation of six dinuclear platinum(II) complexes

Six dinuclear platinum(II) complexes with a chiral tetradentate ligand, (1R,1′R,2R,2′R)-N¹,N^1′-(1,4-phenylenebis(methylene))dicyclohexane-1,2-diamine, have been designed, synthesized and characterized. In vitro cytotoxicity evaluation of these metal complexes against human A549, HCT-116, MCF-7 and HepG-2 cell lines have been carried out. All compounds showed antitumor activity to HepG-2, HCT-116 and A549. Particularly, compounds A1 and A2 exhibited significant better activity than other four compounds and A2 even showed comparable cytotoxicity to cisplatin against HepG-2 cell line.     

Synthesis and evaluation of bi-functional 7-hydroxycoumarin platinum(IV) complexes as antitumor agents

A series of bi-functional 7-hydroxycoumarin platinum(IV) complexes were synthesized, characterized, and evaluated for antitumor activities. The 7-hydroxycoumarin platinum(IV) complexes display moderate to effective antitumor activities toward the tested cell lines and show much potential in overcoming drug resistance of platinum(II) drugs. In reducing microenvironment, the title compounds could be reduced to platinum(II) complex accompanied with two equivalents of coumarin units. By a unique mechanism, the 7-hydroxycoumarin platinum(IV) complex attacks DNA via the released platinum(II) compound, meanwhile it also inhibits the activities of cyclooxygenase by coumarin fragment. This action mechanism might be of much benefit for reducing tumor-related inflammation in the progress of inhibiting tumor proliferation and overcoming cisplatin resistance. The incorporation of 7-hydroxycoumarin leads to significantly enhanced platinum accumulation in both whole tumor cells and DNA. The HSA interaction investigation reveals that the tested coumarin platinum(IV) compound could effectively combine with HSA via van der Waals force and hydrogen bond.     

Effects of geometric isomerism in dinuclear antitumor platinum complexes on their interactions with N-acetyl-L-methionine

In this study, the reactions of N-acetyl-L-methionine (AcMet) with [{trans-PtCl(NH₃)₂}₂-μ-H₂N(CH₂)₆NH₂](NO₃)₂ (BBR3005: 1,1/t,t 1) and its cis analog [{cis-PtCl(NH₃)₂}₂-μ-{H₂N(CH₂)₆NH₂}]Cl₂ (1,1/c,c 2) were analyzed to determine the rate and reaction profile of chloride substitution by methionine sulfur. The reactions were studied in PBS buffer at 37°C by a combination of multinuclear (¹⁹⁵Pt, {¹H-¹⁵N} HSQC) magnetic resonance (NMR) spectroscopy and electrospray ionization time of flight mass spectrometry (ESITOFMS). The diamine linker of the 1,1/t,t trans complex was released as a result of the trans influence of the coordinated sulfur atom, producing trans-[PtCl(AcMet)(NH₃)₂]⁺ (III) and trans-[Pt(AcMet)₂(NH₃)₂]²⁺ (IV). In contrast the cis geometry of the dinuclear compound maintained the diamine bridge intact and a number of novel dinuclear platinum compounds obtained by stepwise substitution of sulfur on both platinum centers were identified. These include (charges omitted for clarity): [{cis-PtCl(NH₃)₂}-μ-NH₂(CH₂)₆NH₂-{cis-Pt(AcMet)(NH₃)₂}] (V); [{cis-Pt(AcMet)(NH₃)₂}₂-μ-NH₂(CH₂)₆NH₂] (VI); [{cis-PtCl(NH₃)₂}-μ-NH₂(CH₂)₆NH₂-{PtCl(AcMet)NH₃] (VII); [{PtCl(AcMet)(NH₃)}₂-μ-NH₂(CH₂)₆NH₂] (VIII); [{trans-Pt(AcMet)₂(NH₃)}-μ-NH₂(CH₂)₆NH₂-{PtCl(AcMet)(NH₃)] (IX) and the fully substituted [{trans-Pt(AcMet)₂(NH₃)}₂-μ-{NH₂(CH₂)₆NH₂] (X). For both compounds the reactions with methionine were slower than those with glutathione (Inorg Chem 2003, 42:5498–5506). Further, the 1,1/c,c geometry resulted in slower reaction than the trans isomer, because of steric hindrance of the bridge, as observed previously in reactions with DNA and model nucleotides.     

Contact-site cross-linking agents

Summary Contact-site cross-linking agents comprise a heterogeneous grouping of cross-linkers which share the common property of being able to cross-link only very closely juxtaposed residues in macromolecular complexes. We have defined contact-site cross-linking arbitrarily as the covalent joining of residues such that they are constrained to a distance which is equivalent to or less than their closest possible steric approach prior to becoming linked (1). We recognize two classes of contact-site cross-linkers, bridge type and zero-length type. The former, such as formaldehyde, become incorporated during cross-linking as one-atom bridges. The latter, such as the carbodiimides, operate as condensing agents with the result that the cross-linked residues become interjoined directly. Contact-site cross-linkers have been used in several ways as specific probes of both the static and dynamic aspects of macromolecular structure. They can yield precise structural information about macromolecular contacts when actual sites of cross-linking are determined by peptide or nucleotide mapping techniques. In this way exact contacs between histones in the nucleosome, between protein and RNA in the ribosome, and between RNA polymerase and DNA have been determined. Contact-site cross-linkers have also been used to probe the perturbation of contacts following macromolecular conformational changes. Certain histonehistone ‘cross-linkable’ sites are rendered unreactive after induction of chromatin conformational changes thus serving to localize sites of perturbation.     

Water-soluble platinum phthalocyanines as potential antitumor agents

Breast cancer represents the second cause of death in the European female population. The lack of specific therapies together with its high invasive potential are the major problems associated to such a tumor. In the last three decades platinum-based drugs have been considered essential constituents of many therapeutic strategies, even though with side effects and frequent generation of drug resistance. These drugs have been the guide for the research, in last years, of novel platinum and ruthenium based compounds, able to overcome these limitations. In this work, ruthenium and platinum based phthalocyanines were synthesized through conventional techniques and their antiproliferative and/or cytotoxic actions were tested. Normal mammary gland (MCF10A) and several models of mammarian carcinoma at different degrees of invasiveness (BT474, MCF-7 and MDA-MB-231) were used. Cells were treated with different concentrations (5–100 μM) of the above reported compounds, to evaluate toxic concentration and to underline possible dose–response effects. The study included growth curves made by trypan blue exclusion test and scratch assay to study cellular motility and its possible negative modulation by phthalocyanine. Moreover, we investigated cell cycle and apoptosis through flow cytometry and AMNIS Image Stream cytometer. Among all the tested drugs, tetrasulfonated phthalocyanine of platinum resulted to be the molecule with the best cytostatic action on neoplastic cell lines at the concentration of 30 μM. Interestingly, platinum tetrasulfophtalocyanine, at low doses, had no antiproliferative effects on normal cells. Therefore, such platinum complex, appears to be a promising drug for mammarian carcinoma treatment.     

Design, synthesis and in vitro cytotoxicity of novel dinuclear platinum(II) complexes

Five dinuclear platinum(II) complexes with a novel chiral ligand, 2-(((1R,2R)-2-aminocyclohexylamino)methyl)phenol (HL), were designed, prepared and spectrally characterized. In vitro cytotoxicity of all the resulting platinum(II) compounds was evaluated against human HEPG-2, A549 and HCT-116 cell lines, respectively. Results indicated that all compounds showed positive biological activity. Particularly, compound D4 has lower IC₅₀ values than carboplatin toward HEPG-2 and A549, while compound D5 shows better activity than carboplatin against A549.     

Glucose-conjugated platinum(IV) complexes as tumor-targeting agents: design,synthesis and biological evaluation

A new series of glucose-conjugated Pt(IV) complexes that target tumor-specific glucose transporters (GLUTs) was designed, synthesized, and evaluated for their anticancer activities. All six compounds, namely, A1-A6, exhibited increased cytotoxicity that were almost six fold higher than that of oxaliplatin to MCF-7 cells. These Pt(IV) complexes can be reduced to release Pt(II) complexes and cause the death of tumor cells. Simultaneously, the glycosylated Pt(IV) complexes (30.21–91.33?μM) showed lower cytotoxicity that normal LO2 cells compared with cisplatin (5.25?μM) and oxaliplatin (8.34?μM). The intervention of phlorizin as a GLUTs inhibitor increased the IC₅₀ value of the glycosylated Pt(IV) complexes, thereby indicating the potential GLUT transportability. The introduction of glucose moiety to Pt(IV) complexes can effectively enhance the Pt cellular uptake and DNA platination. Results suggested glucose-conjugated Pt(IV) complexes had potential for further study as new anticancer agents.     

Copper complexes as therapeutic agents

The importance of transition metals in biological processes has been well established. Copper (Cu) is a transition metal that can exist in oxidised and reduced states. This allows it to participate in redox and catalytic chemistry, making it a suitable cofactor for a diverse range of enzymes and molecules. Cu deficiency or toxicity is implicated in a variety of pathological conditions; therefore inorganic complexes of Cu have been investigated for their therapeutic and diagnostic potential. These Cu complexes have been shown to be effective in cancer treatment due to their cytotoxic action on tumour cells. Alternatively, Cu complexes can also modulate Cu homeostasis in the brain, resulting in protective effects in several models of neurodegeneration. In other diseases such as coronary heart disease and skin disease, the success of Cu complexes as potential therapeutics will most likely be due to their ability to increase SOD activity, leading to relief of oxidative stress. This review seeks to provide a broad insight into some of the diverse actions of Cu complexes and demonstrate the strong future for these compounds as potential therapeutic agents.     

Stable DNA-protein complexes in eukaryotic chromatin

Demembranized sperm and somatic nuclei of mammalian origin were extracted with high salt/urea/2-mercaptoethanol, treated with detergents and purified in CsCl density gradients to isolate DNA. Under these conditions a protein component still remained bound to DNA. This stable DNA-protein complex could be reduced to an oligodeoxynucleotide-peptide complex by extensive sequential digestions with DNase I and Pronase E. Chemical and enzymatic treatments of this complex indicated the presence of a phosphoester bond between DNA and a hydroxyamino acid. Two-dimensional tryptic peptide mapping revealed a remarkable similarity among the covalently linked protein components in all types of chromatin studied. These maps differed from the maps of mammalian topoisomerases I and II.     

B----Z DNA conformational changes induced by a family of dinuclear bis(platinum) complexes.

The reactions of bis(platinum) complexes of general formula [(PtClm(NH3)3-m)2(NH2(CH2)nNH2)]2(2-m)+ were studied with poly(dG-dC).poly(dG-dC), poly(dG-m5dC).poly(dG-m5dC) and poly(dG).poly(dC). When m = 0 (Complexes II, n = 2,4) the complexes are saturated 4+ cations capable only of electrostatic interactions with the polynucleotide. Where m = 1 the complexes contain two monodentate platinum coordination spheres with the chloride trans to the diamine bridge (Complexes I, n = 2,4, 1,1/t,t). Complexes I give CD spectra characteristic of a 'Z-like' conformation upon reaction with poly(dG-dC).poly(dG-dC) and poly(dG-m5dC).poly(dG-m5dC) but not poly(dG).poly(dC). The B----Z transition appears independent of interplatinum diamine chain length. As little as 1 bis(platinum) complex per 25-30 base pairs is sufficient to observe the Z-like spectrum. Covalent binding is however not a prerequisite for Z-DNA formation because the polyvalent cations II are also very effective in inducing the B----Z transition in either poly(dG-dC).poly(dG-dC) or poly (dG-m5dC).poly(dG-m5dC). In these cases, the concentrations of II required are significantly lower than analogous monomeric agents such as [Co(NH3)6]3+. The possible biological consequences of the Z-DNA induction by bis(platinum) complexes are discussed.