Synthesis and structures of (SP-4-2)-diiodobis(2-hydroxyethylamine)platinum(II), (SP-4-2)-dichlorobis(2-hydroxyethylamine)platinum(II) and (OC-6-22)-bis(2-hydroxyethylamine)tetrachloroplatinum(IV) in the crystal

Simple Trans-Platinum Complex Bearing 3-Aminoflavone Ligand Could Be a Useful Drug: Structure-Activity Relationship of Platinum Complex in Comparison with Cisplatin

Following previous studies devoted to trans–Pt(3-af)₂Cl₂, in this paper, the molecular structure and intermolecular interactions of the title complex are compared with other cisplatin analogues of which the crystal structures are presented in the Cambridge Structural Database (CSD). Molecular Hirshfeld surface analysis and computational methods were used to examine a possible relationship between the structure and anticancer activity of trans–Pt(3-af)₂Cl₂. The purpose of the article was also to investigate the effect of hyperthermia on the anticancer activity of cisplatin, cytostatics used in the treatment of patients with ovarian cancer and a new analogue of cisplatin-trans–Pt(3-af)₂Cl₂. The study was conducted on two cell lines of ovarian cancer sensitive to Caov-3 cytostatics and the OVCAR-3 resistant cisplatin line. The study used the MTT (3-(4,5-dimethylthiazol-2,5-diphenyltetrazolium bromide) cell viability assay, LDH (lactate dehydrogenase), and the quantitative evaluation method for measuring gene expression, i.e., qPCR with TagMan probes. Reduced survivability of OVCAR-3 and Caov-3 cells exposed to cytostatics at elevated temperatures (37 °C, 40 °C, 43 °C) was observed. Hyperthermia may increase the sensitivity of cells to platinum-based antineoplastic drugs and paclitaxel, which may be associated with the reduction of gene expression related to apoptotic processes.

Improvements in the Synthesis and Understanding of the Iodo-bridged Intermediate en Route to the Pt(IV) Prodrug Satraplatin

Mixed amine/ammine motifs are important features in newer generation platinum anticancer agents, including the Pt(IV) prodrug satraplatin. One synthetic route that can be used to access platinum molecules with such structures exploits the trans effect during NH3-mediated cleavage of iodo-bridged platinum(II) dimers of the form [Pt(Am)I(μ-I)]2, where Am is an amine. A clear picture of the nature of these dimers that is consistent with the reactivity they exhibit has remained elusive. Moreover, technical aspects of this chemistry have impeded its more widespread use. We present here an improved strategy that permits isolation and use of [Pt(Am)I(μ-I)]2, where Am is cyclohexylamine, within minutes as opposed to weeks, as previously reported. A detailed spectroscopic, crystallographic, and chromatographic investigation of this intermediate in the synthesis of satraplatin is also presented with a discussion of the ability of both cis and trans isomers of the dimer to produce exclusively cis-[Pt(NH2C6H11)(NH3)I2] upon treatment with NH3.

Influence of extracellular pH on the cytotoxicity, cellular accumulation, and DNA interaction of novel pH-sensitive 2-aminoalcoholatoplatinum(II) complexes

Extracellular acidity is a frequent pathophysiological condition of solid tumors offering possibilities for improving the tumor selectivity of molecular therapy. This might be accomplished by prodrugs with low systemic toxicity, attaining their full antitumor potency only under acidic conditions, such as bis(2-aminoalcoholato-κ(2)N,O)platinum(II) complexes that are activated by protonation of alcoholato oxygen, resulting in cleavage of platinum-oxygen bonds. In this work, we examined whether the pH dependency of such compounds is reflected in differential biological activity in vitro. In particular, the pH dependence of cytotoxicity, cellular accumulation, DNA platination, GMP binding, effects on DNA secondary structure, cell cycle alterations, and induction of apoptosis was investigated. Enhanced cytotoxicity of five of these complexes in non-small-cell lung cancer (A549) and colon carcinoma (HT-29) cells at pH 6.0 in comparison with pH 7.4 was confirmed: 50 % growth inhibition concentrations ranged from 42 to 214 μM in A549 cells and from 35 to 87 μM in HT-29 cells at pH 7.4 and decreased at pH 6.0 to 11-50 and 7.3-25 μM, respectively. The effects induced by all five pH-sensitive compounds involve increased 5'-GMP binding, cellular accumulation, and DNA platination as well as stronger effects on DNA secondary structure at pH 6.0 than at pH 7.4. As exemplified by treatment of A549 cells with a 2-amino-4-methyl-1-pentanolato complex, induction of apoptosis is enhanced at pH 6.5. These results confirm the increased reactivity and in vitro activity of these compounds under slightly acidic conditions, encouraging further evaluation of ring-closed aminoalcoholatoplatinum(II) derivatives in solid tumors in vivo.

Synthesis, characterization, and cytotoxic activity of novel potentially pH-sensitive nonclassical platinum(II) complexes featuring 1,3-dihydroxyacetone oxime ligands

The reaction of 1,3-dihydroxyacetone oxime with diam(m)minediaquaplatinum(II) under basic conditions produced zwitterionic diam(m)mine(3-hydroxy-2-(oxidoimino)propan-1-olato-κ(2)N,O)platinum(II) complexes featuring the N,O-chelating ligand. Upon reaction with hydrochloric acid, it was possible to isolate either the singly protonated species still exhibiting the intact N,O-chelate or the open-chain chlorido complex. All complexes were characterized in detail with multinuclear ((1)H, (13)C, and (195)Pt) NMR spectroscopy, ESI mass spectrometry, and in one case X-ray diffraction. Cytotoxicity was investigated in three human cancer cell lines (CH1, SW480, and A549). The obtained IC(50) values are in the medium or even low micromolar range, remarkable for platinum complexes having N(3)O or N(3)Cl coordination spheres. To study the solution behavior of the prepared complexes at physiologically relevant proton concentrations, time-dependent (1)H NMR measurements were performed for the ethane-1,2-diamine-containing series at pH values of 7.4, 6.0, and exemplarily 5.0. While the zwitterionic complex proved to be stable at both pH 7.4 and 6.0, the protonated species were deprotonated at pH 7.4, tending toward ring opening in slightly acidic environments, as characteristic for many solid tumors. Finally, the open-chain form stayed intact at pH 6.0, being completely converted into its chelated analogue at pH 7.4. A pH-dependent evaluation of antiproliferative effects of the two latter complexes at pH 7.4 and pH 6.0 revealed an activation under slightly acidic conditions, which might be of interest for further in vivo studies.

Characterization of interactions between human serum albumin and tumor-inhibiting amino alcohol platinum(II) complexes using capillary electrophoresis

Platinum(II) complexes with amino alcohol ligands are of growing interest as anticancer agents capable of changing their reactivity toward biomolecules at different pH values. The binding of such compounds to the transport protein, human serum albumin (HSA), under simulated physiological conditions (pH 7.4, 100mM chloride, 37 degrees C) has been studied by capillary electrophoresis (CE), with the objective to acquire and compare their binding parameters. The association constants and stoichiometric ratios of the platinum-HSA adducts were determined by measuring the concentration changes of the peak area response of the Pt complex (after a 48 h incubation of the reaction mixture to attain equilibrium), constructing the binding isotherms, and their mathematical analysis. The investigated Pt(II) compounds were found to show moderate affinity toward HSA, with association constants ranging from 1.0 x 10(3) to 2.4 x 10(4)M(-1). Such binding behavior was attributed to a distinctive structural feature of bis(amino alcohol)platinum(II) complexes, that is, existence of an equilibrium between ring-opened and ring-closed forms in solution.

DNA Interactions of pH-Sensitive, Antitumor Bis(aminoalcohol)dichloroplatinum(II) Complexes,

(SP-4-2)-Bis(2-aminoethanol)dichloroplatinum(II) (KP1356) and (SP-4-2)-bis[(R)-(-)-2-aminobutanol)]dichloroplatinum(II) (KP1433) are promising cytotoxic agents capable of changing their chemical structure depending on the pH value. On the basis of this, they are supposed to be active only in or preferentially in hypoxic tumors with low pH. In this study, we investigated the kinetics of changes of the DNA secondary structure, of the DNA modification degree, and of the formation of interstrand cross-links caused by these complexes in comparison to the parental compound cis-diamminedichloroplatinum(II) (cisplatin). All examinations were performed at physiological pH 7.4 and at pH 6.0 mimicking the acidified environment of many tumor tissues. In general, cisplatin displayed a higher reactivity accompanied by more pronounced DNA compaction, untwisting, and formation of interstrand cross-links at both pH values. Additionally, it was shown for the first time that cisplatin generates interstrand cross-links faster at pH 6.0 than at 7.4. However, the difference between pH 7.4 and 6.0 was much larger for KP1356 and KP1433 than for cisplatin, since they were essentially nonreactive and induced almost no secondary structures at pH 7.4, as contrasted to cisplatin. Our data suggest that formed adducts, i.e., intra- and/or interstrand cross-links, may be the sole cause of the cytotoxicity of KP1356 and KP1433 at pH 6.0. The results of this study may stimulate and contribute to further improvement of these novel, specific cytotoxic drugs that are anticipated to exert their full power in the tumor while being reasonably inactive in normal tissue.

Tumour-inhibiting platinum(II) complexes with aminoalcohol ligands: biologically important transformations studied by micellar electrokinetic chromatography, nuclear magnetic resonance spectroscopy and mass spectrometry

(SP-4-2)-Bis[(R)-(-)-2-aminobutanol-kappaN]dichloroplatinum(II) and (SP-4-2)-bis[(R)-(-)-2-aminobutanolato-kappa2N,O]platinum(II) are promising cytotoxic agents exhibiting a strongly pH-dependent rate of reaction with the DNA-modeling nucleotide guanosine 5'-monophosphate (GMP). This potential mode-of-action binding, directly correlating with cytotoxicity, is influenced by the intramolecular chelation of bifunctional aminoalcohol ligands which was examined by means of micellar electrokinetic chromatography (MEKC) and nuclear magnetic resonance (NMR). While NMR clearly proves the existence of equilibrium between the ring-opened and ring-closed species, no such transformation was observed under MEKC conditions. In a kinetic study performed by MEKC, the half-lives of GMP bound to the platinum complexes were determined and compared to the kinetic data acquired by capillary zone electrophoresis. An appreciable increase in binding in the presence of sodium dodecyl sulfate (SDS) micelles was explained in terms of activation of (SP-4-2)-bis[(R)-(-)-2-aminobutanol-kappaN]dichloroplatinum(II). This apparently takes place due to the shifting of the equilibrium towards the ring-opened species, induced by adduct formation between SDS and the platinum complex that was confirmed by electrospray ionization mass spectrometry.

Tumor-inhibiting platinum(II) complexes with aminoalcohol ligands: comparison of the mode of action by capillary electrophoresis and electrospray ionization-mass spectrometry

Capillary electrophoresis (CE) was used as an assay for studying the interaction of (SP-4-2)-bis[(R)-(-)-2-aminobutanol)dichloroplatinum(II) (1) and (SP-4-2)bis(4-aminobutanol)dichloroplatinum(II) (2) with guanosine 5'-monophosphate (GMP). CE kinetic measurements carried out at two physiological pH levels indicated that upon increasing the pH, 1 showed an appreciable change in binding behavior, with the rate of binding increased for more than 10 times as expressed by apparent half-life values of GMP (6.1 and 62.2 h at pH 6.0 and 7.4, respectively). The rate of GMP binding for 2 remained comparatively less affected by pH (half-lives of 8.5 and 10.6 h, respectively). Regardless of the nature of platinum complex and pH, the reaction with GMP tends to be decelerated at increased chloride concentrations in solution, this effect being particularly pronounced when changing from 4 mM (intracellular level) to 100 mM (extracellular level). The kinetic differences of platinum complexes were characterized in terms of the respective GMP-adducts structure, independently identified by means of off-line electrospray ionization-mass spectrometry. Also addressed was the interpretation of binding behavior as based on the structural features of the intact complexes, namely differing inclination to intramolecular chelation.

Examination of the effects of oxidation and ring closure on the cytotoxicities of the platinum complexes of N-(2-hydroxyethyl)ethane-1,2-diamine and ethane-1,2-diamine-N,N'-diacetic acid

The crystal structures, electrochemical properties and cytotoxicities of platinum(II) and platinum(IV) complexes of the multidentate ligands N-(2-hydroxyethyl)ethane-1,2-diamine (NNOH) and ethane-1,2-diamine-N,N'-diacetic acid (H(2)enda) are reported. In the platinum(II) state the NNOH and H(2)enda ligands act as bidentate ligands, coordinating through the two amine groups with the hydroxyethyl and carboxylate groups remaining uncoordinated. Oxidation with hydrogen peroxide followed by refluxing yields the ring closed Pt(IV) complexes in which the NNOH and H(2)enda ligands are deprotonated and coordinate via the two amine groups and either the deprotonated alcohol group in the case of NNO or both carboxylato groups in the case of enda. The platinum(IV) complex of NNO is 2- to 5-fold more active against a panel of cisplatin sensitive and resistant human tumour cell lines than is the platinum(II) complex, whereas in the case of enda, the reverse is true. Ring closure to occupy both axial sites apparently leads to deactivation of platinum(IV) complexes, but a single closure does not necessarily do so.

(Aminoethanol)dichloroplatinum(II) complexes: influence of the hydroxyethyl moiety on 5'-GMP and DNA binding, intramolecular stability, the partition coefficient and anticancer activity

The influence of tethered hydroxyl groups on the binding behavior of the three (aminoethanol)dichloroplatinum complexes, dichloro(N,N'-bis(2-hydroxyethyl)ethylenediamine)-platinum(II) (1), dichloro(N-(2-hydroxyethyl)ethylenediamine)platinum(II) (2) and cis-dichlorobis(2-hydroxyethylamine)platinum(II) (3) towards 5'-GMP and DNA was investigated by 1H NMR and r(b) measurements, respectively. At pH 7.2, the sequence of reactivity with 5'-GMP is 1>2>>3. Complex 3 reacts very slowly with 5'-GMP and DNA and the amount and lifetime of the intermediate 5'-GMP monoadduct are much larger than for 1 and 2. At pH 5.5, the reaction of 3 with 5'-GMP is markedly accelerated and very small amounts of monoadduct are observed, indicating a pH-dependent ability of the pendant hydroxyl group to interact with the platinum moiety. In addition, the effect of the hydroxyethyl functionality on octanol/water partitioning and in vitro anticancer activity was studied. No correlation between lipophilicity and anticancer activity was detected. Furthermore, the lipophilicity and anticancer activity could not be directly correlated to 5'-GMP or DNA binding activity.

Reaction monitoring of platinum(II) complex--5'-guanosine monophosphate adduct formation by ion exchange liquid chromatography/electrospray ionization mass spectrometry

Cisplatin and four structurally related platinum(II) complexes were incubated with guanosine 5'-monophosphate (5'-GMP) in water at 37 degrees C. The adduct formation reactions were monitored with cation- and anion-exchange liquid chromatography/electrospray ionization mass spectrometry. In addition to mono- and bis-adducts of guanosine 5'-monophosphate with the platinum(II) complexes, other molecular species, presumably with a binuclear structure (two platinum(II) centres), were detected in the reaction mixtures, which have not been reported previously, indicating an unexpected complexity of adduct formation. Anion-exchange chromatography revealed the presence of isomers of two complexes which presumably result from the restricted rotation at the platinum-- N-7 (5'-GMP) bonds. All reaction products were characterized in both the positive and negative ion modes. Furthermore, preliminary kinetics and half-times of complex formation were investigated for cisplatin and two other platinum(II) complexes, monitoring the relative concentrations of free 5'-GMP and of mono- and bis-GMP adducts as a function of time (250 h) using an internal standard protocol with thymidine 5'-monophosphate.