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

Development and Validation of Liquid Chromatography-Based Methods to Assess the Lipophilicity of Cytotoxic Platinum(IV) Complexes

Lipophilicity is a crucial parameter for drug discovery, usually determined by the logarithmic partition coefficient (Log P) between octanol and water. However, the available detection methods have restricted the widespread use of the partition coefficient in inorganic medicinal chemistry, and recent investigations have shifted towards chromatographic lipophilicity parameters, frequently without a conversion to derive Log P. As high-performance liquid chromatography (HPLC) instruments are readily available to research groups, a HPLC-based method is presented and validated to derive the partition coefficient of a set of 19 structurally diverse and cytotoxic platinum(IV) complexes exhibiting a dynamic range of at least four orders of magnitude. The chromatographic lipophilicity parameters φ0 and Log kw were experimentally determined for the same set of compounds, and a correlation was obtained that allows interconversion between the two lipophilicity scales, which was applied to an additional set of 34 platinum(IV) drug candidates. Thereby, a φ0 = 58 corresponds to Log P = 0. The same approaches were successfully evaluated to determine the distribution coefficient (Log D) of five ionisable platinum(IV) compounds to sample pH-dependent effects on the lipophilicity. This study provides straight-forward HPLC-based methods to determine the lipophilicity of cytotoxic platinum(IV) complexes in the form of Log P and φ0 that can be interconverted and easily expanded to other metal-based compound classes.

Anticancer activity of a cis-dichloridoplatinum(ii) complex of a chelating nitrogen mustard: insight into unusual guanine binding mode and low deactivation by glutathione

A platinum(ii) complex (2) of a chelating nitrogen mustard shows potency against MIA PaCa2.2displays anti-angiogenic potential and displays excellent cytotoxicity profile even in presence of GSH in hypoxia.

Synthesis, Characterization, and Interaction with Biomolecules of Platinum(II) Complexes with Shikimic Acid-Based Ligands

Starting from the active ingredient shikimic acid (SA) of traditional Chinese medicine and NH₂(CH₂)_nOH, (n = 2–6), we have synthesized a series of new water-soluble Pt(II) complexes PtL^a–eCl₂, where L^a–e are chelating diamine ligands with carbon chain covalently attached to SA (L^a–e = SA-NH(CH₂)_nNHCH₂CH₂NH₂; L^a, n = 2; L^b, n = 3; L^c, n = 4; L^d, n = 5; L^e, n = 6). The results of the elemental analysis, LC-MS, capillary electrophoresis, and ¹H, ¹³C NMR indicated that there was only one product (isomer) formed under the present experimental conditions, in which the coordinate mode of PtL^a–eCl₂ was two-amine bidentate. Their in vitro cytotoxic activities were evaluated by MTT method, where these compounds only exhibited low cytotoxicity towards BEL7404, which should correlate their low lipophilicity. The interactions of the five Pt(II) complexes with DNA were investigated by agarose gel electrophoresis, which suggests that the Pt(II) complexes could induce DNA alteration. We also studied the interactions of the Pt(II) complexes with 5′-GMP with ESI-MS and ¹H NMR and found that PtL^bCl₂, PtL^cCl₂, and PtL^dCl₂ could react with 5′-GMP to form mono-GMP and bis-GMP adducts. Furthermore, the cell-cycle analysis revealed that PtL^bCl₂, PtL^cCl₂ cause cell G₂-phase arrest after incubation for 72 h. Overall, these water-soluble Pt(II) complexes interact with DNA mainly through covalent binding, which blocks the DNA synthesis and replication and thus induces cytotoxicity that weakens as the length of carbon chain increases.

Synthesis, characterization and antitumor properties of two highly cytotoxic ruthenium(iii) complexes with bulky triazolopyrimidine ligands

Two ruthenium(III) complexes composed of 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp) ligands were prepared and structurally characterized by X-ray crystallography, IR, UV-Vis, EPR spectroscopies and cyclic voltammetry (CV). The crystal structures of trans-[RuCl(3)(H(2)O)(dbtp)(2)] 1 and mer-[RuCl(3)(dbtp)(3)]·0.815OCMe(2) 2 showed slightly distorted octahedral geometries with two 1 or three 2 monodentate dbtp ligands bound in a head-to-head orientation. In both complexes, the heterocyclic dbtp ligands were bound to the ruthenium(III) ion through the N3 nitrogen atom. A cytotoxicity assay of both ruthenium(III) compounds against two human cell lines (A549 - non-small cell lung carcinoma and T47D - breast carcinoma) was performed. The ruthenium(III) complexes showed excellent cytotoxicity with IC(50) values in the range of 0.02-2.4 μM against both cancer cell lines. In addition, the in vitro cytotoxic values of the ruthenium(III) compounds were 35-times for 1 and 172-times for 2 higher against T47D than the clinically used antitumor drug cisplatin.

Identification of Binding Mode of a Platinum (II) Complex, PtCl(2)(DIP), and Calf Thymus DNA

The Pt(II) complex, PtCl₂(DIP) (DIP = chelating dinitrogen ligand: 4,7-diphenyl-1,10-phenanthroline), was synthesized and characterized by elemental analysis (CHN) and ¹H NMR and UV-vis techniques. The binding of this complex to calf thymus DNA was investigated using various physicochemical methods such as spectrophotometric, circular dichroism, spectrofluorometric, melting temperature, and viscosimetric techniques. Upon addition of the complex, important changes were observed in the characteristic UV-Vis bands (hyperchromism) of calf thymus DNA (CT-DNA): increase in melting temperature, sharp increase in specific viscosity of DNA, and induced CD spectral changes. Also the fluorescence spectral characteristics and interaction of Pt complex with DNA have been studied. Pt bound to DNA showed a marked decrease in the fluorescence intensity. The results show that both the complex and the NR molecules can intercalate competitively into the DNA double-helix structure. The experimental results show that the mode of binding of the this complex to DNA is classical intercalation.

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.

Mono- and dinuclear platinum(II) compounds with 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine. Structure, cytotoxic activity and reaction with 5'-GMP

Mono- and dinuclear platinum(II) coordination compounds of formula cis-[PtCl(2)(NH(3))(dmtp)], 1, cis-[PtCl(2)(dmtp)(2)], 2 and {H(+)[C(28)H(32)Cl(2)N(16)Pt(2)](2+)(NO(3))(3)(H(2)O)(6)}, 3, in which dmtp is 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine have been synthesized and characterized by infrared and by (1)H, (13)C, (195)Pt NMR spectroscopy. The coordination units of the cationic species of formula [Pt(2)(mu-dmtp)(2)Cl(2)(dmtp)(2)](2+) are built up by two platinum atoms in a square-planar environment. Two sites are occupied by two 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) bridging ligands which are linked to both metal atoms through their nitrogen atoms in positions 3 and 4. The other two positions are occupied by one monodentate 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) molecule and a coordinated chloride. This compound is the first in which the same triazolopyrimidine ligand (dmtp) coordinates to a metal ion in two different ways, i.e. bridging bidentate and non-bridging monodentate. In addition, the interaction of compounds 1 and 2 with 5'-GMP was investigated in solution by (1)H NMR spectroscopy. The cytotoxicity of all the new platinum(II) compounds were studied by using two different cell lines: T47D (breast cancer) and HCV29T (bladder cancer).

Calculation of lipophilicity of a large, diverse dataset of anticancer platinum complexes and the relation to cellular uptake

A quantitative structure--property relationship (QPSR) for the octanol--water partition of platinum complexes was constructed using molecular descriptors derived from density functional (DFT) calculations. A dataset of partition data for 64 complexes, consisting of 43 square-planar platinum(II) and 21 octahedral platinum(IV) complexes, was drawn from literature sources. Not only does this dataset include considerable structural diversity of complexes considered but also a variety of techniques for the measurement of partition coefficients. These data were modeled using descriptors drawn from electrostatic potentials and hardness/softness indices projected onto molecular surfaces. This required initial descriptor selection using a genetic algorithm approach, followed by partial least-squares regression against log Po/w data. In this way, a statistically robust model was constructed, with errors of similar size to the variation in log Po/w from multiple experimental measurements. Implications of lipophilicity for cellular accumulation of Pt-based drugs, and hence for design of new drugs, are discussed, as is the uptake of metabolites of cisplatin.

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.

Contributions of Hydroxyethyl Groups to the DNA Binding Affinities of Anthracene Probes

Contributions of hydroxyethyl functions to the DNA binding affinities of substituted anthracenes are evaluated by calorimetry and spectroscopy. Isothermal titration calorimetry indicated that binding of the ligands to calf thymus DNA (5 mM Tris buffer, 50 mM NaCl, pH 7.2, 25 degrees C) is exothermic. The binding constants increased from 1.5 x 10(4) to 1.7 x 10(6) M(-1) as a function of increase in the number of hydroxyethyl functions (0-4). DNA binding was accompanied by red-shifted absorption (approximately 630 cm(-1)), strong hypochromism (>65%), positive induced-circular dichroism bands, and negative linear dichroism signals. DNA binding, in general, increased the helix stabilities to a significant extent (DeltaT(m) approximately 7 degrees C, DeltaDeltaH approximately 3 kcal/mol, DeltaDeltaS approximately 6-20 cal/K.mol). The binding constants showed a strong correlation with the number of hydroxyethyl groups present on the anthracene ring system. Analysis of the binding data using the hydrophobicity parameter (Log P) showed a poor correlation between the binding affinity and hydrophobicity. This observation was also supported by a comparison of the affinities of probes carrying N-ethyl (Kb = 0.8 x 10(5) M(-1)) versus N-hydroxyethyl side chains (Kb = 5.5 x 10(5) M(-1)). These are the very first examples of a strong quantitative correlation between the DNA binding affinity of a probe and the number of hydroxyethyl groups present on the probe. These quantitative findings are useful in the rational design of new ligands for high-affinity binding to DNA.

Synthesis and Characterization of a New Macrocyclic Copper(II) Complex with anN-Glycosidic Pendant Arm:in vitro Cytotoxicity and Binding Studies with Calf-Thymus DNA

The new macrocyclic complex 2-amino-2-deoxy-N-[2-(1,3,5,8,11-pentaazacyclotridecan-3-yl)ethyl]-beta-D-glucopyranosylamine copper(II) dichloride (1a) was prepared and thoroughly characterized by various techniques. Molar-conductance measurements showed that 1a (and its Ni analogue 1b) are ionic in nature. On the basis of spectroscopic data, both complexes were assigned a square-planar geometry, and found to be highly stabile and hydrolytically robust in H2O over a wide range of pH, as confirmed by cyclic voltammetry (CV). The Cu(II) complex 1a was found to bind to CT-DNA, with a binding constant Kb of 2.4x10(3) M(-1), as derived by UV/VIS titration, and confirmed by CV, circular dichroism (CD), and viscosity measurements. DNA binding seems to occur mostly via H-bonding. In an in vitro antitumor MTT assay, 1a exhibited significant anticancer activity against the SY5Y and PC-12 cell lines, with an estimated IC50 value in the micromolar range for SYSY, similar to the standard drug 5-fluorouracil.

Synthesis, characterization and biological activity of trans-platinum(II) and trans-platinum(IV) complexes with 4-hydroxymethylpyridine

The synthesis and chemical characterization of two new trans platinum complexes, trans-[PtCl(2)NH(3)(4-hydroxymethylpyridine)] (1) and trans-[PtCl(4)NH(3)(4-hydroxymethylpyridine)] (2) are described. Their ability to interact with 5'-GMP by themselves and in the presence of reducing agents in the case of trans-[PtCl(4)NH(3)(4-hydroxymethylpyridine)] were tested. Circular dichroism, electrophoretic mobility in agarose gel, and atomic force microscopy studies showed that the interaction of complex 1 with DNA is stronger than that of complex 2. Cytotoxicity tests against HL-60 tumor cells also showed higher activity for trans-[PtCl(2)NH(3)(4-hydroxymethylpyridine)] than for trans-[PtCl(4)NH(3)(4-hydroxymethylpyridine)]. Complex 1 presents similar behavior to cisplatin, but with a lower IC(50) at 24 h. Complex 1 also showed high apoptosis induction.

Water-soluble platinum(II) complexes of diamine chelating ligands bearing amino-acid type substituents: the effect of the linked amino acid and the diamine chelate ring size on antitumor activity, and interactions with 5'-GMP and DNA

Six new Pt(II) complexes are described having the general formula PtCl(2)(LL), in which LL is a chelating diamine ligand bearing an amino acid as substituent. The amino acids chosen are l-alanine and its methyl ester, and l-phenylalanine. The compounds have been characterized using analytical and spectroscopic methods. The influence on the biological properties of the size of the chelate ring and the structure of the amino acid substituent has been studied. The effect of the presence of a carboxylic or carboxylate group on the amino acid C-terminus has also been determined. It is demonstrated by circular dichroism (CD) that the effect on the secondary structure of DNA induced by the six complexes differ from each other. In all cases, the interaction takes place at the N7 position of the purine bases, as shown by NMR monitoring. The general behavior of these platinum complexes, with one exception, is to uncoil the DNA from the B form to the C form. The interactions with 5'-GMP and DNA have been compared with their expected antitumour activity. The complexes with l-alanine and l-phenylalanine exhibit cytotoxic activity in HeLa and HL-60 cell lines, in a dose- and time-dependent manner. No cytotoxic activity of the methyl ester derivatives have been determined because of their low solubility in aqueous solution.

Intrinsically fluorescent cytotoxic cisplatin analogues as DNA marker molecules

Two square planar derivatives of Pt(en)Cl(2) with intrinsic fluorescence in aqueous solution at room temperature, with quantum yields (Phi) 0.11 and 0.10, respectively, have been synthesized and characterized as [Pt(en)(CG)Cl] (Complex 1) and [Pt(en)(CG)(2)] (Complex 2) (en = ethylenediamine, CG = cholylglycinate). Complexes 1 and 2 exchange just one ligand (chloride or cholylglycinate, respectively) when reacted with water or 5'-GMP to give the same chemical species. After reaction with DNA oligonucleotides or DNA plasmids, they show enhanced emission in the visible region, which lasts for long periods of time and makes them potentially useful DNA marker molecules. Incubation with nucleated blood cells followed by microscopic analyses revealed that they enter the cells within minutes of exposure, selectively stain the DNA, and persist after more than 48 h of exposure. Complexes 1 and 2 display cell cycle phase-independent cytotoxic activity against cisplatin-resistant CHO (Chinese hamster ovarian) tumor cells, with an early onset of their effects. Their slightly different biological effects, as compared to cisplatin, are considered to be linked to the bile acids and their vector properties and to the preferential formation of monoadducts.

The mechanism of action of platinum(IV) complexes in ovarian cancer cell lines

The reduction potentials, lipophilicities, cellular uptake and cytotoxicity have been examined for two series of platinum(IV) complexes that yield common platinum(II) complexes on reduction: cis-[PtCl(4)(NH(3))(2)], cis,trans,cis-[PtCl(2)(OAc)(2)(NH(3))(2)], cis,trans,cis-[PtCl(2)(OH)(2)(NH(3))(2)], [PtCl(4)(en)], cis,trans-[PtCl(2)(OAc)(2)(en)] and cis,trans-[PtCl(2)(OH)(2)(en)] (en=ethane-1,2-diamine, OAc=acetate). As previously reported, the reduction occurs most readily when the axial ligand is chloride and least readily when it is hydroxide. The en series of complexes are marginally more lipophilic than their ammine analogues. The presence of axial chloride or acetate ligands results in a slighter higher lipophilicity compared with the platinum(II) analogue whereas hydroxide ligands lead to a substantially lower lipophilicity. The cellular uptake is similar for the platinum(II) species and their analogous tetrachloro complexes, but is substantially lower for the acetato and hydroxo complexes, resulting in a correlation with the reduction potential. The activities are also correlated with the reduction potentials with the tetrachloro complexes being the most active of the platinum(IV) series and the hydroxo being the least active. These results are interpreted in terms of reduction, followed by aquation reducing the amount of efflux from the cells resulting in an increase in net uptake.

Uptake of antitumor platinum(II)-complexes by cancer cells, assayed by inductively coupled plasma mass spectrometry (ICP-MS)

A systematic study on intracellular Pt uptake and Pt accumulation ratio in breast cancer MCF-7 cell line has been performed on a number of Pt(II)-complexes, namely cisplatin, carboplatin and oxaliplatin, clinically employed as antitumor drugs, trans- and cis-[Pt(Cl)2(pyridine)2] and cis-[Pt(Cl)2(pyridine)(5-SO3H-isoquinoline)] complexes, previously investigated also as potential telomerase inhibitors. In particular, long incubation times have been chosen in order to understand the fate of the complexes in the cells. For this purpose, sub-acute drug concentrations must be employed and, therefore, a very sensitive method of analysis like as inductively coupled plasma mass spectrometry (ICP-MS) superior to the widely employed atomic absorption spectroscopy (AAS) has been adopted. Any relationships among uptake/accumulation and several parameters such as drug structure, lipophilicity, drug concentration and incubation time have been sought and analyzed: the bulk of data point for a passive diffusion mechanism through the cell membrane.

Platinum complexes of diaminocarboxylic acids and their ethyl ester derivatives: the effect of the chelate ring size on antitumor activity and interactions with GMP and DNA

A number of new Pt(II) complexes is described having the general formula PtCl(2)(LL), where LL is a chelating diamine ligand. Ligands LL were chosen as D,L-2,3-diaminopropionic acid and its ethyl ester, and D,L-2,4-diaminobutyric acid and its ethyl ester. The compounds were characterized using analytical and spectroscopic methods. The influence of the size of the chelate ring and its functionalization on the biological properties was studied. It was demonstrated by circular dichroism (CD) that the effects on the secondary structure of DNA induced by the four complexes are different. The interaction takes place at the N7 position of the purine bases, as shown by NMR studies. The platinum complexes of 2,3-diaminopropionic acid and 2,4-diaminobutyric acid are able to form intrastrand adducts with DNA and to distort the double helix by changing the base stacking. The ethyl ester derivatives uncoil the DNA from the B form to the C form. The interactions with 5'-GMP and DNA were compared with their antitumor activity. The platinum complexes of diaminocarboxylic acids exhibit cytotoxic activity in the A431, HeLa, and HL-60 cell lines in a dose- and time-dependent manner.

New clues for platinum antitumor chemistry: kinetically controlled metal binding to DNA

From the metal ions and metal compounds that are known to bind to DNA, many anticancer Pt(II) and Ru(II)Ru(III) compounds are known to have ligand-exchange kinetics in the same order of magnitude as the division of tumor cells. The present article discusses this process in detail with special attention to cisplatin and related compounds and the cellular binding sites and processes of such compounds. Detailed platinated DNA structures are presented and discussed in light of the mechanistic studies of metal antitumor compounds. It is now known that platinum antitumor drugs eventually end up on the DNA. However, it remains a challenge to understand how (fast) they reach the DNA and how they are removed. The kinetics of ligand exchange around platinum appear to play a crucial role, and the possible role of other ligands as intermediates, especially those with S-donor sites, is of great interest. New types of Pt compounds with additional functionalities influencing DNA binding and kinetics are discussed in the context of steric and H-bonding properties. A comparison is made with more sterically crowded Ru complexes. The effects on activity and correlations with structural and kinetic properties are clues in understanding the biological activities of these classes of compounds.