Hydrophobicity parameters for platinum complexes

Synthesis and antiproliferative activity of hindered, chiral 1,2-diaminodiamantane platinum(II) complexes

Platinum-based antineoplastic agents play a major role in the treatment of numerous types of cancer. A new bulky, lipophilic, and chiral ligand based on 1,2-diaminodiamantane in both of its enantiomeric forms was employed for the preparation of new platinum(ii) complexes with chloride and oxalate ligands. The dichloride complexes have a higher solubility and were evaluated as anti-proliferation agents for human ovarian cancer cell lines A2780 and cisplatin-resistant A2780cis. Its R,R-enantiomer showed increased efficacy compared to cisplatin for both cancer cell lines. A chromatographic approach was used to estimate the solvent partition coefficient of the dichloride complex. The binding of diamondoid-based platinum complexes to nucleotides was tested for both enantiomers with guanosine monophosphate (GMP) and deoxyguanosine monophosphate (dGMP) and occurs at a similar or faster rate for both isomers compared to cisplatin despite greatly increased steric demand. These findings highlight the potential in 1,2-diaminodiamantane as a viable pharmacophore.

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.

The cisplatin-based Pt(iv)-diclorofibrato multi-action anticancer prodrug exhibits excellent performances also under hypoxic conditions

The cisplatin/clofibrato combos are multi-action Pt(iv) complexes active on a panel of human tumor cell lines, also under hypoxic conditions.

Tumor microenvironment determines response to a heat-activated thermosensitive liposome formulation of cisplatin in cervical carcinoma

Significant heterogeneity in the tumor microenvironment of human cervical cancer patients is known to challenge treatment outcomes in this population. The current standard of care for cervical cancer patients is radiation therapy and concurrent cisplatin (CDDP) chemotherapy. Yet this treatment strategy fails to control loco-regional disease in 10-30% of patients. In order to improve the loco-regional control rate, a thermosensitive liposome formulation of CDDP (HTLC) was developed to increase local concentrations of drug in response to mild hyperthermia (HT). The HTLC formulation in combination with local HT demonstrated a significant therapeutic advantage in comparison to free drug and Lipoplatin™ in ME-180 and SiHa xenograft models of human cervical cancer, as well as in four distinct cervical patient-derived xenograft models. Differential response to HTLC+HT treatment was observed between the ME-180 and SiHa tumor models. Tumor doubling time, in vitro cell sensitivity, and tumor drug accumulation were found to be non-predictive of treatment efficacy. Rather, tumor microenvironment parameters, in particular elevated levels of both tumor hypoxia and associated stromal content, were found to serve as the overriding factors that limit drug efficacy. The prognostic value of these markers may enable stratification of cervical cancer patients for implementation of personalized medicine in the clinical setting.

Porous palladium aminophosphates: synthesis, characterization, antimicrobial and cytotoxicity studies

Novel palladium aminophosphates have been synthesized at room temperature in solvent free condition. They are characterized in detail. Their antimicrobial and cytotoxicity studies were carried out.

Interaction of cisplatin and two potential antitumoral platinum(ii) complexes with a model lipid membrane: a combined NMR and MD study

Multinuclear NMR and MD calculations highlighted the different interactions of cisplatin and two potential antitumoral Pt(ii) complexes with a model membrane.

Efficient preparation of 6-[18F]fluoroveratraldehyde, the precursor of the multi-step synthesis of [18F]FDOPA

As a clinically well established PET tracer, 6-[18F]fluoro-L-dopa is prepared by a multi-step synthesis if [18F]fluoride is to be used for labelling. The [18F] label is introduced in the first step, i.e. 6-[18F]fluoroveratraldehyde is prepared first with yields reported in the literature ranging between 20 and 50%. To obtain higher over-all yields in the synthesis of 6-[18F]fluoro-L-dopa, the 18F incorporation in the first step was optimised by determining the yield dependencies on solvent, concentration of the precursor, temperature and time of the reaction. Thus, the product is formed with a yield of 89 ± 2% (n = 15) when using 20 mg of 6-nitroveratraldehyde in 1 mL DMF at 140 °C within a reaction time of 10 min.

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.

The tert-butyl dimethyl silyl group as an enhancer of drug cytotoxicity against human tumor cells

In this study, we synthesized a series of enantiomerically pure (2R,3S)-disubstituted tetrahydropyranes with diverse functional groups using known methodologies. In addition to the tert-butyl dimethyl silyl group, other common protecting groups for hydroxyl groups such as allyl, acetate, and benzoate were used to obtain appropriate derivatives. Pure compounds were evaluated in vitro against HL60 human leukemia cells and MCF7 human breast cancer cells. From the growth inhibition data a structure-activity relationship was obtained. Overall the results point to the relevant role of the tert-butyl dimethyl silyl group in the modulation of cytotoxic activity.

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.

Improved potency of cisplatin by hydrophobic ion pairing

Cisplatin is one of the most widely used and effective chemotherapeutic drugs ever discovered against certain forms of cancer. However, its use is limited by toxicity. A more potent form might allow lower doses to be used and would diminish the toxicity. A new analog of cisplatin has been synthesized by stoichiometric replacement of the chloride ligands with the anionic surfactant, Aerosol OT (AOT). The new compound has a very low aqueous solubility (about 2 mg/l) and a log P value of 2.17, which is more than 4 log units higher than cisplatin itself, indicating a dramatic increase in hydrophobicity. While hydrophobic cisplatin analogs have been synthesized previously, this is the first one with readily dissociable ligands replacing the chlorides. The resultant AOT complex is able to penetrate cellular membranes more efficiently, resulting in a threefold to fivefold increase in intracellular platinum levels. These increased intracellular concentrations correlate with lower IC50 values in a number of cancer and normal cell lines. These findings suggest that further development of the AOT complex as a chemotherapeutic agent is warranted, given its marked increase in potency over the parent compound.

Coordination modes vs. antitumor activity: synthesis and antitumor activity of novel platinum(II) complexes of N -substituted amino dicarboxylic acids

The trans-(+/-)-1,2-diaminocyclohexaneplatinum(II) complexes of multidentate L-glutamate (Glu) and L-aspartate (Asp) were prepared and their antitumor activity was examined in relation with their coordination modes. All these complexes were obtained as a mixture of (O,O')- and (O,N)-chelate isomers due to rapid isomerization of the initially formed (O,O')-isomer to the thermodynamically more stable (O,N)-isomer. The (O,O')/(O,N)-isomeric mixture with the mole ratio of 80/20 exhibited excellent antitumor activity while the pure (O,N)-isomer was only marginally active. Therefore, in order to prevent the linkage isomerization of the active (O,O')-isomer to the inactive (O,N)-isomer, we have designed N-substituted amino dicarboxylic acids as a leaving group and prepared a new series of complexes, [Pt(dach)(RGlu)] and [Pt(dach)(RAsp)] (dach=trans-(+/-)-1,2-diaminocyclohexane; R=acetyl (Ac), propionyl (Pro), pivaloyl (Piv), carbobenzyloxy (Cbz) or phthaloyl (Phth)) and characterized by means of elemental analyses, and 1H NMR, 195Pt NMR and IR spectroscopies. The N-substituted amino dicarboxylate ligands were found to coordinate to platinum(II) ion through only the (O,O')-chelation mode, and their Pt(II) complexes were chemically stable in aqueous solution. The present Pt(II) complexes of N-substituted amino dicarboxylic acids showed excellent antitumor activity against both murine leukemia L1210 and human tumor cells. Especially, the highly hydrophobic N-phthaloylglutamate complex, [Pt(dach)(PhthGlu)], exhibited an outstanding in vitro activity (IC50=2.22 microM) on the human stomach cancer cells which are not responsive to cisplatin and carboplatin.

(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.

Calculation of the hydrophobicity of platinum drugs

Models of the hydrophobicity of platinum drugs based on exposed surface areas of polar and nonpolar atoms are presented. For a total of 24 log P(oct) data, the best model resulted in a standard deviation of 0.35 over a range of more than 4 log units, with regression coefficients in broad agreement with previous models of log P(oct) for organic molecules. This model is used to compare log P(oct) to cell uptake for five platinum drugs and hence to establish an exponential relation between these parameters.

Spectroscopic and biological properties of palladium(II) complexes of ethyl 2-quinolylmethylphosphonate

Spectroscopic (1H NMR, UV-visible) and biological (cytostatic, antiviral activity) studies of palladium(II) complexes of monoethyl 2-quinolymethylphosphonate (2-Hmqmp): dihalide adducts trans-Pd(2-Hmqmp)2X2, chelate Pd(2-mqmp)2.2H2O and ion-pair salt complexes [2-H2mqmp]+[Pd(2-Hmqmp)X3]- (X = Cl, Br), have been carried out in order to determine structural and biological properties of these biologically interesting complex compounds. The complexes were evaluated in vitro for their cytostatic activity against murine L1210 and human KB and T-lymphoblast Molt4/C8 and CEM/0 cell lines, and the results obtained were compared with those obtained for the complexes of diethyl 2-quinolylmethylphosphonate (2-dqmp). The L1210 cell was the most responsive line and complexes of diester 2-dqmp were more active than complexes of monoester 2-Hmqmp. A good relationship was observed between the cytostatic activity of the complexes and their lypophilicity or solubility. Some complexes exhibited significant cell growth inhibitory effects, but none of the them was more cytostatic than cisplatin. Both 2-dqmp and 2-Hmqmp complexes were also evaluated in vitro for their antiviral activity in different assay systems, comprising a broad spectrum of DNA and RNA viruses, but no specific antiviral effects were noted. In addition, the complexes did not show any specific anti-HIV activity.

Synthesis and in vitro cytotoxicity of lipophilic platinum(II) complexes

A number of lipophilic platinum(II) complexes of the general structures cis-[Pt(LA)2Cl2] and [Pt(LD)Cl2] were synthesised. Long chain amines (LA) and diamines (LD), prepared from lipidic amino acids, were used as ligands. The in vitro cytotoxicity of the complexes was evaluated against four cell lines (P388, NSCLC-N6, E39, M96). cis-Dichloro-bis(2-aminohexadecanol)platinum(II) was the most active against P388, NSCLC-N6 and E39 (IC50: 11 micrograms/ml, 25 micrograms/ml, 31 micrograms/ml), while dichloro(1,3-heptadecanediamine)platinum(II) presented the highest activity against M96 (IC50: 13 micrograms/ml).

Relationships between the aqueous chemistry and the in vitro cytotoxic activities of mixed-amine cisplatin analogues

The possibility that variations in the cytotoxic activities of cisplatin analogues could be a result of differences in the aqueous chemistry of the compounds was investigated. A series of structurally related mixed-amine dichloroplatinum complexes (cis-coordinated with amine and various diphenylmethylamines and 1,2-diphenylethylamines) was prepared and selected physicochemical properties of the new compounds were characterized. Cytotoxicity was determined in two human breast cancer cell lines (MDA-MB-231 and MCF-7) and one human ovarian cancer cell line (SK-OV-3) by means of a microtiter assay. There is no apparent relationship between the hydrophobicities of the compounds and their cytotoxic potencies. There is no evidence for an inverse relationship between the aqueous stability of the dichloroplatinum complexes and cytotoxic potency, as has been reported for nitrogen mustards and some nitrosoureas. The differences in cytotoxic activity cannot be explained by inter-compound variations in the area under the concentration-time curves (AUC) of the dichloroplatinum complexes in culture medium. Thus, it appears that the differences in the cytotoxic potencies of this series of cisplatin analogues are related to factors other than dissimilarities in these physiochemical properties. Nevertheless, a relationship was found between the AUC of a dichloroplatinum complex in medium and the efficacy of the compound in the MCF-7 cell line. However, the AUC-efficacy relationship does not always hold in the MDA-MB-231 and SK-OV-3 cell lines. In these cells, treatment with a "high" bolus dose of platinum complex over finite exposure times is often less cytotoxic than treatment with lower doses of the same compound but over a continuous exposure time, although the cells are subjected to the same AUC of dichloroplatinum complex.

Effect of the amine non-leaving group on the structure and stability of DNA complexes with cis-[Pt(R-NH2)2(NO3)2]

The antitumor compound cis-[Pt(NH3)2Cl2] (cisplatin), conserves two ammine ligands during the reaction with its cellular target DNA. Modifications of these non-leaving groups change the antineoplastic properties of this compound and its genotoxic effects. It is therefore of interest to determine the influence of non-leaving groups on the structure and stability of DNA in vitro. We have investigated platinum-DNA adducts formed by cis-[Pt(R-NH2)2(NO3)2] (where R-NH2 = NH3, methylamine, cyclobutylamine, cyclopentylamine and cyclohexylamine) as a function of DNA binding. All compounds quantitatively reacted with DNA in less than 1 h at 37 degrees C. They formed bifunctional adducts with adjacent nucleotides judging from the displacement of the intercalating molecule ethidium bromide, ultraviolet absorption spectroscopy and circular dichroism. Substitution of a H on the NH3 ligand by alkyl groups dramatically destabilized the platinum-DNA complex. Thermal stability decreased progressively with an increasing number of carbon atoms, delta tm = -4.4 degrees C for 3 cyclohexylamine-platinum-DNA adducts/1000 nucleotides, conditions where cisplatin had no effect. DNA adducts with cyclobutylamine and cyclohexylamine ligands inhibited the hydrolysis of platinum-DNA complexes by S1 nuclease. Km for the digestion of DNA containing these lesions was 2.3 times greater than for cisplatin, indicating steric inhibition of enzyme-substrate complex formation. These results show that the non-leaving groups of substituted cis-Pt(II) compounds may destabilize DNA and interfere with protein-DNA interactions. These perturbations may have consequences for the genotoxic and antitumor activities of platinum compounds.