Influence of time and chloride ions on the interaction of cisplatin with human albumin in-vitro

Efficacy and Safety of Human Serum Albumin-Cisplatin Complex in U87MG Xenograft Mouse Models

Cisplatin (cis-diamminedichloroplatinum (II), CDDP) is a chemotherapeutic drug widely used against many solid tumors. A pharmacokinetics study found that CDDP can bind to human serum albumin (HSA), which is the most abundant plasma protein in serum. HSA has the advantage of being a nanocarrier and can accumulate in tumors by passive targeting and active targeting mediated by the secreted protein acidic and rich in cysteine (SPARC). In this study, we investigated the possibility of using a CDDP-HSA complex (HSA-CDDP) as a SPARC-mediated therapeutic agent. To investigate the HSA-dependent therapeutic effect of HSA-CDDP, we used two types of U87MG glioma cells that express SPARC differently. HSA-CDDP was highly taken up in SPARC expressing cells and this uptake was enhanced with exogenous SPARC treatment in cells with low expression of SPARC. The cytotoxicity of HSA-CDDP was also higher in SPARC-expressing cells. In the tumor model, HSA-CDDP showed a similar tumor growth and survival rate to CDDP only in SPARC-expressing tumor models. The biosafety test indicated that HSA-CDDP was less nephrotoxic than CDDP, based on blood markers and histopathology examination. Our findings show that HSA-CDDP has the potential to be a novel therapeutic agent for SPARC-expressing tumors, enhancing the tumor targeting effect by HSA and reducing the nephrotoxicity of CDDP.

Cisplatin binding to human serum albumin: a structural study

The reaction between cisplatin and human serum albumin (HSA) was investigated by X-ray crystallography and crystal structures of the cisplatin/HSA adduct were eventually solved for the first time. Structural data unambiguously prove that cisplatin mainly binds to His105 and Met329 side chains; additional binding sites are detected at His288, Met298, and Met548 and at His535, His67 and His247.

A study of the interactions between carboplatin and blood plasma proteins using size exclusion chromatography coupled to inductively coupled plasma mass spectrometry

To study the carboplatin-protein interaction, a sensitive method using size exclusion chromatography coupled to inductively coupled plasma mass spectrometry (SEC-ICP-MS) was developed. The complexes formed between plasma proteins and carboplatin were monitored and identified with this method. Composite blood plasma samples from patients who were undergoing chemotherapy were analyzed, and carboplatin was found to bind plasma proteins. In addition, blank plasma samples were spiked with carboplatin and were analyzed as a time course study, and the results confirmed that carboplatin formed complexes with plasma proteins, primarily albumin and gamma-globulin. To further substantiate the study, these two proteins were incubated with carboplatin. The binding between carboplatin and these proteins was then characterized qualitatively and quantitatively. In addition to a one-to-one binding of Pt to protein, protein aggregation was observed. The kinetics of the binding process of carboplatin to albumin and gamma-globulin was also studied. The initial reaction rate constant of carboplatin binding to albumin was determined to be 0.74 M(-1) min(-1), while that for gamma-globulin was 1.01 M(-1) min(-1), which are both lower than the rate constant of the cisplatin-albumin reaction previously reported.

Determination of binding constants and stoichiometries for platinum anticancer drugs and serum transport proteins by capillary electrophoresis using the Hummel-Dreyer method

A CE method has been developed to evidence and quantitatively characterize the interaction between platinum-based antitumor drugs and human serum proteins. This method is a variant of affinity CE modified regarding both experimental setup and data treatment so as to measure the peaks (or vacancies) that correspond to the bound drug when it slowly binds to the protein. Using the formalism of the Hummel-Dreyer method and cisplatin and oxaliplatin as test compounds, a protocol for determining albumin and transferrin binding constants and stoichiometries, including (and distinguished by) 48 hours of incubation of the reaction mixture, was elaborated. Relative affinities of drugs toward different proteins in aqueous solution at physiological pH, chloride concentration, and temperature were compared in terms of overall binding constants and numbers of drug molecules attached to the protein. The results indicate that both platinum drugs bind to albumin more strongly than to transferrin, supporting the concept that the albumin fraction is a major drug supply route for chemotherapeutical needs. From a comparison with the binding parameters measured previously for cisplatin by other methods, conclusions were drawn about the validity of CE as a simple and convenient method for assaying protein-drug reactions with slow kinetics.

Platinum metallodrug-protein binding studies by capillary electrophoresis-inductively coupled plasma-mass spectrometry: characterization of interactions between Pt(II) complexes and human serum albumin

Characterizing how platinum metallocomplexes bind to human serum albumin (HSA) is essential in evaluating anticancer drug candidates. Using cisplatin as a reference complex, the application of capillary electrophoresis (CE) to reliably assess drug/HSA interactions was validated. Since this complex is small compared to the size of the protein, the binding response could only be recognized when applying CE coupled to a (platinum) metal-specific mode of detection, namely inductively coupled plasma-mass spectrometry (ICP-MS). This coupling allowed for confirmation of a specific affinity of cisplatin and novel Pt complexes to HSA, measurement of the kinetics of binding reactions, and determination of the number of drug molecules attached to the protein. As the cisplatin/HSA molar ratio increased, the reaction rate became faster with a maximum on the kinetic curve appearing at about 50 h of incubation at 20 times excess of cisplatin. The reaction was characterized as a pseudo-first order reaction with the rate constant k = 0.003 min(-1) at 37 degrees C. When incubated with a 20-fold excess of cisplatin, HSA bound up to 10 mol of Pt per mol of the protein. This is indicative for a strong metal-protein coordination occurring at several HSA sites other than the only protein cysteine residue. Structural analogs of cisplatin, bearing aminoalcohol ligands, showed comparable protein binding reactivity and stoichiometry but a common equilibrium was not reached even after one week of incubation. Also apparent was a two-step mechanism of the binding reaction. Results demonstrated the suitability of CE-ICP-MS as a rapid assay for high-throughput studying of drug/HSA interactions.

Human serum albumin: spectroscopic studies of the paclitaxel binding and proximity relationships with cisplatin and adriamycin

The interactions of anti-cancer drugs with blood constituents, particularly with serum albumin (HSA) may have a major influence on drug pharmacology and efficacy. In the present work the binding of paclitaxel (trade name Taxol) to human serum albumin and its effect on cisplatin and adriamycin interactions has been investigated through UV/visible, CD, fluorescence spectroscopy and the inductively couplet plasma atomic emission spectroscopy method. Displacement studies with use of bilirubin, as a competitive agent provided relevant information about the location of the binding site in HSA as well as the possible multidrug interactions.

Effect of cis-, trans-diamminedichloroplatinum(II) and DBP on human serum albumin

Both isomers of diamminedichloroplatinum(II) bind to albumin and induce the formation of the albumin dimer (MW approximately 140 kDa). The trans isomer exhibits a much greater tendency to induce a protein dimerization than the cis isomer. Under similar experimental conditions, the phosphonic derivative of diammineplatinum(II) (DBP) does not induce any dimer formation. The amount of bound complex per mol of human serum albumin (HSA, for an incubation time of 7 days) was found to be 6, 10.5 and 1 mol for cis-, trans-DDP and DBP, respectively. The relative fluorescence intensity of platinum-bound HSA decreases to about 55% for cis-DDP, 45% for trans-DDP and to 85% for DBP when compared to the complex-free protein, suggesting that the binding occurs in the proximity of the Trp214 residue. The structural studies (CD) have shown that only DDP-isomers cause the distinct modification of HSA native structure (alpha-helical content). Pt(II) complexes binding to HSA affect the affinity of HSA towards heme and bilirubin. High excess of DDP prevents the heme and bilirubin binding, while DBP affects this binding much less effectively due to the low amount of the protein-bound complex. Reactions of platinum complexes with albumin are believed to play an important role in the metabolism of this anticancer drug. The minor effect of DBP on HSA may indicate that the toxicity of the phosphonate analog is much lower than toxicities of DDP isomers, most likely due to kinetic reasons.

Crystal and Molecular Structure of a Potential DNA Groove-Spanning Chelate: [MV][Pt(2)(hdta)Cl(2)].4H(2)O (MV(2+) = 1,1'-Dimethyl-4,4'-bipyridinium, hdta(4)(-) = 1,6-Hexanediamine-N,N,N',N'-tetraacetate)

Light yellow crystals of [MV][Pt(2)(hdta)Cl(2)].4H(2)O (1) (MV(2+) = 1,1'-dimethyl-4,4'-bipyridinium, hdta(4)(-) = 1,6-hexanediamine-N,N,N',N'-tetraacetate) were examined by X-ray diffraction. A 0.08 x 0.24 x 0.24 nm crystal was shown to have space group C2/c, having unit cell dimensions of a = 22.757(5) Å, b = 13.566(3) Å, and c = 12.120(2) Å and unit cell angles of alpha = gamma = 90 degrees and beta = 109.07(3) degrees with Z = 4. A total of 3195 independent reflections were refined to R = 0.0454. Each Pt(II) site has the anticipated NO(2)Cl square-planar mer coordination. The Pt-N(1) distance (N(1) is the N donor of the hdta(4)(-) ligand) is 2.001(9) Å, only slightly shorter than typical Pt-N distances (2.04-2.09 Å) for sp(3) donors. The Pt-O distances to the coordinated glycinato donors in 1 are 2.012(7) and 2.000(8) Å, values very similar to those of trans-[Pt(gly)(2)] (gly = glycinate). The Pt-Cl distance of 2.310(3) Å is in the range of 2.27-2.32 Å observed for other Pt(II)-Cl(-) bonds. The bond angles are close to the ideal 90 degrees or 180 degrees value: angleN-Pt-O = 85.4(3) degrees and 83.2(4) degrees; angleN-Pt-Cl = 176.6(2) degrees. The [Pt(2)(hdta)Cl(2)](2)(-) units are packed in an end-to-end fashion such that the [Pt(II)(iminodiacetate)Cl] headgroups are overlapping. This provides square-planar to square-planar stacking of the headgroups. (1)H and (13)C NMR data are presented which show that the [Pt(2)(hdta)Cl(2)](2)(-) coordination of the solid state is maintained in solution. The coordinated glycinato arms of [Pt(2)(hdta)Cl(2)](2)(-) are equivalent, exhibiting only one AB pattern in the (1)H NMR (H(a), 4.31 ppm; H(b), 3.89 ppm; J(ab) = 16.1 Hz) and one type of coordinated carboxylate ((13)C NMR resonance at 189.7 ppm). Time-dependent (1)H and (13)C NMR spectra show that inosine first displaces only Cl(-) in [Pt(2)(hdta)Cl(2)](2)(-) in solutions up to one inosine per Pt(II) center. A higher concentration of inosines (Ino) results in the displacement of one of the glycinato arms, detectable at 175.0 ppm by (13)C NMR. The sequential nature and binding of two Ino ligands, necessarily cis in [Pt(2)(hdta)(Ino)(4)], mimics the steps necessary to allow major groove-spanning ligation of DNA in the manner of the Farrell-type binuclear platinum(II) amine complexes.

Interaction of cisplatin drug with RNase A

cis-Pt(NH3)2Cl2 (cisplatin) is an antitumor drug with many severe toxic side effects including enzymatic structural changes associated with its mechanism of action. This study is designed to examine the interaction of cisplatin drug with ribonuclease A (RNase A) in aqueous solution at physiological pH, using drug concentration of 0.0001 mM to 0.1 mM with final protein concentration of 2% w/v. Absorption spectra and Fourier transform infrared (FTIR) spectroscopy with its self-deconvolution, second derivative resolution enhancement and curve-fitting procedures were used to characterize the drug binding mode, association constant and the protein secondary structure in the cisplatin-RNase complexes. Spectroscopic results show that at low drug concentration (0.0001 mM), no interaction occurs between cisplatin and RNase, while at higher drug concentrations, cisplatin binds indirectly to the polypeptide C=O, C-N (via H2O or NH3 group) and directly to the S-H donor atom with overall binding constant 5.66 x 10(3)M(-1). At high drug concentration, major protein secondary structural changes occur from that of the alpha-helix 29% (free enzyme) to 20% and beta-sheet 39% (free enzyme) to 45% in the cisplatin-RNase complexes. The observed structural changes indicate a partial protein unfolding in the presence of cisplatin at high drug concentration.

Psychopharmacological profile of the selective serotonin reuptake inhibitor, paroxetine: implication of noradrenergic and serotonergic mechanisms

The present study was designed to evaluate the psychopharmacological profile of the selective serotonin reuptake inhibitor paroxetine, and thus assess potential noradrenergic and/or serotonergic activity. Paroxetine dose-dependently increased mobility time in the mouse forced swimming test (8, 16, 32 and 64 mg/kg, i.p.) and reduced spontaneous locomotor activity when administered at a high dose (64 mg/kg, i.p.). Prior administration of 8-hydroxy-2-(di-n-propylamino)tetralin (1 mg/kg, i.p.), (+/-) pindolol (32 mg/kg, i.p.) or 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridyl)-1H-indole (RU 24969) (1 mg/kg, i.p.) potentiated the antidepressant-like effects of subactive doses of paroxetine (1, 2 and 4 mg/kg, i.p.) in the mouse forced swimming test. These effects were antagonized by prior administration of 1-(2-methoxyphenyl)-4-[-(2-phthalimido)butyl]piperazine) (0.5 mg/kg, i.p.). Complementary studies suggested that RU24969-induced anti-immobility effects were a result of an increase in locomotor activity; other interactions were without increase/decrease in locomotor activity. Acute administration of paroxetine (8, 16, and 32 mg/kg, i.p.) antagonized the hypothermia induced by the D2/D1 receptor agonist, apomorphine (16 mg/kg, s.c.), while repeated treatment with paroxetine (32 mg/kg) attenuated clonidine-induced (0.5 mg/kg, i.p.) hypothermia. Pre-treatment with the serotonergic neurotoxin, para-chlorophenylalanine attenuated the anti-immobility effects of low doses of paroxetine (8 and 16 mg/kg, i.p.) in the forced swimming test, whereas a higher dose of paroxetine remained active (32 mg/kg, i.p.). The results of the present study indicated that paroxetine displayed both noradrenergic-like and serotonergic-like activity in the pre-clinical psychopharmacological tests employed.

Cisplatin binding sites on human albumin

Reactions of cisplatin (cis-[PtCl2(NH3)2]) with albumin are thought to play an important role in the metabolism of this anticancer drug. They are investigated here via (i) labeling of cisplatin with 15N and use of two-dimensional 1H,15N NMR spectroscopy, (ii) comparison of natural human serum albumin with recombinant human albumin (higher homogeneity and SH content), (iii) chemical modification of Cys, Met, and His residues, (iv) reactions of bound platinum with thiourea, and (v) gel filtration chromatography. In contrast to previous reports, it is shown that the major sulfur-containing binding site involves Met and not Cys-34, and also a N ligand, in the form of an S,N macrochelate. Additional monofunctional adducts involving other Met residues and Cys-34 are also observed. During the later stages of reactions of cisplatin with albumin, release of NH3 occurs due to the strong trans influence of Met sulfur, which weakens the Pt-NH3 bonds, and protein cross-linking is observed. The consequences of these findings for the biological activity of cisplatin-albumin complexes are discussed.

Interaction of cisplatin with human serum albumin. Drug binding mode and protein secondary structure

Cis-diamminedichloroplatinum(II) (cisplatin) is an antitumor drug, which forms intrastrand cross-links DNA adducts. Protein interaction with cisplatin-DNA complexes induces DNA bending and biopolymer structural changes. This study is designed to examined the interaction of cisplatin with human serum albumin (HSA) in aqueous solution at physiological pH with drug concentrations of 0.0001 mM to 0.1 mM, and HSA (fatty acid free) concentration of 2% w/v. Absorption spectra and Fourier transform infrared (FTIR) spectroscopy with its self-deconvolution and second derivative resolution enhancement, as well as curve-fitting procedures, were used to determine the drug binding mode, drug binding constant and the protein secondary structure in aqueous solution. Spectroscopic evidence showed that at low drug concentration (0.0001 mM), minor cisplatin-protein interaction occurs, while at higher drug content (0.001 mM), major Pt-HSA complexation takes place via protein C=O, C-N and S-H donor groups with overall binding constant K = 8.52 x 10(2) M-1. At high drug concentration, cisplatin binding results in major protein secondary structural changes from that of the alpha-helix 55% (free HSA) to 45% and beta-sheet 22% (free HSA) to 32%, in the cisplatin-HSA complexes. The observed spectral changes indicate a partial unfolding of the protein structure, in the presence of cisplatin at high drug concentrations.

Decomposition kinetics of cisplatin in human biological fluids

Cisplatin is metabolized to high- and low-molecular mass complexes by exchanging of one or both chloride ligands with nucleophilic species. The decomposition of cisplatin and the formation of its metabolites in human biological fluids was investigated in-vitro. In nucleophile-free medium, cisplatin was decomposed by a reversible chloride ligand exchange reaction, which was dependent upon both chloride ion concentration and medium pH. The effect of pH was observed in the second-order rate constant for cisplatin re-formation, which was far smaller in neutral and alkaline media than in acidic media. In the medium containing nucleophilic species (glutathione, human albumin and globulin), cisplatin was irreversibly decomposed according to apparent first-order kinetics. The linear relationship between apparent decomposition rate constant and concentration of nucleophilic species suggested that nucleophilic species in biological fluids might react with cisplatin directly. Both high- and low-molecular mass metabolites were formed in human plasma and ascites; however, only a low-molecular mass metabolite was produced in urine. The faster decomposition of cisplatin and the greater ratio of fixed and mobile metabolites formed in plasma were mainly attributed to higher albumin concentration in plasma than in ascites and urine. The in-vitro decomposition of unchanged cisplatin and formation of high- and low-molecular mass metabolites in human biological fluids were simultaneously evaluated according to the kinetic model which combined both pathways via hydrolysis and by the direct reaction process with nucleophilic species.

Drug sensitivity testing for clinical samples from oesophageal cancer using adhesive tumour cell culture system

A total of 83 specimens of surgically resected tumours from 78 patients with oesophageal cancer were assayed for drug sensitivity using an adhesive tumour cell culture system (LifeTrac CSA assay). Seventyone of 83 specimens had a sufficient number of cells to permit growth in culture and 57 of 71 (80%) were evaluable for drug response. Cells (3 x 10(3) ml-1 well-1) were cultured for 14 days and exposed to drugs on days 3-8. Growing cells were confirmed as cancer cells by immunohistochemical staining. IC90 values against several anti-cancer drugs were determined and population distributions of IC90 for each drug served as the basis for judging sensitivity. The 10th percentiles of IC90 (microgram ml-1) for CDDP, 5-FU, DOX, CPM, MTX, VP16, IFOS, VDS, BLM and CDDP + 5-FU were 0.3, 0.16, 0.005, 0.9, 0.006, 0.09, 0.8, 0.006, 0.04 and 0.15 + 0.09 respectively. The population distribution of IC90 against each drug showed a specific pattern that was very similar among histopathological gradings and stages of the disease. This system appeared to be a clinically applicable drug sensitivity test for human oesophageal cancer.

Stability of cisplatin and its monohydrated complex in blood, plasma and ultrafiltrate--implications for quantitative analysis

The stability of cisplatin and its monohydrated complex has been studied in blood, plasma and plasma ultrafiltrate at 37 degrees C (pH 7.4). Intact cisplatin and the monohydrated complex were determined by liquid chromatography with post-column derivatization. The half lives for cisplatin and the monohydrated complex were 1.43 +/- 0.03 h (SEM) and 0.36 +/- 0.03 h (SEM), respectively, in blood and 0.88 +/- 0.05 h (SEM) and 0.26 +/- 0.02 h (SEM), respectively, in plasma. The compounds were unstable at -25 degrees C (t1/2 for cisplatin was 52 +/- 5 h (SEM) and for the monohydrated compound 26 +/- 2 h (SEM)), but at -70 degrees C both compounds were stable for at least 3 weeks. The monohydrated complex was found to be formed to a small extent when cisplatin was added to plasma (37 degrees C, pH 7.4). A sampling procedure using centripetal ultrafiltration of whole blood was evaluated and found applicable if the samples were stored at 0 degree C and ultracentrifuged within 1 h.

Impact of K2PtCl4 on the structure of human serum albumin and its binding ability of heme and bilirubin

Absorption, CD, gel-filtration chromatography, and immunological tests were used to evaluate the interactions of K2PtCl4 with human serum albumin. Multidentate coordination of Pt(II) to HSA causes distinct variations in the protein conformation including a considerable decrease of the helical structure. The high excess of Pt(II) ions leads to dimerization of the protein. The metal ion binding weakness the interactions of HSA with other molecules like heme or bilirubin.

Fluoxetine: a review of receptor and functional effects and their clinical implications

Downregulation of serotonin 5-HT1 receptors is the most frequently reported central nervous system neural effect of subchronic exposure to fluoxetine in rodents. However, downregulation of these receptors has not been universally demonstrated. Effects of subchronic exposure on 5-HT2 receptors are mixed. Fluoxetine exposure appears to have no effect on cholinergic muscarinic receptors. Effects on beta-adrenergic receptors are controversial, as only one laboratory has reported downregulation. The majority of studies have failed to show an effect on beta-adrenergic-receptor-stimulated cAMP generation. Electrophysiologic studies support the concept that fluoxetine facilitates net serotonergic transmission through downregulation of presynaptic inhibitory autoreceptors. Data suggest that its subchronic specificity and selectivity distinguish fluoxetine from members of other classes of available antidepressants, making it a distinct therapeutic option.