Biotransformations of oxaliplatin in rat blood in vitro

The partitioning and biotransformations of oxaliplatin [trans-l-1,2-diaminocyclohexaneoxalatoplatinum(II)] were investigated in the blood of Wistar male rats in vitro. [3-H]-Oxaliplatin was incubated with rat blood at 37 degrees C in 5% CO2 and the concentrations of all Pt complexes containing the [3-H]-dach carrier ligand were followed for up to 12 hours. Decay for both oxaliplatin and Pt-dach in the plasma ultrafiltrate (PUF) was rapid (t 1/2 oxaliplatin = 0.68 h and t 1/2 for Pt-dach in the PUF = 0.85 h). After 9 hours, the concentration of oxaliplatin fell below the detection limit. By 4 hours, the PUF-Pt-dach reached a plateau, which was 12% of total Pt-dach. The binding of Pt-dach to red blood cells (RBCs) and plasma proteins was also very rapid (t 1/2 RBCs = 0.58 h and t 1/2 plasma proteins = 0.78 h) and reached equilibrium by 4 hours. At equilibrium, 35% of total Pt-dach was bound to plasma proteins, 12% was in the plasma ultrafiltrate, and 53% was found associated with RBCs. Of the Pt-dach associated with RBCs, 23% was bound to the RBC membrane, 58% was bound to RBC cytosolic proteins, and 19% was in the RBC cytosol ultrafiltrate. Thus, these studies confirm previous observations of oxaliplatin accumulation by rat RBCs. To better characterize the determinants of this accumulation, oxaliplatin and other Pt-dach complexes were compared with respect to both their uptake by rat RBCs and their partition coefficients in octanol and water. The rank order for the rate of uptake was ormaplatin approximately Pt(dach)Cl2 > oxaliplatin > Pt(dach)(mal); while the rank order for hydrophobicity was ormaplatin > Pt(dach)Cl2 > Pt(dach)(mal) > oxaliplatin. Thus, in general, Pt-dach complexes appeared to be taken up better by RBCs than cisplatin or carboplatin, and the hydrophobicity of most of the Pt-dach complexes appeared to correlate with uptake. However, factors other than the dach carrier ligand and hydrophobicity clearly influence uptake. The biotransformations of oxaliplatin in rat blood were characterized utilizing reverse-phase high-pressure liquid chromatography (HPLC). In the RBC cytosol, both oxaliplatin and Pt(dach)Cl2 were observed at early times, while Pt(dach)(GSH)2, Pt(dach)(Cys)2, Pt(dach)(GSH), and free dach accumulated and reached steady-state levels by 4 hours. Thus, in the RBC cytosol, only chemically unreactive biotransformation products such as free dach and Pt-dach complexes with cysteine and glutathione accumulated in significant amounts. Furthermore, only Pt(dach)(Cys)2 and free dach appeared to efflux from RBCs. Thus, RBCs do not appear to serve as a reservoir for cytotoxic Pt-dach complexes. Finally, the biotransformation products of oxaliplatin in the plasma were identified as Pt(dach)Cl2, Pt(dach)(Cys)2, Pt(dach)(GSH), Pt(dach)(Met), Pt(dach)(GSH)2, and free dach. Among these compounds, Pt(dach)Cl2 formed transiently, while Pt(dach)(Cys)2, Pt(dach)(Met), and free dach accumulated and were the major biotransformation products by 4 hours. Thus, this study has identified the major inert and reactive biotransformation products of oxaliplatin in both plasma and RBCs and thus provides the information required for detailed pharmacokinetic and biotransformation studies of oxaliplatin. [figure in text]     

The impact of different chelating leaving groups on the substitution kinetics of mononuclear PtII(1,2- trans - R , R -diaminocyclohexane)(X–Y) complexes

A set of three oxaliplatin derivatives containing 1,2-trans-R,R-diaminocyclohexane (dach) as a spectator ligand and different chelating leaving groups X–Y, viz., [Pt(dach)(O,O-cyclobutane-1,1-dicarboxylate)], or Pt(dach)(CBDCA), [Pt(dach)(N,O-glycine)]⁺, or Pt(dach)(gly), and [Pt(dach)(N,S-methionine)]⁺, or Pt(dach)(l-Met), where l-Met is l-methionine, were synthesized and the crystal structure of Pt(dach)(gly) was determined by X-ray diffraction. The effect of the leaving group on the reactivity of the resulting Pt(II) complexes was studied for the nucleophiles thiourea, glutathione (GSH) and l-Met under pseudo-first-order conditions as a function of nucleophile concentration and temperature, using UV–vis spectrophotometric techniques. ¹H NMR spectroscopy was used to follow the substitution of the leaving group by guanosine 5′-monophosphate (5′-GMP²⁻) under second-order conditions. The rate constants indicate for all reactions a direct substitution of the X–Y chelate by the selected nucleophiles, thereby showing that the nature of the chelate, viz., O–O (CBDCA²⁻), N–O (glycine) or S–N (l-Met), respectively, plays an important role in the kinetic and mechanistic behavior of the Pt(II) complex. The k ₁ values for the reaction with thiourea, l-Met, GSH and 5′-GMP²⁻ were found to be as follows (10³ k ₁, 37.5 °C, M⁻¹ s⁻¹): Pt(dach)(CBDCA) 61 ± 2, 21.6 ± 0.1, 23 ± 1, 0.352 ± 0.002; Pt(dach)(gly) 82 ± 3, 6.2 ± 0.2, 37 ± 1, 1.77 ± 0.01; Pt(dach)(l-Met) (thiourea, GSH) 62 ± 2, 24 ± 1. The activation parameters for all reactions studied suggest an associative substitution mechanism. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of diethyldithiocarbamate (ddtc) on the plasma biotransformations of tetrachloro(d,i-trans)-1,2-diaminocyclohexaneplatinum(iv) (tetraplatin) in fischer 344 rats

We have studied the effects of diethyldithiocarbamate (DDTC) on the biotransformations of toxic doses of tetrachloro (d,l-trans)1,2-diaminocyclohexaneplatinum(IV) (tetraplatin) in Fischer 344 rats. In animals not treated with DDTC, tetraplatin was rapidly converted to dichloro(d,I-trans)1,2-diaminocyclohexaneplatinum(II) [PtCl₂(dach]. Subsequent biotransformations included the transient formation of the (d,I-trans)1,2-diaminocyclohexane-aquachloroplatinum(II) [Pt(H₂O)(Cl)(dach)]+ complex, followed by formation of the platinum (Pt)-methionine and either Pt-cysteine or Pt-ornithine complexes. Significant amounts of free (d,I-trans) 1,2-diaminocyclohexane (dach) were observed in plasma as a result of intracellular trans-labilization reactions. DDTC caused a marked decrease in both total and protein-bound platinum in the circulation. A significant increase in the plasma concentration of free dach was also observed as a result of formation of the Pt(DDTC)₂ complex. Some of the free dach could have arisen from intracellular reactions with DDTC, but the displacement of platinum from plasma proteins was more than sufficient to account for the increase in free dach in the circulation. DDTC treatment also decreased plasma concentrations of tetraplatin, PtCl₂(dach), [Pt(H₂O)(Cl)(dach)]⁺, the Pt-methionine complex, and one unidentified biotransformation product, but had no effect on the Pt-cysteine (or Pt-ornithine) complex. These effects of DDTC on protein-bound platinum and low-molecular-weight biotransformation products in plasma may contribute to the decrease in tetraplatin toxicity seen in DDTC-treated rats.     

Comparison of the reactivity of oxaliplatin, pt(diaminocyclohexane)Cl2 and pt(diaminocyclohexane1)(OH2)2(2+) with guanosine and L-methionine

The initial rates of reactivity of oxaliplatin, its metabolites Pt(dach)Cl2 and Pt(dach)(OH2)2(2+) with guanosine and L-met in water, NaCl and phosphate were compared. Versus guanosine, the most reactive molecule was Pt(dach)(OH2)2(2+), about 40 fold that of oxaliplatin, the least reactive was Pt(dach)Cl2, Versus L-met, Pt(dach)(OH2)2(2+), was also the most reactive species but only about 2 fold more reactive than Pt(dach)Cl2 and oxaliplatin. Pt(dach)(OH2)2(2+) was approximately 3 fold less reactive versus methionine than guanosine whereas oxaliplatin and Pt(dach)Cl2 were about seven fold more reactive versus methionine than guanosine. Thus, the three platinum compounds oxaliplatin, Pt(dach)Cl2 and Pt(dach)(OH2)2(2+) react with L-met but only the Pt(dach)(OH2)2(2+) has a high reactivity with guanosine. Oxaliplatin, which is stable in water, has to be transformed in the presence of chloride in chloro-derivatives which are aquated to become active particularly versus guanosine. These data demonstrate that oxaliplatin has similarities with cisplatin in terms of chloride versus water coordination and in terms of dependence on chloride concentration for transformations.     

Effects of diethyldithiocarbamate (DDTC) on the plasma biotransformations of tetrachloro(d,l-trans)-1,2-diaminocyclohexaneplatinum(IV) (tetraplatin) in Fischer 344 rats.

We have studied the effects of diethyldithiocarbamate (DDTC) on the biotransformations of toxic doses of tetrachloro (d,l-trans)1,2-diaminocyclohexaneplatinum(IV) (tetraplatin) in Fischer 344 rats. In animals not treated with DDTC, tetraplatin was rapidly converted to dichloro(d,l-trans)1,2-diaminocyclohexaneplatinum(II) [PtCl2(dach)]. Subsequent biotransformations included the transient formation of the (d,l-trans)1,2-diaminocyclohexane-aquachloroplatinum(II) [Pt(H2O)(Cl)(dach)]+ complex, followed by formation of the platinum (Pt)-methionine and either Pt-cysteine or Pt-ornithine complexes. Significant amounts of free (d,l-trans) 1,2-diaminocyclohexane (dach) were observed in plasma as a result of intracellular trans-labilization reactions. DDTC caused a marked decrease in both total and protein-bound platinum in the circulation. A significant increase in the plasma concentration of free dach was also observed as a result of formation of the Pt(DDTC)2 complex. Some of the free dach could have arisen from intracellular reactions with DDTC, but the displacement of platinum from plasma proteins was more than sufficient to account for the increase in free dach in the circulation. DDTC treatment also decreased plasma concentrations of tetraplatin, PtCl2(dach), [Pt(H2O)(Cl) (dach)]+, the Pt-methionine complex, and one unidentified biotransformation product, but had no effect on the Pt-cysteine (or Pt-ornithine) complex. These effects of DDTC on protein-bound platinum and low-molecular-weight biotransformation products in plasma may contribute to the decrease in tetraplatin toxicity seen in DDTC-treated rats.     

Reaction products of a new anti-cancer agent, Pt(IV)(cyclohexyldiamine)Cl4, with guanosine and 9-methylguanine: first crystal structures of Pt(cyclohexyldiamine) complexes with a nucleobase and a nucleoside

Pt(IV)(dach)Cl4 (dach = cyclohexyldiamine) was reacted with guanosine and 9-methylguanine and their reaction products were analyzed by single-crystal x-ray diffraction. In both cases the resulting complexes, [Pt(dach)(guanosine)2]2+ and [Pt(dach)(9-methylguanine)2]2+ respectively, corresponded to an unanticipated reduction of the octahedral Pt(IV) starting material to a square planar Pt(II) species. The nature of the reducing agent is presently unknown.     

Biophysical analysis of DNA modified by 1,2-diaminocyclohexane platinum(II) complexes.

Modification of DNA and double-stranded deoxyoligonucleotides with antitumour 1,2-diamino-cyclohexanedinitroplatinum(II) (Pt-dach) complexes was investigated with the aid of physico-chemical methods and chemical probes of nucleic acid conformation. The three Pt-dach complexes were used which differed in isomeric forms of the dach nonleaving ligand-Pt(1R,2R-dach), Pt(1S,2S-dach) and Pt(1R,2S-dach) complexes. The latter complex has lower antitumour activity than the other two Pt-dach complexes. Pt(1R,2S-dach) complex exhibits the slowest kinetics of its binding to DNA and of the conversion of monofunctional binding to bifunctional lesions. The anomalously slow electrophoretic mobility of multimers of the platinated and ligated oligomers suggests that bifunctional binding of Pt-dach complexes to a d(GG) site within double-stranded oligonucleotides induces bending of the oligomer. In addition, chemical probing of double-helical deoxyoligonucleotides modified by the Pt-dach complexes at the d(GG) sites reveals that Pt(1R,2S-dach) complex induces more extensive conformational changes in the oligomer than Pt(1R,2R-dach) and Pt(1S,2S-dach) complexes. It is proposed that different effects of the Pt-dach complexes on DNA observed in this work arise mainly from a steric crowding of the axially oriented cyclohexane ring in the DNA adduct of Pt(1R,2S-dach) complex.     

The crystal structures and absolute configurations of the anti-tumor complexes Pt(oxalato)(1R,2R-cyclohexanediamine) and Pt(malonato)(1R,2R-cyclohexanediamine)

The absolute configurations of the anti-tumor complexes [Pt(oxalato)(trans-l-dach)] and [Pt(malonato) (trans-l-dach)] (trans-l-dach = 1R,2R-cyclohexanediamine) have been determined by X-ray anomalous scattering techniques. These complexes are particularly interesting because they show higher anti-tumor activity than the corresponding Pt complexes with other 1,2-cyclohexanediamine(dach) ligands, namely those with trans-d-dach (1S,2S-dach) or cis-dach (1R,2S-dach). The oxalato and malonato ligands are found to bind to the Pt atom in a chelating fashion, through one oxygen atom from each of the two carboxylate groups. Crystallographic details: Pt(oxalato)(trans-l-dach): space group P2₁ (monoclinic); a = 11.230(11) Å, b = 9.914(5) Å, c = 4.716(3) Å, β = 90.86(6)°; R = 4.0% for 1256 reflections. Pt(malonato)(trans-l-dach): space group P2₁ (monoclinic); a = 11.568(5) Å, b = 10.007(5) Å, c = 5.187(3) Å, β = 99.16(4)°; R = 4.8% for 1675 reflections.     

High-performance liquid chromatographic separation of platinum complexes containing the cis-1,2-diaminocyclohexane carrier ligand

Platinum drugs with the 1,2-diaminocyclohexane (dach) carrier ligand have shown great promise in cancer chemotherapy, but little is known about their metabolism in the body. Since it is possible to radiolabel the dach ligand, it should be possible to quantitate the biotransformation products of these drugs, provided a method were available to separate the biotransformation products. In this paper we describe a two-column high-performance liquid chromatography system which can be used to separate many likely dach-platinum biotransformation products from the parent compounds, and allow their identification. An initial separation on a reverse-phase Partisil ODS-3 column allowed resolution of the uncharged species. The peak fractions from this column were concentrated 10-fold and reinjected onto a cation exchange Partisil 10 SCX column to allow resolution of the positively charged species. This system allowed resolution of two prototype dach-platinum drugs, (cis-1,2-diaminocyclohexane)dichloroplatinum(II) and (cis-1,2-diaminocyclohexane)malonatoplatinum(II), the aquated species likely to form from these drugs, and the complexes formed when these compounds react with glutathione, metallothionein, and amino acids. By using cation exchange chromatography at pH 2.3 as well as pH 4 and by using 14C-labeled amino acids to determine stoichiometry, it was also possible to determine the most likely structures for some of the amino acid complexes. Most importantly, this system allowed clear separation of many of the likely biotransformation products tested from the biologically important aquated species. This system should prove useful for separating and identifying the biotransformation products of dach-platinum drugs in blood and urine, in tissue culture media, and inside the cell.     

Inhibitory effect of cisplatin and [Pt(dach)Cl2] on the activity of phospholipase A2

This work has been focused on testing the influence of two selected Pt(II) complexes cisplatin, Pt(NH₃)₂Cl₂, and [Pt(dach)Cl₂] on the activity of porcine pancreatic phospholipase A₂ (PLA₂). It has been assumed that this enzyme plays a role in carcinogenesis and that it could be a target in the tumour therapy. The results of this study show that both Pt(II) complexes inhibit the activity of the enzyme, though they bind to it in a different manner. While cisplatin interacts with the enzyme in an acompetitive manner, the stable interaction of [Pt(dach)Cl₂] with PLA₂ could not be detected under our experimental conditions.     

Reaction of platinum(II) diamine and triamine complexes with selenomethionine

We have reacted [Pt(dien)Cl]Cl, [Pt(en)(D₂O)₂]²⁺, and [Pt(Me₄en)(D₂O)₂]²⁺ [Me₄en = N,N,N′,N′-tetramethylethylenediamine] with selenomethionine (SeMet). When [Pt(dien)Cl]Cl is reacted with SeMet, [Pt(dien)(SeMet-Se)]²⁺ is formed; two Se-CH₃ resonances are observed due to the different chiralities at the Se atom upon platination. In a reaction of [Pt(dien)Cl]Cl with an equimolar mixture of SeMet and Met, the SeMet product forms more quickly though a slow equilibrium with approximately equal amounts of both products is reached. [Pt(Me₄en)(D₂O)₂]²⁺ reacts with SeMet to form [Pt(Me₄en)(SeMet-Se)(D₂O)]²⁺ initially but forms [Pt(Me₄en)(SeMet-Se,N)]⁺ ultimately. One stereoisomer of the chelate, assigned to the R chirality at the Se atom, dominates within the first few minutes of reaction. [Pt(en)(D₂O)₂]²⁺ forms a variety of products depending on reaction stoichiometry; when one equivalent or less of SeMet is added, the dominant product is [Pt(en)(SeMet-Se,N)]⁺. In the presence of excess SeMet, [Pt(en)(SeMet-Se)₂]²⁺ is the dominant initially, but displacement of the en ligand occurs leading to [Pt(SeMet-Se,N)₂] as the eventual product. Displacement of the en ligand from [Pt(en)(SeMet-Se,N)]⁺ does not occur. In reactions of K₂PtCl₄ with two equivalents of SeMet, [Pt(SeMet-Se,N)₂] is formed, and three sets of resonances are observed due to different chiralities at the Se atoms. Only the cis geometric isomers are observed by ¹H and ¹⁹⁵Pt NMR spectroscopy.     

Enhanced antitumor activity [correction for activitiy] of trans(+/-)-1,2-diaminocyclo- hexaneglutamatoplatinum(II) formulated with stealth liposome

The antitumor platinum(II) compound, [Pt(dach)(Glu)] (dach=trans(+/-)-1,2-diaminocyclohexane, Glu=glutamate) was formulated with a stealth liposome to improve its biological activity. Liposomes were composed of PC/PEG2000-PE/CH (PC=1,2-diacyl-glycero-3-phosphocholine; PEG2000-PE=poly(ethylene glycol)2000-1,2-diacyl-glycero-3-phosphoethanolamine; CH=cholesterol) involving different acyl moieties of phospholipids such as DO (dioleoyl), DM (dimyristoyl) or DS (distearoyl) group. Among the different acyl groups in the stealth liposomes, the DM formulation was optimal for the preparation of the liposomal [Pt(dach)(Glu)] at the mole ratio of DMPC/PEG2000-DMPE/CH=50/5/45 and at the weight ratio of drug/lipid=1/20, which is represented as L-[Pt(dach)(Glu)]. In vitro cytotoxicity was examined in sensitive A2780 and ME180 and their cisplatin-resistant A2780/PDD and ME180/PDD cancer cells. L-[Pt(dach)(Glu)] was 2 approximately 3 times more cytotoxic than the free complex [Pt(dach)(Glu)] and cisplatin in sensitive cells, and 4 approximately 8 times more cytotoxic in resistant cells. Thus, the resistance index of L-[Pt(dach)(Glu)] was 1.3 approximately 2 while those of the free complex and cisplatin were 5 approximately 6, which indicates that L-[Pt(dach)(Glu)] overcome the cisplatin resistance in both resistant cells. In vivo antitumor activity was assayed against the L1210/S leukemia. The optimal activities (% T/C) of the free complex and L-[Pt(dach)(Glu)] were >459/20 and >442/200 mg/kg, respectively. Considering the amount of the platinum complex in L-[Pt(dach)(Glu)], the liposomal [Pt(dach)(Glu)] displayed 2-fold higher drug potency than the free complex. The biodistribution experiment using LE52 tumor-bearing mouse showed excellent lung targeting property of L-[Pt(dach)(Glu)].     

Formation mechanism of cross‐linking Maillard compounds in peptide–xylose systems

The formation mechanism of Maillard peptides was explored in Maillard reaction through diglycine/glutathione(GSH)/(Cys‐Glu‐Lys‐His‐Ile‐Met)–xlyose systems by heating at 120 °C for 30–120 min. Maximum fluorescence intensity of Maillard reaction products (MRPs) with an emission wavelength of 420~430 nm in all systems was observed, and the intensity values were proportional to the heating time. Taken diglycine/GSH–[¹³C₅]xylose systems as a control, it was proposed that the compounds with high m/z values of 379 and 616 have the high molecular weight (HMW) products formed by cross‐linking of peptides and sugar. In (Cys‐Glu‐Lys‐His‐Ile‐Met)–xylose system, the m/z value of HMW MRPs was not observed, which might be due to the weak signals of these products. According to the results of gel permeation chromatography, HMW MRPs were formed by Maillard reaction, especially in (Cys‐Glu‐Lys‐His‐Ile‐Met)–xylose system, the percentage of Maillard peptides reached 52.90%. It was concluded that Maillard peptides can be prepared through the cross‐linking of sugar and small peptides with a certain MW range. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Pt(IV) complexes as prodrugs for cisplatin

The antitumor effects of platinum(IV) complexes, considered prodrugs for cisplatin, are believed to be due to biological reduction of Pt(IV) to Pt(II), with the reduction products binding to DNA and other cellular targets. In this work we used pBR322 DNA to capture the products of reduction of oxoplatin, c,t,c-[PtCl₂(OH)₂(NH₃)₂], 3, and a carboxylate-modified analog, c,t,c-[PtCl₂(OH)(O₂CCH₂CH₂CO₂H)(NH₃)₂], 4, by ascorbic acid (AsA) or glutathione (GSH). Since carbonate plays a significant role in the speciation of platinum complexes in solution, we also investigated the effects of carbonate on the reduction/DNA-binding process. In pH 7.4 buffer in the absence of carbonate, both 3 and 4 are reduced by AsA to cisplatin (confirmed using ¹⁹⁵Pt NMR), which binds to and unwinds closed circular DNA in a manner consistent with the formation of the well-known 1, 2 intrastrand DNA crosslink. However, when GSH is used as the reducing agent for 3 and 4, ¹⁹⁵Pt NMR shows that cisplatin is not produced in the reaction medium. Although the Pt(II) products bind to closed circular DNA, their effect on the mobility of Form I DNA is different from that produced by cisplatin. When physiological carbonate is present in the reduction medium, ¹³C NMR shows that Pt(II) carbonato complexes form which block or impede platinum binding to DNA. The results of the study vis-à-vis the ability of the Pt(IV) complexes to act as prodrugs for cisplatin are discussed.     

Novel polynuclear platinum adducts detected during the reactions of [Pt(Met-S,N)Cl2] with gamma-glutathione and L-cysteine

The reactions of platinum(II) complexes with thiol containing molecules are highly relevant to the mechanism of action of platinum-based drugs. This work presents the electrospray mass spectrometry (ESMS) and NMR results on the reactions of [Pt(l-MetH-S,N)Cl(2)] (l-MetH: l-methionine) with gamma-glutathione (GSH) and l-cysteine (l-Cys) at different pH and different molar ratios. Polymeric species such as [Pt(2)(micro-SG-S)(2)(Met-S,N)(2)], [Pt(3)(micro-SG-S)(4)(Met-S,N)(2)], [Pt(4)(micro-SG-S)(6)(Met-S,N)(2)] and [Pt(5)(micro-SG-S)(8)(Met-S,N)(2)] (l-Met: deprotonated l-methionine) were detected and were stable for long hours. For both reactions, the polymerization extent decreased with the increase of pH. For the reaction of l-Cys, only mononuclear complex [Pt(l-Met-S,N)(l-Cys-S,N)] was observed when pH>9. The observation and identification of polymeric (higher than binuclear) adducts of Pt(II)/GSH and Pt(II)/l-Cys appears to be unprecedented.     

Fast cleavage of a diselenide induced by a platinum(II)-methionine complex and its biological implications

Platinum-based anticancer drugs such as cisplatin induce increased oxidative stress and oxidative damage of DNA and other cellular components, while selenium plays an important role in the antioxidant defense system. In this study, the interaction between a platinum(II) methionine (Met) complex [Pt(Met)Cl₂] and a diselenide compound selenocystine [(Sec)₂] was studied by electrospray ionization mass spectrometry, high performance liquid chromatography mass spectrometry, and ¹H NMR spectroscopy. The results demonstrate that the diselenide bond in (Sec)₂ can readily and quickly be cleaved by the platinum complex. Formation of the selenocysteine (Sec) bridged dinuclear complex [Pt₂(Met-S,N)₂(μ-Sec-Se,Cl)]³⁺ and Sec chelated species [Pt(Met-S,N)(Sec-Se,N)]²⁺ was identified at neutral and acidic media, which seems to result from the intermediate [Pt(Met-S,N)(Sec-Se)Cl]⁺. An accelerated formation of S-Se and S-S bonds was also observed when (Sec)₂ reacted with excessive glutathione in the presence of [Pt(Met)Cl₂]. These results imply that the mechanism of activity and toxicity of platinum drugs may be related to their fast reaction with seleno-containing biomolecules, and the chemoprotective property of selenium agents against cisplatin-induced toxicity could also be connected with such reactions.     

Synthesis and cytotoxicity of new platinum(IV) complexes of mixed carboxylates

In order to develop new antitumor platinum(IV) complexes with highly tuned lipophilicity, a series of (diamine)Pt(IV) complexes of the formula [Pt(IV)(dach)L(3)L'] or [Pt(IV)(dach)L(2)L"(2)] (dach=trans-(+/-)-1,2-diaminocyclohexane; L=acetato, propionato; L'=acetato, propionato, valerato or pivalato; L"=trifluoroacetato) have been synthesized by electrophilic substitution of the tris(carboxylato)hydroxoplatinum(IV) complexes, [Pt(IV)(dach)L(3)OH] (L=acetato, propionato), with various carboxylic anhydrides such as acetic, trifluoroacetic, pivalic and valeric anhydrides. The present platinum(IV) complexes were fully characterized by means of elemental analyses, 1H NMR, mass and IR spectroscopies. The complexes 8 and 10, satisfying the appropriate range of lipophilicity (logP=0.18-1.54), exhibited high activity (ED(50), 5.1 and 1.3 microM, respectively) compared with other complexes, which implies that the lipophilicity is an important factor for the antitumor activity of this series of complexes.     

High performance liquid chromatography studies on the interactions of cis-Pt(NH3)2−(H2O)22+ with guanine and methylated g

Time dependence studies, using high performance liquid chromatography (HPLC), on the reaction between cis-diamminediaquoplatinum and guanine, N1-methylguanine, N7-methylguanine, N9-methylguanine, and N1 ,N7-dimethylguanine are reported. Each reaction gave rise to eight or more compounds; the major components have been prepared and characterization by ¹H and ¹⁹⁵Pt nuclear magnetic resonance has been attempted. Species of the form ((NH₃)₂Pt(NO₃)-(G-H)-(NO₃)-Pt(NH₃)₂)⁺, (NH₃)₂,Pt(G-H)(NO₃) monomer and (NH₃)₂Pt(G-H)(NO₃) dimer, where G-H indicates the guanine monoanion, are postulated.     

Synthesis, characterisation and structural studies of [Cu(dach)(μ-NCS)(NCS)]n and [Cu(dach)2(N3)]ClO4 (dach=1,4-diazacycloheptane)

A new singly bridging complex [Cu(dach)(μ-NCS)(NCS)]_n (dach=1,4-diazacycloheptane) has been synthesised and its crystal structure determined. There are many examples of double NCS bridged polymeric chains, but fewer singly bridged ones. IR, ESR and temperature variable magnetic studies are described but no magnetic interaction was found between the copper centres. [Cu(dach)₂(N₃)]ClO₄ has also been characterised by IR, ESR spectra and magnetic studies. The crystal structure determination shows that it is a penta-coordinated monomeric species with an axially coordinated azide linked to the perchlorate counterion by hydrogen bonding.     

Cisplatin induces loop structures and condensation of single DNA molecules

Structural properties of single λ DNA treated with anti-cancer drug cisplatin were studied with magnetic tweezers and AFM. Under the effect of low-concentration cisplatin, the DNA became more flexible, with the persistence length decreased significantly from ~52 to 15 nm. At a high drug concentration, a DNA condensation phenomenon was observed. Based on experimental results from both single-molecule and AFM studies, we propose a model to explain this kind of DNA condensation by cisplatin: first, di-adducts induce local distortions of DNA. Next, micro-loops of ~20 nm appear through distant crosslinks. Then, large aggregates are formed through further crosslinks. Finally, DNA is condensed into a compact globule. Experiments with Pt(dach)Cl₂ indicate that oxaliplatin may modify the DNA structures in the same way as cisplatin. The observed loop structure formation of DNA may be an important feature of the effect of platinum anti-cancer drugs that are analogous to cisplatin in structure.