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.     

Platinum complexes with one radiosensitizing ligand [PtCl2(NH3) (sensitizer)]: radiosensitization and toxicity studies in vitro

Complexes of general formula [PtCl2(NH3)L] with one radiosensitizing ligand per platinum are compared with ligand L alone, complexes with two radiosensitizers per platinum [PtCl2L2], and their analogs with NH3 ligands, with respect to radiosensitizing properties and toxicity in CHO cells. Radiosensitizing ligands, L, were misonidazole, metronidazole, 4(5)-nitroimidazole, and 2-amino-5-nitrothiazole, and the ammine analogs were cis- and trans-DDP [diamminedichloroplatinum(II)] and the monoammine, K[PtCl3(NH3)]. Results are related to a previous study on plasmid DNA binding by these series. The toxicity of the mono series [PtCl2(NH3)L], attributable to DNA binding, is much higher than the corresponding bis complexes, [PtCl2L2]. For L = misonidazole, toxicity is similar to the monoammine, but higher in hypoxic than in aerobic cells. trans-[PtCl2(NH3)-(misonidazole)] is more toxic than the cis isomer. Except for L = 4(5)-nitroimidazole, the complexes [PtCl2(NH3)L] are more toxic than L in air and hypoxia. Hypoxic radiosensitization by the mono complexes is comparable to the monoammine and is not better than free sensitizers, again except for L = 4(5)-nitroimidazole. Significantly lower sensitization is observed in oxic cells. The bis complexes [PtCl2L2], which do not bind to DNA as well as the mono complexes, are less effective radiosensitizers and less toxic than the [PtCl2(NH3)L] series.     

Reaction of cis- and trans-[PtCl2(NH3)2] with reduced glutathione inside human red blood cells, studied by 1H and 15N-[1H] DEPT NMR

Reactions of cis- and trans-[PtCl2(NH3)2] with glutathione (GSH) inside intact red blood cells have been studied by 1H spin-echo nuclear magnetic resonance (NMR). Upon addition of trans-[PtCl2(NH3)2] to a suspension of red cells, there was a gradual decrease in the intensity of the resonances for free GSH, and new peaks were observed that were assignable to coordinated GSH protons in trans-[Pt(SG)Cl(NH3)2], trans-[Pt(SG)2(NH3)2], and possibly the S-bridged complex trans-[[NH3)2PtCl)2SG]+. Formation of trans-[Pt(SG)2(NH3)2] inside the cell was confirmed from the 1H NMR spectrum of hemolyzed cells, which were ultrafiltered to remove large protein molecules; the ABM multiplet of the coordinated GSH cys-beta CH2 protons was resolved using selective-decoupling experiments. Seventy percent of the total intracellular GSH was retained by the ultrafiltration membrane, suggesting that the mixed complex trans-[Pt(SG)(S-hemoglobin)(NH3)2] also is a major metabolite of trans-[PtCl2(NH3)2] inside red cells. The reaction of cis-[PtCl2(NH3)2] with intracellular GSH was slower; only 35% of the GSH had been complexed after a 4-hr incubation compared to 70% for the trans isomer. There was a gradual decrease in the intensity of the GSH 1H spin-echo NMR resonances, but no new peaks were resolved. This was interpreted as formation of high-molecular weight Pt:GSH and mixed GS-Pt-S(hemoglobin) polymers. By using a 15N-[1H] DEPT pulse sequence, we were able to study the reaction of cis-[PtCl2(15NH3)2] with red cells at concentrations as low as 1 mM. 15NH3 ligands were released, and no resonances assignable to Pt-15NH3 species were observed after a 12-hr incubation.     

Synthesis,characterization and antitumor activity of novel octahedral Pt(IV) complexes

Novel platinum(IV) complexes were synthesized having octahedral structure for new antitumor agents. The series of (1,4-butanediamine)Pt(IV) complexes of the type trans,cis-[PtA(2)Cl(2)(1,4-butanediamine)] (A=hydroxo 9, acetato 12, trifluoroacetato 13 as axial ligands) and trans-[PtA(2)(malonate)(1,4-butanediamine)] (A=hydroxo 16, acetato 17, trifluoroacetato 18) were synthesized and characterized by IR, NMR and elemental analysis. The molecular structures of 12, 13 and 18 have been determined by X-ray diffraction methods. The crystals are monoclinic, P2 1/c with a=21.165 (5), b=9.050 (3), c=15.293 (3) A, beta=103.89 (2) degrees and Z=8 for 12, a=10.178 (5), b=12.894 (9), c=12.182 (8) A, beta=91.01 (5) degrees and Z=4 for 13 and a=10.460 (5), b=11.199 (8), c=15.641 (7) A, beta=98.41 (5) degrees, Z=4 for 18. Three crystallographically independent molecules of 12, 13 and 18 have octahedral coordination around Pt(IV) cation. The trans,cis-[PtA(2)Cl(2)(1,4-butanediamine)] were prepared by acetylation or trifluoroacetylation of trans,cis-[Pt(OH)(2)Cl(2)(1,4-butanediamine)]. The trans-[PtA(2)malonate(1,4-butanediamine)] 17 and 18 was prepared by a similar method. The in vitro cytotoxicity of theses Pt(IV) complexes have been evaluated against 12 cancer cell lines assayed by MTS method. The IC(50) values of the compounds 12 and 13 were shown to be lower than those of cisplatin. The in vivo antitumor activity of the Pt(IV) complexes was evaluated using mice bearing L1210 leukemia, B16 melanoma and L1210/cis-DDP cancer animal models. The compound 18 was found to highest activity against cisplatin-resistant cancer cells, L1210/cis-DDP, in vivo.     

Studies of the binding of a series of platinum(IV) complexes to plasma proteins

The platinum(IV) complexes: [PtCl(4)(en)], cis,trans-[PtCl(2)(OAc)(2)(en)], cis,trans-[PtCl(2)(OH)(2)(en)] and trans-[Pt(OH)(2)(ethmal)(en)], encompassing a range of reduction potentials and their platinum(II) analogue [PtCl(2)(en)], have been assayed for their protein binding ability in the presence of albumin, albumin and L-cysteine and RPMI 1640 tissue culture medium supplemented with foetal calf serum (RPMI/FCS). cis,trans-[PtCl(4)(en)] exhibited significant protein binding in all three experiments, in a similar fashion to the platinum(II) complex, presumably as a consequence of its rapid reduction. The remaining three platinum(IV) complexes displayed little if any protein binding, with the greatest amount of binding observed in the RPMI/FCS experiment. The extent of binding in the RPMI/FCS correlated with the reduction potentials of the complexes, with the most readily reduced species binding to the greatest extent.     

Preparation of platinum(II) complexes with L-serine using KI. X-ray crystal structure, HPLC and 195Pt NMR spectra

The preparation of platinum(II) complexes containing L-serine using K(2)[PtCl(4)] and KI as raw materials was undertaken. The cis-trans isomer ratio of the complexes in the reaction mixture differed significantly depending on whether KI was present or absent in the reaction mixture. One of the two [Pt(L-ser-N,O)(2)] complexes (L-ser=L-serinate anion) prepared using KI crystallizes in the monoclinic space group P2(1)2(1)2(1) with unit cell dimensions a=8.710(2) A, b=9.773(3) A, c=11.355(3) A, Z=4. The crystal data revealed that this complex has a cis configuration. The other [Pt(L-ser-N,O)(2)] complex also crystallizes in the monoclinic space group P2(1)2(1)2(1) with unit cell dimensions a=7.0190(9) A, b=7.7445(6) A, c=20.946(2) A, Z=4. The crystal data revealed that this complex has a trans configuration. The 195Pt NMR chemical shifts of trans-[Pt(L-ser-N,O)(2)] and cis-[Pt(L-ser-N,O)(2)] complexes are -1632 and -1832 ppm, respectively. 195Pt NMR and HPLC measurements were conducted to monitor the reactions of the two [Pt(L-ser-N,O)(2)] complexes with HCl. Both 195Pt NMR and HPLC showed that the reactivities of cis- and trans-[Pt(L-ser-N,O)(2)] toward HCl are different: coordinated carboxyl oxygen atoms of trans-[Pt(L-ser-N,O)(2)] were detached faster than those for cis-[Pt(L-ser-N,O)(2)].     

The fate of platinum(II) and platinum(IV) anti-cancer agents in cancer cells and tumours

SRIXE mapping has been used to gain insight into the fate of platinum(II) and platinum(IV) complexes in cells and tumours treated with anticancer active complexes to facilitate the development of improved drugs. SRIXE maps were collected of thin sections of human ovarian (A2780) cancer cells treated with bromine containing platinum complexes, cis-[PtCl(2)(3-Brpyr)(NH(3))] (3-Brpyr=3-bromopyridine) and cis,trans,cis-[PtCl(2)(OAcBr)(2)(NH(3))(2)] (OAcBr=bromoacetate), or a platinum complex with an intercalator attached cis-[PtCl(2)(2-[(3-aminopropyl)amino]-9,10-anthracenedione)(NH(3))]. After 24h the complexes appear to be localised in the cell nucleus with a lower concentration in the surrounding cytoplasm. In cells treated with cis-[PtCl(2)(3-Brpyr)(NH(3))] the concentration of bromine was substantially higher than in control cells and the bromine was co-localised with the platinum consistent with the 3-bromopyridine ligand remaining bound to the platinum. The cells treated with cis,trans,cis-[PtCl(2)(OAcBr)(2)(NH(3))(2)] also showed an increased level of bromine, but to a much lesser extent than for those treated with cis-[PtCl(2)(3-Brpyr)(NH(3))] suggestive of substantial reduction of the platinum(IV) complex. Maps were also collected from thin sections of a 4T1.2 neo 1 mammary tumour xenograft removed from a mouse 3h after treatment with cis,trans,cis-[PtCl(2)(OH)(2)(NH(3))(2)] and revealed selective uptake of platinum by one cell.     

A study of interactions of platinum (II) compounds with DNA by means of CD spectra of solutions and liquid crystalline microphases of DNA

The optical properties of the DNA complexes with divalent platinum compounds of the cis-diamine type differing both in the nature of anionic and neutral ligands and in the spatial arrangement about the platinum atom were studied. The platinum compounds cis-[Pt(NH3)2Cl2], [Pt(en)Cl2], [Pt(tetrameen)Cl2], cis-[Pt(NH3)2NO2Cl], and cis-[PtNH3(Bz)Cl2] at small values of r (r is the molar ratio of a platinum compound to DNA nucleotides in the reaction mixture) were found to induce an increase in the amplitude of the positive band in the circular dichroic (CD) spectrum of linear DNA. All the compounds listed except cis-[Pt(NH3)2NO2Cl] caused a sharp decrease of the amplitude of the negative band in the CD spectrum of a liquid crystalline microphase of DNA formed in solution in the presence of poly(ethylene glycol). All these platinum compounds (except [Pt(tetrameen)Cl2]) exhibit biological (antimitotic, antitumour, etc.) activity. The platinum compounds trans-[Pt(NH3)Cl2], trans-[Pt(NH3)2NO2Cl], cis-[PtNH3PyCl2], cis-[Pt(NH3)2(NO2)2], and [Pt(NH3)3Cl]Cl exhibiting a low (if any) biological activity, either induced a decrease of the amplitude of the positive band in the CD spectrum of linear DNA, or did not affect the CD spectrum at all. The effect of these platinum compounds on the CD spectrum of the liquid crystalline microphase of DNA was either weak or absent. It is assumed that the specific biological action of platinum compounds of the cis-diamine type is determined by the polydentate binding to DNA: in addition to the cis-bidentate covalent binding of platinum to DNA nitrogen bases, a hydrogen bond formation between the DNA and cis-amino ligands occurs by means of protons at nitrogen atoms.     

Pt(II) complexes with N-(3-pyridyl)-2-(4-(trifluoromethyl)phenyl)diazenecarboxamide and their reactions with glutathione

The reaction between [PtCl(dmso)(en)]Cl (dmso=dimethyl sulfoxide, en=ethylenediamine) and N-(3-pyridyl)-2-(4-(trifluoromethyl)phenyl)diazenecarboxamide (L) was studied using multinuclear NMR spectroscopy. The water-soluble complexes [PtCl(en)(L-N1)](+) (1) and [Pt(en)(L-N1)(2)](2+) (2) were isolated and their reactions with glutathione (GSH) were investigated to assess the oxidation properties of coordinated L. Both species 1 and 2 oxidized GSH to GSSG, while the reduced form of L (semicarbazide, SL) remained coordinated to Pt(2+). In complex 1 the labile chloride ion was substituted by the thiol moiety of GSH, which gave rise to the release of en in excess GSH over a period of 7 days. Complexes [PtCl(dmso)(en)]Cl, 1, 2 and ligand L were tested against T24 bladder carcinoma cells. Ligand L and complexes 1 and 2 showed higher cytotoxicity than [PtCl(dmso)(en)]Cl.     

Preparation and cell growth inhibitory activity of [PtR(2)L(2)] (R=polyfluorophenyl,L(2)=diene,cyclohexane-1,2-diamine (chxn) or cis-(dimethyl sulfoxide)(2)) and the X-ray crystal structure of [Pt(C(6)F(5))(2)(cis-chxn)

A range of [PtR(2)(chxn)] (R=C(6)F(5), o-HC(6)F(4), p-HC(6)F(4), p-MeOC(6)F(4) or 3,5-H(2)C(6)F(3); chxn=cyclohexane-1,2-diamine) and cis-[PtR(2)(dmso)(2)] (R=C(6)F(5), p-HC(6)F(4) or p-MeOC(6)F(4); dmso=dimethyl sulfoxide) complexes have been prepared from the corresponding [PtR(2)(diene)] (diene=cis,cis-cycloocta-1,5-diene (cod), hexa-1,5-diene (hex), norbornadiene (nbd) or dicyclopentadiene (dcy)) derivatives and have been spectroscopically characterized. A representative crystal structure of [Pt(C(6)F(5))(2)(cis-chxn)] was determined and shows a slightly distorted square planar geometry for platinum with chxn virtually perpendicular to the coordination plane. The biological activity against L1210 and L1210/DDP cell lines of these compounds together with the behaviour of other organoplatinum complexes, [PtR(2)L(2)] (L(2)=ethane-1,2-diamine (en) or cis-(NH(3))(2)) have been determined. Despite the use of relatively inert fluorocarbon anions as leaving groups, moderate-high cell growth inhibitory activity is observed. None of the fluorocarbon complexes displayed any cross resistance with cisplatin.     

DNA-protein cross-linking by trans-[PtCl(2)(E-iminoether)(2)]. A concept for activation of the trans geometry in platinum antitumor complexes

The structure-pharmacological activity relationships generally accepted for antitumor platinum compounds stressed the necessity for the cis-[PtX(2)(amine)(2)] structure while the trans-[PtX(2)(amine)(2)] structure was considered inactive. However, more recently, several trans-platinum complexes have been identified which are potently toxic, antitumor-active and demonstrate activity distinct from that of conventional cisplatin (cis-[PtCl(2)(NH(3))(2)]). We have shown in the previous report that the replacement of ammine ligands by iminoether in transplatin (trans-[PtCl(2)(NH(3))(2)]) results in a marked enhancement of its cytotoxicity so that it is more cytotoxic than its cis congener and exhibits significant antitumor activity, including activity in cisplatin-resistant tumor cells. In addition, we have also shown previously that this new trans compound (trans-[PtCl(2)(E-iminoether)(2)]) forms mainly monofunctional adducts at guanine residues on DNA, which is generally accepted to be the cellular target of platinum drugs. In order to shed light on the mechanism underlying the antitumor activity of trans-[PtCl(2)(E-iminoether)(2)] we examined oligodeoxyribonucleotide duplexes containing a single, site-specific, monofunctional adduct of this transplatin analog by the methods of molecular biophysics. The results indicate that major monofunctional adducts of trans-[PtCl(2)(E-iminoether)(2)] locally distort DNA, bend the DNA axis by 21 degrees toward the minor groove, are not recognized by HMGB1 proteins and are readily removed from DNA by nucleotide excision repair (NER). In addition, the monofunctional adducts of trans-[PtCl(2)(E-iminoether)(2)] readily cross-link proteins, which markedly enhances the efficiency of this adduct to terminate DNA polymerization by DNA polymerases in vitro and to inhibit removal of this adduct from DNA by NER. It is suggested that DNA-protein ternary cross-links produced by trans-[PtCl(2)(E-iminoether)(2)] could persist considerably longer than the non-cross-linked monofunctional adducts, which would potentiate toxicity of this antitumor platinum compound toward tumor cells sensitive to this drug. Thus, trans-[PtCl(2)(E-iminoether)(2)] represents a quite new class of platinum antitumor drugs in which activation of trans geometry is associated with an increased efficiency to form DNA-protein ternary cross-links thereby acting by a different mechanism from 'classical' cisplatin and its analogs.     

Genotoxicity of novel trans-platinum(II) complex with diethyl (pyridin-4-ylmethyl)phosphate in human non-small cell lung cancer cells A549

The dynamic development of metal-containing anticancer drugs has started since the discovery of cis-diamminedichloroplatinum(II). For many years it was believed that trans platinum(II) compounds were non-active as antitumour agents because trans-diamminedichloroplatinum is biologically inactive although it binds to DNA and also forms monoadducts and cross-links. In the present work the ability of a novel platinum(II) compound trans-[PtCl(2)(4-pmOpe)(2)] to induce DNA damage in human non-small cell lung cancer cells A549 was examined using the alkaline comet assay. The obtained results revealed that the novel trans platinum(II) complex induced DNA strand breaks, which were effectively repaired during 2h of post-incubation, and cross-links which remained unrepaired under these test conditions. Apart from that, the modified comet assay with incubation with proteinase K was used to verify the ability of trans-[PtCl(2)(4-pmOpe)(2)] and cis-DDP to form DNA-protein cross-links. It has been proved that only trans-[PtCl(2)(4-pmOpe)(2)] complex exhibits the ability to induce DNA-protein cross-links. The results suggest a different mechanism of action of this compound in comparison to cis-DDP. It seems that trans geometry and the presence of two diethyl (pyridin-4-ylmethyl)phosphates as non-leaving ligands can determine dissimilar properties of the adducts formed on DNA and the different mechanism of action of trans-[PtCl(2)(4-pmOpe)(2)] and in consequence the efficacy in killing cancer cells.     

The reaction of Pt-antitumor drugs with selected nucleophiles. II. Preparation and characterization of coordination compounds of Pt(II) and L-histidine

Various His-Pt(II) coordination compounds were prepared by reaction of K2PtCl4 or cis-[Pt(NH3)2Cl2](cis-DDP) with His and analyzed by 1H and 13C NMR spectroscopy, electrophoresis, and ion-exchange chromatography. His may be coordinated to Pt by the imidazol iminogroup and/or the alpha-aminogroup; the carboxygroup remains always free. Both bidentate as well as monodentate ligands were identified. Cis-DDP reacts with His to give a mixture of compounds where all these possibilities are present: cis-diamine-(histidine-N,N-)Pt(II) and three different types of cis-diammine-bis(histidine). HCl trans cleavage of compounds with bidentate His ligands leads to a mixture of two compounds having His ligated to Pt by an amino or imin group. The methods applied are suitable for analyzing reactions of His with cis-DDP under model conditions similar to physiological conditions.     

DNA binding by antitumor trans-[PtCl2(NH3)(thiazole)]. Protein recognition and nucleotide excision repair of monofunctional adducts

Antitumor effects of cis-diamminedichloroplatinum(II) (cisplatin) and the clinical inactivity of its trans isomer (transplatin) have been considered a paradigm for the classical structure-activity relationships of platinum drugs. However, several new analogues of transplatin which exhibit a different spectrum of cytostatic activity including activity in tumor cells resistant to cisplatin have been recently identified. Analogues containing the planar amine ligand of the general structure trans-[PtCl(2)(NH(3))(L)], where L = planar amine, represent an example of such compounds. DNA is believed to be the major pharmacological target of platinum compounds. To contribute to the understanding of mechanisms underlying the activation of trans geometry in transplatin analogues containing planar amine ligands, various biochemical and biophysical methods were employed in previous studies to analyze the global modifications of natural DNA by trans-[PtCl(2)(NH(3))(L)]. These initial studies have revealed some unique features of the DNA binding mode of this class of platinum drugs. As the monofunctional lesions represent a significant fraction of stable adducts formed in DNA by bifunctional antitumor trans-platinum compounds with planar ligands, we analyzed in the present work short DNA duplexes containing the single, site-specific monofunctional adduct of a representative of this class of platinum drugs, antitumor trans-[PtCl(2)(NH(3))(thiazole)]. It has been shown that, in contrast to the adducts of monodentate chlorodiethylenetriamineplatinum(II) chloride or [PtCl(NH(3))(3)]Cl, the monofunctional adduct of trans-[PtCl(2)(NH(3))(thiazole)] inhibits DNA synthesis and creates a local conformational distortion similar to that produced in DNA by the major 1,2-GG intrastrand CL of cisplatin, which is considered the lesion most responsible for its anticancer activity. In addition, the monofunctional adducts of trans-[PtCl(2)(NH(3))(thiazole)] are recognized by HMGB1 domain proteins and removed by the nucleotide excision repair system similarly as the 1,2-GG intrastrand CL of cisplatin. The results of the present work further support the view that the simple chemical modification of the structure of an inactive platinum compound alters its DNA binding mode into that of an active drug and that processing of the monofunctional DNA adducts of the trans-platinum analogues in tumor cells may be similar to that of the major bifunctional adducts of "classical" cisplatin.     

Synthesis and antitumour activity of platinum(II) and platinum(IV) complexes containing ethylenediamine-derived ligands having alcohol, carboxylic acid and acetate substituents. Crystal and molecular structure of [PtL4CL2].H20 where L4 is ethylenediamine-N,N'-diacetate

Several cisplatin analogues of ethylenediamine-derived ligands containing alcohol, carboxylic acid and acetate substituents have been prepared and characterised. Oxidation of some of these square planar platinum(II) complexes using aqueous hydrogen peroxide gave octahedral platinum(IV) complexes, containing trans hydroxo ligands. Acetylation of the hydroxo ligands was achieved by reaction with acetic anhydride, giving complexes which are analogues of the antitumour drug, JM-216. Oxidation of the complex [Pt(H2L4)Cl2], where H2L4 is ethylenediamine-N,N'-diacetic acid, with H2O2 gave the platinum(IV) complex [PtL4Cl2].H2O in which L4 is tetradentate as shown by a crystal and molecular structure. This complex was previously reported to be [Pt(HL4)(OH)Cl2] in which HL4 is tridentate. Several of the complexes were tested for antitumour activity against five human ovarian carcinoma cell lines. IC50 values range from 4.0 microM for cis,trans-PtCl2(OH)2(NH2CH2CH2NHCH2CH2OH) against the CH1 cell line to >25 microM indicating moderate to low activity relative to other platinum complexes.     

Synthesis, crystal structure, spectral properties and cytotoxic activity of platinum(II) complexes of 2-acetyl pyridine and pyridine-2-carbaldehyde N(4)-ethyl-thiosemicarbazones

The reactions of Na2PtCl4 with pyridine-2-carbaldehyde and 2-acetyl pyridine N(4)-ethyl-thiosemicarbazones, HFo4Et and HAc4Et respectively, afforded the complexes [Pt(Fo4Et)Cl], [Pt(HFo4Et)2]Cl2, [Pt(Fo4Et)2] and [Pt(Ac4Et)Cl], [Pt(HAc4Et)2]Cl2 x 2H2O, [Pt(Ac4Et)2]. The new complexes have been characterized by elemental analyses and spectroscopic studies. The crystal structure of the complex [Pt(Ac4Et)Cl] has been solved. The anion of Ac4E coordinates in a planar conformation to the central platinum(II) through the pyridyl N, azomethine N and thiolato S atoms. Intermolecular hydrogen, non-hydrogen bonds, pi-pi and weak Pt-pi contacts lead to aggregation and a supramolecular assembly. The cytotoxic activity for the platinum(II) complexes in comparison to that of cisplatin and thiosemicarbazones was evaluated in a pair of cisplatin-sensitive and -resistant ovarian cancer cell lines A2780 and A2780/Cp8. The platinum(II) complexes showed a cytotoxic potency in a very low micromolar range and were found able to overcome the cisplatin resistance of A2780/Cp8 cells.     

Reactions of cisplatin hydrolytes with methionine, cysteine, and plasma ultrafiltrate studied by a combination of HPLC and NMR techniques

The reactions of cis-[PtCl(NH3)2(H2O)]+ with L-methionine have been studied by 1D 195Pt and 15N NMR, and by 2D[1H, 15N] NMR. When the platinum complex is in excess, the initial product, cis-[PtCl(NH3)2(Hmet-S)]+ undergoes slow ring closure to [Pt(NH3)2(Hmet-N,S)]2+. Slow ammine loss then occurs to give the isomer of [PtCl(NH3)(Hmet-N,S)]+ with chloride trans to sulfur. When methionine is in excess, a reaction sequence is proposed in which trans-[PtCl(NH3)(Hmet-S)2]+ isomerises to the cis-isomer, with subsequent ring closure reactions leading to cis-[Pt(Hmet-N,S)2]2+. Near pH 7, methionine is unreactive toward cis-[PtCl(OH)(NH3)2]. By contrast, L-cysteine reacts readily with cis-[PtCl(OH)(NH3)2] at pH 7, but there were many reaction products, including bridged species. Cis-[PtCl(OH)(NH3)2] reacts with reduced thiols in ultrafiltered plasma but these are oxidized if the plasma is not fresh or appropriately stored. With very low concentrations of the platinum complexes (35.5 microM), HPLC experiments (UV detection at 305 nm) indicate that the thiolate (probably cysteine) reactions become simpler as bridging becomes less important.     

Apoptosis induction and inhibition of H-ras overexpression by novel trans-[PtCl2(isopropylamine)(amine')] complexes

Hitherto, it has been generally accepted as a paradigm of the biochemical pharmacology of platinum antitumor drugs that a cis configuration of the leaving groups is necessary for antitumor activity of platinum compounds. However, it has been recently observed that certain trans-platinum complexes have both in vitro and in vivo antitumor activity. We previously reported the synthesis, characterization and cytotoxic activity against ras-transformed cells of several trans-[PtCl2LL'] complexes where L and L' are asymmetric aliphatic amines (L = dimethylamine and butylamine, L' = isopropylamine). The results reported in this paper show that the compounds trans-[PtCl2(isopropylamine)(dimethylamine)] and trans-[PtCl2(isopropylamine)(butylamine)] kill Pam 212-ras cisplatin resistant cells through apoptosis induction. Moreover, Western blot data show that both compounds inhibit overexpression of H-ras oncogene in Pam 212-ras cells. Altogether, these data indicate that, in contrast with cis-DDP, the apoptotic activity of these novel trans-Pt(II) compounds in ras-transformed cells is associated with their ability to abolish ras-overexpression.     

Solution behaviour and biological activity of bisamidine complexes of platinum(II)

A series of platinum(II) amidine complexes were previously prepared with the aim of obtaining a new class of platinum-based antitumour drugs. This series includes compounds of the type cis--[PtCl2{Z-HN=C(NHMe)Me}2] and trans-[PtCl2{Z-HN=C(NHMe)Me}2] (1, 2), cis-[PtCl2{E-HN=C(NMe2)Me}2] and trans-[PtCl2{E-HN=C(NMe2)Me}2] (3, 4), cis-[PtCl2{Z-HN=C(NHMe)Ph}2] and trans-[PtCl2{Z-HN=C(NHMe)Ph}2] (5, 6), and cis-[PtCl2{HN=C(NMe2)Ph}2] and trans-[PtCl2{HN=C(NMe2)Ph}2] (7, 8). The reactions with dimethyl sulfoxide were studied for complexes 5-8; the formation of cationic species containing coordinated dimethyl sulfoxide was demonstrated by NMR experiments and electrospray ionization mass spectrometry. In this work, the amidine platinum(II) complexes were tested for their in vitro cytotoxicity on a panel of various human cancer cell lines. The results indicate that the benzamidine complex 8 was the most effective derivative also circumventing acquired cisplatin resistance as demonstrated by chemosensitivity tests performed on cisplatin-sensitive and cisplatin-resistant cell lines. The studies concerning the cellular DNA damage on both parental chemosensitive and resistant sublines suggest for the new trans-amidine complex a different mechanism of action compared with that exhibited by cisplatin.     

Synthesis, characterization and antitumor activity of quinolone-platinum(II) conjugates.

A new series of quinolone-platinum(II) conjugates, [Pt(Q'-NH2)(dmso)X2] and cis-[Pt(Q"-en)X2], where Q' and Q" are quinolones (flumequine, nalidixic acid or oxolinic acid) linked to monodentate and bidentate amine ligands, respectively, and X2 is Cl2 or 1,1-cyclobutanedicarboxylate, have been synthesized with the aim of examining the synergetic antitumor activity of quinolone intercalation and platinum(II) chelation. The complexes were characterized by elemental analyses and IR and multinuclear (1H and 195Pt) NMR spectroscopies, and then subjected to in vitro and in vivo bioassays using the leukemia L1210 cell line.