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.     

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.     

The new antitumor compound, cis-[Pt(NH3)2(4-methylpyridine)Cl]Cl, does not form N7,N7-d(GpG) chelates with DNA. An unexpected preference for platinum binding at the 5'G in d(GpG)

The reaction of the antitumor active agent cis-[Pt(NH3)2(4-mepy)Cl]Cl (4-mepy stands for 4-methylpyridine) with d(GpG) has been investigated by 1H magnetic resonance spectroscopy. Initially, two mononuclear complexes cis-Pt(NH3)2(4-mepy)[d(GpG)-N7(1)] 1 and cis-Pt(NH3)2(4-mepy)[d(GpG)-N7(2)] 2 are formed in an unexpected ratio 65:35, as determined by 1H NMR and enzymatic digestion techniques. Both products react further with a second equivalent of cis-[Pt(NH3)2(4-mepy)Cl]Cl forming the dinuclear platinum complex [cis-Pt(NH3)2(4-mepy)]2[mu-d(GpG)- N7(1),N7(2)] 3. With [Pt(dien)Cl]Cl and [Pt(NH3)3Cl]Cl similar complexes are formed. No evidence was found for the formation of chelates cis-Pt(NH3)(4-mepy) [d(GpG)-N7(1),N7(2)], which would be formed upon ammonia release from the mononuclear complexes 1 and 2. Even addition of strong nucleophiles, like sodium diethyldithiocarbamate, thiourea, cysteine, or methionine, before or after reaction, do not induce the formation of a chelate. Under all conditions the N-donor ligands remain coordinated to Pt in 1,2 and 3. In addition, the results of bacterial survival and mutagenesis experiments with E. coli strains show that the in vivo formation of bifunctional adducts in DNA, comparable to those induced by cis-Pt(NH3)2Cl2, by treatment of cells with cis-[Pt(NH3)2(4-mepy)Cl]Cl is unlikely. Also, a mechanism of binding and intercalation is not supported by experimental data. All experiments suggest that the mechanism of action of this new class of antitumor agents must be different from that of cis-Pt(NH3)2Cl2.     

DNA-platinum interactions in vitro with trans- and cis-Pt(NH3)2Cl2.

In the present study the nature and the hydrolysis of DNA-Pt complexes with the platinum compounds, [Pt(dien)Cl]Cl, trans- and cis-Pt(NH3)2Cl2, using potentiometric chloride determinations, have been investigated. The trans-Pt(NH3)2Cl2 and the [Pt(dien)Cl]Cl react with the GC planes at the N7(G) sites, while the cis-Pt(NH3)2Cl2 compound reacts with the GC planes and forms a chelate by using the N7(G) and O6(G) sites. The complex is a specific 1:1 Pt:DNA adduct. The platinum atom in cis-Pt(NH3)2Cl2 liberates both chlorine atoms on chelation. A mechanism for the in vivo antitumor activity of the cis-Pt(NH3)2Cl2 is proposed and the structure activity relationship is discussed.     

cis-1,4-diaminocyclohexane-Pt(II) and -(IV) adducts with DNA bases and nucleosides

A series of new platinum(II) and platinum(IV) adducts of type [P(II)(cis-1,4-DACH)LCl]NO(3,) where cis-1,4-DACH=cis-1,4-diaminocyclohexane, and L=9-ethylguanine, 1-methylcytosine, adenine, adenosine, cytosine, cytidine, guanine, and [Pt(IV)(cis-1,4-DACH)Ltrans-(X)(2)Cl]NO(3), (where Y=hydroxo or acetato), were synthesized and characterized by elemental analysis, infrared spectroscopy, and 1H and 195Pt nuclear magnetic resonance spectroscopy.     

Platinum(II), platinum(IV), and palladium (II) complexes of amino substituted phosphine oxides: synthesis, characterization, and antitumor activity

The complexes [Pt(dapo)2Cl2], [PtNH3(dapo)Cl2], [Pt(py)(dapo)Cl2], [Pt(mbpo)Cl2].H2O, [Pt(mbpo)(OH)2Cl2].H2O, [Pd(dapo)2Cl2], and [Pd(mbpo)Cl2], where dapo is dimethyl aminomethylphosphine oxide and mbpo is methyl bis(aminomethyl)phosphite oxide have been synthesized and characterized by elemental analyses, electric conductivity, infrared, 1H NMR and electronic spectra. The ligands are found to be coordinated only via the amino groups. The complexes are of cis-square planar configuration with the exception of [Pt(mbpo)(OH)2Cl2].H2O which is pseudo-octahedral. An in vivo antitumor screening of the complexes against Leukemia L1210 was performed. A considerable activity (T/C = 233%) was observed for [PtNH3(dapo)Cl2]. The activity of the remaining complexes was below the accepted criterion.     

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, 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.     

Spectroscopic, biological, and antitumor studies on N-ethyl- and N-propylimidazole platinum(II) complexes

Platinum(II) halide complexes with N-ethylimidazole (N-EtIm) and N-propylimidazole (N-PropIm) of the Pt(L)2X2 and Pt(L)4X2 types (X = Cl, Br, I) were prepared and characterized by far infrared spectra, electronic spectra, and conductivity measurements. The inhibitorial activity of some complexes on the Ca,Mg-dependent ATPase and the antitumor studies of the Pt(L)4Cl2 derivatives have been investigated. Pt complexes are not inhibitory active in comparison to the same Pd complexes (if c = 10(-4) M). The LD50 in physiological solution for [Pt(N-EtIm)4]Cl2 X 2H2O and [Pt(N-PropIm)4]Cl2 are higher enough with respect to the cis platinum.     

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.     

The synthesis and characterization of N-substituted iminodiacetato cis-, trans-R, R- and trans-S, S-1, 2-diaminocyclohexane platinum(II) complexes: steric effects on the diastereomeric ratios

A series of platinum(II) complexes of the type [Pt(N-R-IDA)(DACH)], where DACH was either cis-1,2-diaminocyclohexane, trans-R, R-1, 2-diaminocyclohexane, or trans-S, S-1, 2-diaminocyclohexane, and N-R-IDA was either the iminodiacetate, N-methyliminodiacetate, N-n-propyliminodiacetate, or N-t-butyliminodiacetate ion, has been prepared and characterized. A detailed NMR investigation shows that the N-R-IDA ions bind to the platinum (II) ion through one of the acetate oxygens and the imino nitrogen, forming a five-membered ring. The second acetate ion does not bind to the platinum. By virtue of the prochiral N-atom of N-R-IDA and the absence of a horizontal plane of symmetry of the Pt(DACH) moiety, two diastereomers are observed corresponding to the two different orientations of the unbound acetate and the R-group with respect to the platinum coordination plane. The ratio of the two geometric isomers is controlled by steric factors depending upon both the isomeric form of 1,2-diaminocyclohexane and the nature of the R group bound to the imino nitrogen of N-R-IDA.     

Syntheses, crystal structure and cytotoxicity of diamine platinum(II) complexes containing maltol

The cationic complexes (1,2-diaminoethane)(maltolato)platinum(II) ([Pt(en)(ma)]+) and (1R,2R-1,2-diaminocyclohexane)(maltolato)platinum(II) ([Pt(R,R-DACH)(ma)]+) have been prepared and the structure of [Pt(R,R-DACH)(ma)]NO3 has been determined by single crystal X-ray diffraction. The geometry of the metal in [Pt(R,R-DACH)(ma)]NO3 is essentially square planar and the maltolate ligand has a geometry similar to other chelate complexes involving this ligand. The cytotoxicities of the compounds have been assessed in the human cell lines HeLa and K562 and the IC50 values are approximately 32 microM in HeLa cells and 26 microM in K562 cells. In these cell lines the cytotoxicity of cisplatin is higher than the maltolate complexes by a factor of 2 to 3 whereas the cytotoxicity of carboplatin is lower than the maltolate complexes.     

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.     

N(4)-Tolyl-2-acetylpyridine thiosemicarbazones and their platinum(II,IV) and gold(III) complexes: cytotoxicity against human glioma cells and studies on the mode of action

Complexes [Au(2Ac4oT)Cl][AuCl₂] (1), [Au(H_py2Ac4mT)Cl₂]Cl·H₂O (2), [Au(H_py2Ac4pT)Cl₂]Cl (3), [Pt(H2Ac4oT)Cl]Cl (4), [Pt(2Ac4mT)Cl]·H₂O (5), [Pt(2Ac4pT)Cl] (6) and [Pt(L)Cl₂OH], L = 2Ac4mT (7), 2Ac4oT (8), 2Ac4pT (9) were prepared with N(4)-ortho- (H2Ac4oT), N(4)-meta- (H2Ac4mT) and N(4)-para- (H2Ac4pT) tolyl-2-acetylpyridine thiosemicarbazone. The cytotoxic activities of all compounds were assayed against U-87 and T-98 human malignant glioma cell lines. Upon coordination cytotoxicity improved in 2, 5 and 8. In general, the gold(III) complexes were more cytotoxic than those with platinum(II,IV). Several of these compounds proved to be more active than cisplatin and auranofin used as controls. The gold(III) complexes probably act by inhibiting the activity of thioredoxin reductase enzyme whereas the mode of action of the platinum(II,IV) complexes involves binding to DNA. Cells treated with the studied compounds presented morphological changes such as cell shrinkage and blebs formation, which indicate cell death by apoptosis induction.     

Triphos as a bidentate ligand: the reactivity of the dangling phosphorus in [PtMe2(triphos-P,P′)]

Complex [PtMe₂(triphos-P,P′)], (1) where the linear triphosphine triphos [=bis(diphenylphosphinoethyl)phenylphosphine] acts as a bidentate ligand, can be easily converted in a variety of new complexes due to the reactivity of the free phosphorus donor. The selective oxidation of the uncoordinated phosphorus gave [PtMe₂(triphosPO-P,P′)] whose X-ray crystal structure is here reported; from the reactions of 1 with platinum and non platinum precursors homotrimetallic [Pt₃Me₄XY(triphos)₂] (X=Y=Me, Cl, I, X=Me, Y=Cl) and heterotrimetallic ([Pt₂PdMe₄Cl₂(triphos)₂] and [Pt₂RhMe₄(cod)(triphos)₂]PF₆) complexes were obtained where triphos acts as a chelating/bridging ligand. When 1 was treated with triflic acid in the presence of a neutral electron donor L (L=SMe₂, pyridine, PPh₃), complexes [PtL(triphos)]²⁺ were rapidly recovered in high yields. The protonolysis of 1 in the presence of CO and methanol gave the new organometallic complex [Pt(COOMe)(triphos)]OTf.     

Synthesis,characterization and antitumor activity of a series of N-substituted iminodiacetato(diammine) platinum(II) complexes

A series of water-soluble N-substituted iminodiacetato (diammine)platinum(II) complexes [Pt(NRIDA)(NH₃)₂] have been synthesized and characterized by measurement of physical properties (conductivity and pH) and by various spectroscopic techniques (infrared, ¹H and ¹³C{¹H} nuclear magnetic resonance). The iminodiacetate ligand is coordinated to platinum through an O,N linkage. The results obtained suggest that these complexes are relatively stable for more than 24 h in aqueous solution. Preliminary in vitro and in vivo screening test for antitumor activity of these complexes against L1210 murine leukemia were performed. Many of complexes had acceptable in vitro cytotoxicity, but none displayed a significant level of in vivo antitumor efficacy.     

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)].     

Synthesis,characterization, DNA interaction,and cytotoxicity of novel Pd(II) and Pt(II) complexes

Four complexes [Pd(L)(bipy)Cl]·4H₂O (1), [Pd(L)(phen)Cl]·4H₂O (2), [Pt(L)(bipy)Cl]·4H₂O (3), and [Pt(L)(phen)Cl]·4H₂O (4), where L = quinolinic acid, bipy = 2,2’-bipyridyl, and phen = 1,10-phenanthroline, have been synthesized and characterized using IR, ¹H NMR, elemental analysis, and single-crystal X-ray diffractometry. The binding of the complexes to FS-DNA was investigated by electronic absorption titration and fluorescence spectroscopy. The results indicate that the complexes bind to FS-DNA in an intercalative mode and the intrinsic binding constants K of the title complexes with FS-DNA are about 3.5?×?10⁴ M^?1, 3.9?×?10⁴ M^?1, 6.1?×?10⁴ M^?1, and 1.4?×?10⁵ M^?1, respectively. Also, the four complexes bind to DNA with different binding affinities, in descending order: complex 4, complex 3, complex 2, complex 1. Gel electrophoresis assay demonstrated the ability of the Pt(II) complexes to cleave pBR322 plasmid DNA.     

Synthesis and characterization of N-methyliminodiacetato trans-R,R-, trans-S,S-, and cis-1,2-diaminocyclohexane platinum (IV) complexes: crystal structure of chloro(trans-R,R-1,2-diaminocyclohexane) (N-methyliminodiacetato) platinum(IV) chloride.

The compounds, chloro(trans-R,R-1,2-diaminocyclohexane) (N-methyliminodiacetato)platinum(IV) chloride, chloro(trans-S,S-1,2-diaminocyclohexane)(N-methyliminodiacetato) platinum(IV) chloride, and chloro(cis-1,2-diaminocyclohexane)(N-methyliminodiacetato)platinum (IV) chloride, were prepared and characterized by elemental analysis, IR, and 195Pt NMR. The crystal structure of one of these three compounds, chloro(trans-R,R-1,2-diaminocyclohexane) (N-methyliminodiacetato) platinum(IV) chloride, was determined by x-ray single crystal diffraction. This compound is particularly interesting because the 1,2-diaminocyclohexane (DACH) ring is in a twist-boat configuration rather than the chair configuration previously reported for other DACH platinum compounds. The crystal structure consists of two independent cations and anions, with all atoms between these two independent molecules (except those in the chiral DACH) related by a pseudo-inversion center. Both platinum atoms have slightly distorted octahedral coordination, with angles ranging from 81.8 to 100.8 degrees. Crystallographic details: space group P2(1) (monoclinic); a = 19.864(5) A, b = 7.026(2) A, c = 12.446(3) A, beta = 106.64(2) degrees; Z = 4; R = 0.036 for 2333 reflections.     

Toxicity of platinum(II) amino acid (N,O) complexes parallels their binding to DNA as measured in a new solid phase assay involving a fluorescent HMG1 protein construct readout

 The compound [Pt(lysine)Cl₂] (Kplatin) was previously identified in a study of platinum amino acid complexes as a potential antitumor drug candidate. The DNA binding properties, high mobility group (HMG)-domain protein affinity for the platinated DNA, and cytotoxicity against HeLa cells of Kplatin and three related (N,O) chelated platinum(II) amino acid complexes, [Pt(arginine)Cl₂] (Rplatin), K[Pt(N_e-acetyllysine)Cl₂] (NacKplatin), and K[Pt(norleucine)Cl₂] (Norplatin), are reported. The four complexes have identical PtCl₂(N,O) coordination environments. A new solid phase screening methodology was devised in which platinated DNA probes are covalently attached to a nylon support and tested for their ability to bind a fluorescently labeled HMG-domain protein. The fluorescent HMG-domain protein was generated by expressing a fusion of the green fluorescent protein (GFP) with recombinant rat HMG1. Binding revealed by the solid phase method correlated well with the results of gel mobility shift and HeLa cytotoxicity assays. These results suggest that the net charge on the complex, rather than the nature of the side chain, is the most important factor underlying the DNA binding properties and toxicity of amino acid (N,O) chelated platinum complexes. This property explains why Kplatin was previously selected from the pool of platinum amino acid complexes based on the ability of its DNA adducts to bind HMG1. Received: 3 February 1999 / Accepted: 7 April 1999