Platinum amine coordination compounds as anti-tumor drugs. Molecular aspects of the mechanism of action

Advancements in the Use of Platinum Complexes as Anticancer Agents

BACKGROUND

The platinum (II) complexes as anticancer agents have been well explored for the development of novel analogs. Yet, none of them achieved clinical importance in oncology. At present, anticancer compounds containing platinum (II) complexes have been employed in the treatment of colorectal, lung, and genitourinary tumors. Among the platinum-based anticancer drugs, Cisplatin (cis-diamine dichloroplatinum (II), cis-[Pt(NH3)2Cl2]) is one of the most potent components of cancer chemotherapy. The nephrotoxicity, neurotoxicity and ototoxicity, and platinum compounds associated resistant cancer are some major disadvantages.

OBJECTIVE

With the rapidly growing interest in platinum (II) complexes in tumor chemotherapy, researchers have synthesized many new platinum analogs as anticancer agents that show better cytotoxicity, and less off-target effects with less cellular resistance. This follows the introduction of oxaliplatin, water-soluble carboplatin, multinuclear platinum and newly synthesized complexes, etc. Method: This review emphasizes recent advancements in drug design and development, the mechanism of platinum (II) complexes, their stereochemistry, current updates, and biomedical applications of platinum-based anticancer agents.

CONCLUSION

In the last few decades, the popularity of platinum complexes as potent anti-cancer agents has risen as scientists have synthesized many new platinum complexes that exhibit better cytotoxicity coupled with less off-target effects.

Synthesis, biological evaluation and SAR studies of novel bicyclic antitumor platinum(IV) complexes

The present study describes the synthesis, anticancer activity and SAR studies of novel platinum(IV) complexes having 1,2-bis(aminomethyl)carbobicyclic or oxabicyclic carrier ligands, bearing chlorido and/or hydroxido ligands in axial position and chlorido or malonato ligands in equatorial position (labile ligands). These complexes were synthetized with the aim of obtaining new anticancer principles more soluble in water and therefore more bioavailable. Several substitution patterns on the platinum atom have been designed in order to evaluate their antiproliferative activity and to establish structure-activity relationship rules. The synthesis of platinum(IV) complexes with axial hydroxyl ligands on the platinum(IV) were carried out by reaction of K2Pt(OH)2Cl4 with the corresponding diamines. The complexes with axial chlorido ligands on the platinum(IV) atom were synthesized by direct reaction of diamines with K2PtCl6. Carboxylated complexes were synthesized by the substitution reaction of equatorial chlorido ligands by silver dicarboxylates. The most actives complexes were those having malonate as a labile ligand, no matter of the structure of the carrier ligand. Regarding the influence of the structure of the non-labile 1,4-diamine carrier ligand on the cytotoxicity, it was found that the complexes having the more lipophilic and symmetrical bicyclo[2.2.2]octane framework were much more active than those having an oxygen or methylene bridge.

Density functional theory calculations on the molecular structures and vibration spectra of platinum(II) antitumor drugs

A comparison of six density functional theory (DFT) methods and six basis sets for predicting the molecular structures and vibration spectra of cisplatin is reported. The theoretical results are discussed and compared with the experimental data. It is remarkable that LSDA/SDD level is clearly superior to all the remaining density functional methods (including mPW1PW) in predicting the structures of cisplatin. Mean deviation between the calculated harmonic and observed fundamental vibration frequencies for each method is also calculated. The results indicate that PBE1PBE/SDD is the best method to predict all frequencies on average for cisplatin molecule in DFT methods.

Peptide targeting of platinum anti-cancer drugs

Besides various side effects caused by platinum anticancer drugs, they are not efficiently absorbed by the tumor cells. Two Pt-peptide conjugates; cyclic mPeg-CNGRC-Pt (7) and cyclic mPeg-CNGRC-Pten (8) bearing the Asn-Gly-Arg (NGR) targeting sequence, a malonoyl linker, and low molecular weight miniPEG groups have been synthesized. The platinum ligand was attached to the peptide via the carboxylic end of the malonate group at the end of the peptide. The pegylated peptide is nontoxic and highly soluble in water. Platinum conjugates synthesized using the pegylated peptides are also water-soluble with reduced or eliminated peptide immunogenicity. The choice of carboplatin as our untargeted platinum complex was due to the fact that the malonate linker chelates platinum in a manner similar to that of carboplatin. Cell toxicity assay and competition assay on the PC-3 cells (CD13 positive receptors) revealed selective delivery and destruction of PC-3 cells using targeted Pt-peptide conjugates 7 and 8 significantly more than untargeted carboplatin. Platinum uptake on PC-3 cells was 12-fold more for conjugate 7 and 3-fold more for conjugate 8 compared to that of the untargeted carboplatin, indicating selective activation of the CD13 receptors and delivery of the conjugates to CD13 positive cells. Further analysis on effects of conjugates 7 and 8 on PC-3 cells using caspase-3/7, fluorescence microscopy, and DNA fragmentation confirmed that the cells were dying by apoptosis.

In vitro cytotoxicity study on platinum (II) complexes with epoxysuccinates as leaving groups

A series of novel cisplatin-type platinum complexes were designed, characteristic of epoxysuccinates as leaving groups. The pertinent compounds were prepared and characterized by IR, (1)H NMR, and ESI-MS spectra with elementary analyses. The in vitro cytotoxic activities of compounds toward SPC-A1 human lung adenocarcinoma cell line and BGC823 human stomach adenocarcinoma cell line were determined. Biological tests have confirmed that complexes containing 4R,5R-DMID [abbreviation of (4R,5R)-4,5-bis (aminomethyl)-2-isopropyl-1,3-dioxolane] as carrier ligands have greater cytotoxicity toward tumor cells than the corresponding compounds with other carrier ligands. Most platinum complexes with trans-epoxysuccinates usually have higher cytotoxicity than those with cis-epoxysuccinates. Complex 4a shows the most effective among those tested platinum complexes in both cell lines, and its cytotoxicity approached that of cisplatin.

Novel cisplatin-type platinum complexes and their cytotoxic activity

A series of novel cisplatin-type platinum complexes, formulated as [PtA2(OCOCH2OR)2] (A2 = two monoamines or one diamine, R is an alkyl group), were designed, characteristic of alkoxyacetate as carboxylato ligands. The pertinent compounds were prepared and characterized by elementary analyses, IR, 1H NMR, and ESI-MS spectra. The cytotoxic activities of compound 1a in vitro toward HL-60 human leukemia and BEL-7402 human hepatocellular carcinoma cell lines were pioneeringly studied. Then, compounds 1b-3d were evaluated for their in vitro cytotoxicity against Ramos human lymphoma, 3AO human ovarian carcinoma, and A549 human non-small cell lung cancer cell lines. Most of them showed better cytotoxic activity than carboplatin against above selected cell lines.

Studies of interaction of trichloro{η2-cis-N,N-dimethyl-1-[6-(N′,N′-dimethyl-ammoniummethyl)-cyclohex-3-ene-1-yl]-methylammonium}platinum(II) chloride with DNA: Effects on secondary and tertiary structures of DNA. Cytotoxic assays on human ovarian cancer cell lines, resistant and non-resistant to cisplatin

The studies of interaction with DNA and the cytotoxic activity of a new organometallic platinum(II) compound are presented. The ability of this new platinum complex to modify secondary DNA structure was explored by circular dichroism (CD). Electrophoretic mobility showed changes in tertiary DNA structure, and atomic force microscopy (AFM) revealed morphological changes of plasmid DNA (pBR322). This compound breaks the traditional structure-activity rules for cis-platinum compounds, but it could be of interest because of its different kinetics. An organometallic bond normally shows a trans-effect higher than that of an amine ligand, and that fact, a priori, could contribute to a higher DNA binding rate. Several ovarian cancer cell lines, resistant and non-resistant to cisplatin, were exposed to increasing concentrations of cisplatin and complex 5 for 24 h, after which time the cell number/viability was determined by the colorimetric MTT assay. A lower cytotoxicity but also a lower resistant factor was observed for organometallic compound 5 than for cisplatin, against A2780 and A2780cisR cell lines. This result is consistent with the DNA interaction degree observed by the aforementioned techniques.

Studies of interaction of dichloro[η2-dimethyl-(2-methylidene-cyclohexylmethyl)-amino]platinum(II) with DNA: Effects on secondary and tertiary structures of DNA – Cytotoxic assays on human cancer cell lines Capan 1 and A431

The interaction with DNA and the cytotoxic activity of a new organometallic platinum(II) compound were studied. Different techniques were used to evaluate changes in secondary and tertiary DNA structures, and to obtain images of DNA morphological changes. The ability of platinum complex to modify secondary DNA structure was explored by circular dichroism (CD). Electrophoretic mobility showed changes in tertiary DNA structure. Finally, Atomic Force Microscopy (AFM) revealed morphological changes of plasmid DNA (pBR322). This compound breaks the traditional structure-activity rules for cis-platinum compounds, but it could be of interest because of its different kinetics. An organometallic bond normally shows a higher trans-effect than an amine ligand, and that fact, a priori, could contribute to a higher DNA binding rate. Human A431 and Capan-1 cells (vulvae carcinoma and pancreatic carcinoma, respectively) were exposed to increasing concentrations of cisplatin and complex 6 for 24 h, after which time the cell number/viability was determined by the colorimetric MTT assay. A low cytotoxicity of organometallic compound 6 against A431 and Capan-1 cancer cell lines was observed and this result is consistent with the low interaction with DNA observed in previous studies.

Synthesis and in vitro cytotoxicity of novel hydrophilic chiral 2-alkoxy-1,4-butanediamine platinum (II) complexes

Twenty-six new hydrophilic chiral 2-alkoxy-1,4-butanediamine platinum (II) complexes having a seven-membered ring structure between a bidentate carrier ligand and a platinum atom have been synthesized and most of them were evaluated for their in vitro cytotoxicity toward A549 human non-small cell lung carcinoma and HCT-116 human colon cancer cell lines. The cytotoxicities of platinum complexes are related to the nature of the carrier ligand and leaving group. Complex 5'b, viz. cis-dichloro[(2R)-ethoxy-1,4-butanediamine] platinum (II), exhibits the greatest potency among those 21 tested platinum complexes in both cell lines.

DNA interaction of dioxycyclobutenedione-(1,2-cyclohexanediamine) platinum(II) complex with potential anticancer activity

Dioxycyclobutenedione-(1,2-cyclohexanediamine)platinum(II), (R,R-DC-Pt) was found to have stronger cytotoxicity against six cancer cell lines than cisplatin and its DNA interactions was studied by calorimetric measurements, (13)C NMR. The binding specificity study of DNA base with R,R-DC-Pt was conducted by HPLC. To understand the molecular mechanism of R,R-DC-Pt with stronger cytotoxicity than that of cisplatin, we studied R,R-DC-Pt interaction with an oligonucleotide, d(ACCACGTGGT)(2), which contained c-H-ras gene encoding GGT by NMR spectroscopy. The oligomer DNA double helix was destroyed almost completely upon the R,R-DC-Pt binding. However under the same condition, the cisplatin binding with DNA was not so affected, and instead another conformation was formed, which suggests that larger damage to DNA can be induced by R,R-DC-Pt complex than that by cisplatin.

Reaction of polynuclear platinum antitumor compounds with reduced glutathione studied by multinuclear (1H, 1H-15N gradient heteronuclear single-quantum coherence, and 195Pt) NMR spectroscopy

A possible explanation for the low bioavailability of platinum antitumor compounds is their high reactivity with the sulfur-containing tripeptide glutathione (GSH; deprotonated GSH = SG). GSH is located in the intracellular matrix of the cell with a normal concentration of 5-10 mM. In vivo, only a small fraction of the administered drug will migrate into the cell, resulting in relatively high concentrations of GSH compared to that of the drug. The products of the reactions of [[trans-PtCl(NH(3))(2)](2)-mu-[trans-Pt(NH(3))(2)(NH(2)(CH(2))(6)NH(2))(2)]](NO(3))(4) (BBR3464; 1,0,1/t,t,t, n = 6), [[trans-PtCl(NH(3))(2)](2)-mu-(H(2)N(CH(2))(6)NH(2))](NO(3))(2) (BBR3005; 1,1/t,t, n = 6), [[trans-PtCl(NH(3))(2)](2)-mu-(H(2)N(CH(2))(3)NH(2)(CH(2))(4)NH(2))]Cl(3) (BBR3571; 1,1/t,t-spermidine, n = 3, 4), and trans-[PtCl(2)(NH(3))(2)] (t-DDP) with reduced GSH in phosphate-buffered saline (pH 7.35) have been characterized by (1)H, (195)Pt, and (1)H(-)(15)N gradient heteronuclear single-quantum coherence NMR spectroscopy and high-performance liquid chromatography (HPLC) coupled with electrospray ionization time-of-flight mass spectrometry to determine likely metabolites of the complexes with GSH. Chemical shifts (NMR) and retention times (HPLC) established via analysis of the t-DDP profile served as a fingerprint to compare results obtained for the products afforded by the degradation of the polynuclear compounds by GSH. Identical kinetic profiles and chemical shifts between the metabolites and the t-DDP/GSH products allowed identification of the final product for the 1:2 Pt:GSH reaction as a dinuclear species [[trans-Pt(SG)(NH(3))(2)](2)-mu-SG], in which glutathione bridges the two platinum centers via only the sulfur atom.

Platinum-based anticancer agents: innovative design strategies and biological perspectives

The impact of cisplatin on cancer chemotherapy cannot be denied. Over the past 20 years, much effort has been dedicated to discover new platinum-based anticancer agents that are superior to cisplatin or its analogue, carboplatin. Most structural modifications are based on changing one or both of the ligand types coordinated to platinum. Altering the leaving group can influence tissue and intracellular distribution of the drug, whereas the carrier ligand usually determines the structure of adducts formed with DNA. DNA-Pt adducts produced by cisplatin and many of its classical analogues are almost identical, and would explain their similar patterns of tumor sensitivity and susceptibility to resistance. Recently some highly innovative design strategies have emerged, aimed at overcoming platinum resistance and/or to introduce novel mechanisms of antitumor action. Platinum compounds bearing the 1,2-diaminocyclohexane carrier ligand; and those of multinuclear Pt complexes giving rise to radically different DNA-Pt adducts, have resulted in novel anticancer agents capable of circumventing cisplatin resistance. Other strategies have focused on integrating biologically active ligands with platinum moieties intended to selectively localizing the anticancer properties. With the rapid advance in molecular biology, combined with innovation, it is possible new Pt-based anticancer agents will materialize in the near future.

Ground-state stability and rotational activation parameters for individual rotamers of (R,S,S,R)-(N,N'-dimethyl-2,3-diaminobutane)PtG(2) complexes (G = 9-EtG, 3'-GMP, and 5'-GMP)

Rate constants for guanine rotation about the Pt-N7 bond in (R,S,S,R)-Me(2)DABPtG(2) complexes (Me(2)DAB = N,N'-dimethyl-2,3-diaminobutane; G = 9-EtG, 3'-GMP, and 5'-GMP) were evaluated from line-shape analysis of H8 resonances. Three diastereomers, two in head-to-tail (DeltaHT and LambdaHT) and one in head-to-head (HH) conformations, exist in equilibrium in solution. The two guanines are equivalent in DeltaHT and LambdaHT conformers and nonequivalent in the HH form; therefore, four rate constants (k(Delta)(HT), k(Lambda)(HT), k(HH)()s, and k(HH)()d; sub-subscripts s and d stand for H8-shielded and -deshielded guanine, respectively) were evaluated. Activation parameters (DeltaH and DeltaS) were evaluated from the rate constant dependence on temperature. High values of DeltaH (78-93 kJ mol(-)(1)) and DeltaS (51-71 J K(-)(1) mol(-)(1)) were found for G rotation in the preferred DeltaHT rotamer having the six-membered ring of each guanine more canted toward the cis-G and a favorable dipole-dipole internucleotide interaction. Lower values of DeltaH() (64-76 kJ mol(-)(1)) and very small values of DeltaS() (-7-11 J K(-)(1) mol(-)(1)) were found for G rotation in the less favorable LambdaHT rotamer, indicating that the ground-state entropy of this rotamer is close to that of the activated complex and the ground-state enthalpy closer to that of the activated complex than for the DeltaHT rotamer. For the two guanines in the HH rotamer there is no large difference in activation parameters. In general DeltaH falls in the range 66-84 kJ mol(-)(1) (rather close to the values for the LambdaHT rotamer) and DeltaS in the range 14-41 J K(-)(1) mol(-)(1). The equilibrium constant between HT and HH rotamers was also evaluated together with the corresponding thermodynamic parameters (DeltaH and DeltaS). It is found that the low enthalpy is the major stabilizing factor for DeltaHT as compared to HH, while the entropy factor would favor the latter rotamer. In contrast the greater entropy is the stabilizing factor for the LambdaHT rotamer (the second most abundant conformer for 9-EtG and 3'-GMP) over the HH rotamer. In the latter case the enthalpy would favor the HH rotamer. In the case of the 5'-GMP derivative the greater entropy of the LambdaHT rotamer is not such to compensate for the lower enthalpy of the HH rotamer, and the latter remains the second most abundant rotamer. This investigation has allowed for the first time the enthalpic and entropic contributions favoring different rotamers to be distinguished.

DNA oligonucleotide duplexes containing intramolecular platinated cross-links: energetics, hydration, sequence, and ionic effects

The anticancer activity of cisplatin arises from its ability to bind covalently to DNA, forming primarily intrastrand cross-links to adjacent purine residues; the most common adducts involve d(GpG) (65%) and d(ApG) (25%) intrastrand cross-links. The incorporation of these platinum adducts in a B-DNA helix induces local distortions, causing bending and unwinding of the DNA. In this work, we used temperature-dependent UV spectroscopy to investigate the unfolding thermodynamics, and associated ionic effects, of two sets of DNA decamer duplexes containing either cis-[Pt(NH(3))(2)[d(GpG]] or cis-[Pt(NH(3))(2) [d(ApG]] cross-links, and their corresponding unmodified duplexes. The platinated duplexes are less stable and unfold with lower T(M)s (and Delta G degrees s) in enthalpy-driven reactions, which indicates a loss of favorable base-pair stacking interactions. The folding thermodynamics and hydration effects for the first set of decamers containing the d(GpG) cross-link was investigated by a combination of titration calorimetry, density, and ultrasound techniques. The hydration parameters showed an uptake of structural water by the platinated duplex and a release of electrostricted water by the control duplex. Relative to the unmodified duplex, the folding of the platinated duplex at 20 degrees C yielded a positive Delta Delta G degrees term [and positive Delta Delta H-Delta(T Delta S) compensation] and a negative differential volume change. The opposite signs of the Delta Delta G degrees and Delta Delta V terms confirmed its uptake of structural water. Further, solvent-accessible surface areas calculations for a similar pair of dodecamer duplexes indicated that the modified duplex has a 503 oeA(2) higher polar and nonpolar surface area that is exposed to the solvent. Therefore, the incorporation of a platinum adduct in duplex DNA disrupts favorable base-pair stacking interactions, yielding a greater exposure of aromatic bases to the solvent, which in turn immobilizes structural water. The overall results correlate nicely with the results reported in the available structural data of nuclear magnetic resonance solution studies.

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.

cis-Dichloro(alpha,omega-diamino carboxylate ethyl ester)palladium(II) as Palladium(II) versus Platinum(II) Model Anticancer Drugs: Synthesis, Solution Equilibria of Their Aqua, Hydroxo, and/or Chloro Species, and in Vitro/in Vivo DNA-Binding Properties

cis-Dichloro(d,l-2,3-diaminopropionate ethyl ester)palladium(II), cis-[Pd(Etdap)Cl(2)] (I), and cis-dichloro(d,l-2,4-diaminobutyrate ethyl ester)palladium(II), cis-[Pd(Etdab)Cl(2)] (II), were synthesized and characterized by elemental analysis, IR spectroscopy, and TG-DTA thermal analysis. The equilibrium model and log beta(pqr) constants of hydrolytic species of I and II were also investigated by potentiometric methods (I = 0.15 M (NaClO(4)) and 37 degrees C). Aqueous solutions of cis-[Pd(Etdaa)(H(2)O)(2)](ClO(4))(2) (Etdaa = Etdap (III) or Etdab (IV)) were prepared by stoichiometric reaction of I or II with AgClO(4). Thus, log beta(pqr) of the corresponding cis-aquahydroxo (pqr = 1,0,-1) and di(&mgr;-hydroxo) (pqr = 2,0,-2) species were obtained from E(H(+)) data of alkalimetric titrations of solutions of III or IV. Such constants were then used as fixed values to obtain log beta(pqr)() of chloro-containing species (cis-dichloro (1,2,0), cis-chloroaqua (1,1,0), and cis-chlorohydroxo (1,1,-1)) from E(H(+)) and E(Cl(-)) data pairs simultaneously obtained by titration of solutions of III or IV with NaOH and NaCl. All log beta(pqr) were fitted by the SUPERQUAD program. Appropriate log beta(pqr)() sets give good simulations of experimental titration curves and several species distribution diagrams. In addition the interaction of I and/or II with DNA in vitro and in vivo was studied by various methods. UV spectral data and melting and renaturation curves indicate that both compounds destabilize the DNA helicoidal structure. Compound II disrupts in vivo the structure and transcription process of polytene chromosomes of Drosophila hydei.

Oxidative Addition of the Dithiobis(formamidinium) Cation to Platinum(II) Chloro Am(m)ine Compounds: Studies on Structure, Spectroscopic Properties, Reactivity, and Cytotoxicity of a New Class of Platinum(IV) Complexes Exhibiting S-Thiourea Coordination

The oxidative addition of the salt [{SC(NMe(2))(2)}(2)]Cl(2).2H(2)O (1), the disulfide-like dimerized form of 1,1,3,3-tetramethylthiourea (tmtu), to Pt(II) chloro am(m)ine compounds is described. Oxidation of the [PtCl(3)(NH(3))](-) anion with 1 in methanol yields cis-[PtCl(4)(NH(3))L] (2; L = tmtu) as the result of the trans addition of one tmtu and one chloro ligand. The same mode of oxidation is found in reactions of 1 with [PtCl(dien)](+) (dien = diethylenetriamine) and trans-[PtCl(2)(NH(3))(2)]. In these cases, however, the oxidation is followed by (light-independent) cis,trans isomerizations, giving trans,mer-[PtCl(2)(dien)L]Cl(2) (4) and fac-[PtCl(3)(NH(3))(2)L]Cl.0.5MeOH (6), respectively. The single-crystal X-ray structures of 2 and trans,mer-[PtCl(2)(dien)L](BF(4))(2) (4a) have been determined. 2: monoclinic, space group P2(1)/n, a = 6.280(1) Å, b = 13.221(3) Å, c = 16.575(2) Å, beta = 96.45(1) degrees, Z = 4. 4a: monoclinic, space group C2/m, a = 21.093(5) Å, b = 8.9411(9) Å, c = 14.208(2) Å, beta = 124.65(2) degrees, Z = 4. The tmtu ligands are S-bound. In 2 a pronounced trans influence of the S-donor ligand on the Pt-Cl bond (2.370(1) Å) trans to sulfur is observed. The unusual acidity of the Pt(IV) complexes exhibiting tmtu coordination trans to chloride is attributed to hydrolysis of the labilized Pt-Cl(trans) bond, which is supported by ion sensitive electrode measurements. An upfield shift of the (195)Pt resonances is found on changing the ligand combination from NCl(4)S (2) to N(3)Cl(2)S (4). This order correlates with the trans influences of the ligands: tmtu > am(m)ine > chloride. The cytotoxicity of 2 and 6 in L1210 cell lines is reported and discussed in terms of a possible mechanism of action of the compounds invivo. It is suggested that tmtu may act as a lipophilic carrier ligand and therefore enhance the cellular uptake of the new potential Pt(IV) drugs.

Preparation, characterization, and antitumor properties of cis-PtCl2 complexes linked to anthraquinones through position number 2

A new series of platinum-anthraquinone complexes of the type cis-PtLL'Cl2 [where L is the monodentate AQ-NH-(CH2)n-NH2 and L' = NH3 or LL' is the bidentate ligand AQ-NH-(CH2)n. NH-(CH2)2-NH2] in which the anthraquinone is linked to the diaminedichloroplatinum (II) moiety through position 2 was prepared and screened in vitro for antileukemic activity against P388 cells. All ligands were characterized by 1H and 13C NMR spectroscopy and all complexes by 195Pt NMR. The platinum complexes of anthraquinones which are modified in position 2 are significantly less potent than their analogs which are substituted in position 1. The activity of the complexes is either equal to or lower than the activity of the free ligands themselves. In the attempt to prepare AQ-NH-(CH2)4-NH-(CH2)2-NH2, a new compound, 2-(N-pyrrolidine)anthraquinone, was obtained and its structure was determined by x-ray crystallography. It crystallized in the monoclinic system in the space group P2(1)/c. The unit cell parameters are a = 9.595(1), b = 12.537(2), c = 11.461(1) A, beta = 94.14(2) degrees, V = 1375(1) A3, and z = 4.

Sequence specificity of DNA-DNA interstrand cross-link formation by cisplatin and dinuclear platinum complexes

The sequence specificity of interstrand cross-links induced in DNA by mononuclear and dinuclear platinum complexes in a 49-base-pair DNA duplex has been determined directly. This new assay takes advantage of the fact that 3'-->5' exonuclease digestion of randomly platinated DNA produces a pool of fragments of different lengths. This treatment allows identification of the spectrum of adducts impeding the exonuclease scission. Interstrand cross-linked adducts produce fragments that may remain complementary in the proximity of the binding site. As a result, these fragments may act as primer templates for extension upon subsequent treatment with a DNA polymerase. This extension increases the size of the oligonucleotide fragments, which may be evidenced by a more slowly migrating band on a sequencing gel. Concomitantly, the original band corresponding to the digested cross-link decreases in intensity. Therefore, comparison of a sequencing gel after digestion only and after the "digestion-extension" treatment should show the disappearance, or diminished band intensity, of only those fragments with interstrand cross-links. This approach was applied to the analysis of DNA interstrand cross-links formed by cis-[PtCl2(NH3)2] (cis-DDP) and [(trans-PtCl(NH3)2)2H2N(CH2)4NH2]Cl2. Cis-DDP was confirmed to form interstrand cross-links at d(GC) sequences but, interestingly, interstrand cross-links predominated in a sequence GCGG, with possible 1,3-intrastrand but no 1,2-intrastrand cross-links forming. The dinuclear compound formed 1,2, 1,3, and 1,4 DNA interstrand cross-links between guanines on opposite strands. In 1,3 and 1,4 cross-links, the guanines are separated by one and two base pairs, respectively, whereas a 1,2 cross-link is formed from guanines on neighboring base pairs.(ABSTRACT TRUNCATED AT 250 WORDS)