Palladium and platinum 3,5-diacetyl-1,2,4-triazol bis(thiosemicarbazones): chemistry, cytotoxic activity and structure-activity relationships

The preparation of platinum(II) complexes derived from 3,5-diacetyl-1,2,4-triazol bis(4-phenylthiosemicarbazone) (H(5)L(1)), 3,5-diacetyl-1,2,4-triazol bis(thiosemicarbazone) (H(7)L(2)), 3,5-diacetyl-1,2,4-triazol bis(4-methylthiosemicarbazone) (H(5)L(3)) and 3,5-diacetyl-1,2,4-triazol bis(4-ethylthiosemicarbazone) (H(5)L(3)) is described. The new complexes [Pt(mu-H(3)L(1))](2), [Pt(mu-H(5)L(2))](2), [Pt(mu-H(3)L(3))](2) and [Pt(mu-H(3)L(4))](2) have been characterized by elemental analyses, fast atom bombardment mass spectrometry (FAB(+)) and spectroscopic studies. The crystal and molecular structure of compounds [Pt(mu-H(3)L(1))](2), parent ligand H(5)L(1) and [Pt(mu-H(3)L(3))](2) have been determined by single crystal X-ray diffraction. The ligands coordinate, in a dideprotonate form to the platinum ions in a new tridentate fashion (NNS) and S-brigding bonding modes. Thus the molecular units of the platinum complexes are stacked as dimers. The testing of the cytotoxic activity of the synthesized compounds together with their palladium analogues against human A2780 and A2780cisR epithelial ovarian carcinoma cells lines suggests that the compounds may be endowed with important antitumor properties since they show IC(50) values in a micromolar range similar to those of cisplatin. The structure and antitumor activity relationships of platinum and palladium complexes are also discussed.     

Synthesis and characterization of palladium(II) and platinum(II) complexes with Schiff bases derivatives of 2-pyridincarboxyaldehyde. Study of their interaction with DNA

Several Schiff bases ligand derivatives of 2-pyridincarboxyaldehyde and different amines, together with their palladium(II) and platinum(II) complexes have been synthesised and characterised. The aim of this study is to probe the influence of substituents beared on the pyridyl/toulene ring at different position to their possible antitumor activity. The amines used were o-, m-, p-toluidine and 4-hydroxyaniline. All the compounds were characterised by elemental analysis, FT-IR spectroscopy, 1H and 195Pt NMR spectroscopy and matrix assisted laser desorption/ionization time-of-flight mass spectroscopy. The formation of DNA adducts were analysed by circular dichroism and electrophoretic mobility. Atomic force microscopy images of the compounds with plasmid DNA pBR322 were also obtained. In all cases changes in the second and tertiary structure of DNA could be observed as a consequence of the covalent interaction of the palladium(II) or platinum(II) ions with the N of the nucleobases. However, there are not significant differences in the behavior of the complexes related to the position of the methyl groups or the presence of the OH group. Values of IC50 were also calculated for the platinum(II) complexes for several pairs of ovarian tumor cell lines which were either sensitive or resistant to cisplatin. Finally in vitro apoptosis studies for platinum(II) complexes with ovarian tumor cell lines A2780/A2780cisR were carried out. The results indicated interesting antiproliferative activity and significant apoptosis induction.     

Dinuclear platinum anticancer complexes with fluorescent N,N′-bis(aminoalkyl)-1,4-diaminoanthraquinones: cellular processing in two cisplatin-resistant cell lines reflects the differences in their resistance profiles

The biological activity of N,N-bis(aminoalkyl)-1,4-diaminoanthraquinones (aminoalkyl is 2-aminoethyl, 3-aminoprop-1-yl and 4-aminobut-1-yl) and their dinuclear platinum complexes has been evaluated in the U2-OS human osteosarcoma cell line and its cisplatin-resistant U2-OS/Pt subline. All the compounds have been found to exhibit high cytotoxicity in the sensitive cell line, and to overcome cisplatin resistance in U2-OS/Pt cells. Cellular processing of N,N-bis(2-aminoethyl)-1,4-diaminoanthraquinone and the respective dinuclear platinum complex in the sensitive and resistant U2-OS cells has been studied over time using digital fluorescence microscopy. Cellular processing of the compounds has been found to be similar in sensitive and resistant U2-OS cells, which is in agreement with the lack of cross-resistance in the U2-OS/Pt cell line. Both the platinum complex and the free ligand quickly enter the cell and accumulate in the nucleus. The platinum complex is excreted from the cell via the Golgi apparatus, while the weakly basic anthraquinone ligand accumulates in the Golgi complex, where it is taken up by lysosomes and then transported to the cell surface. The cellular distribution of the fluorescent anthraquinones and their dinuclear platinum complexes in the sensitive/resistant pair of U2-OS osteosarcoma cell lines is compared with the earlier studied cellular processing in the sensitive/resistant pair of A2780 ovarian carcinoma cell lines. In the A2780cisR cell line, the platinum complexes (and not the free ligands) are sequestered in lysosomes, which is not the case in A2780 sensitive cells. The differences in cellular distribution of the compounds in these two sensitive/resistant pairs of cell lines most likely result from different resistance profiles in A2780cisR and U2-OS/Pt cells. Lysosomes of A2780cisR cells are less acidic than lysosomes of A2780 sensitive cells, which is likely to be the cause of a defect in endocytosis. The disruption of normal endocytosis might facilitate sequestration of the platinum complexes in lysosomes, which partly confers the cross-resistance of these complexes with cisplatin in the A2780cisR cell line. In contrast, sequestration in acidic vesicles does not occur in U2-OS/Pt cells that do not exhibit enhanced lysosomal pH and which are likely to have normal endocytosis.     

Pd(II) and Pt(II) complexes with aromatic diamines: study of their interaction with DNA

Pd(II) and Pt(II) new complexes with simple aromatic diamines were synthesised and characterised with the aim of studying their possible antitumour activity. The aromatic diamines chosen were 2,3-diaminotoluene (2,3 dat), 3,4-diaminotoluene (3,4 dat), 4,5-diaminoxylene (4,5 dax) and 2,3-diaminophenol (2,3 dap). The complexes, of formulae cis-[MCl(2)(diamine)], were characterised by elemental analysis, conductivity measurements, 1H, 13C(1H) and 195Pt NMR spectroscopy. The X-ray crystal structure was also resolved for the palladium complexes with 2,3-diaminotoluene and 4,5-diaminoxylene. The DNA adduct formation of the eight new complexes synthesised was followed by circular dichroism and electrophoretic mobility. Atomic force microscopy images of the modifications caused by the complexes on plasmid DNA pBR322 were also obtained. Values of IC50 were also calculated for the four platinum complexes against the cisplatin resistant tumour cell line A2780cisR.     

Studies on the activity of three palladium(II) compounds of the form: trans-PdL2Cl2 where L=2-hydroxypyridine, 3-hydroxypyridine, and 4-hydroxypyridine

Three planaraminepalladium(II) complexes of the form: trans-PdCl(2)L(2), code named TH5, TH6 and TH7 where L=3-hydroxypyridine, 2-hydroxypyridine and 4-hydroxypyridine respectively have been investigated for antitumour activity against ovarian cancer cell lines: A2780, A2780(cisR) and A2780(ZD0473R). Although the compounds are generally found to be less active than cisplatin, they are often found to be more active against the resistant cell lines than the parent cell line. Among TH5, TH6 and TH7, TH6 which has two 2-hydroxypyridine non-labile ligands is found to be most active against the three cell lines. Variations in activity of TH5, TH6 and TH7 indicate that non-covalent interactions may be playing a significant role in activity. In particular, the results indicate that small changes in planaramine ligands such as the position of the polar OH group can have a more profound effect on activity of the compounds. Palladium compounds are generally found to be toxic rather tumour active because of much higher reactivity. Low but significant activity of trans-palladium(II) complexes TH5, TH6 and TH7 against the ovarian cancer cell lines indicates that it is believed to be associated with the decrease in their reactivity due to the presence of two sterically hindered planaramine ligands.     

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.     

Cellular pharmacology of cis and trans pairs of platinum complexes in cisplatin-sensitive and -resistant human ovarian carcinoma cells

The cellular pharmacology of two pairs of cis and trans platinum complexes has been studied in three human ovarian carcinoma cell lines, a parental relatively cisplatin-sensitive line (CH1), a subline possessing acquired cisplatin resistance (3-fold; CH1cisR) and an intrinsically cisplatin resistant line (13-fold; SKOV-3). Growth inhibition studies showed that both JM335 [trans ammine (cyclohexylaminedichloro dihydroxo) platinum(IV)] and its platinum(II) dichloro homolog JM334 were relatively less cross-resistant against both acquired and intrinsic cisplatin resistant cells. In contrast, resistance circumvention was not apparent in these cell lines with their cis isomeric counterparts (JM149 for JM335 and JM118 for JM334). The trans compound JM335 was more potent than its cis isomer against all three cell lines. There was no clear correlation between intracellular accumulation following 2 h exposure to each compound and resulting DNA platination or growth inhibition. The selective activity of the trans platinum complexes against the SKOV-3 cell line correlated with a deficiency in the repair of adducts within a fragment of the N-ras gene induced by trans compounds whereas adducts induced by the cis counterparts, and cisplatin, were repaired. The CH 1 parental line appeared repair deficient at the gene-specific level to adducts induced by both cis (including cisplatin) and trans compounds. Resistance in CH1cisR was associated with a lack of gene-specific repair of lesions formed by JM118 and JM149. All four compounds induced apoptosis in all three cell lines, as measured by fluorescent microscopy and field inverted gel electrophoresis, although the kinetics of apoptosis was markedly faster for the trans versus cis compounds. In summary, the trans platinum complexes JM335 and JM334 possess unique cellular properties compared to their cis counterparts particularly with respect to gene specific repair of DNA adducts and the rate of induction of apoptosis.     

Three new asymmetric trans-amine(azole)dichloridoplatinum complexes that overcome cisplatin resistance and their reactions with 5'-GMP

Three new asymmetric platinum(II) complexes comprising an isopropylamine ligand trans to an azole ligand were synthesized and fully characterized by ¹H NMR, ¹⁹⁵Pt NMR, IR and elemental analysis. In addition the X-ray crystal structure of all three complexes was determined. The reaction kinetics of the complexes with DNA model base guanosine-5′-monophosphate (GMP) was studied, revealing reaction kinetics comparable to cisplatin. To gain insight in the complexes as potential antitumor agents, cytotoxicity assays were performed on a variety of human tumor cell lines. These assays showed the complexes all to possess cytotoxicity profiles comparable to cisplatin. Furthermore, the complexes largely retain their activity in a human ovarian carcinoma cell line resistant to cisplatin, A2780R, compared to the cisplatin sensitive parent cell line A2780. These results are of fundamental importance, illustrating how platinum complexes of trans geometry can show improved activity compared to cisplatin in both cisplatin sensitive and cisplatin resistant cell lines.     

Glutathione induces cellular resistance against cationic dinuclear platinum anticancer drugs

The sulfur-containing tripeptide glutathione (GSH) is one of the most abundant molecules in cells. Elevated levels of GSH render some types of cancer cells resistant against well-known platinum anti-cancer drugs such as cisplatin and carboplatin. Platinum complexes are often very reactive towards the cysteine residue of GSH, which detoxifies these compounds by a rapid binding mechanism. Clearly, this resistance mechanism poses a severe obstacle to any new platinum drugs designed to overcome cisplatin resistance. In the present study the cytotoxicity of dinuclear platinum compounds of the 1,1/t,t type, as developed by Farrell, is determined in human ovarium A2780 cells and in the cisplatin-resistant cell line A2780cisR, which possesses elevated levels of GSH. Further, the effect of depletion of GSH levels by L-buthionine-S,R-sulfoximine (L-BSO) in A2780cisR was investigated. The experiments show that detoxification by GSH is an effective resistance mechanism against dinuclear platinum compounds. However, the dinuclear complexes are less sensitive towards detoxification compared to cisplatin. This is probably because of the rapid binding of dinuclear cationic complexes to DNA. Compared to cisplatin, the rapid binding to DNA reduces the time during which the drug molecules are exposed to GSH in the cytosol. The reaction of a representative dinuclear compound with glutathione (pH 7, 37 degrees C) was studied in detail by 195Pt NMR. The dinuclear complex BBR3005 ([trans-PtCl(2)(NH(3))(2)(mu-H(2)N(CH(2))(6)NH(2))](2+), abbreviated as 1,1/t,t n=6), follows different pathways in the reaction with GSH, depending on the molar ratio of the reactants. When reacted in stoichiometric amounts (1:1), first a chloride on each platinum is replaced by a sulfur, forming a PtN(3)S product at -2977 ppm. After 2-3 h, this intermediate reacts further to form a sulfur-bridged N(3)Pt-S-PtN(3) species as the main product at -2811 ppm. When BBR3005 is reacted with GSH in a ratio of 1:4, the sulfur-bridged species is not observed. Instead, the final product is trans-Pt(GS)(2)(NH(3))(2) (at -3215 ppm); the same product appears if GSH is reacted with trans-PtCl(2)(NH(3))(2). Apparently, GSH first replaces the chlorides and subsequently degrades the dinuclear compound by replacement of the diaminealkyl linker.     

cis-Dichloroplatinum(II) complexes tethered to 9-aminoacridine-4-carboxamides: synthesis and action in resistant cell lines in vitro.

A series of intercalator-tethered platinum(II) complexes PtLCl(2) have been prepared where L are the diamine ligands N-[2-[(aminoethyl)amino]ethyl]-9-aminoacridine-4-carboxamide, N-[3-[(2-aminoethyl)amino]propyl]-9-aminoacridine-4-carboxamide, N-[4-[(2-aminoethyl)amino]butyl]-9-aminoacridine-4-carboxamide and N-[5-[(aminoethyl)amino]pentyl]-9-aminoacridine-4-carboxamide and N-[6-[(aminoethyl)amino]hexyl]-9-aminoacridine-4-carboxamide. The activity of the complexes was assessed in the CH-1, CH-1cisR, 41M, 41McisR and SKOV-3 cell lines. The compounds with the shorter linker chain lengths are generally the most active against these cell lines and are much more toxic than Pt(en)C1(2). For example, for the n=2 compound the IC(50) values are 0.017 microM (CH-1), 1.7 microM (41M), 1.4 microM (SKOV-3) and the resistance ratios are 51 (CH-1cisR) and 1.6 (41McisR). For the untethered analogue Pt(en)C1(2) the IC(50) values are 2.5 microM (CH-1), 2.9 microM (41M), 45 microM (SKOV-3) and the resistance ratios are 2.8 (CH-1cisR) and 4.1 (41McisR). The very large differential in IC(50) values between the CH-1 and CH-1cisR pair of cell lines for the 9-aminoacridine-4-carboxamide tethered platinum complexes indicates that repair of platinum-induced DNA damage may be a major determinant of the activity of these compounds.     

Three new asymmetric trans-amine(azole)dichloridoplatinum complexes that overcome cisplatin resistance and their reactions with 5′-GMP

Three new asymmetric platinum(II) complexes comprising an isopropylamine ligand trans to an azole ligand were synthesized and fully characterized by ¹H NMR, ¹⁹⁵Pt NMR, IR and elemental analysis. In addition the X-ray crystal structure of all three complexes was determined. The reaction kinetics of the complexes with DNA model base guanosine-5′-monophosphate (GMP) was studied, revealing reaction kinetics comparable to cisplatin. To gain insight in the complexes as potential antitumor agents, cytotoxicity assays were performed on a variety of human tumor cell lines. These assays showed the complexes all to possess cytotoxicity profiles comparable to cisplatin. Furthermore, the complexes largely retain their activity in a human ovarian carcinoma cell line resistant to cisplatin, A2780R, compared to the cisplatin sensitive parent cell line A2780. These results are of fundamental importance, illustrating how platinum complexes of trans geometry can show improved activity compared to cisplatin in both cisplatin sensitive and cisplatin resistant cell lines.     

Studies of interaction of trichloro{eta2-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 on activities, cell up take and DNA binding of four multinuclear complexes of the form: [[trans-PtCl(NH(3))(2)](2)mu-[trans-Pd(NH(3))(2)-(H(2)N(CH(2))(n)NH(2))(2)]]Cl(4) where n=4-7

The activity against human cancer cell lines including ovarian: A2780, A2780(cisR), cell up take, DNA-binding and nature of interaction with pBR322 plasmid DNA have been studied for four multinuclear complexes code named DH4Cl, DH5Cl, DH6Cl and DH7Cl, having the general formula: [[trans-PtCl(NH(3))(2)](2)mu-[trans-Pd(NH(3))(2)-(H(2)N(CH(2))(n)NH(2))(2)]]Cl(4) where n=4, 5, 6 and 7 for DH4Cl, DH5Cl, DH6Cl and DH7Cl, respectively. The compounds are found to exhibit significant anticancer activity against ovarian cancer cell lines: A2780, A2780(cisR) and A2780(ZD0473R). DH6Cl in which the linking diamine has six carbon atoms is found to be the most active compound. As the number of carbon atoms in the linking diamine is decreased below six and increased above six, the activity is found to decrease, illustrating structure-activity relationship. All the multinuclear compounds are believed to form a plethora of long-range interstrand GG adducts with DNA dictated by the sequence of bases in the DNA strands. Increasing prevention of BamH1 digestion with the increase in concentration of the compounds is due to global changes in DNA conformation brought about by interstrand long-range binding of the compounds with DNA.     

Antitumor activity of phenylene bridged binuclear bis(imino-quinolyl)palladium(II) and platinum(II) complexes

Antitumor effects of a known bis(imino-quinolyl)palladium(II) complex 1 and its newly synthesized platinum(II) analogue 2 were evaluated against human breast (MCF-7) and human colon (HT-29) cancer cell lines. The complexes gave cytotoxicity profiles that were better than the reference drug cisplatin. The highest cytotoxic activities were pronounced in complex 2 across the two examined cancer cell lines. Both compounds represent potential active drugs based on bimetallic complexes.     

Studies on activities, cell uptake and DNA binding of four trans-planaramineplatinum(II) complexes of the form: trans-PtL(NH3)Cl2, where L=2-hydroxypyridine, imidazole, 3-hydroxypyridine and imidazo(1,2-alpha)pyridine

Four trans-planaramineplatinum(II) complexes code named YH9, YH10, YH11 and YH12 each of the form trans-PtL(NH(3))Cl(2), where L=2-hydroxypyridine and 3-hydroxypyridine, imidazole, and imidazo(1,2-alpha)pyridine for YH9, YH10, YH11 and YH12, respectively, have been synthesized and the activity of the compounds against human cancer cell lines, cell uptake, DNA-binding and nature of interaction with pBR322 plasmid DNA have been studied. The compound having imidazo(1,2-alpha)pyridine ligand as one the carrier ligands in the trans-configuration is found to be significantly more active than cis-platin against ovarian A2780(cisR) cancer cell line corresponding with higher Pt-DNA binding. All other compounds have resistance factors less than that for cis-platin in the A2780 and A2780(cisR) cell lines. A greater prevention of BamH1 digestion with increasing concentration of the compounds indicates that as the compounds bind with nucleobases in DNA, the DNA conformation is changed sufficiently so as to prevent BamH1 digestion at the specific GG site. Gel electrophoresis results also indicate that as the compounds bind to DNA, unwinding of supercoiled form I DNA takes place to change it from the negatively supercoiled form I through relaxed circular form I to the positively supercoiled form I.     

3,5-diacetyl-1,2,4-triazol bis(4N-substituted thiosemicarbazone) palladium(II) complexes: synthesis, structure, antiproliferative activity and low toxicity on normal kidney cells

Treatment of ⁴N-monosubstituted bis(thiosemicarbazone) ligands of 3,5-diacetyl-1,2,4-triazol series with lithium tetrachloridopalladate gave the dinuclear complexes of general formula [Pd(μ-H₃L^1-5)]₂, but using dichloridobistriphenylphosphinepalladium(II) salt, the first mononuclear bis(thiosemicarbazone)-palladium-triphenylphosphine complexes of the 3,5-diacetyl-1,2,4-triazol series, [Pd(H₃L^1-5)PPh₃], have been obtained. All the compounds have been characterized by elemental analysis and by IR and NMR spectroscopy, and the crystal and molecular structures of dinuclear complexes [Pd(μ-H₃L³)]₂ and [Pd(μ-H₃L⁵)]₂ as well as mononuclear complexes [Pd(H₃L¹)PPh₃], [Pd(H₃L²)PPh₃], [Pd(H₃L³)PPh₃] and [Pd(H₃L⁴)PPh₃] have been determined by X-ray crystallography. The new compounds synthesized have been evaluated for antiproliferative activity in vitro against NCI-H460, A2780 and A2780cisR human cancer cell lines. Subsequent toxicity study, on normal renal LLC-PK1 cells, shows that all compounds investigated exhibit very low toxicity on kidney cells with respect to cisplatin.     

New Pd(II) and Pt(II) complexes with N,S-chelated pyrazolonate ligands: molecular and supramolecular structure and preliminary study of their in vitro antitumoral activity

New Pd(II) and Pt(II) complexes [ML2] (HL=a substituted 2,5-dihydro-5-oxo-1H-pyrazolone-1-carbothioamide) have been synthesized by reacting K2MCl4 (M=Pd, Pt) or Pd(OAc)2 with beta-ketoester thiosemicarbazones. The structures of seven of these complexes were determined by X-ray diffraction. Although all exhibit a distorted square-planar coordination with trans- or (in one case) cis-[MN2S2] kernels, their supramolecular arrangements vary widely from isolated molecules to 3D-networks. The in vitro antitumoral assays performed with two HL ligands and their metal complexes showed significant cytostatic activity for the latter, with the most active [ML2] derivative (a palladium complex) being about sixteen times more active than cis-DDP against the cisplatinum-resistant cell line A2780cisR.     

Cellular accumulation and DNA platination of two new platinum(II) anticancer compounds based on anthracene derivatives as carrier ligands

The anticancer properties of two new fluorescent platinum(II) compounds, cis-[Pt(A9opy)Cl₂] and cis-[Pt(A9pyp)(dmso)Cl₂] are described. These compounds are highly active against several human tumor cell lines, including human ovarian carcinoma sensitive and cisplatin-resistant cell lines (A2780 and A2780R). To study the cellular processing of these new compounds, a series of in vitro studies have been performed, including the investigation of intracellular platinum accumulation and DNA-platination experiments in A2780 and A2780R cells. Compared to cisplatin, both compounds are accumulated highly in both sensitive and resistant cell lines, and more platinum has been found to bind to the nuclear DNA. Interestingly, cis-[Pt(A9opy)Cl₂] shows high accumulation and DNA adduct formation in the resistant cell line A2780R, as compared to the sensitive counterpart A2780 cell line. This suggests that cis-[Pt(A9opy)Cl₂] is able to overcome some of the well-known resistance mechanisms in this cell line, such as decreased cellular uptake and increased DNA repair.     

Preparation, characterization, and antitumor activity of new cisplatin analogs with homopiperazines: crystal structure of [PtII(1-methylhomopiperazine)(methylmalonato)].2H2O

A series of new platinum(II) and (IV) complexes with homopiperazine have been synthesized and characterized by elemental analysis, infrared, and 195Pt nuclear magnetic resonance spectroscopic techniques. The complexes are of two types: [PtIILX] (where L = homopiperazine (hpip), 1-methylhomopiperazine (mhpip), or 1,4-dimethylhomopiperazine (dmhpip), and X = 1,1-cyclobutanedicarboxylato (CBDCA), or methylmalonato ligand) and [PtIV(L-)trans-(Y)2Cl2] (where Y = hydroxo, acetato, or chloro ligand). Among the complexes synthesized, the crystal structure of [PtII(mhpip)(methylmalonato)].2H2O was determined by the single crystal X-ray diffraction method. The crystallographic parameters were orthorhombic, P2(1)2(1)2(1) (no. 19), a = 7.2014(14), b = 7.3348(15), c = 26.971(5) A, and Z = 4. The structure refinements converged to R1 = 0.0641 and wR2 = 0.1847. In this complex, platinum has a slightly distorted square planar geometry with the two adjacent corners being occupied by two nitrogens of the mhpip ligand, whereas the remaining cis positions are coordinated with two oxygen atoms of the methylmalonato group. The mhpip ligand is in a boat conformation and forms five and six membered chelating rings with platinum. The intricate network of intermolecular hydrogen bonds holds the crystal lattice together. Some of these synthesized cisplatin analogs have good in vitro cytotoxic activity against the cisplatin-sensitive human ovarian A2780 (IC50 = 0.083-17.8 microM) and the isogenic cisplatin-resistant 2780CP (IC50 = 20.1-118.1 microM) cell lines.     

Biochemical and molecular properties of cisplatin-resistant A2780 cells grown in folinic acid

In this study, A2780 human ovarian carcinoma cells were grown in folinic acid in contrast to folic acid, and the molecular and biochemical properties of cisplatin-resistant A2780 cells were analyzed for changes in the dTMP synthase cycle. At concentrations of folinic acid that were optimal for cell growth (10(-8) M), the ED50 for cisplatin was 2.5 and 43 microM in the A2780S and A2780DDP cells, respectively. Resistance to cisplatin was associated with a 2-fold cross-resistance to 5-fluorodeoxyuridine and 5-fluorouracil as well as a 3-fold increase in both dTMP synthase activity and mRNA. The ED50 for methotrexate was similar in both A2780S and A2780DDP cells (1.2 microM). When both the A2780S and A2780DDP cells were grown in folinic acid, there was no significant difference in the level of dihydrofolate reductase activity. This data would suggest that cisplatin resistance is associated with changes in folate metabolism.