Synthesis, DNA-binding affinity and cytotoxicity of the dinuclear platinum(II) complexes with berenil and amines ligands

A series of platinium(II) complexes of formula [Pt2L4(berenil)2]Cl4.4HCl.2H2O where L is piperidine (1), 4-picoline (2), 3-picoline (3) or isopropylamine (4) was prepared and their cytotoxicity have been tested against the growth of human breast cancer cells. Evaluation of the cytotoxicity of these compounds employing a MTT assay and inhibition of [3H]thymidine incorporation into DNA in both MDA-MB-231 and MCF-7 breast cancer cells demonstrated that these compounds were more active than cisplatin. Data from the ethidium displacement assay indicated that these compounds show moderate specificity for AT base pairs of DNA. Compounds 1-4 were also potent topoisomerase II inhibitors, with 50% inhibitory concentrations (IC50) ranging from 5 to 50 microM.     

The effect of a novel dinuclear platinum complex with berenil and 2-picoline ligands on growth of human breast cancer cells

Evaluation of the cytotoxicity of a novel dinuclear platinum(II) complex of formula Pt2(2-picoline)4(berenil)2 employing a MTT assay and inhibition of [3H]thymidine incorporation into DNA in both MDA-MB-231 and MCF-7 breast cancer cells demonstrated that the complex was more potent anti-proliferative agent than cisplatin. Data from the ethidium displacement assay indicated that the complex showed specificity for AT base pairs of DNA. Our study showed that Pt2(2-picoline)4(berenil), was a potent catalytic inhibitor of topoisomerase II in opposition to cisplatin.     

Cytotoxicity and induction of apoptosis of human breast cancer cells by novel platinum(II) complexes

The current work investigates the influence of novel dinuclear platinum(II) compounds of structure: Pt₂(3-ethylpyridine)₄(berenil)₂ (Pt10) and Pt₂(3-butylpyridine)₄(berenil)₂ (Pt11) on growth and viability of MDA-MB-231 and MCF-7 breast cancer cells as well as their putative mechanism of cytotoxicity. Evaluation of the cytotoxicity of Pt10 and Pt11 employing a MTT assay and inhibition of [³H]thymidine incorporation into DNA in both MDA-MB-231 and MCF-7 breast cancer cells demonstrated that these compounds were more potent antiproliferative agents than cisplatin. In our study the induction of apoptosis by Pt10 and Pt11 in human breast cancer cells was confirmed by several biochemical markers, such as: phosphatidylserine externalization, loss of mitochondrial membrane potential ΔΨ_m, caspase-3, -8, -9 activity, and DNA degradation. Pt10 and Pt11 induce apoptosis of breast cancer cells via mechanisms dependent on caspases activation and associated with mitochondrial membrane potential disruption.     

Synthesis, DNA binding, topoisomerase inhibition and cytotoxic properties of 2-chloroethylnitrosourea derivatives of hoechst 33258

A number of novel 2-chloroethylnitrosourea derivatives of Hoechst 33258 were synthesized and examined for cytotoxicity in breast cancer cell cultures and for inhibition of topoisomerases I and II. Evaluation of the cytotoxicity of these compounds employing a MTT assay and inhibition of [3H]thymidine incorporation into DNA in both MDA-MB-231 and MCF-7 breast cancer cells demonstrated that these compounds were more active than Hoechst 33258. The DNA-binding ability of these compounds was evaluated by an ultrafiltration method using calf thymus DNA, poly(dA-dT)2 and poly(dG-dC)2, indicated that these compounds as well as Hoechst 33258 well interact with AT base pair compared with GC pair. Binding studies indicate that these compounds bind more tightly to double-stranded DNA than the parent compound Hoechst 33258. The degree to which these compounds inhibited cell growth breast cancer cells was generally consistent with their relative DNA binding affinity. Mechanistic studies revealed that these compounds act as topoisomerase I (topo I) or topoisomerase II (topo II) inhibitors in plasmid relaxation assays.     

Cytotoxic efficacy of a novel dinuclear platinum(II) complex in human breast cancer cells

Evaluation of the cytotoxicity of a novel dinuclear platinum(II) complex of formula Pt₂(2-picoline)₄(berenil)₂ employing a MTT assay and inhibition of [³H]thymidine incorporation into DNA in both MDA-MB-231 and MCF-7 breast cancer cells demonstrated that the complex was more of a potent antiproliferative agent than cisplatin. The DNA-binding ability of Pt₂(2-picoline)₄(berenil)₂ estimated by an ethidium displacement assay indicated that the complex showed strong specificity for AT base pairs in the minor groove of DNA. Our study showed that Pt₂(2-picoline)₄(berenil)₂ was a potent catalytic inhibitor of topoisomerase II in opposition to cisplatin. Pt₂(2-picoline)₄(berenil)₂ was found to be a more active inhibitor of collagen biosynthesis than cisplatin. The up regulation of β₁-integrin and insulin-like growth factor I (IGF-I) receptor expression by the complex was shown to be accompanied by an increase in the expression of mitogen activated protein kinases in breast cell lines. The phenomenon was related to the increased expression of nuclear factor-kappaB (ΝF-κΒ) by Pt₂(2-picoline)₄(berenil)₂ as shown by the Western immunoblot analysis. Flow cytometric analysis and a fluorescent microscopy assay demonstrated that cell death appeared to result from apoptosis, with the possibility of secondary necrosis. The data presented suggested that Pt₂(2-picoline)₄(berenil)₂ impaired growth and metabolism of breast cancer cells more efficiently than cisplatin. These results indicated also the different properties of Pt₂(2-picoline)₄(berenil)₂ and cisplatin.     

Synthesis and biological evaluation of new cyclic amidine analogs of chlorambucil

A number of novel cyclic amidine analogs of chlorambucil were synthesized and examined for cytotoxicity in breast cancer cell cultures and for inhibition of topoisomerases I and II. Evaluation of the cytotoxicity of these compounds employing a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and inhibition of [(3)H]-thymidine incorporation into DNA in both MDA-MB-231 and MCF-7 breast cancer cells demonstrated that these compounds were more active than chlorambucil. The degree to which these compounds inhibited cell growth breast cancer cells was directly correlated to DNA-binding affinity. These studies indicate that cyclic amidine analogs of chlorambucil are a potent catalytic inhibitor of topoisomerase II but not topoisomerase I. The highest degree of DNA binding and cytotoxicity in both MDA-MB-231 and MCF-7 breast cancer cells was observed for the compound, which possess a 4,5-dihydro-1H-imidazol moiety.     

1, 2-Bis(2, 6-difluoro-3-hydroxyphenyl)ethylene-diamine]platinum(II) complexes, compounds for the endocrine therapy of breast cancer - mode of action II: contribution of drug inactivation, cellular drug uptake and sterical factors in the drug-target interaction to the antitumor activity

The marked activity of [meso-1, 2-bis(2, 6-difluoro-3-hydroxyphenyl)ethylenediamine]platinum(II) (meso-3-PtLL', L, L' = Cl(2) or L = OH(2), L' = OSO(3)) on the hormone-sensitive MXT-M-3, 2 breast cancer implanted in mice is most probably due to a mechanism based on the reduction of the endogenous estrogen level. Cytotoxic effects which are poorly pronounced in experiments on several breast cancer cell lines (e.g. MCF-7), do not significantly contribute to the anti-breast cancer activity of this compound. In contrast to this, the standard cisplatin and the structurally related comparison compound [meso-1, 2-bis(4-fluorophenyl)ethylenediamine]platinum(II) (meso-4-PtLL', L, L' = Cl(2) or L = OH(2), L' = OSO(3)) are strongly active in vivo as well as in vitro. Both effects entail programmed cell death, which is responsible for the inhibition of the tumor growth. The minor cytotoxicity of meso-3-PtLL' in breast cancer cell cultures is caused neither by an inappropriate rate of reaction with bionucleophiles (e.g. by a too fast inactivation by plasma proteins) nor solely by the observed poor absorption by the tumor cells resulting in an insufficient drug concentration at the DNA. Additionally, an impeded reaction with biologically important, guanine-rich sequences of DNA (owing to the 2, 6-standing F atoms which hinder the drug-target inter action) must be assumed as cause of its marginal cytotoxicity.     

Cytotoxic effects of novel polyoxotungstates and a platinum compound on human cancer cell lines

The cytotoxicity of a new platinum compound Pt1 [2,9-dimethyl-4,7-diphenyl-1,10-phenanthrolinedichloroplatin(II)] and six polyoxometalates (POM1-6) on two neuroblastoma cell lines (SHEP-SF and KCN) and an Ewing's Sarcoma cell line (CADO-ES-1) was studied. Cisplatin [cis-diamminedichloroplatinum(II)] and carboplatin [cis-diammine(cyclobutanedicarboxylato)platinum(II)] were used as reference agents. Using MTT tests, the cytotoxicity (LD50: lethal doses 50%) of the compounds were measured at different concentrations. After 72 h exposure, the LD50 data for the platinum-containing substances ranged between 4.47 x 10(-6) and 1.91 x 10(-4) M. The SHEP-SF cell line displayed the highest sensitivity to cisplatin. The novel platinum agent Pt1 had a similar cytotoxic effect to the reference agent cisplatin. Both cisplatin and Pt1 were more cytotoxic than carboplatin. The POMs reduced cell viability compared to untreated cells at concentrations between 8.4 x 10(-7) and 3.47 x 10(-5) M. POM1 ([(CH3)4N]2Na6.5(NH4)2[SnII1.5(WO2(OH))0.5(WO2)2(SbW9O33)2] x 32H2O) was the most effective polyoxoanion with a mean LD50 value of 8.83 x 10(-6) M in the three cell lines tested. With CADO-ES-1 and KCN cells, POM1 was found to be more effective than the platinum compounds cisplatin, carboplatin and Pt1.     

Antiproliferative activity of derivatives of ouabain, digoxin and proscillaridin A in human MCF-7 and MDA-MB-231 breast cancer cells

Three derivatives of ouabain, digoxin and proscillaridin A containing the carboxylic group instead of the lactone moiety were synthesized and examined for cytotoxicity in human breast cancer cells. Evaluation of the cytotoxicity of these compounds employing an MTT assay and inhibition of [3H]thymidine incorporation into DNA in both MCF-7 and MDA-MB-231 breast cancer cells demonstrated that compound 3, the most active of the series, proved to be only slightly less potent than proscillaridin A. We evaluated the effects of these compounds 1-3 on change in intracellular Ca2+, appearance of apoptosis, inhibition of DNA topoisomerase I and II, and the activity of caspase-3 in breast cancer cells. These studies indicate that the increase in potency for 3 may be related, in part, to an activation of caspase-3, increasing free calcium concentration and topoisomerase II inhibition. All these data emphasize the potential usefulness of these derivatives of cardiac glycosides as anticancer agents.     

Investigation of the pharmacological profiles of dinuclear metal complexes as novel,potent and selective cytotoxic agents against ras-transformed cells

Around the world scientists try to design successful cures against still incurable diseases, especially cancers. New targets for prevention and new agents for therapy need to be identified. We synthesized novel metal complexes [Au(L1)(L2)Pt]Cl2 and [Ru(L1)2(L2)Pt]Cl2 for determining their cytotoxic and apoptotic effects. The complexes are synthesized by using 1,8-diaminonaphthalene (L1), and bis-1,4-di[([1,10]phenanthroline-5-il)aminomethyl]cyclohexane (L2) as ligands. This is the first study to examine these metals and these molecules in cancer treatment. We elucidated the effects of test compounds with embryonic rat fibroblast-like cells (F2408) and H-ras oncogene activated embryonic rat fibroblast-like cancer cells (5RP7). Results showed that our complexes are more effective than cisplatin to kill ras-transformed cells. Although the [Au(L1)(L2)Pt]Cl2 compound showed a cytotoxic potency higher than [Ru(L1)2(L2)Pt]Cl2 against cancer cells, it proved to be almost five times less effective in decreasing cell viability over healthy cells. Au(III) compound selectively targets the cancer cells but not the healthy cells.     

Photoactivatable platinum complexes

The development of photoactivatable prodrugs of platinum-based antitumor agents is aimed at increasing the selectivity and hence lowering toxicity of this important class of antitumor drugs. These drugs could find use in treating localized tumors accessible to laser-based fiber-optic devices. Pt(IV) complexes appeared attractive because these octahedral complexes are usually substitution inert and require reduction to the Pt(II) species to become cytotoxic. Based on the knowledge of Pt(IV) photochemistry, Pt(IV) analogs of cisplatin, [Pt(en)Cl(2)] and transplatin were designed, synthesized and investigated for their ability to be photoreduced to cytotoxic Pt(II) species. Two classes of photoactivatable Pt complexes have been looked at thus far: diiodo-Pt(IV) and diazido-Pt(IV) diam(m)ine complexes. The first generation, diiodo-Pt(IV) complexes, represented by cis, trans-[Pt(en)(I)(2)(OAc)(2)], react to visible light by binding irreversibly to DNA and forming adducts with 5'-GMP in the same manner as [Pt(en)Cl(2)]. Furthermore, the photolysis products are cytotoxic to human cancer cells in vitro. However, these complexes are too reactive towards biological thiols (i.e., glutathione), which rapidly reduced them to cytotoxic Pt(II) species, thus making them unsuitable as drugs. The second generation, diazido-Pt(IV) complexes, represented by cis, trans, cis-[Pt(N(3))(2)(OH)(2)(NH(3))(2)] and cis, trans-[Pt(en)(N(3))(2)(OH)(2)], are also photosensitive, binding irreversibly to DNA and forming similar products with DNA and 5'-GMP in the presence of light as the respective Pt(II) complexes. However, they are stable to glutathione and thus show very low dark cytotoxicity. Light of lambda(irr) = 366 nm activates both complexes to cytotoxic species that effectively kill cancer cells by destroying their nuclei, leaving behind shrunken cell ghosts. Interestingly, the all-trans analog, trans, trans, trans-[Pt(N(3))(2)(OH)(2)(NH(3))(2)] is non-toxic to HaCaT keratinocytes in the dark, but as active as cisplatin in the light. These studies show that photoactivatable Pt(IV) antitumor agents represent a promising area for new drug development.     

Synthesis, cytotoxicity, cell uptake and DNA interstrand cross-linking of 4,4'-dipyrazolylmethane-linked multinuclear platinum anti-cancer complexes

Two cationic multinuclear platinum complexes linked with the 4,4'-dipyrazolylmethane (dpzm) ligand, trans-[[Pt(NH3)2Cl]2-mu-dpzm]Cl2 (di-Pt) and trans-[trans-[Pt(NH3)2Cl]2[trans-[Pt(NH3)2(mu-dpzm)2]]]Cl4 (tri-Pt), have been synthesized. Both complexes show activity in the murine leukaemia cell line L1210 (IC50 = 3.8 and 2.5 microm, respectively) and the cisplatin-resistant subline L1210/DDP (8.8 and 3.6 microM), and in the human ovarian carcinoma 2008 (2.5 and 17.8 microM) and its cisplatin-resistant subline C13*5 (20.9 and 37.7 microM). Both complexes show high levels of uptake into 2008 cells, when administered at 100 microM, but significantly reduced uptake in the cisplatin-resistant cell line C13*5 (di-Pt, 66% decrease; tri-Pt, 42%; cisplatin, 86%). Both complexes form very high levels of DNA interstrand cross-links in vitro, with 50% interstrand cross-linking observed at far lower concentrations (di-Pt, 12 nM; tri-Pt, 22 nM) than cisplatin (450 nM). It is proposed that the higher extent of interstrand cross-linking may be due to the rigid nature of the dpzm linking ligand, which prevents the complexes from forming short-range intrastrand adducts, like the GpG adduct formed by cisplatin. The results of this study indicate the importance of the flexibility of the linking ligand for the cytotoxicity of di- and trinuclear platinum anti-cancer complexes.     

Structure-activity studies of novel amidine analogues of chlorambucil: correlation of cytotoxic activity with DNA-binding affinity and topoisomerase II inhibition

A series of amidine analogues of chlorambucil (9-12), where 5-[4-(N-alkylamidino)phenyl]-2-furancarboxamide and the chlorambucil moiety are linked by a NH(CH(2))(2)NH chain, was synthesized and their cytotoxicity has been tested against the growth of human breast cancer MCF-7 cells. Evaluation of the cytotoxicity of compounds 9-12 employing a MTT assay and inhibition of [(3)H]thymidine incorporation into DNA demonstrated that these conjugates were more active than chlorambucil. Data from the ethidium displacement assay indicated that these compounds bind in the minor groove of DNA and show moderate specificity for AT base pairs. Compounds 9-12 were potent topoisomerase II inhibitors, with 50% inhibitory concentrations (IC(50))ranging from 10 to 40 microM. The cytotoxicity of the compounds 9-12 correlates with their DNA-binding affinities and their relative potency as topoisomerase II inhibitors. Altogether, these data suggest (i) that the cytotoxic activity of compounds 9-12 may be due to the combined effects of alkylation, DNA-minor groove binding, and (ii) that N-(2-aminoethyl)-5-(4-N-alkylamidinophenyl)-2-furancarboxamides (5-8) ligands are suitable linkers that favors DNA targeting by chlorambucil derivatives.     

Mono- and polynuclear [alkylamine]platinum(II) complexes of [1,2-bis(4-fluorophenyl)ethylenediamine]platinum(II): synthesis and investigations on cytotoxicity, cellular distribution, and DNA and protein binding

A series of mononuclear and dinuclear alkylamine derivatives of [meso-1,2-bis(4-fluorophenyl)ethylenediamine]platinum(II) (m-4F-PtL-R1 and (m-4F-PtL)2-R2; R(1) = alkylamine, R(2) = alkyldiamine, L = DMSO or Cl) as well as the DAB(PA)(4) polyimine dendrimer complex ((m-4F-PtDMSO)4DAB(PA)4; DAB(PA)4 = N,N,N',N'-tetrakis(3-aminopropyl)butane-1,4-diamine) were synthesized and tested for cytotoxicity, intracellular distribution, and DNA and protein binding. All compounds strongly bound to human serum albumin by hydrophobic and electrostatic interactions. These inactivation reactions hindered the uptake into tumor cells and prevented strong cytotoxic effects. If serum-free medium was used, a high accumulation grade in MCF-7 breast cancer cells and a high DNA binding was observed. As most efficient compound (m-4F-PtDMSO)4DAB(PA)4 was identified. It showed a 20-fold higher cellular uptake and an approximately 700-fold higher DNA binding than cisplatin.     

Synthesis and Cytotoxic Activity of Novel Amidine Analogues of Bis(2‐chloroethyl)amine

Novel nitrogen mustard agents 7 – 12 involving 4‐(N,N‐bis(2‐chloroethyl)aminophenyl)propylamine linked to a 5‐(4‐N‐alkylamidinophenyl)‐2‐furancarboxylic acid moiety by the formation of an amide bond have been synthesized, characterized, and evaluated for their in‐vitro cytotoxic activity against MDA‐MB‐231 and MCF‐7 human breast cancer cells. Evaluation of the cytotoxicity of 7 – 12 employing a MTT assay and inhibition of [³H]thymidine incorporation into DNA demonstrated that these compounds exhibit remarkable cytotoxic effects in comparison with 4‐[bis(2‐chloroethyl)amino]benzenebutanoic acid. Compounds 7 and 9 , which possess a cationic amidine and 4,5‐dihydro‐1H‐imidazol function moiety are approximately ten times more potent than 4‐[bis(2‐chloroethyl)amino]benzenebutanoic acid. The new compounds were evaluated as DNA topoisomerase II inhibitors. The cytotoxicity of the compounds 7 – 12 correlates with their DNA‐binding affinities and their relative potency as topoisomerase II inhibitors.     

The formation of DNA interstrand cross-links by a novel bis-[Pt2Cl4(diminazene aceturate)2]Cl4.4H2O complex inhibits the B to Z transition

We present data demonstrating that the cytotoxic compound [Pt2Cl4(diminazene aceturate)2]Cl4.4H2O (Pt-berenil) circumvents cisplatin resistance in ovarian carcinoma cells. The analysis of the interaction of Pt-berenil with linear and supercoiled DNA indicates that this compound induces the formation of a large number of covalent interstrand cross-links on DNA and that this number is significantly higher than that produced by cis-diamminedichloroplatinum(II) (cis-DDP). Renaturation experiments, interstrand cross-link assays, and electron microscopy indicate that the kinetics of DNA interstrand cross-link formation caused by Pt-berenil binding is faster than that caused by cis-DDP at similar levels of platinum bound to DNA. Furthermore, the number of DNA interstrand cross-links in Pt-berenil-DNA complexes is influenced by supercoiling. Circular dichroism experiments show that Pt-berenil strongly inhibits the B-DNA-to-Z-DNA transition of poly(dG-m5 dC). poly(dG-m5dC) at salt concentrations (3 mM MgCl2) at which the native methylated polynucleotide readily adopts the Z-DNA conformation, which suggests that the induction of interstrand cross-links by Pt-berenil inhibits the Z-DNA transition. On the basis of these results, we propose that bis(platinum) compounds with structure similar to Pt-berenil may act as blockers of DNA conformational changes and may also display activity in cisplatin-resistant cells.     

In vitro and in vivo antitumor activities and DNA binding mode of five coordinated cyclometalated organoplatinum(II) complexes containing biphosphine ligands

New complexes [Pt(C(∧)N)Cl(dppa)] (1), and [Pt(C(∧)N)Cl(dppm)] (2), (C(∧)N. deprotonated 2-phenylpyridine; dppa. bis(diphenylphosphino)amine; dppm. bis(diphenylphosphino)methane) were suggested to have pentacoordinated geometry as investigated by NMR and conductometry. Pharmacological effects of 1 and 2 were evaluated for their proteasome-inhibitory and apoptosis-inducing activities under in vitro and in vivo conditions, showing significant proteasome-inhibitory activity against purified 20S proteasome, while 2 demonstrated superior inhibitory activity against cellular 26S proteasome. Consistently, this effect was associated with higher levels of proteasome target proteins and apoptosis induction in breast cancer cells. Importantly, preliminary studies show 1 and 2 were able to exert a similar effect in vivo by inhibiting the growth of breast cancer xenografts in mice, which was associated with proteasome inhibition and apoptosis induction. Interaction of 1 and 2 with herring sperm DNA was investigated by fluorimeteric emission, suggesting that Pt(II)-containing biphosphine complexes with DNA binding capabilities can also target and inhibit the tumor proteasome.     

Toxicity of cisplatin and hydroxymalonatodiammine platinum (II) towards mouse bone marrow and B16 melanoma in relation to DNA binding in vivo

The antitumour selectivity of cisplatin and hydroxymalonatodiammine platinum II (Pt[OHmal(NH3)2]), a second generation platinum drug, was evaluated in C57B1/Cbi mice bearing advanced intramuscular B16 melanoma. At maximally tolerated doses, Pt[OHmal(NH3)2] produced greater inhibition of growth of the advanced B16 melanoma than did cisplatin. Comparison of dose-response curves for survival of B16 lung colony-forming cells and bone marrow stem cells treated in vivo indicated that selective killing of B16 cells was achieved with Pt[OHmal(NH3)2], whereas cisplatin was relatively nonselective. The extent of reaction of platinum with DNA at doses producing measurable levels of survival in tumour and marrow in vivo was similar to values previously observed in cultured cells treated with cisplatin in vitro. Studies of the amount of platinum bound to DNA in tumour and marrow following administration of the two drugs revealed that the improved selectivity of Pt[OHmal(NH3)2] was associated with a selective increase in the amount of platinum bound to tumour DNA, relative to cisplatin. In addition, platinum lesions produced in DNA by Pt[OHmal(NH3)2] appeared to be more effective in producing tumour cell killing than those produced by cisplatin. No significant excision of total DNA-bound platinum from tumour was observed up to 48 h after administration of either drug.     

Platinum(II) and palladium(II) complexes with 2-acetylpyridine thiosemicarbazone: cytogenetic and antineoplastic effects

The effect of three novel complexes of Pt(II) and three complexes of Pd(II) with 2-acetylpyridine thiosemicarbazone (HAcTsc) on sister chromatid exchange (SCE) rates and human lymphocyte proliferation kinetics on a molar basis was studied. Also, the effect of Pt(II) and Pd(II) complexes against leukemia P388 was investigated. Among these compounds, the most effective in inducing antitumor and cytogenetic effects were the complexes [Pt(AcTsc)2] x H2O and [Pd(AcTsc)2] while the rest, i.e. (HAcTsc), [Pt(AcTsc)Cl], [Pt(HAcTsc)2]Cl2 x 2H2O, [Pd(AcTsc)Cl] and [Pd(HAcTsc)2]Cl2, displayed marginal cytogenetic and antitumor effects.     

Pt(O,O'-acac)(gamma-acac)(DMS)], a new Pt compound exerting fast cytotoxicity in MCF-7 breast cancer cells via the mitochondrial apoptotic pathway

BACKGROUND AND PURPOSE: We showed previously that a new Pt complex containing an O,O'-chelated acetylacetonate ligand (acac) and a dimethylsulphide in the Pt coordination sphere, [Pt(O,O'-acac)(gamma-acac)(DMS)], induces apoptosis in HeLa cells. The objective of this study was to investigate the hypothesis that [Pt(O,O'-acac)(gamma-acac)(DMS)] is also cytotoxic in a MCF-7 breast cancer cell line relatively insensitive to cisplatin, and to gain a more detailed analysis of the cell death pathways. EXPERIMENTAL APPROACH: Cells were treated with Pt compounds and cytotoxicity tests were performed, together with Western blotting of various proteins involved in apoptosis. The mitochondrial membrane potential was assessed by fluorescence microscopy and spectrofluorometry and the Pt bound to cell fractions was measured by atomic absorption spectrometry. KEY RESULTS: In contrast to cisplatin, the cytotoxicity of [Pt(O,O'-acac)(gamma-acac)(DMS)] correlated with cellular accumulation but not with DNA binding. Also, the Pt content in DNA bases was considerably higher for cisplatin than for [Pt(O,O'-acac)(gamma-acac)(DMS)], thus excluding DNA as a target of [Pt(O,O'-acac)(gamma-acac)(DMS)]. [Pt(O,O'-acac)(gamma-acac)(DMS)] exerted high and fast apoptotic processes in MCF-7 cells since it provoked: (a) mitochondria depolarization; (b) cytochrome c accumulation in the cytosol; (c) translocation of Bax and truncated-Bid from cytosol to mitochondria and decreased expression of Bcl-2; (d) cleavage of caspases -7 and -9, and PARP degradation; (e) chromatin condensation and DNA fragmentation. CONCLUSIONS AND IMPLICATIONS:[Pt(O,O'-acac)(gamma-acac)(DMS)] is highly cytotoxic for MCF-7 cells, cells relatively resistant to many chemotherapeutic agents, as it activates the mitochondrial apoptotic pathway. Hence, [Pt(O,O'-acac)(gamma-acac)(DMS)] has the potential to provide us with new opportunities for therapeutic intervention.