In vitro action of platinum (II) and platinum (IV) complexes on Trypanosoma cruzi and Leishmania donovani

The in vitro activities of 22 neutral Pt(II) complexes, 4 Pt(IV) complex salts, and one Pt(II) complex salt on epimastigote forms of Trypanosoma cruzi and promastigote forms of Leishmania donovani were studied. Only 2 out of the 18 complexes with cis-Pt(DDH)Xn structure completely inhibited the growth of the epimastigote forms of T. cruzi and the promastigote of L. donovani. Against T. cruzi the cis-Pt(L)n(Cl)2 complexes showed no activities, but the complex in which the (L) ligand was stilbamidine did show a limited activity against L. donovani. Of the Pt(IV)complex salts, [Pt X6]H2(L) were very active against the epimastigote forms of T. cruzi. However, the Pt(II) complex salt [cis-Pt Cl4]H2 (pentamidine) showed no activity. The actions of the Pt(IV) complex salts on the promastigote forms of L. donovani were different and only those salts in which the (L) ligand was pentamidine or stilbamidine induced parasite growth inhibition. The one Pt(II) salt tested showed no antiparasitic activity. At the same time, the known antiparasitic activities of the nifurtimox and pentamidine molecules were confirmed.     

(2,2':6',2"-Terpyridine)platinum(II) complexes are irreversible inhibitors of Trypanosoma cruzi trypanothione reductase but not of human glutathione reductase

(2,2':6',2"-terpyridine)platinum(II) complexes possess pronounced cytostatic activities against trypanosomes and leishmania. As shown here, the complexes are irreversible inhibitors of trypanothione reductase (TR) from Trypanosoma cruzi, the causative agent of Chagas' disease. The most effective derivatives are the (4'-chloro-2, 2':6',2"-terpyridine)platinum(II) ammine and the (4-picoline)(4'-p-bromophenyl-2,2':6',2" -terpyridine)platinum(II) complexes which in the presence of NADPH inhibit TR with second-order rate constants of about 1.3 x 10(4) M(-1) s(-1). The modified enzyme species possess increased oxidase activities. The inhibition is not reversed upon dialysis or treatment with low-molecular-mass thiols. Kinetic and spectroscopic data suggest that Cys52 in the active site has been specifically altered. Inhibition of this key enzyme of parasite thiol metabolism probably contributes to the antitrypanosomal activity of the compounds. In contrast to the parasite enzyme, most (terpyridine)platinum complexes interact only reversibly with human glutathione reductase and an initial inhibition is completely abolished during the course of the assay.     

Cytotoxicity of 2,2':6',2' '-terpyridineplatinum(II) complexes against human ovarian carcinoma.

2,2':6',2'-Terpyridineplatinum(II) complexes are shown to possess cytotoxicity against a number of human ovarian tumor cell lines. Many of the complexes show similar activity against cisplatin- and doxorubicin-resistant cell lines as the parental cells suggesting that there is little or no cross-resistance with cisplatin or doxorubicin. The cytotoxicity of bis[2,2':6',2'-terpyridineplatinum(II)] complexes is strongly dependent on the nature of the linker. Bis[2,2':6',2'-terpyridineplatinum(II)] complexes with a flexible linker at the 4'-position show poor cytotoxicity; by contrast bis[2,2':6',2'- terpyridineplatinum(II)] complexes with rigid and short linkers at platinum(II) are strikingly effective. Several of the compounds show greater cytotoxicity against human ovarian cell lines than carboplatin, the therapeutic agent currently advocated for the treatment of human ovarian cancers.     

Human thioredoxin reductase is efficiently inhibited by (2,2':6',2' '-terpyridine)platinum(II) complexes. Possible implications for a novel antitumor strategy

Malignant neoplasms of the brain represent the second leading cause of cancer-related mortality in children under the age of 15. The prognosis of patients with glioblastoma multiforme, the most malignant type of gliomas, remains poor offering a median survival time of only 1 year. (2,2':6',2"-Terpyridine)platinum(II) complexes are known to possess DNA-intercalating activity and have been shown to be potential chemotherapeutic agents. In the present study we identified the selenoenzyme thioredoxin reductase (TrxR) as a major target of (2,2':6',2"-terpyridine)platinum(II) complexes. New complexes were synthesized in order to optimize this inhibition. The NADPH-reduced enzyme is inhibited almost stoichiometrically by the complexes involving a reversible competitive and an irreversible tight-binding component. For the most potent inhibitor, N,S-bis(2,2':6',2"-terpyridine)platinum(II)-thioacetimine trinitrate, the K(i) for the competitive component of the inhibition is 4 nM and the IC(50) for the tight-binding component is 2 nM after an incubation time of 5 min. The closely related but non-selenium-containing enzyme glutathione reductase is much less inhibited (by a factor of >1000). The platinum complexes were found to strongly inhibit the proliferation of three different glioblastoma cell lines as well as of two different head-and-neck squamous carcinoma cell lines. In a glioblastoma cell culture, less than 10 microM of a platinum(II) compound caused an initial drop of hTrxR activity which was followed by an increase of activity in the surviving cells. A 10 microM inhibitor added every 24 h led to 4% residual hTrxR activity but 100% glutathione reductase activity in the cells surviving for 67 h. The potential of (2,2':6',2"-terpyridine)platinum(II) complexes acting simultaneously at two different intracellular targets-hTrxR and DNA-as antitumor agents is discussed.     

Bisphosphonates inhibit the growth of Trypanosoma brucei, Trypanosoma cruzi, Leishmania donovani, Toxoplasma gondii, and Plasmodium falciparum: a potential route to chemotherapy

We have investigated the effects in vitro of a series of bisphosphonates on the proliferation of Trypanosoma cruzi, Trypanosoma brucei rhodesiense, Leishmania donovani, Toxoplasma gondii, and Plasmodium falciparum. The results show that nitrogen-containing bisphosphonates of the type used in bone resorption therapy have significant activity against parasites, with the aromatic species having in some cases nanomolar or low-micromolar IC(50) activity values against parasite replication (e.g. o-risedronate, IC(50) = 220 nM for T. brucei rhodesiense; risedronate, IC(50) = 490 nM for T. gondii). In T. cruzi, the nitrogen-containing bisphosphonate risedronate is shown to inhibit sterol biosynthesis at a pre-squalene level, most likely by inhibiting farnesylpyrophosphate synthase. Bisphosphonates therefore appear to have potential in treating parasitic protozoan diseases.     

Activities of Pt(II) and Ru(III) triazole-pyrimidine complexes against Trypanosoma cruzi and T. brucei brucei

We studied the biological activity of three newly synthesized metal complexes of triazole-pyrimidine derivatives that were previously observed to inhibit in vitro growth of epimastigotes of Trypanosoma cruzi and procyclic forms of Trypanosoma brucei brucei. We analyzed the possible inhibitory effect of these compounds on the synthesis of DNA, RNA and protein, ultrastructure and excretion of metabolites by these parasites. RNA synthesis was inhibited by all three complexes assayed. These complexes also led to anomalies of the main organelles (e.g. nucleus, kinetoplast and mitochondria). In addition, these complexes may be capable of altering the excretion of metabolites by the parasites.     

In vitro screening of traditional South African malaria remedies against Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani, and Plasmodium falciparum

Three hundred extracts were prepared from plants traditionally used in South Africa to treat malaria and screened in vitro for activity against Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani, and Plasmodium falciparum. For the 43 extracts which inhibited the growth of one or more parasites to more than 95?% at 9.7?μg/mL, the IC?? values against all four protozoal parasites and cytotoxic IC??s against rat myoblast L6 cells were determined. Amongst the most notable results are the activities of AGATHOSMA APICULATA (IC?? of 0.3?μg/mL) against Plasmodium falciparum, as well as Salvia repens and Maytenus undata against Leishmania donovani with IC??s of 5.4?μg/mL and 5.6?μg/mL, respectively. This screening is the starting point for a HPLC-based activity profiling project in antiprotozoal lead discovery.     

Therapeutic potential of new Pt(II) and Ru(III) triazole-pyrimidine complexes against Leishmania donovani

We have already established an in vitro culture system using murine macrophages infected with Leishmania donovani in which the time course of parasite growth is determined quantitatively. We adopted this system for the screening of three triazole-pyrimidine derivatives that would ideally prove to be effective against L. donovani with no toxicity to the host cell. Amphotericin B deoxycholate was used as the standard drug and gave a IC50 value of 3.89 microg/ml. The three triazole-pyrimidine compounds assayed have been reported to be potent growth inhibitors of L. donovani promastigote and amastigote stages. Compounds SPIV and SPVI exhibited the highest toxicity for extracellular forms of parasites, with IC50 values of 19.95 and 21.61 microg/ml, respectively. The triazole-pyrimidine SPV, although to a lower degree, also showed pronounced effects against promastigote forms with IC50 of 33.14 microg/ml. Drug activity was higher against amastigote than against promastigote stages. The compounds SPIV and SPVI interfered with the synthesis of macromolecules, affecting primarily DNA at the lower concentration tested (5 microg/ml), while SPV also showed interference, though to a lesser extent, and at a higher concentration (15 microg/ml) the percentage of inhibition rose considerably. The synthesis or RNA and proteins was also depressed significantly by these compounds at administration rates of 15 microg/ml. Ultrastructural alterations were evident in the main organelles of L. donovani (nucleus, kinetoplast, mitochondria), after the addition of the three compounds at a concentration of 5 microg/ml, to the in vitro culture. The in vitro promastigote forms of L. donovani can degrade glucose to carbon dioxide, and part of the carbon skeleton of the glucose is excreted as end metabolites. The excretion of these metabolites, mainly acetate, was also inhibited by the three compounds assayed, suggesting that this could be due to a direct effect on some of the enzymes related to this fermentation pathway or to the inhibition exerted by the compounds on enzyme synthesis.     

Activity of rhodium(III) complexes against Trypanosoma cruzi

In the present paper the antiprotozoan activity of several rhodium(III) complexes was studied by analysis of the [3H]-thymidine, [3H]-uridine and [3H]-leucine uptake occurring in epimastigotes of Trypanosoma cruzi in the presence of the drug as well as their effect on the viability and motility of infective forms. It has been found that the complexes do not interact with native DNA but that some of them inhibit both the precursor uptake and the viability of metacyclic forms. It seems that the mode of action on the epimastigotes should be different from that observed on metacyclic forms.     

Analysis of 6-(2,2-Dichloroacetamido)chrysene interaction with the hypoxanthine phosphoribosyltransferase from Trypanosoma cruzi

Selective inhibition is needed for drugs targeting the hypoxanthine phosphoribosyltransferase of Trypanosoma cruzi, etiologic agent of Chagas' disease. 6-(2,2-Dichloroacetamido)chrysene, was shown herein to be a selective inhibitor of the trypanosomal enzyme. SAR analysis revealed that the 6-amido moiety was essential, but the dichloroaceto moiety was not essential for achieving the low K(i) for this inhibitor. Understanding the molecular basis for these interactions could facilitate the design of selective inhibitors without a chrysene moiety.     

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.     

Evaluation of the toxicity of Rh(III) and Pt(II) complexes against Trypanosoma cruzi culture forms

In the present study the activity of 15 complexes of Rh(III) and 19 of Pt(II) against Trypanosoma cruzi epimastigote forms was investigated. The results obtained show that complexes of Rh(III) with the highest antitumoural activity also appear to be more effective against cultured epimastigotes. Thus, complexes [Rh(L)4X2]+X- where L is a derivative of thiazole present high activity against the parasite, and were even more active when Cl- (X) was present in their structure. Complexes cis-Pt(L)m(X)n that present 1,2-diamminecyclohexane (DDH) in their molecule, e.g. cis-Pt(DDH)Cl2 and cis-Pt(DDH)(metafluorobenzoic)2 of high and moderate antitumoural activity, respectively, have shown greater effectiveness than cis-Pt(NH3)2Cl2 (DDP). The effect produced by cis-Pt(pentamidine)Cl2 complex, obtained in order to enforce the action of pentamidine, was considerably high. On the other hand, no positive correlation can be established between the antitumour effects of the Pt(II) complexes and its antitrypanosomic activity.     

Antitumor platinum(II) complexes with substituted 2-aminomethylpyridine ligands]

Reaction of K2PtCl4 with the substituted 2-aminomethylpyridines 9, 14, and 22 affords the corresponding dichloroplatinum(II) complexes 3-5. Compounds 3 and 22 show remarkable relative binding affinities for the estrogen receptor. Towards the hormone-independent P388-tumor of the CD2F1-mouse the platinum(II) complexes 4 and 5 are weakly active, complex 3 is inactive. Towards the hormone-independent MDA-MB 231-cell line, compounds 3-5, 9, 14, and 22 exhibit no significant antitumor activity. Towards the hormone-dependent MCF-7 cell line, compounds 3-5, 9, 14 show weak antitumor activity, whereas compound 22 exhibits strong inhibition.     

In vitro and in vivo activity of new rhodium (III) complexes against Leishmania donovani

The activities of 17 new rhodium drug complexes were determined against Leishmania donovani promastigotes. The five most active salts were selected: [Rh(III)(2-amino-6-ethoxybenzothiazole)(4)Br(2)](+)Br(-); [Rh(III)(2-bromothiazole)(4)(Br)(2)](+)Br(-); [Rh(III)(mefloquine)(4)(Cl)(2)](+)Cl(-); [Rh(III)(2-mepacrine)(4)(Cl)(2)](+)Cl(-), and [Rh(III)(oxamniquine)(4)(Cl)(2)](+)Cl(-), which induced growth-inhibition rates of more than 50% at 24 h of treatment and at the maximum dosage tested. The cytotoxicity assays on the macrophage cell line J-774 showed high cytotoxicity for the salts [Rh(III) (mefloquine)(4)(Cl)(2)](+)Cl(-), [Rh(III)(2-mepacrine)(4)(Cl)(2)](+)Cl(-) and [Rh(III)(oxaminquine)(4)(Cl)(2)](+)Cl(-) with a percentage of specific (15)Cr release of 49.3, 64.8 and 53.2% at 24 h of incubation and 100 microg/ml. Meanwhile, assays of the other compounds showed practically no cytotoxicity. The ultrastructural studies in the flagellates treated with the salt [Rh(III)(2-amino-6-ethoxybenzothiazole)(4)Br(2)](+)Br(-) showed some alterations in the nucleus of the parasites with a very condensed chromatin and an electrodense endosome. This compound showed a high in vivo activity in parasitized Wistar rats.     

Characterisation of Leishmania donovani promastigotes resistant to hexadecylphosphocholine (miltefosine)

Leishmania donovani promastigote lines resistant to hexadecylphosphocholine (HePC, miltefosine) at 2.5, 5.0, 10.0, 20.0 and 40.0 microM were developed in vitro by continuous step-wise drug pressure. The 40 microM line was 15 times more resistant to HePC than the wild-type clone and showed cross-resistance to the ether lipid ET-18-OCH3 (edelfosine) but not to the standard anti-leishmanial drugs. Resistance was stable up to 12 weeks in drug-free culture medium. No amplification of specific genes, including the multidrug resistance P-glycoprotein gene, could be detected in the resistant parasites.     

新抗肿瘤药铂(Ⅱ),(Ⅳ)配合物的合成

The synthesis of sixteen new analogs of cis-platinum (CDDP) and seven known Pt analogs, as well as the antitumor activity of seven Pt analogs against solid sarcoma 180 are reported. The new congeners consist of Pt (Ⅱ) and Pt (Ⅳ) complexes containing primary amine ligands (eg· NH3, en, pren) with variable anionic ligands such as malonate and 2-substituted malonates. In the experimental antitumor activity tests, 7 new platinum complexes were given on days 1～7, 24 hours after implanted with 10⁶ cells of solid sarcoma 180 tumor and producedT/C (treated/control) value between 15～35% with less toxicity than the parent cisplatinum. The experimental data indicate that it is favorable to introduce certain hydrophilic groups into the platinum complexes, in the view of increasing their aqueous solubility and lowering their toxicity while retaining their effectiveness.     

Synthesis and structure-activity relationships of parasiticidal thiosemicarbazone cysteine protease inhibitors against Plasmodium falciparum, Trypanosoma brucei, and Trypanosoma cruzi

We have synthesized a library of thiosemicarbazones and screened them against three parasitic cysteine proteases, cruzain, falcipain-2, and rhodesain, and against the respective parasite sources of these three proteases, Trypanosoma cruzi, Plasmodium falciparum, and Trypanosoma brucei. The screens identified compounds that were effective against the enzymes and the parasites but also some compounds that were parasiticidal despite a lack of activity against the proteases. Several compounds were effective in killing all tested parasites. These promising lead compounds were tested for general toxicity in mice, and only one produced observable toxicity after 62 h. Our results suggest that thiosemicarbazones represent validated drug leads that kill several species of protozoan parasites through the inhibition of cysteine proteases as well as other novel targets.     

In situ kinetic characterization of methylthioadenosine transport by the adenosine transporter (P2) of the African Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense

African trypanosomes are parasitic flagellates that live in the connective tissues of the host. Trypanosomes must obtain from their host adenine/adenosine and other nucleosides that can be salvaged through enzymatic cleavage. Methylthioadenosine (MTA) is a byproduct of polyamine metabolism, formed from the donation of an aminopropyl moiety by decarboxylated S-adenosylmethionine (dcAdoMet) to form spermidine. MTA is then cleaved phosphorolytically by MTA phosphorylase to methylthioribose-1-phosphate (MTR-1-P) and adenine. The uptake of MTA was compared with that of adenosine in two strains: Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense. The K(m) values for MTA and adenosine (with 5 mM inosine) transport by T. b. brucei were 1.4 and 0.175 mM, and the V(max) values were 70 and 7.8 micromol/L/min, respectively. The K(m) values for T. b. rhodesiense MTA and adenosine (with 5 mM inosine) transport were 1.2 and 0.11 mM, and the V(max) values were 52.6 and 2.9 micromol/L/min, respectively. Since MTA was not competitive with either AdoMet (100 microM), inosine (100 microM), or the methionine precursor ketomethylthiobutyrate (100 microM), it appears that MTA enters through the P(2) (adenosine/adenine) transport site. From this study and our previous work, we determined that these organisms transport adenylated intermediates of methionine metabolism found in sera for purine salvage and as an ancillary source of methionine. The significant ability of African trypanosomes to transport MTA and related intermediates is an important consideration in the design and development of selective chemotherapeutic agents.     

Cytotoxicity and antitumor activity of bis(platinum) complexes. A novel class of platinum complexes active in cell lines resistant to both cisplatin and 1,2-diaminocyclohexane complexes

The in vitro cytotoxicity and in vivo antitumor activity of bis(platinum) complexes of general formula [(PtX2-(L))2H2N(CH2)nNH2] (L = NH3, X = Cl or X2 = malonato or where L = py, X = Cl) is reported. Chloride complexes [(PtCl2(NH3]2H2N(CH2)nNH2] may exist as three possible isomers: those containing both coordination units in the cis configuration (2,2/c,c), both coordination units in the trans configuration (2,2/t,t), and the mixed cis,trans species (2,2/c,t), whose synthesis is reported here. The preparation of further complexes with sterically hindered diamine backbones, such as 2,5-dimethyl-2,5-hexanediamine, is exemplified. The biological activity of all complexes were compared. The 2,2/c,c complexes are particularly active in tissue culture in cells resistant both to cisplatin and its 1,2-diaminocyclohexane (dach) analogue. The inhibition of DNA synthesis in L1210/0 cells by the 2,2/c,c complexes is equivalent to that of cisplatin. The presence of at least one cis-[Pt(amine)2] unit appears necessary for activity in cell lines sensitive to cisplatin.     

Water-soluble third generation antitumor platinum complexes, [2,2-bis (aminomethyl)-1,3-propanediol-N,N']-[1,1-cyclobutanedicarboxylato (2-)-O,O']platinum(II) and [1,1-cyclobutanedicarboxylato(2-)-O,O'] [tetrahydro-4H-pyran-4,4-dimethanamine-N,N']platinum(II)

The synthesis, stability, and antitumor activity of a series of water-soluble third generation platinum(II) complexes have been described. Among these complexes, [2,2-bis(aminomethyl)-1,3- propanediol-N,N'] [1,1-cyclobutanedicarboxylato(2-)-O,O']platinum(II) and [1,1-cyclobutanedicarboxylate(2-)-O,O'](tetrahydro-4H-pyran-4,4- dimethanamine-N,N'-)platinum(II) have shown the greatest promise for further investigation and are currently under clinical evaluation.