S100P Interacts with p53 while Pentamidine Inhibits This Interaction.

S100P, a small calcium-binding protein, associates with the p53 protein with micromolar affinity. It has been hypothesized that the oncogenic function of S100P may involve binding-induced inactivation of p53. We used 1H-15N HSQC experiments and molecular modeling to study the molecular interactions between S100P and p53 in the presence and absence of pentamidine. Our experimental analysis indicates that the S100P-53 complex formation is successfully disrupted by pentamidine, since S100P shares the same binding site for p53 and pentamidine. In addition, we showed that pentamidine treatment of ZR-75-1 breast cancer cells resulted in reduced proliferation and increased p53 and p21 protein levels, indicating that pentamidine is an effective antagonist that interferes with the S100P-p53 interaction, leading to re-activation of the p53-21 pathway and inhibition of cancer cell proliferation. Collectively, our findings suggest that blocking the association between S100P and p53 by pentamidine will prevent cancer progression and, therefore, provide a new avenue for cancer therapy by targeting the S100P-p53 interaction.

Rationally designed hyaluronic acid-based nano-complexes for pentamidine delivery.

Nanoparticles of polymeric complexes made of hyaluronic acid and polyarginine were investigated for the encapsulation of the cationic hydrophilic drug pentamidine isethionate. The interaction between the anionic hyaluronic acid and the cationic pentamidine resulting in the formation of polyelectrolyte complexes was firstly studied. Then, nanoparticles made of hyaluronic acid and polyarginine loaded with pentamidine were developed. These drug delivery systems consist of a monodisperse population of negatively charged pentamidine-loaded nanoparticles with a high drug encapsulation rate (80%). Such high encapsulation efficiency coming from ion exchange was confirmed by measurements of the counterion isethionate released from pentamidine during nanoparticles formation. Besides, freeze-dried pentamidine-loaded nanoparticles kept their integrity after their reconstitution in water. In vitro studies on human lung (A549) and breast (MDA-MB-231) cancer cell lines showed that pentamidine-loaded nanoparticles were more cytotoxic in comparison to the free drug, suggesting an enhanced internalization of encapsulated drug by cancer cells.

Comparative in vitro transportation of pentamidine across the blood-brain barrier using polycaprolactone nanoparticles and phosphatidylcholine liposomes.

Nanoparticles (NPs) have gained importance in addressing drug delivery challenges across biological barriers. Here, we reformulated pentamidine, a drug used to treat Human African Trypanosomiasis (HAT) in polymer based nanoparticles and liposomes and compared their capability to enhance pentamidine penetration across blood brain barrier (BBB). Size, polydispersity index, zeta potential, morphology, pentamidine loading and drug release profiles were determined by various methods. Cytotoxicity was tested against the immortalized mouse brain endothelioma cells over 96 h. Moreover, cells monolayer integrity and transportation ability were examined for 24 h. Pentamidine-loaded polycaprolactone (PCL) nanoparticles had a mean size of 267.58, PDI of 0.25 and zeta potential of -28.1 mV and pentamidine-loaded liposomes had a mean size of 119.61 nm, PDI of 0.25 and zeta potential 11.78. Pentamidine loading was 0.16 µg/mg (w/w) and 0.17 µg/mg (w/w) in PCL NPs and liposomes respectively. PCL nanoparticles and liposomes released 12.13% and 22.21% of pentamidine respectively after 24 h. Liposomes transported 87% of the dose, PCL NPs 66% of the dose and free pentamidine penetration was 63% of the dose. These results suggest that liposomes are comparatively promising nanocarriers for transportation of pentamidine across BBB.

Semicarbazone derivatives as promising therapeutic alternatives in leishmaniasis.

In the present study, we investigated the in vitro and in vivo leishmanicidal activity of synthetic compounds, containing a semicarbazone scaffold as a peptide mimetic framework. The leishmanicidal effect against amastigotes of Leishmania amazonensis was also evaluated at concentration of 100 µM-0.01 nM. The derivatives 2e, 2f, 2g and 1g, beyond the standards miltefosine and pentamidine, significantly diminished the number of L. amazonensis amastigotes in macrophages. These derivatives were also active against amastigotes of L. braziliensis. As 2g presented potent leishmanicidal activity against the amastigotes of L. amazonensis in macrophages, we also investigated the in vivo leishmanicidal activity of this compound against L. amazonensis. Approximately 105L. amazonensis promastigotes were subcutaneously inoculated into the dermis of the right ear of BALB/c mice, which were subsequently treated with 2g (p.o. or i.p.), miltefosine (p.o.) or glucantime (i.p.) at 30 µmol/kg/day x 28 days. Thus, a similar reduction in the lesion size was observed after the administration of 2g through oral (63.7 ±â€¯10.1%) and intraperitoneal (61.8 ±â€¯3.7%) routes. A larger effect was observed after treatment with miltefosine (97.7 ±â€¯0.4%), and glucantime did not exhibit activity at the dose administered. With respect to the ear parasite load, 2g diminished the number of parasites by p.o. (30.5 ±â€¯5.1%) and i.p. (33.3 ±â€¯4.3%) administration. In addition, 2g induced in vitro apoptosis, autophagy and cell cycle alterations on L. amazonensis promastigotes. In summary, the derivative 2g might represent a lead candidate for antileishmanial drugs, as this compound displayed pronounced leishmanicidal activity.

In silico and in vitro comparative activity of green tea components against Leishmania infantum.

OBJECTIVES: Green tea contains a predominant set of polyphenolic compounds with biological activities. The aim of this study was to investigate the antileishmanial activities of the main components of green tea, including catechin, (-)-epicatechin, epicatechin gallate (ECG) and (-)-epigallocatechin 3-O-gallate (EGCG), against Leishmania infantum promastigotes. METHODS: Green tea ligands and the control drug pentamidine were docked using AutoDock 4.3 software into the active sites of trypanothione synthetase and arginase, which were modelled using homology modelling programs. The colorimetric MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay was used to measure L. infantum promastigotes at different concentrations of green tea compounds in a concentration- and time-dependent manner. Results were expressed as 50% and 90% inhibitory concentrations (IC50 and IC90, respectively). RESULTS: In silico and in vitro assays showed that all of the green tea compounds have antileishmanial activity. EGCG and ECG were the most active compounds against L. infantum promastigotes, with IC50 values of 27.7µM and 75µM and IC90 values of 88.4µM and 188.7µM, respectively. Pentamidine displayed greater growth inhibition than all of the other tested compounds in a concentration- and time-dependent manner. CONCLUSION: In this study, in silico and docking results were in accordance with the in vitro activity of the compounds. Moreover, EGCG and ECG showed reasonable levels of selectivity for Leishmania.

Pentamidine blocks the interaction between mutant S100A5 and RAGE V domain and inhibits the RAGE signaling pathway.

The human S100 protein family contains small, dimeric and acidic proteins that contain two EF-hand motifs and bind calcium. When S100A5 binds calcium, its conformation changes and promotes interaction with the target protein. The extracellular domain of RAGE (Receptor of Advanced Glycation End products) contain three domains: C1, C2 and V. The RAGE V domain is the target protein of S100A5 that promotes cell survival, growth and differentiation by activating several signaling pathways. Pentamidine is an apoptotic and antiparasitic drug that is used to treat or prevent pneumonia. Here, we found that pentamidine interacts with S100A5 using HSQC titration. We elucidated the interactions of S100A5 with RAGE V domain and pentamidine using fluorescence and NMR spectroscopy. We generated two binary models-the S100A5-RAGE V domain and S100A5-Pentamidine complex-and then observed that the pentamidine and RAGE V domain share a similar binding region in mS100A5. We also used the WST-1 assay to investigate the bioactivity of S100A5, RAGE V domain and pentamidine. These results indicated that pentamidine blocks the binding between S100A5 and RAGE V domain. This finding is useful for the development of new anti-proliferation drugs.

Small Molecule Inhibitors of Ca(2+)-S100B Reveal Two Protein Conformations.

The drug pentamidine inhibits calcium-dependent complex formation with p53 ((Ca)S100B·p53) in malignant melanoma (MM) and restores p53 tumor suppressor activity in vivo. However, off-target effects associated with this drug were problematic in MM patients. Structure-activity relationship (SAR) studies were therefore completed here with 23 pentamidine analogues, and X-ray structures of (Ca)S100B·inhibitor complexes revealed that the C-terminus of S100B adopts two different conformations, with location of Phe87 and Phe88 being the distinguishing feature and termed the "FF-gate". For symmetric pentamidine analogues ((Ca)S100B·5a, (Ca)S100B·6b) a channel between sites 1 and 2 on S100B was occluded by residue Phe88, but for an asymmetric pentamidine analogue ((Ca)S100B·17), this same channel was open. The (Ca)S100B·17 structure illustrates, for the first time, a pentamidine analog capable of binding the "open" form of the "FF-gate" and provides a means to block all three "hot spots" on (Ca)S100B, which will impact next generation (Ca)S100B·p53 inhibitor design.

Synthesis and antiprotozoal activities of benzyl phenyl ether diamidine derivatives.

Sixty-two cationic benzyl phenyl ether derivatives (36 amidines and 26 prodrugs) were prepared and assayed for activities in vitro and in vivo against Trypanosoma brucei rhodesiense (STIB900), and in vitro against Plasmodium falciparum (K1) and Leishmania donovani axenic amastigotes. 3-Amidinobenzyl 4-amidino-2-iodo-6-methoxyphenyl ether dihydrochloride (55, IC50 = 3.0 nM) and seven other compounds exhibited IC50 values below 10 nM against T. b. rhodesiense in vitro. The 2-bromo-4,4'-diamidino analogue 19 (IC50 = 4.0 nM) and 12 other analogues were more potent than pentamidine (IC50 = 46 nM) against P. falciparum. The 3',4-diamidino-2,6-diiodo analogue 49 (IC50 = 1.4 µM) and two other compounds were more effective than pentamidine (IC50 = 1.8 µM) against L. donovani. A prodrug, 3',4-bis(N″-methoxy)amidino-2-bromo derivative 38, was the most efficacious against trypanosome infected mice, attaining 4/4 cures in four daily 25 mg/kg oral doses, and the 2-chloro-4,4'-diamidine 18 cured 3/4 mice in four daily 5 mg/kg intraperitoneal doses.

Structure-activity relationships of pentamidine-affected ion channel trafficking and dofetilide mediated rescue.

BACKGROUND AND PURPOSE: Drug interference with normal hERG protein trafficking substantially reduces the channel density in the plasma membrane and thereby poses an arrhythmic threat. The chemical substructures important for hERG trafficking inhibition were investigated using pentamidine as a model drug. Furthermore, the relationship between acute ion channel block and correction of trafficking by dofetilide was studied. EXPERIMENTAL APPROACH: hERG and K(IR)2.1 trafficking in HEK293 cells was evaluated by Western blot and immunofluorescence microscopy after treatment with pentamidine and six pentamidine analogues, and correction with dofetilide and four dofetilide analogues that displayed different abilities to inhibit IKr . Molecular dynamics simulations were used to address mode, number and type of interactions between hERG and dofetilide analogues. KEY RESULTS: Structural modifications of pentamidine differentially affected plasma membrane levels of hERG and K(IR)2.1. Modification of the phenyl ring or substituents directly attached to it had the largest effect, affirming the importance of these chemical residues in ion channel binding. PA-4 had the mildest effects on both ion channels. Dofetilide corrected pentamidine-induced hERG, but not K(IR)2.1 trafficking defects. Dofetilide analogues that displayed high channel affinity, mediated by pi-pi stacks and hydrophobic interactions, also restored hERG protein levels, whereas analogues with low affinity were ineffective. CONCLUSIONS AND IMPLICATIONS: Drug-induced trafficking defects can be minimized if certain chemical features are avoided or 'synthesized out'; this could influence the design and development of future drugs. Further analysis of such features in hERG trafficking correctors may facilitate the design of a non-blocking corrector for trafficking defective hERG proteins in both congenital and acquired LQTS.

Radical-induced DNA damage by cytotoxic square-planar copper(II) complexes incorporating o-phthalate and 1,10-phenanthroline or 2,2'-dipyridyl.

DNA-targeting copper(II) reagents have emerged as suitable drug candidates owing to the clinical success of the copper-activated, natural chemotherapeutic drug bleomycin. This agent and the synthetic chemical nuclease copper(II) bis-1,10-phenanthroline represent important templates for inorganic drug design owing to their ability to initiate free radical DNA scission. Herein, we report the synthesis and biological properties of 1:1:1 square-planar copper(II) complexes incorporating the dicarboxylate o-phthalate and 1,10-phenanthroline (1) or 2,2'-dipyridyl (2) ligands. Their broad-spectrum chemotherapeutic potential has been assessed at 24- and 96-h intervals, along with that of the clinical agent cisplatin, using breast (MCF-7), prostate (DU145), colon (HT29), and intrinsically cisplatin-resistant ovarian (SK-OV-3) human cancer cells. 1 represents a potent cytotoxic agent with IC(50) values ranging from 5.6 to 3.4µM across all cell lines, including SK-OV-3. The production of endogenous reactive oxygen species within SK-OV-3 cancer cells was monitored using the fluorophore 2',7'-dichlorodihydrofluorescin diacetate, and results indicate a concentration-dependent propensity toward ROS generation by 1 and 2 that mirrors their antitumoral behavior. DNA interaction studies, using fluorescence and viscosity measurements, were conducted in tandem with the DNA-targeting drugs actinomycin D and pentamidine, using calf thymus DNA, poly[d(A-T)(2)], and poly[d(G-C)(2)], with intercalation of 1 and 2 at the minor groove appearing to be the likely interaction mode. DNA cleavage reactions using superhelical plasmid DNA, in the presence of exogenous reductant, l-ascorbic acid, revealed excellent agreement between double-stranded DNA scission capability and antitumoral IC(50) concentration. The presence of double-strand DNA breaks (DSBs) was confirmed within SK-OV-3 cancer cells using immunodetection of γ-H2AX foci by confocal microscopy and flow cytometry, with complex 1 quantitatively producing superior numbers of DSBs compared with complex 2. Superoxide dismutase and catalase mimetic activity assays were conducted, and these activities are related to the ability of both complexes to cleave DNA through free radical generation.

Synthesis, DNA/RNA affinity and antitumour activity of new aromatic diamidines linked by 3,4-ethylenedioxythiophene.

A series of novel 2,5-bis(amidinophenyl)-3,4-ethylenedioxythiophenes (5-10 and 15) has been synthesized. Compounds 5-10 bind to the DNA minor groove as the dominant binding site and strongly stabilize the double helix of ct-DNA. Surprisingly, the same compounds also thermally stabilize ds-RNA, whereby most of them form stacked dimers along the RNA double helix. The only exception is compound 15 which, due to its structural features, showed no interaction with DNA or RNA. Compounds 5-10 have shown a moderate to strong cytotoxic effect (GI50=1.5-9.0 µM) on a panel of seven tumour cell lines. The diimidazoline derivative 9, due to its highest inhibitory potential on the growth of all tested tumour cell lines, was investigated in more detail by testing its ability to enter into cells and influence the cell cycle. Compound 9 (5 µM) was internalized successfully in cell cytoplasm during a 30-min incubation period, followed by nuclear localization upon 90-min incubation. Significant arrest in HeLa cells in the G2/M phase, shown by cell cycle analysis at an equitoxic (50 µM) concentration, suggests interaction of a studied compound with cellular DNA as the main mode of biological action.

Evaluation of nucleoside hydrolase inhibitors for treatment of African trypanosomiasis.

In this paper, we present the biochemical and biological evaluation of N-arylmethyl-substituted iminoribitol derivatives as potential chemotherapeutic agents against trypanosomiasis. Previously, a library of 52 compounds was designed and synthesized as potent and selective inhibitors of Trypanosoma vivax inosine-adenosine-guanosine nucleoside hydrolase (IAG-NH). However, when the compounds were tested against bloodstream-form Trypanosoma brucei brucei, only one inhibitor, N-(9-deaza-adenin-9-yl)methyl-1,4-dideoxy-1,4-imino-d-ribitol (UAMC-00363), displayed significant activity (mean 50% inhibitory concentration [IC(50)] +/- standard error, 0.49 +/- 0.31 microM). Validation in an in vivo model of African trypanosomiasis showed promising results for this compound. Several experiments were performed to investigate why only UAMC-00363 showed antiparasitic activity. First, the compound library was screened against T. b. brucei IAG-NH and inosine-guanosine nucleoside hydrolase (IG-NH) to confirm the previously demonstrated inhibitory effects of the compounds on T. vivax IAG-NH. Second, to verify the uptake of these compounds by T. b. brucei, their affinities for the nucleoside P1 and nucleoside/nucleobase P2 transporters of T. b. brucei were tested. Only UAMC-00363 displayed significant affinity for the P2 transporter. It was also shown that UAMC-00363 is concentrated in the cell via at least one additional transporter, since P2 knockout mutants of T. b. brucei displayed no resistance to the compound. Consequently, no cross-resistance to the diamidine or the melaminophenyl arsenical classes of trypanocides is expected. Third, three enzymes of the purine salvage pathway of procyclic T. b. brucei (IAG-NH, IG-NH, and methylthioadenosine phosphorylase [MTAP]) were investigated using RNA interference. The findings from all these studies showed that it is probably not sufficient to target only the nucleoside hydrolase activity to block the purine salvage pathway of T. b. brucei and that, therefore, it is possible that UAMC-00363 acts on an additional target.

Discovery of novel antileishmanial agents in an attempt to synthesize pentamidine-aplysinopsin hybrid molecule.

In an attempt to synthesize pentamidine-aplysinopsin hybrid molecule 25, a lead molecule 8 (containing Z-configured aplysinopsin moiety) was identified for antileishmanial activity. Optimization of lead 8 provided 24 (containing E-configured aplysinopsin) possessing 10 times more activity and 401-fold less toxicity than the drug pentamidine in cell based assays. Synthesis of 24 was possible, surprisingly, because of two innate reactivities of indole-3-carbaldehyde which provided it in diastereo- and regio-selectively pure form without recourse to the long reaction pathway.

Experimental chemotherapy for Chagas disease: 15 years of research contributions from in vivo and in vitro studies

Chagas disease, which is caused by the intracellular parasite Trypanosoma cruzi, is a neglected illness with 12-14 million reported cases in endemic geographic regions of Latin America. While the disease still represents an important public health problem in these affected areas, the available therapy, which was introduced more than four decades ago, is far from ideal due to its substantial toxicity, its limited effects on different parasite stocks, and its poor activity during the chronic phase of the disease. For the past 15 years, our group, in collaboration with research groups focused on medicinal chemistry, has been working on experimental chemotherapies for Chagas disease, investigating the biological activity, toxicity, selectivity and cellular targets of different classes of compounds on T. cruzi. In this report, we present an overview of these in vitro and in vivo studies, focusing on the most promising classes of compounds with the aim of contributing to the current knowledge of the treatment of Chagas disease and aiding in the development of a new arsenal of candidates with anti-T. cruzi efficacy.

The usefulness of cyclic diamidines with different core-substituents as antitumor agents.

A series of related polycationic compounds has been screened for potential antitumor activity by the NCI's in vitro testing (one dose primary anticancer assay and the NCI-60 full panel screening). The GI50 values of triazines 3 and 4 are on average 1.9 microM and 2.4 microM, respectively. Furan 8 deserves mention too (1.9 microM). The biological test results showed that carbazole 10 possessed cytotoxic activity in the nanomolar range, much better than the other compounds tested, only against several cancer cell lines: CCRF-CEM, HL-60(TB), MOLT-4, NCI-H522, COLO 205, SF-268, but the average GI50 value was higher (15 microM). The activity appears closely dependent on the core-shape and length of the bisimidazoline molecules (important for both high cytotoxicity and DNA binding). The mechanism of DNA minor-groove binding of diamidines 1-12, based on the anticancer parameters, is highly probable.

Novel high-throughput electrochemiluminescent assay for identification of human tyrosyl-DNA phosphodiesterase (Tdp1) inhibitors and characterization of furamidine (NSC 305831) as an inhibitor of Tdp1.

By enzymatically hydrolyzing the terminal phosphodiester bond at the 3'-ends of DNA breaks, tyrosyl-DNA phosphodiesterase (Tdp1) repairs topoisomerase-DNA covalent complexes and processes the DNA ends for DNA repair. To identify novel Tdp1 inhibitors, we developed a high-throughput assay that uses electrochemiluminescent (ECL) substrates. Subsequent to screening of 1981 compounds from the 'diversity set' of the NCI-Developmental Therapeutics Program, here we report that furamidine inhibits Tdp1 at low micromolar concentrations. Inhibition of Tdp1 by furamidine is effective both with single- and double-stranded substrates but is slightly stronger with the duplex DNA. Surface plasmon resonance studies show that furamidine binds both single- and double-stranded DNA, though more weakly with the single-stranded substrate DNA. Thus, the inhibition of Tdp1 activity could in part be due to the binding of furamidine to DNA. However, the inhibition of Tdp1 by furamidine is independent of the substrate DNA sequence. The kinetics of Tdp1 inhibition by furamidine was influenced by the drug to enzyme ratio and duration of the reaction. Comparison with related dications shows that furamidine inhibits Tdp1 more effectively than berenil, while pentamidine was inactive. Thus, furamidine represents the most potent Tdp1 inhibitor reported to date.

Identification and characterization of small molecule inhibitors of the calcium-dependent S100B-p53 tumor suppressor interaction.

The binding of S100B to p53 down-regulates wild-type p53 tumor suppressor activity in cancer cells such as malignant melanoma, so a search for small molecules that bind S100B and prevent S100B-p53 complex formation was undertaken. Chemical databases were computationally searched for potential inhibitors of S100B, and 60 compounds were selected for testing on the basis of energy scoring, commercial availability, and chemical similarity clustering. Seven of these compounds bound to S100B as determined by steady state fluorescence spectroscopy (1.0 microM < or = K(D) < or = 120 microM) and five inhibited the growth of primary malignant melanoma cells (C8146A) at comparable concentrations (1.0 microM < or = IC(50) < or = 50 microM). Additionally, saturation transfer difference (STD) NMR experiments confirmed binding and qualitatively identified protons from the small molecule at the small molecule-S100B interface. Heteronuclear single quantum coherence (HSQC) NMR titrations indicate that these compounds interact with the p53 binding site on S100B. An NMR-docked model of one such inhibitor, pentamidine, bound to Ca(2+)-loaded S100B was calculated using intermolecular NOE data between S100B and the drug, and indicates that pentamidine binds into the p53 binding site on S100B defined by helices 3 and 4 and loop 2 (termed the hinge region).

The DNA double-stranded break repair protein endo-exonuclease as a therapeutic target for cancer.

DNA repair mechanisms are crucial for the maintenance of genomic stability and are emerging as potential therapeutic targets for cancer. In this study, we report that the endo-exonuclease, a protein involved in the recombination repair process of the DNA double-stranded break pathway, is overexpressed in a variety of cancer cells and could represent an effective target for developing anticancer drugs. We identify a dicationic diarylfuran, pentamidine, which has been used clinically to treat opportunistic infections and is an inhibitor of the endo-exonuclease as determined by enzyme kinetic assay. In clonogenic and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays as well as in the in vivo Lewis lung carcinoma mouse tumor model, pentamidine is shown to possess the ability to selectively kill cancer cells. The LD50 of pentamidine on cancer cells maintained in vitro is correlated with the endo-exonuclease enzyme activity. Tumor cell that has been treated with pentamidine is reduced in the endo-exonuclease as compared with the untreated control. Furthermore, pentamidine synergistically potentiates the cytotoxic effect of DNA strand break and cross-link-inducing agents such as mitomycin C, etoposide, and cisplatin. In addition, we used the small interfering RNA for the mouse homologue of the endo-exonuclease to down-regulate the level of endo-exonuclease in the mouse myeloma cell line B16F10. Down-regulation of the endo-exonuclease sensitizes the cell to 5-fluorouracil. These studies suggested the endo-exonuclease enzyme as a novel potential therapeutic target for cancer.

In vitro effect of diamidines on intracellular polyamines of Acanthamoeba polyphaga.

Treatment with the drugs berenil, dibromopropamidine, pentamidine and CGP-4O-215 were found to alter levels of intracellular polyamines of Acanthamoeba polyphagia trophozoites in organisms. While the polyamine, spermidine, consistently remained higher in the control organisms incubated at 8, 16 and 32 h respectively, the level fluctuated significantly from below 5% to 40% in drug-treated organisms. A novel polyamine (polyamine F), yet to be identified, representing 80% of the total polyamine extracts and seen in control organisms after 48 h of incubation (stationary phase), was seen much earlier in the drug treated organisms. Pentamidine, dibromopropamidine and CGP-4O-215 induced the appearance of the novel polyamine in the trophozoites after only 8 h of incubation with the drugs while induction by berenil occurred after 32 h. It is suggested that diamidine drugs either induce encystment or alter the pathway of polyamine metabolism in Acanthamoeba. If inducing encystment is the main mode of reaction, then drugs that induce early encystment will be less effective in treatment than those that delay it.

Pentamidine: a non-peptide GPIIb/IIIa antagonist--in vitro studies on platelets from humans and other species.

In this paper we show that the non-peptide anti-parasite agent pentamidine is a broad spectrum anti-platelet agent with an IC50 of 1.1 microM in ADP-induced platelet aggregation in human platelet rich plasma (PRP). It had similar activity when collagen, arachidonic acid, platelet activating factor, thrombin and epinephrine were used. It had no effect on platelet intracellular cAMP levels. It inhibited 125I-fibrinogen, 125I-fibronectin and 125I-von Willebrand factor binding to ADP-activated fixed platelets with IC50 values of 160, 160 and 60 nM respectively. Pentamidine showed a high degree of species selectivity with slightly less activity in monkey and dog PRP and little activity in guinea pig, rabbit, rat and mouse PRP compared with human. This was similar to the other RGD analogues tested. This species specificity was shown to be dependent on the species of platelets and independent of the species of fibrinogen. Thus, pentamidine is a potent non-peptide inhibitor of fibrinogen binding to GPIIb/IIIa.