Tien L. Huang

Synthesis and anti-Pneumocystis carinii activity of conformationally restricted analogues of pentamidine

Abstract Aseries of conformationally restricted analogues of pentamidine in which the flexible central bridge has been replaced by trans-cyclopropyl, phenyl, pyridinyl, piperazinyl or homopiperazinyl groups as conformationally restricted linkers have been synthesized. The anti-Pneumocystis carinii activity of these compounds was evaluated in a cell culture model and the DNA binding affinity was determined by thermal denaturation measurements. At 1 μM, compounds 2, 3, 5, 7, 9 and pentamidine were highly effective and caused total inhibition of P. carinii growth in culture. At 0.1 μM, compounds 2, 5, 7 and 10 were more active than pentamidine with N, N′-bis(4-amidinophenyl)piperazine 7 being approximately 15-fold more effective than pentamidine. The most active compounds, 7 and 10, showed strong binding affinities for calf thymus DNA and poly(dA-dT); however, a clear correlation between DNA binding affinity and the in vitro anti-P. carinii activity of these compounds was not observed. The results suggest that the nature of the central linker influences the biological actions of these compounds.

Highly Active Anti-Pneumocystis carinii Compounds in a Library of Novel Piperazine-Linked Bisbenzamidines and Related Compounds

ABSTRACT Trimethoprim-sulfamethoxazole and pentamidine isethionate have been used extensively for the prophylaxis and therapy of pneumonia caused by Pneumocystis jirovecii. Problems associated with toxicity and potential emerging resistance for both therapies necessitate the development of safe and effective analogs or new treatment strategies. In the present study, a library of 36 compounds was synthesized by using the pentamidine molecule as the parent compound modified by a 1,4-piperazinediyl moiety as the central linker to restrict conformation flexibility. The compounds were evaluated for anti-Pneumocystis carinii activity in a bioluminescent ATP-driven assay. Four of the compounds were highly active, with 50% inhibitory concentration (IC50) values of <0.01 μg/ml; four had very marked activity (IC50 < 0.10 μg/ml); ten had marked activity (IC50 < 1.0 μg/ml); nine had moderate activity (IC50 < 10 μg/ml); one had slight activity (IC50 = 34.1 μg/ml); and the remaining eight did not demonstrate activity in this assay system. The high level of activity was specifically associated with an alkyl chain length of five to six carbons attached to one of the nitrogens of the bisamidinium groups. None of the highly active compounds and only one of the very marked compounds exhibited any toxicity when evaluated in three mammalian cell lines. The strategy of substitution of 1,4-piperazine-linked bisbenzamidines produced compounds with the highest level of activity observed in the ATP assay and holds great promise for the development of efficacious anti-P. carinii therapy.

In Vitro Selection and In Vivo Efficacy of Piperazine- and Alkanediamide-Linked Bisbenzamidines against Pneumocystis Pneumonia in Mice

ABSTRACT Bisbenzamidines, such as pentamidine isethionate, are aromatic dicationic compounds that are active against Pneumocystis and other microbes but are oftentimes toxic to the host. To identify potential anti-Pneumocystis agents, we synthesized bisbenzamidine derivatives in which the parent compound pentamidine was modified by a 1,4-piperazinediyl, alkanediamide, or 1,3-phenylenediamide moiety as the central linker. Several of the compounds were more active against P. carinii and less toxic than pentamidine in cytotoxicity assays. For this study, we evaluated nine bisbenzamidine derivatives representing a range of in vitro activities, from highly active to inactive, for the treatment of pneumocystosis in an immunosuppressed mouse model. Six of these in vitro-active compounds, 01, 02, 04, 06, 100, and 101, exhibited marked efficacies against infection at a dose of 10 mg/kg of body weight, and four compounds, 01, 04, 100, and 101, showed significant increases in survival versus that of untreated infected control mice. Compound 100 was highly efficacious against the infection at 20 mg/kg and 40 mg/kg, with >1,000-fold reductions in burden, and resulted in improved survival curves versus those for pentamidine-treated mice (at the same doses). All six bisbenzamidine compounds that exhibited high in vitro activity significantly decreased the infection in vivo; two compounds, 12 and 102, with marked to moderate in vitro activities had slight or no activity in vivo, while compound 31 was inactive in vitro and was also inactive in vivo. Thus, the selection of highly active compounds from in vitro cytotoxicity assays was predictive of activity in the mouse model of Pneumocystis pneumonia. We conclude that a number of these bisbenzamidine compounds, especially compound 100, may show promise as new anti-Pneumocystis drugs.

Fragment-based design of symmetrical bis-benzimidazoles as selective inhibitors of the trimethoprim-resistant, type II R67 dihydrofolate reductase.

The continuously increasing use of trimethoprim as a common antibiotic for medical use and for prophylactic application in terrestrial and aquatic animal farming has increased its prevalence in the environment. This has been accompanied by increased drug resistance, generally in the form of alterations in the drug target, dihydrofolate reductase (DHFR). The most highly resistant variants of DHFR are known as type II DHFR, among which R67 DHFR is the most broadly studied variant. We report the first attempt at designing specific inhibitors to this emerging drug target by fragment-based design. The detection of inhibition in R67 DHFR was accompanied by parallel monitoring of the human DHFR, as an assessment of compound selectivity. By those means, small aromatic molecules of 150-250 g/mol (fragments) inhibiting R67 DHFR selectively in the low millimolar range were identified. More complex, symmetrical bis-benzimidazoles and a bis-carboxyphenyl were then assayed as fragment-based leads, which procured selective inhibition of the target in the low micromolar range (K(i) = 2-4 μM). The putative mode of inhibition is discussed according to molecular modeling supported by in vitro tests.

Peptidyl aldehyde inhibitors of calpain incorporating P2-Proline mimetics

Four new peptidyl aldehydes bearing proline mimetics at the P(2)-position were synthesized and studied as inhibitors of calpain I, cathepsin B, and selected serine proteases. The ring size of the P(2)-constraining residue influenced the inhibitory potency and selectivity of the compounds for calpain I compared to the other proteases.

Synthesis and anti-pneumocystis carinii activity of piperidine-linked aromatic diimidazolines

Abstract A series of novel piperidine-linked aromatic diimidazolines ( 3–7 ) have been synthesized as conformationally restricted congeners of the anti- Pneumocystis carinii drug, Pentamidine. These compounds significantly inhibited the growth of Pneumocystis carinii in culture at 1 μg/mL.

Anti-plasmodial and anti-leishmanial activity of conformationally restricted pentamidine congeners

A library of 52 pentamidine congeners in which the flexible pentyldioxy linker in pentamidine was replaced with various restricted linkers was tested for in‐vitro activity against two Plasmodium falciparum strains and Leishmania donovani. The tested compounds were generally more effective against P. falciparum than L. donovani. The most active compounds against the chloroquine‐sensitive (D6, Sierra Leone) and ‐resistant (W2, Indochina) strains of P. falciparum were bisbenzamidines linked with a 1,4‐piperazinediyl or 1, 4‐homopiperazinediyl moiety, with IC50 values (50% inhibitory concentration, inhibiting parasite growth by 50% in relation to drug‐free control) as low as 7 nM based on the parasite lactate dehydrogenase assay. Seven piperazine‐linked bisbenzamidines substituted at the amidinium nitrogens with a linear alkyl group of 3–6 carbons (22, 25, 27, 31) or cycloalkyl group of 4, 6 or 7 carbons (26, 32, 34) were more potent (IC50 < 40 nM) than chloroquine or pentamidine as anti‐plasmodial agents. The most active anti‐leishmanial agents were 4,4′‐[1,4‐phenylenebis(methyleneoxy)]bisbenzenecarboximidamide (2, IC50 ∼ 0.290 μM) and 1,4‐bis[4‐(1H‐benzimidazol‐2‐yl)phenyl] piperazine (44, IC50∼0.410 μM), which were 10‐ and 7‐fold more potent than pentamidine (IC50 ∼ 2.90 μM). Several of the more active anti‐plasmodial agents (e.g. 2,31, 33, 36–38) were also potent anti‐leishmanial agents, indicating broad antiprotozoal properties. However, a number of analogues that showed potent anti‐plasmodial activity (1, 18, 21, 22, 25–28, 32, 43, 45) were not significantly active against the Leishmania parasite. This indicates differential modes of anti‐plasmodial and anti‐leishmanial actions for this class of compounds. These compounds provide important structure‐activity relationship data for the design of improved chemotherapeutic agents against parasitic infections.

Novel bisbenzamidines and bisbenzimidazolines as noncompetitive NMDA receptor antagonists.

A series of novel bisbenzamidines and bisbenzimidazolines with different linkers connecting the aromatic groups was tested in vitro for NMDA receptor antagonist activity. IC50 values for these compounds ranged from 1.2 to >200 microM. The bisbenzamidine with a homopiperazine ring as the central linker was found to be the most potent NMDA receptor antagonist among all the pentamidine analogues tested so far.

Some non-conventional biomolecular targets for diamidines. A short survey.

Increasing the affinity of diamidines for AT-rich regions of DNA has long been an important goal of medicinal chemists who wanted to improve the antiparasitic and antifungal properties of that class of derivatives. In recent years it was demonstrated that diamidines could interfere with many other biomolecular targets including ion channels as well as enzymes and modulate some RNA-protein, DNA-protein, and protein-protein interactions. It is therefore not surprising that diamidines now emerge as novel potential drug candidates for the treatment of various diseases, i.a. neurodegenerative disorders, acidosis-related pathological conditions, hypertension, thrombosis, type 2 diabetes, myotonic dystrophy, and cancers. A summary of the most striking results obtained to date in those domains is presented is this review.

Antitumor and Anti-Pneumocystis Carinii Activities of Novel Bisbenzamidines

Among a library of 17 bisbenzamidines connected with various linkers, compounds with a flexible pentanediamide (10) or hexanediamide (12) linker were the most potent derivatives against rat Pneumocystis carinii (IC50 values of 3 and 2 nM, respectively) and had the highest selectivity index ratios (GI50 of human tumor cells/IC50 of rat P. carinii cells) of >104. Seven compounds caused 50% growth inhibition (GI50) of tumor cells at concentrations of <100 μM while the remaining ten were not cytotoxic. DNA binding affinity (ΔTm) of the tested compounds did not correlate with either their anti-P. carinii activity or cytotoxicity.