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Karl A Werbovetz

Publications and source records attributed to Karl A Werbovetz.

At least 19 recordsLinked to original sources
PubMed2006

Synthesis and antiparasitic evaluation of bis-2,5-[4-guanidinophenyl]thiophenes.

A series of bis-2,5-[4-guanidinophenyl]thiophenes were prepared in a five step process starting from 2,5-bis[trimethylstannyl]thiophene. The compounds were evaluated in vitro against Trypanosoma brucei rhodesiense (T. b. r.), Plasmodium falciparum (P. f.), Leshmania donovani (L. d.) and Trypanasoma cruzi (T. c.), and in vivo against T. b. r. Certain compounds show promising in vitro activity against T. b. r. and P. f. and have superior in vivo activity against T. b. r. to that of pentamidine and furamidine.

Animals↗
PubMed2006

Activity of and initial mechanistic studies on a novel antileishmanial agent identified through in silico pharmacophore development and database searching.

A 3D pharmacophore was generated to describe the antileishmanial activity of dinitroaniline sulfonamides by CATALYST 3D-QSAR methodology, and this pharmacophore was used to search the Maybridge database. Two compounds identified in this search, BTB 06237 and BTB 06256, were highly active with IC(50) values against L. donovani amastigotes of 0.5 +/- 0.2 and 2.3 +/- 0.8 microM, respectively. BTB 06237 also reduced parasite burdens in L. mexicana-infected J774 macrophages at low micromolar concentrations. Unlike the dinitroaniline sulfonamides, the active compounds did not display antimitotic effects against Leishmania. Transmission electron microscopy showed that the single parasite mitochondrion becomes dilated following incubation with BTB 06237, and fluorescence microscopy demonstrated that this organelle fragments into intensely staining spheres when treated with a mitochondrion-specific dye. The mitochondrial membrane potential was also dissipated in BTB 06237-treated parasites. These results indicate that BTB 06237 is an intriguing antileishmanial lead compound that likely interferes with mitochondrial function.

Aniline Compounds↗
PubMed2006

Leishmania tarentolae: purification and characterization of tubulin and its suitability for antileishmanial drug screening.

Previously, tubulin has been purified from Leishmania amazonensis and used to identify novel molecules with selective antimitotic activity. However, L. amazonensis is pathogenic and requires a relatively expensive medium for large-scale cultivation. Herein, the purification and characterization of tubulin from the non-pathogenic Leishmania tarentolae is reported, together with the sequence of alpha- and beta-tubulin from this organism. This protein was purified by sonication, diethylaminoethyl-Sepharose chromatography, and one assembly disassembly cycle in 1% overall recovery based on total cellular protein. Leishmania tarentolae tubulin was indistinguishable from the corresponding L. amazonensis protein in terms of binding affinity for dinitroaniline sulfanilamides and sensitivity to assembly inhibition by these compounds. The amino acid sequences derived from the L. tarentolae alpha- and beta-tubulin genes were 99.6 and 99.4% identical to the corresponding amino acid sequences from the Leishmania major Friedlin strain. These results indicate that tubulin from L. tarentolae is suitable for use in drug screening.

Amino Acid Sequence↗
PubMed2006

Antikinetoplastid antimitotic activity and metabolic stability of dinitroaniline sulfonamides and benzamides.

N(1)-Phenyl-3,5-dinitro-N(4),N(4)-di-n-propylsulfanilamide (1) and N(1)-phenyl-3,5-dinitro-N(4),N(4)-di-n-butylsulfanilamide (2) show potent in vitro antimitotic activity against kinetoplastid parasites but display poor in vivo activity. Seventeen new dinitroaniline sulfonamide and eleven new benzamide analogs of these leads are reported here. Nine of the sulfonamides display in vitro IC(50) values under 500 nM against African trypanosomes, and the most active antikinetoplastid compounds also inhibit the in vitro assembly of purified leishmanial tubulin with potencies similar to that of 2. While several of the potent compounds are rapidly degraded by rat liver S9 fractions in vitro, N(1)-(3-hydroxy)phenyl-3,5-dinitro-N(4),N(4)-di-n-butylsulfanilamide (21) displays an IC(50) value of 260 nM against African trypanosomes in vitro and is more stable than 2 in the in vitro metabolism assay.

Animals↗
PubMed2006

Cytotoxic 5-aryl-1-(4-nitrophenyl)-3-oxo-1,4-pentadienes mounted on alicyclic scaffolds.

The 5-aryl-1-(4-nitrophenyl)-3-oxo-1,4-pentadienyl pharmacophore was incorporated into four series of compounds 1-4. Compounds 1a-g comprised a cluster of 3-arylidene-1-(4-nitrophenylmethylene)-2-oxo-3,4-dihydro-1H-naphthalenes while the analogues 2a-g consisted of a group of 6-arylidene-2-(4-nitrophenylmethylene)cyclohexanones. Three other compounds prepared in this study were 1-(4-nitrophenylmethylene)-3-(3,4,5-trimethoxyphenylmethylene)-2-oxo-2,3-dihydro-1H-indene 3a as well as two 5-arylidene-2-(4-nitrophenylmethylene)cyclopentanones 4a,b. The compounds were evaluated against human Molt 4/C8 and CEM T-lymphocytes as well as murine L1210 cells. In general, the compounds in series 1 displayed marked cytotoxicity having IC50 values in the 1-5 microM range while the related cyclohexyl analogues in series 2 were slightly less potent (IC50 figures were mainly 5-10 microM). The relative locations of two aryl rings present in all four series were considered to contribute significantly to bioactivity and may have accounted for the virtual absence of cytotoxic properties in series 3 and 4. Most of the compounds were administered intraperitoneally to mice using doses up to and including 300 mg/kg. No mortalities were noted. The inhibiting effect of most of the compounds towards Helicobacter pylori is noteworthy. The modes of action of representative compounds include the induction of apoptosis while some compounds weakly inhibited tubulin polymerisation and human N-myristoyltransferase.

Alkadienes↗
PubMed2006

Pre-systemic metabolism prevents in vivo antikinetoplastid activity of N1,N4-substituted 3,5-dinitro sulfanilamide, GB-II-150.

We previously showed that N1-phenyl-3,5-dinitro-N4,N4-di-n-butylsulfanilamide (denoted GB-II-150) possesses selective antimicrotubule activity against Leishmania donovani and Trypanosoma brucei in vitro [Bhattacharya, G., Herman, J., Delfin, D., Salem, M.M., Barszcz, T., Mollet, M., Riccio, G., Brun, R., Werbovetz, K.A., 2004. Synthesis and antitubulin activity of N(1)- and N(4)-substituted 3,5-dinitro sulfanilamides against African trypanosomes and Leishmania. Journal of Medicinal Chemistry 47, 1823-1832]. When GB-II-150 was administered orally to male Sprague-Dawley rats, extensive first-pass metabolism of the compound was observed and the oral bioavailability was zero. GB-II-150 displayed a half-life of 170 min and a clearance of 31.5 mL/min/kg in rats when administered intravenously. In vitro metabolism studies indicated that less than 5% of GB-II-150 remained intact after a 60-min incubation with rat liver S9 fraction. As expected, the compound was extensively metabolized, with the major products resulting from N1-ring oxidation, N4-alkane oxidation, N4-oxidation, and nitro reduction. These data indicate that GB-II-150 undergoes rapid and extensive first-pass metabolism, precluding the attainment of effective systemic drug concentrations and explaining the lack of in vivo antitrypanosomal activity of this compound.

Administration, Oral↗
PubMed2006

Isoflavonoids and other compounds from Psorothamnus arborescens with antiprotozoal activities.

Bioactivity-guided fractionation of the root extract of Psorothamnus arborescens yielded the new isoflavone 5,7,3',4'-tetrahydroxy-2'-(3,3-dimethylallyl)isoflavone (1a) and the new 2-arylbenzofuran 2-(2'-hydroxy-4',5'-methylenedioxyphenyl)-6-methoxybenzofuran-3-carbaldehyde (2), together with seven known compounds, including three isoflavones, fremontin (3a), glycyrrhisoflavone (4a), and calycosin (5), two pterocarpans, maackiain (6) and 4-hydroxymaackiain (7), one triterpene, oleanolic acid (8), and one chalcone, isoliquiritigenin (9). In addition, the structure of the isoflavone fremontin was revised using spectroscopic and chemical methods and was assigned the new structure 3a. The isoflavone 1a and the chalcone 9 displayed leishmanicidal activity with IC50 values of 13.0 and 20.7 microM, respectively, against Leishmania donovani axenic amastigotes. Calycosin (5) exhibited selective toxicity against Trypanosoma brucei brucei (IC50 12.7 microM) compared to L. donovani amastigotes and Vero cells (IC50 100 and 159 microM, respectively). These results prompted us to test a small group of structurally related isoflavones for their antitrypanosomal activities. Genistein and 7,3',4'-trihydroxyisoflavone displayed promising activity (IC50 values 4.2 and 7.1 microM, respectively) and selectivity (IC50 versus Vero cells: 32.9 and 135 microM, respectively). These studies suggest that the isoflavone skeleton deserves further investigation as a template for novel antileishmanial and trypanocidal compounds.

Animals↗
PubMed2006

Natural products from plants as drug candidates and lead compounds against leishmaniasis and trypanosomiasis.

Millions of people in the developing world are affected by diseases caused by the kinetoplastid parasites: the leishmaniases, African trypanosomiasis, and Chagas disease. In many cases the drugs employed for treatment are toxic, marginally effective, given by injection, and/or compromised by the development of resistance. Since safe, effective, and affordable chemotherapeutic agents for leishmaniasis and trypanosomiasis are clearly needed, the identification of new antikinetoplastid drug candidates should be an urgent priority. Numerous plant-derived natural products from different structural classes have been investigated as antileishmanial and antitrypanosomal candidates, including various alkaloids, terpenoids, flavonoids, and quinonoids. This review outlines the antikinetoplastid activities of plant-derived natural products reported in the literature and also provides an overview of mechanistic studies that have been conducted with these compounds. Given the activities of these agents and their diverse range of effects on parasite biology, natural products are a potentially rich source of drug candidates and leads against leishmaniasis and trypanosomiasis.

Biological Products↗
PubMed2005

Antiprotozoal compounds from Psorothamnus polydenius.

Bioactivity-guided fractionation of the methanolic extract of Psorothamnus polydenius yielded the new chalcone 2,2',4'-trihydroxy-6'-methoxy-3',5'-dimethylchalcone (2), together with six other known compounds, 2',4'-dihydroxy-6'-methoxy-3',5'-dimethylchalcone (1), dalrubone (3), demethoxymatteucinol (4), eriodictyol (5), and photodalrubone (6a and 6b). This is the first report of chalcones in P. polydenius. The extracts and isolated compounds were tested in vitro for their antiprotozoal activity against Leishmania donovani and Trypanosoma brucei. Chalcones 1 and 2 and dalrubone (3) exhibited leishmanicidal (IC(50) 5.0, 7.5, and 7.5 microg/mL, respectively) and trypanocidal (IC(50) 6.3, 6.8, and 21.6 microg/mL, respectively) properties. Dalrubone (3) displayed 6-fold selectivity for axenic L. donovani parasites over Vero cells. Furthermore, treatment of L. mexicana-preinfected macrophages with chalcones 1 and 2 and dalrubone (3) (12.5, 12.5, and 25 microg/mL, respectively) reduced the number of infected macrophages by at least 96% while posing no toxicity to the host cell.

Animals↗
PubMed2004

Antikinetoplastid activity of 3-aryl-5-thiocyanatomethyl-1,2,4-oxadiazoles.

A series of 5-thiocyanatomethyl- and 5-alkyl-3-aryl-1,2,4-oxadiazoles were synthesized and evaluated for their activity against kinetoplastid parasites. Formation of the oxadiazole ring was accomplished through the reaction of benzamidoximes with acyl chlorides, while the thiocyanate group was inserted by reacting the appropriate 5-halomethyl oxadiazole with ammonium thiocyanate. The thiocyanate-containing compounds possessed low micromolar activity against Leishmania donovani and Trypanosoma brucei, while the 5-alkyl oxadiazoles were less active against these parasites. 3-(4-Chlorophenyl)-5-(thiocyanatomethyl)-1,2,4-oxadiazole (compound 4b) displayed modest selectivity for L. donovani axenic amastigote-like parasites over J774 macrophages, PC3 prostate cancer cells, and Vero cells (6.4-fold, 3.8-fold, and 9.1-fold, respectively), while 3-(3,4-dichlorophenyl)-5-(thiocyanatomethyl)-1,2,4-oxadiazole (compound 4 h) showed 30-fold selectivity against Vero cells but was not selective against PC3 cells. In a murine model of visceral leishmaniasis, compound 4b decreased liver parasitemia caused by L. donovani by 48% when given in five daily i.v. doses at 5mg/kg and by 61% when administered orally for 5 days at 50 mg/kg. These results indicate that aromatic thiocyanates hold promise for the treatment of leishmanial infections if the selectivity of these compounds can be improved.

Animals↗
PubMed2004

Synthesis and antitubulin activity of N1- and N4-substituted 3,5-dinitro sulfanilamides against African trypanosomes and Leishmania.

Thirty analogues of N(1)-phenyl-3,5-dinitro-N(4),N(4)-di-n-propylsulfanilamide (GB-II-5, compound 3), a new antikinetoplastid antimitotic agent, have been synthesized and evaluated. The addition of simple functional groups to the N1 aromatic ring generally decreases antiparasitic and antimitotic potency, but placement of a dibutyl substituent at the N4 nitrogen to give N(1)-phenyl-3,5-dinitro-N(4),N(4)-di-n-butylsulfanilamide (compound 35) augments antitrypanosomal and antileishmanial activity. Compound 35 possesses IC(50) values of 0.12 and 2.6 microM against cultured T. brucei and L. donovani amastigote-like forms, surpassing the activity of compound 3 against these parasites by 3.4- and 1.9-fold, respectively. Compound 35 inhibits the assembly of leishmanial tubulin with an IC(50) of 6.9 microM and displays antimitotic effects in cultured T. brucei as assessed by flow cytometry, but shows little effect on purified mammalian tubulin, and displays 100-fold selectivity for trypanosomes over two mammalian cell lines. Although 3 and 35 were not effective in initial in vivo antitrypanosomal assays, the in vitro potency and selectivity of these compounds make N(1)-aryl-3,5-dinitro-N(4),N(4)-dialkylsulfanilamides a promising new class of antikinetoplastid agents that act on parasite tubulin.

Animals↗
PubMed2003

The activity of diguanidino and 'reversed' diamidino 2,5-diarylfurans versus Trypanosoma cruzi and Leishmania donovani.

The in vitro activity of 20 dicationic molecules containing either diguanidino or reversed amidine cationic groups were evaluated versus Trypanosoma cruzi and Leishmania donovani. The most active compounds were in the reversed amidine series and six exhibited IC(50) values of less than 1 micro mol versus T. cruzi and five gave similar values versus L. donovani.

Amidines↗
PubMed2003

Selective antimicrotubule activity of N1-phenyl-3,5-dinitro-N4,N4-di-n-propylsulfanilamide (GB-II-5) against kinetoplastid parasites.

Analogs of the antimitotic herbicide oryzalin (3,5-dinitro-N4,N4-di-n-propylsulfanilamide) were recently prepared that were more potent in vitro than the parent compound against the kinetoplastid parasite Leishmania donovani (Bioorg Med Chem Lett 12:2395-2398, 2002). In the present work, we show that the most active molecule in the group, N1-phenyl-3,5-dinitro-N4,N4-di-n-propylsulfanilamide (GB-II-5), is a potent, selective antimitotic agent against kinetoplastid parasites. GB-II-5 possesses IC50 values of 0.41 and 0.73 microM in vitro against two strains of the related parasite Trypanosoma brucei but is much less toxic to J774 murine macrophages and PC3 prostate cancer cells, exhibiting IC50 values of 29 and 35 microM against these lines, respectively. Selectivity is also observed for GB-II-5 with purified leishmanial and mammalian tubulin. The assembly of 15 microM leishmanial tubulin is completely inhibited by 10 microM GB-II-5, whereas 40 microM GB-II-5 inhibits the assembly of 15 microM porcine brain tubulin by only 17%. In cultured L. donovani and T. brucei, treatment with 5 and 0.5 microM GB-II-5, respectively, causes a striking increase in the fraction of G2M cells compared with control. Given the potency and selectivity of this agent against kinetoplastid tubulin, GB-II-5 emerges as an exciting new antitrypanosomal and antileishmanial lead compound.

Animals↗
PubMed2002

Antileishmanial dinitroaniline sulfonamides with activity against parasite tubulin.

Novel dinitroaniline sulfonamides based on the herbicide oryzalin 3 were synthesized and evaluated for activity against the parasitic protozoan Leishmania donovani and against leishmanial tubulin, the putative antiparasitic target of oryzalin. A subset of these compounds possess more activity against both Leishmania and the target protein in vitro. Compound 20 displays improved potency against leishmanial tubulin and is 13.4-fold more active against L. donovani axenic amastigotes than oryzalin.

Animals↗
PubMed2002

Analysis of stereoelectronic properties, mechanism of action and pharmacophore of synthetic indolo[2,1-b]quinazoline-6,12-dione derivatives in relation to antileishmanial activity using quantum chemical, cyclic voltammetry and 3-D-QSAR CATALYST procedures.

Several indolo[2,1-b]quinazoline-6,12-dione (tryptanthrin) derivatives exhibited remarkable activity at concentrations below 100 ng/mL when tested against in vitro Leishmania donovani amastigotes. The in vitro toxicity studies indicate that the compounds are fairly well tolerated in both macrophage and neuronal lines. An analysis based on qualitative and quantitative structure-activity relationship studies between in vitro antileishmanial activity and molecular electronic structure of 27 analogues of indolo[2,1-b]quinazoline-6,12-dione is presented here by using a combination of semi-empirical AM1 quantum chemical, cyclic voltammetry and a pharmacophore generation (CATALYST) methods. A modest to good correlation is observed between activity and a few calculated molecular properties such as molecular density, octanol-water partition coefficient, molecular orbital energies, and redox potentials. Electron transfer seems to be a plausible path in the mechanism of action of the compounds. A pharmacophore generated by using the 3-D QSAR of CATALYST produced a fairly accurate predictive model of antileishmanial activity of the tryptanthrins. The validity of the pharmacophore model extends to structurally different class of compounds that could open new frontiers for study. The carbonyl group of the five- and six-membered rings in the indolo[2,1-b]quinazoline-6,12-dione skeleton and the electron transfer ability to the carbonyl atom appear to be crucial for activity.

Animals↗
PubMed2002

Antileishmanial activities of several classes of aromatic dications.

Aromatic dicationic molecules possess impressive activity against a broad spectrum of microbial pathogens, including Pneumocystis carinii, Cryptosporidium parvum, and Candida albicans. In this work, 58 aromatic cations were examined for inhibitory activity against axenic amastigote-like Leishmania donovani parasites. In general, the most potent of the compounds were substituted diphenyl furan and thiophene dications. 2,5-Bis-(4-amidinophenyl)thiophene was the most active compound. This agent displayed a 50% inhibitory concentration (IC50) of 0.42 +/- 0.08 microM against L. donovani and an in vitro antileishmanial potency 6.2-fold greater than that of the clinical antileishmanial dication pentamidine and was 155-fold more toxic to the parasites than to a mouse macrophage cell line. 2,4-Bis-(4-amidinopheny)furan was twice as active as pentamidine (IC50), 1.30 +/- 0.21 microM), while 2,5-bis-(4-amidinopheny)furan and pentamidine were essentially equipotent in our in vitro antileishmanial assay. Carbazoles, dibenzofurans, dibenzothiophenes, and benzimidazoles containing amidine or substituted amidine groups were generally less active than the diphenyl furans and thiophenes. In all cases, aromatic dications possessing strong antileishmanial activity were severalfold more toxic to the parasites than to a cultured mouse macrophage cell line. These structure-activity relationships demonstrate the potent antileishmanial activity of several aromatic dications and provide valuable information for the future design and synthesis of more potent antiparasitic agents.

Adult↗
PubMed2002

Promising therapeutic targets for antileishmanial drugs.

Current treatments for the parasitic disease leishmaniasis are unsatisfactory due to their route of administration, toxicity and expense. Resistance is also developing to first-line antimonial drugs. Fortunately, a handful of antileishmanial agents, such as the orally available compound miltefosine, are currently in clinical trials. In addition, several promising drug targets and lead molecules are being studied with the goal of developing new antileishmanial agents. Drug candidates have been identified through the continued investigation of parasite sterol metabolism and parasite proteases. New antileishmanial molecules have also been discovered through the study of novel targets and pathways, such as the bisphosphonate inhibitors of isoprenoid biosynthesis. This review presents a synopsis of the drug targets and lead compounds that have been investigated over the last few years against leishmaniasis, gives a perspective on the chemotherapeutic potential of each and discusses some of the obstacles to antileishmanial drug development.

Animals↗