Donald A. Patrick

Antileishmanial Activities of Several Classes of Aromatic Dications

ABSTRACT 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 μM 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 μM), 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.

Anti-Pneumocystis carinii pneumonia activity of dicationic carbazoles

Summary A series of 2,7- and 3,6-bis cationic carbazoles was synthesized and evaluated for activity against a rat model of Pneumocystis carinii pneumonia (PCP). The compounds were also tested for inhibition of topoisomerase II and binding to DNA. Several of the compounds proved to be more potent and less toxic than a standard anti-PCP drug (pentamidine). While no quantitative correlation was seen between anti-PCP activity, topoisomerase inhibition and DNA binding, a minimal level of DNA binding was found to be necessary for antimicrobial activity.

Structure−Activity Study of Pentamidine Analogues as Antiprotozoal Agents

Diamidine 1 (pentamidine) and 65 analogues (2-66) have been tested for in vitro antiprotozoal activities against Trypanosoma brucei rhodesiense, Plasmodium falciparum, and Leishmania donovani, and for cytotoxicity against mammalian cells. Dications 32, 64, and 66 exhibited antitrypanosomal potencies equal or greater than melarsoprol (IC(50) = 4 nM). Nine congeners (2-4, 12, 27, 30, and 64-66) were more active against P. falciparum than artemisinin (IC(50) = 6 nM). Eight compounds (12, 32, 33, 44, 59, 62, 64, and 66) exhibited equal or better antileishmanial activities than 1 (IC(50) = 1.8 microM). Several congeners were more active than 1 in vivo, curing at least 2/4 infected animals in the acute mouse model of trypanosomiasis. The diimidazoline 66 was the most promising compound in the series, showing excellent in vitro activities and high selectivities against T. b. rhodesiense, P. falciparum, and L. donovani combined with high antitrypanosomal efficacy in vivo.

Synthesis and anti-Pneumocystis carinii pneumonia activity of novel dicationic dibenzothiophenes and orally active prodrugs.

Dicationic carbazoles have been found to be highly active against a rat model of Pneumocystis carinii pneumonia (PCP). Unfortunately, amidoxime derivatives, designed as prodrugs, were inactive against PCP even though the corresponding amidines were highly active. In the present work, a series of 2,8- and 3,7-bis cationic dibenzothiophenes was synthesized and assayed for anti-PCP activity. Three of the compounds proved to be more potent and less toxic than a standard anti-PCP drug (pentamidine) when given intravenously. Unlike the carbazoles, a dibenzothiophene amidoxime prodrug given orally reduced the parasite load by more than 99%. While no quantitative correlation was seen between anti-PCP activity and DNA binding, a strong level of DNA binding was found to be necessary for antimicrobial activity.

Synthesis and antiprotozoal activity of dicationic m-terphenyl and 1,3-dipyridylbenzene derivatives

4,4″-Diamidino-m-terphenyl (1) and 36 analogues were prepared and assayed in vitro against T rypanosoma brucei rhodesiense , Trypanosoma cruzi , Plasmodium falciparum , and Leishmania amazonensis . Twenty-three compounds were highly active against T. b. rhodesiense or P. falciparum. Most noteworthy were amidines 1, 10, and 11 with IC50 of 4 nM against T. b. rhodesiense, and dimethyltetrahydropyrimidinyl analogues 4 and 9 with IC50 values of ≤ 3 nM against P. falciparum. Bis-pyridylimidamide derivative 31 was 25 times more potent than benznidazole against T. cruzi and slightly more potent than amphotericin B against L. amazonensis. Terphenyldiamidine 1 and dipyridylbenzene analogues 23 and 25 each cured 4/4 mice infected with T. b. rhodesiense STIB900 with four daily 5 mg/kg intraperitoneal doses, as well as with single doses of ≤ 10 mg/kg. Derivatives 5 and 28 (prodrugs of 1 and 25) each cured 3/4 mice with four daily 25 mg/kg oral doses.

Dicationic dibenzofuran derivatives as anti-Pneumocystis carinii pneumonia agents: synthesis, DNA binding affinity, and anti-P. carinii activity in an immunosuppressed rat model

Abstract Previous work from our laboratory shows that compounds with two cations linked by a carbazole spacer were highly potent antiP. carinii agents. A prodrug approach designed to increase oral activity of the dicationic carbazoles by converting amidine groups to amidoxime groups was unsuccessful. The ring nitrogen was implicated as playing a role in the lack of activity of carbazole amidoximes. The current study was designed to determine if replacement of the carbazole ring nitrogen by isosteric oxygen to form dibenzofurans would improve effectiveness of amidoxime prodrugs. Eight dibenzofuran dicationic derivatives were synthesized and evaluated for anti-P. carinii activity in an immunosuppressed rat model. Since DNA binding has been hypothesized to play a key role in antimicrobial activity of dicationic compounds, the compounds were examined for their binding affinity to calf thymus DNA and a poly-dA•poly-dT oligomer. While several of the compounds were more potent anti-P. carinii agents than pentamidine, the corresponding amidoximes were significantly less effective than the amidoxime of pentamidine. No direct quantitative correlation was determined between DNA binding affinity and anti-P. carinii activity, but all active compounds were strong DNA binding agents.

Synthesis and antitrypanosomal evaluation of derivatives of N-benzyl-1,2-dihydroquinolin-6-ols: Effect of core substitutions and salt formation.

Analogs of the trypanocidal lead compound 1-benzyl-1,2-dihydro-2,2,4-trimethylquinolin-6-yl acetate were prepared to extend the structure-activity relationship in this series of molecules, improve the in vivo antitrypanosomal activity of the lead, and determine whether ester prodrugs are needed to overcome the instability of the dihydroquinolin-6-ols. Two of the most active compounds identified in this study were 1-benzyl-1,2-dihydro-2,2,4-trimethylquinolin-6-ol hydrochloride and 1-(2-methoxy)benzyl-1,2-dihydro-2,2,4-trimethylquinolin-6-ol hydrochloride. These stable solids possessed low nanomolar IC(50) values against Trypanosoma brucei rhodesiense STIB900 in vitro and provided cures in an early treatment acute mouse model of African trypanosomiasis when given ip at 50mg/kg/day for four consecutive days.

In Vitro and In Vivo Evaluation of 28DAP010, a Novel Diamidine for Treatment of Second-Stage African Sleeping Sickness

ABSTRACT African sleeping sickness is a neglected tropical disease transmitted by tsetse flies. New and better drugs are still needed especially for its second stage, which is fatal if untreated. 28DAP010, a dipyridylbenzene analogue of DB829, is the second simple diamidine found to cure mice with central nervous system infections by a parenteral route of administration. 28DAP010 showed efficacy similar to that of DB829 in dose-response studies in mouse models of first- and second-stage African sleeping sickness. The in vitro time to kill, determined by microcalorimetry, and the parasite clearance time in mice were shorter for 28DAP010 than for DB829. No cross-resistance was observed between 28DAP010 and pentamidine on the tested Trypanosoma brucei gambiense isolates from melarsoprol-refractory patients. 28DAP010 is the second promising preclinical candidate among the diamidines for the treatment of second-stage African sleeping sickness.

Synthesis and antiprotozoal activities of dicationic bis(phenoxymethyl)benzenes, bis(phenoxymethyl)naphthalenes, and bis(benzyloxy)naphthalenes

A series of 37 dicationically substituted bis(phenoxymethyl)benzene bis(phenoxymethyl)naphthalene, and bis(benzyloxy)naphthalene analogues of pentamidine was prepared and evaluated for antiprotozoal activities and cytotoxicity in in vitro. 1,3-Bis(4-amidinophenoxymethyl)benzene (1) was the most active against Trypanosoma brucei rhodesiense (IC(50)=2.1 nM). 1,3-Bis[4-(N-isopropylamidino)phenoxymethyl]benzene (2) was most active against Plasmodium falciparum (IC(50)=3.6 nM) and displayed a selectivity index more than 50 times greater than that of pentamidine. Several other compounds displayed lower antiplasmodial IC(50) values and higher selectivity indices relative to pentamidine. 1,4-Bis(4-amidinophenoxymethyl)benzene (14) was the most active against Leishmania donovani (IC(50)=1.3 microM). Compound 2 displayed the greatest activity against T. b. rhodesiense in vivo, curing three of four infected mice dosed intraperitoneally at 5 mg/kg x 4 days.

In vitro and in vivo biological effects of novel arylimidamide derivatives against Trypanosoma cruzi

ABSTRACT Chagas disease (CD), a neglected tropical disease caused by Trypanosoma cruzi, remains a serious public health problem in several Latin American countries. The available chemotherapies for CD have limited efficacy and exhibit undesirable side effects. Aromatic diamidines and arylimidamides (AIAs) have shown broad-spectrum activity against intracellular parasites, including T. cruzi. Therefore, our aim was to evaluate the biological activity of eight novel AIAs (16DAP002, 16SAB079, 18SAB075, 23SMB022, 23SMB026, 23SMB054, 26SMB070, and 27SMB009) against experimental models of T. cruzi infection in vitro and in vivo. Our data show that none of the compounds induced a loss of cellular viability up to 32 μM. Two AIAs, 18SAB075 and 16DAP002, exhibited good in vitro activity against different parasite strains (Y and Tulahuen) and against the two relevant forms of the parasite for mammalian hosts. Due to the excellent selective indexes of 18SAB075, this AIA was moved to in vivo tests for acute toxicity and parasite efficacy; nontoxic doses (no-observed-adverse-effect level [NOAEL], 50 mg/kg) were employed in the tests for parasite efficacy. In experimental models of acute T. cruzi infection, 18SAB075 reduced parasitemia levels only up to 50% and led to 40% protection against mortality (at 5 mg/kg of body weight), being less effective than the reference drug, benznidazole.