Nanoparticle formulations of decoquinate increase antimalarial efficacy against liver stage Plasmodium infections in mice.

Decoquinate has potent activity against both Plasmodium hepatic development and red cell replication when tested in vitro. Decoquinate, however, is practically insoluble in water. To achieve its maximal in vivo efficacy, we generated nanoparticle formulations of decoquinate with a mean particle size less than 400 nm. Three separate preparations at doses of decoquinate 0.5-5 mg/kg were examined in mice infected with Plasmodium berghei. Oral administration of nanoparticle decoquinate at a dose of 1.25 mg/kg effectively inhibited the liver-stage parasite growth and provided complete causal prophylactic protection. This efficacy is 15 fold greater than that observed for microparticle decoquinate, which requires minimal dose of 20 mg/kg for the same inhibitory effect. Further in vitro studies utilizing dose-response assays revealed that decoquinate nanoformulation was substantially more potent than decoquinate microsuspension in killing both liver and blood stage malarial parasites, proving its potential for therapeutic development. FROM THE CLINICAL EDITOR: In this study, a nanoparticle formulation of decoquinate is shown to have superior bioavailability and efficacy in a mouse model of malaria, paving the way to the development of novel, potentially less toxic and more effective therapeutics to combat a disease that still has an enormous impact on a global scale despite the available partially effective therapies.

The use of a prodrug approach to minimize potential CNS exposure of next generation quinoline methanols while maintaining efficacy in in vivo animal models.

The use of mefloquine (MQ) for antimalarial treatment and prophylaxis has diminished largely in response to concerns about its neurologic side effects. An analog campaign designed to maintain the efficacy of MQ while minimizing blood-brain barrier (BBB) penetration has resulted in the synthesis of a prodrug with comparable-to-superior in vivo efficacy versus mefloquine in a P. berghei mouse model while exhibiting a sixfold reduction in CNS drug levels. The prodrug, WR319670, performed poorly compared to MQ in in vitro efficacy assays, but had promising in vitro permeability in an MDCK-MDR1 cell line BBB permeability screen. Its metabolite, WR308245, exhibited high predicted BBB penetration with excellent in vitro efficacy. Both WR319670 and WR308245 cured 5/5 animals in separate in vivo efficacy studies. The in vivo efficacy of WR319670 was thought to be due to the formation of a more active metabolite, specifically WR308245. This was supported by pharmacokinetics studies in non-infected mice, which showed that both IV and oral administration of WR319670 produced essentially identical levels of WR319670 and WR308245 in both plasma and brain samples at all time points. In these studies, the levels of WR308245 in the brain were 1/4 and 1/6 that of MQ in similar IV and oral studies, respectively. These data show that the use of WR319670 as an antimalarial prodrug was able to maintain efficacy in in vivo efficacy screens, while significantly lowering overall penetration of drug and metabolites across the BBB.

CYP450 phenotyping and accurate mass identification of metabolites of the 8-aminoquinoline, anti-malarial drug primaquine.

BACKGROUND: The 8-aminoquinoline (8AQ) drug primaquine (PQ) is currently the only approved drug effective against the persistent liver stage of the hypnozoite forming strains Plasmodium vivax and Plasmodium ovale as well as Stage V gametocytes of Plasmodium falciparum. To date, several groups have investigated the toxicity observed in the 8AQ class, however, exact mechanisms and/or metabolic species responsible for PQ's haemotoxic and anti-malarial properties are not fully understood. METHODS: In the present study, the metabolism of PQ was evaluated using in vitro recombinant metabolic enzymes from the cytochrome P450 (CYP) and mono-amine oxidase (MAO) families. Based on this information, metabolite identification experiments were performed using nominal and accurate mass measurements. RESULTS: Relative activity factor (RAF)-weighted intrinsic clearance values show the relative role of each enzyme to be MAO-A, 2C19, 3A4, and 2D6, with 76.1, 17.0, 5.2, and 1.7% contributions to PQ metabolism, respectively. CYP 2D6 was shown to produce at least six different oxidative metabolites along with demethylations, while MAO-A products derived from the PQ aldehyde, a pre-cursor to carboxy PQ. CYPs 2C19 and 3A4 produced only trace levels of hydroxylated species. CONCLUSIONS: As a result of this work, CYP 2D6 and MAO-A have been implicated as the key enzymes associated with PQ metabolism, and metabolites previously identified as potentially playing a role in efficacy and haemolytic toxicity have been attributed to production via CYP 2D6 mediated pathways.

Ketotifen is an antimalarial prodrug of norketotifen with blood schizonticidal and liver-stage efficacy.

Ketotifen is known to exhibit antimalarial activity in mouse and monkey malaria models. However, the low plasma levels and short half life of the drug do not adequately explain its in vivo efficacy. We synthesized most of the known metabolites of ketotifen and evaluated their antimalarial activity and pharmacokinetics in mice. Norketotifen, the de-methylated metabolite of ketotifen, was a more potent antimalarial in vitro as compared to ketotifen, and exhibited equivalent activity in vivo against asexual blood and developing liver-stage parasites. After ketotifen dosing, norketotifen levels were much higher than ketotifen relative to the IC50s of the compounds against Plasmodium falciparum in vitro. The data support the notion that the antimalarial activity of ketotifen in mice is mediated through norketotifen.

New imidazolidinedione derivatives as antimalarial agents.

A series of new N-alky- and N-alkoxy-imidazolidinediones was prepared and assessed for prophylactic and radical curative activities in mouse and Rhesus monkey models. New compounds are generally metabolically stable, weakly active in vitro against Plasmodium falciparum clones (D6 and W2) and in mice infected with Plasmodium berghei sporozoites. Representative compounds 8e and 9c showed good causal prophylactic activity in Rhesus monkeys dosed 30 mg/kg/day for 3 consecutive days by IM, delayed patency for 19-21 days and 54-86 days, respectively, as compared to the untreated control. By oral, 9c showed only marginal activity in causal prophylactic and radical curative tests at 50 mg/kg/day×3 and 30 mg/kg/day×7 plus chloroquine 10 mg/kg for 7 days, respectively.

In vitro biotransformation, in vivo efficacy and pharmacokinetics of antimalarial chalcones.

4'-n-Butoxy-2,4-dimethoxy-chalcone (MBC) has been described as protecting mice from an otherwise lethal infection with Plasmodium yoelii when dosed orally at 50 mg/kg/dose, daily for 5 days. In contrast, we found that oral dosing of MBC at 640 mg/kg/dose, daily for 5 days, failed to extend the survivability of P. berghei-infected mice. The timing of compound administration and metabolic activation likely contribute to the outcome of efficacy testing in vivo. Microsomal digest of MBC yielded 4'-n-butoxy-4-hydroxy-2-methoxy-chalcone and 4'-(1-hydroxy-n-butoxy)-2,4-dimethoxy-chalcone. We propose that the latter will hydrolyze in vivo to 4'-hydroxy-2,4-dimethoxy-chalcone, which has greater efficacy than MBC in our P. berghei-infected mouse model and was detected in plasma following oral dosing of mice with MBC. Pharmacokinetic parameters suggest that poor absorption, distribution, metabolism and excretion properties contribute to the limited in vivo efficacy observed for MBC and its analogs.

Role of specific cytochrome P450 isoforms in the conversion of phenoxypropoxybiguanide analogs in human liver microsomes to potent antimalarial dihydrotriazines.

Phenoxypropoxybiguanides, such as PS-15, are antimalarial prodrugs analogous to the relationship of proguanil and its active metabolite cycloguanil. Unlike cycloguanil, however, WR99210, the active metabolite of PS-15, has retained in vitro potency against newly emerging antifolate-resistant malaria parasites. Recently, in vitro metabolism of a new series of phenoxypropoxybiguanide analogs has examined the production of the active triazine metabolites by human liver microsomes. The purpose of this investigation was to elucidate the primary cytochrome P450 isoforms involved in the production of active metabolites in the current lead candidate. By using expressed human recombinant isoform preparations, specific chemical inhibitors, and isoform-specific inhibitory antibodies, the primary cytochrome P450 isoforms involved in the in vitro metabolic activation of JPC-2056 were elucidated. Unlike proguanil, which is metabolized primarily by CYP2C19, the results indicate that CYP3A4 plays a more important role in the metabolism of both PS-15 and JPC-2056. Whereas CYP2D6 appears to play a major role in the metabolism of PS-15 to WR99210, it appears less important in the conversion of JPC-2056 to JPC-2067. These results are encouraging, considering the prominence of CYP2C19 and CYP2D6 polymorphisms in certain populations at risk for contracting malaria, because the current clinical prodrug candidate from this series may be less dependent on these enzymes for metabolic activation.

Malaria causal prophylactic activity of imidazolidinedione derivatives.

A series of acid-stable carboxamide derivatives of 2-guanidinoimidazolidinedione (5a-c and 6a-c) were prepared as potential malaria prophylactic and radical cure agents. The new compounds showed moderate to good causal prophylactic activity in mice infected with Plasmodium yoelii sporozoites. Three compounds were further tested for causal prophylactic activity in Rhesus monkeys infected with Plasmodium cynomolgi sporozoites, and all showed a delay in patency from 13 to 40 days at 30 mg/kg/day x 3 days by IM dosing. Two out of four compounds tested for radical curative activity in Rhesus showed cure at 30 mg/kg/day x 3 days. The other two compounds showed delay in relapse from 16 to 68 days. Conversion of new carboxamides (5 and 6) to s-triazine derivatives (7) was demonstrated in mouse and human microsomal preparations and in rat plasma. The results suggest the metabolites, s-triazine derivatives 7, may be the active species of the new carboxamides 5a-c and 6a-c prepared in this study.

In vitro metabolism of phenoxypropoxybiguanide analogues in human liver microsomes to potent antimalarial dihydrotriazines.

Phenoxypropoxybiguanides, such as 1 (PS-15), are prodrugs analogous to the relationship of proguanil and its active metabolite cycloguanil. Unlike cycloguanil, however, 1a (WR99210), the active metabolite of 1, has retained in vitro potency against newly emerging antifolate-resistant malaria parasites. Unfortunately, manufacturing processes and gastrointestinal intolerance have prevented the clinical development of 1. In vitro antimalarial activity and in vitro metabolism studies have been performed on newly synthesized phenoxypropoxybiguanide analogues. All of the active dihydrotriazine metabolites exhibited potent antimalarial activity with in vitro IC(50) values less than 0.04 ng/mL. In vitro metabolism studies in human liver microsomes identified the production of not only the active dihydrotriazine metabolite, but also a desalkylation on the carbonyl chain, and multiple hydroxylated metabolites. The V(max) for production of the active metabolites ranged from 10.8 to 27.7 pmol/min/mg protein with the K(m) ranging from 44.8 to 221 microM. The results of these studies will be used to guide the selection of a lead candidate.

Trace analysis of muramic acid in indoor air using an automated derivatization instrument and GC-MS(2) or GC-MS(3).

An automated derivatization instrument has been developed for the preparation of alditol acetates from bacterial hydrolysates for analysis by gas chromatography-mass spectrometry (GC-MS). The current report demonstrates the utility of the automated instrument for the more demanding task of trace analysis of muramic acid (Mur) in airborne dust using gas chromatography-tandem mass spectrometry (GC-MS(2)). Conditions for efficient derivatization of Mur, vital for trace analysis, are rigorous including lactam and imido group formation under anhydrous conditions. Furthermore, as the detection limit is lowered, possible contamination or carry-over of samples becomes an increasingly greater consideration and must not occur. The instrument meets these criteria and was successfully used for assaying the levels of Mur in laboratory air, which were found to be much lower than in the previous studies of heavily occupied schools and agricultural environments. The potential for GC-MS(3) in further lowering the detection limit was also demonstrated.

Analysis of a stable halogenated derivative of muramic acid by gas chromatography-negative ion chemical ionization tandem mass spectrometry.

Muramic acid (Mur) is present in the cell wall of Eubacteria and serves as a chemical marker for the trace detection of bacteria and bacterial cell wall debris in complex matrices. There have been numerous studies using a variety of derivatives of Mur, particularly in combination with gas chromatography-tandem mass spectrometry (GC-MS-MS) where the detection limit has been steadily lowered. A stable, halogenated derivative, the pentafluorobenzyl oxime (PFBO) acetate of Mur, has been developed by others and successfully used for GC with electron-capture detection. The current report is the first use of this derivative for GC-MS-MS analysis of Mur, or indeed any other carbohydrate, using negative ion chemical ionization (NICI) with GC-MS-MS. Mur was readily detected in settled surface dust (166 ng/mg), as well as dust collected from indoor air (1.4-5.9 ng/mg). Analyses of Mur as a PFBO acetate by GC-NICI-MS-MS or as alditol acetates by electron impact GC-electron impact ionization MS-MS serve as complementary approaches for trace detection in complex matrices.

Causal prophylactic efficacy of primaquine, tafenoquine, and atovaquone-proguanil against Plasmodium cynomolgi in a rhesus monkey model.

Since the 1940s, the large animal model to assess novel causal prophylactic antimalarial agents has been the Plasmodium cynomolgi sporozoite-infected Indian-origin rhesus monkey. In 2009 the model was reassessed with 3 clinical standards: primaquine (PQ), tafenoquine (TQ), and atovaquone-proguanil. Both control monkeys were parasitemic on day 8 post-sporozoite inoculation on day 0. Primaquine at 1.78 mg base/kg/day on days (-1) to 8 protected 1 monkey and delayed parasitemia patency of the other monkey to day 49. Tafenoquine at 6 mg base/kg/day on days (-1) to 1 protected both monkeys. However, atovaquone-proguanil at 10 mg atovaquone/kg/day on days (-1) to 8 did not protect either monkey and delayed patency only to days 18-19. Primaquine and TQ at the employed regimens are proposed as appropriate doses of positive control drugs for the model at present.

Formulation and particle size reduction improve bioavailability of poorly water-soluble compounds with antimalarial activity.

Decoquinate (DQ) is highly effective at killing malaria parasites in vitro; however, it is extremely insoluble in water. In this study, solid dispersion method was used for DQ formulation which created a suitable physical form of DQ in aqueous phase for particle manipulation. Among many polymers and surfactants tested, polyvinylpyrrolidone 10, a polymer, and L- α -phosphatidylcholine or polysorbate, two surfactants, were chosen as DQ formulation components. The formulation particles were reduced to a mean size between 200 to 400 nm, which was stable in aqueous medium for at least three weeks. Pharmacokinetic (PK) studies showed that compared to DQ microparticle suspension, a nanoparticle formulation orally dosed to mice showed a 14.47-fold increase in area under the curve (AUC) of DQ plasma concentration and a 4.53-fold increase in AUC of DQ liver distribution. WR 299666, a poorly water-soluble compound with antimalarial activity, was also tested and successfully made into nanoparticle formulation without undergoing solid dispersion procedure. We concluded that nanoparticles generated by using appropriate formulation components and sufficient particle size reduction significantly increased the bioavailability of DQ and could potentially turn this antimalarial agent to a therapeutic drug.

The elution of colistimethate sodium from polymethylmethacrylate and calcium phosphate cement beads.

Gram-negative bacilli resistance to all antibiotics, except for colistimethate sodium (CMS), is an emerging healthcare concern. Incorporating CMS into orthopedic cement to treat bone and soft-tissue infections due to these bacteria is attractive, but the data regarding the elution of CMS from cement are conflicting. The in vitro analysis of the elution of CMS from polymethylmethacrylate (PMMA) and calcium phosphate (CP) cement beads is reported. PMMA and CP beads containing CMS were incubated in phosphate-buffered saline and the eluate sampled at sequential time points. The inhibition of the growth of a strain of Acinetobacter baumannii complex by the eluate was measured by disk diffusion and microbroth dilution assays, and the presence of CMS in the eluate was measured by mass spectroscopy. Bacterial growth was inhibited by the eluate from both PMMA and CP beads. Mass spectroscopy demonstrated greater elution of CMS from CP beads than PMMA beads. The dose of CMS in PMMA beads was limited by failure of bead integrity. CMS elutes from both CP and PMMA beads in amounts sufficient to inhibit bacterial growth in vitro. The clinical implications of these findings require further study.

Synthesis and antimalarial activity of 2-guanidino-4-oxoimidazoline derivatives.

A series of 2-guanidino-4-oxoimidazoline (deoxo-IZ) derivatives was prepared and showed potent antimalarial activities in rodent and Rhesus models. Compound 8e, the most potent analogues of this series, is the first non-8-aminoqinoline antimalarial that demonstrated radical curative activity in non-human primate by oral route and showed causal prophylactic activity comparable to that of the commonly used clinical drugs in Rhesus monkeys infected with sporozoites of Plasmodium cynomolgi. The metabolic stability and metabolites profile indicated that the new deoxo-IZ derivatives (8) may act as prodrugs of the corresponding IZ (1 and 2) derivatives.

Antimalarial activities of new guanidylimidazole and guanidylimidazoline derivatives.

A series of new guanidylimidazole derivatives was prepared and evaluated in mice and Rhesus monkeys infected with malarial sporozoites. The majority of the new compounds showed poor metabolic stability and weak in vitro activities in three clones of Plasmodium falciparum. Compounds 8a, 8h, 9a, 16a, and 16e cured the mice infected with sporozoites of P. berghei at 160 and 320 mg/kg/day × 3 po. Compounds 8a showed better causal prophylactic activity than primaquine, tafenoquine, and Malarone in the Rhesus test. In the radical curative test, 8a cured one monkey and delayed relapse of another for 74 days at 30 mg/kg/day × 7 by im. By oral dosing, 8a delayed relapse 81 days for one and 32 days for other vs 11-12 days for control monkeys treated with 10 mg/kg of chloroquine by po alone. Compound 8h, which showed superior activity to 8a in mouse test, delayed the relapse of treated monkeys for 21-26 days at 30 mg/kg/day × 7 by oral.

Antimalarial activity of novel 5-aryl-8-aminoquinoline derivatives.

In an attempt to separate the antimalarial activity of tafenoquine (3) from its hemolytic side effects in glucose-6-phosphate dehydrogenase (G6PD) deficiency patients, a series of 5-aryl-8-aminoquinoline derivatives was prepared and assessed for antimalarial activities. The new compounds were found metabolically stable in human and mouse microsomal preparations, with t(1/2) > 60 min, and were equal to or more potent than primaquine (2) and 3 against Plasmodium falciparum cell growth. The new agents were more active against the chloroquine (CQ) resistant clone than to the CQ-sensitive clone. Analogues with electron donating groups showed better activity than those with electron withdrawing substituents. Compounds 4bc, 4bd, and 4be showed comparable therapeutic index (TI) to that of 2 and 3, with TI ranging from 5 to 8 based on IC(50) data. The new compounds showed no significant causal prophylactic activity in mice infected with Plasmodium berghei sporozoites, but are substantially less toxic than 2 and 3 in mouse tests.

Pharmacokinetics, safety, and hydrolysis of oral pyrroloquinazolinediamines administered in single and multiple doses in rats.

Pyrroloquinazolinediamine (PQD) derivatives such as tetra-acetamide PQD (PQD-A4) and bis-ethylcarbamyl PQD (PQD-BE) were much safer (with therapeutic indices of 80 and 32, respectively) than their parent compound, PQD (therapeutic index, 10). Further evaluation of PQD-A4 and PQD-BE in single and multiple pharmacokinetic (PK) studies as well as corresponding toxicity studies was conducted with rats. PQD-A4 could be converted to two intermediate metabolites (monoacetamide PQD and bisacetamide PQD) first and then to the final metabolite, PQD, while PQD-BE was directly hydrolyzed to PQD without precursor and intermediate metabolites. Maximum tolerant doses showed that PQD-A4 and PQD-BE have only 1/12 and 1/6, respectively, of the toxicity of PQD after a single oral dose. Compared to the area under the concentration-time curve for PQD alone (2,965 ng.h/ml), values measured in animals treated with PQD-A4 and PQD-BE were one-third (1,047 ng.h/ml) and one-half (1,381 ng.h/ml) as high, respectively, after an equimolar dosage, suggesting that PQD was the only agent to induce the toxicity. Similar results were also shown in multiple treatments; PQD-A4 and PQD-BE generated two-fifths and three-fifths, respectively, of PQD concentrations, with 8.8-fold and 3.8-fold safety margins, respectively, over the parent drug. PK data indicated that the bioavailability of oral PQD-A4 was greatly limited at high dose levels, that PQD-A4 was slowly converted to PQD via a sequential three-step process of conversion, and that PQD-A4 was significantly less toxic than the one-step hydrolysis drug, PQD-BE. It was concluded that the slow and smaller release of PQD was the main reason for the reduction in toxicity and that the active intermediate metabolites can still maintain antimalarial potency. Therefore, the candidate with multiple-step hydrolysis of PQD could be developed as a safer potential agent for malaria treatment.

Muramic acid is not generally present in the human spleen as determined by gas chromatography-tandem mass spectrometry.

It has been hypothesized that bacterial debris may accumulate in tissues of the reticuloendothelial system (RES) serving as an inflammatory stimulus for human disease. In support of this hypothesis, muramic acid (Mur), a component of bacterial peptidoglycan (PG), has previously been reported to be present in culture-negative human spleen. High-performance liquid chromatography (HPLC) was employed in these analyses, and a peak was detected at the retention time of Mur. However, HPLC is best used as a screening technique, and it is vital that these tentative observations be reexamined by the state-of-the-art approach (gas chromatography-tandem mass spectrometry [GC-MS(2)]). Indeed, in the present work using GC-MS(2), Mur was not detected in six out of seven human spleens previously examined by HPLC. However, Mur was categorically detected at minute concentrations, 50 ppb, in one spleen. In conclusion, since Mur is not generally found in culture-negative human spleen, in future studies, these tissues can serve as negative controls. The study of Mur levels in inflammation (e.g., reactive arthritis) could prove important in testing the hypothesis that bacterial debris persisting in tissues could serve as a depot inciting diseases of unknown etiology.