Antimalarial Dibenzannulated Medium-Ring Keto Lactams

We discovered dibenzannulated medium-ring keto lactams (11,12-dihydro-5H-dibenzo[b,g]azonine-6,13-diones) as a new antimalarial chemotype. Most of these had chromatographic LogD7.4 values ranging from <0 to 3 and good kinetic solubilities (12.5 to >100 μg/mL at pH 6.5). The more polar compounds in the series (LogD7.4 values of <2) had the best metabolic stability (CLint values of <50 μL/min/mg protein in human liver microsomes). Most of the compounds had relatively low cytotoxicity, with IC50 values >30 μM, and there was no correlation between antiplasmodial activity and cytotoxicity. The four most potent compounds had Plasmodium falciparum IC50 values of 4.2 to 9.4 nM and in vitro selectivity indices of 670 to >12,000. They were more than 4 orders-of-magnitude less potent against three other protozoal pathogens (Trypanosoma brucei rhodesiense, Trypanosoma cruzi, and Leishmania donovani) but did have relatively high potency against Toxoplasma gondii, with IC50 values ranging from 80 to 200 nM. These keto lactams are converted into their poorly soluble 4(1H)-quinolone transannular condensation products in vitro in culture medium and in vivo in mouse blood. The similar antiplasmodial potencies of three keto lactam-quinolone pairs suggest that the quinolones likely contribute to the antimalarial activity of the lactams.

Synthesis and antimalarial activity of amide and ester conjugates of siderophores and ozonides

Despite advances in chemotherapeutic interventions for the treatment of malaria, there is a continuing need for the development of new antimalarial agents. Previous studies indicated that co-administration of chloroquine with antioxidants such as the iron chelator deferoxamine (DFO) prevented the development of persistent cognitive damage in surrogate models of cerebral malaria. The work described herein reports the syntheses and antimalarial activities of covalent conjugates of both natural (siderophores) and artificial iron chelators, namely DFO, ferricrocin and ICL-670, with antimalarial 1,2,4-trioxolanes (ozonides). All of the synthesized conjugates had potent antimalarial activities against the in vitro cultures of drug resistant and drug sensitive strains of Plasmodium falciparum. The work described herein provides the basis for future development of covalent combination of iron chelators and antimalarial chemotherapeutic agents for the treatment of cerebral malaria.

In Vitro and In Vivo Antischistosomal Activity Profiling and Pharmacokinetics of Ozonide Carboxylic Acids

Praziquantel, the only drug in clinical use for the treatment and control of schistosomiasis, is inactive against developing infections. Ozonides are synthetic peroxide derivatives inspired by the naturally occurring artemisinin and show particularly promising activity against juvenile schistosomes. We conducted an in-depth characterization of the in vitro and in vivo antischistosomal activity and pharmacokinetics of lead ozonide carboxylic acid OZ418 and four of its active analogs. In vitro, the ozonides featured rapid and consistent activity against schistosomula and adult schistosomes at double-digit micromolar EC50 values. Potency did not vary considerably between Schistosoma spp. The zwitterionic OZ740 and OZ772 were more active in vivo compared to their non-amphoteric carboxylic acids OZ418 and OZ748, despite their much lower systemic plasma exposure (AUC). The most active compound in vivo was ethyl ester OZ780, which was rapidly transformed to its parent zwitterion OZ740 and achieved ED50 values of 35 ± 2.4 and 29 ± 2.4 mg/kg against adult and juvenile Schistosoma mansoni, respectively. Ozonide carboxylic acids represent promising candidates for further optimization and development due to their good efficacy against both life stages together with their broad activity range against all relevant parasite species.

Metabolic, Pharmacokinetic, and Activity Profile of the Liver Stage Antimalarial (RC-12)

The catechol derivative RC-12 (WR 27653) (1) is one of the few non-8-aminoquinolines with good activity against hypnozoites in the gold-standard Plasmodium cynomolgi-rhesus monkey (Macaca mulatta) model, but in a small clinical trial, it had no efficacy against Plasmodium vivax hypnozoites. In an attempt to better understand the pharmacokinetic and pharmacodynamic profile of 1 and to identify potential active metabolites, we now describe the phase I metabolism, rat pharmacokinetics, and in vitro liver-stage activity of 1 and its metabolites. Compound 1 had a distinct metabolic profile in human vs monkey liver microsomes, and the data suggested that the O-desmethyl, combined O-desmethyl/N-desethyl, and N,N-didesethyl metabolites (or a combination thereof) could potentially account for the superior liver stage antimalarial efficacy of 1 in rhesus monkeys vs that seen in humans. Indeed, the rate of metabolism was considerably lower in human liver microsomes in comparison to rhesus monkey microsomes, as was the formation of the combined O-desmethyl/N-desethyl metabolite, which was the only metabolite tested that had any activity against liver-stage P. vivax; however, it was not consistently active against liver-stage P. cynomolgi. As 1 and all but one of its identified Phase I metabolites had no in vitro activity against P. vivax or P. cynomolgi liver-stage malaria parasites, we suggest that there may be additional unidentified active metabolites of 1 or that the exposure of 1 achieved in the reported unsuccessful clinical trial of this drug candidate was insufficient to kill the P. vivax hypnozoites.

Antischistosomal tetrahydro-γ-carboline sulfonamides

We discovered tetrahydro-γ-carboline sulfonamides as a new antischistosomal chemotype. The aryl sulfonamide and tetrahydro-γ-carboline substructures were required for high antischistosomal activity. Increasing polarity improved solubility and metabolic stability but decreased antischistosomal activity. We identified two compounds with IC₅₀ values <5 µM against ex vivo Schistosoma mansoni.

Therapeutic efficacy of antimalarial drugs targeting DosRS signaling in Mycobacterium abscessus

A search for alternative Mycobacterium abscessus treatments led to our interest in the two-component regulator DosRS, which, in Mycobacterium tuberculosis, is required for the bacterium to establish a state of nonreplicating, drug-tolerant persistence in response to a variety of host stresses. We show here that the genetic disruption of dosRS impairs the adaptation of M. abscessus to hypoxia, resulting in decreased bacterial survival after oxygen depletion, reduced tolerance to a number of antibiotics in vitro and in vivo, and the inhibition of biofilm formation. We determined that three antimalarial drugs or drug candidates, artemisinin, OZ277, and OZ439, can target DosS-mediated hypoxic signaling in M. abscessus and recapitulate the phenotypic effects of genetically disrupting dosS. OZ439 displayed bactericidal activity comparable to standard-of-care antibiotics in chronically infected mice, in addition to potentiating the activity of antibiotics used in combination. The identification of antimalarial drugs as potent inhibitors and adjunct inhibitors of M. abscessus in vivo offers repurposing opportunities that could have an immediate impact in the clinic.

Peroxide Antimalarial Drugs Target Redox Homeostasis in Plasmodium falciparum Infected Red Blood Cells

Plasmodium falciparum causes the most lethal form of malaria. Peroxide antimalarials based on artemisinin underpin the frontline treatments for malaria, but artemisinin resistance is rapidly spreading. Synthetic peroxide antimalarials, known as ozonides, are in clinical development and offer a potential alternative. Here, we used chemoproteomics to investigate the protein alkylation targets of artemisinin and ozonide probes, including an analogue of the ozonide clinical candidate, artefenomel. We greatly expanded the list of proteins alkylated by peroxide antimalarials and identified significant enrichment of redox-related proteins for both artemisinins and ozonides. Disrupted redox homeostasis was confirmed by dynamic live imaging of the glutathione redox potential using a genetically encoded redox-sensitive fluorescence-based biosensor. Targeted liquid chromatography-mass spectrometry (LC-MS)-based thiol metabolomics also confirmed changes in cellular thiol levels. This work shows that peroxide antimalarials disproportionately alkylate proteins involved in redox homeostasis and that disrupted redox processes are involved in the mechanism of action of these important antimalarials.

Cytochrome P450-Mediated Metabolism and CYP Inhibition for the Synthetic Peroxide Antimalarial OZ439

OZ439 is a potent synthetic ozonide evaluated for the treatment of uncomplicated malaria. The metabolite profile of OZ439 was characterized in vitro using human liver microsomes combined with LC/MS-MS, chemical derivatization, and metabolite synthesis. The primary biotransformations were monohydroxylation at the three distal carbon atoms of the spiroadamantane substructure, with minor contributions from N-oxidation of the morpholine nitrogen and deethylation cleavage of the morpholine ring. Secondary transformations resulted in the formation of dihydroxylation metabolites and metabolites containing both monohydroxylation and morpholine N-oxidation. With the exception of two minor metabolites, none of the other metabolites had appreciable antimalarial activity. Reaction phenotyping indicated that CYP3A4 is the enzyme responsible for the metabolism of OZ439, and it was found to inhibit CYP3A via both direct and mechanism-based inhibition. Elucidation of the metabolic pathways and kinetics will assist with efforts to predict potential metabolic drug-drug interactions and support physiologically based pharmacokinetic (PBPK) modeling.

Efficacy, metabolism and pharmacokinetics of Ro 15-5458, a forgotten schistosomicidal 9-acridanone hydrazone

BACKGROUND

Treatment of schistosomiasis, a neglected disease, relies on just one partially effective drug, praziquantel. We revisited the 9-acridanone hydrazone, Ro 15-5458, a largely forgotten antischistosomal lead compound.

METHODS

Ro 15-5458 was evaluated in juvenile and adult Schistosoma mansoni-infected mice. We studied dose-response, hepatic shift and stage specificity. The metabolic stability of Ro 15-5458 was measured in the presence of human and mouse liver microsomes, and human hepatocytes; the latter also served to identify metabolites. Pharmacokinetic parameters were measured in naive mice. The efficacy of Ro 15-5458 was also assessed in S. haematobium-infected hamsters and S. japonicum-infected mice.

RESULTS

Ro 15-5458 had single-dose ED50 values of 15 and 5.3 mg/kg in mice harbouring juvenile and adult S. mansoni infections, respectively. An ED50 value of 17 mg/kg was measured in S. haematobium-infected hamsters; however, the compound was inactive at up to 100 mg/kg in S. japonicum-infected mice. The drug-induced hepatic shift occurred between 48 and 66 h post treatment. A single oral dose of 50 mg/kg of Ro 15-5458 had high activity against all tested S. mansoni stages (1-, 7-, 14-, 21- and 49-day-old). In vitro, human hepatocytes produced N-desethyl and glucuronide metabolites; otherwise Ro 15-5458 was metabolically stable in the presence of microsomes or whole hepatocytes. The maximum plasma concentration was approximately 8.13 μg/mL 3 h after a 50 mg/kg oral dose and the half-life was approximately 4.9 h.

CONCLUSIONS

Ro 15-5458 has high activity against S. mansoni and S. haematobium, yet lacks activity against S. japonicum, which is striking. This will require further investigation, as a broad-spectrum antischistosomal drug is desirable.

Diaryl Ureas as an Antiprotozoal Chemotype

We now describe the physicochemical profiling, in vitro ADME, and antiparasitic activity of eight N,N'-diarylureas to assess their potential as a broad-spectrum antiprotozoal chemotype. Chromatographic LogD_7.4 values ranged from 2.5 to 4.5; kinetic aq. solubilities were ≤6.3 μg/mL, and plasma protein binding ranged from 95 to 99%. All of the compounds had low intrinsic clearance values in human, but not mouse, liver microsomes. Although no N,N'-diarylurea had submicromolar potency against Trypanosoma cruzi, two had submicromolar potencies against Toxoplasma gondii and Trypanosoma brucei rhodesiense, and five had submicromolar potencies against Leishmania donovani. Plasmodium falciparum appeared to be the most susceptible to growth inhibition by this compound series. Most of the N,N'-diarylureas had antiprotozoal selectivities ≥10. One N,N'-diarylurea had demonstrable activity in mouse models of malaria and toxoplasmosis.

Targeted Amino Acid Substitution Overcomes Scale-Up Challenges with the Human C5a-Derived Decapeptide Immunostimulant EP67

EP67 is a second-generation, human C5a-derived decapeptide agonist of C5a receptor 1 (C5aR1/CD88) that selectively activates mononuclear phagocytes over neutrophils to potentiate protective innate and adaptive immune responses while potentially minimizing neutrophil-mediated toxicity. Pro7 and N-methyl-Leu8 (Me-Leu8) amino acid residues within EP67 likely induce backbone structural changes that increase potency and selective activation of mononuclear phagocytes over neutrophils versus first-generation EP54. The low coupling efficiency between Pro7 and Me-Leu8 and challenging purification by HPLC, however, greatly increase scale-up costs of EP67 for clinical use. Thus, the goal of this study was to determine whether replacing Pro7 and/or Me-Leu8 with large-scale amenable amino acid residues predicted to induce similar structural changes (cyclohexylalanine7 and/or leucine8) sufficiently preserves EP67 activity in primary human mononuclear phagocytes and neutrophils. We found that EP67 analogues had similar potency, efficacy, and selective activation of mononuclear phagocytes over neutrophils. Thus, replacing Pro7 and/or Me-Leu8 with large-scale amenable amino acid residues predicted to induce similar structural changes is a suitable strategy to overcome scale-up challenges with EP67.

Structure-Activity Relationship of Antischistosomal Ozonide Carboxylic Acids

Semisynthetic artemisinins and other bioactive peroxides are best known for their powerful antimalarial activities, and they also show substantial activity against schistosomes-another hemoglobin-degrading pathogen. Building on this discovery, we now describe the initial structure-activity relationship (SAR) of antischistosomal ozonide carboxylic acids OZ418 (2) and OZ165 (3). Irrespective of lipophilicity, these ozonide weak acids have relatively low aqueous solubilities and high protein binding values. Ozonides with para-substituted carboxymethoxy and N-benzylglycine substituents had high antischistosomal efficacies. It was possible to increase solubility, decrease protein binding, and maintain the high antischistosomal activity in mice infected with juvenile and adult Schistosoma mansoni by incorporating a weak base functional group in these compounds. In some cases, adding polar functional groups and heteroatoms to the spiroadamantane substructure increased the solubility and metabolic stability, but in all cases decreased the antischistosomal activity.

Tricyclic Imidazolidin-4-ones by Witkop Oxidation of Tetrahydro-β-carbolines

1-Substituted and 1,1-disubstituted tetrahydro-β-carbolines undergo sodium periodate oxidative ring expansion in the presence of formaldehyde and other aldehydes to form 5,6-dihydro-7H-1,4-methanobenzo[e][1,4]diazonine-2,7(3H)-diones in 30-81% yield. In most cases, the reaction to form this new 6/8/5-tricyclic ring system proceeds with high diastereoselectivity. These benzannulated medium-ring keto imidazolidin-4-ones expand the menu of tetrahydro-β-carboline oxidation products.

Ligand-based design of GLUT inhibitors as potential antitumor agents

Glucose transporters (GLUTs) regulate glucose uptake and are often overexpressed in several human tumors. To identify new chemotypes targeting GLUT1, we built a pharmacophore model and searched against a NCI compound database. Sixteen hit molecules with good docking scores were screened for GLUT1 inhibition and antiproliferative activities. From these, we identified that compounds 2, 5, 6 and 13 inhibited the cell viability in a dose-dependent manner and that the IC₅₀s of 2 and 6 are<10 µM concentration in the HCT116 colon cancer cell line. Lead compound 13 (NSC295720) was a GLUT1 inhibitor. Docking studies show that GLUT1 residues Phe291, Phe379, Glu380, Trp388, and Trp412 were important for inhibitor binding.

A new chemotype with promise against Trypanosoma cruzi

Pyridyl benzamide 2 is a potent inhibitor of Trypanosoma cruzi, but not other protozoan parasites, and had a selectivity-index of ≥10. The initial structure-activity relationship (SAR) indicates that benzamide and sulfonamide functional groups, and N-methylpiperazine and sterically unhindered 3-pyridyl substructures are required for high activity against T. cruzi. Compound 2 and its active analogs had low to moderate metabolic stabilities in human and mouse liver microsomes.

Ozonide Antimalarials Alkylate Heme in the Malaria Parasite Plasmodium falciparum

The mechanism of action of ozonide antimalarials involves activation by intraparasitic iron and the formation of highly reactive carbon-centered radicals that alkylate malaria parasite proteins. Given free intraparasitic heme is generally thought to be the iron source responsible for ozonide activation and its likely close proximity to the activated drug, we investigated heme as a possible molecular target of the ozonides. Using an extraction method optimized for solubilization of free heme, untargeted LC-MS analysis of ozonide-treated parasites identified several regioisomers of ozonide-alkylated heme, which resulted from covalent modification of the heme porphyrin ring by an ozonide-derived carbon-centered radical. In addition to the intact alkylated heme adduct, putative ozonide-alkylated heme degradation products were also detected. This study directly demonstrates ozonide modification of heme within the malaria parasite Plasmodium falciparum, revealing that this process may be important for the biological activity of ozonide antimalarials.

Stochastic Protein Alkylation by Antimalarial Peroxides

Antimalarial peroxides such as the phytochemical artemisinin or the synthetic ozonides arterolane and artefenomel undergo reductive cleavage of the pharmacophoric peroxide bond by ferrous heme, released by parasite hemoglobin digestion. The generated carbon-centered radicals alkylate heme in an intramolecular reaction and proteins in an intermolecular reaction. Here, we determine the proteinaceous alkylation signatures of artemisinin and synthetic ozonides in Plasmodium falciparum using alkyne click chemistry probes to identify target proteins by affinity purification and mass spectrometry-based proteomics. Using stringent controls and purification procedures, we identified 25 P. falciparum proteins that were alkylated by the antimalarial peroxides in a peroxide-dependent manner, but the alkylation patterns were more random than we had anticipated. Moreover, there was little overlap in the alkylation signatures identified in this work and those disclosed in previous studies. Our findings suggest that alkylation of parasite proteins by antimalarial peroxides is likely to be a nonspecific, stochastic process.

SAR of a new antischistosomal urea carboxylic acid

Urea carboxylic acids, products of aryl hydantoin hydrolysis, were recently identified as a new antischistosomal chemotype. We now describe a baseline structure-activity relationship (SAR) for this compound series. With one exception, analogs of lead urea carboxylic acid 2 were quite polar with Log D_7.4 values ranging from -1.9 to 1.8, had high aqueous solubilities in the range of 25-100 µg/mL, and were metabolically stable. None of the compounds had measurable in vitro antischistosomal activity or cytotoxicity, but four of these had moderate worm burden reduction (WBR) values of 42-70% when they were administered as single 100 mg/kg oral doses to S. mansoni-infected mice. These data indicate that with the exception of the gem-dimethyl substructure and the distal nitrogen atom of the urea functional group, the rest of the structure of 2 is required for in vivo antischistosomal activity.

Synthesis of 2-Azaadamantan-6-one: A Missing Isomer

2-Azaadamantan-6-one and its Boc and ethylene ketal derivatives were synthesized from 9-oxo endo-bicyclo[3.3.1]non-6-ene-3-carboxylic acid. Similarly, the Cbz, Boc, and ethylene ketal derivatives of 2-azaadamantan-4-one were synthesized from endo-bicyclo[3.3.1]non-6-ene-3-carboxylic acid. Key steps were Curtius rearrangements to form benzyl carbamates, followed by spontaneous intramolecular attack of the carbamate nitrogen on transient bromonium ion or epoxide intermediates to effect ring closure to azaadamantane intermediates. The reaction sequence leading to 2-azaadamantan-6-one is consistent with the formation of a transient tetracyclic keto aziridine intermediate.

Absolute Oral Bioavailability of Creatine Monohydrate in Rats: Debunking a Myth

Creatine is an ergogenic compound used by athletes to enhance performance. Supplementation with creatine monohydrate (CM) has been suggested for musculoskeletal and neurological disorders. Until now, little is known about its pharmacokinetic profile. Our objective was to determine the oral bioavailability of CM and the influence of dose on oral absorption. Rats were dosed orally with low dose (10 mg/kg) or high dose (70 mg/kg) 13C-labeled CM. Blood samples were removed at various time points. Muscle and brain tissue were collected at the conclusion of the study. Plasma and tissue levels of 13C-labeled creatine were determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Physiologically based pharmacokinetic (PBPK) models of CM were built using GastroPlus™. These models were used to predict the plasma concentration-time profiles of creatine hydrochloride (CHCL), which has improved aqueous solubility compared to CM. Absolute oral bioavailability for low dose CM was 53% while high dose CM was only 16%. The simulated Cmax of 70 mg/kg CHCL was around 35 μg/mL compared to 14 μg/mL for CM with a predicted oral bioavailability of 66% with CHCL compared to 17% with CM. Our results suggest that the oral bioavailability of CM is less than complete and subject to dose and that further examination of improved dosage formulations of creatine is warranted.

Formation of 2-Imino Benzo[e]-1,3-oxazin-4-ones from Reactions of Salicylic Acids and Anilines with HATU: Mechanistic and Synthetic Studies

We describe a new 1-[Bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide hexafluorophosphate (HATU)-mediated coupling reaction to produce 2-imino benzo[e]-1,3-oxazin-4-ones from salicylic acids and anilines. Mechanistic studies support a reaction pathway in which HATU mediates carbon transfer to the initially formed salicylanilides to form in succession reactive tetramethylisouronium and N-acyl(dimethyl)isouronium intermediates, which then undergo imine-iminium exchange to generate the desired oxazinones.

Novel Toxoplasma gondii inhibitor chemotypes

We profiled three novel T. gondii inhibitors identified from an antimalarial phenotypic high throughput screen (HTS) campaign: styryl 4-oxo-1,3-benzoxazin-4-one KG3, tetrahydrobenzo[b]pyran KG7, and benzoquinone hydrazone KG8. These compounds inhibit T. gondii in vitro with IC₅₀ values ranging from 0.3 to 2μM, comparable to that of 0.25 to 1.5μM for the control drug pyrimethamine. KG3 had no measurable cytotoxicity against five mammalian cell lines, whereas KG7 and KG8 inhibited the growth of 2 of 5 cell lines with KG8 being the least selective for T. gondii. None of the compounds were mutagenic in an Ames assay. Experimental gLogD_7.4 and calculated PSA values for the three compounds were well within the ranges predicted to be favorable for good ADME, even though each compound had relatively low aqueous solubility. All three compounds were metabolically unstable, especially KG3 and KG7. Multiple IP doses of 5mg/kg KG7 and KG8 increased survival in a T. gondii mouse model. Despite their liabilities, we suggest that these compounds are useful starting points for chemical prospecting, scaffold-hopping, and optimization.

Progress in antischistosomal N,N'-diaryl urea SAR

N,N'-Diaryl ureas have recently emerged as a new antischistosomal chemotype. We now describe physicochemical profiling, in vitro ADME, plasma exposure, and ex vivo and in vivo activities against Schistosoma mansoni for twenty new N,N'-diaryl ureas designed primarily to increase aqueous solubility, but also to maximize structural diversity. Replacement of one of the 4-fluoro-3-trifluoromethylphenyl substructures of lead N,N'-diaryl urea 1 with azaheterocycles and benzoic acids, benzamides, or benzonitriles decreased lipophilicity, and in most cases, increased aqueous solubility. There was no clear relationship between lipophilicity and metabolic stability, although all compounds with 3-trifluoromethyl-4-pyridyl substructures were metabolically stable. N,N'-diaryl ureas containing 4-fluoro-3-trifluoromethylphenyl, 3-trifluoromethyl-4-pyridyl, 2,2-difluorobenzodioxole, or 4-benzonitrile substructures had high activity against ex vivo S. mansoni and relatively low cytotoxicity. N,N-diaryl ureas with 3-trifluoromethyl-4-pyridyl and 2,2-difluorobenzodioxole substructures had the highest exposures whereas those with 4-fluoro-3-trifluoromethylphenyl substructures had the best in vivo antischistosomal activities. There was no direct correlation between compound exposure and in vivo activity.

One-Pot, Metal-Free Conversion of Anilines to Aryl Bromides and Iodides

A metal-free synthesis of aryl bromides and iodides from anilines via halogen abstraction from bromotrichloromethane and diiodomethane is described. This one-pot reaction affords aryl halides from the corresponding anilines in moderate to excellent yields without isolation of diazonium salts. The transformation has short reaction times, a simple workup, and insensitivity to moisture and air and avoids excess halogenation. DFT calculations support a S_RN1 mechanism. This method represents a convenient alternative to the classic Sandmeyer reaction.

Revisiting the SAR of the Antischistosomal Aryl Hydantoin (Ro 13-3978)

The aryl hydantoin 1 (Ro 13-3978) was identified in the early 1980s as a promising antischistosomal lead compound. However, this series of aryl hydantoins produced antiandrogenic side effects in the host, a not unexpected outcome given their close structural similarity to the antiandrogenic drug nilutamide. Building on the known SAR of this compound series, we now describe a number of analogs of 1 designed to maximize structural diversity guided by incorporation of substructures and functional groups known to diminish ligand–androgen receptor interactions. These analogs had calculated polar surface area (PSA), measured LogD_7.4, aqueous kinetic solubility, and estimated plasma protein binding values in ranges predictive of good ADME profiles. The principal SAR insight was that the hydantoin core of 1 is required for high antischistosomal activity. We identified several compounds with high antischistosomal efficacy that were less antiandrogenic than 1. These data provide direction for the ongoing optimization of antischistosomal hydantoins.

Treatment of a chemoresistant neuroblastoma cell line with the antimalarial ozonide OZ513

BACKGROUND

Evaluate the anti-tumor activity of ozonide antimalarials using a chemoresistant neuroblastoma cell line, BE (2)-c.

METHODS

The activity of 12 ozonides, artemisinin, and two semisynthetic artemisinins were tested for activity against two neuroblastoma cell-lines (BE (2)-c and IMR-32) and the Ewing's Sarcoma cell line A673 in an MTT viability assay. Time course data indicated that peak effect was seen 18 h after the start of treatment thus 18 h pre-treatment was used for all subsequent experiments. The most active ozonide (OZ513) was assessed in a propidium iodide cell cycle flow cytometry analysis which measured cell cycle transit and apoptosis. Metabolic effects of OZ513 in BE (2)-c cells was evaluated. Western blots for the apoptotic proteins cleaved capase-3 and cleaved PARP, the highly amplified oncogene MYCN, and the cell cycle regulator CyclinD1, were performed. These in-vitro experiments were followed by an in-vivo experiment in which NOD-scid gamma immunodeficient mice were injected subcutaneously with 1 × 10⁶ BE (2)-c cells followed by immediate treatment with 50-100 mg/kg/day doses of OZ513 administered IP three times per week out to 23 days after injection of tumor. Incidence of tumor development, time to tumor development, and rate of tumor growth were assessed in DMSO treated controls (N = 6), and OZ513 treated mice (N = 5).

RESULTS

It was confirmed that five commonly used chemotherapy drugs had no cytotoxic activity in BE (2)-c cells. Six of 12 ozonides tested were active in-vitro at concentrations achievable in vivo with OZ513 being most active (IC50 = 0.5 mcg/ml). OZ513 activity was confirmed in IMR-32 and A673 cells. The Ao peak on cell-cycle analysis was increased after treatment with OZ513 in a concentration dependent fashion which when coupled with results from western blot analysis which showed an increase in cleaved capase-3 and cleaved PARP supported an increase in apoptosis. There was a concentration dependent decline in the MYCN and a cyclinD1 protein indicative of anti-proliferative activity and cell cycle disruption. OXPHOS metabolism was unaffected by OZ513 treatment while glycolysis was increased. There was a significant delay in time to tumor development in mice treated with OZ513 and a decline in the rate of tumor growth.

CONCLUSIONS

The antimalarial ozonide OZ513 has effective in-vitro and in-vivo activity against a pleiotropic drug resistant neuroblastoma cell-line. Treatment with OZ513 increased apoptotic markers and glycolysis with a decline in the MYCN oncogene and the cell cycle regulator cyclinD1. These effects suggest adaptation to cellular stress by mechanism which remain unclear.

Monoclonal Antibodies That Recognize the Alkylation Signature of Antimalarial Ozonides OZ277 (Arterolane) and OZ439 (Artefenomel)

The singular structure of artemisinin, with its embedded 1,2,4-trioxane heterocycle, has inspired the discovery of numerous semisynthetic artemisinin and structurally diverse synthetic peroxide antimalarials, including ozonides OZ277 (arterolane) and OZ439 (artefenomel). Despite the critical importance of artemisinin combination therapies (ACTs), the precise mode of action of peroxidic antimalarials is not fully understood. However, it has long been proposed that the peroxide bond in artemisinin and other antimalarial peroxides undergoes reductive activation by ferrous heme released during hemoglobin digestion to produce carbon-centered radicals that alkylate heme and parasite proteins. To probe the mode of action of OZ277 and OZ439, this paper now describes initial studies with monoclonal antibodies that recognize the alkylation signature (sum of heme and protein alkylation) of these synthetic peroxides. Immunofluorescence experiments conducted with ozonide-treated parasite cultures showed that ozonide alkylation is restricted to the parasite, as no signal was found in the erythrocyte or its membrane. In Western blot experiments with ozonide-treated Plasmodium falciparum malaria parasites, distinct protein bands were observed. Significantly, no protein bands were detected in parallel Western blot experiments performed with lysates from ozonide-treated Babesia divergens, parasites that also proliferate inside erythrocytes but, in contrast to P. falciparum, do not catabolize hemoglobin. However, subsequent immunoprecipitation experiments with these antibodies failed to identify the P. falciparum proteins alkylated by OZ277 and OZ439. To the best of the authors’ knowledge, this shows for the first time that antimalarial ozonides, such as the artemisinins, alkylate proteins in P. falciparum.

Antiprotozoal Selectivity of Diimidazoline N-Phenylbenzamides

We discovered three diimidazolines with high antiplasmodial selectivity that had IC50 values of 1.9-28 nM against cultured Plasmodium falciparum. We also identified a gem-dimethyl diimidazoline with high antitrypanosomal selectivity that had an IC50 value of 26 nM against cultured Trypanosoma brucei rhodesiense. Two 2-imidazoline heterocycles in a para orientation on a N-phenylbenzamide or similar core structure were required for high antiprotozoal activity. Ring expansion of the imidazoline as well as heterocyclic variants with pKa values of <7 all decreased activity significantly.

Aryl hydantoin Ro 13-3978, a broad-spectrum antischistosomal

OBJECTIVES

Praziquantel is the only drug available for the treatment of schistosomiasis and the state of the exhausted drug discovery pipeline is alarming. We restarted investigations on the abandoned antischistosomal Ro 13-3978, an aryl hydantoin discovered in the early 1980s by Hoffmann La-Roche.

METHODS

Newly transformed schistosomula and adult Schistosoma mansoni were studied in the presence of Ro 13-3978 in vitro. The metabolic stability of Ro 13-3978 was determined in vitro using human and mouse liver S9 fractions. Dose-response relationship, stage specificity, hepatic shift and scanning electron microscopy studies were carried out in S. mansoni-infected mice. In addition, efficacy experiments were conducted in rodents infected with Echinostoma caproni and Fasciola hepatica as well as in S. mansoni-infected immunocompromised nude (Foxn1(nu)) mice.

RESULTS

Ro 13-3978 showed minor in vitro activity and no damage to the tegument was found. No cytotoxicity was detected for Ro 13-3978. Ro 13-3978 was metabolically stable. ED50 values of 138.9 and 14.6 mg/kg were calculated for the treatment of juvenile and adult S. mansoni infections, respectively, with a single oral dose of Ro 13-3978. SEM studies revealed severe damage to the worms 48 h post-treatment of infected mice. A single oral dose of Ro 13-3978 (100 mg/kg) administered to S. mansoni-infected (Foxn1(nu)) mice reduced the worm burden by 88%. Ro 13-3978 was not active against E. caproni and F. hepatica in vivo.

CONCLUSIONS

Ro 13-3978 has excellent antischistosomal properties in vivo. Structure-activity relationship studies with the aryl hydantoins have been launched in order to elucidate active pharmacophores, further investigate the mechanism of action and to identify a derivative with minimal antiandrogenic effects.

Tetrasubstituted pyrazinones derived from the reaction of praziquantel with N-bromosuccinimide

When praziquantel was exposed to N-bromosuccinimide in the presence of ethanol, a tricyclic 3-bromo-1-ethoxy pyrazinone was formed. From this and the analogous 1,3-dibromopyrazinone, a small library of 3-alkylamino-1-ethoxy, 1,3-dialkoxy, 3-alkoxy-1-bromo, and 3-alkylamino-1-bromo substituted pyrazinones were synthesized in high yields.

Antischistosomal versus antiandrogenic properties of aryl hydantoin Ro 13-3978

In the early 1980s, the antischistosomal aryl hydantoin Ro 13-3978 (AH01), a close structural analogue of the androgen receptor antagonist nilutamide, was discovered. Administration of 100 mg/kg oral doses of AH01 to mice infected with adult and juvenile Schistosoma mansoni produced 95% and 64% total worm burden reductions, confirming its high activity against adult worms, and showing that AH01 is also effective against juvenile infections. AH01 had no measureable interaction with the androgen receptor in a ligand competition assay, but it did block dihydrotestosterone-induced cell proliferation in an androgen-dependent human prostate cancer cell line. For AH01, nilutamide, and three closely related aryl hydantoin derivatives, there was no correlation between antischistosomal activity and androgen receptor interaction.

pH-dependent stability of creatine ethyl ester: relevance to oral absorption

Creatine ethyl ester hydrochloride (CEE) was synthesized as a prodrug of creatine (CRT) to improve aqueous solubility, gastrointestinal permeability, and ultimately the pharmacodynamics of CRT. We used high-performance liquid chromatography (HPLC) and proton nuclear magnetic resonance (NMR) to characterize the pH-dependent stability of CEE in aqueous solution and compared the permeability of CEE to CRT and creatinine (CRN) across Caco-2 human epithelial cell monolayers and transdermal permeability across porcine skin. CEE was most stable in a strongly acidic condition (half-life = 570 hours at pH 1.0) where it undergoes ester hydrolysis to CRT and ethanol. At pH ≥ 1.0, CEE cyclizes to CRN with the logarithm of the first order rate constant increasing linearly with pH. Above pH 8.0 (half-life = 23 sec) the rate of degradation was too rapid to be determined. The rate of degradation of CEE in cell culture media and simulated intestinal fluid (SIF) was a function of pH and correlated well with the stability in aqueous buffered solutions. The permeability of CEE across Caco-2 monolayers and porcine skin was significantly greater than that of CRT or CRN. The stability of CEE in acidic media together with its improved permeability suggests that CEE has potential for improved oral absorption compared to CRT.

Activity of diimidazoline amides against African trypanosomiasis

We identified several diimidazoline mono- and diamides that were as potent as pentamidine against Trypanosoma brucei rhodesiense in vitro. All of these were also less cytotoxic than pentamidine, but none was as effective as the latter in a T. brucei rhodesiense-infected mouse model. A single imidazoline may be sufficient for high antitrypanosomal activity provided that a second weak base functional group is present.

Anticancer properties of distinct antimalarial drug classes

We have tested five distinct classes of established and experimental antimalarial drugs for their anticancer potential, using a panel of 91 human cancer lines. Three classes of drugs: artemisinins, synthetic peroxides and DHFR (dihydrofolate reductase) inhibitors effected potent inhibition of proliferation with IC50s in the nM- low µM range, whereas a DHODH (dihydroorotate dehydrogenase) and a putative kinase inhibitor displayed no activity. Furthermore, significant synergies were identified with erlotinib, imatinib, cisplatin, dasatinib and vincristine. Cluster analysis of the antimalarials based on their differential inhibition of the various cancer lines clearly segregated the synthetic peroxides OZ277 and OZ439 from the artemisinin cluster that included artesunate, dihydroartemisinin and artemisone, and from the DHFR inhibitors pyrimethamine and P218 (a parasite DHFR inhibitor), emphasizing their shared mode of action. In order to further understand the basis of the selectivity of these compounds against different cancers, microarray-based gene expression data for 85 of the used cell lines were generated. For each compound, distinct sets of genes were identified whose expression significantly correlated with compound sensitivity. Several of the antimalarials tested in this study have well-established and excellent safety profiles with a plasma exposure, when conservatively used in malaria, that is well above the IC50s that we identified in this study. Given their unique mode of action and potential for unique synergies with established anticancer drugs, our results provide a strong basis to further explore the potential application of these compounds in cancer in pre-clinical or and clinical settings.

Mechanisms ofin situactivation for peroxidic antimalarials

This review describes mechanisms of action of artemisinin-related antimalarials, emphasizing the site and target of activation, pathways of generating reactive species, and possible targets of free radicals with implications for antimalarial peroxide drug design. It also presents a useful link between the mode of action of artemisinin and that of chloroquine, and highlights redox cycles involved in the interaction between the drug and vital biomolecules.

First-in-man safety and pharmacokinetics of synthetic ozonide OZ439 demonstrates an improved exposure profile relative to other peroxide antimalarials

Aims

To assess the safety and pharmacokinetics of a new synthetic ozonide antimalarial, OZ439, in a first-in-man, double-blind study in healthy volunteers.

Methods

OZ439 was administered as single oral daily doses of a capsule formulation (50–1200 mg) or an oral dispersion (400–1600 mg, fed and fasted states) and for up to 3 days as an oral dispersion (200–800 mg day⁻¹). Plasma concentrations of OZ439 and its metabolites were measured by LC-MS.

Results

The pharmacokinetic (PK) profile of OZ439 was characterized by a t_max of around 3 h, followed by a multiphasic profile with a terminal half-life of 25–30 h. The PK parameters were approximately dose proportional for each group and profiles of the metabolites followed a similar pattern to that of the parent compound. Following dosing for 3 days, accumulation was less than two-fold but steady-state was not achieved. In the presence of food, no effect was observed on the t_1/2 of OZ439 while the exposure was increased by 3 to 4.5-fold. Exposure was higher and inter-subject variability was reduced when OZ439 was administered as an oral dispersion compared with a capsule. The urinary clearance of OZ439 and its metabolites was found to be negligible and OZ439 did not induce CYP3A4. The antimalarial activity profiles of a subset of serum samples suggested that the major antimalarial activity originated from OZ439 rather than from any of the metabolites.

Conclusion

The safety and pharmacokinetic profile of OZ439 merits progression to phase 2a proof of concept studies in the target population of acute uncomplicated malaria.

Comparative antimalarial activities and ADME profiles of ozonides (1,2,4-trioxolanes) OZ277, OZ439, and their 1,2-dioxolane, 1,2,4-trioxane, and 1,2,4,5-tetraoxane isosteres

To ascertain the structure-activity relationship of the core 1,2,4-trioxolane substructure of dispiro ozonides OZ277 and OZ439, we compared the antimalarial activities and ADME profiles of the 1,2-dioxolane, 1,2,4-trioxane, and 1,2,4,5-tetraoxane isosteres. Consistent with previous data, both dioxolanes had very weak antimalarial properties. For the OZ277 series, the trioxane isostere had the best ADME profile, but its overall antimalarial efficacy was not superior to that of the trioxolane or tetraoxane isosteres. For the OZ439 series, there was a good correlation between the antimalarial efficacy and ADME profiles in the rank order trioxolane > trioxane > tetraoxane. As we have previously observed for OZ439 versus OZ277, the OZ439 series peroxides had superior exposure and efficacy in mice compared to the corresponding OZ277 series peroxides.

Artemisinin-resistant malaria: research challenges, opportunities, and public health implications

Artemisinin-based combination therapies are the most effective drugs to treat Plasmodium falciparum malaria. Reduced sensitivity to artemisinin monotherapy, coupled with the emergence of parasite resistance to all partner drugs, threaten to place millions of patients at risk of inadequate treatment of malaria. Recognizing the significance and immediacy of this possibility, the Fogarty International Center and the National Institute of Allergy and Infectious Diseases of the U.S. National Institutes of Health convened a conference in November 2010 to bring together the diverse array of stakeholders responding to the growing threat of artemisinin resistance, including scientists from malarious countries in peril. This conference encouraged and enabled experts to share their recent unpublished data from studies that may improve our understanding of artemisinin resistance. Conference sessions addressed research priorities to forestall artemisinin resistance and fostered collaborations between field- and laboratory-based researchers and international programs, with the aim of translating new scientific evidence into public health solutions. Inspired by this conference, this review summarizes novel findings and perspectives on artemisinin resistance, approaches for translating research data into relevant public health information, and opportunities for interdisciplinary collaboration to combat artemisinin resistance.

Physicochemical characterization of creatine N-methylguanidinium salts

Creatine is widely used as a dietary supplement for body builders to enhance athletic performance. As the monohydrate, its low solubility in water and high dose lead to water retention and gastrointestinal discomfort. Hence, alternative creatine derivatives with enhanced water solubility and potential therapeutic advantages have been synthesized. As a zwitterionic compound, creatine can form salts at the N-methyl guanidinium or carboxylic acid functional groups. In this study, we determined the aqueous solubilities and partition coefficients of six N-methyl guanidinium salts of creatine compared to those of creatine monohydrate; two of these were new salts, namely, creatine mesylate and creatine hydrogen maleate. The aqueous solubilities of the salts were significantly more than that of creatine monohydrate with the hydrochloride and mesylate being 38 and 30 times more soluble, respectively. The partition coefficients of the creatine salts were very low indicating their relatively high polarity. Permeabilities of creatine pyruvate, citrate, and hydrochloride in Caco-2 monolayers were compared to that of creatine monohydrate. Aside from the creatine citrate salt form that had reduced permeability, there were no significant differences in permeability characteristics in Caco-2 monolayers. Typical of an amphoteric compound, creatine is least soluble in the pH region near the isoelectric point.

In vivo activity of aryl ozonides against Schistosoma species

We evaluated the in vivo antischistosomal activities of 11 structurally diverse synthetic peroxides. Of all compounds tested, ozonide (1,2,4-trioxolane) OZ418 had the highest activity against adult Schistosoma mansoni, with total and female worm burden reductions of 80 and 90% (P < 0.05), respectively. Furthermore, treatment of S. haematobium-infected mice with OZ418 reduced the total worm burden by 86%. In conclusion, OZ418 is a promising antischistosomal lead compound.

Biological evaluation and docking studies of recently identified inhibitors of phosphoinositide-3-kinases

The alpha isoform of the phosphatidylinositol-3-kinases (PI3Kα) is often mutated, amplified and overexpressed in human tumors. In an effort to develop new inhibitors targeting this enzyme, we carried out a pharmacophore model study based on six PI3Kα-selective compounds. The pharmacophore searching identified three structurally novel inhibitors of PI3Kα and its H1047R mutant. Our biological studies show that two of our hit molecules suppressed the formation of pAKT, a downstream effector of PI3Kα, and induced apoptosis in the HCT116 colon cancer cell line. QPLD-based docking showed that residues Asp933, Glu849, Val851, and Gln859 appeared to be key binding residues for active inhibitors.

Semisynthetic Artemisinin and Synthetic Peroxide Antimalarials

Since the discovery of the endoperoxide sesquiterpene lactone artemisinin, numerous second-generation semisynthetic artemisinins and synthetic peroxides have been prepared and tested for their antimalarial properties. Using a case-study approach, we describe the discovery of the investigational semisynthetic artemisinins artelinic acid (8) and artemisone (9), and the structurally diverse synthetic peroxides arteflene (10), fenozan B07 (11), arterolane (12), PA1103/SAR116242 (13), and RKA182 (14).

The activity of dispiro peroxides against Fasciola hepatica

Dispiro 1,2,4-trioxanes and 1,2,4,5-tetraoxanes had superior efficacy against Fasciola hepatica than the corresponding ozonides (1,2,4-trioxolanes). For highest efficacy, spiroadamantane and carboxymethyl substructures were required. Three compounds completely cured F. hepatica-infected mice at single oral doses of 50mg/kg and two were partially curative at single doses of 25mg/kg.

Activity of OZ78 analogues against Fasciola hepatica and Echinostoma caproni

The rapid spread of triclabendazole resistance in veterinary medicine is an important motivation for the discovery and development of novel fasciocidal drugs. The aim of this study was to characterize the fasciocidal properties of 1,2,4,5-tetraoxane (MT04 and MT14) and 1,2,4-trioxane (ST16 and ST28) analogues of the fasciocidal drug candidate OZ78, a 1,2,4-trioxolane. Dose response relationships were determined against juvenile and adult Fasciola hepatica in rats and Echinostoma caproni in mice. The temporal effects of MT04, MT14, ST16, and ST28 compared to OZ78 on the viability of F. hepatica were tested in vitro. The heat flow of OZ78 and MT04 treated flukes was studied with isothermal microcalorimetry. Finally, surface changes to adult flukes were monitored by scanning electron microscopy (SEM) 18, 24, and 48 h post-treatment of rats with 50 mg/kg MT04. Administration of 50-100 mg/kg of the synthetic peroxides resulted in complete elimination of adult F. hepatica from rats. SEM pictures revealed sloughing and blebbing already 18 h post-treatment with MT04. MT04 (100mg/kg) cured infections with juvenile F. hepatica, whereas MT14, ST16, and ST28 showed only low to moderate worm burden reductions. At 300 mg/kg, MT14 was the only compound to completely eliminate worms from E. caproni infected mice. MT14 showed the highest activity against juvenile F. hepatica in vitro. MT04 was very active against adult F. hepatica in vitro, which was confirmed by heat flow measurements. In conclusion, we have identified MT04 as another lead compound with potential against F. hepatica, hence further preclinical studies are necessary to determine if MT04 can be considered a drug development candidate.

Synthetic ozonide drug candidate OZ439 offers new hope for a single-dose cure of uncomplicated malaria

Ozonide OZ439 is a synthetic peroxide antimalarial drug candidate designed to provide a single-dose oral cure in humans. OZ439 has successfully completed Phase I clinical trials, where it was shown to be safe at doses up to 1,600 mg and is currently undergoing Phase IIa trials in malaria patients. Herein, we describe the discovery of OZ439 and the exceptional antimalarial and pharmacokinetic properties that led to its selection as a clinical drug development candidate. In vitro, OZ439 is fast-acting against all asexual erythrocytic Plasmodium falciparum stages with IC(50) values comparable to those for the clinically used artemisinin derivatives. Unlike all other synthetic peroxides and semisynthetic artemisinin derivatives, OZ439 completely cures Plasmodium berghei-infected mice with a single oral dose of 20 mg/kg and exhibits prophylactic activity superior to that of the benchmark chemoprophylactic agent, mefloquine. Compared with other peroxide-containing antimalarial agents, such as the artemisinin derivatives and the first-generation ozonide OZ277, OZ439 exhibits a substantial increase in the pharmacokinetic half-life and blood concentration versus time profile in three preclinical species. The outstanding efficacy and prolonged blood concentrations of OZ439 are the result of a design strategy that stabilizes the intrinsically unstable pharmacophoric peroxide bond, thereby reducing clearance yet maintaining the necessary Fe(II)-reactivity to elicit parasite death.

Docking studies on isoform-specific inhibition of phosphoinositide-3-kinases

Phosphatidylinositol 3-kinase α (PI3Kα) is a promising target for anticancer drug design. Oncogenic mutation H1047R in the catalytic domain is observed in many tumors and may enhance PI3Kα kinase activity by affecting loop confirmations as well as membrane binding. We applied docking methods to 33 PI3K inhibitors against the wild type (wt) PI3Kα, the H1047R mutant of PI3Kα and the γ isoform of PI3K (PI3Kγ). We also investigated the effect of protein flexibility on ligand binding by docking the same set of ligands to conformations of the wt and mutant PI3Kα generated by molecular dynamics simulations. Our data suggests that conformational differences in Gln859, Ser854, Tyr836, and Ser774 between the PI3Kα wt and H1047R mutant may be used to design ligands that are active against both the wt and H1047R mutant isoforms. Gln859, Ser854 and Ser774 may play critical roles in ligand binding to the α isoform H1047R mutant while formation of H-bonds with Ser806 of PI3Kγ may enhance γ-isoform-specific inhibition. In addition to H-bond interactions, structural and size differences in the activation and hydrophobic domains of PI3Kα, PI3Kγ, and the PI3Kα H1047R mutant could be exploited to direct the design of isoform- and/or mutant-specific PI3K inhibitors. Our data provide a reasonable explanation for the activity and selectivity of small molecular PI3K inhibitors and are in good agreement with available experimental and computational data.