Synthesis and antimalarial evaluation of amide and urea derivatives based on the thiaplakortone A natural product scaffold.

A series of amide (8­32, 40­45) and urea (33, 34, 36­39) analogues based on the thiaplakortone A natural product scaffold were synthesised and screened for in vitro antimalarial activity against chloroquine-sensitive (3D7) and chloroquine- and mefloquine-resistant (Dd2) Plasmodium falciparum parasite lines. Several analogues displayed potent inhibition of P. falciparum growth (IC50 <500 nM) and good selectivity for P. falciparum versus human neonatal foreskin fibroblast cells (selectivity index >100). Two of these compounds, 8 and 33, exhibited good aqueous solubility and metabolic stability, and when administered subcutaneously to mice (32 mg kg(-1)), plasma concentrations remained above 0.2 µM for at least 8 h. Both 8 and 33 were well tolerated in mice after subcutaneous administration of 32 mg kg(-1) twice daily for 4 days. Using this regimen blood stage P. berghei was suppressed by 52% for 8 and 26% for 33, relative to the vehicle control.

Do large pores in the glomerular capillary wall account for albuminuria in nephrotic states?

Albuminuria in nephrotic states is thought to arise from the formation of large pores in the glomerular capillary wall as large hydrodynamic probes, like Ficoll, have increased fractional clearance. In the present study, we tested for large pore formation in a novel manner. We accounted for the rates of plasma elimination as determined for tritium-labeled tracers of uncharged polydisperse Ficoll (radii range: 35-85 Å) and two globular (14)C-labeled proteins, albumin (radius: 36 Å) and IgG (radius: 55 Å), in control and puromycin aminonucleoside nephrotic (PAN) Sprague-Dawley rats. The plasma elimination rates were then matched to the urinary excretion of these labeled materials (n = 7). Albumin and IgG plasma retention rates were identical and far enhanced compared with the retention rates of inert transport markers of equivalent hydrodynamic radius; their elimination rate corresponded to the elimination of a 75-Å radius Ficoll (n = 5) and >105-Å radius dextran (n = 5). In PAN, they were eliminated as ∼36- and ∼55-Å radii Ficoll, respectively, equivalent to their hydrodynamic radii. In contrast, there was no comparable increase in the elimination rate of Ficoll in PAN. The total plasma clearance of Ficoll in control and PAN rats and the urinary clearance in PAN rats were essentially the same for all radii. On the other hand, the urinary clearance of >45-Å radii Ficoll in controls was considerably lower with increasing radii, demonstrating a postfiltration cellular uptake in controls, which, when inhibited in nephrotic states, would account for apparent large pore formation.

Antitrypanosomal activity of fexinidazole metabolites, potential new drug candidates for Chagas disease.

This study was designed to verify the in vivo efficacy of sulfoxide and sulfone fexinidazole metabolites following oral administration in a murine model of Chagas disease. Female Swiss mice infected with the Y strain of Trypanosoma cruzi were treated orally once per day with each metabolite at doses of 10 to 100 mg/kg of body weight for a period of 20 days. Parasitemia was monitored throughout, and cures were detected by parasitological and PCR assays. The results were compared with those achieved with benznidazole treatment at the same doses. Fexinidazole metabolites were effective in reducing the numbers of circulating parasites and protecting mice against death, compared with untreated mice, but without providing cures at daily doses of 10 and 25 mg/kg. Both metabolites were effective in curing mice at 50 mg/kg/day (30% to 40%) and 100 mg/kg/day (100%). In the benznidazole-treated group, parasitological cure was detected only in animals treated with the higher dose of 100 mg/kg/day (80%). Single-dose pharmacokinetic parameters for each metabolite were obtained from a parallel group of uninfected mice and were used to estimate the profiles following repeated doses. Pharmacokinetic data suggested that biological efficacy most likely resides with the sulfone metabolite (or subsequent reactive metabolites formed following reduction of the nitro group) following administration of either the sulfoxide or the sulfone and that prolonged plasma exposure over the 24-h dosing window is required to achieve high cure rates. Fexinidazole metabolites were effective in treating T. cruzi in a mouse model of acute infection, with cure rates superior to those achieved with either fexinidazole itself or benznidazole.

Two analogues of fenarimol show curative activity in an experimental model of Chagas disease.

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi (T. cruzi), is an increasing threat to global health. Available medicines were introduced over 40 years ago, have undesirable side effects, and give equivocal results of cure in the chronic stage of the disease. We report the development of two compounds, 6 and (S)-7, with PCR-confirmed curative activity in a mouse model of established T. cruzi infection after once daily oral dosing for 20 days at 20 mg/kg 6 and 10 mg/kg (S)-7. Compounds 6 and (S)-7 have potent in vitro activity, are noncytotoxic, show no adverse effects in vivo following repeat dosing, are prepared by a short synthetic route, and have druglike properties suitable for preclinical development.

Structure-guided lead optimization of triazolopyrimidine-ring substituents identifies potent Plasmodium falciparum dihydroorotate dehydrogenase inhibitors with clinical candidate potential.

Drug therapy is the mainstay of antimalarial therapy, yet current drugs are threatened by the development of resistance. In an effort to identify new potential antimalarials, we have undertaken a lead optimization program around our previously identified triazolopyrimidine-based series of Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) inhibitors. The X-ray structure of PfDHODH was used to inform the medicinal chemistry program allowing the identification of a potent and selective inhibitor (DSM265) that acts through DHODH inhibition to kill both sensitive and drug resistant strains of the parasite. This compound has similar potency to chloroquine in the humanized SCID mouse P. falciparum model, can be synthesized by a simple route, and rodent pharmacokinetic studies demonstrated it has excellent oral bioavailability, a long half-life and low clearance. These studies have identified the first candidate in the triazolopyrimidine series to meet previously established progression criteria for efficacy and ADME properties, justifying further development of this compound toward clinical candidate status.

Preclinical comparison of intravenous melphalan pharmacokinetics administered in formulations containing either (SBE)7 m-ß-cyclodextrin or a co-solvent system.

The aim of this work was to evaluate the impact of sulfobutyl ether ß-cyclodextrin ((SBE)(7 m)-ß-CD; Captisol(®)) on the in vivo pharmacokinetics of melphalan in rats. Melphalan is a chemically unstable antineoplastic drug which in the current commercial formulation (Alkeran(®) for Injection) has some limitations with regard to solubility, stability and biocompatibility. Melphalan formulations containing (SBE)(7 m)-ß-CD have previously been evaluated in vitro and shown to significantly reduce the rate of degradation and to simplify the reconstitution procedure for lyophilised melphalan. In this study, melphalan was administered intravenously in rats in formulations that either contain (SBE)(7 m)-ß-CD or a co-solvent system (i.e. the commercial formulation). Pharmacokinetic parameters, including half-life, volume of distribution, clearance and extent of renal elimination of melphalan were essentially unchanged between the two formulations. These findings indicate that the pharmacokinetics of melphalan are not altered in the presence of (SBE)(7 m)-ß-CD consistent with a rapid shift in the equilibrium to the fully dissociated drug from the fraction associated with the cyclodextrin host molecule upon intravenous administration.

The structure-activity relationship of the antimalarial ozonide arterolane (OZ277).

The structure and stereochemistry of the cyclohexane substituents of analogues of arterolane (OZ277) had little effect on potency against Plasmodium falciparum in vitro. Weak base functional groups were not required for high antimalarial potency, but they were essential for high antimalarial efficacy in P. berghei-infected mice. Five new ozonides with antimalarial efficacy and ADME profiles superior or equal to that of arterolane were identified.

Mechanism of hypoalbuminemia in rodents.

Normal albumin loss from the plasma is thought to be minimized by a number of mechanisms, including charge repulsion with the capillary wall and an intracellular rescue pathway involving the major histocompatibility complex-related Fc receptor (FcRn)-mediated mechanism. This study investigates how these factors may influence the mechanism of hypoalbuminemia. Hypoalbuminemia in rats was induced by treatment with puromycin aminonucleoside (PA). To test the effects of PA on capillary wall permeability, plasma elimination rates were determined for tritium-labeled tracers of different-sized Ficolls, negatively charged Ficolls, and (14)C-labeled tracer of albumin in control and PA-treated Sprague-Dawley rats. Urinary excretion and tissue uptake were also measured. Hypoalbuminemia was also examined in two strains of FcRn-deficient mice: beta(2)-microglobulin (beta(2)M) knockout (KO) mice and FcRn alpha-chain KO mice. The excretion rates of albumin and albumin-derived fragments were measured. PA-induced hypoalbuminemia was associated with a 2.5-fold increase in the plasma elimination rate of albumin. This increase could be completely accounted for by the increase in urinary albumin excretion. Changes in the permeability of the capillary wall were not apparent, inasmuch as there was no comparable increase in the plasma elimination rate of 36- to 85-A Ficoll or negatively charged 50- to 80-A Ficoll. In contrast, hypoalbuminemic states in beta(2)M and FcRn KO mice were associated with decreases in excretion of albumin and albumin-derived fragments. This demonstrates that the mechanism of hypoalbuminemia consists of at least two distinct forms: one specifically associated with the renal handling of albumin and the other mediated by systemic processes.

Retention of albumin in the circulation is governed by saturable renal cell-mediated processes.

OBJECTIVE: To examine the role of renal processing in the turnover of circulating albumin in the model of reversible overload proteinuria. Specifically, this study determines whether proteinuria due to hyperalbuminemia may be attributed to saturation of renal cell processing of albumin or alterations in diffusive/convective transport of albumin across the glomerular capillary wall. METHODS: Overload proteinuria was induced in male Wistar rats by daily intraperitoneal injections of 1.5 g bovine serum albumin (BSA; endotoxin free) for 3 days. Plasma concentration and urinary excretion of total protein and rat serum albumin (RSA) were determined by the biuret assay and radioimmunoassay, respectively. Glomerular size selectivity was assessed by examining the fractional clearance (FC) of neutral [3H]Ficoll using a short-term, steady-state approach. Cellular processing was examined by size exclusion chromatography analysis of urinary [14C]albumin and [14C]transferrin structural integrity. RESULTS: Total protein excretion (n = 4-15) increased 7-fold in BSA-treated rats (58 +/- 26 mg/24 h at baseline vs. 417 +/- 259 mg/24 h at day 3), while intact RSA excretion (n = 4-6) increased 200-fold (0.27 +/- 0.15 mg/24 h vs. 53 +/- 26 mg/24 h) despite a significant decrease in its plasma concentration. Total protein and albumin excretion returned to basal levels by day 7 (82 +/- 16 mg/24 h and 0.93 +/- 0.42 mg/24 h, respectively). FC of [3H]Ficoll of equivalent size to albumin did not change in BSA-treated rats as compared to vehicle controls. Tubular lysosomal processing of proteins was altered at peak proteinuria, as determined by changes in the structural integrity of urinary [14C]albumin, as well as [14C]transferrin, but returned to normal by day 7. CONCLUSIONS: This study demonstrates the lack of proportionality between changes in plasma concentration and urinary excretion of albumin, as well as the lack of change in the glomerular size selectivity to albumin. The profound but reversible changes in the amount and integrity of excreted protein suggest that cell-mediated processes are saturated by albumin concentrations, leading to the development of proteinuria in this model.