dSarm/Sarm1 is required for activation of an injury-induced axon death pathway

Axonal and synaptic degeneration is a hallmark of peripheral neuropathy, brain injury, and neurodegenerative disease. Axonal degeneration has been proposed to be mediated by an active autodestruction program, akin to apoptotic cell death; however, loss-of-function mutations capable of potently blocking axon self-destruction have not been described. Here, we show that loss of the Drosophila Toll receptor adaptor dSarm (sterile α/Armadillo/Toll-Interleukin receptor homology domain protein) cell-autonomously suppresses Wallerian degeneration for weeks after axotomy. Severed mouse Sarm1 null axons exhibit remarkable long-term survival both in vivo and in vitro, indicating that Sarm1 prodegenerative signaling is conserved in mammals. Our results provide direct evidence that axons actively promote their own destruction after injury and identify dSarm/Sarm1 as a member of an ancient axon death signaling pathway.

WldS prevents axon degeneration through increased mitochondrial flux and enhanced mitochondrial Ca2+ buffering

Wld(S) (slow Wallerian degeneration) is a remarkable protein that can suppress Wallerian degeneration of axons and synapses, but how it exerts this effect remains unclear. Here, using Drosophila and mouse models, we identify mitochondria as a key site of action for Wld(S) neuroprotective function. Targeting the NAD(+) biosynthetic enzyme Nmnat to mitochondria was sufficient to fully phenocopy Wld(S), and Wld(S) was specifically localized to mitochondria in synaptic preparations from mouse brain. Axotomy of live wild-type axons induced a dramatic spike in axoplasmic Ca(2+) and termination of mitochondrial movement-Wld(S) potently suppressed both of these events. Surprisingly, Wld(S) also promoted increased basal mitochondrial motility in axons before injury, and genetically suppressing mitochondrial motility in vivo dramatically reduced the protective effect of Wld(S). Intriguingly, purified mitochondria from Wld(S) mice exhibited enhanced Ca(2+) buffering capacity. We propose that the enhanced Ca(2+) buffering capacity of Wld(S+) mitochondria leads to increased mitochondrial motility, suppression of axotomy-induced Ca(2+) elevation in axons, and thereby suppression of Wallerian degeneration.

Wld S requires Nmnat1 enzymatic activity and N16-VCP interactions to suppress Wallerian degeneration

Slow Wallerian degeneration (Wld(S)) encodes a chimeric Ube4b/nicotinamide mononucleotide adenylyl transferase 1 (Nmnat1) fusion protein that potently suppresses Wallerian degeneration, but the mechanistic action of Wld(S) remains controversial. In this study, we characterize Wld(S)-mediated axon protection in vivo using Drosophila melanogaster. We show that Nmnat1 can protect severed axons from autodestruction but at levels significantly lower than Wld(S), and enzyme-dead versions of Nmnat1 and Wld(S) exhibit severely reduced axon-protective function. Interestingly, a 16-amino acid N-terminal domain of Wld(S) (termed N16) accounts for the differences in axon-sparing activity between Wld(S) and Nmnat1, and N16-dependent enhancement of Nmnat1-protective activity in Wld(S) requires the N16-binding protein valosin-containing protein (VCP)/TER94. Thus, Wld(S)-mediated suppression of Wallerian degeneration results from VCP-N16 interactions and Nmnat1 activity converging in vivo. Surprisingly, mouse Nmnat3, a mitochondrial Nmnat enzyme that localizes to the cytoplasm in Drosophila cells, protects severed axons at levels indistinguishable from Wld(S). Thus, nuclear Nmnat activity does not appear to be essential for Wld(S)-like axon protection.

Second-generation antimalarial endoperoxides

Artemisinin, derived from a Chinese herbal remedy, is a potent peroxide-containing antimalarial. New types of peroxides, derived from this structure, as well as other naturally occurring antimalarial peroxides, have been synthesized and found to have potent antimalarial activities. Studies on the activities, modes of action, and toxicities of these compounds are discussed here by Steven Meshnick and colleagues.

Transformation of artemisinin by Cunninghamella elegans

Semi-synthetic derivatives of the anti-malarial drug artemisinin hold great promise in the search for an effective and economical treatment of chloroquine-resistant forms of malaria. Unfortunately, synthetic functionalization of the artemisinin skeleton is often tedious and/or impractical. We seek to utilize 7beta-hydroxyartemisinin, obtained from microbial transformation, as a semi-synthetic precursor for the synthesis of novel 7beta-substituted artemisinin anti-malarial agents. Here we employ liquid cultures of Cunninghamella elegans as a means for the rational and economical bioconversion of artemisinin to 7beta-hydroxyartemisinin in 78.6% yield. In addition, there were three other bioconversion products: 7beta-hydroxy-9alpha-artemisinin (6.0%), 4alpha-hydroxy-1-deoxoartemisinin (5.4%), and 6beta-hydroxyartemisinin (6.5%).

Structural Characterization of Vivapain-2 and Vivapain-3, Cysteine Proteases fromPlasmodium vivax: Comparative Protein Modeling and Docking Studies

Malaria remains one of the most important infectious diseases in the world. Plasmodial cysteine proteases are proposed to be promising targets for novel antimalarial drug design. Vivapain-2 and vivapain-3 are cysteine proteases from Plasmodium vivax and apparent orthologs of falcipain-2 and falcipain-3 from Plasmodium falciparum. Model structures of vivapain-2 and vivapain-3 have been derived using the comparative protein modeling approach and validated by various structure/geometry verification tools. Correlation between the interaction energies calculated based on the docking studies of the inhibitors and the corresponding association constants (k(ass)) provide additional validation for the structures. Moreover, some of the biochemical differences observed between the vivapains may be explained by the results of the docking studies. The overall structures of the two vivapains are similar to each other as well as to the falcipains with most of the catalytic residues conserved. At the same time, some important differences are observed between the sizes of the binding pockets as well as some of the residues involved in binding. The study suggests a likelihood of developing common inhibitors for these enzymes provided the interesting differences in the binding pockets of these enzymes are critically considered during such an attempt. The results of the current study can be utilized in de novo drug design for effective treatment of malaria.

Solution-phase parallel synthesis of an isoflavone library for the discovery of novel antigiardial agents

Combinatorial chemistry has become a dramatically useful tool for the development of new medicinal agents. In the search to discover a novel and effective lead for the treatment of giardiasis, solution-phase synthesis of a library of isoflavone derivatives has been accomplished. Of the products screened, several compounds such as P(A1,B1) and P(A1,B11) exhibited potent antigiardial activity. The details of synthesis, in vitro antigiardial assay, and preliminary structure-activity relationships of these compounds are described.

Total synthesis of epothilone B

[structure-see text] A convergent and stereoselective total synthesis of epothilone B (2) is described. The key steps are Normant reaction, Wadsworth-Emmons reaction of a methyl ketone 14 with the phosphonate reagent 7, diastereoselective aldol condensation of aldehyde 3 with enolate 4 to form the C6-C7 bond, and macrolactonization.

Antigiardial activity of isoflavones from Dalbergia frutescens bark

Several isoflavones [formononetin (1), castanin (5), odoratin (6), glycitein (7), pseudobaptogenin (8), fujikinetin (9), and cuneatin (10)] were isolated from Dalbergia frutescens, and their antiprotozoal activities were determined against Giardia intestinalis. Among these compounds, formononetin (1) was the most potent antigiardial agent, with an IC(50) value of 30 ng/mL (approximately 0.1 microM), as compared to the value for metronidazole, the current drug of choice, of 100 ng/mL (approximately 0.6 microM). Three isoflavones closely related to formononetin [daidzein (2), biochanin A (3) and genistein (4)] were also evaluated, but they were at least 100 times less active than 1. Formononetin (1) may thus be an interesting lead for development of new antigiardial agents or as a probe for a new mechanistic target.

Rapid determination of artemisinin and related analogues using high-performance liquid chromatography and an evaporative light scattering detector

Artemisinin and its analogues are a class of compounds of current interest in the treatment of drug-resistant malaria. These antimalarials are preferentially taken up into malaria infected erythrocytes as compared to uninfected erythrocytes, a fact that may represent an important parameter in drug potency. Numerous methods for the analysis of specific artemisinin analogues have been developed, but most are not widely adaptable to a large range of analogues. In this paper we describe a high-performance liquid chromatographic method developed and validated for artemisinin and several analogues of artemisinin using a readily available evaporative light scattering detector. This quantitation method was found to be straight forward, rapid, inexpensive and reproducible. Standard calibration curves constructed for six artemisinin compounds were linear with the detection limit determined between 6 and 60 ng. The intra- and inter-day accuracy were found to be 2.75% and 4.15%, respectively with less than 3% variation in precision. The validated assay was applied to a mixture of artemisinin derivatives, where they were easily separated and quantitated.

Current progress in the chemistry, medicinal chemistry and drug design of artemisinin based antimalarials

This review covers developments in relation to artemisinin-based antimalarial agents. Topics covered include a brief introduction to the history and treatment of malaria, and more recently, drug resistant malaria; the discovery of the naturally occurring novel peroxidic antimalarial artemisinin; artemisinin biosynthesis, metabolism and biotransformations; the diversity of proposed mechanisms of action; pharmacokinetics; the insight into structure-toxicity relationships; the total syntheses and the progress made in the syntheses of its analogs; and, ultimately the contribution of these efforts towards rational drug design in order to access potent, non-toxic antimalarial drugs based on artemisinin.

Quantitative structure-activity relationship studies of a series of sulfa drugs as inhibitors of Pneumocystis carinii dihydropteroate synthetase

Sulfone and sulfanilamide sulfa drugs have been shown to inhibit dihydropteroate synthetase (DHPS) isolated from Pneumocystis carinii. In order to develop a pharmacophoric model for this inhibition, quantitative structure-activity relationships (QSAR) for sulfa drugs active against DHPS have been studied. Accurate 50% inhibitory concentrations were collected for 44 analogs, and other parameters, such as partition coefficients and molar refractivity, were calculated. Conventional multiple regression analysis of these data did not provide acceptable QSAR. However, three-dimensional QSAR provided by comparative molecular field analysis did give excellent results. Upon removal of poorly correlated analogs, a data set of 36 analogs, all having a common NHSO2 group, provided a cross-validated r2 value of 0.699 and conventional r2 value of 0.964. The resulting pharmacophore model should be useful for understanding and predicting the binding of DHPS by new sulfa drugs.

Serial in vivo observations of cerebral vasculature after treatment with a large single fraction of radiation

To test whether single high doses of radiation, similar to those used with radiosurgery, given to normal cerebral vasculature can cause changes in leukocyte-vessel wall interactions and tissue perfusion, a rat pial window model was used to view the cerebral vasculature, facilitating repeated in vivo observations of microcirculatory function. An attachment for a 4 MV linear accelerator was designed to deliver a well-collimated 2.2-mm beam of radiation to a selected region of rat brain. Sequential measurements of leukocyte-endothelial cell interactions, relative change in blood flow with laser Doppler flowmetry and vessel length density were performed prior to and at 24 h and 3 weeks after treatment with 15, 22.5 or 30 Gy, given in a single fraction. Significant increases in leukocyte-endothelial cell interactions were seen 24 h and 3 weeks after irradiation that were dependent on dose, particularly in arteries. Changes were apparent in both arteries and veins at 24 h, but by 3 weeks the effects in arteries predominated. Decreases in vessel length density and blood flow were observed and became greater with time after treatment. A variety of morphological changes were observed in irradiated arteries, including formation of aneurysmal structures, endothelial denudation and thrombus formation. These results suggest that: (1) An increase in leukocyte-vessel wall interactions occurs after irradiation; (2) cerebral arterioles are more sensitive than veins to radiation administered in this fashion; and (3) the increase in leukocyte-vessel wall interactions likely contributes to reduction of or loss of arteriolar flow, with resultant loss of flow to dependent microvascular vessels.

Comparison of 3D quantitative structure-activity relationship methods: analysis of the in vitro antimalarial activity of 154 artemisinin analogues by hypothetical active-site lattice and comparative molecular field analysis

Two three-dimensional quantitative structure-activity relationship (3D-QSAR) methods, comparative molecular field analysis (CoMFA) and hypothetical active site lattice (HASL), were compared with respect to the analysis of a training set of 154 artemisinin analogues. Five models were created, including a complete HASL and two trimmed versions, as well as two CoMFA models (leave-one-out standard CoMFA and the guided-region selection protocol). Similar r2 and q2 values were obtained by each method, although some striking differences existed between CoMFA contour maps and the HASL output. Each of the four predictive models exhibited a similar ability to predict the activity of a test set of 23 artemisinin analogues, although some differences were noted as to which compounds were described well by either model.

Structure-activity relationships of the antimalarial agent artemisinin. 5. Analogs of 10-deoxoartemisinin substituted at C-3 and C-9

Novel 3- and 9-substituted analogs (4-19) of 10-deoxoartemisinin, 3, were prepared from the corresponding known lactones by one-pot reduction with sodium borohydride and boron trifluoride etherate. Reproducibility problems associated with this heterogeneous reaction were encountered on small reaction scales, and thus alternative methodology was sought for this reduction. Conversion of the lactones to tetrahydropyrans via the corresponding intermediate lactols was made more reproducible using a two-step sequence involving low-temperature reduction with diisobutylaluminum hydride followed by deoxygenation with boron trifluoride etherate in the presence of triethylsilane. In this manner, 10-deoxoartemisinin (3) could be obtained from artemisinin (1) in greater than 95% overall yield. All analogs were tested in vitro against W-2 and D-6 strains of Plasmodium falciparum. Several of the analogs were much more active than the natural product (+)-artemisinin (1) or 10-deoxoartemisinin (3). Conventional structure-activity relationships are discussed in relation to the bioassay data.

Structure-activity relationships of the antimalarial agent artemisinin. 4. Effect of substitution at C-3

Novel antimalarial artemisinin analogs, 3-alkylartemisinins as well as 3-(arylalkyl)- and 3-(carboxyalkyl)artemisinins, were prepared via the synthetic intermediate 2. Formation of the N,N-dimethylhydrazones 5 and 24 and then regio- and chemoselective deprotonation followed by alkylation provided initially alkylated hydrazones that upon chromatography gave ketones 6-13 and 25-30. Direct ozonolysis of the ketones followed by in situ acidification lead directly to the formation of title compounds 14-21 and 31-36. The analogs were tested in vitro against W-2 and D-6 strains of Plasmodium falciparum and found to be in some cases much more active than the natural product (+)-artemisinin. The results were included in structure-activity relationship (CoMFA) studies for further analog design.

Structure-activity relationships of the antimalarial agent artemisinin. 3. Total synthesis of (+)-13-carbaartemisinin and related tetra- and tricyclic structures

Provided by total synthesis, endoperoxides 18, 20, and 22 underwent intramolecular oxymercuration-demercuration leading respectively to formation of an isomeric tetracycle, (1aS, 3S, 5aS, 6R, 8aS, 9R, 12S)-10-deoxo-13-carbaartemisinin (19), (+)-10-deoxo-13-carbaartemisinin (21), and (+)-13-carbaartemisinin (4). Structure assignment to 19 and 21 was based on single-crystal X-ray crystallographic analysis. Tricyclic endoperoxide 20 was converted to methyl and benzyl ethers 23 and 24 and reduced to saturated analog 25 which was also converted to ethers 26 and 27. In vitro antimalarial screening of both tri- and tetracyclic analogs was conducted using the W-2 and D-6 clones of Plasmodium falciparum. Neither target 4 nor 21 displayed substantial antimalarial potency in vitro against P. falciparum, but the diastereomeric peroxide 19 possessed good antimalarial potency in vitro. Tricyclic analogs were uniformly impotent. Iron(II) bromide-promoted rearrangement of 21 gave, in 79% yield, the unique tetracyclic alcohol 35, while 19 provided ring-opened cyclohexanone 41 (39%) along with the tricyclic epoxide 42 (20%). Neither 41 nor 42 possessed in vitro antimalarial activity, suggesting that epoxide-like intermediates are not responsible for the mode of action of this subclass of antimalarials. Rearrangement of 10-deoxoartemisinin (43) with FeBr2 gave a major product (79%) not encountered in the rearrangement of artemisinin that resulted from unraveling of the tetracyclic system cyclohexanone 46. Minor amounts of 1,10-dideoxoartemisinin (49) (8%) were also produced in this reaction.

Structure-activity relationships of the antimalarial agent artemisinin. 2. Effect of heteroatom substitution at O-11: synthesis and bioassay of N-alkyl-11-aza-9-desmethylartemisinins

A novel class of artemisinin analogs, N-alkyl-11-aza-9-desmethylartemisinins 17-29, were synthesized via ozonolysis and acid-catalyzed cyclization of precursor amides 5-16. These amides were prepared through condensation of an activated ester of the known intermediate acid 2 with the corresponding primary amine. The analogs were tested in vitro against W-2 and D-6 strains of Plasmodium falciparum and found in some cases to be more active than artemisinin. A comparison of the in vitro testing methods of Milhous and Makler was conducted and gave similar relative antimalarial activities for these artemisinin analogs. Log P values were determined for most of the compounds, but no apparent correlation between log P and in vitro activity was found.

Resistance to artemisinin of malaria parasites (Plasmodium falciparum) infecting alpha-thalassemic erythrocytes in vitro. Competition in drug accumulation with uninfected erythrocytes

Plasmodium falciparum infecting hemoglobin (Hb)H and/or Hb Constant Spring erythrocytes has higher resistance to artemisinin in vitro than when infecting normal erythrocytes. This is due to low drug accumulation of infected erythrocytes resulting from competition with uninfected variant erythrocytes, which have a higher accumulation capacity than genetically normal cells. Drug accumulation of the parasite was shown to be saturable and dependent on metabolic energy. The 50% inhibitory concentrations (IC50's) for the parasite in HbH/Hb Constant Spring erythrocytes were decreased when normal erythrocytes were added to the infected cells, and correspondingly, the IC50's in normal erythrocytes were increased when HbH/Hb Constant Spring erythrocytes were added to the infected cells. The changes of IC50 corresponded to the variation in drug accumulation of mixtures of normal and variant erythrocytes of different compositions. The IC50's for the parasite in variant erythrocytes were also greatly decreased when the hematocrit of the culture was lowered, while the IC50's in normal erythrocytes were independent of the hematocrit. The increase in IC50 values for the parasites infecting variant erythrocytes was also related to the decrease in parasite accumulation, indicating that drug accumulation capacity of the parasite also has a role in determining drug sensitivity. Artemisinin sensitivity therefore is determined by its accessibility to the parasite, which is decreased in infected variant erythrocytes.

Structure-activity relationships of the antimalarial agent artemisinin. 1. Synthesis and comparative molecular field analysis of C-9 analogs of artemisinin and 10-deoxoartemisinin

A series of C-9 beta-substituted artemisinin analogs (2-21) were synthesized via dianion alkylation of the total synthetic intermediate 57 followed by subsequent ozonolysis/acidification, or by alkylation of the enolate derived from (+)-9-desmethylartemisinin, 2. Inactive acyclic analogs 22 and 23 were synthesized by nucleophilic epoxide opening and the ring contracted analog 24 was prepared by an alternate route. 10-Deoxo-9-alkyl derivatives 68 and 70 were synthesized convergently from intermediates in the preparation of 9-alkyl derivatives. In vitro bioassay was conducted in W-2 and D-6 clones of drug resistant Plasmodium falciparum. Comparative molecular field analysis (CoMFA) of the 9-alkyl lactone derivatives provided a model with a cross-validated r2 = 0.793. Inclusion of inactive 1-deoxyartemisinin analogs 26-42 provided a model with a value of 0.857. The activities of a number of other analogs of divergent structure (43-56) were predicted with good accuracy using the CoMFA model.

Synthesis and antiinflammatory activity of novel 12 beta-substituted analogues of betamethasone

A series of 9 alpha-halo-12 beta-hydroxy and 12 beta-acyloxy analogues of betamethasone 17,21-dipropionate were synthesized and tested for topical antiinflammatory potency in the croton oil ear assay. The compounds were assayed for systemic absorption in the contralateral ear assay, in which it was found that 12 beta-hydroxy analogues 9, 13, and 15 were all absorbed but the corresponding 12 beta-esters 11a-e, 14, and 16 were not. On repeated high-dose applications to the mouse ear, there was no evidence of systemic absorption of any 12 beta-propionate ester as gauged by thymus weights (thymic involution) and plasma cortisol levels (adrenal suppression). Results of limited SAR studies showed that topical antiinflammatory activity and systemic absorption were not greatly influenced by the 9 alpha-halogen but were largely dependent on the polarity and size of the 12 substituent. While the optimal compounds 14 and 16 were less topically active than the controls beta- and beclomethasone dipropionate, unlike the controls, they displayed no systemic effects, even after repeated high-dose applications. Surprisingly, propionate 14 was devoid of atrophogenic activity.

Synthesis and testing of 17a beta-hydroxy-7 alpha-methyl-D-homoestra-4,16-dien-3-one: a highly potent orally active androgen

The title compound, 17a beta-hydroxy-7 alpha-methyl-D-homoestra-4,16-dien-3-one (3), was synthesized in five steps (17% overall yield) from 7 alpha-methylestrone methyl ether (5) and was found to possess oral androgenic activity, in excess of other known androgens, without using 17 alpha-alkyl substitution.

11 beta-nitrate estrane analogues: potent estrogens

Various estrane derivatives 1 reacted with cerium ammonium nitrate (CAN) selectively and efficiently to provide 9 alpha,11 beta-defunctionalized derivatives 2, which were subsequently deoxygenated at C-9 with triethylsilane/boron trifluoride etherate to the desired target 11 beta-nitratoestranes 3a, 3b, and 5. When examined for estrogenic and postcoital antifertility activity, 11 beta-nitrates 2c, 2d, and 3b most notably displayed more potent oral activity than did ethynylestradiol.

17-Desoxy estrogen analogues

A series of 17-substituted, 17-desoxyestratrienes have been synthesized and tested as potential postcoital antifertility agents. Estrogen-relative binding affinities were determined, in vivo assays for estrogenic and postcoital antifertility activity were conducted in rats, and selected candidate compounds were further tested for estrogenic activity in monkeys. In the rat, the 17-desoxyestratriene derivatives 8a, 8b, and 30 have shown low estrogenic activity while retaining potent antifertility activity. Structural modifications at the outset included a variety of 17-substituents and an omission of the 17-oxygen functionality, which was previously thought to be necessary for potent activity. The 17 beta-ethyl side chain exhibited the greatest antifertility activity with the largest separation ratio to estrogenicity. Nuclear modification of 17-desoxyethylestrane derivatives at positions 7 and 11 further increased the desired separation of activity, with the 11-hydroxy moiety enhancing separation more than other features.

Analogues of [(triethylsilyl)ethynyl]estradiol as potential antifertility agents

Various 17 alpha-ethynylsteroids were prepared and derivatized as the corresponding triethylsilyl compounds 2-35, which were examined for a ratio of antifertility to estrogenic activity that would be more beneficial than that of the presently used agent. Among the triethylsilyl compounds evaluated, only 23 displayed this desired ratio, although two other compounds without the triethylsilyl moiety, 18 and 26, shared similar characteristics.

Steroidal silicon side-chain analogues as potential antifertility agents

A number of silicon-substituted analogues of ethynylestradiol that exhibit modified and enhanced biological activities have been synthesized. Particularly noteworthy are a group of [(trialkylsilyl)ethynyl]estradiol analogues that exhibit high antifertility potency and markedly reduced estrogenic activity. The best compounds synthesized are 17 alpha-[(triethylsilyl)ethynyl]estradiol (5) and 17 alpha-[(tert-butyldimethylsilyl)ethynyl]estradiol (33), which show a separation of antifertility from estrogenic activity in the rat. The results of structure-activity studies indicate a good correlation between the observed biological activities and the calculated van der Waals volumes of the three variable silicon substituents.

Conjugates of catecholamines. 6. Synthesis and beta-adrenergic activity of N-(hydroxyalkyl)catecholamine derivatives

A new series of catecholamines has been prepared in which the N-alkyl substituent of dl-epinephrine or dl-isoproterenol has been extended by a methylene chain terminated by a hydroxyl group or derived functionality (e.g., carbamate or ester). These functionalized catecholamines (congeners) and model compounds were prepared with the goal of eventual attachment to polymeric carrier molecules. The beta-adrenergic agonist activity of the derivatives was evaluated in vitro by measuring the intracellular accumulation of cyclic AMP in S49 mouse lymphoma cells and by the displacement of iodocyanopindolol (ICYP). A n-butylcarbamate derivative (compound 15) was the most active compound in this series with a potency 190 times greater than dl-isoproterenol in the S49 assay. The biological results indicate that minor modifications in structure in the N-alkyl substituent of the catecholamine can influence the pharmacologic activity.