Fungal Planet description sheets: 1436-1477

Novel species of fungi described in this study include those from various countries as follows: Argentina, Colletotrichum araujiae on leaves, stems and fruits of Araujia hortorum. Australia, Agaricus pateritonsus on soil, Curvularia fraserae on dying leaf of Bothriochloa insculpta, Curvularia millisiae from yellowing leaf tips of Cyperus aromaticus, Marasmius brunneolorobustus on well-rotted wood, Nigrospora cooperae from necrotic leaf of Heteropogon contortus, Penicillium tealii from the body of a dead spider, Pseudocercospora robertsiorum from leaf spots of Senna tora, Talaromyces atkinsoniae from gills of Marasmius crinis-equi and Zasmidium pearceae from leaf spots of Smilaxglyciphylla. Brazil, Preussia bezerrensis from air. Chile, Paraconiothyrium kelleni from the rhizosphere of Fragaria chiloensis subsp. chiloensis f. chiloensis. Finland, Inocybe udicola on soil in mixed forest with Betula pendula, Populus tremula, Picea abies and Alnus incana. France, Myrmecridium normannianum on dead culm of unidentified Poaceae. Germany, Vexillomyces fraxinicola from symptomless stem wood of Fraxinus excelsior. India, Diaporthe limoniae on infected fruit of Limonia acidissima, Didymella naikii on leaves of Cajanus cajan, and Fulvifomes mangroviensis on basal trunk of Aegiceras corniculatum. Indonesia, Penicillium ezekielii from Zea mays kernels. Namibia, Neocamarosporium calicoremae and Neocladosporium calicoremae on stems of Calicorema capitata, and Pleiochaeta adenolobi on symptomatic leaves of Adenolobus pechuelii. Netherlands, Chalara pteridii on stems of Pteridium aquilinum, Neomackenziella juncicola (incl. Neomackenziella gen. nov.) and Sporidesmiella junci from dead culms of Juncus effusus. Pakistan, Inocybe longistipitata on soil in a Quercus forest. Poland, Phytophthora viadrina from rhizosphere soil of Quercus robur, and Septoria krystynae on leaf spots of Viscum album. Portugal (Azores), Acrogenospora stellata on dead wood or bark. South Africa, Phyllactinia greyiae on leaves of Greyia sutherlandii and Punctelia anae on bark of Vachellia karroo. Spain, Anteaglonium lusitanicum on decaying wood of Prunus lusitanica subsp. lusitanica, Hawksworthiomyces riparius from fluvial sediments, Lophiostoma carabassense endophytic in roots of Limbarda crithmoides, and Tuber mohedanoi from calcareus soils. Spain (Canary Islands), Mycena laurisilvae on stumps and woody debris. Sweden, Elaphomyces geminus from soil under Quercus robur. Thailand, Lactifluus chiangraiensis on soil under Pinus merkusii, Lactifluus nakhonphanomensis and Xerocomus sisongkhramensis on soil under Dipterocarpus trees. Ukraine, Valsonectria robiniae on dead twigs of Robinia hispida. USA, Spiralomyces americanus (incl. Spiralomyces gen. nov.) from office air. Morphological and culture characteristics are supported by DNA barcodes. Citation: Tan YP, Bishop-Hurley SL, Shivas RG, et al. 2022. Fungal Planet description sheets: 1436-1477. Persoonia 49: 261-350. https://doi.org/10.3767/persoonia.2022.49.08.

Cancer stem cell drugs target K-ras signaling in a stemness context

Cancer stem cells (CSCs) are considered to be responsible for treatment relapse and have therefore become a major target in cancer research. Salinomycin is the most established CSC inhibitor. However, its primary mechanistic target is still unclear, impeding the discovery of compounds with similar anti-CSC activity. Here, we show that salinomycin very specifically interferes with the activity of K-ras4B, but not H-ras, by disrupting its nanoscale membrane organization. We found that caveolae negatively regulate the sensitivity to this drug. On the basis of this novel mechanistic insight, we defined a K-ras-associated and stem cell-derived gene expression signature that predicts the drug response of cancer cells to salinomycin. Consistent with therapy resistance of CSC, 8% of tumor samples in the TCGA-database displayed our signature and were associated with a significantly higher mortality. Using our K-ras-specific screening platform, we identified several new candidate CSC drugs. Two of these, ophiobolin A and conglobatin A, possessed a similar or higher potency than salinomycin. Finally, we established that the most potent compound, ophiobolin A, exerts its K-ras4B-specific activity through inactivation of calmodulin. Our data suggest that specific interference with the K-ras4B/calmodulin interaction selectively inhibits CSC.

Oligomycins as inhibitors of K-Ras plasma membrane localisation

Frequently present in pancreatic, colorectal and non-small cell lung carcinomas, oncogenic mutant K-Ras must be localised to the plasma membrane (PM) to be functional. Inhibitors of K-Ras PM localisation are therefore putative cancer chemotherapeutics. By screening a microbial extract library in a high content cell-based assay we detected the rare oligomycin class of Streptomyces polyketides as inhibitors of K-Ras PM localisation. Cultivation and fractionation of three unique oligomycin producing Streptomyces strains yielded oligomycins A-E (1-5) and 21-hydroxy-oligomycin A (6), together with the new 21-hydroxy-oligomycin C (7) and 40-hydroxy-oligomycin B (8). Structures for 1-8 were assigned by detailed spectroscopic analysis. Cancer cell viability screening confirmed 1-8 were cytotoxic to human colorectal carcinoma cells (IC50 > 3 μM), and were inhibitors of the ABC transporter efflux pump P-glycoprotein (P-gp), with 5 being comparable in potency to the positive control verapamil. Significantly, oligomycins 1-8 proved to be exceptionally potent inhibitors of K-Ras PM localisation (Emax 0.67-0.75 with an IC50 ~ 1.5-14 nM).

The isolation and synthesis of novel nematocidal dithiocyanates from an Australian marine sponge, Oceanapia sp

Bioassay-directed fractionation of the EtOH extract of an Oceanapia sp. collected off the northern Rottnest Shelf, Australia, has yielded three novel dithiocyanates, thiocyanatins A (1), B (2a), and C (2b). The structures were determined by detailed spectroscopic analysis and confirmed by total synthesis. In addition to featuring an unprecedented dithiocyanate functionality, thiocyanatins possess an unusual 1,16-difunctionalized n-hexadecane carbon skeleton and are revealed as a hitherto unknown class of nematocidal agent.

Onnamide F: a new nematocide from a southern Australian marine sponge, Trachycladus laevispirulifer

A southern Australian marine sponge, Trachycladus laevispirulifer, has yielded a potent new nematocide with antifungal activity which has been identified as onnamide F (1). The structure for 1 was assigned by detailed spectroscopic analysis and chemical conversion to the methyl ester 2. Onnamide F contains a common structural motif previously described in a number of natural products exhibiting interesting pharmacological activities, including the insect chemical defense agent pederin (3), and the sponge metabolites the onnamides, mycalamides, and theopederins.

Lorneamides A and B: two new aromatic amides from a southern Australian marine actinomycete

A marine actinomycete (MST-MA190) isolated from a sample of beach sand collected near Lorne on the southwest coast of Victoria, Australia, has yielded two new aromatic amides, lorneamide A (1) and lorneamide B (2). The lorneamides belong to a novel class of tri-alkyl-substituted benzenes, and their structures were determined by spectroscopic methods.

Cachexia induction by EL-4 lymphoma in mice and possible involvement of impaired lipoprotein lipase activity

Several lines of evidence have postulated that reduction in the activity of lipoprotein lipase (LPL) is involved in cachexia induction in cancer patients. Recently we have demonstrated that murine melanoma B16 has the ability to reduce the LPL activity and thereby induce cachexia symptoms in mice following intraperitoneal inoculation. In order to further investigate the relationship between LPL activity and cachectic syndrome, cachexia models other than melanoma B16 are required. However, there are few animal cachexia models in which LPL activity is involved in the induction of cachectic symptoms. In this study, cachectic symptoms and plasma LPL activity were investigated in mice bearing EL-4 mouse lymphoma. In EL-4 bearing mice the body weight including tumor weight in the abdominal cavity was rather higher than that of normal mice without tumor, whereas weights of carcass wet and gastrocnemius muscle were significantly decreased in EL-4 bearing mice. Elevated blood levels of triglyceride and non-esterified fatty acid were observed in mice bearing EL-4, associated with the impaired plasma LPL activity. Overall, this study indicated that EL-4 lymphoma in mice results in a severe cachexia which is possibly related to impaired LPL activity and also provided a useful cachexia model for understanding the role of LPL in the development of cancer cachexia.

The binding of closantel to ovine serum albumin, and homogenate fractions of Haemonchus contortus

Closantel binds to the serum proteins of the host and affects blood sucking parasites when they ingest the blood of treated hosts. Closantel binds specifically to ovine serum albumin (K(a) of 9. 3x10(6)M(-1)) at site I, the warfarin/phenylbutazone binding site of albumin Closantel also binds to invertebrate haemocyanin and haemolymph. The strongest binding of closantel in homogenates of H. contortus is found in fractions containing soluble proteins. This binding is of low affinity and, because the site itself is not fully denaturable, it may not be proteinaceous. There is no detectable difference in binding affinity between homogenate fractions from closantel susceptible and resistant isolates of adult or larval worms suggesting that closantel resistance is not due to changes in the closantel receptor or carrier.

Structures of flagranones A, B and C, cyclohexenoxide antibiotics from the nematode-trapping fungus Duddingtonia flagrans

Spectroscopic data define the structures of the flagranones A (2), B (3) and C (4) from the nematode-trapping fungus Duddingtonia flagrans. These antibiotics are structurally related to the farnesylated cyclohexenoxides of the oligosporon group recently isolated from the nematode-trapping fungus Arthrobotrys oligospora, and show similar antimicrobial activity.

Ponalrestat, an aldose reductase inhibitor, inhibits cachexia syndrome in nude mice bearing human melanomas G361 and SEKI

Our recent study has demonstrated that ponalrestat, an aldose reductase inhibitor, activates lipoprotein lipase (LPL) activity in the adipose tissue and alleviates the cachectic symptoms induced by B16 melanoma in mice. In this study, the effect of ponalrestat on cachexia symptoms in nude mice bearing human melanomas G361 and SEKI was investigated because it has been suggested that the suppression of LPL has an important role in cachexia induction by these two melanomas in nude mice. Mice bearing G361 subcutaneously did not gain weight and became cachectic, associated with the tumor growth. Tumor growth was not affected by ponalrestat, nevertheless treatment with ponalrestat resulted in an amelioration of the reduction in the weight of body mass, epididymal fat, gastrocnemius muscle, carcass and whole body lipid induced by the presence of G361. A severe weight loss observed in nude mice bearing SEKI was also partially attenuated by ponalrestat treatment. Overall, this study showed that ponalrestat is effective in the attenuation of the cachectic symptoms induced by human melanomas G361 and SEKI in nude mice, suggesting that ponalrestat has a potential usefulness for the treatment of cancer cachexia.

Ponalrestat, an aldose reductase inhibitor, inhibits cachexia syndrome induced by colon26 adenocarcinoma in mice

Our recent study has demonstrated that ponalrestat, an aldose reductase inhibitor, activates lipoprotein lipase activity and alleviates B16 melanoma-induced cachexia in mice. In this study, the effect of ponalrestat on murine adenocarcinoma colon26-induced cachexia was investigated in mice. Mice bearing colon26 subcutaneously lost weight and became cachectic, associated with the tumor growth. Although tumor growth was slightly stimulated when tumor bearing mice were treated with ponalrestat: nevertheless, the drug attenuated the reduction in the weight of body mass, epididymal fat, gastrocnemius muscle and carcass induced by colon26, as well as significantly prolonged the survival of the colon26 bearing mice. Ponalrestat inhibited the production of interleukin-1 (IL-1) from human monocytes stimulated by Lipopolysaccharide (LPS) in vitro, and also suppressed LPS-induced increase of IL-1 in the blood in mice. Overall, this study showed that ponalrestat suppresses IL-1 production both in vitro and in vivo, and inhibits the cachectic symptoms induced by colon26 adenocarcinoma in mice, suggesting that ponalrestat has a therapeutic potential for the treatment of cancer cachexia.

Geodin A magnesium salt: A novel nematocide from a southern australian marine sponge, geodia

A Geodia species collected from southern Australian waters of the Great Australian Bight has yielded a potent new in vitro nematocidal agent identified as geodin A Mg salt (1), a new macrocyclic polyketide lactam tetramic acid magnesium salt. The structure for 1 was assigned on the basis of detailed spectroscopic analysis.

Intratumoral injection of oligonucleotides to the NF kappa B binding site inhibits cachexia in a mouse tumor model

Cancer cachexia, characterized by anorexia, weight loss and progressive tissue wasting, has been postulated to be mediated by various cytokines. However, the precise mechanism of cachexia induction is not fully explained. We have developed synthetic double-stranded oligodeoxynucleotides (ODN) as 'decoy' cis-elements that block the binding of nuclear factors to promoter regions of targeted genes, resulting in the inhibition of gene transactivation in vivo as well as in vitro. This novel molecular strategy could be useful for treating a broad range of human diseases including cancer. In this study, we injected decoy ODN targeting the transcriptional factor, NF-kappa B (NF kappa B) binding cis-elements, which are essential for transactivation of gene expression of cytokines, directly into tumors of adenocarcinoma colon26 in mice, in order to examine whether or not cachexia is alleviated by inhibiting the action of cytokines. Tumor growth was not affected by transfection of NF kappa B decoy ODN as compared with scrambled decoy ODN. Nevertheless, transfection of NF kappa B decoy, but not scrambled decoy, ODN resulted in attenuation of the reductions in body weight, epididymal fat, gastrocnemius muscle mass and food intake, which were induced by the tumor presence. Interleukin 6 mRNA in the tumor was also markedly decreased by the transfection of NF kappa B decoy ODN. It is known that the transcriptional factor E2F plays a pivotal role in the coordinated transactivation of cell cycle regulatory genes. Therefore, we hypothesized that the introduction of synthetic double-stranded DNA with high affinity for E2F in vivo as 'decoy' cis-elements might inhibit the tumor growth of colon26, resulting in turn in inhibition of cachexia induction. However, injection of E2F decoy ODN failed to inhibit tumor growth and cachexia induction, as compared with mismatched decoy ODN. Overall, the present study demonstrated that cachexia induced by adenocarcinoma colon26 was inhibited by blocking of NF kappa B, using a novel molecular decoy strategy, without an effect on tumor growth, and also that tumor growth and cachexia induction in the colon26 model were not affected by E2F decoy ODN. These results suggest that cytokines regulated by NF kappa B may play a pivotal role in the induction of cachexia by colon26, providing a new therapeutic strategy for cancer cachexia.

Structure of actinotetraose hexatiglate, a unique glucotetraose from an actinomycete bacterium

An Actinomycete strain A499 belonging to the genera Amycolatopsis or Amycolata isolated from a Western Australian soil sample produced the cyclic decapeptide antibiotic quinaldopeptin (1), together with the actinotetraose hexatiglate (2), the hexa-ester of a novel non-reducing glucotetraose.

Avermectin/milbemycin resistance in trichostrongyloid nematodes

Resistance to levamisole and the benzimidazoles appears to be achieved by one or, at most, two mechanisms in the common trichostrongyloid parasites of sheep. For the avermectin/milbemycin anthelmintic class the picture is more complex. In-vitro assays employing the free-living stages of trichostrongyloid nematodes were used to investigate structure-activity relationships for the avermectins/milbemycins. While avermectin/milbemycin-susceptible isolates of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia circumcincta were found to differ in their intrinsic sensitivities to avermectin/milbemycin inhibition of larval development and L3 motility, structure-activity profiles against all three species were similar. In-vivo avermectin/milbemycin resistance was associated with a reduced sensitivity to avermectin/milbemycin inhibition of larval motility and/or development in some, but not all, isolates. Where a reduced sensitivity to avermectin/milbemycin inhibition of larval development was observed, different groups of resistant isolates displayed different structure-activity profiles. Many avermectin/milbemycin-resistant isolates showed an increased sensitivity to paraherquamide. These in-vitro data have allowed the classification of avermectin/milbemycin-resistant isolates into a number of distinct types. Study of the inheritance of avermectin/milbemycin resistance in two resistance types suggests that the in-vitro differences between resistant isolates reflect important differences in the mechanism of resistance present. The kinetics of expulsion of H. contortus, T. colubriformis and O. circumcincta from sheep following treatment with ivermectin indicate that, in vivo, the critical action of avermectins/milbemycin against O. circumcincta may be different to that which results in H. contortus and T. colubriformis elimination. This observation provides some explanation for the differences between resistant isolates. If, for different species, the critical event(s) leading to expulsion are different, then it follows that the mechanisms of resistance observed may also differ.

Evidence of multiple mechanisms of avermectin resistance in haemonchus contortus--comparison of selection protocols

Three isolates of Haemonchus contortus selected for avermectin resistance in sheep were compared in three in vitro pharmacological tests previously shown to discriminate between field isolates of H. contortus resistant and susceptible to the avermectins. Two isolates, F7-A and IVC, were selected for avermectin resistance in the laboratory from a reference susceptible isolate using suboptimal doses of ivermectin (LD95) for 7 and 16 generations, respectively. In these isolates avermectin resistance was not associated with a decreased sensitivity to avermectin inhibition of larval development or L3 motility but was associated with an increased sensitivity to paraherquamide. The third isolate, Warren, was derived from an overwhelmingly avermectin-susceptible, mixed species field isolate in a single generation by propagating the small number of survivors of a 0.2 mg/kg ivermectin treatment (i.e. 10 x LD95). This isolate, like previously characterised avermectin-resistant H. contortus isolates derived from the field in South Africa and Australia, showed a markedly reduced sensitivity to avermectin inhibition of larval development and L3 motility, as well as an increased sensitivity to paraherquamide. These results suggest that avermectin resistance can manifest itself in different ways and that the two selection protocols used to generate the F7-A, IVC and Warren isolates have resulted in the selection of different resistance phenotypes.

Parental effects on seed mass: seed coat but not embryo/endosperm effects

Many biologists studying environmentally induced parental effects have indirectly suggested that the parental environment alters seed mass by altering the amount of endosperm or embryo tissue in the seed. We tested this hypothesis by measuring the effects of parental temperature on total seed mass, seed coat mass, and embryo/endosperm mass in offspring of Plantago lanceolata. Parental temperature significantly affected total seed and coat mass but not endosperm/embryo mass. Thus, larger seeds do not contain more resources in the embryo or endosperm than do small seeds. Rather they have more coat mass, which probably strongly influences germination. These results suggest caution when making assumptions about the pathways by which environmentally induced parental effects are transmitted in plant species. We also observed that controlled crosses differed significantly in their response to parental temperature, which provides evidence for genetic variation in environmentally induced parental effects, i.e., intergenerational phenotypic plasticity, in natural populations of P. lanceolata.

Mechanism of growth inhibition by calpain inhibitor in MCF-7 cells

BACKGROUND

A calpain inhibitor, calpeptin, inhibited the cell growth of ER (estrogen receptor) positive breast cancer cells, such as MCF-7, T-47D, and ZR-75-1 in the presence of E2. The mechanism of this inhibition has not been clarified yet.

MATERIALS AND METHODS

MCF-7 cells were employed to investigate the mechanism of the inhibition. We studied the effect of calpeptin on the secretion of insulin-like growth factor-I (IGF-I) and transforming growth factor (TGF-alpha).

RESULTS

The secretion of IGF-I or TGF-alpha was not changed by calpeptin either in the presence or absence of E2. Moreover, the binding of IGF-I or TGF-alpha to MCF-7 cells augmented by the addition of E2 was not affected by calpeptin.

CONCLUSIONS

These results indicated that the inhibition of cell growth in MCF-7 by calpeptin was not due to the modulation of autocrine growth factors and their receptors.

A new aromatase inhibitor, FR901537. II. Pharmacological and antitumor effects

The pharmacological and antitumor effects of FR901537, a new aromatase inhibitor, isolated from Bacillus sp. No. 3072, were studied. Treatment for four consecutive days with FR901537 inhibited the androstenedione-induced increase in the uterus weight in immature rats. FR901537 had no effect on the uterus, adrenal glands, ovary or pituitary weights in mature rats following 14 days of treatment. The antitumor activity of FR901537 on 7,12-dimethylbenz(a)anthracene-induced mammary tumors was studied in ovariectomized, testosterone propionate (TP)-treated rats as a postmenopausal tumor model. Ovariectomy caused the regression of the mammary tumors and the growth of tumors was remarkably stimulated following TP treatment. Further, in the rats treated with FR901537 and TP, the TP-induced tumor growth was significantly inhibited by FR901537. These results suggest that FR901537 is a promising drug in the treatment of estrogen-dependent mammary tumors in postmenopausal women.

Characterisation of an avermectin resistant strain of Australian Haemonchus contortus

A strain of Haemonchus contortus (CAVR) isolated in Australia was found to be resistant to ivermectin (IVM) with 0.4 mg kg-1 of the anthelmintic failing to significantly reduce worm burdens. Resistance to IVM was sex-influenced in the CAVR strain with adult males showing a greater sensitivity to IVM. Cross resistance to moxidectin was evident with approximately 15% of the population surviving a dose of 0.1 mg kg-1. The free-living stages of the CAVR isolate had a reduced sensitivity to avermectin (AVM) inhibition of development and motility. Similar structure-activity patterns and resistance factors were obtained for a series of related AVMs as inhibitors of larval development and L3 motility in CAVR and White River II, an IVM-resistant H. contortus isolate from South Africa. Further, both isolates were found to be 3 times more sensitive to paraherquamide than a susceptible H. contortus isolate. This suggest that the same resistance mechanism is operating in both isolates. The CAVR strain is susceptible to the benzimidazoles, levamisole and closantel.

Inhibition of [3H]mebendazole binding to tubulin by structurally diverse microtubule inhibitors which interact at the colchicine binding site

A rapid and convenient radioligand assay was used to characterise the interaction of several structurally diverse microtubule inhibitors with the colchicine binding domain of tubulin. Values determined for the inhibition of [3H]mebendazole binding to tubulin by colchicine, combretastatin A4, NSC 181928, NSC 321567, podophyllotoxin and tubulozole-C provided an independent measure of the relative potency of these compounds. This methodology has several advantages over the inhibition of [3H]colchicine binding as a technique for investigating the molecular mechanisms involved in determining tubulin-ligand interactions.

Avermectin inhibition of larval development in Haemonchus contortus--effects of ivermectin resistance

Avermectin (AVM) inhibition of the development of the free-living stages of Haemonchus contortus has been quantified in an assay in which nematode eggs are placed on an agar matrix containing serial dilutions of a drug in the wells of a microtitre plate. Development is allowed to proceed for 6 days by which time larvae in control wells (no drug) have reached the infective, third (L3) stage. At high concentrations (> 30 nM) ivermectin (IVM) paralyses L1 larvae soon after hatching, however, much lower concentrations (approximately 1 nM) are sufficient to inhibit development to the L3 stage which suggests that effects of the drug other than those relating to gross motor activity are responsible for the latter effect. The larval stages of IVM-susceptible H. contortus isolates from both Australia and South Africa, including isolates known to be resistant to levamisole or rafoxanide and/or the benzimidazoles, were equally sensitive to inhibition by AVMs. In contrast, 6 isolates of H. contortus resistant to IVM in vivo showed a reduced sensitivity to AVM inhibition of development. The order of potency of a limited range of AVMs as inhibitors of larval development was consistent with in vivo efficacy. Resistance ratios for IVM-resistant isolates were dependent on AVM structure, with AVM B2 the most sensitive probe for IVM resistance in the isolates tested.

Bafilolides, potent inhibitors of the motility and development of the free-living stages of parasitic nematodes

Three Streptomyces isolates were identified as producing macrolide antibiotics of the bafilomycin or leucanicidin types during an evaluation of Australian actinomyces for the production of inhibitors of larval development in the parasitic nematode, Haemonchus contortus. Bafilomycins A1, B1, C1, and D were obtained from culture A239 and the 2-O-methyl-L-rhamnosyl derivative of bafilomycin A1, leucanicidin, from cultures A223 and A240. All these 'bafilolides' gave similar patterns of inhibition typified by an initial paralysis of newly hatched L1 larvae and a lethal toxicity within 24 h. LD50 values for inhibition of larval development of McMaster H. contortus ranged from 0.23 micrograms ml-1 for leucanicidin to 2.5 micrograms ml-1 for bafilomycin D. The bafilolides had broad spectrum nematocidal activity, being equi-potent as inhibitors of H. contortus, Trichostrongylus colubriformis and Ostertagia circumcincta larval development. Further, all bafilolides caused some inhibition of H. contortus L3 motility, with the semi-synthetic analogue, bafilomycin B2, the most potent inhibitor (LP50 against McMaster H. contortus 1.9 microgram ml-1). Nematode strains resistant to the known benzimidazole, levamisole and avermectin anthelmintics showed no cross resistance to the bafilolides, supporting the hypothesis that the bafilolides act by an independent mechanism.

Binding sites of droloxifene in the cytosol of 7,12-dimethylbenz[a]anthracene-induced rat mammary tumor cells

The binding sites, other than the estrogen receptor (ER), of the antiestrogens droloxifene (DROL, (E)-a-[p-[2-(dimethylamino)ethoxy]-phenyl]-a'-ethyl-3-stilbenol) and tamoxifen (TAM), and estradiol-17 beta (E2) in the cytosol of 7,12-dimethylbenz[a]anthracene-induced rat mammary ER-positive tumor cells were studied using a high-performance liquid chromatography (HPLC) gel filtration assay. The cytosol was incubated with 3H-labeled drug with or without unlabeled drug, and separated by HPLC gel filtration. 3H-E2 produced two major peaks of radioactivity at fractions No. 40 and No. 70. The peak at fraction No. 70 was identified as the ER in an ER-enzyme-immuno assay. This peak was dose-dependently inhibited by unlabeled DROL or TAM, DROL being a more potent inhibitor than TAM. The peak at fraction No. 40 was also inhibited by co-incubation with unlabeled DROL or TAM. 3H-DROL or 3H-TAM provided only one peak at fraction No. 43. This peak was thought to be an antiestrogen binding site (AEBS), because it was inhibited by unlabeled antiestrogen but not by E2. The results suggest that the antiestrogens DROL and TAM have a higher affinity for the AEBS than for the ER in the absence of E2, while in the presence of E2 both have an affinity for the ER and inhibit E2 binding to the ER.

The effect of droloxifene on the insulin-like growth factor-I-stimulated growth of breast cancer cells

Insulin-like growth factor-I (IGF-I) is an important mitogen in breast cancer. We studied here the effects of a new antiestrogen drug, droloxifene (DROL, (E)-alpha-[p-[2-(dimethylamino) ethoxy]-phenyl]-alpha'-ethyl-3-stilbenol) and tamoxifen (TAM) on the IGF-I-stimulated growth of estrogen receptor (ER) positive breast cancer cells, MCF-7 and their mechanism of action. IGF-I secretion from MCF-7 was increased by the addition of estrogen. Externally added IGF-I stimulated the growth of MCF-7 but not ER negative breast cancer cells, MDA-MB-231. DROL and TAM inhibited the IGF-I-stimulated growth of MCF-7. A 2 hr treatment with both drugs did not block IGF-I binding to the receptors in MCF-7. However, a 4 day treatment with DROL decreased the number of IGF-I receptors without altering the binding affinity in MCF-7. These results suggest that DROL can exert its antitumor activity against ER positive breast cancer not only by blocking the E2 binding to the ER, but also by counteracting the mitogenic effect of IGF-I.

Biochemistry of benzimidazole resistance

Heavy reliance on the benzimidazole (BZ) anthelmintics since their introduction in the 1960's for the control of gastrointestinal parasites of livestock has led to widespread BZ resistance in target parasite species. The BZs exert their primary action by binding to tubulin, the major protein component of microtubules. This review discusses the biochemistry of the interaction between the BZs and tubulin from mammalian and BZ-resistant and -susceptible parasite sources, exploring aspects of the selective toxicity of these drugs and examining the mechanism of BZ resistance. Although tubulin is a highly conserved protein present in both the host and the parasite, the BZs demonstrate relatively low mammalian toxicity. The selectivity of these drugs can be explained by the much higher affinity of the BZs for tubulin from the parasite at 37 degrees C compared to their affinity for tubulin from the host. This difference in affinity reflects the considerably slower rate of BZ dissociation from parasite tubulin. BZ-resistance in parasitic nematodes is characterised by a loss of high affinity BZ-parasite tubulin interactions and a corresponding increase in lower affinity interactions, although there are still significant differences between BZ-resistant parasite tubulin and tubulin from the host. These differences suggest the potential for the design of new generation BZs active against 'BZ-resistant' parasites.

The estrogenic and antiestrogenic activities of droloxifene in human breast cancers

The effects of a new antiestrogen, droloxifene (DROL, (E)-alpha-[p-[2-(dimethylamino)ethoxy]-phenyl]-alpha'-ethyl-3- stilbenol), on human breast cancer cells in vitro and in vivo were studied. Since phenol red has a binding affinity to the estrogen receptor (ER), we studied the activities of drugs in medium with or without this indicator. Estradiol-17 beta (E2) stimulated the growth of ER-positive breast cancer cells, MCF-7, ZR-75-1 and T-47D, in medium without phenol red, but not in medium containing this indicator. In medium without phenol red, DROL had no marked effects on the growth of MCF-7 and ZR-75-1, but slightly stimulated the growth of T-47D. Tamoxifen (TAM) stimulated the growth of these 3 cells. DROL dose-dependently inhibited the E2-induced stimulation of growth of these cells in medium without phenol red, but TAM inhibited the growth only at high concentrations. The growth of ER-negative breast cancer cells, MDA-MB-231, was not influenced by E2, DROL or TAM. DROL was more effective than TAM against ER-positive Br-10 breast carcinoma in nude mice, but neither drug had effects on ER-negative MX-1 breast carcinoma. These results suggest that DROL shows an antitumor effect on ER-positive breast cancers, being less estrogenic and more antiestrogenic than TAM.

In vitro activity of paraherquamide against the free-living stages of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia circumcincta

Paraherquamide, an oxindole alkaloid recently reported to have potent nematocidal activity, was shown to have a marked inhibitory effect on the motility of the free-living larval stages of H. contortus, T. colubriformis and O. circumcincta. The effect of paraherquamide on larval motility could be distinguished from that caused by levamisole and the avermectins. After 72 h exposure, the concentration of paraherquamide required to inhibit the motility of 50% of L3 larvae present was 0.033, 0.058 and 2.7 micrograms ml-1 for O. circumcincta, T. colubriformis and H. contortus, respectively. Ivermectin (IVM)-resistant isolates of H. contortus were significantly more sensitive to the paralytic effects of paraherquamide than IVM-susceptible isolates of this species. Paraherquamide had no effect on the time for development from the egg to the L3 larval stage of H. contortus, T. colubriformis and O. circumcincta.

The kinetics of mebendazole binding to Haemonchus contortus tubulin

The kinetics of the binding of mebendazole (MBZ) to tubulin from the third-stage (L3) larvae of the parasitic nematode, Haemonchus contortus, have been characterized. In partially purified preparations, the association of [3H]MBZ to nematode tubulin was rapid, k1 = (2.6 +/- 0.3) x 10(5) M-1 min-1, but dissociation was slow, k-1 = (1.58 +/- 0.02) x 10(-3) min-1. The affinity constant (K(a)) for the interaction, determined by the ratio k1/k-1, was (1.6 +/- 0.2) x 10(8) M-1. Similar results were obtained with crude cytosolic fractions. In equilibrium studies, performed with partially purified nematode tubulin under similar conditions, a K(a) of (5.3 +/- 1.6) x 10(6) M-1 was obtained. The best estimate for the K(a) of the MBZ-nematode tubulin interaction is considered to be the 'kinetic' value determined from the ratio of rate constants. The slow dissociation of MBZ from nematode tubulin, which contrasts with the rapid dissociation of MBZ from mammalian tubulin, supports the hypothesis that the selective toxicity of the benzimidazole anthelmintics results from a difference between the affinities of mammalian and nematode tubulins for these drugs.

Differential stability of the benzimidazole (BZ)-tubulin complex in BZ-resistant and BZ-susceptible isolates of Haemonchus contortus and Trichostrongylus colubriformis

The binding of [3H]mebendazole ([3H]MBZ) to tubulin from BZ-susceptible (BZ-S) and BZ-resistant (BZ-R) isolates of Haemonchus contortus and Trichostrongylus colubriformis was investigated using charcoal extraction and gel filtration techniques. The amount of [3H]MBZ bound at infinite free ligand concentration (Bmax) was significantly reduced for the BZ-R isolate compared with the BZ-S isolate in both species when assayed by charcoal extraction. However, Bmax was increased to comparable levels for both BZ-S and BZ-R isolates of each species when assayed by the less stringent gel filtration technique. These results indicate that the BZ-tubulin interaction in trichostrongylid nematodes is comprised of a minimum of two components. As similar levels of total [3H]MBZ binding were observed for both BZ-S and BZ-R isolates of each species when assayed by gel filtration, it is suggested that the reduction in the pseudo-irreversible BZ binding component in BZ-R isolates results in an increase in the level of reversible BZ binding and therefore provides a survival advantage to BZ-R nematodes.

Binding of [3H]benzimidazole carbamates to mammalian brain tubulin and the mechanism of selective toxicity of the benzimidazole anthelmintics

The binding of tritiated benzimidazole carbamates ([3H]BZCs) to mammalian brain tubulin was examined to investigate the kinetics of the BZC-tubulin interaction and to establish the mechanism of the selective toxicity of the BZC based anthelmintics. [3H]BZC binding to tubulin was markedly greater at 4 degrees than at 37 degrees for all ligands. The association constant (Ka) and maximum amount of [3H]BZC bound (Bmax) were temperature dependent for [3H]mebendazole ([3H]MBZ), [3H]oxibendazole ([3H]-OBZ) and [3H]oxfendazole ([3H]OFZ). The Ka and Bmax values obtained for [3H]MBZ, [3H]OBZ and [3H]OFZ, and the comparatively weak binding of [3H]carbendazim, reflected the known in vitro potency of these compounds as microtubule inhibitors. Dissociation of the [3H]MBZ-tubulin complex was also temperature dependent, the first order dissociation rate constant being reduced by two orders of magnitude at 4 degrees compared with that observed for 37 degrees. These results indicate that the binding of BZCs to mammalian brain tubulin is temperature dependent and suggest that temperature induced conformational changes in the tubulin dimer influence the ability of the BZCs to form a stable BZC-tubulin complex. The temperature dependence of BZC binding and the affinity of the BZCs for mammalian tubulin are therefore unlike the BZC-tubulin interaction observed for parasitic nematodes, where optimum BZC binding occurs at 37 degrees and results in the formation of a pseudo-irreversible complex.

The effect of co-administration of parbendazole on the disposition of oxfendazole in sheep

The effect of intraruminal administration of parbendazole (PBZ) on the flow rate of bile and the pharmacokinetic behaviour of oxfendazole (OFZ) was examined in sheep. PBZ given at 18, 9 and 4.5 mg/kg resulted in a dose-related reduction in bile flow rate which was also inversely related to changing concentration of PBZ and its metabolites in plasma. Co-administration of 4.5 mg PBZ/kg with 5.0 mg [14C]-OFZ/kg resulted in increased concentrations of fenbendazole (FBZ), OFZ and fenbendazole sulphone (FBZ-SO2) in plasma, although total 14C levels remained unchanged compared with that observed when OFZ alone was administered. The presence of PBZ also reduced biliary secretion of 14C by 22% and altered the relative proportions of OFZ metabolites in bile during the 72-h experimental period. The ratio of 4'-hydroxy-OFZ (OH-OFZ) to 4'-hydroxy-FBZ (OH-FBZ) changed from 7:1 in the absence of PBZ to approximately 1:1 in the presence of PBZ. There was no change in urinary or faecal 14C excretion. The PBZ-induced effects were temporary since the pharmacokinetic behaviour of OFZ given alone two weeks before was similar to that given two weeks after PBZ co-administration. It is suggested that the presence of PBZ temporarily slowed hepatic metabolism and biliary secretion of OFZ metabolites but concomitantly increased extra-biliary transfer of OFZ and/or its metabolites from plasma into the gastrointestinal tract. Elevated exposure of parasites in the gut wall to plasma-derived drug, coupled with higher concentrations of anthelmintically active OH-FBZ secreted in bile, could contribute to the previously reported increased efficacy of OFZ when co-administered with PBZ.

Temperature dependent binding of mebendazole to tubulin in benzimidazole-susceptible and -resistant strains of Trichostrongylus colubriformis and Caenorhabditis elegans

The binding of [3H]mebendazole ([3H]MBZ) to tubulin in benzimidazole-susceptible (BZ-S) and benzimidazole-resistant (BZ-R) strains of Trichostrongylus colubriformis and Caenorhabditis elegans was examined in order to investigate the biochemical changes to tubulin that result in BZ resistance in parasitic and free-living nematodes. In both species the extent of [3H]MBZ binding to tubulin was significantly reduced in the BZ-R strain compared with the BZ-S strain. The decrease in [3H]MBZ binding in the BZ-R strain of each species was the result of a significant reduction in the amount of charcoal stable [3H]MBZ-tubulin complexes and was not related to a change in the association constant of the [3H]MBZ-tubulin interaction. [3H]MBZ binding to tubulin was temperature dependent, reaching maximum levels at 37 degrees C in BZ-S T. colubriformis and 10 degrees C in BZ-R T. colubriformis. Both the BZ-S and BZ-R strains of C. elegans displayed maximum [3H]MBZ binding at 4 degrees C. Resistance ratios derived from the amount of [3H]MBZ binding in the BZ-S and BZ-R strains and in vitro development assays demonstrated that the temperature dependence and extent of drug binding was indicative of BZ resistance status and was species specific in the BZ-S isolates. These results indicate that biochemical differences exist in the binding of benzimidazole carbamates to tubulin in nematode species, and suggest that the susceptibility of the parasitic nematodes to the benzimidazole anthelmintics is the result of a unique high affinity and/or high capacity interaction of benzimidazole carbamates with tubulin.

Detection of resistance to ivermectin in Haemonchus contortus

Infective, third-stage (L3) larvae of Haemonchus contortus isolates resistant to ivermectin (IVM) show a decreased sensitivity to IVM-induced paralysis in vitro. The inhibition of larval motility by IVM can be detected in L3 larvae incubated in the dark on an agar matrix containing IVM, by the failure of affected larvae to move when stimulated by exposure to light. Optimally, avermectin (AVM) potency is quantified after three cycles, each involving storage in the dark for 24 h followed by a brief exposure to light. For IVM-susceptible isolates, a 50% inhibition of motility (LP50) was achieved with IVM concentrations between 0.30 and 0.49 microM, while LP50 values in IVM-resistant isolates ranged from 0.8 to 2.6 microM depending on the in vivo resistance status of the isolate. A limited study of structure-activity relationships within the AVM class indicated that in vitro inhibition of L3 motility was consistent with the known in vivo efficacy of each analogue. Resistance factors for IVM-resistant isolates were dependent on AVM structure with the more polar AVM B2 analogue being a particularly sensitive probe of IVM-resistance status.

Effect of phomopsin A on the alkylation of tubulin

Phomopsin A, a macrocyclic heptapeptide isolated from the fungus Phomopsis leptostromiformis, is a potent inhibitor of microtubule assembly and of vinblastine binding to tubulin. Like vinblastine, phomopsin A stabilizes colchicine binding to tubulin. Because phomopsin A is structurally very different from either vinblastine or maytansine, it was of interest to compare its effects on tubulin sulfhydryls to those of the other two drugs. Our results indicate that the effects of phomopsin A combine those of maytansine and vinblastine. Like maytansine, phomopsin A completely inhibited formation of a covalent cross-link between cysteines 12 and 201 or 211, induced by N,N'-ethylenebis(iodoacetamide); like vinblastine, phomopsin A strongly inhibited alkylation of tubulin by iodo[14C]acetamide. Our results are consistent with the hypothesis that phomopsin A binds to regions on tubulin overlapping those to which vinblastine and maytansine bind. We have shown previously that phomopsin A is a potent stabilizer of the tubulin molecule. We now find that when both phomopsin A and colchicine are bound to tubulin, the rate of decay of colchicine binding becomes insignificant.

Mode of action of benzimidazoles

Benzimidazoles represent the only class of truly broad-spectrum anthelmintics, however, they also show activity against fungi and mammalian cells. This raises the question as to why benzimidazoles can selectively kill helminths and yet exhibit little or no mammalian toxicity. In this paper, Ernest Lacey examines this example of selectivity of drug action to the ubiquitous target of these drugs, the structural protein, tubulin.

Isolation of mammalian brain tubulin by amino-activated gel chromatography

In the present study, we report the isolation of the acidic structural protein tubulin using a number of amino-activated gels. Crude 100,000 g supernatant derived from sheep brain was applied to gels activated with either aminohexyl, aminoethyl, argininyl, diethylaminoethyl, lysinyl and polylysinyl residues and eluted with three distinct sequential buffer changes (pH 6.5): (i) 0.025-0.4 M morpholinoethanesulphonic acid; (ii) 0.076 and 0.379 M ammonium sulphate in 0.025 M morpholinoethanesulphonic acid; and (iii) 0.8 M sodium chloride in 0.025 M morpholinoethanesulphonic acid. Tubulin was recovered from all columns in an enriched form. However, the elution profile and purity, as judged by [3H]colchicine binding and electrophoresis, varied with the ligand. Hydrophobic gels, such as diethylaminoethyl and aminohexyl, required elution with high-ionic-strength buffers (0.8 M sodium chloride) and significant inhibition of [3H]colchicine activity resulted. This problem was avoided with the hydrophilic ligands such as arginine, polylysine and aminoethyl. Manipulation of elution conditions enabled complete elution of tubulin from arginine-activated gels in 2.5% ammonium sulphate without detectable losses of [3H]colchicine binding activity and with purity comparable to that achieved using diethylaminoethyl Sephacel.

Colchicine binding in the free-living nematode Caenorhabditis elegans

The [3H]colchicine-binding activity of a crude supernatant of the free-living nematode Caenorhabditis elegans was resolved into a non-saturable component and a tubulin-specific component after partial purification of tubulin by polylysine affinity chromatography. The two fractions displayed opposing thermal dependencies of [3H]colchicine binding, with non-saturable binding increasing, and tubulin binding decreasing, at 4 degrees C. Binding of [3H]colchicine to C.elegans tubulin at 37 degrees C is a pseudo-first-order rate process with a long equilibration time. The affinity of C. elegans tubulin for [3H]colchicine is relatively low (Ka = 1.7 x 10(5) M(-1)) and is characteristic of the colchicine binding affinities observed for tubulins derived from parasitic nematodes. [3H]Colchicine binding to C. elegans tubulin was inhibited by unlabelled colchicine, podophyllotoxin and mebendazole, and was enhanced by vinblastine. The inhibition of [3H]colchicine binding by mebendazole was 10-fold greater for C. elegans tubulin than for ovine brain tubulin. The inhibition of [3H]colchicine binding to C. elegans tubulin by mebendazole is consistent with the recognised anthelmintic action of the benzimidazole carbamates. These data indicate that C. elegans is a useful model for examining the interactions between microtubule inhibitors and the colchicine binding site of nematode tubulin.

The disposition of albendazole in sheep

Albendazole (ABZ) was administered intraruminally at 4.75 mg/kg to sheep fitted with a permanent bile-duct cannula to determine if its metabolites might contribute to its flukicidal action. ABZ metabolism was consistent with first-pass clearance by the liver, resulting in ABZ sulphoxide (ABZ-SO) and ABZ sulphone (ABZ-SO2) being present in plasma at maximum concentrations (mean Cmax +/- SD) of 2.0 +/- 0.2 micrograms/ml and 0.4 +/- 0.1 micrograms/ml after 8 +/- 3 h and 24 +/- 5 h, respectively. ABZ-SO, but more particularly ABZ-SO2, appeared to bind to plasma proteins but their clearance rates from plasma were similar. Biliary ABZ metabolites were mainly unconjugated ABZ-SO and 2OH-ABZ-SO (8.0% dose) or conjugated glucuronide and sulphate esters (6.3% dose) mainly of 2OH-ABZ-SO and 2OH-ABZ-SO2. The concentration of the major biliary metabolite, unconjugated ABZ-SO, followed a similar time profile to that of ABZ-SO in plasma except that Cmax was much higher (6.2 +/- 2.2 micrograms/ml). Intraruminal administration of ABZ reduced bile flow rate by 30% which may be attributable to an inhibitory effect of ABZ on microtubule formation in hepatic secretory cells. It is suggested that ABZ is sequestered in the liver. This is unlikely to contribute to its flukicidal action, which is probably attributable to ingestion of ABZ-SO from bile and blood by the fluke.

The interaction of phomopsin A with bovine brain tubulin

Phomopsin A is an anti-mitotic compound from the fungus Phomopsis leptostroniformis which is a potent inhibitor of microtubule assembly in vitro; like maytansine, it is known to compete with vinblastine for binding to tubulin (E. Lacey, J. A. Edgar, and C. C. J. Culvenor (1987) Biochem. Pharmacol. 36, 2133-2138). A major difference between the effects of maytansine and vinblastine is that vinblastine is a potent inhibitor of tubulin decay, whereas maytansine has little or no effect on decay. Since phomopsin A is structurally distinct from either maytansine or vinblastine, tubulin decay may be measured by either the time-dependent loss of the ability to bind to [3H]colchicine or the time-dependent increase in the binding of bis(8-anilinonaphthalene 1-sulfonate) (BisANS) to tubulin. By either method, phomopsin A was found to be a much stronger inhibitor of tubulin decay than is vinblastine or any other drug yet tested, and in fact, when decay is measured by the increase of BisANS binding, phomopsin A appears to stop the process entirely. This may prove to be useful in the determination of the higher-order structure of the tubulin molecule.