Synthesis and biological activity of novel macrocyclic antifungals: acylated conjugates of the ornithine moiety of the lipopeptidolactone FR901469

A series of acylated analogues of the novel macrocyclic lipopeptidolactone FR901469 has been prepared and evaluated for antifungal and hemolytic activity. Several analogues displayed markedly reduced hemolytic potential and comparable protective effects to the natural product in a mouse model of candidiasis.     

From natural products to clinically useful antifungals

In our search for natural products with a broad spectrum of antifungal activity as lead compounds for novel treatments for mycoses, we have isolated echinocandin-type lipopeptide FR901379 and lipopeptidolactone FR901469, as novel water-soluble antifungal agents that inhibit the synthesis of 1,3-beta-glucan, a key component of the fungal cell wall. Since the cell wall is a feature unique to fungi and is not present in nonfungal eukaryotic cells, inhibitors of the synthesis of fungal cell wall components such as 1,3-beta-glucan have potential for selective toxicity to fungi and not to the host. In this short review, we describe efforts directed at synthetic modification of FR901469 and FR901379 with the ultimate goal of identifying new entities with suitable profiles as development candidate compounds. The main thrust of our work to date has been replacement of the highly flexible lipophilic side chains of the natural products with a view to reducing the hemolytic potential associated with these compounds, and to enhance chemical stability and/or in vivo antifungal efficacy. As a result of these efforts, we recently discovered a novel analog, FK463 (micafungin). Micafungin is currently in phase III clinical trials worldwide as a parenteral agent for various mycoses, and a new drug application (NDA) was recently filed in Japan.     

Novel echinocandin antifungals. Part 1: novel side-chain analogs of the natural product FR901379

A series of novel acylated analogs of the novel water-soluble echinocandin FR901379 have been prepared and evaluated for antifungal and hemolytic activity. A relationship between antifungal activity and lipophilicity of the acyl side chain, expressed as ClogP was demonstrated, and an analog (3c) with 5.5- to 8-fold superior in vivo activity relative to the previously disclosed 4-(n-octyloxy)benzoyl side chain analog, FR131535 obtained.     

FR131535, a novel water-soluble echinocandin-like lipopeptide: synthesis and biological properties

The synthesis and biological properties of a novel water-soluble echinocandin-like lipopeptide, FR131535, are described. This compound displayed potent in vitro and in vivo antifungal activities. The hemolytic activity of FR901379 was reduced by replacing the acyl side chain. This compound showed good water-solubility, comparable to the natural product FR901379.     

Novel echinocandin antifungals. Part 2: Optimization of the side chain of the natural product FR901379. Discovery of micafungin

Further optimization of the potent antifungal activity of side chain analogs of the natural product FR901379 led to the discovery of compound 8 with an excellent, well-balanced profile. Potent compounds with reduced hemolytic potential were designed based upon a disruption of the linearity of the terphenyl lipophilic side chain. The optimized compound (8, FK463, micafungin) displayed the best balance and was selected as the clinical candidate.     

Bordetella pertussis adenylate cyclase toxin. Structural and functional independence of the catalytic and hemolytic activities.

The Bordetella pertussis calmodulin-dependent adenylate cyclase (CyaA) is a 1706-residue-long toxin, endowed with hemolytic activity. We have constructed B. pertussis mutant strains producing modified CyaAs devoid of adenylate cyclase activity. Our results show that such modified CyaAs display hemolytic activity identical to the wild-type toxin, thus demonstrating that the hemolytic activity is independent of the adenylate cyclase activity. Furthermore, B. pertussis and Escherichia coli strains producing CyaA lacking the catalytic domain (residues 1-373) were constructed. The truncated protein exhibits hemolytic activity comparable to the wild-type toxin, thus establishing that the carboxyl-terminal 1332 residues alone are endowed with hemolytic activity. Together, these findings show that adenylate cyclase and hemolytic activities are located in two distinct regions of the molecule (respectively, approximately amino acids 1-400 and 401-1706) and that the two regions of CyaA are functionally independent.     

FR207944, an antifungal antibiotic from Chaetomium sp. no. 217 I. Taxonomy, fermentation, and biological properties

An antifungal antibiotic, FR207944, was isolated from the culture broth of a fungal strain Chaetomium sp. no. 217. FR207944 is a triterpene glucoside with antifungal activity against Aspergillus fumigatus and Candida albicans. Specifically, FR207944 exhibits in vitro and in vivo antifungal activity against A. fumigatus. The effects of FR207944 on the morphology of A. fumigatus were shown to be similar to those of FR901379, a known 1,3-beta-glucan synthase inhibitor. The MECs of FR207944 against A. fumigatus FP1305 and C. albicans FP633 in micro-broth dilution test were 0.039 and 1.6 mug/ml respectively. FR207944 showed good potency by subcutaneous injection and oral administration against A. fumigatus in a murine systemic infection model, with ED(50)s of 5.7 and 17 mg/kg respectively.     

Influence on adipocyte plasma membrane bound protein kinase by feedback regulator.

Protein kinase, phosphodiesterase and adenylate cyclase of plasma membrane of adipocytes and the effect of the feedback regulator (FR) on these three enzymes was measured and compared. The basal level ratio of adenylate cyclase to phosphodiesterase to protein kinase was 1:1.9:3.0. Epinephrine and/or FR alters this ratio. FR stimulated protein kinase activity up to 3 fold in the presence of a wide range of enzyme concentrations, 5-50 mug membrane protein/tube. The concentration of FR effective for stimulation of membrane protein kinase was much greater than that needed for inhibition of adenylate cyclase and phosphodiesterases. The inhibition by FR on adenylate cyclase was the most potent effect among the 3 enzymes. 1 U (or 2 U/ml) of FR inhibited 50% of the adenylate cyclase activity in a defined system. The maximum effective concentration of FR for stimulation of membrane protein kinase was greater than 10 U/ml. Histone type 11A was the best substrate for protein phosphorylation so far observed. The FR stimulatory effect was observed at all substrate concentrations used ranging from 1-5 mg/ml. A NaF concentration curve shows that 15 mM NaF gave maximum phosphorylation. The stimulatory effect of FR was observed both in the presence and absence of NaF. Protein kinase of adipocyte plasma membrane was mainly cAMP-independent. The effect of FR (20 U/ml) in stimulation of protein phosphorylation was much greater than that of cAMP (1 X 10(-6) M). The cAMP and FR effects seemed to be additive. Preincubation of plasma membrane with FR in the absence of ATP resulted in no decrease but slight increase in protein kinase activity. A shift in protein kinase, phosphodiesterase and adenylate cyclase ratios by FR suggests the regulatory role of FR in cAMP metabolism in adipocytes.     

Studies on antiviral glycosides. II. Chemical modifications of the envelope of Sendai virus

Treatment of Sendai virus with p-azidophenyl-6-chloro-6-deoxy-beta-D-glucopyranoside (APG) caused chemical modification of the viral envelope under UV irradiation, which did not affect the hemagglutinin activity of the virus but inhibited the hemolytic activity. Also, the transfer of phospholipid from the viral envelope to chicken erythrocytes was measured using a spinlabel technique by electron spin resonance (ESR). In this experiment, the phospholipid transfer was depressed by the treatment with APG under the conditions which inhibited the hemolytic activity of the virus. These results suggest that APG bound covalently to lipid may disturb the specific interaction between the protein and the lipid of the viral envelope, resulting in the inhibition of the hemolytic activity. The effects of APG on the hemolysis and phospholipid transfer were compared with the results for the concanavalin A- and amphotericin B-treated viruses.     

Trypsin Action on the Growth of Sendai Virus in Tissue Culture Cells II. Restoration of the Hemolytic Activity of L Cell-Borne Sendai Virus by Trypsin

Sendai virus grown in L cells (L Sendai) caused little hemolysis, whereas the one grown in fertile eggs (egg Sendai) induced distinct hemolysis. Enzymatic treatment with trypsin at low concentrations markedly enhanced the hemolytic activity of L Sendai but not that of egg Sendai. Both sonic treatment and freezing and thawing greatly enhanced the hemolytic activity of egg Sendai, but they gave little enhancing effect on that of L Sendai which could, however, be greatly increased by successive treatment with trypsin. Dose response and kinetic experiments on the trypsin effect have suggested that a similarity exists in the inhibitory mechanism of infectivity for L cells and hemolytic activity of L Sendai. Treatment of L cells with trypsin at later stages of infection released a highly hemolytic L Sendai from those cells. The present study, by reference to the density centrifugation studies in a previous report (4), has shown that a variation in infectivity for L cells and in the hemolytic activity of L Sendai is a type of host-controlled modification distinguishable from the density variation.     

Site-directed mutagenesis of the region around Cys-241 of complement component C2. Evidence for a C4b binding site

We probed the functional significance of the region around Cys-241 in human C2 by testing the hemolytic activity of a series of mutant rC2. Mutant C2 cDNA were constructed by oligonucleotide-directed site-specific mutagenesis and expressed transiently in COS cells. Wild-type rC2 had threefold higher specific hemolytic activity than native serum C2. Substitution of Gly, Ala, or Ser for Cys-241 resulted in a slightly, but significantly, increased activity. In addition, I2 had no effect on the activity of these mutant C2. Substitution of Lys for Gln-243 increased the hemolytic activity by more than two-fold. Increased activity in all cases was due to slower decay rates of the C3 convertase. Finally, substitution of Leu or Ala for Asp-240 or Ser-244, respectively, resulted in more than 100-fold decrease of hemolytic activity. The results suggest that residues 240 to 244 of human C2 represent an important structural determinant of the C4b binding site of C2a. They also confirm that Cys-241 is the residue responsible for the increased activity of C2 reacted with I2.     

Replacing the cyclohexene-linker of FR181157 leading to novel IP receptor agonists: orally active prostacyclin mimetics. Part 6

The synthesis and biological activity of novel derivatives of our previously reported IP receptor agonist FR181157 is described. SAR studies to replace the cyclohexene-linker of FR181157 led to the discovery of compound 1i (FR207845) as a potent non-prostanoid PGI2 mimetic with good oral bioavailability.     

Studies on the toxin of Aspergillus fumigatus. XVIII. Photooxidation of asp-hemolysin in the presence of various dyes and its relation to the site of hemolytic activity

The site of hemolytic activity of a toxin isolated from Aspergillus fumigatus designated Asp-hemolysin was determined by photooxidation techniques. The hemolytic activity of this toxin was strongly inhibited by photooxidation with methylene blue, rose bengal, riboflavin, or eosin G as a sensitizer, whereas crystal violet, hematoxylin, naphthol yellow S, bromothymol blue, methyl orange, and cresol red had no effect. pH dependence of the inactivation with methylene blue was observed in the narrow range of pH values from 7.0 to 8.0, like that of the inactivation with rose bengal or riboflavin. The histidine, cysteine, methionine, tryptophan, and tyrosine content of methylene blue-photooxidized Asp-hemolysin was significantly decreased, while other amino acids were not affected. The hemolytic activity of the toxin was lost more slowly than the histidine residue, being maintained at about 50% even at the time when the histidine residue was completely lost after 30 min. Photooxidation of Asp-hemolysin in the presence of rose bengal also caused a decrease in histidine, methionine, and threonine content. These findings suggest that residues of cysteine, methionine, threonine, tryptophan, and/or tyrosine but not histidine may play an important role through stereostructure in the manifestation of the hemolytic activity of Asp-hemolysin.     

A critical comparison of the hemolytic and fungicidal activities of cationic antimicrobial peptides.

The hemolytic and fungicidal activity of a number of cationic antimicrobial peptides was investigated. Histatins and magainins were inactive against human erythrocytes and Candida albicans cells in phosphate buffered saline, but displayed strong activity against both cell types when tested in 1 mM potassium phosphate buffer supplemented with 287 mM glucose. The HC50/IC50 ratio, indicative of the therapeutic index, was about 30 for all peptides tested. PGLa was most hemolytic (HC50 = 0.6 microM) and had the lowest therapeutic index (HC50/IC50 = 0.5). Susceptibility to hemolysis was shown to increase with storage duration of the erythrocytes and also significant differences were found between blood collected from different individuals. In this report, a sensitive assay is proposed for the testing of the hemolytic activities of cationic peptides. This assay detects subtle differences between peptides and allows the comparison between the hemolytic and fungicidal potency of cationic peptides.     

Science of hemolytic activity of some radiation-resistant micrococci in food.

Micrococci resistant to 1 Mrad of gamma radiation were isolated from irradiated chicken. Three isolates were hemolytic on blood agar plates and were selected for further study. Two other radiation-resistant micrococci, Micrococcus radiodurans and Micrococcus radiophilus, were included in the study because there is only a very limited amount of information regarding hemolytic activity of these organisms and their potential role of public health importance. Tests to determine hemolytic patterns, hemolytic activity of extracellular substances, leukocytic activity, presence of enzymes commonly associated with pathogenicity (coagulase, deoxyribonuclease, phosphatase), and pathogenicity for laboratory animals all suggested that the organisms would not be of public health significance.     

Differential ability of heparan sulfate proteoglycans to assemble the fibroblast growth factor receptor complex in situ.

Fibroblast growth factors (FGFs) require heparan sulfate proteoglycans (HSPGs) as cofactors for signaling. The heparan sulfate chains (HS) mediate stable high affinity binding of FGFs to their receptor tyrosine kinases (FR) and may specifically regulate FGF activity. A novel in situ binding assay was developed to examine the ability of HSPGs to promote FGF/FR binding using a soluble FR fusion construct (FR1-AP). This fusion protein probe forms a dimer in solution, simulating the dimerization or oligomerization that is thought to occur at the cell surface physiologically. In frozen sections of human skin, FGF-2 binds to keratinocytes and basement membranes of epidermis and dermal blood vessels. In contrast, in skin preincubated with FGF-2, FR1-AP binds avidly to FGF-2 immobilized on keratinocyte cell surfaces, but fails to bind to basement membranes at the dermo-epidermal junction or dermal microvessels despite the fact that these structures bind large amounts of FGF-2. Apparently, basement membrane and cell surface HSPGs differ in their ability to mediate the assembly of a FGF/FR signaling complex presumably due to structural differences of the heparan sulfate chains.     

Consequences of introducing a disulfide bond into an antibacterial and hemolytic peptide.

The effect of introducing a disulfide bridge between the N- and C-terminal ends on the structure and biological activities of the 13-residue linear peptide PKLLKTFLSKWIG(SPFK), which has both antibacterial and hemolytic activity, have been investigated. The terminal amino acids P and G in SPFK were replaced by cysteines to form a disulfide bridge. The linear peptides C(Acm)KLLKTFLSKWIC(Acm) and C(Acm) KLLKTFLSKWIC(Acm)-amide, where Acm is acetamidomethyl group, showed antibacterial activity but did not possess hemolytic activity unlike SPFK. Introduction of an S-S bridge resulted in enhanced hemolytic activity compared with SPFK. The hemolytic activity was particularly pronounced in the cyclic peptide CKLLKTFLSKWIC-amide. Circular dichroism studies indicate that the cyclic peptides tend to adopt distorted helical structures. The cyclic peptides also have a greater affinity for lipid vesicles, which could be the reason for the effective perturbation of the erythrocyte membrane.     

Role of p38 mitogen-activated protein kinase in the healing of gastric ulcers in rats.

p38 belongs to the mitogen-activated protein kinase family and plays a crucial role in cellular responses to both cytokines and various stresses. We investigated the role of p38 in the healing of experimental gastric ulcers. Gastric ulcers were induced by submucosal injection of acetic acid solution into male rats. Western blotting and a kinase assay examined the p38 activity and phosphorylation state in ulcerated tisue. After orally administering FR167653 (p38 kinase inhibitor) for 3 to 14 days, the production level of cytokines and the protein-level expression of cyclooxygenase and inducible nitric oxide synthase were examined by enzyme-linked immunosorbent assay and Western blotting. Only in fibroblasts and macrophages/monocytes in ulcerated tissue, p38 was found to be phosphorylated with an elevated kinase activity level. FR 167653 inhibited the activity of p38, yet had no effect on its phosphorylation state. The drug significantly impaired ulcer healing (without affecting acid secretion) and angiogenesis in the ulcer base. The production of interleukin-1beta and tumor necrosis factor-alpha were significantly reduced after FR167653 treatment. In addition the expression of cyclooxygenase-2 and inducible nitric oxide synthase proteins increased PGE2 generation and NOx secretion in the ulcerated stomach were suppressed by FR167653. From these findings, we conclude that p38, activated by gastric ulceration, might play some role in the healing of gastic ulcers in rats.     

Role of a cysteine residue in the active site of ERK and the MAPKK family

Kinases of mitogen-activated protein kinase (MAPK) cascades, including extracellular signal-regulated protein kinase (ERK), represent likely targets for pharmacological intervention in proliferative diseases. Here, we report that FR148083 inhibits ERK2 enzyme activity and TGFbeta-induced AP-1-dependent luciferase expression with respective IC50 values of 0.08 and 0.05 microM. FR265083 (1'-2' dihydro form) and FR263574 (1'-2' and 7'-8' tetrahydro form) exhibited 5.5-fold less and no activity, respectively, indicating that both the alpha,beta-unsaturated ketone and the conformation of the lactone ring contribute to this inhibitory activity. The X-ray crystal structure of the ERK2/FR148083 complex revealed that the compound binds to the ATP binding site of ERK2, involving a covalent bond to Sgamma of ERK2 Cys166, hydrogen bonds with the backbone NH of Met108, Nzeta of Lys114, backbone C=O of Ser153, Ndelta2 of Asn154, and hydrophobic interactions with the side chains of Ile31, Val39, Ala52, and Leu156. The covalent bond motif in the ERK2/FR148083 complex assures that the inhibitor has high activity for ERK2 and no activity for other MAPKs such as JNK1 and p38MAPKalpha/beta/gamma/delta which have leucine residues at the site corresponding to Cys166 in ERK2. On the other hand, MEK1 and MKK7, kinases of the MAPKK family which also can be inhibited by FR148083, contain a cysteine residue corresponding to Cys166 of ERK2. The covalent binding to the common cysteine residue in the ATP-binding site is therefore likely to play a crucial role in the inhibitory activity for these MAP kinases. These findings on the molecular recognition mechanisms of FR148083 for kinases with Cys166 should provide a novel strategy for the pharmacological intervention of MAPK cascades.