Induction of differentiation of HL-60 cells by the anti-fungal antibiotic, radicicol

Antimicrobial Natural Products from Plant Pathogenic Fungi

Isolates of a variety of fungal plant pathogens (Alternaria radicina ICMP 5619, Cercospora beticola ICMP 15907, Dactylonectria macrodidyma ICMP 16789, D. torresensis ICMP 20542, Ilyonectria europaea ICMP 16794, and I. liriodendra ICMP 16795) were screened for antimicrobial activity against the human pathogenic bacteria Acinetobacter baumannii, Pseudomonas aeruginosa, Escherichia coli, Mycobacterium abscessus, and M. marinum and were found to have some activity. Investigation of the secondary metabolites of these fungal isolates led to the isolation of ten natural products (1-10) of which one was novel, (E)-4,7-dihydroxyoct-2-enoic acid (1). Structure elucidation of all natural products was achieved by a combination of NMR spectroscopy and mass spectrometry. We also investigated the antimicrobial activity of a number of the isolated natural products. While we did not find (E)-4,7-dihydroxyoct-2-enoic acid (1) to have any activity against the bacteria and fungi in our assays, we did find that cercosporin (7) exhibited potent activity against Methicillin resistant Staphylococcus aureus (MRSA), dehydro-curvularin (6) and radicicol (10) exhibited antimycobacterial activity against M. marinum, and brefeldin A (8) and radicicol (10) exhibited antifungal activity against Candida albicans. Investigation of the cytotoxicity and haemolytic activities of these natural products (6-8 and 10) found that only one of the four active compounds, radicicol (10), was non-cytotoxic and non-haemolytic.

A study of the binding between radicicol and four proteins by means of spectroscopy and molecular docking

The interactions between radicicol and four proteins (catalase, trypsin, pepsin, and human serum protein) are investigated by spectroscopic techniques and molecular docking. A static quenching process is confirmed. The binding constant value between radicicol and human serum protein is the largest among the four proteins. Results reveal changes in the micro-environment of the protein by the addition of radicicol. It is found that radicicol shows an inhibitory effect on the activity of proteins (catalase, trypsin, and pepsin). Molecular docking results are consistent with the thermodynamic experimental results. This work provides clues to the elucidation of the mechanisms of the interactions between radicicol and proteins.

Antibacterial Radicicol Analogues from Pochonia chlamydosporia and Their Biosynthetic Gene Cluster

Chemical investigation of fungus Pochonia chlamydosporia strain 170, derived from rice fermentation sediment samples, afforded seven radicicol analogues, including two new compounds, monocillin VI (1) and monocillin VII (2), and five known compounds, monocillin II (3), monorden D (4), monocillin IV (5), monocillin V (6), and pochonin M (7). The structures of compounds 1-7 were established primarily by analysis of nuclear magnetic resonance data, and the absolute configurations of the secondary alcohol in compounds 1 and 2 were assigned by the modified Mosher method. All seven compounds have modest antibacterial activities, with a minimal inhibitory concentration (MIC) of 25.6 μg/mL for compounds 1 and 3-7 and 51.2 μg/mL for compound 2, on inhibition of the growth of the plant pathogen Xanthomonas campestris (the positive control ampicillin showed a MIC value of 12.8 μg/mL), indicating that the fungus has the potential to control bacterial disease. The biosynthetic gene cluster and putative biosynthetic pathways of these radicicol analogues in the P. chlamydosporia genome were proposed. These findings increase our knowledge of the chemical potential of P. chlamydosporia and may allow us to better utilize the fungus as a biological control agent.

Association of sustained ERK activity with integrin beta3 induction during receptor activator of nuclear factor kappaB ligand (RANKL)-directed osteoclast differentiation

Osteoclast differentiation is a multi-step process that involves cell proliferation, commitment, and fusion. Some adhesion molecules, including integrin alphavbeta3, have been shown to have roles in osteoclast fusion. In the course of studying with pharmacologic agents known to inhibit protein tyrosine kinases of the Src family, we found that radicicol increased cell fusion during receptor activator of nuclear factor kappaB ligand (RANKL)-driven differentiation of osteoclasts at concentrations far below the ones shown to inhibit its targets in previous studies. Treatments of low doses of radicicol to RAW 264.7 cells that undergo osteoclastic differentiation in the presence of RANKL enhanced the RANKL-induced gene expression of integrin beta3 without any effect on the expression of integrin alphav, which was constitutively high. The cell surface level of integrin alphavbeta3 complexes was consequently augmented by radicicol. In addition, sustained ERK and MEK activation was observed in cells treated with both radicicol and RANKL. More importantly, modulation of ERK activity by the MEK inhibitor U0126 or the gene transduction of a constitutively active form of MEK resulted in a suppression and increment, respectively, of integrin beta3 induction by RANKL. Our data indicate that sustained ERK activity is associated with integrin beta3 induction and subsequent cell surface expression of the alphavbeta3 integrin complex, which may contribute to cell fusion during RANKL-directed osteoclastogenesis.

Pochonins A-F, new antiviral and antiparasitic resorcylic acid lactones from Pochonia chlamydosporia var. catenulata

Monorden (1) and the novel resorcylic acid lactones pochonins A (2), B (4), C (6), D (7), and E (8) as well as tetrahydromonorden (5) and pseurotin A (22) were isolated from cultures of the clavicipitaceous hyphomycete Pochonia chlamydosporia var. catenulata strain P 0297. Fermentation of P 0297 in bromide-containing culture media led to a shift in secondary metabolite production and yielded monocillins III (3) and II (9) as major metabolites besides monorden (1) as well as the novel compounds pochonin F (10) and a monocillin II glycoside (11) as minor metabolites. Most of these compounds showed moderate activities in a cellular replication assay against Herpes Simplex Virus 1 (HSV1) and against the parasitic protozoan Eimeria tenella. In contrast to the structurally related zearalenone derivatives none of the metabolites of strain P 0297 were found to be active in a fluorescence polarization assay for determination of modulatory activities on the human estrogenic receptor ERbeta. Beta-zearalenol (17), but not zearalenone (15) and alpha-zearalenol (16), showed antiherpetic effects. We report the production, isolation, and structure elucidation of compounds 1-11 and their biological characterization.

Halohydrin and oxime derivatives of radicicol: synthesis and antitumor activities

Novel halohydrin and oxime derivatives of radicicol (1) were prepared and evaluated for their v-src tyrosine kinase inhibitory, antiproliferative, and antitumor activities. Some of the resulting derivatives showed significantly improved antitumor activities than those of 1 in vitro as tested in a cell proliferation assay and in vivo using sc-inoculated human breast carcinoma and epidermoid tumor models. Design and synthesis of radicicol-based novel affinity probes are also described.

Akt forms an intracellular complex with heat shock protein 90 (Hsp90) and Cdc37 and is destabilized by inhibitors of Hsp90 function

Hsp90 is a chaperone required for the conformational maturation of certain signaling proteins including Raf, cdk4, and steroid receptors. Natural products and synthetic small molecules that bind to the ATP-binding pocket in the amino-terminal domain of Hsp90 inhibit its function and cause the degradation of these client proteins. Inhibition of Hsp90 function in cells causes down-regulation of an Akt kinase-dependent pathway required for D-cyclin expression and retinoblastoma protein-dependent G(1) arrest. Intracellular Akt is associated with Hsp90 and Cdc37 in a complex in which Akt kinase is active and regulated by phosphatidylinositol 3-kinase. Functional Hsp90 is required for the stability of Akt in the complex. Occupancy of the ATP-binding pocket by inhibitors is associated with the ubiquitination of Akt and its targeting to the proteasome, where it is degraded. This results in a shortening of the half-life of Akt from 36 to 12 h and an 80% reduction in its expression. Akt and its activating kinase, PDK1, are the only members of the protein kinase A/protein kinase B/protein kinase C-like kinase family that are affected by Hsp90 inhibitors. Thus, transduction of growth factor signaling via the Akt and Raf pathways requires functional Hsp90 and can be coordinately blocked by its inhibition.

Radicicol binds and inhibits mammalian ATP citrate lyase

Six different biotinylated radicicol derivatives were synthesized as affinity probes for identification of cellular radicicol-binding proteins. Derivatives biotinylated at the C-17 (BR-1) and C-11 (BR-6) positions retained the activity of morphological reversion in v-src-transformed 3Y1 fibroblasts. Two radicicol-binding proteins, 120 and 90-kDa in size, were detected in HeLa cell extracts by employing BR-1 and BR-6, respectively. The 90-kDa protein bound to BR-6 was identified to be Hsp90 by immunoblotting. The 120-kDa protein bound to BR-1 was purified from rabbit reticulocyte lysate, and its internal amino acid sequence was identical to that of human and rat ATP citrate lyase. The identity of the 120-kDa protein as ATP citrate lyase was confirmed by immunoblotting. Interaction between BR-1 and ATP citrate lyase was blocked by radicicol but not by herbimycin A that interacts with Hsp90. These results suggest that radicicol binds the two proteins through different molecular portions of its structure. BR-1-bound ATP citrate lyase isolated from rabbit reticulocyte lysate showed no enzymatic activity. The activity of rat liver ATP citrate lyase was inhibited by radicicol and BR-1 but not by BR-6. Kinetic analysis demonstrated that radicicol was a non-competitive inhibitor of ATP citrate lyase with K(i) values for citrate and ATP of 13 and 7 microm, respectively.

Structural basis for inhibition of the Hsp90 molecular chaperone by the antitumor antibiotics radicicol and geldanamycin

The cellular activity of several regulatory and signal transduction proteins, which depend on the Hsp90 molecular chaperone for folding, is markedly decreased by geldanamycin and by radicicol (monorden). We now show that these unrelated compounds both bind to the N-terminal ATP/ADP-binding domain of Hsp90, with radicicol displaying nanomolar affinity, and both inhibit the inherent ATPase activity of Hsp90 which is essential for its function in vivo. Crystal structure determinations of Hsp90 N-terminal domain complexes with geldanamycin and radicicol identify key aspects of their nucleotide mimicry and suggest a rational basis for the design of novel antichaperone drugs.

Antifungal activity of radicicol against Mucor flavus IFO 9560

The antifungal activity of radicicol against Mucor flavus IFO 9560 was investigated. Radicicol induced bursting of spores during germination and morphological changes of the mycelial tip such as overbranching and swelling during exponential growth. In addition, radicicol showed a dose-dependent inhibitory effect on spore germination. Radicicol also inhibited the incorporation of radioactive precursors into DNA, RNA, protein, and chitin fractions by 20-30%, but not into the lipid fraction. There were no inhibitory effects on either endogenous or exogenous cellular respiration. Moreover, leakage of UV-absorbing, phenol sulfate-positive, or folin reagent-positive materials from the mycelia was not observed at an early stage of growth inhibition. On the other hand, kinetic studies of chitin synthase in the untreated mycelia revealed that radicicol noncompetitively inhibited the enzyme at Ki of 87 microM. Furthermore, upon incubation of the normal mycelia with radicicol in 50 mM KH2PO4-NaOH buffer (pH 6.5) containing 10 mM MgCl2, chitin synthase from the mycelia was inactivated gradually at first, and completely after 24-h incubation. These results suggested that radicicol exhibits the antifungal activity by disturbing cell wall biosynthesis through the inactivation of chitin synthase. However, at an early stage of growth inhibition, radicicol was thought to affect cellular function including nucleic acid and protein syntheses, in addition to the reversible noncompetitive inhibition of chitin synthase.