Bioprobes are low molecular weight compounds which are useful for investigating mammalian cell functions. The use of bioprobes has substantially assisted the investigation of complex biochemical processes of the mammalian cell cycle. In this review, cell cycle inhibitors mainly isolated from the microorganism are described and their possibility as an antitumor agents is considered. Most cancer cells have some abnormality in the control mechanism of cell cycle progression. Cyclin-dependent kinases (Cdk), which are activated by the binding with the cyclin and simultaneously by the phosphorylation/dephosphorylation of itself, play important roles as engines in the cell cycle. Tubulins are considered to be one of the most important proteins of the cell division machinery. Therefore, Cdk inhibitors and tubulin binders are possible anticancer drugs. Since the function of proteins controlling the cell cycle is also regulated by phosphorylation and dephosphorylation, inhibitors of protein kinases and phosphatases are considered as possible an antitumor agents. We expect that some bioprobes will be developed for clinical use.
A κ opioid receptor binding inhibitor was isolated from the fermentation broth of a basidiomycete, Hericium ramosum CL24240 and identified as erinacine E (1). Three analogs of 1 were produced by fermentation in other media and by microbial biotransformation. Of these compounds, 1 was shown to be the most potent binding inhibitor. Preliminary SAR studies of these compounds indicated that all functional groups and side chains were required for the activity. Compound 1 was a highly-selective binding inhibitor for the κ opioid receptor: 0.8 μM (IC50) for κ, > 200 μM for μ, and > 200 μM for δ opioid receptor. Compound 1 suppressed electrically-stimulated twitch responses of rabbit vas deferens with an ED50 of 14 μM. The suppression was recovered by adding a selective κ opioid receptor antagonist nor-binaltorphimine, indicating that 1 is a κ opioid receptor agonist.
A novel inhibitor of topoisomerases designated as topostatin was isolated from the culture filtrate of Thermomonospora alba strain No. 1520. Topostatin inhibited the relaxation of supercoiled pBR322 DNA by calf thymus topoisomerase I, and also inhibited the relaxation of supercoiled pBR322 DNA and decatenation of kinetoplast DNA by human placenta topoisomerase II. Topostatin had neither ability to stabilize the cleavable complex nor ability to intercalate into DNA strands. The inhibitor exhibited growth inhibitory activity against the tumor cells (SNB-75 and SNB-78) of central nervous system, but did not exhibit any antimicrobial activity against Gram-positive and Gram-negative bacteria, yeasts and fungi.
Topostatin is a new topoisomerase inhibitor isolated from the culture filtrate of Thermomonospora alba strain No. 1520. The inhibitor inhibits topoisomerases I and II, and it has neither ability to stabilize the cleavable complex nor ability to intercalate into DNA strands. The molecular formula of topostatin was determined as C36H58N4O11S based on the FAB-MS analyses, and the structure was elucidated to be a novel 14-membered ring containing peptide and terpenoid by various NMR spectroscopies.
Novel brominated and halogen-less azaphilone (oxoisochromane) derivatives, 5-bromoochrephilone and dechloroisochromophilone IV, and known derivatives, dechloroisochromophilone III and isorotiorin, were isolated from the culture broth of a producing organism of isochromophilones I and II (azaphilones inhibiting gp120-CD4 binding), Penicillium multicolor FO-2338, fermented in a medium containing potassium bromide. Nineteen azaphilone-related compounds isolated from the above strain and from other fungi were tested for the inhibition of gp120-CD4 binding and the structure-activity relationship is discussed. Consequently, 5-bromoochrephilone is the strongest inhibitor (IC50, 2.5 μM). A halogen atom at C-5, a proton at C-8 and a diene structure in C-3 side chain of 6-oxoisochromane ring are necessary for gp120-CD4 binding.
The isolation and structure determination of 6 analogues of the fungal protein synthesis inhibitor GR135402, from Graphium putredinis, is described. The relative potencies of the compounds as protein synthesis inhibitors and as in vitro antifungal agents provide interesting insights into the structure-activity relationships in this series.
Two novel inhibitors of aflatoxin production by Aspergillus parasiticus were isolated from the mycelial extracts of Streptomyces sp. MRI142 and termed aflastatin A and B. The structures of aflastatin A (1) and B (5) were elucidated by NMR and chemical degradation experiments. These compounds have a novel skeleton of a tetramic acid derivative with a highly oxygenated long alkyl chain. The incorporation experiments using 13C-labeled acetates, propionate, glucose and glycolate suggested that most of the C2 and C3 units involved in the alkyl chain moiety of aflastatin A were biosynthesized from acetic and propionic acids, but five C2 units in the alkyl chain originated from glycolic acid.
In a previous report, a plasmid, pIG1, which contained the loading domain from the Streptomyces avermitilis polyketide synthase (PKS), promoters from Streptomyces coelicolor and the DEBS1-TE truncated PKS from Saccharopolyspora erythraea, was integrated into the S. erythraea chromosome, effectively replacing the natural erythromycin loading domain with the avermectin loading domain. In this paper, we report the feeding of short-chained fatty acids to this recombinant strain, and its parent, NRRL 2338. Both strains incorporated exogenously supplied fatty acids to produce novel, biologically active, C-13 substituted erythromycins.
Fattiviracin A1, showed potent antiviral activities against herpes simplex virus type 1 (HSV-1), varicella-zoster virus (VZV), influenza A virus and human immunodeficiency virus type 1 (HIV-1). It showed no cytotoxicity against Vero cells. Fattiviracin A1 exhibited no significant antibacterial or antifungal activities. Treatment of HSV-1 with fattiviracin A1 decreased its infectivity to Vero cells. The mechanism of its antiviral activity may be due to inactivation of the viral particles and inhibition of viral entry into host cells.