Cell surface oligosaccharides play a role in a variety of biological events such as cell adhesion and signal transduction. We have shown that BMY-28864, a semi-synthetic analog of pradimicin, induced apoptosis of U937 cells which had been incubated with 1-deoxymannojirimycin, an inhibitor of mannosidase I. BMY-28864 was not cytotoxic to the cells which had been cultivated with other glycosidase inhibitors such as castanospermine and swainsonine. We thus propose that BMY-28864 induces apoptosis by acting on a specific mannose-rich oligosaccharide, presumably (Man)9(GlcNAc)2.
Pradimicin (PRM) induces apoptosis in mammalian cells which had been incubated with 1-deoxymannojirimycin (DMJ). Flow cytometric analysis revealed that PRM preferentially induced apoptosis to the cells of the G1 phase. Two possible mediators in this apoptotic cascade were identified. Exposure of DMJ-treated cells to PRM resulted in a rapid (-5 seconds) and slow (-30 minutes) elevation of the intracellular calcium level. Reactive oxygen species (ROS) were proved to be involved in this system by the fact that the apoptosis was completely inhibited by treating the cells with a ROS scavenger, N-acetylcysteine in prior to the PRM stimulation.
A novel inhibitor of topoisomerases designated as topostatin was isolated from the culture filtrate of Thermomonospora alba strain No. 1520. The inhibitory activity of topostatin was shown to be pH- and temperature-dependent with a maximum around at pH 6 and 28°C. The stability of topostatin decreased with decreasing pH and rising temperature. Topostatin inhibited topoisomerases I and II in a competitive manner with respect to DNA. The inhibitor also inhibited some restriction endonucleases such as ScaI, HindIII and PstI, but not AluI, BamHI, EcoRI, RNase A, DNase I, DNase II and DNA ligase. Topostatin did not induce the nuclear accumulation of p53 protein by DNA damage in the normal human cells.
A novel class of macrolides for which the name sanglifehrins is proposed, has been discovered from actinomycete strains based on their high affinity binding for cyclophilin A (CypA), an immunophilin originally identified as a cytosolic protein binding cyclosporin A (CsA). The sanglifehrins were produced by Streptomyces sp. A92-308110. They were isolated and purified by extraction and several chromatographic, activity-guided steps. Sanglifehrins A and B exhibit a 10-20 fold higher affinity for CypA than CsA, whereas the affinity of sanglifehrins C and D for CypA is comparable to that of CsA. Sanglifehrins exhibit a lower immunosuppressive activity than CsA when tested in the mixed lymphocyte reaction. Their in vitro activity indicates that they belong to a novel class of immunosuppressants.
A novel class of macrolides, the sanglifehrins, was discovered by screening of actinomycete strains with a cyclophilin-binding assay. The chemical structures and absolute stereochemistries of the sanglifehrins A, B, C and D were determined unambiguously by NMR-techniques and by X-ray crystallography of the complex with cyclophilin A. Sanglifehrin A consists of a 22-membered macrocycle containing a tripeptide subunit and features in position 23 a chain of nine carbon atoms bearing a spirocyclic substituent. Sanglifehrins A and B are genuine metabolites whereas sanglifehrins C and D are artefacts.
UK-2A, a novel antifungal antibiotic, is a structural relative of antimycin A3 (AA) and its mode of action is similar to that of AA which inhibits mitochondrial electron transport at complex III. In spite of their structural resemblance, AA had strong cytotoxicity while UK-2A had little cytotoxicity against LLC-PK1 cells as well as other types of cultured cells. When cells were treated with UK-2A or with A A the intracellular ATP content decreased significantly within 5 minutes in glucose-free medium to almost the same extent in both cases. Moreover, under the same conditions, UK-2A killed cells at a similar rate to AA. This suggested that UK-2A entered into the cells and, like AA, inhibited mitochondrial electron transport. On the other hand, AA stimulated reactive oxygen species (ROS) production within 5 minutes even at a low concentration of 1 μM whereas UK-2A did not show such an effect. The difference in the ROS-producing abilities of UK-2A and AA may account for the different cytotoxic effects of the two compounds.
Thiazinotrienomycin B (TT-B), an ansamycin isolated from fermentation broths of Streptomyces sp. MJ672-m3, inhibited the growth in vitro of human stomach tumor SC-6 cells over 10 times more strongly than the growth of other human tumor cells, such as HeLa (cervix), T24 (bladder) and LX-1 (lung). The extent of growth inhibition by TT-B of SC-6, but not of LX-1 nor T24, was lowered in a competitive manner by raising serum concentrations in the culture medium. TT-B inhibited the cell cycle progression of SC-6 at an early stage of the progression from GO/G1 to S. The inhibition was again competitive with serum concentrations in the culture medium. No direct inhibition of DNA synthesis was observed at the concentration range which caused the cell cycle arrest. TT-B and anti-epidermal growth factor receptor (anti-EGFR) were antagonistic to each other in inhibiting the cell cycle progression of SC-6 from G0/G1 to S, suggesting that the two compounds share the same target, EGFR. The kinase activity of EGFR was little inhibited by TT-B in a cell-free system.
To improve the oral absorption of ceftizoxime (CZX), 7β-[(Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetamido]-3-cephem-4-carboxylic acid, we synthesized and evaluated a novel series of bifunctional prodrugs, in which L-alanine was introduced into the aminothiazole-oxime moiety at the C-7 position of the various lipophilic esters of CZX. Among these prodrugs, pivaloyloxymethyl 7β[(Z)-2-(2-(S)-alanylaminothiazol-4-yl)-2-methoxyiminoacetamido]-3-cephem-4-carboxylate hydrochloride (ceftizoxime alapivoxil, AS-924) was well absorbed after oral administration in experimental animals and showed potent therapeutic effects in mice infected with Gram-positive and Gram-negative bacteria.