Mechanism of action of dnacin B1, a new benzoquinoid antibiotic with antitumor properties

Mechanism of action of dipropofol and synergistic action with other antibacterial agents in vitro

The mode of action of dipropofol and its antibacterial activity in combination with other antibiotics against Gram-positive and -negative bacteria were investigated. Dipropofol showed a bactericidal effect against Staphylococcus aureus 209P, and inhibited the incorporations of 3H-glutamate and 3H-leucine into S. aureus 209P and Bacillus subtilis PCI219 cells. These results indicated that the mechanism of action of dipropofol was mediated by the inhibition of protein synthesis or amino acid incorporation. A synergistic effect was performed by checkerboard titration with Muller-Hinton agar plates containing dipropofol (0.39 microg/ml, 1/4 x MIC) and various concentrations of nine other antibiotics in vitro. The synergism against vancomycin resistant Enterococcus faecium was confirmed in the combination of dipropofol with rifampicin. The MIC of rifampicin was decreased from 0.39 microg/ml to <0.005 microg/ml by the addition of dipropofol. This combinational effect in reversing vancomycin resistance of enterococci highlights novel drug targets and has importance in the design of new therapeutic regimens against resistant pathogens.

Dnacin A1 and dnacin B1 are antitumor antibiotics that inhibit cdc25B phosphatase activity

The p80cdc25 protein is a protein phosphatase directly involved in p34cdc2 protein kinase activation by dephosphorylation. The cdc25B gene is one of three human cdc25 homologs which can complement the temperature-sensitive cdc25 mutation of Schizosaccharomyces pombe, and is expressed a high levels in human cell lines, particularly in some cancer cells. A fusion protein of glutathione-S-transferase (GST) and the catalytic domain of cdc25B protein was constructed and found to retain phosphatase activity in the manner of a p80cdc25 phosphatase by using a chromogenic substrate, p-nitrophenylphosphate. Two benzoquinoid antitumor compounds, dnacin A1 and dnacin B1, inhibited phosphatase activity in a non-competitive manner.

DNA strand scission by the novel antitumor antibiotic leinamycin

Leinamycin is a recently discovered antitumor antibiotic with an unusual 1,3-dioxo-1,2-dithiolane structure. It preferentially inhibits the incorporation of [3H]thymidine into the acid-insoluble fraction of Bacillus subtilis. In vitro, leinamycin causes single-strand cleavage of supercoiled double-helical pBR322 DNA in the presence of thiol cofactors. Scavengers of oxygen radical did not supress the DNA-cleaving activity. Thiol-activated leinamycin binds calf thymus DNA at 4 degrees C and thermal treatment of the leinamycin-DNA adduct released a chemically modified leinamycin from the complex. The lack of cytotoxicity and DNA-cleaving activity for S-deoxyleinamycin indicates that the 1,3-dioxo-1,2-dithiolane moiety is essential for the activity of leinamycin. Thus, the primary cellular target of leinamycin appears to be DNA. It binds DNA and causes single-strand break at low concentrations, which may account for the potent antitumor activity.

Action of citrinin on bacterial chromosomal and plasmid DNA in vivo and in vitro

Citrinin, a mycotoxin of Penicillium citrinum and other species of the genera Penicillium and Aspergillus, caused the following effects at different concentrations in Escherichia coli. In vivo at 100 micrograms/ml single-strand breaks were caused in the chromosomal DNA. In the presence of 100 micrograms/ml, UV (254 nm)-induced DNA damage was repaired in the bacterial cells without need for a complete growth medium. At 300 micrograms/ml lambda ts prophage was induced in a lysogenic E. coli strain. In an E. coli strain carrying a F' lac plasmid, 4.7% of the cells displayed the Lac- phenotype after treatment with 200 micrograms of citrinin per ml, suggesting elimination of the F' factor. In vitro, DNA repair synthesis was observed at 5 micrograms of citrinin per ml in permeabilized cells, and replicative DNA synthesis was inhibited at 200 micrograms/ml. In these systems synthesis of stable RNAs was slightly diminished at 300 micrograms/ml, and protein synthesis was not affected at concentrations up to 450 micrograms/ml. Lambda and ColE1 plasmid DNA were cleaved in vitro when small amounts of copper ions were present. This DNA-attacking activity was prevented by NADPH, catalase, and superoxide dismutase and by higher concentrations of hydroxyl radical scavengers, suggesting the involvement of free radicals in the mechanism of action of citrinin on DNA.