Phleomycin B2

Bleomycin is hypothesized to cause cell growth inhibition and cell death via DNA cleavage. We have attempted to determine if net DNA cleavage is directly related to growth inhibition by measuring whether both parameters vary in parallel. Of primary importance to these studies was use of several bleomycin congeners. We have shown that these congeners vary in their abilities both to inhibit cell growth and to cause DNA damage. Bleomycin B2, tallysomycin, and phleomycin were the most potent growth inhibitors, and bleomycin B2 caused the most DNA damage. N-Acetylbleomycin A2 was inactive in both assays. The net amount of DNA damage measured at two levels of growth inhibition was compared for each congener and was found to vary widely among the congeners. Similarly, the degree of growth inhibition at a given level of submaximal DNA damage was found to vary widely when individual congeners were compared to each other. Hence, growth inhibition and net DNA damage due to bleomycin are not directly correlated with each other when individual congeners are compared to each other.

Bleomycin (BLM) is used clinically in combination with a number of other agents for the treatment of several types of tumours. Members of the BLM family of drugs include zorbamycin (ZBM), phleomycin D1, BLM A2 and BLM B2. By manipulating the BLM biosynthetic machinery, we have produced two new BLM analogues, BLM Z and 6'-deoxy-BLM Z, with the latter exhibiting significantly improved DNA cleavage activity. Here we determined the DNA sequence specificity of BLM Z, 6'-deoxy-BLM Z and ZBM, in comparison with BLM, with high precision using purified plasmid DNA and our recently developed technique. It was found that ZBM had a different DNA sequence specificity compared with BLM and the BLM analogues. While BLM and the BLM analogues showed a similar DNA sequence specificity, with TGTA sequences as the main site of cleavage, ZBM exhibited a distinct DNA sequence specificity, with both TGTA and TGTG as the predominant cleavage sites. These differences in DNA sequence specificity are discussed in relation to the structures of ZBM, BLM and the BLM analogues. Our findings support the strategy of manipulating the BLM biosynthetic machinery for the production of novel BLM analogues, difficult to prepare by total synthesis; some of which could have beneficial cancer chemotherapeutic properties.

The filamentous fungus Acremonium chrysogenum is of enormous biotechnological importance as it represents the natural producer of the beta-lactam antibiotic cephalosporin C. However, a limitation in genetic tools, e.g. promoters for conditional gene expression, impedes genetic engineering of this fungus. Here we demonstrate that in A. chrysogenum iron starvation induces the production of the extracellular siderophores dimerumic acid, coprogen B, 2-N-methylcoprogen B and dimethylcoprogen as well as expression of the putative siderophore transporter gene, mir1. Moreover, we show that the promoter of mir1, mir1(P), is suitable for conditional expression of target genes in A. chrysogenum as shown by mir1(P)-driven and iron starvation-induced expression of genes encoding green fluorescence protein and phleomycin resistance. The obtained iron-starvation dependent phleomycin resistance indicates the potential use of this promoter for selection marker recycling. Together with easy scorable siderophore production, the co-regulation of mir1 expression and siderophore production facilitates the optimization of the inducing conditions of this expression system.