Mechanistic studies on bleomycin-mediated DNA damage: multiple binding modes can result in double-stranded DNA cleavage

Double-strand break formation during nucleotide excision repair of a DNA interstrand cross-link

The DNA interstrand cross-link (ICL) resulting from the C4'-oxidized abasic site (C4-AP) is a unique clustered lesion comprised of a cross-link adjacent to a nick. The ICL is a substrate for the UvrABC nucleotide excision repair system. The strand containing the nick is preferentially incised, but the nick influences the cleavage sites. Moreover, in approximately 15% of the molecules, the strand opposite the nick is incised, resulting in a more toxic double-strand break. This is the first example in which an interstrand cross-link is converted by nucleotide excision misrepair into a more deleterious double-strand break.

Ecology-based screen identifies new metabolites from a Cordyceps-colonizing fungus as cancer cell proliferation inhibitors and apoptosis inducers

OBJECTIVES

This study aims to identify new anti-cancer agents from Cordyceps-colonizing fungi, using an ecology-based approach. It also aims to explore their anti-cell proliferative mechanisms, and to evaluate their anti-tumour effects in vivo.

MATERIALS AND METHODS

Extracts from Cordyceps-colonizing fungi were tested on HeLa cells, and active extracts were separated to obtain anti-tumour metabolites; their structures were elucidated by mass and nuclear magnetic resonance spectroscopy. Cell cycle analysis was evaluated using flow cytometry. Tumour formation assays were performed using C57BL/6J mice.

RESULTS

Based on ecological considerations, the selected extracts were subjected to initial anti-tumour screening. Bioassay-guided fractionation of the active extract afforded two new epipolythiodioxopiperazines, named gliocladicillins A (1) and B (2). (A) 1 and B (2) inhibited growth of HeLa, HepG2 and MCF-7 tumour cells. Further study demonstrated that both preparations arrested the cell cycle at G(2)/M phase in a dose-dependent manner, and induced apoptosis through up-regulation of expression of p53, p21, and cyclin B, and activation of caspases-8, -9 and -3. These data imply that gliocladicillins A (1) and B (2) induce tumour cell apoptosis through both extrinsic and intrinsic pathways. In addition, in vivo studies showed that they displayed significant inhibitory effects on cell population growth of melanoma B16 cells implanted into immunodeficient mice.

CONCLUSIONS

Gliocladicillins A (1) and B (2) are effective anti-tumour agents in vitro and in vivo and should be further evaluated for their potential in clinical use.