DNA-PK inhibitor wortmannin enhances DNA damage induced
by bleomycin in V79 Chinese hamster cells.
Oliveira NG, Castro M, Rodrigues AS, Gil OM, Toscano-Rico JM, Rueff J.
Department of Genetics, Faculty of Medical Sciences, New University of Lisbon,
The fungal metabolite wortmannin (WM) is a potent and irreversible inhibitor of
the enzyme DNA-dependent protein kinase (DNA-PK), a nuclear serine-threonine
kinase, member of the phosphaditylinositol-3 kinase related kinase family. WM
has been used in the last few years as a promising radiosensitizer mainly
throughout cell survival experiments. However, few studies have addressed the
role of DNA-PK inhibition in the repair of DNA lesions generated by antitumor
agents. Bleomycin (BLM) is an antitumor agent used in the treatment of various
neoplasia with a unique genotoxicity profile that mimics the ionizing radiation
effects. In this study, we evaluated the effect of different concentrations of
WM on the DNA damage induced by BLM. The cytokinesis-block micronucleus assay (CBMN)
in V79 Chinese hamster cells was used as the end-point. WM significantly
increased the frequency of micronucleated cells (%MNBN) by about 2.2-fold, the
number of micronuclei per binucleated cell (MN/BN) by about 2.4-fold, and also
changed the pattern of the distribution of micronuclei induced by BLM. The
frequency of micronucleated cells with 2 MN per cell and with > or = 3 MN per
cell increased, whereas the frequency of micronucleated cells with 1 MN per cell
decreased. WM was not genotoxic but decreased cell proliferation as assessed by
the frequency of binucleated cells. Our results show that WM clearly enhances
the efficacy of BLM in terms of DNA damage inflicted and therefore reinforces
its use as a chemosensitizer. Copyright 2002 Wiley-Liss, Inc.