The epipodophyllotoxin etoposide (VP-16) is utilized extensively in cancer chemotherapy. A wide variety of experiments indicate that VP-16 stabilizes covalent adducts between DNA and the nuclear enzyme topoisomerase (topo) II. Upon removal of VP-16, the adducts are reversed, yet the cells proceed to die. These observations suggest that the topo II-DNA adducts initiate a series of event which culminate in cell death. This grant proposal is aimed at elucidating the poorly understood events between the formation of topo II-DNA adducts and the death of target cells. Preliminary results suggest that treatment of human leukemia cells with VP-16 in the presence of nucleic acid synthesis inhibitors-- particularly RNA synthesis inhibitors-- markedly diminishes the cytotoxicity of VP-16 without altering the number of topo II-DNA adducts. This observation suggests that ongoing nucleic acid synthesis is required to convert reversible topo II-mediated lesions into cytotoxic damage. It has been proposed that topo II-mediated nonhomologous recombination is involved. Consistent with this view, VP-16 has been observed to be mutagenic and possibly leukemogenic. We now propose to utilize two model systems (Saccharomyces cerevisiae bearing a temperature sensitive mutation in RNA polymerase b and mouse L cells transfected with a plasmid bearing the chloramphenicol acetyltransferase gene behind an inducible promotor) to test the hypothesis that ongoing RNA synthesis helps convert the reversible topo II-DNA adducts into cytotoxic DNA lesions and to assess the nature of this irreversible DNA damage. These experiments should provide insight into he mechanism of cytotoxicity of VP-16, into the nature of DNA damage induced by this agent, and into potential mechanisms of resistance.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
1R01CA055642-01
Application #
3200149
Study Section
Experimental Therapeutics Subcommittee 1 (ET)
Project Start
1992-03-05
Project End
1995-02-28
Budget Start
1992-03-05
Budget End
1993-02-28
Support Year
1
Fiscal Year
1992
Total Cost
Indirect Cost
Name
Johns Hopkins University
Department
Type
Schools of Medicine
DUNS #
045911138
City
Baltimore
State
MD
Country
United States
Zip Code
21218
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