Project: Research project

Project Details


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.
Effective start/end date3/5/922/29/96


  • National Institutes of Health
  • National Institutes of Health: $169,307.00
  • National Institutes of Health: $36,640.00
  • National Institutes of Health


  • Medicine(all)


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