<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A substance that is being studied in the treatment of leukemia. It belongs to the family of drugs called topoisomerase inhibitors.</n0:def-definition><n0:def-source>NCI-GLOSS</n0:def-source></n0:ComplexDefinition>
<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>The R-isomer of a synthetic quinoxaline phenoxypropionic acid derivative with proapoptotic and antiproliferative activities. R(+)XK469 selectively inhibits topoisomerase II-beta, blocks activation of MEK/MAPK signaling kinases, stimulates caspases, and upregulates p53-dependent proteins, including cyclins A and B1, thereby arresting cancer cells in the G2/M phase of the cell cycle. Both R(+) and S(-) isomers of this agent are cytotoxic, although the R-isomer is more potent. (NCI05)</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>