This invention relates to novel cancer treatment compositions and associated therapeutic methods. More particularly, this invention relates in part to small chemical bifunctional inhibitors of DNA replication and repair proteins Metnase and/or Intnase (also termed Gypsy Integrase, Gypsy Integrease-1, Gypsy Retransposon Integrase 1, or GIN-I) that simultaneously damage DNA, and to a therapeutic method that utilizes the inhibitors to increase the effectiveness of cancer treatment protocols, including radiation therapy. In preferred embodiments, compounds, compositions and methods of treatment of the invention are used to treat a patient suffering from leukemia (e.g. acute myeloid leukemia (AML) and related cancers. In certain aspects of such treatments, compounds, compositions and methods of treatment of the invention are administered as a monotherapy (in some cases, to patients who have exhibited resistance to Topo IIalpha inhibitors such as VP-16), or are co-administered with a Topo IIalpha inhibitor or other anti-cancer agents as otherwise described herein or in combination with radiation therapy.