The tremendous success of cisplatin, cis-[Pt(NH3)2Cl2], in human cancer chemotherapy has led to interest in the potential for complexes of another transition metal, Ru (II), to function as an anti-cancer agents. We have developed a class of ruthenium complexes which incorporate a redox-active intercalating ligand denoted tatpp. These ruthenium-tatpp complexes have been shown to tightly bind DNA and to cause DNA cleavage under conditions of low oxygen tension (hypoxia) and in the presence of common cellular reductants, e.g. glutathione. In our initial grant period, we have shown that mice implanted with either mouse melanoma (B16) or nude mice implanted with human non-small cell lung carcinoma (H358) tumor cells show arrested tumor growth and extended lifetimes when treated with two specific ruthenium-tatpp complexes. We have also shown that these complexes are cytotoxic towards a broad range of cancer cell lines but are considerably (~10 fold difference) less toxic to normal cells. Animal acute-toxicity studies show that chiral versions of these complexes are not appreciably toxic and can be safely be used and drugs. Thus all of our initial data suggests that this class of compounds may have potential an future chemotherapeutic drugs for cancer treatment. In our initial grant period, we established a number of structure-activity relationships and established that only complexes containing redox-active bridging ligands were promising drug candidates. In this proposal, we aim to prepare a number of new complexes in which both the reduction potential of the bridging ligand and the other anciallary ligands are varied to further delineate the structure-activity relationships for this class of compounds. The new complexes will be screened for DNA binding, DNA cleavage and cytotoxicty towards two cancer cells lines. Promising candidates will be further examined in animal models. In addition to establishing structure-activity relationships, we propose to examine the mechanism of DNA cleavage in detail using combination of EPR techniques and DNA product analysis studies. The unusual behavior under hypoxic conditions suggests a novel mechanism of action. We also will examine the detailed mechanism of chemical action for the DNA cleavage reaction and examine the biological pathways affected by drug treatment. In particular, we will examine the affect of these complexes on factors, e.g. HIF-1/2, VEGF, LDH-A, associated with hypoxic stress in both cells and in animals.
We are developing a class of potential anti-cancer drugs based on ruthenium metal complexes in which one ligand is redox-active under common biological conditions. These compounds are able to arrest tumor growth in mice and show high specificity for killing tumor cells over normal cells. These compounds bind and cleave DNA and recently we have shown that they do so better under conditions of low oxygen tension (hypoxia). This is promising because tumor cells under hypoxic stress are one of the most difficult subpopulations of cancer cells to treat and few compounds show better activity under hypoxic conditions over normal conditions.
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