Antiproliferative hybrids and their metal complexes as topoisomerase II

Targeted chemotherapy has become a topic of tremendous importance over the last decades. Metal complexes and organometallic compounds with biologically active ligands in this regard offer opportunities for novel modes of action, specific targeting of enzymes, and overcoming resistances of classical anticancer chemotherapeutics. This research proposal is focussed on the design and synthesis of novel (iso)chalcogensemicarbazone- and aminoguanisone-proline (L and D) and other related conjugates able to form water-soluble transition metal complexes with a square-planar coordination geometry as potential chemotherapeutic agents oriented a priori towards topoisomerase IIa/ß as cancer specific target. The application is based on quite recent results reported by us (Inorg. Chem. 2012, 51, 9309-9321) and others (J. Med. Chem. 2011, 54, 2391-2398) showing the role of metalation in antiproliferative activity and topoisomerase IIa and RNR inhibition of a number of thiosemicarbazones and thiosemicarbazone-proline hybrids. Thesquare-planar coordination geometry ofcopper(II) complexes with thiosemicarbazones and thiosemicarbazone-proline conjugates is likely the biologically active configuration in Topo IIa inhibition via an ATP binding-site-based mechanism. Our main aim is the exploration of these preliminary knowledge for creation of an effective topoisomerase IIa inhibitor, which can be used for further preclinical and clinical developments as a targeted anticancer agent. To this end novel organic compounds will be prepared and their complexation behaviour towards transition metal ions, which prefer a square-planar coordination environment, will be investigated in solution by potentiometric and spectroscopic (UV-vis, CD, fluorometry, NMR, EPR). These data will be used for the synthesis of desired metal complexes, which will be then characterised in the solid state by X-ray diffraction and spectroscopic methods. The prepared compounds will be tested for Topo IIa/ß inhibiting activity by using quite recently developed (Anal. Chem. 2013, 85, 6866-6870; Anal. Chem. 2014, 86, 1005910064) rapid and sensitive methods for selective detection of PO43 ions, which can be applied to quantify the activity of topoisomerase IIa/ß, and cytotoxicity in cancer cell lines in order to find a correlation between the enzyme inhibiting potency and antiproliferative activity in vitro. Particular emphasis will be laid on the impact of coordination geometry, ligand chirality and metal identity on structure-Topo IIa/ß inhibiting activity, and on structure-antiproliferative activity in cancer cell lines. As another possible target for this class of chelators is supposed to be the ribonucleotide reductase. Therefore the ability of new bioconjugates to inhibit the hR2 RNR enzyme will be also investigated. The work will be carried out by the Austrian team in collaboration with groups in Hungary, Serbia, Spain, Sweden, Norway and New Zealand, which have complementary expertise to accomplish the proposed research project.

Targeted chemotherapy has become a topic of tremendous importance over the last decades. Metal complexes and organometallic compounds with biologically active ligands in this regard offer opportunities for novel modes of action, specific targeting of enzymes, and overcoming resistances of classical anticancer chemotherapeutics. This project is focused on the design and synthesis of novel (iso)chalcogensemicarbazone-, aminoguanisone- and other related compounds coupled to specific organic molecules able to form water-soluble transition metal complexes with a square-planar coordination geometry as potential chemotherapeutic agents oriented a priori towards ribonucleotide reductase (RNR) and topoisomerase II/ß as cancer specific targets. The project was based on recent results reported by us (e.g., Inorg. Chem. 2012, 51, 9309; J. Med. Chem. 2011, 54, 2391) showing the role of metal coordination on antiproliferative activity and topoisomerase II and RNR inhibition of a number of thiosemicarbazones and thiosemicarbazone-proline hybrids. Two types of thiosemicarbazones (TSCs) based on 2-formylpyridine (FTSCs)- and 2-hydroxybenzaldehyde (STSCs)- were structurally modified in order to discover the most potent candidates for further development as anticancer drugs. The FTSC hybrid with the morpholine moiety at the pyridine ring and the phenyl group at the terminal N-atom of the thiosemicarbazide moiety and its Cu(II) complex, were chosen as the lead compounds due to their cytotoxic activities in nanomolar range against human ovarian carcinoma cells (A2780), the antibacterial effect against S. aureus and the ablity to quench tyrosyl radical (Y) of R2 RNR protein in the presence of dithiothreitol (DTT). The study showed that other biomolecular targets are also involved in their mechanism of action and that the hybrids could be developed as drugs with dual anticancer and antibacterial activity. The activity of triapine derivatives, with 2-pyridinamidrazone- and S-methylisothiosemicarbazide moiety and their corresponding copper(II) and iron(III) complexes was not related to the inhibition of R2 protein, but rather to cancer cell homeostasis disturbance-leading to the disruption of cancer cell signaling. Iminodiacetate STSCs is another hybrid that showed marked tyrosyl radical inhibition, while sulfonyl derivatives exhibited remarkable antiproliferative activity that was based on the induction of reactive oxygen species (ROS) and the promotion of antioxidant stress. The copper(II) complexes of trimethylammonium STSCs showed antiproliferative effect towards neuroblastoma cancer cells and marked interaction with organic cation transporters, what paves the way for the development of more potent and selective anticancer drugs and/or OCT inhibitors.