Novel antitumor Cu(I) and Cu(II) complexes based on bioconjugate ligands rationally designed to act through synergistic mechanisms

Lonidamine (LND) is an antineoplastic drug able to sensitize tumors to radio-, chemo- and photodynamic-therapy and even if its anticancer activity as single agent is limited, this drug has a great potential in increasing the efficacy of traditional chemotherapeutic agents. A recent approach concerned the biological study of platinum complexes conjugated with LND or its derivatives: many of them showed interesting antitumor activity profiles in vitro, with improved cytotoxic effects compared to reference drugs. Based on these considerations, we have functionalized LND with ligands able to form stable Cu(I) and Cu(II) complexes. This metal has been chosen because several copper complexes have been recently described as promising anticancer agents both in vitro and in vivo: they show broader spectra of activities and lower toxicity, thereby providing the possibility of circumventing the problems encountered by Pt drugs. For this purpose, considering that we have recently reported the anticancer activity of Cu complexes with heteroscorpionate ligands, obtained by conjugation with nitroimidazole, glucosamine and more recently with a noncompetitive NMDA receptor antagonist [1], LND was converted into the 2-hydroxyethylester and 2-aminoethylamide derivatives, respectively, which were conjugated to the bifunctional species bis(pyrazol-1-yl)- and bis(3,5-dimethyl-pyrazol-1-yl)-acetic acid, to form bioconjugated ligands. They were used for the preparation of Cu(I) and Cu(II) complexes that might act through synergistic mechanisms of action, due to the presence of LND and Cu in the same chemical entity. Concerning the Cu(I) complexes, to stabilize copper in +1 oxidation state the lipophilic triphenylphosphine and the hydrophilic 1,3,5-triaza-7-phosphaadamantane were selected as co-ligands, in order to confer different solubility properties to the complexes. The new Cu complexes, the relative ligands and LND were investigated for their antitumor activity on human tumor cell lines of different histology and cisplatin sensitive or resistant or with Multi-Drug Resistant phenotype. Interestingly, all the complexes show IC50 values lower than those of the corresponding uncoordinated precursors in all the studied cell lines. In addition, they proved to be significantly more active than cisplatin even in 3D spheroids of 2008 and PSN-1 cancer cells, increasing the relevance of the in vitro results.