Mechanisms of new Ru-ferrocene and binuclear Ru metallochemotherapeutics and the Ru metastasis inhibitor NAMI-A

Ruthenium-based anticancer compounds have become a leading area of development in medicinal chemistry. Ru(III) complexes, such as the antimetastatic compound imidazolium [trans-RuCl4(1H-imidazole)(DMSO-S)] (NAMI-A), where DMSO = dimethyl sulfoxide, have shown promising results in clinical trials. Furthermore, reports of organometallic Ru(II) arene complexes, such as [RuCl2(η6-p-cymene)(pta)] (RAPTA-C), where pta = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane, demonstrate that these types of compounds also have excellent chemotherapeutic potential. In this work, three families of new bimetallic drug candidates based on these types of Ru anticancer compounds have been developed, with the goal of generating multifunctional complexes with new biological activities. The first type of complex is ferrocene-functionalized pyridine analogues of NAMI-A. Inclusion of ferrocene generates bifunctional complexes with cytotoxicity from the ferrocene groups and antimetastatic activity from the Ru center. The second family of complexes described in this work is analogues of RAPTA-C with the pta ligand replaced with ferrocene-functionalized pyridine, imidazole, and piperidine ligands. These compounds have strong anticancer and antibiotic activities, which correlate quantitatively with the reduction potential of the ferrocene centers, implicating generation of reactive oxygen species as the origin of activity. The third family of complexes, asymmetric bimetallic complexes comprised of a Ru(III) NAMI-A-type center coupled to Ru(III) DNA intercalating groups via pyrimidine, have been synthesized. Functionalization with dipyrido[3,2-a:2’, 3’-c]phenazine (dppz) in particular led to strong DNA interactions and high cytotoxic activity. In this work, electron paramagnetic resonance (EPR) and NMR have been used to study the ligand-exchange processes of the complexes and their interactions with proteins. In particular, NMR was used to investigate the complicated solution behavior of NAMI-A. Furthermore, NMR studies of the complex with human serum albumin and human serum transferrin indicate non-specific coordination to histidine residues and changes in ligand exchange kinetics due to protein interactions.