Chemotherapy remains one of the dominant treatments to cure cancer. However, due to the many inherent drawbacks, there is a surge for new chemotherapeutic drugs. More specifically, the discovery of new drug candidates able to overcome severe side effects, the occurrence of resistance and the inefficacy toward metastatic tumours is highly desirable. In this work, we designed a new chemotherapeutic drug candidate against cancer, namely [Ru(DIP)2(sq)]PF6 (Ru-sq) (DIP = 4,7-diphenyl-1,10-phenanthroline; sq = semiquinonate ligand). The aim was to combine the great potential expressed by Ru(II) polypyridyl complexes and the singular redox and biological properties associated to the catecholate moiety. Several pieces of experimental evidence (e.g., X-ray crystallography, electron paramagnetic resonance, electrochemistry) demonstrate that the semiquinonate is the preferred oxidation state of the dioxo ligand in this complex. The biological activity of Ru-sq was then scrutinised in vitro and in vivo, and the results highlight the tremendous potential of this complex as a chemotherapeutic agent against cancer. Ru-sq was notably found have a much higher cytotoxic activity than cisplatin on several cell lines (i.e. in the nanomolar range), and, contrary to cisplatin, to have mitochondrial disfunction as one of its modes of action. The multicellular targets of Ru-sq could potentially be the key to overcome one of the main drawbacks of cisplatin i.e. the occurrence of resistance. Moreover, Ru-sq exhibited impressing activity on Multi Cellular Tumour Spheroids (MCTS) model, leading to a growth inhibition of the tumour even 13 days after treatment (20 μM). Very importantly, using two different in vivo models, it could be demonstrated that this compound is extremely well-tolerated by mice and has a very promising activity, curing, in some cases, tumour-bearing mice.<br>

Due to the great potential expressed by an anticancer drug candidate previously reported by our group, namely, Ru-sq ([Ru(DIP)2(sq)](PF6) (DIP: 4,7-diphenyl-1,10phenanthroline, sq: semiquinonate ligand), we describe in this work a structure-activity relationship (SAR) that involves a broader range of derivatives resulting from the coordination of different catecholate-type dioxo ligands to the same Ru(DIP)2 core. More in detail, we chose catechols carrying either electron-donating or electronwithdrawing groups EDG or EWG and investigated the physico-chemical and biological properties of their complexes. Several pieces of experimental evidences demonstrated that the coordination of catechols bearing EDGs led to deep red positively charged complexes 1-4 in which the preferred oxidation state of the dioxo ligand is the uninegatively charged semiquinonate. Complexes 5 and 6, on the other hand, are blue/violet neutral complexes, which carry an EWG substituted dinegatively charged catecholate ligand. The biological investigation of complexes 1-6 led to the conclusion that the difference in their physico-chemical properties has a strong impact on their biological activity. Thus, complexes 1-4 expressed much higher cytotoxicities than complexes 5 and 6. Complex 1 constitutes the most promising compound of the series and was selected for a more in-depth biological investigation. Apart from its remarkably high cytotoxicity (IC50 = 0.07-0.7 µM in different cancerous cell lines) complex 1 was taken up by HeLa cells very efficiently by a passive transportation mechanism. Moreover, its moderate accumulation in several cellular compartments (i.e. nucleus, lysosomes, mitochondria and cytoplasm) is extremely advantageous in the search of a potential drug with multiple modes of action. Further DNA metalation and metabolic studies pointed to the direct interaction of complex 1 with DNA and to the severe impairment of the mitochondrial function. Multiple targets, together with its 4 outstanding cytotoxicity, make complex 1 a valuable candidate in the field of chemotherapy research. Noteworthy, a preliminary biodistribution study on healthy mice demonstrated the suitability of complex 1 for further in vivo studies.

We report here on ruthenium alkenyl complexes 2 and 3 derived from 2,2'-bipyridine and their Re(CO)3X adducts 4a,b and 5. Detailed electrochemical studies on these complexes and spectroscopic characterization of their oxidized forms by IR, UV/vis/NIR, and electron paramagnetic resonance spectroscopies as well as quantum chemical studies reveal sizable (bridging) ligand contributions to the redox orbitals. Engagement of the free bipy functions of complexes 2 and 3 in binding to the electron-withdrawing fac-Re(CO)3X (X = Br, Cl) moiety enhances the metal-to-ligand charge-transfer character of the optical excitations, causes sizable anodic shifts of the redox potentials, and decreases the number of observable anodic redox waves by one when compared to complexes 2 and 3. Despite the decreasing electron density at the terminal or bridging alkenyl bipyridine ligand, the anodic redox processes still maintain appreciable ligand character as is seen by the shifts of the Ru(CO) and Re(CO)3 stretching frequencies on oxidation. Binding of the fac-Re(CO)3X moiety also attenuates the degree of ground-state delocalization in the mixed-valent states.

Chemotherapy remains one of the dominant treatments to cure cancer. However, due to the many inherent drawbacks, there is a surge for new chemotherapeutic drugs. Many classes of compounds have been investigated over the years in order to discover new targets and synergistic mechanisms of action including multicellular targets. In this work, we designed a new chemotherapeutic drug candidate against cancer, namely [Ru(DIP)2(sq)]PF6 (Ru-sq) (DIP = 4,7-diphenyl-1,10-phenanthroline; sq = semiquinonate ligand). The aim was to combine the great potential expressed by Ru(II) polypyridyl complexes and the singular redox and biological properties associated to the catecholate moiety. Experimental evidences (e.g. X-ray crystallography, electron paramagnetic resonance, electrochemistry) demonstrate that the semiquinonate is the preferred oxidation state of the dioxo ligand in this complex. The biological activity of Ru-sq was then scrutinised in vitro and in vivo, and the results highlight the auspicious potential of this complex as a chemotherapeutic agent against cancer.

We present four new divinylarylene-bridged diruthenium complexes of the type {Ru­(CO)­Cl­(P i Pr3)2}2(μ-CHCH–Ar–CHCH) with naphthalene-1,4-diyl (Ru 2 NA), 2,1,3-benzothiadiazole (Ru 2 BTD), bis­(benzothiadiazolyl)­ethene (Ru 2 v BTD 2 ), or bis­(benzothiadiazolyl)­ethyne (Ru 2 e BTD 2 ) as the arylene units. The radical cations of the complexes with shorter arylene bridges are intrinsically valence-delocalized on the IR time scale. In contrast to phenylene-bridged [{Ru­(CO)­Cl­(P i Pr3)2}2(μ-CHCH–C6H4-1,4-CHCH)]2+ (Ru 2 -p-phen 2+ ), the dioxidized forms of complexes Ru 2 BTD and Ru 2 NA are electron paramagnetic resonance (EPR) silent. Replacing the E-stilbenediyl linker of the complex {Ru­(CO)­Cl­(P i Pr3)2}2(μ-CHCH–C6H4–CHCH–C6H4–CHCH) (Ru 2 v p-phen 2 ) by vBTD2 or eBTD2 enhances electronic coupling and charge delocalization of their one-electron-oxidized mixed-valent forms. While the latter radical cations are still charge-localized species on the IR time scale, they are fully delocalized on the slower EPR time scale. As a token of a quinoidally distorted bridge, Ru 2 e BTD 2 2+ features a characteristic IR stretch of a cumulenic CCCC increment. For compound Ru 2 v BTD 2 , rearrangement to a quinoidal structure is manifested through potential inversion (i.e., the half-wave potential of the second oxidation is lower than that of the 0/1+ redox couple) in the CH2Cl2/NBu4BArF electrolyte. The BTD complexes are intensely colored in their neutral states and exhibit strong NIR absorptions of their radical cations as well as of their dioxidized forms.