Increasing the Cytotoxicity of Ru(II) Polypyridyl Complexes by Tuning the Electronic Structure of Dioxo Ligands

Abstract

<div>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-1,10-phenanthroline, 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-like dioxoligands 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 dioxoligand 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 outstanding cytotoxicity, make complex 1 a valuable candidate in the field of chemotherapy research.</div>

Synthesis, Characterization, Cytotoxic Activity, and Metabolic Studies of Ruthenium(II) Polypyridyl Complexes Containing Flavonoid Ligands

“…Furthermore, the lack of response to the oligomycin injection in cells treated with both complexes, agrees with the results obtained via the mito stress test, which suggests non-functioning mitochondria after both treatments. Interestingly, the complexes [Ru(DIP) 2 (sq)](PF 6 ), [Ru(DIP) 2 (mal)](PF 6 ) and [Ru(DIP) 2 (3-methoxysq)](PF 6 ), recentlyreported by our group, also showed impaired mitochondrial function but did not show any effect on the glycolysis process [66][67][68]. This illustrates how subtle structural changes in the complexes bearing the same Ru(DIP)2 core but different dioxo ligands, can result in significantly different behaviour of the complexes in living cells.…”

Note of Caution for the Aqueous Behavior of Metal-based Drug Candidates

“…[29], [30] Experimental Section in our laboratories. [7], [8] All solvents were purchased (analytical or HPLC grade) and…”

“…Those aggregates were not found to be stable after being incubated at 28 °C for 24 h, as two main population distributions of ~ 65 nm and ~ 95 nm were observed ( Figure S4). It is noteworthy that despite their extremely similar structure, as reflected by their very close physical properties, [7], [8] These results demonstrate that compounds that appear completely soluble to the naked eye and display a linear relationship when their UV absorbance is measured versus their concentration might actually be in the form of colloids. Moreover, this study shows that minor changes in the chemical structure of some compounds might lead to a dramatic change in their self-assembly.…”

“…[19]- [21] However, in this case, the stability of [Ru(DIP) 2 (sq)](PF 6 ) and [Ru(DIP) 2 (3-methoxysq)](PF 6 ) in DMSO was found to be very high, the nature of both compounds remaining unaltered up to at least 4 days. [7], [8] In this communication, of ruthenium complexes (e.g., NMR or mass spectrometry techniques). [22]- [24] However, conventional methods for solubility screens (e.g., UV-vis absorbance) could have easily led to the misidentification of these colloids as solutions, especially if a non-instinctive fine filtration step would have been skipped.…”

Photochemical and Photobiological Properties of Pyridyl-pyrazol(in)e-Based Ruthenium(II) Complexes with Sub-micromolar Cytotoxicity for Phototherapy

“…The investigation of new ruthenium-based compounds as alternatives to anticancer platinum drugs is a developing trend in modern medicinal inorganic chemistry. 1 − 6 Based on the specific chemical features of ruthenium complexes, drug discovery efforts can be divided into two categories: (1) development of agents which are prone to ligand exchange (for example, NAMI-A and KP1339, which were in phase II clinical trials, and RAPTA-C, which is progressing toward clinical trials), 7 − 10 and (2) investigation of kinetically inert ruthenium(II) polypyridyl complexes as either agents possessing anticancer potency without irradiation 11 − 13 or prodrugs for photodynamic therapy (PDT; for example, TLD1433, now in phase II clinical trials) and photoactivated chemotherapy (PACT). 2 , 6 , 14 − 16 …”