The in vitro cell toxicity of some phenanthroline coordinated inorganic complexes

The application of small molecules for the control of microbial or cancer cell growth has been applied as an effective solution in clinical contexts. In particular, the value of phenanthroline-coordinated inorganic complexes largely remains recognised in developmental stages and the mode of action of target cell and non-cancerous human cell toxicity has yet to be understood. Throughout this work a series of cell toxicity studies have been carried out to provide further insight into the development of antimicrobial copper(II) and ruthenium(II) complexes, and anticancer platinum(II) complexes with 1,10- phenanthroline (phen) and diaminocyclohexane (dach) -like ligands. The antimicrobial spectrum of activity of copper(II) complexes [Cu(L1)(L2)]2+ (where L1 is dach and L2 is TMP = 3,4,7,8-tetramethyl-1,10-phenanthroline or DIP = 4,7-diphenyl- 1,10-phenanthroline) were confirmed to be largely effective against Gram-positive bacteria and fungi in an expanded panel (MIC 4-16 μg /mL). Rapid antimicrobial efficacy against Gram-positive bacteria was noted within 0.5 h of exposure and in contrast to ampicillin, demonstrated bactericidal activity in non-proliferating conditions. Like other phen-based metal complexes, the copper(II) complexes exhibit significant DNA binding affinity. Evidence of DNA as a molecular target implies potential toxicity to mammalian cells. These copper(II) complexes were found to exhibit similar growth inhibitory concentrations (IC50 2-2.5 μM) in a human renal proximal tubule cell line, while their renal cell toxicity is associated with cytoplasmic vacuolisation, reactive oxygen species generation and necrosis. The renal cell potency of both copper(II) complexes can be reduced by catalase, and that of the TMP complex can be greatly reduced by copper sulfate. Coincubation with organic cation transporter OCT inhibitors cimetidine or disopyramide does not affect their mammalian cell toxicity, suggesting a non-OCT dependent mode of uptake. Previously reported antimicrobial ruthenium(II) complexes of phen, TMP or 2,9-dimethyl-1,10- phenanthroline (29Me2phen) demonstrated a much lower cytotoxicity than the copper(II) complexes (IC50 > 60 μM). Neither copper(II) or ruthenium(II) phen-based complexes induce cell cycle arrest or micronuclei formation to the same degree as etoposide or cisplatin. Platinum(II) dach and phen coordinated complexes are known to exhibit greater DNA binding affinities than copper(II) complexes however few investigations have considered their non-cancerous cell toxicity or genotoxicity. Unconventional platinum(II) complexes [Pt(RR-dach or SS-dach)(phen, TMP or DIP)]2+ exhibit lower cytotoxicity in renal cells than cisplatin-resistant ovarian cancer cells. Organic cation transporter (OCT) inhibitors cimetidine and disopyramide reduce the cytotoxicity of the platinum(II) complexes and likely play a significant role in in their uptake. Their mode of action in renal cells is associated with cellular elongation, pronounced F-actin formation and increased β-galactosidase activity. They also induce a lower proportion of apoptosis and cell death than cisplatin, as well as a lack of oxidative stress and similar cell cycle proportions to untreated cultures. In comparison, cisplatin treatment induces nuclei enlargement, accumulation in G2/M cell cycle phase and eventual apoptosis and necrosis. The phen-based platinum(II) complexes show slightly elevated micronuclei generation which is significantly lower than cisplatin or etoposide. These results provide insight into phenanthroline-based metal complexes with potential as disinfectant, antimicrobial and anticancer agents. Promising evidence includes the efficacy of copper(II) complexes against non-proliferating bacteria, and the low renal cell toxicity of antimicrobial ruthenium (II) complexes. Also noteworthy is the cytotoxicity of unconventional platinum(II)-phen complexes against cisplatin-resistant cancer cells, and comparably cytostatic mode of action in renal cells. Although DNA binding is likely involved in their biological activity, these complexes are less likely to induce genotoxic consequences than conventional DNA adduct-forming compounds like cisplatin