Spectroscopic investigations of fluorinated Ru(III) anticancer theranostics

Trifluoromethyl derivatives of the Ru(III) anticancer complexes indazolium [trans-RuCl4(1H-indazole)2] (KP1019), sodium [trans-RuCl4(1H-indazole)2] (NKP-1339), and their imidazole- and pyridine-based analogues have been synthesized and characterized. The aqueous solution behaviour of these compounds and their interactions with proteins were investigated using 19F nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and UV-Visible spectroscopies. Furthermore, the lipophilicity of the new CF3 complexes was quantified using the distribution co-efficient (logD). Fluorescence competition studies and EPR showed that CF3 functionalization enhances non-coordinate interactions with human serum albumin (HSA), correlating with increased hydrophobicity. EPR and 19F NMR experiments demonstrated coordination of Ru(III) to the protein at longer incubation times. The more hydrophobic complexes also exhibited higher cytotoxic activity against the HT-29 human colon carcinoma and A549 non-small cell lung carcinoma cell lines. Proof-of-principle 19F magnetic resonance imaging (MRI) experiments show that these compounds can be used to monitor the tissue penetration behaviour and oxidation state of Ru(III) anticancer compounds.