Potent carbonic anhydrase inhibition by ruthenium(II)-acetazolamide conjugates uncoupled from antiproliferative activity in vitro.

The novel ruthenium(II) complexes [RuCl(κ3N-tpm)(PPh3)(κ1N-AcmH2)]Cl (5) and [Ru(κ3N-tpm)(PPh3)(κ2N,N'-AcmH)]NO3 (6) were synthesized in 46-57 % yields via thermal reactions of [RuCl(κ3N-tpm)(PPh3)2]Cl (4) with AcmH2, conducted in THF and ethanol, respectively [tpm = tris(pyrazolyl)methane; AcmH2 = acetazolamide]. Both complexes were fully characterized by single crystal X-ray diffraction, IR and NMR spectroscopy. Their solubility in D2O, octanol/water partition coefficients (Log Pow) and speciation in physiological-like solutions were assessed by 1H NMR and UV-Vis methods. Additionally, DFT calculations provided insights into the structural and thermodynamic properties of 5. Complexes 5-6, together with the previously reported ruthenium(II) arene acetazolamide adducts [RuCl2(κ1N-AcmH2)(η6-p-cymene)] (1), [RuCl(κ2N,N'-AcmH)(η6-p-cymene)] (2) and [Ru(κ2N,N'-Acm)(κP-PTA)(η6-p-cymene)] (3, PTA = 1,3,5-triaza-7-phosphaadamantane), exhibited potent inhibitory activity against human carbonic anhydrase isoforms I, II, IX and XII, with KI values in the low to sub-nanomolar range. Under hypoxic conditions, complexes 5 and 6 showed a moderate antiproliferative activity against the human triple negative breast cancer cell line MDA-MB-231 (IC50 = 143.3, 40.9 μM), while complexes 2 and 3 were inactive (IC50 > 200 μM).