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).