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

The novel ruthenium(II) complexes [RuCl(κ3 N -tpm)(PPh3)(κ1 N -AcmH2)]Cl ( 5 ) and [Ru(κ3 N -tpm)(PPh3)(κ2 N,N′ -AcmH)]NO3 ( 6 ) were synthesized in 46–57 % yields via thermal reactions of [RuCl(κ3 N -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 P ow ) 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(κ1 N -AcmH2)(η6- p -cymene)] ( 1 ) , [RuCl(κ2 N , N ′-AcmH)(η6- p -cymene)] ( 2 ) and [Ru(κ2 N , N ′-Acm)(κ P -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).