In the presence of carboxypeptidase, the hydrolytically stable complex EOs(eta(6)-pcym)(L2)Cl]PF6 (2) partially released the bioactive substituent indomethacin, bound through the amide bond to the chelating 2-(1,3,4-thiadiazol-2-yl)pyridine-based moiety of L2. Stability in the presence of other relevant biomolecules (GSH, NADH, GMP) and cancer cell viability were also studied.