Abstract
A series of heteropentanuclear oxalate-bridged Ru(NO)-Ln (4d–4f) metal complexes of the general formula (nBu4N)5[Ln{RuCl3(μ-ox)(NO)}4], where Ln=Y (2), Gd (3), Tb (4), Dy (5) and ox=oxalate anion, were obtained by treatment of (nBu4N)2[RuCl3(ox)(NO)] (1) with the respective lanthanide salt in 4:1 molar ratio. The compounds were characterized by elemental analysis, IR spectroscopy, electrospray ionization (ESI) mass spectrometry, while 1, 2, and 5 were in addition analyzed by X-ray crystallography, 1 by Ru K-edge XAS and 1 and 2 by 13C NMR spectroscopy. X-ray diffraction showed that in 2 and 5 four complex anions [RuCl3(ox)(NO)]2− are coordinated to YIII and DyIII, respectively, with formation of [Ln{RuCl3(μ-ox)(NO)}4]5− (Ln=Y, Dy). While YIII is eight-coordinate in 2, DyIII is nine-coordinate in 5, with an additional coordination of an EtOH molecule. The negative charge is counterbalanced by five nBu4N+ ions present in the crystal structure. The stability of complexes 2 and 5 in aqueous medium was monitored by UV/Vis spectroscopy. The antiproliferative activity of ruthenium-lanthanide complexes 2–5 were assayed in two human cancer cell lines (HeLa and A549) and in a noncancerous cell line (MRC-5) and compared with those obtained for the previously reported Os(NO)-Ln (5d–4f) analogues (nBu4N)5[Ln{OsCl3(ox)(NO)}4] (Ln=Y (6), Gd (7), Tb (8), Dy (9)). Complexes 2–5 were found to be slightly more active than 1 in inhibiting the proliferation of HeLa and A549 cells, and significantly more cytotoxic than 5d–4f metal complexes 6–9 in terms of IC50 values. The highest antiproliferative activity with IC50 values of 20.0 and 22.4 μM was found for 4 in HeLa and A549 cell lines, respectively. These cytotoxicity results are in accord with the presented ICP-MS data, indicating five- to eightfold greater accumulation of ruthenium versus osmium in human A549 cancer cells.
Highlights
Quite recently we became interested in ruthenium and osmium nitrosyl complexes with the prospect to create prodrugs able to release clinically effective levels of NO and metal complex within cancer cells.[1,2,3] This took into account the fact that several classes of, mostly mononuclear, ruthenium and osmium coordination compounds have demonstrated promising anticancer potential both in vitro and in vivo.[4]
As mentioned in the Introduction we were interested in labeling our ruthenium and osmium–nitrosyl complexes with lanthanide ions
Quite recently we reported the synthesis of the osmium–nitrosyl analogues 6–9 (Scheme 1).[30]
Summary
Quite recently we became interested in ruthenium and osmium nitrosyl complexes with the prospect to create prodrugs able to release clinically effective levels of NO and metal complex within cancer cells.[1,2,3] This took into account the fact that several classes of, mostly mononuclear, ruthenium and osmium coordination compounds have demonstrated promising anticancer potential both in vitro and in vivo.[4]. The lanthanide has been coupled to the ruthenium by a bridging oxalate, which is a well-known bioligand incorporated in the anticancer agent oxaliplatin.[31] The complexes of the general formula (nBu4N)5[Ln{RuCl3(ox)(NO)}4], where Ln = Y (2), Gd (3), Tb (4), Dy (5; Scheme 1), have been characterized by elemental analysis, ESI mass spectrometry and IR spectroscopy and, in case of 2 and 5 by X-ray diffraction.
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