Strong in Vitro Cytotoxic Potential of New Ruthenium-Cymene Complexes

Two p-cymenerutheniumchlorido complexes with thiourea derivative of 7-chloroquinoline (C1) and pyridine-3-imidazole (C2) were synthesized starting from [(eta(6)-p-cymene)RuCl2](2) and corresponding ligands. The structures of complexes were determined with elemental analysis and IR, ESIMS, H-1 and C-13{H-1} NMR, and 2D H-1-N-15 correlation NMR spectroscopy. Cytotoxic activities examined by the MTT assay were performed in five human neoplastic cell lines (HeLa, K562, A549, MDA-MB-231, EA.hy926) and one nontumor human fetal lung fibroblast cell line (MRC-5). Tested complexes exhibited low micromolar activities with IC50 in the range 11.03-56.45 mu M, while ligands L1 and L2 were significantly less active. Complex C1 showed cytoselective activity toward the K562 cell line (IC50 = 11.03 +/- 1.39 mu M) and was 3 times less active against the nontumor MRC-5 cell line. Flow cytometry analysis indicated that complexes C1 and C2 after 24 h treatment caused a concentration-dependent increase of the apoptotic sub-G1 fraction (up to 18.4%), comparable to cis-diamminedichloridoplatinum(II) (cisplatin, CDDP), although without other substantial alterations of the cell cycle. A drug-accumulation and DNA-binding study performed by ICP-MS in the K562 cell line revealed that complex C1 had a high intracellular uptake (1.38 mu g Ru/10 (6) cells), which significantly exceeded the intracellular uptake levels of CDDP (0.29 mu g Pt/10 (6) cells) and C2 (0.08 mu g Ru/10 (6) cells). However, both ruthenium complexes C1 and C2 bind to cellular DNA less efficiently in comparison to CDDP. The structure-activity relationship clearly suggested that introduction of a 7-chloroquinoline moiety in the ruthenium(II)-p-cymene complex significantly contributed to the intracellular uptake of C1 and higher cytotoxicity and cytoselectivity.