Synthesis and Characterization of New Palladium(II) Thiosemicarbazone Complexes and Their Cytotoxic Activity against Various Human Tumor Cell Lines

The palladium(II) bis-chelate complexes of the type [Pd(TSC(1-5))(2)] (6–10), with their corresponding ligands 4-phenyl-1-(acetone)-thiosemicarbazone, HTSC(1) (1), 4-phenyl-1-(2′-chloro-benzaldehyde)-thiosemicarbazone, HTSC(2) (2), 4-phenyl-1-(3′-hydroxy-benzaldehyde)-thiosemicarbazone, HTSC(3) (3), 4-phenyl-1-(2′-naphthaldehyde)-thiosemicarbazone, HTSC(4) (4), and 4-phenyl-1-(1′-nitro-2′-naphthaldehyde)-thiosemicarbazone, HTSC(5) (5), were synthesized and characterized by elemental analysis and spectroscopic techniques (IR and (1)H- and (13)C-NMR). The molecular structure of HTSC(3), HTSC(4), and [Pd(TSC(1))(2)] (6) have been determined by single crystal X-ray crystallography. Complex 6 shows a square planar geometry with two deprotonated ligands coordinated to Pd(II) through the azomethine nitrogen and thione sulfur atoms in a cis arrangement. The in vitro cytotoxic activity measurements indicate that the palladium(II) complexes (IC(50) = 0.01–9.87 μM) exhibited higher antiproliferative activity than their free ligands (IC(50) = 23.48–70.86 and >250 μM) against different types of human tumor cell lines. Among all the studied palladium(II) complexes, the [Pd(TSC(3))(2)] (8) complex exhibited high antitumor activity on the DU145 prostate carcinoma and K562 chronic myelogenous leukemia cells, with low values of the inhibitory concentration (0.01 and 0.02 μM, resp.).