Antiproliferative and apoptotic effects of two new Pd(II) methylsarcosinedithiocarbamate derivatives on human acute myeloid leukemia cells in vitro

[Pd(MSDT)Cl]_n palladium, chloro[methyl N-(dithiocarboxy-kS, kS′)-N-methylglycinate], and [Pd(MSDT) Br]_n palladium, bromo[methyl N-(dithiocarboxy-kS,kS′)-N-methylglycinate], palladium (Pd)(II) derivatives are two newly synthesized Pd(II) derivatives of methylsarcosinedithiocarbamate (MSDT), containing a sulfur chelating ligand that is able to strongly bind the metal center, so preventing interactions with sulfur-containing enzymes. In fact, these reactions are believed to be responsible for the nephrotoxicity induced by platinum (II)-based drugs. Their activity has been evaluated in a panel of acute myeloid leukemia (AML) cell lines representing different French-American-British (FAB) subtypes and in the Philadelphia (Ph)-positive cell line K-562 and compared to cisplatin. Both compounds suppressed, in a dose-dependent manner, colony formation in methylcellulose with ID₅₀ values comparable to those of the reference drug cisplatin, excluding the ML-3 cell line (ID₅₀ 10-fold lower than cisplatin). Exposure of HL-60, ML-3, NB-4, and THP-1 cell lines to a cytotoxic concentration of [Pd(MSDT)Br]_n (5 μM) determined: downregulation of the antiapoptotic molecule Bcl-2, upregulation of the proapoptotic molecule Bax; apoptosis induction, as evaluated by APO2.7 and annexin V staining; mitochondrial membrane permeabilization; and DNA fragmentation. In ML-3 cells the Pd(II) complexes were more active than cisplatin in apoptosis induction. Finally, [Pd(MSDT)Br]_n showed an inhibitory effect on clonogenic growth of hematopoietic progenitors (CFU-GM, CFU-GEMM, and BFU-E) with both ID₅₀ and ID₉₀ comparable to those of cisplatin. Remarkably, the Pd(II) complex was more potent in inhibiting the clonogenic growth of the less differentiated AML cell lines KG-1a, HL-60, NB-4, ML-3, and THP-1 (ID₅₀ ranging from 0.02 ± 0.001 to 0.52 ± 0.04 μM), compared to normal hematopoietic progenitors (ID₅₀ of 2.1 ± 0.1, 3.8 ± 0.4, and 2.5 ± 0.2 μM) for CFU-GEMM, BFU-E, and CFU-GM, respectively). These data suggest that leukemic cells of myelomonoblast lineage might represent a preferential target for its cytotoxic activity compared to normal committed hemopoietic progenitor cells. Altogether, our results indicate that these new Pd(II) dithiocarbamate derivatives might represent novel potentially active drugs for the management of some selected myeloid leukemia strains, able to conjugate cytostatic and apoptotic activity with reduced toxicity.