New halogenated thiourea derivatives were synthesized via the reaction of substituted phenylisothiocyanates with aromatic amines. Their cytotoxic activity was examined in in vitro studies against solid tumors (SW480, SW620, PC3), a hematological malignance (K‐562), and normal keratinocytes (HaCaT). Most of the compounds were more effective against SW480 (1a, 3a, 3b, 5j), K‐562 (2b, 3a, 4a), or PC3 (5d) cells than cisplatin, with favorable selectivity. Their anticancer mechanisms were studied by Annexin V‐fluorescein‐5‐isothiocyanate apoptosis, caspase‐3/caspase‐7 assessment, cell cycle analysis, interleukin‐6 (IL‐6) release inhibition, and reactive oxygen species (ROS) generation assay. Thioureas 1a, 2b, 3a, and 4a were the most potent activators of early apoptosis in K‐562 cells, and substances 1a, 3b, 5j triggered late‐apoptosis or necrosis in SW480 cells. This proapoptotic effect was proved by the significant increase of caspase‐3/caspase‐7 activation. Cell cycle analysis revealed that derivatives 1a, 3a, 5j increased the number of SW480 and K‐562 cells in the sub‐G1 and/or G0/G1 phases, and one evoked cycle arrest at the G2 phase. The most potent thioureas inhibited IL‐6 cytokine secretion from PC3 cells and both colon cancer cell lines. Apoptosis‐inducing compounds also increased ROS production in all tumor cell cultures, which may enhance their anticancer properties.
