A new pyridazinone exhibits potent cytotoxicity on human cancer cells via apoptosis and poly-ubiquitinated protein accumulation

In the last 15 years, pyridazinone derivatives have acquired extensive attention due to their widespread biological activities and pharmacological applications. Pyridazinones are well known for their anti-microbial, anti-viral, anti-inflammatory, anti-cancer, and cardiovascular activities, among others. In this study, we evaluated the anti-cancer activity of a new pyridazinone derivative and propose it as a potential anti-neoplastic agent in acute promyelocytic leukemia cells. Pyr-1 cytotoxicity was assessed on several human cancer and two non-cancerous cell lines by the DNS assay. Pyr-1 demonstrated potent cytotoxicity against 22 human cancer cell lines, exhibiting the most favorable selective cytotoxicity on leukemia (CEM and HL-60), breast (MDA-MB-231 and MDA-MB-468), and lung (A-549) cancer cell lines, when compared with non-cancerous breast epithelial MCF-10A cells. Analyses of apoptosis/necrosis pathways, reactive oxygen species (ROS) production, mitochondria health, caspase-3 activation, and cell cycle profile were performed via flow cytometry. Both hmox-1 RNA and protein expression levels were evaluated by quantitative real-time PCR and Western blotting assays, respectively. Pyr-1 induced apoptosis in acute promyelocytic leukemia cells as confirmed by phosphatidylserine externalization, mitochondrial depolarization, caspase-3 activation, DNA fragmentation, and disrupted cell cycle progression. Additionally, it was determined that Pyr-1 generates oxidative and proteotoxic stress by provoking the accumulation of ROS, resulting in the overexpression of the stress-related hmox-1 mRNA transcripts and protein and a marked increase in poly-ubiquitinated proteins. Our data demonstrate that Pyr-1 induces cell death via the intrinsic apoptosis pathway by accumulating ROS and by impairing proteasome activity.