Honokiol induces an autophagy and apoptosis imbalance by modulating the p62 and Nrf2 signaling loop in canine osteosarcoma

Canine osteosarcoma is one of the most common cancers in dogs, primarily affecting large breeds, and is characterized by high metastatic potential and recurrence rates. However, effective treatments remain limited, necessitating the development of novel therapeutic agents. Therefore, we investigated the effects of honokiol, a bioactive compound extracted from the bark of Magnolia species, with a focus on apoptosis and autophagy, using the canine osteosarcoma cell lines DSN and D-17. Our results demonstrated that honokiol inhibited cell viability and migration while inducing apoptosis in DSN and D-17 cells. Honokiol also increased ROS generation, disrupted calcium homeostasis, and decreased mitochondrial membrane potential. In addition, honokiol downregulated Keap1 protein levels and upregulated Nrf2, phosphorylated p62, total p62, and LC3B expression in osteosarcoma cells. Furthermore, autophagic flux was confirmed by pretreatment with chloroquine, an autophagosome-lysosome fusion inhibitor. Additionally, increased numbers of acidic vesicular organelles (AVOs) were observed in honokiol-treated cells, suggesting that honokiol induces excessive autophagic flux, which may contribute to apoptosis. These findings indicate the therapeutic potential of honokiol as a novel agent against canine osteosarcoma.