Kaurenoic Acid Suppresses Osteosarcoma Progression by Reprogramming Tumor-Associated Macrophages to M1 Phenotype

Osteosarcoma (OS) is the most prevalent primary malignant bone tumor. M2 type tumor-associated macrophages (TAMs) are the predominant infiltrating cells within the OS microenvironment and play a key role in promoting OS progression. Although kaurenoic acid (KA) has demonstrated notable antitumor properties, it remains vacant whether KA exerts its effects against OS by modulating TAM. In vitro, THP-1 monocytes were polarized into different macrophage phenotypes using specific cytokines and supernatants from OS cells. qRT-PCR, ELISA and flow cytometry assays were conducted to investigate the effects of KA on macrophage reprogramming. The effects of KA on the proliferation, migration, invasion and vasculogenic mimicry of OS cells in the context of M2 macrophages were examined in vitro. Western blot, immunofluorescence staining, and rescue experiments were performed to explore the molecular mechanism underlying the effect of KA. The K7M2 OS mouse model was employed to scrutinize the effects of KA on OS growth and TAM polarization in vivo. The results demonstrated that KA induced a dose-dependent shift of M2 macrophages toward the M1 phenotype, as evidenced by the downregulation of M2 markers, upregulation of M1 markers, and enhanced macrophage-mediated phagocytosis. Additionally, KA inhibited M2 macrophage-mediated enhancement of malignant behaviors in OS cells. We discovered that the activation of the MAPK and NF-κB signaling pathways was involved in KA-induced macrophage polarization. In vivo data demonstrated that KA suppressed OS growth and switched TAMs to the M1 phenotype, while exhibiting low toxicity. These findings suggest that KA can reprogram M2 macrophages into M1 phenotype and inhibit the progression of OS, highlighting its potential as a new macrophage-based therapeutic agent against OS.