LL-37 inhibits osteosarcoma progression by suppressing SQLE-mediated cholesterol synthesis via the PTEN/AKT/mTOR pathway.

UNLABELLED: Osteosarcoma (OS) is an aggressive primary bone malignancy with poor prognosis for metastatic and recurrent cases, highlighting an urgent need for novel therapeutic strategies. The human cathelicidin peptide LL-37 exerts context-dependent anti-tumor effects, yet its functional role in OS remains largely undefined. This study aimed to explore the anti-OS activity and underlying mechanisms of LL-37.

METHODS: In vitro experiments were performed using OS cell lines and normal human bone marrow mesenchymal stem cells (hBMSCs) to assess cell viability, clonogenic survival, migration, invasion, cell cycle distribution, cell death, and cholesterol metabolism. Transcriptomic profiling, siRNA-mediated knockdown, plasmid overexpression, and rescue experiments were conducted to validate key signaling pathways. The in vivo therapeutic efficacy of LL-37 was evaluated using a 143B cell xenograft model.

RESULTS: LL-37 selectively inhibited the viability of OS cells with minimal toxicity to hBMSCs. It significantly suppressed clonogenic survival, migration, and invasion, induced S-phase cell cycle arrest, and triggered both mitochondrial apoptosis and caspase-1/GSDMD-dependent pyroptosis. Transcriptomic analysis identified cholesterol biosynthesis as a key pathway downregulated by LL-37, with the rate-limiting enzyme squalene epoxidase (SQLE) markedly reduced. Mechanistically, LL-37 upregulated the tumor suppressor PTEN, thereby inhibiting the AKT/mTOR pathway and suppressing SREBP2/SQLE-mediated cholesterol synthesis. Rescue experiments confirmed that SQLE inhibition was required for the pro-apoptotic effects of LL-37. In vivo, LL-37 dose-dependently inhibited the growth of OS xenografts with efficacy comparable to cisplatin, without causing obvious systemic toxicity.

CONCLUSION: LL-37 exerts anti-OS effects by targeting the PTEN/AKT/mTOR-SREBP2/SQLE axis to suppress cholesterol synthesis and induce dual cell death. It represents a promising and selective candidate, providing a theoretical basis for cholesterol metabolism-targeted therapy in osteosarcoma.