Pleuromutilins Suppress Hepatocellular Carcinoma Growth via ABCA1 Inhibition-Induced Cholesterol Accumulation.

Bcakground: Hepatocellular carcinoma (HCC) is a prevalent malignancy with limited therapeutic options. Drug repurposing offers an attractive strategy to accelerate anticancer discovery. The pleuromutilin class of antibiotics, including the human-approved agent lefamulin and the veterinary drug tiamulin, has shown preliminary anticancer potential, but its efficacy and mechanism in HCC remain unexplored. METHODS: The anti-tumor effects of lefamulin and tiamulin were evaluated in HCC cell lines, patient-derived organoids, and a C57BL/6 mouse subcutaneous tumor model. Safety was assessed in a human normal hepatocyte cell line and by histopathological examination of major organs in treated mice. Mechanistic investigations were performed using RNA-sequencing, RT-qPCR, immunohistochemistry (IHC), filipin staining, pharmacological rescue assays, and shRNA-mediated gene silencing. RESULTS: In this study, we found that both lefamulin and tiamulin markedly inhibited HCC cell proliferation in vitro and significantly suppressed tumor growth in vivo (lefamulin vs. control, p = 0.014; tiamulin vs. control, p = 0.021), without causing significant toxicity. RNA-sequencing analysis revealed consistent downregulation of the cholesterol transporter Abca1 (ATP-binding cassette transporter A1) and alterations in cell adhesion molecule pathways. Functional studies confirmed that treatment reduced ABCA1 protein levels, leading to intracellular cholesterol accumulation and aberrant distribution. Furthermore, treated tumors exhibited a significant increase in CD8(+) T-cell infiltration, with CD4(+) T cells and macrophage infiltration remained unchanged, indicating a specific modulation of the tumor immune microenvironment. CONCLUSIONS: These findings suggest that lefamulin and tiamulin are promising therapeutic candidates for HCC.