Oleanolic acid inhibits hypoxic tumor-derived exosomes-induced premetastatic niche formation in hepatocellular carcinoma by targeting ERK1/2-NFκB signaling

Pulmonary premetastatic niche (PMN) formation plays a key role in the lung metastasis of hepatocellular carcinoma (HCC). Hypoxia promotes the secretion of tumor-derived exosomes (TDEs) and facilitates the formation of PMN. However, the mechanisms remain unexplored.TDEs from normoxic (N-TDEs) or hypoxic (H-TDEs) HCC cells were used to induce fibroblast activation in vitro and PMN formation in vivo. Oleanolic acid (OA) was intragastrically administered to TDEs-preconditioned mice. Bioinformatics analysis and drug affinity responsive target stability (DARTS) assays were performed to identify targets of OA in fibroblasts.H-TDEs induced activation of pulmonary fibroblasts, promoted formation of pulmonary PMN and subsequently facilitated lung metastasis of HCC. OA inhibited TDEs-induced PMN formation and lung metastasis and suppressed TDEs-mediated fibroblast activation. MAPK1 and MAPK3 (ERK1/2) were the potential targets of OA. Furthermore, H-TDEs enhanced ERK1/2 phosphorylation in fibroblasts in vitro and in vivo, which was suppressed by OA treatment. Blocking ERK1/2 signaling with its inhibitor abated H-TDEs-induced activation of fibroblasts and PMN formation. H-TDEs-induced phosphorylation of ERK1/2 in fibroblasts touched off the activation NF-κB p65, which was mitigated by OA. In addition, the ERK activator C16-PAF recovered the activation of ERK1/2 and NF-κB p65 in H-TDEs-stimulated MRC5 cells upon OA treatment.The present study offers insights into the prevention of TDEs-induced PMN, which has been insufficiently investigated. OA suppresses the activation of inflammatory fibroblasts and the development of pulmonary PMN by targeting ERK1/2 and thereby has therapeutic potential in the prevention of lung metastasis of HCC.