Eriocalyxin B Inhibits Autophagy in Hepatocellular Carcinoma Cells via mTOR/ULK1 Signaling Pathway Inactivation

Background Hepatocellular carcinoma (HCC) has become one of the most common malignancies worldwide. Eriocalyxin B (EriB) is a natural, ent-kaurane diterpenoid isolated from Isodon eriocalyx that has been reported to exhibit remarkable antitumor and immunoregulatory activities. Objectives The aim of this study is to explore the role of autophagy in EriB-induced cell death in HCC cell lines. Methods The Cell Counting Kit-8 (CCK-8) was used to assess the EriB effects on HCC cell proliferation. Flow cytometry and confocal microscopy were performed to detect cell apoptosis and autophagic flux. Western blot and immunohistochemistry analyses were used to evaluate the expressions of related proteins. The antitumor effects were observed in a xenograft tumor model of HCCLM3. Results EriB significantly suppresses HCC cell proliferation while concurrently inducing apoptosis. Mechanistically, EriB triggers dose-dependent accumulation of autophagy markers LC3B-II and p62, accompanied by increased autophagosome formation. Paradoxically, EriB impedes late-stage autophagy by reducing acidified autophagic vesicles (RFP + GFP−) and attenuating autophagic flux, suggesting blockade of autophagosome-lysosome fusion. This autophagy-inhibitory effect is mediated through suppression of the mTOR/ULK1 signaling axis. In vivo , EriB markedly inhibits HCC tumor growth. Notably, EriB overcomes sorafenib resistance by antagonizing therapy-induced protective autophagy. Combination therapy with sorafenib synergistically enhances anti-HCC efficacy, as evidenced by significantly reduced tumor burden and weight compared to monotherapy regimens. The chemosensitizing effect of EriB is attributed to its ability to inhibit mTOR/ULK1-driven autophagy, thereby disrupting cancer cell survival mechanisms. Conclusion EriB offers a novel therapeutic strategy for natural product-based combination targeted therapy, demonstrating promising potential to overcome sorafenib resistance in hepatocellular carcinoma HCC.