Sorafenib is the first-line chemotherapeutic therapy for advanced hepatocellular carcinoma (HCC). However, sorafenib resistance significantly limits its therapeutic efficacy, and the mechanisms underlying resistance have not been fully clarified. Here we report that a circular RNA, circRNA-SORE (a circular RNA upregulated in sorafenib-resistant HCC cells), plays a significant role in sorafenib resistance in HCC. We found that circRNA-SORE is upregulated in sorafenib-resistant HCC cells and depletion of circRNA-SORE substantially increases the cell-killing ability of sorafenib. Further studies revealed that circRNA-SORE binds the master oncogenic protein YBX1 in the cytoplasm, which prevents YBX1 nuclear interaction with the E3 ubiquitin ligase PRP19 and thus blocks PRP19-mediated YBX1 degradation. Moreover, our in vitro and in vivo results suggest that circRNA-SORE is transported by exosomes to spread sorafenib resistance among HCC cells. Using different HCC mouse models, we demonstrated that silencing circRNA-SORE by injection of siRNA could substantially overcome sorafenib resistance. Our study provides a proof-of-concept demonstration for a potential strategy to overcome sorafenib resistance in HCC patients by targeting circRNA-SORE or YBX1.

Background and aims: Accumulating evidence suggests that the primary and acquired resistance of hepatocellular carcinoma (HCC) to sorafenib is mediated by multiple molecular, cellular, and microenvironmental mechanisms. Understanding these mechanisms will enhance the likelihood of effective sorafenib therapy.Methods: In vitro and in vivo experiments were performed and clinical samples and online databases were acquired for clinical investigation.Results: In this study, we found that a circular RNA, circRNA-SORE, which is up-regulated insorafenib-resistant HCC cells, was necessary for the maintenance of sorafenib resistance, and that silencing circRNA-SORE substantially increased the efficacy of sorafenib-induced apoptosis. Mechanistic studies determined that circRNA-SORE sequestered miR-103a-2-5p and miR-660-3p by acting as a microRNA sponge, thereby competitively activating the Wnt/β-catenin pathway and inducing sorafenib resistance. The increased level of circRNA-SORE in sorafenib-resistant cells resulted from increased RNA stability. This was caused by an increased level of N⁶-methyladenosine (m⁶A) at a specific adenosine in circRNA-SORE. In vivo delivery of circRNA-SORE interfering RNA by local short hairpin RNA lentivirus injection substantially enhanced sorafenib efficacy in animal models.Conclusions: This work indicates a novel mechanism for maintaining sorafenib resistance and is a proof-of-concept study for targeting circRNA-SORE in sorafenib-treated HCC patients as a novel pharmaceutical intervention for advanced HCC.

The treatment for hepatocellular carcinoma (HCC) is promising in recent years, but still facing critical challenges. The first targeted therapy, sorafenib, prolonged the overall survival by months. However, resistance often occurs, largely limits its efficacy. Sorafenib was found to target the electron transport chain complexes, which results in the generation of reactive oxygen species (ROS). To maintain sorafenib resistance and further facilitate tumor progression, cancer cells develop strategies to overcome excessive ROS production and obtain resistance to oxidative stress-induced cell death. In the present study, we investigated the roles of ROS in sorafenib resistance, and found suppressed ROS levels and reductive redox states in sorafenib-resistant HCC cells. Mitochondria in sorafenib-resistant cells maintained greater functional and morphological integrity under the treatment of sorafenib. However, cellular oxygen consumption rate and mitochondria DNA content analyses revealed fewer numbers of mitochondria in sorafenib-resistant cells. Further investigation attributed this finding to decreased mitochondrial biogenesis, likely caused by the accelerated degradation of peroxisome proliferator-activated receptor γ coactivator 1β (PGC1β). Mechanistic dissection showed that upregulated UBQLN1 induced PGC1β degradation in a ubiquitination-independent manner to attenuate mitochondrial biogenesis and ROS production in sorafenib-resistant cells under sorafenib treatment. Furthermore, clinical investigations further indicated that the patients with higher UBQLN1 levels experienced worse recurrence-free survival. In conclusion, we propose a novel mechanism involving mitochondrial biogenesis and ROS homeostasis in sorafenib resistance, which may offer new therapeutic targets and strategies for HCC patients.

Although sorafenib is currently used as a standard treatment for advanced hepatocellular carcinoma, low response rate, transient and limited efficacy, primary and acquired resistance and negative side-effects gain increasing attentions, suggesting the need for better efficacious combination therapy. Here, we demonstrated that the sorafenib-induced or hypoxia-induced hypoxia inducible factor (HIF)-2α could bind to an hypoxia responsive element within 500 bp region of androgen receptor (AR) promoter and thus transcriptionally suppress AR. Importantly, In vitro and In vivo studies suggested a specific and potent HIF-2α inhibitor, PT-2385, could significantly enhance sorafenib efficacy by suppressing HIF-2α, increasing AR and suppressing downstream pSTAT3/pAKT/pERK pathways. Clinical samples further confirmed the role of HIF-2α and AR. It is promising that PT-2385 could alleviate the undesirable side-effects of sorafenib treatment by sorafenib-PT-2385 combination therapy, which may shed light for late-stage HCC patients.

Background. N-Acetyltransferase 10 (NAT10) has been reported to be expressed at high levels in hepatocellular carcinoma (HCC); however, its role in chemoresistance is unclear. This study is aimed at investigating whether NAT10 regulates the epithelial-mesenchymal transition (EMT) and chemoresistance in HCC. Methods. HCC cell lines (Huh-7, Bel-7402, SNU387, and SNU449) were treated with remodelin, an inhibitor of NAT10, or transfected with small inhibitory RNAs (siRNAs) targeting NAT10 or Twist. The EMT was induced by hypoxia. The CCK-8 assay was used to quantify cell viability, the EdU incorporation assay to assess cell proliferation. siRNA knockdown efficiency and epithelial/mesenchymal marker expression were assessed by western blotting. Results. Knockdown of NAT10 using siRNA or inhibition of NAT10 using remodelin increased the sensitivity of HCC cell lines to doxorubicin; similar effects were observed in cells transfected with the Twist siRNA. Inhibition of NAT10 using remodelin also reversed the ability of doxorubicin to induce the EMT in HCC cells. Furthermore, inhibiting NAT10 reversed the hypoxia-induced EMT. Finally, we confirmed that combining doxorubicin with remodelin delayed tumor growth and reduced tumor cell proliferation in a mouse xenograft model of HCC. Conclusions. NAT10 may contribute to chemoresistance in HCC by regulating the EMT. The mechanism by which NAT10 regulates the EMT and doxorubicin sensitivity in HCC cells merits further investigation.