Liver cancer is an often fatal malignant tumor with a high recurrence rate and chemoresistance. The major malignant phenotypes of cancer, including recurrence, metastasis, and chemoresistance, are related to the presence of cancer stem cells (CSCs). In the past few decades, CSCs have been identified and characterized in many tumors including liver cancer. Accumulated evidence has revealed many aspects of the biological behavior of liver CSCs and the mechanism of their regulation. Based on these findings, a number of studies have investigated eradication of liver CSCs. This review focuses on the recent advances in our understanding of the biology of liver CSCs and the development of strategies for their treatment.

Since hepatocellular carcinoma (HCC) is a typical hypervascular malignant tumor with poor prognosis, targeting angiogenesis is an important therapeutic strategy for advanced HCC. Involvement of bone morphologic protein 9 (BMP9), a transforming growth factor-beta superfamily member, has recently been reported in the development of liver diseases and angiogenesis. Here, we aimed to elucidate the role of BMP9 signaling in promoting HCC angiogenesis and to assess the antiangiogenic effect of BMP receptor inhibitors in HCC. By analyzing HCC tissue gene expression profiles, we found that BMP9 expression was significantly correlated with angiogenesis-associated genes, including HIF-1α and VEGFR2. In vitro, BMP9 induced HCC cell HIF-1α/VEGFA expression and VEGFA secretion. Silencing of the inhibitor of DNA-binding protein 1 (ID1), a transcription factor targeted by BMP9 signaling, suppressed BMP9-induced HIF-1α/VEGFA expression and VEGFA secretion, resulting in decreased human umbilical vein endothelial cell (HUVEC) lumen formation. BMP receptor inhibitors, which inhibit BMP9-ID1 signaling, suppressed BMP9-induced HIF-1α/VEGFA expression, VEGFA secretion, and HUVEC lumen formation. In vivo, the BMP receptor inhibitor LDN-212854 successfully inhibited HCC tumor growth and angiogenesis by inhibiting BMP9-ID1 signaling. In summary, BMP9-ID1 signaling promotes HCC angiogenesis by activating HIF-1α/VEGFA expression. Thus, targeting BMP9-ID1 signaling could be a pivotal therapeutic option for advanced HCC.

Sorafenib is a multiple receptor tyrosine kinase inhibitor known to prolong overall survival in patients with advanced hepatocellular carcinoma (HCC). Predicting this drug’s survival benefits is challenging because clinical responses are rarely measurable during treatment. In this study, we hypothesized that serum cytokines levels could predict the survival of advanced HCC patients, as sorafenib targets signaling pathways activated in the tumor stromal microenvironment and potentially affects serum cytokine profiles. Of 143 patients with advanced-stage HCC, 104 who were recruited between 2003 and 2007 received hepatic arterial infusion chemotherapy (HAIC) that mainly targets tumor epithelial cells at S-phase (cohort 1); additionally, 39 recruited between 2010 and 2012 received sorafenib, which primarily targets the stromal vascular endothelial cells. Serum samples were collected and aliquoted prior to the treatment. Serum EGF, bFGF, HGF, IFN-γ, IL-10, IL-12, IL-2, IL-4, IL-5, IL-6, IL-8, IP-10, MIG, PDGF-BB, SCF, SDF1, TGF-β, TGF-α, TNF-α, and VEGF-A were measured via enzyme-linked immunosorbent assays. The Modified Response Evaluation Criteria in Solid Tumors were used to assess tumor responses. The median survival time of HCC patients in cohorts 1 (HAIC-treated) and 2 (sorafenib-treated) were 12.0 and 12.4 months, respectively. Kaplan-Meier analysis revealed no significant survival differences between the 2 groups. Patients who survived more than 2 years after sorafenib treatment exhibited higher serum levels of IL-10, IL-12, TNF-a, IL-8, SDF-1, EGF, PDGF-BB, SCF, and TGF-α. Furthermore, cohort 2 patients with higher serum IL-5 (>12 pg/mL), IL-8 (>10 pg/mL), PDGF-BB (>300 pg/mL), and VEGF-A (>50 pg/mL) levels achieved longer survival; cohort 1 patients did not. Hierarchical cluster analysis of 6 cytokines robustly enriched for comparison analysis between cohorts 1 and 2 (IL-5, IL-8, TGF-α, PDGF-BB, CXCL9, and VEGF-A) revealed that elevation of these cytokines correlated with better survival when treated with sorafenib but not with HAIC. Patients who exhibited survival benefits owing to sorafenib treatment tended to present higher serum cytokines levels, potentially reflecting the activation of stromal signaling in the tumor microenvironment. Our study thus introduces novel biomarkers that may identify advanced HCC patients who may experience survival benefits with sorafenib treatment.

Cancer stemness evinces interest owing to the resulting malignancy and poor prognosis. We previously demonstrated that hepatic stem cell-like hepatocellular carcinoma (HpSC-HCC) is associated with high vascular invasion and poor prognosis. Dickkopf-1 (DKK-1), a Wnt signaling regulator, is highly expressed in HpSC-HCC. Here, we assessed the diagnostic and prognostic potential of serum DKK-1. Its levels were significantly higher in 391 patients with HCC compared with 205 patients with chronic liver disease. Receiver operating characteristic curve analysis revealed the optimal cutoff value of DKK-1 to diagnose HCC and predict the 3-year survival as 262.2 and 365.9 pg/mL, respectively. HCC patients with high-serum DKK-1 levels showed poor prognosis. We evaluated the effects of anti-DKK-1 antibody treatment on tumor growth in vivo and of recombinant DKK-1 on cell proliferation, invasion, and angiogenesis in vitro. DKK-1 knockdown decreased cancer cell proliferation, migration, and invasion. DKK-1 supplementation promoted angiogenesis in vitro; this effect was abolished by an anti-DKK-1 antibody. Co-injection of the anti-DKK-1 antibody with Huh7 cells inhibited their growth in NOD/SCID mice. Thus, DKK-1 promotes proliferation, migration, and invasion of HCC cells and activates angiogenesis in vascular endothelial cells. DKK-1 is a prognostic biomarker for HCC and a functional molecule for targeted therapy.

Liver diseases have become a major comorbidity health concern for people living with HIV-1 (PLWH) treated with combination antiretroviral therapy (cART). To investigate if HIV-1 infection and cART interact to lead to liver diseases, humanized mice reconstituted with progenitor cells from human fetal livers were infected with HIV-1 and treated with cART. We report here that chronic HIV-1 infection with cART induced hepatitis and liver fibrosis in humanized mice, associated with accumulation of M2-like macrophages (M2LMs), elevated TGF-β, and IFN signaling in the liver. Interestingly, IFN-I and TGF-β cooperatively activated human hepatic stellate cells (HepSCs) in vitro. Mechanistically, IFN-I enhanced TGF-β–induced SMAD2/3 activation in HepSCs. Finally, blockade of IFN-I signaling reversed HIV/cART-induced liver diseases in humanized mice. Consistent with the findings in humanized mice with HIV-1 and cART, we detected elevated markers of liver injury, M2LMs, and of IFN signaling in blood specimens from PLWH compared with those of healthy individuals. These findings identify the IFN-I/M2LM/HepSC axis in HIV/cART-induced liver diseases and suggest that inhibiting IFN-I signaling or M2LM may provide a novel therapeutic strategy for treating HIV/cART-associated liver diseases in PLWH treated with antiretroviral therapy.

Sorafenib is a multireceptor tyrosine kinase inhibitor that can prolong overall survival in patients with advanced hepatocellular carcinoma (HCC). Although most HCC patients who receive sorafenib ultimately show disease progression, it still is unclear whether and how HCC cells acquire chemoresistance during sorafenib treatment in human beings. We analyzed surgically resected HCC tissues from a patient who received sorafenib for prevention of HCC recurrence after surgery (Adjuvant Sorafenib for Hepatocellular Carcinoma after Resection or Ablation trial) and established patient-derived HCC cells. Whole-exome sequence analysis was performed to detect mutations in sorafenib-resistant clones. We examined 30 advanced HCC cases immunohistochemically and 140 HCC cases enrolled in the Adjuvant Sorafenib for Hepatocellular Carcinoma after Resection or Ablation trial using microarray analysis to evaluate the association of CIC status with sorafenib treatment response. We found a CIC mutation in recurrent HCC specimens after sorafenib. CIC encodes Capicua, a general sensor of receptor tyrosine kinase signaling. HCC cells established from the recurrent tumor specimen showed chemoresistance to sorafenib in vitro and in vivo. Established sorafenib-resistant Huh1 and Huh7 cell lines showed reduced expression of Capicua without mutations. Immunohistochemical analysis showed that HCC patients with low Capicua expression showed poor overall survival. Microarray analysis showed that the CIC gene signature could predict the preventive effect of adjuvant sorafenib treatment on HCC recurrence. Intriguingly, although CIC knockdown induced sorafenib resistance in HCC cell lines, regorafenib suppressed growth of sorafenib-resistant, Capicua-inactivated HCC cells and inhibited extracellular signal-regulated kinase phosphorylation. Evaluation of Capicua status may be pivotal to predict response to sorafenib, and regorafenib treatment could be effective to treat HCC with functional Capicua impairment.