Survey of survival among patients with hepatitis C virus-related hepatocellular carcinoma treated with peretinoin, an acyclic retinoid, after the completion of a randomized, placebo-controlled trial

Serum MYCN as a predictive biomarker of prognosis and therapeutic response in the prevention of hepatocellular carcinoma recurrence

The proto-oncogene MYCN expression marked a cancer stem-like cell population in hepatocellular carcinoma (HCC) and served as a therapeutic target of acyclic retinoid (ACR), an orally administered vitamin A derivative that has demonstrated promising efficacy and safety in reducing HCC recurrence. This study investigated the role of MYCN as a predictive biomarker for therapeutic response to ACR and prognosis of HCC. MYCN gene expression in HCC was analyzed in the Cancer Genome Atlas and a Taiwanese cohort (N = 118). Serum MYCN protein levels were assessed in healthy controls (N = 15), patients with HCC (N = 116), pre- and post-surgical patients with HCC (N = 20), and a subset of patients from a phase 3 clinical trial of ACR (N = 68, NCT01640808). The results showed increased MYCN gene expression in HCC tumors, which positively correlated with HCC recurrence in non-cirrhotic or single-tumor patients. Serum MYCN protein levels were higher in patients with HCC, decreased after surgical resection of HCC, and were associated with liver functional reserve and fibrosis markers, as well as long-term HCC prognosis (>4 years). Subgroup analysis of a phase 3 clinical trial of ACR identified serum MYCN as the risk factor most strongly associated with HCC recurrence. Patients with HCC with higher serum MYCN levels after a 4-week treatment of ACR exhibited a significantly higher risk of recurrence (hazard ratio 3.27; p = .022). In conclusion, serum MYCN holds promise for biomarker-based precision medicine for the prevention of HCC, long-term prognosis of early-stage HCC, and identification of high-response subgroups for ACR-based treatment.

Induction of Hepatoma Cell Pyroptosis by Endogenous Lipid Geranylgeranoic Acid-A Comparison with Palmitic Acid and Retinoic Acid

Research on retinoid-based cancer prevention, spurred by the effects of vitamin A deficiency on gastric cancer and subsequent clinical studies on digestive tract cancer, unveils novel avenues for chemoprevention. Acyclic retinoids like 4,5-didehydrogeranylgeranoic acid (4,5-didehydroGGA) have emerged as potent agents against hepatocellular carcinoma (HCC), distinct from natural retinoids such as all-trans retinoic acid (ATRA). Mechanistic studies reveal GGA's unique induction of pyroptosis, a rapid cell death pathway, in HCC cells. GGA triggers mitochondrial superoxide hyperproduction and ER stress responses through Toll-like receptor 4 (TLR4) signaling and modulates autophagy, ultimately activating pyroptotic cell death in HCC cells. Unlike ATRA-induced apoptosis, GGA and palmitic acid (PA) induce pyroptosis, underscoring their distinct mechanisms. While all three fatty acids evoke mitochondrial dysfunction and ER stress responses, GGA and PA inhibit autophagy, leading to incomplete autophagic responses and pyroptosis, whereas ATRA promotes autophagic flux. In vivo experiments demonstrate GGA's potential as an anti-oncometabolite, inducing cell death selectively in tumor cells and thus suppressing liver cancer development. This review provides a comprehensive overview of the molecular mechanisms underlying GGA's anti-HCC effects and underscores its promising role in cancer prevention, highlighting its importance in HCC prevention.

Targeting transglutaminase 2 mediated exostosin glycosyltransferase 1 signaling in liver cancer stem cells with acyclic retinoid

Transglutaminase 2 (TG2) is a multifunctional protein that promotes or suppresses tumorigenesis, depending on intracellular location and conformational structure. Acyclic retinoid (ACR) is an orally administered vitamin A derivative that prevents hepatocellular carcinoma (HCC) recurrence by targeting liver cancer stem cells (CSCs). In this study, we examined the subcellular location-dependent effects of ACR on TG2 activity at a structural level and characterized the functional role of TG2 and its downstream molecular mechanism in the selective depletion of liver CSCs. A binding assay with high-performance magnetic nanobeads and structural dynamic analysis with native gel electrophoresis and size-exclusion chromatography-coupled multi-angle light scattering or small-angle X-ray scattering showed that ACR binds directly to TG2, induces oligomer formation of TG2, and inhibits the transamidase activity of cytoplasmic TG2 in HCC cells. The loss-of-function of TG2 suppressed the expression of stemness-related genes, spheroid proliferation and selectively induced cell death in an EpCAM+ liver CSC subpopulation in HCC cells. Proteome analysis revealed that TG2 inhibition suppressed the gene and protein expression of exostosin glycosyltransferase 1 (EXT1) and heparan sulfate biosynthesis in HCC cells. In contrast, high levels of ACR increased intracellular Ca²⁺ concentrations along with an increase in apoptotic cells, which probably contributed to the enhanced transamidase activity of nuclear TG2. This study demonstrates that ACR could act as a novel TG2 inhibitor; TG2-mediated EXT1 signaling is a promising therapeutic target in the prevention of HCC by disrupting liver CSCs.

Retinoids in cancer chemoprevention and therapy: Meta-analysis of randomized controlled trials

Retinoids, natural and synthetic derivatives of vitamin A, have many regulatory functions in human body, including regulating cellular proliferation, differentiation, apoptosis. Moreover, retinoids have been used successfully for the treatment of certain malignancies, especially acute promyelocytic leukemia (APL) in adults and neuroblastoma in children. However, retinoids have not yet been translated into effective systemic treatments for most solid cancers. Some recent studies have shown that retinoids promote tumorigenesis. Therefore, we performed this meta-analysis to systematically evaluate the efficacy of retinoids in the chemoprevention and treatment of cancers. We performed literature search of several electronic databases, including PubMed, Embase and Cochrane Library from 2000 January to 2021 November. Various outcomes were applied to investigate the potential of retinoids for prevention and treatment of cancers. The primary outcomes in this study were disease recurrence and clinical response. The secondary outcomes included overall survival (OS), cancer development, disease progression and event-free survival. We identified 39 randomized controlled trials with 15,627 patients in this study. Our results showed that lower recurrence rate and better clinical response were obtained in retinoids treated patients with cancer or premalignancy as compared with control. The differences were statistically significant (RR = 0.85, 95% CI = 0.74-0.96, p = 0.01; RR = 1.24, 95% CI = 1.03-1.49, p = 0.02, respectively). Retinoids treatment was not associated with improvement in overall survival, cancer development, disease progression or event-free survival. Subgroup analysis conducted based on cancer type showed that patients benefited from retinoids treatment in APL, renal cell carcinoma, hepatocellular carcinoma, lung cancer, Kaposi sarcoma, and complete hydatidiform mole. No significant therapeutic effect was noted in head and neck cancer, acute myeloid leukemia (AML), melanoma, breast cancer, bladder cancer, cervical intraepithelial neoplasia (CIN) or cervical carcinoma. Subgroup analysis based on tumor classification demonstrated that retinoids group obtained a lower recurrence rate and better clinical response than control group in solid cancers. In conclusion, clinical application of retinoids was associated with reduction in disease recurrence and improvement in clinical response, illustrating that retinoids play a key role in cancer prevention and therapy. Further research is needed to broaden the utility of retinoids in other types of cancers. Systematic Review Registration: PROSPERO, identifier CRD42022296706.

A rapid increase in lysophospholipids after geranylgeranoic acid treatment in human hepatoma-derived HuH-7 cells revealed by metabolomics analysis

Geranylgeranoic acid (GGA) was developed as a preventative agent against second primary hepatoma, and was reported to induce cell death in human hepatoma cells via Toll-like receptor 4 (TLR4)-mediated pyroptosis. We recently reported that GGA is enzymatically biosynthesized from mevalonic acid in human hepatoma-derived HuH-7 cells and that endogenous GGA is found in most rat organs including the liver. An unbiased metabolomics analysis of ice-cold 50% acetonitrile extracts from control and GGA-treated cells was performed in this study to characterize the intracellular metabolic changes in GGA-induced pyroptosis and to analyze their relationship with the mechanism of GGA-induced cell death. The total positive ion chromatograms of the cellular extracts in ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry were apparently unchanged after GGA treatment, but an orthogonal partial least squares-discriminant analysis score plot clearly discriminated the intracellular metabolite profiles of GGA-treated cells from that of control cells. S-plot analysis revealed 15 potential biomarkers up-regulated by 24-h GGA treatment according to their variable importance in the projection value of more than 1, and the subsequent metabolomics analysis identified nine of these metabolites as a group of lysophospholipids containing lysophosphatidylcholine with C16:0, C20:4, or C20:3 fatty acids. The possible roles of these lysophospholipids in GGA-induced pyroptosis are discussed.

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Metabolomics analysis was performed on geranylgeranoic acid (GGA)-treated cells.

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Total positive ion chromatograms were apparently similar after GGA treatment.

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The OPLS-DA score plot distinguished the GGA-treated cells from control cells.

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The S-plot analysis revealed GGA-induced upregulation of lysophospholipids.

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The possible roles of lysophospholipids in GGA-induced pyroptosis are discussed.

Age-Dependent Decrease in Hepatic Geranylgeranoic Acid Content in C3H/HeN Mice and Its Oral Supplementation Prevents Spontaneous Hepatoma

Geranylgeranoic acid (GGA) has been developed as a preventive agent against second primary hepatoma. Recently, GGA was reported to induce cell death in human hepatoma cells via TLR4-mediated pyroptosis. We have reported that GGA is enzymatically biosynthesized from mevalonic acid in human hepatoma-derived cells and that endogenous GGA is found in most organs of rats. In addition, we found that upregulation of endogenous GGA levels by zaragozic acid A (ZAA) induced cell death in human hepatoma-derived cells. Therefore, we investigated the age-related changes in hepatic GGA and the possibility of suppressing hepatocarcinogenesis by GGA supplementation using male C3H/HeN mice that spontaneously develop hepatoma. We measured endogenous GGA and mRNA of monoamine oxidase (BMAOB), a key enzyme of GGA biosynthesis, in the liver of male C3H/HeN mice aged 6–93 weeks. We also tried suppressing spontaneous hepatocarcinogenesis by a single administration of GGA to C3H/HeN mice. Hepatic GGA content and Maob mRNA expression level age-dependently decreased in male C3H/HeN mice; some of which produced spontaneous hepatoma in 2 years. A single oral administration of GGA at 11 months of age significantly prevented hepatoma in terms of the number and weight of tumors per mouse at 24 months. Oral supplementation with GGA or geranylgeraniol significantly increased endogenous hepatic GGA contents dose-dependently; and ZAA dramatically upregulated hepatic GGA. In this study; we found an age-dependent decrease in hepatic endogenous GGA in male C3H/HeN mice and efficient prevention of spontaneous hepatoma by a single administration of GGA at 11 months of age.

Sulfarotene, a synthetic retinoid, overcomes stemness and sorafenib resistance of hepatocellular carcinoma via suppressing SOS2-RAS pathway

BACKGROUND

Recurrent hepatocellular carcinoma (HCC) shows strong resistance to sorafenib, and the tumor-repopulating cells (TRCs) with cancer stem cell-like properties are considered a driver for its high recurrent rate and drug resistance.

METHODS

Suppression of TRCs may thus be an effective therapeutic strategy for treating this fatal disease. We evaluated the pharmacology and mechanism of sulfarotene, a new type of synthetic retinoid, on the cancer stem cell-like properties of HCC TRCs, and assessed its preclinical efficacy in models of HCC patient-derived xenografts (PDXs).

RESULTS

Sulfarotene selectively inhibited the growth of HCC TRCs in vitro and significantly deterred TRC-mediated tumor formation and lung metastasis in vivo without apparent toxicity, with an IC₅₀ superior to that of acyclic retinoid and sorafenib, to which the recurrent HCC exhibits significant resistance at advanced stage. Sulfarotene promoted the expression and activation of RARα, which down-regulated SOS2, a key signal mediator associated with RAS activation and signal transduction involved in multiple downstream pathways. Moreover, sulfarotene selectively inhibited tumorigenesis of HCC PDXs with high expression for SOS2.

CONCLUSIONS

Our study identified sulfarotene as a selective inhibitor for the TRCs of HCC, which targets a novel RARα-SOS2-RAS signal nexus, shedding light on a new, promising strategy of target therapy for advanced liver cancer.

Non-Genomic Control of Dynamic MYCN Gene Expression in Liver Cancer

Upregulated MYCN gene expression is restricted to specialized cell populations such as EpCAM⁺ cancer stem cells in liver cancer, regardless of DNA amplification and mutation. Here, we reviewed the role of MYCN gene expression in liver homeostasis, regeneration, and tumorigenesis, and discussed the potential non-genomic mechanisms involved in controlling MYCN gene expression in liver cancer, with a focus on inflammation-mediated signal transduction and microRNA-associated post-transcriptional regulation. We concluded that dynamic MYCN gene expression is an integrated consequence of multiple signals in the tumor microenvironment, including tumor growth-promoting signals, lipid desaturation-mediated endoplasmic reticulum stress adaptation signals, and tumor suppressive miRNAs, making it a potential predictive biomarker of tumor stemness and plasticity. Therefore, understanding and tracing the dynamic changes and functions of MYCN gene expression will shed light on the origin of liver tumorigenesis at the cellular level and the development of novel therapeutic and diagnostic strategies for liver cancer treatment.

TLR4-mediated pyroptosis in human hepatoma-derived HuH-7 cells induced by a branched-chain polyunsaturated fatty acid, geranylgeranoic acid

A branched-chain polyunsaturated fatty acid, geranylgeranoic acid (GGA; C_20:4), which is an endogenous metabolite derived from the mevalonate pathway in mammals, has been reported to induce cell death in human hepatoma cells. We have previously shown that the lipid-induced unfolded protein response (UPR) is an upstream cellular process for an incomplete autophagic response that might be involved in GGA-induced cell death. Here, we found that Toll-like receptor 4 (TLR4)-mediated pyroptosis in HuH-7 cells occurred by GGA treatment. The TLR4-specific inhibitor VIPER prevented both GGA-induced cell death and UPR. Knockdown of the TLR4 gene attenuated GGA-induced cell death significantly. Upon GGA-induced UPR, caspase (CASP) 4 (CASP4) was activated immediately and gasdermin D (GSDMD) was translocated concomitantly to the plasma membrane after production of the N-terminal fragment of GSDMD. Then, cellular CASP1 activation occurred following a second gradual up-regulation of the intracellular Ca²⁺ concentration, suggesting that GGA activated the inflammasome. Indeed, the mRNA levels of NOD-like receptor family pyrin domain containing 3 (NLRP3) and interleukin-1 β (IL1B) genes were up-regulated dramatically with translocation of cytoplasmic nuclear factor-κB (NF-κB) to nuclei after GGA treatment, indicating that GGA induced priming of the NLRP3 inflammasome through NF-κB activation. GGA-induced up-regulation of CASP1 activity was blocked by either oleic acid, VIPER, MCC950 (a selective inhibitor of the NLRP3 inflammasome), or CASP4-specific inhibitor peptide cotreatment. Pyroptotic cell death was also confirmed morphologically by bleb formation in time-series live cell imaging of GGA-treated cells. Taken together, the present results strongly indicate that GGA causes pyroptotic cell death in human hepatoma-derived HuH-7 via TLR4 signalling.

Peretinoin, an Acyclic Retinoid, for the Secondary Prevention of Hepatocellular Carcinoma

The high rates of hepatocellular carcinoma (HCC) recurrence after initially successful curative therapy emphasize ongoing unmet needs to prevent or reduce HCC recurrence. Retinoid acid (RA), a metabolite of vitamin A and its related analogues (termed retinoids) has been suggested as a promising chemotherapeutic agent in cancer treatment. The synthetic oral retinoid peretinoin is the only agent for the secondary chemoprevention of HCC after curative therapy that is currently well applied into clinical development. Here we present an updated summary of the molecular pathogenesis of HCC and of preclinical and clinical findings with peretinoin, including its clinical characteristics, safety and tolerability profile and future perspectives for clinical use.

Dedifferentiation of hepatocellular carcinoma: molecular mechanisms and therapeutic implications

Hepatocellular carcinoma (HCC) is a common cancer with high morbidity and mortality. Poorer differentiation status indicates worse prognosis of HCC patients. Regain of better differentiation status may improve the prognosis. Differentiation therapy for HCC is based on the fact that agents may reverse the dedifferentiation process from hepatocytes to HCC cells and thus improve tumor differentiation status. Reversal of progenitor-like property and restoration of hepatic characteristics are main objectives of HCC differentiation therapy. Comprehending the mechanisms of HCC dedifferentiation provides ideas for drug design. Diverse dysregulated molecules and signalings cooperatively cause HCC dedifferentiation. Dysregulation of liver enriched transcription factors, especially hepatocyte nuclear factor 4α, was a critical determinant of HCC dedifferentiation. Aberrant pivotal signaling molecules such as transforming factor-β, β-catenin and Yes-associated protein caused disordered signalings, which promoted HCC dedifferentiation. Loss of epithelial morphology during epithelial-mesenchymal transition (EMT) concurred with HCC dedifferentiation. Some EMT-related molecules exerted double-sided role in concurrently inducing EMT and HCC dedifferentiation. Besides, microRNAs (e.g. miR-122 and miR-148a) as well as some impressive proteins (i.e. KLF4, gankyrin and CHD1L) functioned in manipulating HCC differentiation status. Restoring normal expression levels of these molecules could induce HCC differentiation and inhibited malignant tumor behaviors. Based on the knowledge above, some agents have been found effective in lab, but need more data to support their reliability. Additionally, peretinoin as a potential drug is in progress of several phase III clinical trials. It's promising that differentiation therapy for HCC may be a part of options in future HCC treatment.

Hepatic monoamine oxidase B is involved in endogenous geranylgeranoic acid synthesis in mammalian liver cells

Geranylgeranoic acid (GGA) originally was identified in some animals and has been developed as an agent for preventing second primary hepatoma. We previously have also identified GGA as an acyclic diterpenoid in some medicinal herbs. Recently, we reported that in human hepatoma-derived HuH-7 cells, GGA is metabolically labeled from ¹³C-mevalonate. Several cell-free experiments have demonstrated that GGA is synthesized through geranylgeranial by oxygen-dependent oxidation of geranylgeraniol (GGOH), but the exact biochemical events giving rise to GGA in hepatoma cells remain unclear. Monoamine oxidase B (MOAB) has been suggested to be involved in GGOH oxidation. Here, using two human hepatoma cell lines, we investigated whether MAOB contributes to GGA biosynthesis. Using either HuH-7 cell lysates or recombinant human MAOB, we found that: 1) the MAO inhibitor tranylcypromine dose-dependently downregulates endogenous GGA levels in HuH-7 cells; and 2) siRNA-mediated MAOB silencing reduces intracellular GGA levels in HuH-7 and Hep3B cells. Unexpectedly, however, CRISPR/Cas9-generated MAOB-KO human hepatoma Hep3B cells had GGA levels similar to those in MAOB-WT cells. A sensitivity of GGA levels to siRNA-mediated MAOB downregulation was recovered when the MAOB-KO cells were transfected with a MAOB-expression plasmid, suggesting that MAOB is the enzyme primarily responsible for GGOH oxidation and that some other latent metabolic pathways may maintain endogenous GGA levels in the MAOB-KO hepatoma cells. Along with the previous findings, these results provide critical insights into the biological roles of human MAOB and provide evidence that hepatic MAOB is involved in endogenous GGA biosynthesis via GGOH oxidation.

Cytoplasmic translocation of nuclear LSD1 (KDM1A) in human hepatoma cells is induced by its inhibitors

Aim

Histone-modifiable lysine-specific demethylase-1 (LSD1/KDM1A) is an oncoprotein upregulated in cancers, including hepatoma. We previously reported that the hepatoma-preventive geranylgeranoic acid (GGA) inhibits KDM1A at the same IC₅₀ as that of the clinically used tranylcypromine. Here, we report that these inhibitors induce the cytoplasmic translocation of nuclear KDM1A in a human hepatoma-derived cell line.

Methods & results

Immunofluorescence studies revealed that KDM1A was cytoplasmically localized in HuH-7 cells 3 h after GGA or tranylcypromine addition. However, GGA did not affect the subcellular localization of another histone lysine-specific demethylase, KDM5A. This suggests that GGA-induced translocation is KDM1A specific.

Conclusion

These data demonstrate, for the first time, that KDM1A inhibitors specifically induce the cytoplasmic translocation of nuclear KDM1A.

Unequivocal evidence for endogenous geranylgeranoic acid biosynthesized from mevalonate in mammalian cells

Geranylgeranoic acid (GGA) has been reported to induce autophagic cell death via upregulation of lipid-induced unfolded protein response in several human hepatoma-derived cell lines, and its 4,5-didehydro derivative has been developed as a preventive agent against second primary hepatoma in clinical trials. We have previously reported that GGA is a natural diterpenoid synthesized in several medicinal herbs. Here, we provide unequivocal evidence for de novo GGA biosynthesis in mammals. First, with normal male Wistar rats, the levels of GGA in liver were found to be far greater than those in other organs analyzed. Second, we demonstrated the metabolic GGA labeling from the ¹³C-labeled mevalonolactone in the human hepatoma-derived cell line, HuH-7. Isotopomer spectral analysis revealed that approximately 80% of the cellular GGA was newly synthesized from mevalonate (MVA) in 12 h and the acid picked up preexisting farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP), suggesting that GGA is derived from FPP and GGPP through the MVA pathway. Third, zaragozic acid A, a squalene synthase inhibitor, induced dose-dependent upregulation of endogenous GGA content in HuH-7 cells and their concomitant cell death. These results strongly suggest that a cancer-preventive GGA is biosynthesized via the MVA pathway in mammals.

Generic chemoprevention of hepatocellular carcinoma

Chronic fibrotic liver disease caused by viral or metabolic etiologies is a high-risk condition for developing hepatocellular carcinoma (HCC). Even after curative treatment of early-stage HCC tumor, the carcinogenic microenvironment persists in the remnant diseased liver and supports the development of de novo HCC tumors (de novo HCC recurrence). Therefore, prevention of HCC development in patients at risk of not only first-primary but also second-primary HCC tumors is theoretically the most impactful strategy to improve patient prognosis. However, no such therapy has been established to date. One major challenge is the identification of clinically relevant targets that can be achieved by utilizing the reverse-engineering strategy of chemoprevention discovery, which integrates omics information from clinical cohorts with completed follow-up for cancer development. Clinical and experimental studies have suggested etiology-specific and generic candidate HCC chemoprevention strategies, including statins, antidiabetic drugs, selective molecular targeted agents, and dietary and nutritional substances. Clinical testing of the candidate compounds can be cost-effectively performed by combining it with HCC risk biomarker evaluation to specify the target patient population most likely to benefit from the therapy. Nontoxic, generic agents will have broad clinical applicability across the diverse HCC etiologies and clinical contexts and are expected to substantially improve the still dismal prognosis of HCC.

Involvement of MAFB and MAFF in Retinoid-Mediated Suppression of Hepatocellular Carcinoma Invasion

Retinoids exert antitumor effects through the retinoic acid receptor α (RARα). In the present study, we sought to identify the factors involved in the RARα-mediated transcriptional regulation of the tumor suppressor gene and the tissue factor pathway inhibitor 2 (TFPI2) in hepatocellular carcinoma (HCC). All-trans-retinoic acid (ATRA) was used in the in vitro experiments. Cell invasiveness was measured using trans-well invasion assay. ATRA significantly increased TFPI2 expression through RARα in a human HCC cell line known as HuH7. TFPI2 was vital in the ATRA-mediated suppression of HuH7 cell invasion. The musculo-aponeurotic fibrosarcoma oncogene homolog B (MAFB) significantly enhanced the activation of the TFPI2 promoter via RARα while MAFF inhibited it. The knockdown of RARα or MAFB counteracted the ATRA-mediated suppression of HuH7 cell invasion while the knockdown of MAFF inhibited the invasion. TFPI2 expression in HCC tissues was significantly downregulated possibly due to the decreased expression of RARβ and MAFB. Patients with HCC expressing low MAFB and high MAFF levels showed the shortest disease-free survival time. These results suggest that MAFB and MAFF play critical roles in the antitumor effects of retinoids by regulating the expression of retinoid target genes such as TFPI2 and can be promising for developing therapies to combat HCC invasion.

Prevention of hepatocellular carcinoma by targeting MYCN-positive liver cancer stem cells with acyclic retinoid

Hepatocellular carcinoma (HCC) is a highly lethal cancer, partly because of its high rate of recurrence, which is caused by the presence of liver cancer stem cells (CSCs). Here, using a selective chemopreventive agent, acyclic retinoid (ACR), as a bioprobe, we identified MYCN, which is mostly recognized as an oncogene in neuroblastoma, as a therapeutic target of ACR for HCC through a selective deletion of MYCN⁺ liver CSCs. We also demonstrated that the expression of MYCN in HCC served as a prognostic biomarker and positively correlated with recurrence of de novo HCC after curative treatment. Our study highlighted MYCN as a biomarker and therapeutic target in drug discovery for screening chemopreventive agents against the recurrence of HCC.

Hepatocellular carcinoma (HCC) is a highly lethal cancer that has a high rate of recurrence, in part because of cancer stem cell (CSC)-dependent field cancerization. Acyclic retinoid (ACR) is a synthetic vitamin A-like compound capable of preventing the recurrence of HCC. Here, we performed a genome-wide transcriptome screen and showed that ACR selectively suppressed the expression of MYCN, a member of the MYC family of basic helix–loop–helix–zipper transcription factors, in HCC cell cultures, animal models, and liver biopsies obtained from HCC patients. MYCN expression in human HCC was correlated positively with both CSC and Wnt/β-catenin signaling markers but negatively with mature hepatocyte markers. Functional analysis showed repressed cell-cycle progression, proliferation, and colony formation, activated caspase-8, and induced cell death in HCC cells following silencing of MYCN expression. High-content single-cell imaging analysis and flow cytometric analysis identified a MYCN⁺ CSC subpopulation in the heterogeneous HCC cell cultures and showed that these cells were selectively killed by ACR. Particularly, EpCAM⁺ cells isolated using a cell-sorting system showed increased MYCN expression and sensitivity to ACR compared with EpCAM⁻ cells. In a long-term (>10 y) follow-up study of 102 patients with HCC, MYCN was expressed at higher levels in the HCC tumor region than in nontumor regions, and there was a positive correlation between MYCN expression and recurrence of de novo HCC but not metastatic HCC after curative treatment. In summary, these results suggest that MYCN serves as a prognostic biomarker and therapeutic target of ACR for liver CSCs in de novo HCC.

Risk factors and prevention of hepatocellular carcinoma in the era of precision medicine

Patients who develop chronic fibrotic liver disease, caused by viral or metabolic aetiologies, are at a high risk of developing hepatocellular carcinoma (HCC). Even after complete HCC tumour resection or ablation, the carcinogenic tissue microenvironment in the remnant liver can give rise to recurrent de novo HCC tumours, which progress into incurable, advanced-stage disease in most patients. Thus, early detection and prevention of HCC development is, in principle, the most impactful strategy to improve patient prognosis. However, a "one-size-fits-all" approach to HCC screening for early tumour detection, as recommended by clinical practice guidelines, is utilised in less than 20% of the target population, and the performance of screening modalities, including ultrasound and alpha-fetoprotein, is suboptimal. Furthermore, optimal screening strategies for emerging at-risk patient populations, such as those with chronic hepatitis C after viral cure, or those with non-cirrhotic, non-alcoholic fatty liver disease remain controversial. New HCC biomarkers and imaging modalities may improve the sensitivity and specificity of HCC detection. Clinical and molecular HCC risk scores will enable precise HCC risk prediction followed by tailoured HCC screening of individual patients, maximising cost-effectiveness and optimising allocation of limited medical resources. Several aetiology-specific and generic HCC chemoprevention strategies are evolving. Epidemiological and experimental studies have identified candidate chemoprevention targets and therapies, including statins, anti-diabetic drugs, and selective molecular targeted agents, although their clinical testing has been limited by the lengthy process of cancer development that requires long-term, costly studies. Individual HCC risk prediction is expected to overcome the challenge by enabling personalised chemoprevention, targeting high-risk patients for precision HCC prevention and substantially improving the dismal prognosis of HCC.

Epidemic of non-alcoholic fatty liver disease and hepatocellular carcinoma

Non-alcoholic fatty liver disease (NAFLD) associated hepatocellular carcinoma (HCC) incidence is increasing worldwide, paralleling the obesity epidemic. Although most cases are associated with cirrhosis, HCC can occur without cirrhosis in NAFLD. Diabetes and obesity are associated risk factors for HCC in patients. Given the sheer magnitude of the underlying risk factors (diabetes, obesity, non-cirrhotic NAFLD) screening for HCC in the non-cirrhotic population is not recommended. Optimal screening strategies in NAFLD cirrhosis are not completely elucidated with Ultrasound having significant limitations in detection of liver lesions in the presence of obesity and steatosis. Consequently NAFLD-HCC is more often diagnosed at a later stage with larger tumors and reduced opportunities for curative treatments as opposed to HCC in other causes of cirrhosis. When HCC is found at a curative stage treatments including liver transplantation, resection and loco-regional therapies are associated with good results similar to that seen in HCV-HCC. Future strategies under study include the use of chemopreventive and antioxidant agents to reduce development of cirrhosis and non-alcoholic steatohepatitis (NASH). Strategies to reverse NASH via weight loss, control of associated conditions like diabetes are key strategies in reducing the increasing incidence of NASH-HCC. Novel therapeutic agents for NASH are in trials and if successful in achieving reversal of NASH will be an important strategy in reducing NAFLD-HCC.

Asia-Pacific clinical practice guidelines on the management of hepatocellular carcinoma: a 2017 update

There is great geographical variation in the distribution of hepatocellular carcinoma (HCC), with the majority of all cases worldwide found in the Asia–Pacific region, where HCC is one of the leading public health problems. Since the “Toward Revision of the Asian Pacific Association for the Study of the Liver (APASL) HCC Guidelines” meeting held at the 25th annual conference of the APASL in Tokyo, the newest guidelines for the treatment of HCC published by the APASL has been discussed. This latest guidelines recommend evidence-based management of HCC and are considered suitable for universal use in the Asia–Pacific region, which has a diversity of medical environments.

Peretinoin as an adjuvant therapy for hepatocellular carcinoma

The current curative treatment modalities for hepatocellular carcinoma (HCC) are unfortunately fraught with high rates of HCC recurrence. Hence there is a need to prevent or reduce HCC recurrence after initial curative therapy. Peretinoin is a synthetic oral retinoid showing significant reduction in the incidence of recurrent or new HCC in patients who had received curative HCC therapy. Areas covered: Peretinoin is analysed against the background of molecular pathogenesis of the different causes of HCC. Publications related to peretinoin since 1996 are reviewed, covering clinical characteristics, safety and tolerance profile as well as the current status of clinical development. Expert commentary: Early phase studies are promising but we need to await the results of the ongoing phase III study of peretinoin in hepatitis C related HCC. Long term impact of peretinoin may be diminished by the foreseeable near eradication of hepatitis C by the direct acting antivirals.

Upregulation of energy metabolism-related, p53-target TIGAR and SCO2 in HuH-7 cells with p53 mutation by geranylgeranoic acid treatment

Metabolic alternation in cancer cells is one of the most common characteristics that distinguish malignant cells from normal cells. Many studies have explained the Warburg hypothesis that cancer cells obtain more energy from aerobic glycolysis than mitochondrial respiration. Here, we show that a branched-chain C-20 polyunsaturated fatty acid, geranylgeranoic acid (GGA), induces upregulation of the cellular protein levels of TP53-induced glycolysis and apoptosis regulator (TIGAR) and synthesis of cytochrome c oxidase 2 (SCO2) in human hepatoma-derived HuH-7cells harboring the mutant TP53 gene, suggesting that GGA may shift an energetic state of the tumor cells from aerobic glycolysis to mitochondrial respiration. In addition, UPLC/TOF/MS-based metabolomics analysis supported the GGA-induced energetic shift, as it revealed that GGA induced a time-dependent increase in the cellular contents of fructose 6-phosphate and decrease of fructose 1,6-diphosphate. Furthermore, metabolomics analysis revealed that GGA rapidly induced spermine accumulation with slight decrease of spermidine. Taken together, the present study strongly suggests that GGA may shift HuH-7 cells from aerobic glycolysis to mitochondrial respiration through the immediate upregulation of TIGAR and SCO2 protein levels.

Supportive therapies for prevention of hepatocellular carcinoma recurrence and preservation of liver function

Hepatocellular carcinoma (HCC) is one of the deadliest cancers in the world and is associated with a high risk of recurrence. The development of a wide range of new therapies is therefore essential. In this study, from the perspective of supportive therapy for the prevention of HCC recurrence and preservation of liver function in HCC patients, we surveyed a variety of different therapeutic agents. We show that branched chain amino acids (BCAA) supplementation and late evening snack with BCAA, strategies that address issues of protein-energy malnutrition, are important for liver cirrhotic patients with HCC. For chemoprevention of HCC recurrence, we show that viral control after radical treatment is important. We also reviewed the therapeutic potential of antiviral drugs, sorafenib, peretinoin, iron chelators. Sorafenib is a kinase inhibitor and a standard therapy in the treatment of advanced HCC. Peretinoin is a vitamin A-like molecule that targets the retinoid nuclear receptor to induce apoptosis and inhibit tumor growth in HCC cells. Iron chelators, such as deferoxamine and deferasirox, act to prevent cancer cell growth. These chelators may have potential as combination therapies in conjunction with peretinoin. Finally, we review the potential inhibitory effect of bone marrow cells on hepatocarcinogenesis.

Metabolome Analyses Uncovered a Novel Inhibitory Effect of Acyclic Retinoid on Aberrant Lipogenesis in a Mouse Diethylnitrosamine-Induced Hepatic Tumorigenesis Model

Acyclic retinoid (ACR) is a promising drug under clinical trials for preventing recurrence of hepatocellular carcinoma. The objective of this study was to gain insights into molecular basis of the antitumorigenic action of ACR from a metabolic point of view. To achieve this, comprehensive cationic and lipophilic liver metabolic profiling was performed in mouse diethylnitrosamine (DEN)-induced hepatic tumorigenesis model using both capillary electrophoresis time-of-flight mass spectrometry and liquid chromatography time-of-flight mass spectrometry. ACR significantly counteracted against acceleration of lipogenesis but not glucose metabolism in DEN-treated mice liver, suggesting an important role of lipid metabolic reprogramming in the initiation step of hepatic tumorigenesis. Knowledge-based pathway analysis suggested that inhibition of linoleic acid metabolites such as arachidonic acid, a proinflammatory precursor, played a crucial role in the prevention by ACR of DEN-induced chronic inflammation-mediated tumorigenesis of the liver. As a molecular mechanism of the ACR's effect to prevent the aberrant lipogenesis, microarray analysis identified that a key transcription regulator of both embryogenesis and tumorigenesis, COUP transcription factor 2, also known as NR2F2, was associated with the metabolic effect of ACR in human hepatocellular carcinoma cells. Our study provided potential therapeutic targets for the chemoprevention of hepatocellular carcinoma as well as new insights into the mechanisms underlying prevention of hepatic tumorigenesis.

Retinoids and rexinoids in cancer prevention: from laboratory to clinic

Early in the age of modern medicine the consequences of vitamin A deficiency drew attention to the fundamental link between retinoid-dependent homeostatic regulation and malignant hyperproliferative diseases. The term "retinoid" includes a handful of endogenous and a large group of synthetic derivatives of vitamin A. These multifunctional lipid-soluble compounds directly regulate target genes of specific biological functions and critical signaling pathways to orchestrate complex functions from vision to development, metabolism, and inflammation. Many of the retinoid activities on the cellular level have been well characterized and translated to the regulation of processes like differentiation and cell death, which play critical roles in the outcome of malignant transformation of tissues. In fact, retinoid-based differentiation therapy of acute promyelocytic leukemia was one of the first successful examples of molecularly targeted treatment strategies. The selectivity, high receptor binding affinity and the ability of retinoids to directly modulate gene expression programs present a distinct pharmacological opportunity for cancer treatment and prevention. However, to fully exploit their potential, the adverse effects of retinoids must be averted. In this review we provide an overview of the biology of retinoid (activated by nuclear retinoic acid receptors [RARs]) and rexinoid (engaged by nuclear retinoid X receptors [RXRs]) action concluded from a long line of preclinical studies, in relation to normal and transformed states of cells. We will also discuss the past and current uses of retinoids in the treatment of malignancies, the potential of rexinoids in the cancer prevention setting, both as single agents and in combinations.

Vitamin K and hepatocellular carcinoma: The basic and clinic

Vitamin K (VK), which was originally identified as a cofactor involved in the production of functional coagulation factors in the liver, has been shown to be involved in various aspects of physiological and pathological events, including bone metabolism, cardiovascular diseases and tumor biology. The mechanisms and roles of VK are gradually becoming clear. Several novel enzymes involved in the VK cycle were identified and have been shown to be linked to tumorigenesis. The VKs have been shown to suppress liver cancer cell growth through multiple signaling pathways via the transcription factors and protein kinases. A VK2 analog was applied to the chemoprevention of hepatocellular carcinoma (HCC) recurrence after curative therapy and was shown to have beneficial effects, both in the suppression of HCC recurrence and in patient survival. Although a large scale randomized control study failed to demonstrate the suppression of HCC recurrence, a meta-analysis suggested a beneficial effect on the long-term survival of HCC patients. However, the beneficial effects of VK administration alone were not sufficient to prevent or treat HCC in clinical settings. Thus its combination with other anti-cancer reagents and the development of more potent novel VK derivatives are the focus of ongoing research which seeks to achieve satisfactory therapeutic effects against HCC.

Retinoid roles in blocking hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major health issue in many countries. The prognosis of HCC is still poor due to its high recurrence rate and its resistance to chemotherapy. Retinoids have long been known to have a connection with liver diseases, including HCC. Many experimental and clinical investigations have demonstrated associations between retinoids and hepatic disease, including the loss of retinoid activity in HCC cell lines and decreased hepatic retinoid stores and altered retinoid signaling in patients with cirrhosis and HCC. Based on these findings, preclinical and clinical investigations of retinoid effects on HCC have been undertaken. Recently, clinical trial results for the use of a synthetic retinoid, acyclic retinoid (ACR), to prevent HCC recurrence were published. In addition, extensive experimental studies on the action of retinoids in liver disease, including chronic viral hepatitis and non-alcoholic fatty liver disease (NAFLD), which lead to HCC have been performed. In the first section of this review, we will summarize the effectiveness and roles of retinoid for treating liver disease and blocking HCC. Subsequently, we will focus on ACR actions in blocking HCC.

Acyclic retinoid induces differentiation and apoptosis of murine hepatic stem cells

Introduction

The therapeutic potential of acyclic retinoid (ACR), a synthetic retinoid, has been confirmed in experimental and clinical studies. Therapeutic targets include precancerous and cancer stem cells. As ACR is also involved in developmental processes, its effect on normal hepatic stem cells (HpSCs) should be investigated for understanding the underlying mechanisms. Here, we examined effects of the acyclic retinoid peretinoin on fresh isolated murine HpSCs.

Methods

We isolated c-kit⁻CD29⁺CD49f^+/lowCD45⁻Ter119⁻ cells from murine fetal livers using flow cytometry. To evaluate the effect of ACR, we traced clonal expansion and analyzed cell differentiation as well as apoptosis during the induction process by immunofluorescent staining and marker gene expression.

Results

ACR dose-dependently inhibited HpSCs expansion. Stem cell clonal expansion was markedly inhibited during the culture period. Moreover, ACR showed a significant promotion of HpSC differentiation and induction of cellular apoptosis. The expression of stem cell marker genes, Afp, Cd44, and Dlk, was downregulated, while that of mature hepatocyte genes, Alb and Tat, and apoptosis-related genes, Annexin V and Caspase-3, were upregulated. Flow cytometry showed that the proportion of Annexin V-positive cells increased after ACR incubation compared with the control. Data obtained by immunofluorescent staining for albumin and Caspase-3 corroborated the data on gene expression. Finally, we found that ACR directly regulates the expression of retinoic acid receptors and retinoid X receptors.

Conclusions

These findings indicate that ACR inhibits the clonal expansion of normal HpSCs in vitro and promotes the differentiation of immature cells by regulating receptors of retinoic acid.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0046-9) contains supplementary material, which is available to authorized users.

Chemopreventive potential of green tea catechins in hepatocellular carcinoma

Hepatocellular carcinoma (HCC), which is a common malignancy worldwide, usually develops in a cirrhotic liver due to hepatitis virus infection. Metabolic syndrome, which is frequently complicated by obesity and diabetes mellitus, is also a critical risk factor for liver carcinogenesis. Green tea catechins (GTCs) may possess potent anticancer and chemopreventive properties for a number of different malignancies, including liver cancer. Antioxidant and anti-inflammatory activities are key mechanisms through which GTCs prevent the development of neoplasms, and they also exert cancer chemopreventive effects by modulating several signaling transduction and metabolic pathways. Furthermore, GTCs are considered to be useful for the prevention of obesity- and metabolic syndrome-related carcinogenesis by improving metabolic disorders. Several interventional trials in humans have shown that GTCs may ameliorate metabolic abnormalities and prevent the development of precancerous lesions. The purpose of this article is to review the key mechanisms by which GTCs exert chemopreventive effects in liver carcinogenesis, focusing especially on their ability to inhibit receptor tyrosine kinases and improve metabolic abnormalities. We also review the evidence for GTCs acting to prevent metabolic syndrome-associated liver carcinogenesis.