Harnessing the RNA interference pathway to advance treatment and prevention of hepatocellular carcinoma

Recent Advances in RNA Interference-Based Therapy for Hepatocellular Carcinoma: Emphasis on siRNA

Even though RNA treatments were first proposed as a way to change aberrant signaling in cancer, research in this field is currently ongoing. The term "RNAi" refers to the use of several RNAi technologies, including ribozymes, riboswitches, Aptamers, small interfering RNA (siRNA), antisense oligonucleotides (ASOs), and CRISPR/Cas9 technology. The siRNA therapy has already achieved a remarkable feat by revolutionizing the treatment arena of cancers. Unlike small molecules and antibodies, which need administration every three months or even every two years, RNAi may be given every quarter to attain therapeutic results. In order to overcome complex challenges, delivering siRNAs to the targeted tissues and cells effectively and safely and improving the effectiveness of siRNAs in terms of their action, stability, specificity, and potential adverse consequences are required. In this context, the three primary techniques of siRNA therapies for hepatocellular carcinoma (HCC) are accomplished for inhibiting angiogenesis, decreasing cell proliferation, and promoting apoptosis, are discussed in this review. We also deliberate targeting issues, immunogenic reactions to siRNA therapy, and the difficulties with their intrinsic chemistry and transportation.

HIF-1α RNAi Combined with Asparagus Polysaccharide Exerts an Antiangiogenesis Effect on Hepatocellular Carcinoma In Vitro and In Vivo

Background

Hepatocellular carcinoma (HCC) is the main form of primary liver cancer and is one of the most prevalent and life-threatening malignancies globally. Hypoxia activates hypoxia-inducible factor-1α (HIF-1α), which is the key factor in promoting angiogenesis in HCC. Currently, there are few studies on the effects of HIF-1α-targeted gene therapy combined with traditional Chinese herbal extracts.

Objective

We investigated the effects of HIF-1α RNA interference (RNAi) combined with asparagus polysaccharide (ASP) on HCC in vitro and in vivo.

Methods

CCK-8, wound-healing, transwell, and human umbilical vein endothelial cell tube formation assays were performed to evaluate the proliferation, migration, invasion, and angiogenesis of HCC cells in vitro. In addition, western blotting, qPCR, and immunohistochemistry were performed to detect the expression of HIF-1α, vascular endothelial growth factor, AKT, p-AKT, ERK, p-ERK, and CD34 in HCC cells.

Results

The combination of HIF-1α RNAi and ASP significantly inhibited the proliferation, migration, invasion, and angiogenesis of SK-Hep1 and Hep-3B cells compared with the use of HIF-1α RNAi or ASP alone. In addition, this combined treatment was shown to exert these effects by regulating the PI3K and MAPK signaling pathways. These results were observed both in vitro and in vivo.

Conclusion

Our study indicates that HIF-1α RNAi combined with ASP inhibits angiogenesis in HCC via the PI3K and MAPK signaling pathways. Thus, we suggest that this combination may be an effective method for the comprehensive treatment of HCC, which may provide new ideas for the treatment of other malignant tumors.

Target-specific delivery of siRNA into hepatoma cells' cytoplasm by bifunctional carrier peptide

RNA interference (RNAi) is among the most potential approach for the therapy of hepatocellular carcinoma and the major barrier hindering siRNA therapeutics is the low efficiency of delivery to the desired cells. The current study aimed at developing a novel peptide for more efficient hepatoma targeted siRNA delivery, by combining luteinizing hormone-releasing hormone with hepatoma targeting specificity and MPG^△NLS with cytoplasm-delivery tendency. The developed bifunctional peptide LHRH-MPG^△NLS and siRNA were mixed together and resulted in LHRH-MPG^△NLS/siRNA polyplexes through self-assembly. The polyplexes were characterized by agarose gel retardation and dynamic light scatting analysis. Hepatoma targeting specificity was analyzed with the GE IN Cell Analyzer 2000 High-Content Cellular Analysis System after cell transfection, and the effect of RNA interference was detected by RT-PCR. The results demonstrated that LHRH-MPG^△NLS was able to assemble with siRNA to form stable and nano-sized peptide/siRNA polyplexes, which could inhibit the expression of the target gene and was essentially non-cytotoxic, as compared with the commercial transfection reagent lipofectamine 2000.

MicroRNAs Expressed during Viral Infection: Biomarker Potential and Therapeutic Considerations

MicroRNAs (miRNAs) are short sequences of noncoding single-stranded RNAs that exhibit inhibitory effects on complementary target mRNAs. Recently, it has been discovered that certain viruses express their own miRNAs, while other viruses activate the transcription of cellular miRNAs for their own benefit. This review summarizes the viral and/or cellular miRNAs that are transcribed during infection, with a focus on the biomarker and therapeutic potential of miRNAs (or their antagomirs). Several human viruses of clinical importance are discussed, namely, herpesviruses, polyomaviruses, hepatitis B virus, hepatitis C virus, human papillomavirus, and human immunodeficiency virus.

Tissue biomarkers of prognostic significance in hepatocellular carcinoma

Despite major advancements in the clinical management of hepatocellular carcinoma (HCC), the natural history of this disease is characterized by an invariably poor prognosis. However, there are significant interindividual variations in the biologic behavior of this tumor and this combined with the confounding effect of liver function on patient survival makes prognostic prediction particularly difficult. Several studies have attempted to investigate the prognostic role of tissue biomarkers to better understand the molecular basis of HCC progression. These studies have looked at several aspects of cancer biology including proliferative potential, invasive capacity, and angiogenic promotion utilizing different methodologies. The aim of this review is to summarize the role of tissue biomarkers in the prognostic prediction of HCC and to outline questions and strategies in the prognostic assessment of HCC.

TAT-LHRH conjugated low molecular weight chitosan as a gene carrier specific for hepatocellular carcinoma cells

To develop a chitosan-based nonviral gene carrier capable of delivering genes specifically into hepatoma cells, a bifunctional peptide composed of the TAT (transactivator of transcription) peptide and luteinizing hormone-releasing hormone (LHRH) was conjugated with low molecular weight chitosan, resulting in a TAT-LHRH-chitosan conjugate (TLC). TLC/DNA nanoparticles (TLCDNPs) were characterized by agarose gel retardation, atomic force microscopy, and dynamic light scattering analysis. In vitro targeting specificity and transfection efficiency were analyzed with a GE IN Cell Analyzer 2000 High-Content Cellular Analysis System. The results demonstrated that TLC had stronger DNA condensing power than unmodified chitosan, and that TLCDNPs were of roughly round shape with average diameter of 70-85 nm and zeta potential of +30 mV and were relatively stable in solution. The in vitro study demonstrated TLC was highly selective for hepatoma cells and essentially nontoxic.

Tissue-specific attenuation of oncolytic sindbis virus without compromised genetic stability

Wild-type Sindbis virus (SV) shows promise as an oncolytic agent, although potential off-target replication is a safety concern. To remove possible pathology reflecting virus replication in liver, muscle, and/or hematopoietic cells, microRNA (miR)-response elements (MREs) to liver-specific miR122, muscle-specific miR133a and miR206, or hematopoietic-specific miR142-3p were inserted into the Sindbis viral genome. We compared the effectiveness of MREs in two distinct genomic locations and found better tissue-specific attenuation when they were inserted into the structural polyprotein coding region (up to 6000-fold selectivity with miR142-3p) rather than into the 3' untranslated region (up to 850-fold with miR142-3p). While this degree of tissue-specific attenuation may be effective for relieving pathology in vivo, genetic instability of RNA viruses raises concerns over the mutation or loss of MREs conferring safety. Genetically modified SVs containing a reporter transgene, used as a surrogate for virus replication, mutated quickly in vitro, losing 50% transgene sequence within 6.2 passages. Using a shorter insert containing MREs but no transgene, complete genetic stability was observed over at least 10 passages. We conclude that SV may be genetically modified to improve clinical properties, but attention must be paid to ensure that genetic stability is sufficient for intended applications.

Study of RNA Interference Targeting NET-1 Combination with Sorafenib for Hepatocellular Carcinoma Therapy In Vitro and In Vivo

The aim of this study is to explore the inhibitory effects of RNA interference (RNAi) targeting NET-1 or combined with sorafenib on HCC in vitro and in vivo and the possible underlying mechanisms. The expressions of NET-1 mRNA and protein were detected by RT-QPCR and western blot. The ability of proliferation was determined by CCK-8 assay. Apoptosis was examined by flow cytometry (FCM). Abilities of migration and invasion were measured by scratch-wound assay and transwell assay. MHCC97H cells with stable transfection of NET-1shRNA were injected subcutaneously to prepare nude mice model of HCC and Caspase-3, Caspase-8, and Caspase-9 mRNAs of tumor tissues in different groups were examined. NET-1 mRNA and protein were reduced sharply in MHCC97H cells transfected with NET-1shRNA. The abilities of proliferation and migration were inhibited and apoptosis was promoted in either NET-1shRNA or sorafenib as compared with untreated cells in vitro and in vivo (P < 0.05). The mRNA levels of caspase-3, caspase-8, and caspase-9 of tumor tissues were reduced in different treatment groups compared with untreated group, particularly in combination group. (P < 0.05). The combination NET-1shRNA with sorafenib dramatically enhanced the effects of sorafenib antitumor ,which may involve in blocking ras signaling pathway and stimulating apoptotic pathways simultaneously.

Biodistribution of polymer hydrogel capsules for the delivery of therapeutics

A key phase in the development of intelligently designed nanoparticle delivery vehicles for new therapeutic agents is to gain an understanding of their interaction with tissues and cells. We report a series of in vitro and in vivo experiments aimed at tracking a potential delivery vehicle for therapeutic agents, including vaccine peptides and drugs derived from poly(methacrylic acid) hydrogel capsules in certain organs and cell types. For the in vitro studies, two immortal liver-derived cell lines (Huh7 and Hepa1-6) and primary cultures of mouse hepatocytes were incubated with Alexa 647 labelled fluorescent capsules to track their internalization and intracellular distribution by confocal microscopy. Capsules, 500nm in diameter, were taken up into the cells in a time-dependent manner in all three cell lines. Capsules were observed in plasma membrane-derived vesicles within the cells. After 24h a significant proportion of the capsules was observed in lysosomes. To understand the behaviour of the capsules in vivo, Alexa 488 labelled fluorescent capsules were intravenously injected into Sprague-Dawley rats and after 24h the fate of the capsules in a number of organs was determined by flow cytometry and confocal microscopy. By flow cytometry, the majority of the capsules were detected in the spleen whilst similar numbers were found in the lung and liver. By confocal microscopy, the majority of the capsules were found in the liver and spleen with significantly less capsules in the lung, heart and kidney. Colocalization of capsules with cell-type specific markers indicated that in lung, heart and kidney, the majority of the capsules were located in endothelial cells. In the spleen ~50% of the capsules were found in CD163-positive cells, whereas in the liver, almost all capsules were located in CD163-positive cells, indicating uptake by Kupffer cells. Electron microscopy confirmed the presence of capsules within Kupffer cells.

miR-615-5p is restrictedly expressed in cirrhotic and cancerous liver tissues and its overexpression alleviates the tumorigenic effects in hepatocellular carcinoma

microRNAs aberrant behavior in heptocellular carcinoma (HCC) plays a major role in HCC pathogenesis. miR-615-5p expression has never been evaluated in HCC. We showed that miR-615-5p was preferentially expressed in HCC, cirrhotic liver tissues and HCC cell lines, but undetected in normal livers. Forced miR-615-5p expression in HCC cell lines led to significant decrease in cell growth and migration. In-silico predication revealed insulin-like growth factor-II (IGF-II) as a potential downstream target for miR-615-5p. Forcing the expression of miR-615-5p showed downregulation of IGF-II mRNA, as well as inhibition of the luciferase activity in a luciferase reporter vector harboring the IGF-II-3'UTR target sequence. miR-615-5p acts as tumor-suppressor in HCC through targeting IGF-II.

Lipid nanoparticles for hepatic delivery of small interfering RNA

Clinical application of small interfering RNA (siRNA) requires safe and efficient delivery in vivo. Here, we report the design and synthesis of lipid nanoparticles (LNPs) for siRNA delivery based on cationic lipids with multiple tertiary amines and hydrophobic linoleyl chains. LNPs incorporating the lipid containing tris(2-aminoethyl)amine (TREN) and 3 linoleyl chains, termed TRENL3, were found to have exceptionally high siRNA transfection efficacy that was markedly superior to lipofectamine, a commercial transfection agent. In addition, inclusion of polyunsaturated fatty acids, such as linoleic acid and linolenic acid in the formulation further enhanced the siRNA delivery efficiency. TRENL3 LNPs were further shown to transport siRNA into the cytosol primarily via macropinocytosis rather than clathrin-mediated endocytosis. The new LNPs have demonstrated preferential uptake by the liver and hepatocellular carcinoma in mice, thereby leading to high siRNA gene-silencing activity. These data suggest potential therapeutic applications of TRENL3 mediated delivery of siRNA for liver diseases.

The role of microRNAs in the management of liver cancer

Four major components of epigenetic regulation are promoter methylation, histone modification, chromatin conformation changes, and altered expression of noncoding RNAs, especially microRNAs (miRNAs). MiRNAs are noncoding RNAs of single-stranded RNA molecules consisting of ∼22 nucleotides that regulate gene expression at the posttranscriptional level. MiRNAs are endogenous and potentially can regulate every aspect of cellular activity, including development and proliferation, differentiation, metabolism, viral infection, epigenetic modulation, apoptotic cell death, and tumor genesis. Recent studies provide evidence that miRNAs are abundant in the liver and affect a diverse spectrum of liver functions. MiRNA expression and deregulation of miRNAs may be a major pathogenetic factor in many liver diseases. Although global downregulation is a common trait in human malignancies, including viral hepatitis, hepatocellular carcinoma, and polycystic liver diseases, specific miRNAs are upregulated in cancer and offer new diagnostic and therapeutic strategies to manage liver diseases. Here, the current status of the role of miRNAs in liver cancer is discussed along with areas for future research.

Hepatocellular carcinoma: insight from animal models

Hepatocellular carcinoma (HCC) ranks as the third most common cause of death from cancer worldwide. Although major risk factors for the development of HCC have been defined, many aspects of the evolution of hepatocellular carcinogenesis and metastasis are still unknown. Suitable animal models are, therefore, essential to promote our understanding of the molecular, cellular and pathophysiological mechanisms of HCC and for the development of new therapeutic strategies. This Review provides an overview of animal models that are relevant to HCC development, metastasis and treatment. For HCC development, this Review focuses on transgenic mouse models of HBV and HCV infection, which provide experimental evidence that viral genes could initiate or promote liver carcinogenesis. Animal models of HCC metastasis provide platforms to elucidate the mechanisms of HCC metastasis, to study the interaction between the microenvironment and HCC invasion and to conduct intervention studies. In addition, animal models have been developed to investigate the effects of new treatment modalities. The criteria for establishing ideal HCC animal models are also discussed.

Countering hepatitis B virus infection using RNAi: how far are we from the clinic?

Globally, persistent HBV infection is a significant cause of public health problems. Currently available HBV therapies have variable efficacy and there is a need to develop improved treatment to prevent cirrhosis and hepatocellular carcinoma. Although RNA interference (RNAi)-based approaches have shown promise, accomplishing safe and sustained silencing by RNAi activators, as well as their efficient delivery to hepatocytes have hampered clinical translation of this very promising technology. Expressed silencers may be produced in a sustained manner from stable DNA templates, which makes them suited to treatment of chronic HBV infection. DNA expression cassettes can be incorporated into both viral and non-viral vectors, but in vivo delivery of these cassettes with non-viral vectors is currently inefficient. Synthetic short interfering RNAs (siRNAs), which may be chemically modified to improve stability, specificity and efficacy, are more conveniently delivered to their cytoplasmic sites of action with synthetic non-viral vectors. However, the short duration of action of this class of RNAi activator is a drawback for treatment of chronic HBV infection. Despite the impressive progress that has been made in developing highly effective HBV gene silencers, challenges continue to face implementation of RNAi-based HBV therapy. This review will discuss the current status of the topic and consider the developments that are required to advance RNAi-based HBV therapy to clinical application.

MicroRNA-like antivirals

Employing engineered DNA templates to express antiviral microRNA (miRNA) sequences has considerable therapeutic potential. The durable silencing that may be achieved with these RNAi activators is valuable to counter chronic viral infections, such as those caused by HIV-1, hepatitis B, hepatitis C and dengue viruses. Early use of expressed antiviral miRNAs entailed generation of cassettes containing Pol III promoters (e.g. U6 and H1) that transcribe virus-targeting short hairpin RNA mimics of precursor miRNAs. Virus escape from single gene silencing elements prompted later development of combinatorial antiviral miRNA expression cassettes that form multitargeting siRNAs from transcribed long hairpin RNA and polycistronic primary miRNA sequences. Weaker Pol III and Pol II promoters have also been employed to control production of antiviral miRNA mimics, improve dose regulation and address concerns about toxicity caused by saturation of the endogenous miRNA pathway. Efficient delivery of expressed antiviral sequences remains challenging and utilizing viral vectors, which include recombinant adenoviruses, adeno-associated viruses and lentiviruses, has been favored. Investigations using recombinant lentiviruses to transduce CD34+ hematological precursor cells with expressed HIV-1 gene silencers are at advanced stages and show promise in preclinical and clinical trials. Although the use of expressed antiviral miRNA sequences to treat viral infections is encouraging, eventual therapeutic application will be dependent on rigorously proving their safety, efficient delivery to target tissues and uncomplicated large scale preparation of vector formulations. This article is part of a special issue entitled: MicroRNAs in viral gene regulation.

Therapeutic potential of adenoviral vectors for delivery of expressed RNAi activators

IMPORTANCE OF THE FIELD

Harnessing RNA interference (RNAi) to silence pathology-causing genes has shown promise as a mode of therapy. The sustained gene inhibition that may be achieved with expressed sequences is potentially useful for treatment of chronic viral infections, but efficient and safe delivery of these sequences remains a challenge. It is generally recognized that there is no ideal vector for all therapeutic RNAi applications, but recombinant adenovirus vectors are well suited to hepatic delivery of expressed RNAi activators.

AREAS COVERED IN THIS REVIEW

Adenoviruses are hepatotropic after systemic administration, and this is useful for delivering expressed RNAi activators that silence pathology-causing genes in the liver. However, drawbacks of adenoviruses are toxicity and diminished efficacy, which result from induction of innate and adaptive immune responses. In this review, the advantages and hurdles facing therapeutic application of adenoviral vectors for liver delivery of RNAi effectors are covered.

WHAT THE READER WILL GAIN

Insights into adenovirus vectorology and the methods that have been used to make these vectors safer for advancing clinical application of RNAi-based therapy.

TAKE HOME MESSAGE

Adenoviruses are very powerful hepatotropic vectors. To make adenoviruses more effective for clinical use, polymer conjugation and deletion of viral vector sequences have been used successfully. However, further modifications to attenuate immunostimulation as well as improvements in large-scale production are necessary before the therapeutic potential of adenovirus-mediated delivery of RNAi activators is realized.

Small interfering RNAs induce target-independent inhibition of tumor growth and vasculature remodeling in a mouse model of hepatocellular carcinoma

RNA interference mediated by small interfering RNAs (siRNAs) has emerged as a potential therapeutic approach to treat various diseases, including cancer. Recent studies with several animal models of posttraumatic revascularization demonstrated that synthetic siRNAs may produce therapeutic effects in a target-independent manner through the stimulation of the toll-like receptor-3 (TLR3)/interferon pathway and suppression of angiogenesis. To analyze the impact of siRNAs on tumor angiogenesis, we injected transgenic mice developing hepatocellular carcinoma (HCC) with either control siRNAs or siRNA targeting neuropilin-1. We found that treatment with these siRNAs led to a comparable reduction in tumor liver volume and to inhibition of tumor vasculature remodeling. We further determined that TLR3, which recognizes double-stranded siRNA, was up-regulated in mouse HCC. Treatment of HCC mice with polyinosinic-polycytidylic acid [poly(I:C)], a TLR3 agonist, led to both a reduction of tumor liver enlargement and a decrease in hepatic arterial blood flow, indicating that TLR3 is functional and may mediate both anti-angiogenic and anti-tumor responses. We also demonstrated that siRNAs increased interferon-γ levels in the liver. In vitro, interferon-γ inhibited proliferation of endothelial cells. In addition, we found that siRNAs inhibited endothelial cell proliferation and morphogenesis in an interferon-γ-independent manner. Our results suggest that synthetic siRNAs inhibit target-independently HCC growth and angiogenesis through the activation of the innate interferon response and by directly inhibiting endothelial cell function.

Leveraging therapeutic potential of multi-targeted siRNA inhibitors

While the discovery of RNA interference (RNAi) has been considered one of the most significant breakthroughs in biomedicine, its prospects for novel therapeutic applications are even more exciting. The high specificity, exquisite selectivity and chemical homogeneity of small interfering RNAs (siRNA; intermediates in RNAi activity), provide unique advantages for these moieties as multi-targeted inhibitory drugs. Many such applications have demonstrated significant benefit compared with single gene-targeted siRNA inhibitors. In this article, we will review the current status of using a multi-targeted siRNA cocktail for novel therapeutic development in the treatment of cancer and viral infections. We will also propose the characteristics of various types of siRNA cocktails and their design, while recognizing the potential future impact of and challenges facing this unique therapeutic modality.

Lentiviral delivery of short hairpin RNAs

In less than a decade after discovery, RNA interference-mediated gene silencing is already being tested as potential therapy in clinical trials for a number of diseases. Lentiviral vectors provide a means to express short hairpin RNA (shRNA) to induce stable and long-term gene silencing in both dividing and non-dividing cells and thus, are being intensively investigated for this purpose. However, induction of long-term shRNA expression can also cause toxicities by inducing off-target effects and interference with the endogenous micro-RNA (miRNA) pathway that regulates cellular gene expression. Recently, several advances have been made in the shRNA vector design to mimic cellular miRNA processing and to express multiplex siRNAs in a tightly regulated and reversible manner to overcome toxicities. In this review we describe some of these advances, focusing on the progress made in the development of lentiviral shRNA delivery strategies to combat viral infections.

Effective inhibition of hepatitis E virus replication in A549 cells and piglets by RNA interference (RNAi) targeting RNA-dependent RNA polymerase

RNA interference (RNAi) is a natural mechanism for suppressing or silencing expression of aberrant or foreign genes. It is a powerful antiviral strategy that has been widely employed to protect hosts from viral infection. Hepatitis E (HE) is an acute fulminant hepatitis in adults that has particularly high mortality in pregnant women. At this point in time, there is no vaccine or antiviral treatment that is effective against the infectious agent, HEV. The nonstructural polyprotein region possesses an RNA-dependent RNA polymerase (RdRp) that is responsible for the replication of the viral RNA genome. RdRp is therefore regarded as one of the most attractive candidates for RNA interference (RNAi). In the present study, the high efficiency and specificity of siRNA were evaluated by Real-Time quantitative PCR and Western blot assays. Protective effects against HEV infection were achieved in A549 cells and in piglets. In piglets treated with a shRNA-RdRp-1 expression plasmid prior to HEV inoculation, HEV antigens were significantly reduced in the liver, spleen, and kidneys, and the activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and total bilirubin (TBIL) were clearly decreased. These results suggested that RNAi is a potentially effective antiviral strategy against HEV replication and infection.

Dual knockdown of N-ras and epiregulin synergistically suppressed the growth of human hepatoma cells

Hepatocellular carcinoma (HCC) is a major challenge because of its resistance to conventional cytotoxic chemotherapy and radiotherapy. Multi-targeted therapy might be a new option for HCC treatment. Our previous study showed that N-ras gene was activated in HCC and was inhibited by RNA interference. In the present study, we investigated the alternation of gene expression by microarray in N-Ras-siRNA-treated HepG2 cells. The results revealed that the EREG gene, encoding epiregulin, was dramatically up-regulated in response to silence of N-ras. We speculated that the up-regulation of epiregulin was involved in the compensatory mechanism of N-ras knockdown for cell growth. Therefore, we evaluated whether dual silence of N-ras and epiregulin display a greater suppression of cell growth. The results confirmed that dual knockdown of N-ras and epiregulin synergistically inhibited cell growth. Our results also showed that dual knockdown of N-ras and epiregulin significantly induced cell arrest at G0/G1 phase. Furthermore, Western blot assay showed that dual knockdown of N-ras and epiregulin markedly reduced the phosphorylations of ERK1/2, Akt and Rb, and inhibited the expression of cyclin D1. Our findings imply that multi-targeted silence of oncogenes might be an effective treatment for HCC.

Novel therapeutic approaches for hepatocellulcar carcinoma: fact and fiction

Hepatocellular carcinoma (HCC) is the most common primary liver cancer and accounts for 80%-90% of this class of malignancy. So far, understanding of its pathogenesis and effective therapeutic methods are rather limited. In this issue, 11 invited review articles are published to address current advance of underlying molecular mechanisms for the development of HCC, and novel therapeutic approaches for HCC. This series of review articles provide an in-depth unders-tanding of HCC that has led to or may lead to the development of novel therapies for HCC.