Mechanisms of hepatocellular carcinoma and challenges and opportunities for molecular targeted therapy

The incidence and mortality of hepatocellular carcinoma(HCC) have fallen dramatically in China and elsewhere over the past several decades. Nonetheless, HCC remains a major public health issue as one of the most common malignant tumors worldwide and one of the leading causes of death caused by cancer in China. Hepatocarcinogenesis is a very complex biological process associated with many environmental risk factors and factors in heredity, including abnormal activation of cellular and molecular signaling pathways such as Wnt/β-catenin, hedgehog, MAPK, AKT, and ERK signaling pathways, and the balance between the activation and inactivation of the proto-oncogenes and anti-oncogenes, and the differentiation of liver cancer stem cells. Molecule-targeted therapy, a new approach for the treatment of liver cancer, blocks the growth of cancer cells by interfering with the molecules required for carcinogenesis and tumor growth, making it both specific and selective. However, there is no one drug completely designed for liver cancer, and further development in the research of liver cancer targeted drugs is now almost stagnant. The purpose of this review is to discuss recent advances in our understanding of the molecular mechanisms underlying the development of HCC and in the development of novel strategies for cancer therapeutics.     

Hyperinsulinaemia and insulin signalling in the pathogenesis and the clinical course of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most prevalent cancer and is one of the leading causes of cancer‐related death. The risk factors for HCC include cirrhosis, chronic viral hepatitis, heavy alcohol intake and metabolic diseases such as obesity, type 2 diabetes and metabolic syndrome. Insulin resistance is a common denominator of all of these conditions and is tethered to hyperinsulinaemia. Here, we give an overview of the recent advances linking hyperinsulinaemia to HCC development and progression. In particular, we summarise the underlying causes of hyperinsulinaemia in the setting of chronic liver diseases. We present epidemiological evidence linking metabolic diseases to HCC risk and HCC‐related mortality, as well as the pathogenic cellular and molecular mechanisms explaining this relation. A better understanding of the mechanisms by which insulin participates in HCC biology might ultimately provide novel opportunities for prevention and treatment.     

Role of innate immunity in the development of hepatocellular carcinoma

Hepatocellular carcinoma(HCC)is the most common form of liver cancer worldwide.It is caused by a variety of risk factors,most common ones being infection with hepatitis viruses,alcohol,and obesity.HCC often develops in the background of underlying cirrhosis,and even though a number of interventional treatment methods are currently in use,recurrence is fairly common among patients who have had a resection.Therefore,whole liver transplantation remains the most practical treatment option for HCC.Due to the growing incidence of HCC,intense research efforts are being made to understand cellular and molecular mechanisms of the disease so that novel therapeutic strategies can be developed to combat liver cancer.In recent years,it has become clear that innate immunity plays a critical role in the development of a number of liver diseases,including HCC.In particular,the activation of Toll-like receptor signaling results in the generation of immune responses that often results in the production of proinflammatory cytokines and chemokines,and could cause acute inflammation in the liver.In this review,the current knowledge on the role of innate immune responses in the development and progression of HCC is examined,and emerging therapeutic strategies based on molecular mechanisms of HCC are discussed.     

Obesity-associated mechanisms of hepatocarcinogenesis

Obesity has been recognized as a key component of the metabolic syndrome, a cluster of risk factors associated with diabetes and cardiovascular morbidity. In addition, obesity has been linked to higher frequency of cancers in a variety of tissues including the liver. Liver cancer most often occurs as hepatocellular carcinoma (HCC) complicating cirrhosis due to chronic viral infection or toxic injury and remains the third leading cause of cancer death in the world. However, HCC is increasingly diagnosed among individuals with obesity and related disorders. As these metabolic conditions have become globally prevalent, they coexist with well-established risk factors of HCC and create a unique challenge for the liver as a chronically diseased organ. Obesity-associated HCC has recently been attributed to molecular mechanisms such as chronic inflammation due to adipose tissue remodeling and pro-inflammatory adipokine secretion, ectopic lipid accumulation and lipotoxicity, altered gut microbiota, and disrupted senescence in stellate cells, as well as insulin resistance leading to increased levels of insulin and insulin-like growth factors. These mechanisms synergize with those occurring in chronic liver disease resulting from other etiologies and accelerate the development of HCC before or after the onset of cirrhosis. Increasingly common interactions between oncogenic pathways linked to obesity and chronic liver disease may explain why HCC is one of the few malignancies with rising incidence in developed countries. Better understanding of this complex process will improve our strategies of cancer prevention, prediction, and surveillance.     

Protein MRI contrast agent with unprecedented metal selectivity and sensitivity for liver cancer imaging

With available MRI techniques, primary and metastatic liver cancers that are associated with high mortality rates and poor treatment responses are only diagnosed at late stages, due to the lack of highly sensitive contrast agents without Gd³⁺ toxicity. We have developed a protein contrast agent (ProCA32) that exhibits high stability for Gd³⁺ and a 10¹¹-fold greater selectivity for Gd³⁺ over Zn²⁺ compared with existing contrast agents. ProCA32, modified from parvalbumin, possesses high relaxivities (r₁/r₂: 66.8 mmol⁻¹⋅s⁻¹/89.2 mmol⁻¹⋅s⁻¹ per particle). Using T₁- and T₂-weighted, as well as T₂/T₁ ratio imaging, we have achieved, for the first time (to our knowledge), robust MRI detection of early liver metastases as small as ∼0.24 mm in diameter, much smaller than the current detection limit of 10–20 mm. Furthermore, ProCA32 exhibits appropriate in vivo preference for liver sinusoidal spaces and pharmacokinetics for high-quality imaging. ProCA32 will be invaluable for noninvasive early detection of primary and metastatic liver cancers as well as for monitoring treatment and guiding therapeutic interventions, including drug delivery.Tumor metastasis is the main cause of nearly all human cancer-related deaths. Liver is a common site for metastases of a variety of cancers, including melanoma, breast, pancreatic, and colon cancers (1, 2). For example, uveal melanoma, the most common primary intraocular tumor, has a 40% risk of metastasizing to the liver within 10 y of diagnosis of the primary tumor. Hepatic metastases, which occur in 95% of patients with uveal melanoma metastasis, result in death in almost all cases. This high death rate is related to the recognition of liver metastasis at a late clinical stage (at stage II or later in the TNM system) in which the metastatic uveal melanoma is resistant to currently available systemic chemotherapies (3, 4). The liver may also give rise to primary tumors such as hepatocellular carcinoma (HCC), which is the most common primary malignancy worldwide (5). However, currently there is no reliable way to detect primary liver cancer and hepatic metastases at early stages with high sensitivity and specificity.MRI is a widely used clinical imaging modality that provides exquisite soft-tissue contrast without using ionizing radiation (6, 7). More than 35% of MRI scans use MRI contrast agents, particularly paramagnetic gadolinium (Gd³⁺)-based contrast agents, which shorten T₁ and lead to an increase in MRI intensity (8). All clinically approved Gd³⁺-containing contrast agents are based on small chelators with relaxivity (r₁ and r₂) values around 4–6 mM⁻¹⋅s⁻¹. Their low relaxivities severely limit the sensitivity of current MR imaging methods with respect to detection of lesions and treatment planning and monitoring. Repeat MRI scans are frequently requested for patients with ambiguous small lesions and are used as a routine follow-up modality for high-risk patients, but they are clinically suboptimal and cost ineffective and may lead to mistreatment and metal toxicity related to the high injection doses required. Imaging of liver lesions is particularly challenging due to rapid liver excretion of contrast agents. Detection of small liver lesions at early disease stages requires contrast agents that have a significantly improved sensitivity and a large dynamic range with reduced background water signal in tissue, as well as appropriate liver distributions and retention times for high-quality imaging. The most commonly used clinically approved T₁-weighted liver contrast agents, gadolinium–ethoxybenzyl–diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) (Eovist, United States; Primovist, Europe; Bayer) and gadobenate dimeglumine (Gd-BOPTA) (Multihance; Bracco), have 50% and 5% hepatocyte uptake, respectively (9). They cannot detect early-stage small liver tumors and metastases (size, <0.5 mm), differentiate dysplastic nodules from HCC, or discriminate tumor thrombosis from platelet-fibrin thrombosis. Thus, there are pressing unmet needs for innovative MRI contrast agents with markedly improved sensitivity, metal stability, and pharmacokinetics, as well as more robust imaging methodologies to enable the earlier detection of small tumors, thereby leading to earlier diagnosis and more efficacious treatments as well as to monitor disease progression of high-risk patients.Herein, we report the development of a protein-based MRI contrast agent, ProCA32, which has both unprecedented metal selectivity and relaxivities in r₁ and r₂, and appropriate liver retention time and distribution. It enables us to noninvasively detect micrometastatic liver tumors at early stages using T₁-weighted, T₂-weighted, or T₂/T₁ imaging as confirmed with histological analysis. Our developed protein MRI contrast agents and imaging methodology are expected to be robust in the early detection of primary liver cancer, liver metastasis, and other liver diseases, such as cirrhosis and liver fibrosis, and in guiding the treatment of these diseases.     

Hepatitis C virus infection and hepatocellular carcinoma

Primary liver cancer is the sixth most common cancer in the world and the third most common cause of death attributable to cancer. Most primary liver cancers are hepatocellular carcinoma (HCC), accounting for 85% to 90% of cases. There is a trend of growing incidence of HCC in the United States. One of the most important risk factors for developing HCC is chronic hepatitis C virus (HCV) infection. Although several studies suggested the preventive effect of interferon from developing HCC in HCV-infected individuals, these findings need to be validated in large prospective and randomized trials.     

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.     

TM6SF2 E167K Variant,a Novel Genetic Susceptibility Variant,Contributing to Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of liver dysfunction worldwide, and its prevalence is highly associated with genetic susceptibility. The transmembrane 6 superfamily member 2 (TM6SF2) E167K variant represents a general genetic determinant of hepatic triglyceride content and lobular inflammation, and its presence appears to be directly involved in the pathogenesis and development of NAFLD. Although this variant appears to be a novel powerful modifier in the development of NAFLD, whether it is associated with an increased risk of NAFLD-related liver fibrosis and hepatocellular carcinoma (HCC) remains to be determined. The aim of this review is to describe the functions of the TM6SF2 E167K variant and its association with NAFLD, with particular emphasis on the underlying mechanisms of its role in the development and progression of NAFLD. Additionally, the links between the TM6SF2 E167K variant and NAFLD-related liver fibrosis and HCC will be discussed.     

Accelerated carcinogenesis following liver regeneration is associated with chronic inflammation-induced double-strand DNA breaks

Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality worldwide and is considered to be the outcome of chronic liver inflammation. Currently, the main treatment for HCC is surgical resection. However, survival rates are suboptimal partially because of tumor recurrence in the remaining liver. Our aim was to understand the molecular mechanisms linking liver regeneration under chronic inflammation to hepatic tumorigenesis. Mdr2-KO mice, a model of inflammation-associated cancer, underwent partial hepatectomy (PHx), which led to enhanced hepatocarcinogenesis. Moreover, liver regeneration in these mice was severely attenuated. We demonstrate the activation of the DNA damage-response machinery and increased genomic instability during early liver inflammatory stages resulting in hepatocyte apoptosis, cell-cycle arrest, and senescence and suggest their involvement in tumor growth acceleration subsequent to PHx. We propose that under the regenerative proliferative stress induced by liver resection, the genomic unstable hepatocytes generated during chronic inflammation escape senescence and apoptosis and reenter the cell cycle, triggering the enhanced tumorigenesis. Thus, we clarify the immediate and long-term contributions of the DNA damage response to HCC development and recurrence.     

Nonalcoholic fatty liver disease,metabolic risk factors,and hepatocellular carcinoma: An open question

Non-alcoholic liver disease(NAFLD) defines liver abnormalities ranging from simple steatosis to nonalcoholic steatohepatitis with or without cirrhosis development, occurring in the absence of significant alcohol consumption, use of teratogenic medication, or hereditary disorders. The association between NAFLD and metabolic syndrome is well documented and widely recognized. Obesity, type 2 diabetes mellitus(T2DM), and dyslipidemia are the most common metabolic risk factors associated with NAFLD. Among the components of metabolic syndrome, current evidence strongly indicates obesity and diabetes as hepatocellular carcinoma(HCC) risk factors. There is also growing evidence that suggests an increased risk of HCC in NAFLD patients, even surpassing other etiologies in some high-income countries. Epidemiologic data demonstrate a parallel rise in prevalence of obesity, diabetes, NAFLD, and HCC. As obesity and its related diseases have steadily afflicted larger populations, HCC incidence is expected to increase in the future. Pathophysiologic mechanisms that underlie NAFLD development and subsequent progression to nonalcoholic steatohepatitis and cirrhosis(insulin resistance and hyperinsulinemia, oxidative stress, hepatic stellate cell activation, cytokine/adipocytokine signaling pathways, and genetic and environmental factors) appear to play a significant role in the development of NAFLD-related HCC. However, a comprehensive view of molecular mechanisms linking obesity, T2 DM, and NAFLD-related HCC, as well as the exact sequence of molecular events, is still not understood in its entirety. Good-quality data are still necessary, and efforts should continue towards better understanding the underlying carcinogenic mechanisms of NAFLD-related HCC. In this paper, we aimed to centralize the most important links supporting these relationships, focusing on obesity, T2 DM, and NAFLD-related HCC, as well as point out the major gaps in knowledge regarding the underlying molecular mechanisms behind them.     

Hepatitis C virus core protein modulates several signaling pathways involved in hepatocellular carcinoma

Hepatocellular carcinoma(HCC) is the fifth most common cancer, and hepatitis C virus(HCV) infection plays a major role in HCC development. The molecular mechanisms by which HCV infection leads to HCC are varied. HCV core protein is an important risk factor in HCV-associated liver pathogenesis and can modulate several signaling pathways involved in cell cycle regulation, cell growth promotion, cell proliferation, apoptosis, oxidative stress and lipid metabolism. The dysregulation of signaling pathways such as transforming growth factor β(TGF-β), vascular endothelial growth factor(VEGF), Wnt/β-catenin(WNT), cyclooxygenase-2(COX-2) and peroxisome proliferator-activated receptor α(PPARα) by HCV core protein is implicated in the development of HCC. Therefore, it has been suggested that this protein be considered a favorable target for further studies in the development of HCC. In addition, considering the axial role of these signaling pathways in HCC, they are considered druggable targets for cancer therapy. Therefore, using strategies to limit the dysregulation effects of core protein on these signaling pathways seems necessary to prevent HCV-related HCC.     

Mechanisms of hepatocellular carcinoma progression

Hepatocellular carcinoma(HCC) is the most common primary malignancy of the liver. It is the second leading cause of cancer-related deaths worldwide, with a very poor prognosis. In the United States, there has been only minimal improvement in the prognosis for HCC patients over the past 15 years. Details of the molecular mechanisms and other mechanisms of HCC progression remain unclear. Consequently, there is an urgent need for better understanding of these mechanisms. HCC is often diagnosed at advanced stages, and most patients will therefore need systemic therapy, with sorafenib being the most common at the present time. However, sorafenib therapy only minimally enhances patient survival. This review provides a summary of some of the known mechanisms that either cause HCC or contribute to its progression. Included in this review are the roles of viral hepatitis, non-viral hepatitis, chronic alcohol intake, genetic predisposition and congenital abnormalities, toxic exposures, and autoimmune diseases of the liver. Well-established molecular mechanisms of HCC progression such as epithelial-mesenchymal transition, tumor-stromal interactions and the tumor microenvironment, cancer stem cells, and senescence bypass are also discussed. Additionally, we discuss the roles of circulating tumor cells,immunomodulation, and neural regulation as potential new mechanisms of HCC progression. A better understanding of these mechanisms could have implications for the development of novel and more effective therapeutic and prognostic strategies, which are critically needed.     

Annexin A2 promotion of hepatocellular carcinoma tumorigenesis via the immune microenvironment

Hepatocellular carcinoma(HCC) is the most common primary liver cancer with a dismal prognosis, especially when diagnosed at advanced stages. Annexin A2(ANXA2), is found to promote cancer progression and therapeutic resistance.However, the underlining mechanisms of ANXA2 in immune escape of HCC remain poorly understood up to now. Herein, we summarized the molecular function of ANXA2 in HCC and its relationship with prognosis. Furthermore, we tentatively elucidated the underlying mechanism of ANXA2 immune escape of HCC by upregulating the proportion of regulatory T cells and the expression of several inhibitory molecules, and by downregulating the proportion of natural killer cells and dendritic cells and the expression of several inhibitory molecules or effector molecules. We expect a lot of in-depth studies to further reveal the underlying mechanism of ANXA2 in immune escape of HCC in the future.     

Role of hepatitis B virus DNA integration in human hepatocarcinogenesis

Liver cancer ranks sixth in cancer incidence, and is the third leading cause of cancer-related deaths worldwide. Hepatocellular carcinoma (HCC) is the most common type of liver cancer, which arises from hepatocytes and accounts for approximately 70%-85% of cases. Hepatitis B virus (HBV) frequently causes liver inflammation, hepatic damage and subsequent cirrhosis. Integrated viral DNA is found in 85%-90% of HBV-related HCCs. Its presence in tumors from non-cirrhotic livers of children or young adults further supports the role of viral DNA integration in hepatocarcinogenesis. Integration of subgenomic HBV DNA fragments into different locations within the host DNA is a significant feature of chronic HBV infection. Integration has two potential consequences: (1) the host genome becomes altered (“cis” effect); and (2) the HBV genome becomes altered (“trans” effect). The cis effect includes insertional mutagenesis, which can potentially disrupt host gene function or alter host gene regulation. Tumor progression is frequently associated with rearrangement and partial gain or loss of both viral and host sequences. However, the role of integrated HBV DNA in hepatocarcinogenesis remains controversial. Modern technology has provided a new paradigm to further our understanding of disease mechanisms. This review summarizes the role of HBV DNA integration in human carcinogenesis.     

Hepatocellular carcinoma in non-cirrhotic liver: A comprehensive review

Hepatocellular carcinoma(HCC) is the most common type of primary liver cancer, which in turns accounts for the sixth most common cancer worldwide.Despite being the 6 th most common cancer it is the second leading cause of cancer related deaths. HCC typically arises in the background of cirrhosis, however,about 20% of cases can develop in a non-cirrhotic liver. This particular subgroup of HCC generally presents at an advanced stage as surveillance is not performed in a non-cirrhotic liver. HCC in non-cirrhotic patients is clinically silent in its early stages because of lack of symptoms and surveillance imaging; and higher hepatic reserve in this population. Interestingly, F3 fibrosis in non-alcoholic fatty liver disease, hepatitis B virus and hepatitis C virus infections are associated with high risk of developing HCC. Even though considerable progress has been made in the management of this entity, there is a dire need for implementation of surveillance strategies in the patient population at risk, to decrease the disease burden at presentation and improve the prognosis of these patients. This comprehensive review details the epidemiology, risk factors, clinical features,diagnosis and management of HCC in non-cirrhotic patients and provides future directions for research.     

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 deve-lopment 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.     

Biology and significance of alpha‐fetoprotein in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common causes of cancer‐related deaths globally due, in part, to the majority of patients being diagnosed with intermediate or advanced stage disease. Our increased understanding of the heterogeneous molecular pathogenesis of HCC has led to significant developments in novel targeted therapies. Despite these advances, there remains a high unmet need for new treatment options. HCC is a complex disease with multiple pathogenic mechanisms caused by a variety of risk factors, making it difficult to characterize with a single biomarker. In fact, numerous biomarkers have been studied in HCC, but alpha‐fetoprotein (AFP) remains the most widely used and accepted serum marker since its discovery over 60 years ago. This review summarizes the most relevant studies associated with the regulation of AFP at the gene and protein levels; the pathophysiology of AFP as a pro‐proliferative protein; and the correlation of AFP with molecular HCC subclasses, the vascular endothelial growth factor pathway and angiogenesis. Also described are the historical and current uses of AFP for screening and surveillance, diagnosis, its utility as a prognostic and predictive biomarker and its role as a tumour antigen in HCC. Taken together, these data demonstrate the relevance of AFP for patients with HCC and identify several remaining questions that will benefit from future research.     

Molecular mechanisms of viral hepatitis induced hepatocellular carcinoma

Chronic infection with viral hepatitis affects half a billion individuals worldwide and can lead to cirrhosis, cancer, and liver failure. Liver cancer is the third leading cause of cancer-associated mortality, of which hepatocellular carcinoma (HCC)represents 90%of all primary liver cancers. Solid tumors like HCC are complex and have heterogeneous tumor genomic profiles contributing to complexity in diagnosis and management. Chronic infection with hepatitis B virus (HBV),hepatitis delta virus (HDV), and hepatitis C virus (HCV) are the greatest etiological risk factors for HCC. Due to the significant role of chronic viral infection in HCC development, it is important to investigate direct (viral associated) and indirect (immune-associated) mechanisms involved in the pathogenesis of HCC. Common mechanisms used by HBV, HCV, and HDV that drive hepatocarcinogenesis include persistent liver inflammation with an impaired antiviral immune response, immune and viral protein-mediated oxidative stress, and deregulation of cellular signaling pathways by viral proteins.DNA integration to promote genome instability is a feature of HBV infection, and metabolic reprogramming leading to steatosis is driven by HCV infection. The current review aims to provide a brief overview of HBV, HCV and HDV molecular biology, and highlight specific viral-associated oncogenic mechanisms and common molecular pathways deregulated in HCC, and current as well as emerging treatments for HCC.