Epigenetic mechanisms of liver tumor resistance to immunotherapy

Hepatocellular carcinoma (HCC) is the most common primary liver tumor, which stands fourth in rank of cancer-related deaths worldwide. The incidence of HCC is constantly increasing in correlation with the epidemic in diabetes and obesity, arguing for an urgent need for new treatments for this lethal cancer refractory to conventional treatments. HCC is the paradigm of inflammation-associated cancer, since more than 80% of HCC emerge consecutively to cirrhosis associated with a vast remodeling of liver microenvironment. In the recent decade, immunomodulatory drugs have been developed and have given impressive results in melanoma and later in several other cancers. In the present review, we will discuss the recent advancements concerning the use of immunotherapies in HCC, in particular those targeting immune checkpoints, used alone or in combination with other anti-cancers agents. We will address why these drugs demonstrate unsatisfactory results in a high proportion of liver cancers and the mechanisms of resistance developed by HCC to evade immune response with a focus on the epigenetic-related mechanisms.

Non-coding RNAs open a new chapter in liver cancer treatment

Despite the intensive efforts to identify the molecular events responsible for the emergence of liver cancer, hepatocellular carcinoma (HCC) remains a major health problem in the world. Thus, the identification of new therapeutic opportunities is a short-term necessity. These last few decades, non-coding RNAs appeared as interesting therapeutic strategies with their pleiotropic inhibitory action in the cell itself but also in recipient cells via their secretion into extracellular vesicles. This short review recapitulates recent advancements concerning non-coding RNAs and their deregulations in liver cancer.

The concomitant loss of APC and HNF4α in adult hepatocytes does not contribute to hepatocarcinogenesis driven by β-catenin activation

BACKGROUND & AIMS

Loss of hepatocyte nuclear factor-4α (HNF4α), a critical factor driving liver development and differentiation, is frequently associated with hepatocellular carcinoma (HCC). Our recent data revealed that HNF4α level was decreased in mouse and human HCCs with activated β-catenin signalling. In addition, increasing HNF4α level by miR-34a inhibition slowed tumour progression of β-catenin-activated HCC in mice.

METHODS

We generated a Hnf4aflox/flox/ Apcflox/flox /TTR-CreERT2 (Hnf4a/Apc∆Hep ) mouse line and evaluated the impact of Hnf4a disruption on HCC development and liver homoeostasis.

RESULTS

There was no significant impact of Hnf4a disruption on tumour onset and progression in Apc∆Hep model. However, we observed an unexpected phenotype in 28% of Hnf4a∆Hep mice maintained in a conventional animal facility, which presented disorganized portal triads, characterized by stenosis of the portal vein and increased number and size of hepatic arteries and bile ducts. These abnormal portal structures resemble the human idiopathic non-cirrhotic portal hypertension syndrome. We correlated the presence of portal remodelling with a higher expression of protein and mRNA levels of TGFβ and BMP7, a key regulator of the TGFβ-dependent endothelial-to-mesenchymal transition.

CONCLUSION

These data demonstrate that HNF4α does not play a major role during β-catenin-driven HCC, thus revealing that the tumour suppressor role of HNF4α is far more complex and dependent probably on its temporal expression and tumour context. However, HNF4α loss in adult hepatocytes could induce abnormal portal structures resembling the human idiopathic non-cirrhotic portal hypertension syndrome, which may result from endothelial- and epithelial-to-mesenchymal transitions.

Exosomal microRNAs as a potential therapeutic strategy in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer and the second cause of cancer-related death worldwide. The incidence of HCC is constantly increasing in correlation with the rise in diabetes and obesity, arguing for an urgent need for new developments in the treatment of this lethal cancer. Exosomes are small double-membrane vesicles loaded with distinct cargos, particularly small non-coding RNAs called microRNAs, representative of each donor cell and secreted to affect the features of neighboring cells or recipient cells located further away, like in the case of metastasis. A better understanding of the role of exosomes with a microRNA signature in cancer pathogenesis gave rise to the concept of their use as a non-invasive diagnostic biomarker and in the treatment of cancer, including HCC. In this communication, we review recent works that demonstrate that hepatic stellate cells establish an epigenetic communication with liver cancer cells, which affects their pro-malignant features. If naturally secreted patient-derived exosomes show major limitations concerning their clinical use, bio-engineered exosome mimetics that incorporate controlled components and exhibit no protumoral properties could be promising carriers for the treatment of liver cancers, which is the organ preferentially targeted by systemic injection of exosomes.

Antitumour activity of an inhibitor of miR-34a in liver cancer with β-catenin-mutations

OBJECTIVE

Hepatocellular carcinoma (HCC) is the most prevalent primary tumour of the liver. About a third of these tumours presents activating mutations of the β-catenin gene. The molecular pathogenesis of HCC has been elucidated, but mortality remains high, and new therapeutic approaches, including treatments based on microRNAs, are required. We aimed to identify candidate microRNAs, regulated by β-catenin, potentially involved in liver tumorigenesis.

DESIGN

We used a mouse model, in which β-catenin signalling was overactivated exclusively in the liver by the tamoxifen-inducible and Cre-Lox-mediated inactivation of the Apc gene. This model develops tumours with properties similar to human HCC.

RESULTS

We found that miR-34a was regulated by β-catenin, and significantly induced by the overactivation of β-catenin signalling in mouse tumours and in patients with HCC. An inhibitor of miR-34a (locked nucleic acid, LNA-34a) exerted antiproliferative activity in primary cultures of hepatocyte. This inhibition of proliferation was associated with a decrease in cyclin D1 levels, orchestrated principally by HNF-4α, a target of miR-34a considered to act as a tumour suppressor in the liver. In vivo, LNA-34a approximately halved progression rates for tumours displaying β-catenin activation together with an activation of caspases 2 and 3.

CONCLUSIONS

This work demonstrates the key oncogenic role of miR-34a in liver tumours with β-catenin gene mutations. We suggest that patients diagnosed with HCC with β-catenin mutations could be treated with an inhibitor of miR-34a. The potential value of this strategy lies in the modulation of the tumour suppressor HNF-4α, which targets cyclin D1, and the induction of a proapoptotic programme.

MicroRNA-feedback loop as a key modulator of liver tumorigenesis and inflammation

A recent work of Iliopoulos et al published in Cell highlighted a circuit orchestrated by microRNAs (miRNAs) that results in liver tumorigenesis and inflammation. This feedback loop, governed by miR-24 and miR-629, promotes a hepatocyte nuclear factor-4α transient inhibition resulting in miR-124 induction and signal transducer and activator of transcription 3 activation. These promising data support the use of miRNA mimics or inhibitors as potent therapeutic approaches in liver cancer.