Generic chemoprevention of hepatocellular carcinoma

Abstract

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 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 identification of clinically relevant targets, which can be achieved by utilizing the reverse-engineering strategy of chemoprevention discovery, integrating 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 benefit from the therapy. Non-toxic, 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.

Introduction

Hepatocellular carcinoma (HCC) is the major histological type of primary liver cancer, and the second leading cause of cancer mortality globally.^1–4 In the United States, HCC mortality has been rising over the past 30 years across virtually all regions of the nation, especially along the Texas-Mexico border.⁵ HCC typically develops in chronically diseased livers with progressive fibrosis caused by viral and metabolic etiologies.⁶ Rapidly emerging predisposing conditions include non-alcoholic fatty liver disease (NAFLD), estimated to affect one-third to one-fourth of global population due to the obesity epidemic and metabolic disorders such as diabetes.⁷ Chronic infection by hepatitis C virus (HCV) has been a major HCC etiology, especially in developed countries.⁶ The recent development and widespread use of direct-acting antivirals (DAAs) have enabled a revolutionary improvement in viral clearance rate. Despite earlier concern about the higher incidence of HCC development and recurrence after DAA-based treatment compared to interferon-based regimens, more recent meta-analyses reported no obvious difference between the two strategies.^8,9 However, the risk of developing HCC persists even after a decade of viral cure.⁸ It is predicted that HCV-related HCC incidence will keep increasing in the coming decades unless HCV diagnosis and treatment uptake rates are substantially improved.^6,8

It is important to note that the magnitude of HCC risk needs to be determined according to each etiology and specific clinical scenario.¹⁰ It is clinically well known that male patients are more susceptible to HCC development in all major etiologies,^11,12 including NAFLD. Studies have suggested the involvement of several molecular pathways in the sex disparity, including estrogen receptor signaling, the interleukin (IL)-6 pathway, and nuclear receptor signaling, such as through the peroxisome proliferator-activated receptor (PPAR) γ, liver × receptors, and farnesoid × receptor. These pathways may need to be taken into account when developing HCC chemopreventive strategies according to sex.^13–21 Besides the major viral and metabolic etiologies of HCC, several predisposing factors have been noted. Family history has been implicated, with higher HCC risk in hepatitis B virus (HBV)/HCV–infected population.²² Type 2 diabetes and obesity have been shown to independently increase the risk of developing HCC.^12,23,24 A study suggested that thalassemia with iron overload accompanied by chronic infection with HBV or HCV could contribute to hepatic injury, which could ultimately lead to HCC development.²⁵ Thus, prognostication with regard to HCC risk under specific clinical scenarios is critical to identify the patients who would most benefit from the preventive interventions studied in recent publications.^26–28

In clinical practice guidelines, regular biannual HCC screening is recommended as a measure for early tumor detection in patients with predisposing conditions, although it is still unclear how to screen the emerging at-risk population having relatively low annual incidence rates.^6,29,30 More advanced liver fibrosis and portal hypertension have been implicated in increased risk of HCC, whereas HCC can also develop in non-cirrhotic livers in some etiologies, that is, HBV infection and NAFLD.^31–34 Localized early-stage HCC tumors mainly diagnosed by contrast-enhanced CT or MRI can be curatively treated by surgical resection, thermal ablation, or liver transplantation. However, even after application of these potentially curative therapies, approximately 70% of the cases suffer tumor recurrence in the remnant diseased liver within 5 years after treatment. Once the tumors have progressed to an advanced stage, the survival benefit of currently available medical therapies is limited to several months and no curative treatment option is available.^6,35–42 Thus, chemoprevention of HCC development in patients at risk is theoretically the most impactful strategy, although no such therapy has been established to date.

Clinically, HCC recurrence after curative treatment can be classified into two groups, namely growth of disseminated cancer cells from the treated primary tumor (disseminative recurrence), and development of second primary cancer clonally unrelated to the treated first primary tumor (de novo recurrence).⁶ Early tumor detection by the regular screening can control the former, but not the latter, which needs chemopreventive intervention. In this article, we provide an overview of generic HCC chemoprevention strategies that are potentially applicable across diverse HCC etiologies and clinical scenarios (Table 1).

Table 1.

Potential generic HCC chemoprevention agents evaluated in clinical settings.

Category of agent	Agent	Type of prevention	Study type(s)	Observed effect size
Anti-inflammatory agent	Aspirin	Secondary	Cohort, meta-analysis	Pooled HR = 0.68
Metabolic disorder correction	Metformin	Secondary	Case-control, meta-analysis	Pooled OR = 0.52
	Statins	Secondary	Cohort	HR = 0.29–0.66
Dietary/nutritional agent	Coffee/caffeine	Secondary	Case-control, cohort, meta-analysis	Pooled OR = 0.53–0.71, HR = 0.41
	Vitamin D/25(OH)D	Secondary	Case-control, cohort	OR = 0.51, HR = 0.53
Targeted agent	mTOR inhibitors	Tertiary	Clinical trial	HR = 0.84
	Peretinoin	Secondary	Clinical trial	HR = 0.73 (entire study period), HR = 0.27 (> 2 years)

HCC, hepatocellular carcinoma; HR, hazard ratio; OR, odds ratio; BCAA, branched-chain amino acids. See Ref. 6 for definition of type of prevention.

Anti-inflammatory and anti-fibrotic therapies

Progressive liver fibrosis and subsequent carcinogenesis are typically accompanied by chronic inflammation in the liver that causes hepatocyte injury and regeneration. Therefore, anti-inflammatory therapies have been sought as potential measures for HCC chemoprevention. In HCV-infected patients, low-dose maintenance interferon therapy has been extensively tested for its capability to reduce hepatic inflammation and HCC incidence.^6,43–45 Although HCC reduction was observed in patient with more advanced fibrosis and who could complete the planned regimens, the high dropout rate due to toxicity precludes its clinical adaptation. There is conflicting epidemiological evidence about HCC-preventive effect of non-steroidal anti-inflammatory drugs (NSAIDs), including asprin.⁴⁶ In a meta-analysis of ten U.S. patient cohorts involving 679 HCC cases, aspirin shows a protective effect against HCC development at a hazard ratio of 0.68.⁴⁷ In mice, the gut microbial environment can induce innate immune signaling through TLR4 and support transformation of neoplastic cells in the liver; these effects are inhibited by gut sterilization.⁴⁸

Experimental studies have suggested that antifibrotic therapies may serve as HCC chemoprevention by resolving the fibrosis that provides a tissue microenvironment supporting carcinogenesis.⁴⁹ Several recent clinical trials of antifibrotic agents have shown promising results. Selonsertib, a small molecule inhibitor of apoptosis signal-regulating kinase 1 (ASK1), reduced fibrosis in patients with non-alcoholic steatohepatitis (NASH).⁵⁰ Cenicriviroc, a dual inhibitor of C-C motif chemokine receptor 2/5 (CCR2/CCR5), reduced liver fibrosis in NASH patients,⁵¹ and is now being followed up in a Phase III trial (NCT03028740).

PPARs are nuclear receptor members that transcriptionally regulate several essential processes, including fatty acid metabolism, to maintain energy equilibrium.⁴⁹ Elafibranor, an agonist of PPARα/δ, reduced steatohepatitis without worsening fibrosis in a phase II trial in NASH patients,⁵² which led to a phase III trial (NCT02704403). Extended clinical observation in these trials may provide insights about antifibrotic therapy as an option for HCC chemoprevention.

Treatment of metabolic disorders

Metformin, a biguanide derivative, is one of the first-line therapies for type 2 diabetes; it reduces hepatic gluconeogenesis via activation of adenosine monophosphate-activated protein kinase (AMPK) and inhibition of the mitochondrial respiratory chain, cyclic adenosine monophosphate (cAMP), and protein kinase A (PKA) activity, among other mechanisms. Experimental studies have also reported anti-cancer activities for metformin, including blockade of the mammalian target of rapamycin (mTOR) pathway by AMPK activation; antiangiogenesis by suppressing vascular endothelial growth factor (VEGF); induction of cell cycle arrest by decreasing cyclin D1 expression; and induction of cell death by suppressing nuclear factor-κB (NF-κB) pathway or inducing apoptosis.^53–57 Multiple epidemiological studies have suggested that metformin use is associated with reduced HCC incidence in patients with chronic liver diseases. A meta-analysis of 19 studies, involving > 500,000 diabetic patients, reported reduced HCC incidence in metformin users compared to placebo or non-users.⁵⁸ Subgroup analysis showed consistent association with lower HCC incidence in patients with hepatitis virus infection, obesity, or cirrhosis. However, prospective trials have failed to validate these findings,⁶ and it still needs to be confirmed in future trials. In a rat model of cirrhosis-driven hepatocarcinogenesis, metformin lowers HCC burden by suppressing activation of progenitor cells when the treatment is started earlier.⁵⁹

Statins are 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors that are widely used for lowering circulating LDL cholesterol levels^60,61. Besides this effect, anti-cancer properties for statins have also been noted. In experimental studies, statins inhibit oncogenesis drivers such as Myc, Akt, integrins, Rho-dependent kinase, NF-κB, tumor necrosis factor (TNF)–mediated IL-6 production, the Hippo pathway, and extracellular signal–regulated kinase 1/2 (ERK1/2), whereas AMPK and p38/mitogen-activated protein kinase (MAPK) pathways are activated and p53-dependent apoptosis is induced.^62–70 Statins also limit liver fibrogenesis in diet/chemical-induced rodent models by inhibiting hepatic stellate cell activation via nitric oxide synthase, paracrine signals from hepatocytes and endothelial cells, induction of sterol regulatory element-binding protein 1 (SREBP-1) and PPARs.^71–74 Statins may reduce cirrhotic portal hypertension via non-canonical Hedgehog signaling.⁷⁵ A case-control study of type 2 diabetes that included 229 HCC patients reported a reduced risk of HCC development in association with statin use in individuals with liver disease, and this reduction increased with higher statin doses.^76,77 A similar association was observed in HBV- or HCV-infected patients.^78,79 Analysis of > 7000 HCV-infected individuals in the U.S. Electronically Retrieved Cohort of HCV Infected Veterans (ERCHIVES) database showed that statin use was associated with approximately half the risk of HCC.⁸⁰ Fibrosis progression was reduced by statins in the HALT-C cohort.⁸¹ In cirrhotic patients with HBV, HCV, alcoholism, as well as non-cirrhotic NAFLD, statin use reduced decompensation, death, and HCC.^82,83 Meta-analyses of these retrospective observational studies reproduced the trend of reduced HCC incidence despite significant heterogeneity in the study population and confounding factors.^17,84 However, the protective effect was not confirmed in meta-analyses of 27 prospective studies involving 175,000 individuals for various cancers, including HCC.^84,85 In a systematic comparison based on meta-analysis of five observational studies, fluvastatin showed the highest association with reduced HCC risk compared to other statins.⁸⁶ Atorvastatin and fluvastatin showed higher association with antifibrotic effects compared to lovastatin, pravastatin, rosuvastatin, and simvastatin.⁸⁰ Prospective randomized clinical trials are currently underway to determine the role of statins in HCC chemoprevention (Table 2). A preventive effect of simvastatin in patients with cirrhosis is being tested in a phase II trial, using change in serum AFP-L3% as the primary endpoint (NCT02968810). Atorvastatin is being evaluated in a phase IV trial for prevention of de novo recurrence after HCC resection or ablation (NCT03024684).

Table 2.

HCC chemoprevention agents tested in ongoing clinical trials

Trial number	Agent	Type of agent	Phase	Target population	Primary endpoint	Estimated completion data
NCT02224456	Tenofovir disoproxil fumarate	Anti-viral	IV	CHB with advanced fibrosis	HCC incidence and progression	1/2021
NCT02968810	Simvastatin	Statin	II	Cirrhosis	Change in AFP-L3	1/2020
NCT02779465	Vitamin D3	Dietary/nutritional supplement	IV	CHB on anti-viral	Change in serum levels of 25(OH)D	12/2026
NCT02098785	Caffeine citrate	Dietary/nutritional supplement	I	Healthy	VAP-1 serum levels	9/2018
NCT02273362	Erlotinib	Kinase inhibitor	I	Cirrhosis	Safety, pEGFR, 186-gene signature	1/2019
NCT03024684	Atorvastatin	Statin	IV	Early-stage HCC after curative ablation or hepatectomy	HCC recurrence	1/2022
NCT03184493	Metformin, celecoxib	Anti-inflammation, Anti-diabetic	III	HCC after hepatectomy	HCC recurrence	6/2021
NCT02281266	Thymalfasin	Immune modulator	IV	HBV-HCC after hepatectomy	Recurrence-free survival	10/2018
NCT02686372	HBV antigen specific TCR redirected T cell	Immune modulator	I	CHB after transplantation	Safety	11/2020
NCT01924624	Thalidomide	Immune modulator, anti-angiogenesis	IV	HCC after hepatectomy	Disease-free survival	12/2019
NCT02447679	Thalidomide, tegafur-uracil	Immune modulator, anti-angiogenesis, cytotoxic agent	II	HCC after hepatectomy	HCC recurrence	Completed, not reported
NCT03178929	SAM	Dietary/nutritional supplement	n.a.	Early-stage HCC after radical treatment	HCC recurrence	8/2020
NCT01770431	Huaier granule	Traditional herbal medicine	IV	HCC after hepatectomy	HCC recurrence, metastasis	Completed, not reported
NCT02399033	Xihuang capsules	Traditional herbal medicine	IV	HCC after hepatectomy	HCC recurrence	12/2019
NCT01717066	Ginsenoside Rg3	Chemo-sensitizer, anti-angiogenesis	III	HCC after hepatectomy	HCC recurrence	Completed, not reported
NCT00116454	131I-lipiodol	Cytotoxic agent	III	Viral/alcohol-HCC after hepatectomy or ablation (≤ 2 tumors)	HCC recurrence	Completed, not reported
NCT02767375	Hepatic arterial infusion chemotherapy	Cytotoxic agent	II-III	HCC after hepatectomy	Disease-free survival	12/2018

HCC, hepatocellular carcinoma; CHB, chronic hepatitis B; AFP-L3, lens culinaris agglutinin-reactive fraction of α-fetoprotein; LSM, liver stiffness measurement; 25(OH)D, 25-hydroxy vitamin D; VAP-1, vascular adhesion protein 1; HBV, hepatitis B virus; TCR, T cell receptor; SAM, S-adenosylmethionine. Information from ClinicalTrials.gov, accessed in March 2018.

Life style change and dietary/nutritional agents

Coffee use has been associated with reduced HCC risk in a series of systematic reviews of multiple liver disease patient cohorts, irrespective of liver disease severity, alcohol usage, body mass index, diabetes, smoking, or hepatitis infection.⁸⁷ Caffeinated coffee was associated with higher HCC reduction compared to decaffeinated coffee in some cohort studies. The reduced HCC risk with coffee use was associated with reduced inflammation and hepatic injury, based on biomarkers such as IL-6, hepatic transaminases, and γ-glutamyltransferase.^88,89 In a multi-ethnic cohort of > 215,000 individuals, a dose-dependent inverse association was observed between coffee use and the progression of chronic liver disease caused by HCV, alcohol, and NAFLD.⁹⁰ In a prospective cohort of > 480,000 participants that included 201 HCC cases, tea intake was associated with reduction of HCC risk to a lesser extent than coffee.⁹¹ Coffee consumption of more than 3 cups per day was associated with improved sensitivity to anti-HCV therapy.⁹² A phase I trial of caffeine citrate is planned to assess its effect in NASH on serum vascular adhesion protein 1 (VAP-1) level, hepatic inflammation, and fibrosis (NCT02098785).⁴⁹ Experimentally, the caffeine analog CGS 15943 inhibits HCC cell growth by targeting the PI3K/AKT pathway.⁹³

Dietary phytochemicals, including curcumin (from turmeric extract), resveratrol (a polyphenol in grapes, red wine, and berries), silymarin (a herbal flavonoid), and carotenoids, have been assessed as potential HCC chemoprevention agents, although clinical proof is still lacking.⁹⁴ Shared features of this class of agents include activation of cytoprotective mechanisms such as the Keap1/Nrf2 pathway, as shown in experimental models.⁹⁴ Markers of DNA damage such as 8-hydroxydeoxyguanosine (8-OHdG) in urine was reduced in humans by several agents, such as epigallocatechin gallate (EGCG, a green tea polyphenol) and broccoli sprouts, although their HCC-preventive effect has not yet been determined.⁹⁴ Normalization of the levels of hepatic transaminases by glycyrrhizin (from licorice root extract) has been associated with reduced HCC incidence.⁹⁵ S-adenosylmethionine (SAM), a ubiquitous, major methyl donor, suppresses HCC development in an experimental model.⁹⁴ In a phase II trial of SAM in HCV cirrhosis, the levels of the biomarkers for liver injury and oxidative stress as well as of serum α-fetoprotein did not change in the subjects.⁹⁶

Dietary intake of unsaturated fat was inversely associated with HCC incidence in a European cohort.⁹⁷ In a population-based cohort of > 90,000 Japanese subjects, consumption of n-3 polyunsaturated fatty acid (PUFA)-rich fish and of individual n-3 PUFAs such as eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA) was associated with lower HCC incidence.⁹⁸ Omega-3 PUFAs, DHA, and EPA inhibit cyclooxygenase 2 (COX2) and suppress HCC growth.⁹⁹ Fat-1 transgenic mice, which endogenously form omega-3 PUFAs are protected from chemically-induced hepatocarcinogenesis and have reduced hepatic COX2 expression.¹⁰⁰ White meat has been associated with a lower risk of chronic liver disease and HCC compared to red meat in a large-scale U.S. cohort.¹⁰¹

Low serum levels of vitamin D (25(OH)D3) have been associated with the risk of HCC, variceal bleeding, and ascites in patients with chronic hepatitis B, and with more frequent death in patients with HCC.^102,103 Higher 25(OH)D levels have been associated with lower HCC risk.¹⁰⁴ In alcoholic liver disease patients, low 25(OH)D levels have been associated with higher liver damage and mortality.¹⁰⁵ Vitamin D3 up-regulated protein 1 (VDUP1) suppresses TNF and NF-κB signaling, and reduces chemical carcinogenesis in rat liver.¹⁰⁶ Artificial sunlight therapy increases serum levels of 25(OH)D3 and reduces liver inflammation and fibrosis in NASH rats fed a choline-deficient, L-amino acid-defined (CDAA) diet.¹⁰⁷ 1,25(OH)2D3 inhibits thioacetamide (TAA)-induced fibrosis.¹⁰⁸ SQSTM1 (p62) promotes heterodimerization of the vitamin D receptor (VDR) with retinoid × receptor (RXR) and inhibits hepatic stellate cell activation, liver fibrosis, and HCC progression.¹⁰⁹ A phase IV trial of vitamin D3 is planned for the prevention of HBV-related HCC (NCT02779465).

Hereditary hemochromatosis is caused by HFE gene mutations (C282Y and H63D) and associated with increased iron content in the liver and elevated risk of HCC^110–112. Iron depletion by chelate therapy and phlebotomy have been explored as measures for HCC chemoprevention not only in hemochromatosis patients but also in viral hepatitis patients, although none of these have been adopted in clinical care.^94,113 Phlebotomy reduces hepatic iron content and inflammation and HCC in HCV-infected patients.¹¹⁴ Liver-specific β-catenin knockout increases susceptibility to excess dietary iron, which leads to the development of steatohepatitis, fibrosis, and HCC by activating the AKT, ERK, and NF-κB pathways in mice.¹¹⁵ Deferasirox, an iron chelator, upregulates hepcidin, transferrin receptor 1, and hypoxia inducible factor-1α, and suppresses chemically-induced HCC in mice; however, its toxicity limits its clinical use.¹¹⁶

Dietary supplementation with branched-chain amino acids (BCAA) is used for treatment of hepatic encephalopathy in cirrhotics.¹¹⁷ BCAA induces mTOR-mediated cellular senescence and suppresses liver fibrosis and HCC in rats.^118,119 In HCV-transgenic mice, BCAA reduces hepatic iron accumulation by inducing hepcidin-25, which reduces reactive oxygen species.¹²⁰ In a NASH mouse model, BCAA represses profibrogenic activation of hepatic stellate cells via TGF-β1 and reduces cellular transformation in an mTOR-dependent manner.¹²¹ In C57BL/KsJ-db/db obese mice, BCAA reduces inflammation in the liver and white adipose tissues, and inhibits spontaneous hepatic carcinogenesis by inducing PPARγ, p21^CIP1, and p27^KIP1, and suppressing IL-6, IL-1β, IL-18, and TNF.¹²² BCAA increased serum hepcidin-25 levels in HCV-infected patients with advanced liver fibrosis. In a prospective observational study, BCAA supplementation was associated with reduced incidence of HCC and death.¹²³ N-acetyl-l-(+)-cysteine (NAC) protects the animals from hepatic injury and fibrogenesis.

Molecular targeted therapies

The phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway is involved in cell survival, making it a candidate HCC chemoprevention target.⁶ AKT was identified as a key HCC risk driver in a human hepatic transcriptome meta-analysis.¹²⁴ Clinical studies have suggested that immunosuppression by mTOR pathway inhibition reduces post-transplantation HCC recurrence,¹²⁵ but adverse effects such as arterial thrombosis and poorer patient and graft survival have been noted.¹²⁶ In animal models of chemical/obesity-driven HCC, sirolimus (rapamycin) activates IL-6/signal transducer and activator of transcription 3 (STAT3) and enhances HCC development.¹²⁷ Sirolimus and everolimus have been tested in prospective trials for prevention of post-transplantation HCC recurrence.¹²⁸ A phase III trial of sirolimus enrolling 525 patients did not improve recurrence-free survival beyond 5 years after transplantation, although subgroup analyses suggested that less advanced tumors or younger age may predict a better outcome.¹²⁹

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are bioactive lipids that can regulate cell survival, differentiation, proliferation, and migration.¹³⁰ In liver, hepatocyte-derived autotaxin (ATX), which converts lysophosphatidylcholine into LPA, is elevated in the serum of HCV-infected and NAFLD patients with liver fibrosis and HCC.^131,132 In a transcriptome meta-analysis of human fibrotic livers, LPA receptor 1 (LPAR1) was identified as a pan-etiology HCC risk driver.¹²⁴ Genetic knockout of ATX as well as pharmacological inhibition of ATX or LPAR1 attenuates progression of liver fibrosis and HCC development in rodent models.^124,133

Activation of receptor tyrosine kinase signaling, such as through the epidermal growth factor receptor (EGFR) pathway, in hepatic stellate cells and macrophages has been implicated in hepatocarcinogenesis in rodent models.^134,135 A small molecule EGFR inhibitor such as erlotinib reversed a gene signature pattern associated with a high risk of HCC and suppressed HCC development in rodent models.¹³⁶ Based on these findings, a phase I trial of erlotinib has been started (NCT02273362). A multi-kinase inhibitor, sorafenib, did not affect recurrence-free survival after curative treatment of primary HCC tumors in a phase III trial.¹³⁷

The renin-angiotensin system has been implicated in pathogenesis of liver fibrosis and HCC risk.⁹⁴ NF-κB activation mediated by angiotensin II promotes fibrogenesis, which can be inhibited by captopril, an angiotensin-converting enzyme (ACE) inhibitor.¹³⁸ Angiotensin II type 1 receptor blockers (ARBs) such as losartan and telmisartan can suppress hepatic stellate cell activation, reduce liver fibrosis, and prevent HCC in rodents.^139,140 In a retrospective single-center study, ARB use was associated with delayed HCC recurrence and extended patient survival after HCC tumor ablation.¹⁴¹ An ACE inhibitor, perindopril, in combination with vitamin K2 or branched-chain amino acids, reduced HCC recurrence after curative treatment.^142,143

Peretinoin (acyclic retinoid) is a synthetic vitamin A analog that inhibits the Wnt and platelet-derived growth factor (PDGF) pathways, induces cellular differentiation and apoptosis of hepatic stem cells, and apparently depletes neoplastic clones.^144–146 Peretinoin also suppresses HCV replication and the release of infectious virus in vitro.¹⁴⁷ In mice fed a high-fat diet, peretinoin induced autophagy and suppressed HCC development.¹⁴⁸ In a phase III trial of peretinoin in patients with curatively treated HCV-related HCC, reduced HCC recurrence was observed after 2 years.¹⁴⁹ A follow-up study reported extended overall survival in patients treated with the higher dose.¹⁵⁰ Prospective trials in HBV-related HCC patients are underway.¹⁴⁴

It has been speculated that the estrogen pathway underlies the sex disparity in HCC risk.¹⁵¹ Genetic variations in estrogen receptor 1 (ESR1) gene were associated with increased HCC risk in a meta-analysis of 87 studies.¹⁵² Estrogen replacement as post-menopausal hormone therapy was associated with a reduced risk of HCC and prolonged patient survival.¹⁵³ The microRNA miR-101 is down-regulated in HCC tissue, and its administration inhibits known HCC chemoprevention targets such as COX2 and Rho-GTPase, and reduces HCC in mice.¹⁵⁴

Conclusions

Given the diversity of HCC etiology and clinical conditions, generically applicable chemoprevention therapies will have broader clinical applicability compared to etiology-specific interventions such as anti-viral therapies. Moreover, such generic chemoprevention could be used in combination with etiology-specific therapies for potentially synergistic effects. Identification of clinically relevant HCC chemoprevention targets has been challenging due to the logistical difficulty in validating experimentally-derived hypothesis in humans, which typically requires long observation periods in large patient cohorts. Integrative omics analysis of clinical specimens with already completed clinical follow-up, so-called “reverse-engineering” chemoprevention discovery, may overcome this challenge.¹²⁴ The prediction of drug toxicity is another critical factor because cirrhotic patients are the major target of chemopreventive therapy.¹⁵⁵ Safe generic compounds in combination with HCC risk biomarkers will enable flexible and cost-effective HCC chemoprevention and contribute to substantial improvement of the dismal prognosis of HCC.