Eag1 channels as potential early-stage biomarkers of hepatocellular carcinoma
Authors Chávez-López M, Zúñiga-García V, Pérez-Carreón J, Avalos-Fuentes A, Escobar Y, Javier Camacho
Received 15 June 2016
Accepted for publication 6 August 2016
Published 20 September 2016 Volume 2016:10 Pages 139—148
Checked for plagiarism Yes
Review by Single anonymous peer review
Peer reviewer comments 2
Editor who approved publication: Dr Wei-Qun Ding
María de Guadalupe Chávez-López,1 Violeta Zúñiga-García,1 Julio Isael Pérez-Carreón,2 Arturo Avalos-Fuentes,3 Yesenia Escobar,4 Javier Camacho1
1Department of Pharmacology, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, 2Instituto Nacional de Medicina Genómica, 3Department of Physiology, Biophysics and Neuroscience, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, 4Centro de Investigación Clínica Acelerada Sc, Mexico City, Mexico
Abstract: Hepatocellular carcinoma (HCC) is a major cause of cancer death worldwide. HCC is usually asymptomatic at potential curative stages, and it has very poor prognosis if detected later. Thus, the identification of early biomarkers and novel therapies is essential to improve HCC patient survival. Ion channels have been proposed as potential tumor markers and therapeutic targets for several cancers including HCC. Especially, the ether à-go-go-1 (Eag1) voltage-gated potassium channel has been suggested as an early marker for HCC. Eag1 is overexpressed during HCC development from the cirrhotic and the preneoplastic lesions preceding HCC in a rat model. The channel is also overexpressed in human HCC. Astemizole has gained great interest as a potential anticancer drug because it targets several proteins involved in cancer including Eag1. Actually, in vivo studies have shown that astemizole may have clinical utility for HCC prevention and treatment. Here, we will review first some general aspects of HCC including the current biomarkers and therapies, and then we will focus on Eag1 channels as promising tools in the early diagnosis of HCC.
Keywords: ion channels, Eag1, hepatocellular carcinoma, astemizole, diethylnitrosamine
Primary liver cancer is a major health problem,1 representing the second leading cause of cancer-related deaths in the world.2 Hepatocellular carcinoma (HCC) accounts for up to 90% of primary liver cancers.1 Other liver cancer types include childhood hepatoblastoma, adult cholangiocarcinoma (originating from the intrahepatic biliary ducts), and angiosarcoma (from the intrahepatic blood vessels).3
HCC affects men three times more frequently than women worldwide. It is the fifth most frequently diagnosed cancer in adult men, and the seventh most commonly diagnosed cancer in adult women.4 Interestingly, significant differences have been noted between the races. Asians are affected two times more than blacks, and Hispanics are affected two times more than whites. The ethnic variability reflects the contribution of specific causal factor differences among populations.4 Because of its poor prognosis, it is compulsory to find novel early markers of the disease as well as new therapeutic approaches for HCC prevention and treatment.
Liver cirrhosis is the strongest HCC predisposing factor. Actually, 80% of HCC cases formerly developed cirrhosis. Other well-defined risk factors comprise viral infections (chronic hepatitis B and C), toxics (alcohol and aflatoxin B1), and altered metabolic conditions (diabetes, nonalcoholic fatty liver disease, hereditary hemochromatosis).5–7 Recently, tobacco and obesity have also been proposed as potential risk factors for the development of HCC.8 The major risk factors for HCC are described in Table 1.
Hepatocarcinogenesis is a multistep process in which a number of genetic alterations accumulate in the cells. After hepatic injury due to major predisposing risk factors for HCC, necrosis arises followed by hepatocyte proliferation. This continuous process of destructive–regenerative cycles in the hepatocyte promotes chronic liver injury and progressive liver fibrosis resulting in cirrhosis. If the process continues, the next step is the progressive malignant transformation of cirrhotic nodules and premalignant lesions, which will ﬁnally lead to HCC9,10 (Figure 1).
Figure 1 Eag1 expression in the progression of HCC.
Notes: The principal risk factors for the development of HCC induce serious liver damage, causing necrosis and proliferation in the hepatocyte. This phase is known as chronic liver disease and may continue to liver cirrhosis. Cirrhosis is characterized by the presence of fibrosis; during this process, the connective tissue separates the liver into multiple regeneration nodules, that is, the fibrosis surrounds the nodules completely. The hyperplastic nodules evolve to dysplastic ones and ultimately to HCC. The use of astemizole in the cirrhosis stage may prevent the development of HCC and even produce HCC regression. Eag1 channels have been shown to be expressed at early stages of HCC development.32
Abbreviations: Eag1, ether à-go-go-1; HCC, hepatocellular carcinoma.
Because most HCC cases are associated with chronic viral hepatitis, prevention of virus infection should lead to the prevention of HCC.11–13 Some preventive strategies already used include vaccination (the universal vaccination was introduced in all newborns and high-risk groups as routine immunization13–15), antiviral treatment (it has been shown that antiviral treatment of chronic hepatitis B virus and hepatitis C virus infections may reduce the risk of HCC13,16,17), and periodical surveillance in patients at risk of developing a disease (Figure 2).11,13,18
HCC diagnosis and treatment
HCC is frequently diagnosed at an asymptomatic stage while the patients are being evaluated for liver transplantation or as part of routine screening in cirrhotic patients. The classic clinical features of HCC include right upper quadrant pain, weight loss, and worsening of liver function. Patients with chronic liver diseases belong to a high-risk group for HCC and a follow-up based on imaging and tumor marker levels11,19 should be regularly made for early diagnosis.
Current and emerging potential HCC biomarkers
Alfa-fetoprotein (AFP) is commonly used as an HCC marker; serum AFP levels may be helpful in the diagnosis and management of HCC. AFP is higher than 20 ng/mL in more than 70% of HCC patients. However, AFP levels from 10 to 500 ng/mL and even up to 1,000 ng/mL may be found in patients with other liver diseases who do not have HCC. AFP is useful mainly in monitoring the response to treatment and detecting recurrence after treatment of HCC, if the AFP levels were elevated before treatment.11,12,19,20
Despite that an ideal biomarker should have high sensitivity and specificity21 and be detectable in any of different samples such as blood, urine, or tissues,22 the coexistence of inflammation and cirrhosis in HCC makes the early diagnosis and prognostic assessment much more difficult. This complication highlights the need to identify valuable biomarkers for the diagnosis and treatment of HCC.22
Recent advances in genomics and proteomics have facilitated the identification of many biomarkers, including new HCC molecular markers. However, only a few biomarkers are acceptable for clinical utility because the rest have low predictive accuracy and/or high cost.23,24 The most relevant biomarkers in liver cancer are described in Table 2.
Most of these markers have been studied in a retrospective manner, and only a few prospective trials have evaluated their clinical significance. However, as HCC is a complex disease with multiple underlying pathogenic mechanisms caused by a variety of risk factors, it is difficult to characterize HCC with a single biomarker. In addition, most of the used
biomarkers are associated with liver damage and not HCC itself. Therefore, novel HCC markers and diagnostic approaches are needed. The combination of biomarkers in a detection kit may be more valuable for the diagnosis and prognosis of HCC. It is also important to identify noninvasive and cost-effective biomarkers for early diagnosis.
Ultrasound (US) studies still play an important role in detecting HCC because US is able to detect small liver lesions and has relatively high sensitivity and specificity. Its use in diagnosis is being replaced by computed tomography and magnetic resonance imaging, especially for those patients whose liver cannot be fully imaged by US because the tumors are very small or whose echograms do not show lesions clearly.11,12,19
If a tumor is detected by imaging, a biopsy can be obtained typically with a needle under US radiologic guidance. The material obtained by fine-needle aspiration is evaluated to determine HCC staging.11,12,19 Because HCC patients are diagnosed at advanced stages of the disease, it is advisable to screen patients who are at risk of developing the disease like those with chronic hepatitis and cirrhosis for early diagnosis (Figure 2). The most common classification of HCC depends on its stage (from early to terminal) and its differentiation grade (well, moderately, or poorly differentiated).13
HCC treatment depends on the tumor stage, patient performance status, and liver function and requires a multidisciplinary approach. The treatment strategies of HCC are summarized in Table 3.
Table 3 Therapies according to the HCC stage
Abbreviation: HCC, hepatocellular carcinoma.
Unfortunately, HCC is among the most chemoresistant tumors. Chemotherapy with cytotoxic agents, such as doxorubicin, gemcitabine, cisplatin, and 5-fluorouracil, or combined regimen for palliative care is associated with low response rates. Interestingly, targeted chemotherapy with multikinase inhibitors (Table 4) seems to be an attractive alternative to conventional systemic chemotherapy.
Table 4 Molecular targeted therapies for HCC
Abbreviations: FGFR, fibroblast growth factor receptor; mTOR, mechanistic target of rapamycin; PDGFR, platelet-derived growth factor receptor; VEGFR; vascular endothelial growth factor receptor.
Electrochemotherapy is a treatment used in cutaneous and subcutaneous tumors with positive results. Its use in deep tumors has been studied. The study showed favorable results in the treatment of liver metastases. Therefore this treatment was proposed to be used in other types of liver tumors including HCC.25
Due to the very poor prognosis of HCC and its late detection, it is essential to find early tumor markers as well as new therapeutic targets and potential anticancer drugs. Ion channels seem to be promising alternative tools in oncology to reach these goals.
Eag1 potassium channels as potential early biomarkers and alternative tools for HCC prevention and treatment
Several reports have shown the abnormal expression of potassium channels in many tumors. Especially, the voltage-gated potassium channel ether à-go-go-1 (Eag1, KCNH1, Kv10.1) has gained enormous interest in cancer research because of its oncogenic properties.26–28 Eag1 is overexpressed in most human tumors, including liver, cervical, lung, breast, colon, and prostate cancer.26–32 Eag1 channels have been also proposed as early tumor biomarkers and therapeutic targets for different types of cancers.30–36 In accordance with its role in cell proliferation, inhibition of Eag1 reduces tumor cell proliferation in vitro and in vivo.26,28,32,33,35,37–40 Astemizole is an antihistamine that has gained great interest as a potential anticancer drug because it targets several proteins involved in cancer, including Eag1 channels, histamine receptors, and proteins involved in drug resistance41 Cells expressing Eag1 and treated with astemizole display lower cell proliferation; it is hypothesized that this cell proliferation inhibition may be due to astemizole’s blockage of the Eag1 channel.32,33,37,42 In vivo studies showed that astemizole administration reduced the growth rate of xenograft tumors in mice implanted with Eag1-expressing cells.42 Thus, Eag1 channels are inhibited by astemizole and may be potential targets for cancer therapy.26,27,32,41 Because Eag1 expression has been reported in human biopsies from liver tumors,30 astemizole may be used as an anticancer therapy in patients with liver cancer.
Considering the poor prognosis of HCC, our research group investigated if Eag1 channels could serve as early HCC markers by studying Eag1 expression during tumor development in vivo. We used the already established animal model of HCC development, where chronicle injection with diethylnitrosamine (DEN) induces liver injury in rats. This model recapitulates the sequential change from cirrhosis to HCC, as it occurs in humans. Interestingly, we observed high Eag1 mRNA expression in most of the DEN-treated groups, and strong Eag1 protein expression was observed at early stages of HCC development32 (Figure 1). Eag1 expression at the mRNA and protein level was clearly higher in cirrhotic tissues and preneoplastic lesions, in comparison to normal livers.32 Thus, our results showed the potential of Eag1 channels as HCC early biomarkers.
We also observed that astemizole clearly prevented the development of HCC; the antihistamine prevented tumor formation when administered either from the start of DEN treatment or from week 12 of DEN treatment, when cirrhosis is already present.32 These results suggest that astemizole might be used as a chemopreventive agent in patients at risk of developing liver cancer. Additionally, astemizole could be used as an antineoplastic because when administered at the end of the DEN treatment, the animals did not develop big tumors as those receiving astemizole,32 suggesting that this compound may induce tumor regression.
Eag1 mRNA and protein are expressed in the human HCC cell lines HepG2 and HuH7; accordingly, astemizole decreased their cell proliferation and induced apoptosis.32 Taken together, all these results suggest that astemizole may be a novel therapeutic approach for HCC patients.
Other types of channels and transporters also displayed a differential expression during HCC development, suggesting other channels as potential early markers and/or therapeutic targets of HCC.43
Future research on Eag1 channels as HCC biomarkers and challenges
The discovery of cancer biomarkers in recent years has become a major focus of cancer research. The development of new technologies, especially genomics and proteomics, has made possible the identification and discovery of potential biomarkers. In the recent years, the study of microRNAs and exosomes has gained great interest to diagnose HCC in at-risk patients.44–48 An ideal tumor marker would be DNA-, RNA-, protein-, or antibody-based measurable in serum, urine, or sputum.49,50
Because Eag1 may have clinical potential as an early biomarker for HCC,32 it would be very interesting to track Eag1 protein expression using sensitive imaging techniques in human livers. Actually, when Eag1-expressing cells were injected into mice, the channel was detected in non-palpable tumors51 using dye-tagged antibodies and imaging techniques. This type of approach might also be used to screen Eag1 expression in the liver of patients at risk of developing HCC and in HCC animal models. It would be also very important to study exosomes containing Eag1 at different stages of HCC in liquid biopsies. Astemizole may be a very promising preventive option for patients at risk of developing HCC as well as a hopeful therapeutic option for HCC patients.32 Therefore, clinical trials testing the effect of astemizole alone or in combination with other antineoplastic drugs in patients either at risk of developing or with HCC should be performed. In addition, detection of Eag1 could be included in the surveillance scheme for patients who are at risk of developing HCC for timely diagnosis (Figure 2).
The precise role of Eag1 channels in HCC development remains to be elucidated. This might be accomplished in different manners, such as the use of mouse models like Eag1 knockout mice.52 It would be very interesting to investigate whether these knockout mice are resistant to the development of liver cirrhosis and HCC.32
Another very important issue to investigate is the mechanism of the oncogenic potential of the channel. Eag1 expression is regulated by the p53-mir-34-E2F1pathway.53 It has been suggested that mutated or inactive p53 increases Eag1 expression; p53 is mutated in most tumors including HCC.54 The increased Eag1 expression could lead to the activation of different proteins such as HIF-1, cyclins D/E, ERK1/2, and FAK complex as well as increase the intracellular calcium concentration and induce vascular endothelial growth factor release. All these changes may lead to angiogenesis, therapy resistance, cell proliferation, migration, and survival, contributing to carcinogenesis.55 However, the precise molecular mechanism of how Eag1 may contribute to HCC development remains to be elucidated.
Liquid biopsies studying HCC circulating cells may provide novel insights into HCC diagnosis and prognosis.56,57 Because Eag1 channels might serve as early markers for different types of cancer, it may be very useful to detect Eag1 mRNA/protein expression in such liquid biopsies. This approach may help to find the urgently needed HCC markers, which are hardly available. However, one of the biggest challenges to overcome would be the sensitivity and specificity of the HCC detection method based on Eag1 expression. In addition, prospective studies should be made to know if cirrhotic patients expressing Eag1 channels would develop HCC.
Because of the poor prognosis of HCC, it is very important to find novel preventive and therapeutic alternatives. Recent studies have suggested that astemizole may be a very promising preventive option for patients at risk of developing HCC as well as a hopeful therapeutic option for HCC patients. It has also been recently proposed that Eag1 may be a potential early biomarker of HCC. Astemizole-based prevention and therapy and early Eag1 detection in the liver should help to reduce mortality from this disease.
The authors report no conflicts of interest in this work.
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