The Circulating IGF System in Hepatocellular Carcinoma: The Impact of Liver Status and Treatment
Introduction
Hepatocellular carcinoma (HCC) is a common disease on a global scale and associated with chronic viral hepatitis, exposure to dietary aflatoxin B1, and liver cirrhosis [1]. Irrespective of etiology, the common trait in HCC consists of an imbalance between pro-apoptotic and anti-apoptotic signaling. Anti-apoptotic signaling in hepatocytes is maintained through the PI3-K/Akt and Ras/Raf/MEK/MAPK pathways [2], two major downstream targets of the IGF-I receptor (IGF-IR) [3]. As both IGF-I and IGF-II activate the IGF-IR, both growth factors may influence hepatocyte survival and enrich hepatocellular cancer stem cell populations [4].
The physiology, pathophysiology, and clinical utility of IGF-II have recently been reviewed [5]. Excess IGF-II stimulates cancer cell proliferation and increases cancer cell survival both in vitro and in vivo [6], including in HCC cells [7]. IGF-II is essential for intrauterine growth and placental development. Within the first weeks after birth, there is a shift from potent fetal promoters to a weaker adult promoter, resulting in a very low expression of the igf2 gene in the normal adult liver [8]. By contrast, an elevated igf2 gene expression has been demonstrated in neoplastic tissues from patients with HCC and in animal models of HCC [8], and this over-expression is linked to reactivation of the fetal promoters and deactivation of the adult promoter [9]. Indeed, reducing IGF-II mRNA levels with anti-sense oligonucleotides resulted in decreased cell proliferation in human hepatoma cell lines with high IGF-II secretion [10]. At the molecular level hepatitis B virus (HBV) and hepatitis C virus (HCV) increase the production of IGF-II, thus promoting growth and viability of malignant cells [8].
Several clinical studies have demonstrated elevated IGF-II levels (mRNA and protein) in both tumors and blood from HCC patients, hereby suggesting a role of IGF-II as a marker of HCC [11], [12], [13], [14], [15]. By contrast, others have found sparse evidence of an association between IGF-II and HCC [16]. The reasons for this discrepancy have not been thoroughly investigated. Furthermore, it remains to be clarified whether serum IGF-II may be used as a biomarker of the response to HCC treatment.
We hypothesized that IGF-II would be elevated in HCC and normalize with radio-frequency ablation (RFA) or transarterial chemo-embolization (TACE). IGF-II exerts its biological effects via interaction with the IGF-IR [3], and accordingly, we found it of interest to investigate the ability of serum from HCC patients to activate the IGF-IR under physiological conditions. To this end, an IGF-IR kinase receptor activation (KIRA) assay, developed and validated in our laboratory [17], was applied to compare serum obtained from well-characterized patients with HCC, patients with liver cirrhosis and healthy control subjects. This measure of IGF bioactivity was compared with measurements of IGF-I, IGF-II, and pro-IGF-II, using size exclusion gel chromatography at low pH, which is the gold standard method to eliminate IGFBP interference [18]. Finally, we assessed the impact of the marked reduction in tumor burden following RFA and TACE of HCC tumors on the circulating IGF system.
Section snippets
Patient Characteristics
The HCC patients included in this study were referred to the Department of Hepatology and Gastroenterology, Aarhus University Hospital, Denmark, from December 2007 through October 2010. The Department is a tertiary treatment center for the Western part of Denmark with a population of 2 million inhabitants. Patients were diagnosed, staged and allocated to treatment according to international guidelines for management of HCC [19], [20] independently of study participation. This study focused on
IGF Values in HCC Patients are Markedly Different From Those of LC Patients and Healthy Controls
The baseline comparison showed marked differences in IGF-related measures (Table 2). The HCC patients had twice as high levels of bioactive IGF compared to LC patients, but for both groups levels were markedly below those observed in healthy controls (P < 0.001). Similar patterns were observed for IGF-I, IGF-II, and IGFBP-3, whereas pro-IGF-II and the IGF-I to IGFBP-3 ratio showed less pronounced but nevertheless significant differences (Table 2). IGFBP-2 was 10-fold elevated in LC patients and
Discussion
We have investigated the IGF system in HCC patients, using state of the art IGF-assays. As a novel finding, we report that tumor ablation does not affect serum IGF-II or IGF bioactivity. Furthermore, we demonstrate a strong influence of liver status on IGF variables, which may impact the interpretation of the existing literature on IGF variables in HCC patients.
In this study, patients with HCC showed serum IGF-II levels ranging between healthy controls and LC patients. Furthermore, serum IGF-II
Declaration of Interest
The authors declare no conflicts of interest.
Funding
This study was supported by grants from the Danish Cancer Society (DP08022) and from the Department of Clinical Medicine, Aarhus University. Henning Grønbæk is supported by a clinical research grant from the NOVO Nordisk Foundation.
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