Several strategies targeting this system including monoclonal antibodies against the IGF 1 receptor (IGF-1R) and small molecule inhibitors of the tyrosine kinase function of IGF-1R are under active investigation

Several strategies targeting this system including monoclonal antibodies against the IGF 1 receptor (IGF-1R) and small molecule inhibitors of the tyrosine kinase function of IGF-1R are under active investigation. less than 50% [3]. Currently sorafenib is the only medication that shows overall survival advantage compared to placebo in patients with advanced HCC [4,5]. However, the benefits with sorafenib are moderate and its toxicities can be challenging to manage. For patients who fail or cannot tolerate sorafenib, there are currently no standard treatments. Therefore, there is an urgent need to search for novel effective therapies in advanced HCC. Recently, the insulin-like growth factor (IGF) axis has emerged as an important pathway in the development and progression of HCC and as a potential therapeutic target. Here we review the complexity of IGF axis, the supporting preclinical and clinical data highlighting the significance of this pathway in HCC, and the early clinical trials of targeting this axis in advanced HCC. Components of IGF Axis The insulin-like growth factor (IGF) pathway has highly conserved function in mammals and plays a critical role in energy metabolism and cell renewal in response to nutrients [6-11]. IGF pathway is Flt4 not only involved in cell MRT-83 growth in tissue culture [12,13], but it also promotes cell proliferation, migration and transformation into malignant clone [12,14]. The IGF-1 pathway revolves around 4 essential components. (1) Ligands The first component contains the IGF ligands, which include both insulin-like growth factor 1 (IGF-1) and IGF-2. Their names are based on the observation that both IGF-1 and IGF-2 are peptides, much like insulin, and they share MRT-83 40% homology with proinsulin [15,16]. They are, however, slightly different from insulin structurally by made up of an additional domain name, which could account for their dramatically different role in neoplasms in comparison with insulin [16]. (2) Receptors The IGF ligands bind to the second component of the IGF axis, the receptors which include IGF-1 receptor (IGF-1R), IGF-2 receptor (IGF-2R), insulin receptor and cross receptors consisting of IGF-1R and insulin receptor hemireceptors (IGF-1R/insulin receptor) (Physique ?(Figure1).1). IGF-1 and IGF-2 both bind to IGF-1R with high affinities, and IGF-2 is the only ligand for IGF-2R [6,12,15]. IGF-1 only binds to insulin receptor at extremely high doses, as IGF-1 has 100 fold higher affinity for IGF-1R compared to insulin receptor [16]. IGF-2 usually binds to insulin receptor during fetal development, as later in development when IGF-1R is usually expressed, IGF-2 binds to IGF-1R more tightly [16,17]. Each IGF-1R/insulin receptor hemireceptor only contains one and one subunit; IGF-1 is the favored ligand for IGF-1R/insulin receptor hybrid receptors compared to insulin, as IGF-1 can tightly bind in the presence of only one subunit of the MRT-83 hemireceptor, while insulin requires two subunits of the hemireceptor to provide optimal binding [16]. Open in a separate windows Physique 1 Binding of insulin and IGF ligands to their receptors. Insulin receptor and IGF-1 receptor are both tyrosine kinases. IGF-2R functions as a clearance site for IGF-2. Insulin receptor and IGF-1R are homologous and form hemireceptors. IGF-1 binds to IGF-1R and to IGF-1R/Insulin Receptor hemireceptor; it binds to insulin MRT-83 receptor only at very high concentrations. IGF-2 binds to IGF-1R, MRT-83 IGF-2R and binds to insulin receptor only during early fetal development. Insulin binds to insulin receptor, and it binds to IGF-1R/Insulin Receptor hemireceptor at high concentration. Signal transduction is usually activated after the activation of IGF-1R, IGF-1R/Insulin Receptor hemireceptor and insulin.