Further, CSC-mediated IL-8 production leads to increased self-renewal ability, amplified endothelial tube formation in vitro and enhanced tumorigenicity in vivo. Moreover, we have also

provided evidence that the preferential expression of IL-8 in CD133+ liver BVD-523 order CSCs is mediated through a neurotensin-activated mitogen-activated protein kinase (MAPK)-signaling cascade (Tang et al., unpubl. data, 2011 [manuscript submitted]). The identification of novel therapeutic targets for HCC treatment has begun in earnest in the field of basic liver cancer research. Although there has been a significant improvement in the detection and treatment of early stage HCC, the disease remains largely incurable because HIF inhibitor the current therapeutic regimen is unable to provide a lasting cure for patients with advanced HCC. Recent findings in the identification (Table 2) and characterization of liver CSCs have lent insight and offered great promise for developing better therapeutic strategies against the disease. CD90+CD44+ HCC cells, as discussed previously, possess a high tumorigenic capacity.23 Researchers who have characterized this

subpopulation of cells have also examined the potential benefits of targeting CD44 via a neutralizing antibody approach. The systemic administration of anti-human CD44 antibodies in immunodeficient mice, formed by the intrahepatic inoculation of CD90+ liver CSCs, suppressed tumor nodule formation in the liver and metastatic lesions in the lung.23 Furthermore, the administration of CD44 antibodies was also shown to induce apoptosis in both CD90+ and CD90- cells in vitro.23 In addition to CD44, CD133 has also been suggested as a putative therapeutic target in HCC.46 Using a murine anti-human

CD133 antibody conjugated to the cytotoxic drug, monomethyl auristatin F, Smith et al. found that the antibody-drug conjugate was able to productively induce the inhibition of CD133+ liver CSC-driven cancer cell growth both in vitro and in vivo.46 The granulin-epithelin precursor (GEP), which has been suggested to play a role in Axenfeld syndrome liver cancer cell chemoresistance,33 has also been identified as a potential target for antibody therapy.47 Indeed, anti-GEP monoclonal antibody treatment has resulted in the inhibition of tumor growth in immunodeficient mice, decreased serum GEP levels and reduced tumor angiogenesis.33 The recent work by Haraguchi et al. on the study of CD13+ liver CSCs has also demonstrated that CD13 inhibition by a CD13-neutralizing antibody could elicit cellular apoptosis and inhibit the proliferation of CD13+ liver CSCs-driven HCC. Further, when the CD13 inhibitor, ubenimex, is used in conjunction with the chemotherapeutic drug, 5-fluorouracil, a greater tumor regression was observed than when either agent was used alone.