The etiology of hepatocellular carcinoma and consequences for treatment

Functional significance of the ATP-binding cassette transporter B6 in hepatocellular carcinoma

ABCB6 is a mitochondrial transporter that regulates porphyrin biosynthesis. ABCB6 expression is upregulated in hepatocellular carcinoma (HCC) but the significance of this upregulation to HCC is not known. In the present study, we investigated: 1) ABCB6 expression in 18 resected human hepatocellular carcinoma (HCC) tissues and 3 human hepatoma cell lines; 2) pattern of ABCB6 expression during liver disease progression; and 3) functional significance of ABCB6 expression to HCC using the hepatoma cell line Huh7. ABCB6 expression was determined by real-time quantitative reverse transcription-polymerase chain reaction and western blotting. ABCB6 expression was upregulated in all the HCC specimens and the three-hepatoma cell lines. Increased ABCB6 expression correlated with liver disease progression with the pattern of expression being HCC > cirrhosis > steatosis. Small hairpin RNA (shRNA)-mediated knockdown of ABCB6 in Huh7 cells lead to decreased cellular proliferation and colony formation. Attenuation of ABCB6 expression did not affect Huh7 apoptosis but lead to a delay in G2/M phase of the cell cycle. In contrast, ABCB6 overexpression resulted in increased growth and proliferation of Huh7 cells. Since ABCB6 expression is induced in multiple tumor types we explored the role of ABCB6 in other cancer cells. ShRNA mediated knockdown of ABCB6 in HEK293 and K562 cells reduced cellular proliferation leading to a delay in G2/M phase, while ABCB6 overexpression promoted cell growth and proliferation. Collectively, these findings, obtained by loss of function and gain of function analysis, suggest that ABCB6 plays a role in cell growth and proliferation by targeting the cell cycle.

Current approaches to the treatment of early hepatocellular carcinoma

For patients with early-stage hepatocellular carcinoma (HCC), potentially curative treatment options exist, including liver transplantation, surgical resection, and ablation therapy. These treatments are associated with survival benefits, and outcomes are optimized by identification of appropriate patients. However, further studies are needed to definitively confirm optimal treatment approaches for all patients. Treatment patterns vary in different parts of the world as a result of geographic differences in the incidence and presentation of the disease. In particular, because of successful screening programs, a high proportion of tumors that are identified in Japan are amenable to curative treatments, which are appropriate in a smaller proportion of patients in the west, although screening is now widely carried out in industrialized countries. Differences in the applicability of transplantation are also evident between the west and Asia. Although existing treatments for early-stage HCC are supported by considerable evidence, there remain significant data gaps. For example, further data, ideally from randomized controlled trials, are needed regarding: the use of neoadjuvant and adjuvant therapy to decrease the rate of recurrence after resection or ablation, further investigation of the role of chemoprevention following resection, and prospective analysis of outcomes of living donor compared with deceased donor liver transplantation.