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BackgroundHepatocellular carcinoma has a high mortality rate due to its rate of recurrence. Acyclic retinoid prevents recurrence of hepatocellular carcinoma in patients after surgical removal of their primary tumors by inducing apoptosis in hepatocellular carcinoma cells, although the molecular mechanisms of action are not understood.MethodsHuman hepatocellular carcinoma cells in culture, as well as nude mice transplanted with hepatocellular carcinoma cells and rats given with N-diethylnitrosamine were treated with acyclic retinoid. Changes in activated caspase 3 and transglutaminase 2 (TG2) levels, Sp1 cross-linking and its activities, expression of epidermal growth factor receptor, and apoptotic levels were measured.ResultsAcyclic retinoid simultaneously stimulated the activation of caspase 3, and the expression, nuclear localization and crosslinking activity of TG2, resulting in crosslinking and inactivation of the transcription factor, Sp1, thereby reducing expression of epidermal growth factor receptor and cell death in three hepatocellular carcinoma cell lines. These effects were partially restored by a caspase inhibitor, transfection of antisense TG2, restoration of functional Sp1, or an excess of epidermal growth factor. Nuclear expression of TG2 and crosslinked Sp1, as also activated caspase 3 were found in both hepatocellular carcinoma cells transplanted into nude mice and cancerous regions within the liver in N-diethylnitrosamine-induced hepatocarcinogenesis model in rats, following treatment of animals with acyclic retinoid.ConclusionsTreatment with acyclic retinoid produces a dual activation of caspase 3 and TG2 induced apoptosis of hepatocellular carcinoma cells via modification and inactivation of Sp1, resulting in reduced expression of epidermal growth factor receptor.

The present study was designed to determine the effects of NIK-333, a synthetic acyclic retinoid, on N-diethylnitrosamine (DEN)-induced hepatocarcinogenesis in male F344 rats. Animals were given DEN dissolved in drinking water at a concentration of 40 p.p.m. for 5 weeks and then provided with drinking water free of DEN for 15 weeks to induce hepatocellular neoplasms. NIK-333 was administered orally (once a day) to rats at doses of 10, 40 and 80 mg/kg body wt for 14 weeks, starting 1 week after the completion of administration of DEN. At 20 weeks after the start of DEN administration, histopathological evaluation was carried out on all animals. The effects of NIK-333 on the cell proliferation activity of non-tumorous areas and liver tumor cells and the immunohistochemical expression of transforming growth factor-alpha (TGF-alpha) were also evaluated. NIK-333 at 40 and 80 mg/kg body wt significantly inhibited hepatocarcinogenesis (P < 0.05). In addition, NIK-333 at the same doses decreased DEN-induced overexpression of TGF-alpha in hepatocellular neoplasms (adenomas and carcinomas) and their surrounding tissue. Furthermore, NIK-333 significantly inhibited cell proliferation activity in the lesions and in non-tumorous areas (P < 0.01). Our results suggest that NIK-333 inhibits DEN-induced hepatocarcinogenesis through suppression of TGF-alpha expression and cell proliferation.

We investigated the preventive effects of a synthetic acyclic retinoid, NIK-333, on the early and late events of hepatocarcinogenesis in male F344 rats treated with 3'-methyl-4-dimethylaminoazobenzene (3'-MeDAB). NIK-333 was administered once a day on consecutive days at a dose of 10, 40, or 80 mg/kg body weight along with the supplementation with 3'-MeDAB-containing diet for 16 wk. Animals from each group were sacrificed at 4 and 16 wk after the commencement of the experiment to determine the effect of NIK-333 on the early and late stages of carcinogenesis, respectively. NIK-333 suppressed the emergence of both oval-like cells expressing transforming growth factor (TGF)-alpha, putative progenitors of hepatocellular carcinoma (HCC), and activated hepatic stellate cells, major matrix-producing cells of the liver, in the early stage and inhibited the incidence of HCC in the late phase. These results suggest that NIK-333 is a promising drug for the chemoprevention of HCC by uniquely suppressing the early events of hepatocarcinogenesis, that is, development of both oval-like cells and fibrogenesis.

H epatocellular carcinoma (HCC) is characterized by its high incidence in hepatitis virus-associated liver diseases, reaching approximately 3% in hepatitis B virus (HBV)-infected cirrhotic patients and 7% in hepatitis C virus (HCV)-infected cirrhotic patients. 1,2 Moreover, the incidence of posttherapeutic recurrence is approximately 20% to 25% a year in cirrhotic patients who have already undergone curative treatment of the primary HCC. 3,4 Importantly, at least one third of the second tumors are primary de novo cancers because of multicentric carcinogenesis and not intrahepatic recurrence or metastatic tumor. 5 Therefore, strategies to prevent a second primary HCC are required to improve the prognosis. 6 Clinical trials have succeeded in inhibiting the development of HCC with the compounds, including a retinoid analog (vitamin A and its derivatives), acyclic retinoid, 7,8 and interferon alfa and beta (IFN-␣ and -␤). 9-12 Acyclic retinoid is a member of the family of chemopreventive agents, whereas IFNs belong to a category of biopreventive agents, functioning as biologic response modifiers.Acyclic retinoid is a synthetic retinoid 13 and transactivates the 2 retinoid receptors, retinoic acid receptor (RAR), and retinoid X receptor (RXR). 14 Oral administration of the retinoid induces apoptosis in human HCC cell lines 15 and a clinical study we previously reported demonstrated a reduced incidence of posttherapeutic recurrence of HCC and, thereby, a significant improvement of survival rate. 7,8 In that clinical study, we