Experimental Modeling SD Rats Metastatic Hepatocellular Carcinomas Induced By DEN And NMOR

Hepatocellular carcinoma (HCC) is the fifth most common carcinoma and the third leading cause of death by cancer in the world. Although surgery is thus far the most efficient treatment for HCC, recurrence and metastasis of cancer cells after removal of cancer tumor or transplantation of liver may result in bad prognosis. To study the mechanisms underlying metastasis, many methods and models have been developed. In most studies, cancer cell lines or transplantable tumors were injected into blood vessels or the intraperitoneal cavity, or transplanted into the cecum, spleen or subcutis. Those approaches have demonstrated their advantages in analysis of individual steps in the metastatic process. However, in order to analyze the natural course of metastasis, it is necessary to develop animal cancer models that are able to simulate frequent metastasis of primary tumors to distant organs and assess the efficacy of therapeutic treatments for advanced cancers as well. Induced metastatic hepatocellular carcinoma rat model appears as a good candidate. Diethylnitrosamine (DEN) is a general inducer, but the hepatocellular carcinomas induced by DEN is usually well-differentiated and has low metastasis efficiency. Foreign researchers have developed models on metastatic hepatocellular carcinoma induced by Diethylnitrosamine in combination with N-nitrosomorpholine (NMOR) in F344 rat which belongs to inbred line. However, Spreque-Dawley (SD) rat or Wistar rat from closed population is more frequently used internally and it has not been reported whether DEN and NMOR can induce metastatic hepatocellular carcinoma in either of these two strains.Objective: To establish DEN and NMOR-induced metastatic hepatocellular carcinomas model in SD rats and find out proper dose and treatment period. Methods: One hundred 5-week-old male SD rats were randomly divided into four groups: DEN+NMOR, DEN, NMOR and control group. Group DEN+NMOR (60 Rats) and Group DEN (15 Rats) were given a single i.p. injection of DEN as an initiator of liver carcinogenesis at a dose of 100 mg/kg body weight. And then groups DEN+NMOR, NMOR (15 Rats) were given 100 ppm NMOR in the drinking water for 20 weeks. Control group (10 rats) was only given a single i.p. injection of sodium chloride as the same volume as DEN solution.Results: By the end of 16 weeks, the HCCs incidences in group DEN+NMOR, DEN, NMOR and control group were 60.0%(6/10), 20.0%(1/5), 0.00%(0/5), 0.00%(0/2). And, by the end of 20 weeks the HCCs incidences in group DEN+NMOR, DEN, NMOR and control group were 87.5%(21/24), 16.7%(1/6), 14.3%(1/7), 0%(0/2), respectively. Lung Metastases incidences in group DEN+NMOR at the end of 16th week and 20th week were 31.3%(2/6), 47.6%(10/21). However, Lung Metastases incidence was not observed in other groups.Conclusions: (1) The model on hepatocarcinogenesis induced by DEN and NMOR in SD rat provides an efficient means for rapid induction of metastatic HCC and represents the natural course of metastasis of malignant tumors to lung. This model not only sheds light on the mechanisms underlying metastasis, but also tests the efficacy of anti-metastatic agents. (2) Our results suggest that a single i.p. injection of DEN as an initiator of liver carcinogenesis at a dose of 100 mg/kg body weight and sequentia 100 ppm NMOR in the drinking water for 20 week probably is an appropriate treatment.