OBJECTIVETo evaluate the antitumor efficiency of IL-12 gene induced by RU486 regulatory system in a mouse model of orthotopically transplanted hepatoma.

METHODSThe orthotopic hepatoma model was prepared by inoculation of H22 hepatoma cells into the mouse liver. Murine interleukin-12 (IL-12) expressing plasmid pRS22 containing RU486 regulatory system was injected into mice by a hydrodynamic injection 3 days after H22 cells inoculation. Three days after hydrodynamic injection, the mice were induced with RU486 (250 µg/kg) consecutive intraperitoneal administration for 6 days. Blood samples were taken at 10 h after the first and third induction for the determination of IL-12, IFN-γ and NO. Five mice were sacrificed at 2 days after the treatment with RU486. The tumor size was measured. HE and immunohistochemical stainings were applied to evaluate the proliferative activity and angiogenesis in the tumors. The other 7 mice were kept to monitor their survival.

RESULTSIn mice receiving saline plus RU486, pRS-LacZ plus RU486, or pRS22 plus sesame oil, the liver tumors were big in size: (409.90 ± 137.03) mm(3), (271.80 ± 182.63) mm(3) and (251.00 ± 76.55) mm(3), respectively. Strong PCNA positive expression [(82.10 ± 4.62)%, (83.45 ± 2.34)% and (77.46 ± 2.99)%] and extensive microvessel density (74.58 ± 18.47, 63.60 ± 13.36 and 53.52 ± 11.74 per 400 × field), respectively, in these tumor tissues were observed after immunohistochemical staining. The survival period was shorter in these mice. In contrast, in mice treated with pRS22 plus RU486, the tumor was smaller in size. Extensive necrosis, weak PCNA proliferative activity (50.67 ± 8.09)%, and a marked paucity of microvessel density (25.38 ± 10.87) were seen. The survival of mice was obviously prolonged. Compared with the 3 control groups, a significant elevation of serum IL-12, IFN-γ and NO levels were detected in the mice treated with pRS22 plus RU486.

CONCLUSIONExpression of IL-12 gene can be effectively controlled by a RU486 regulatory system. The inducible IL-12 can delay the growth of orthotopically transplanted hepatoma and prolong the survival of mice.