Anti-tumor activities and apoptosis-regulated mechanisms of bufalin on the orthotopic transplantation tumor model of human hepatocellular carcinoma in nude mice.

Aim: To investigate anti-tumor activities and apoptosis-regulated mechanisms of bufalin in the orthotopic transplantation tumor model of human hepatocellular carcinoma in nude mice.

Methods: BEL-7402 cells of human hepatocellular carcinoma were inoculated to form subcutaneous tumors, and were implanted into the liver to establish orthotopic transplantation tumor models of human hepatocellular carcinoma in nude mice. Seventy-five animals were randomized divided into five groups (n = 15). Bufalin was injected intraperitoneally into three groups at doses of 1.5 mg/kg (BF1), 1 mg/kg (BF2) and 0.5 mg/kg (BF3) for d 15-24, respectively. The NS group was injected an equal volume of saline as above and adriamycin was injected intraperitoneally into the ADM group at a dose of 8.0 mg/kg for d 15. Ten mice in each group were killed at d 25 and the survival time in each group was calculated. We also observed the morphologic alterations in the myocardium, brain, liver, kidney and tumor tissues by pathology and electron microscopy, measured the apoptotic rate by TUNEL staining method, and detected the expression of apoptosis-regulated genes bcl-2 and bax by immunohistochemical staining and RT-PCR in tumor tissues.

Results: The tumor volumes in each group of bufalin were reduced significantly (35.21 +/- 12.51 vs 170.39 +/- 25.29; 49.83 +/- 11.46 vs 170.39 +/- 25.29; 83.99 +/- 24.63 vs 170.39 +/- 25.29, P < 0.01, respectively), and the survival times were prolonged in group BF1-2 (31.8 +/- 4.2 vs 23.4 +/- 2.1 and 29.4 +/- 3.4 vs 23.4 +/- 2.1, P < 0.05, respectively), and necrosis was mainly in severe or moderate degree in group BF1-2. No morphological changes were detected in the myocardium, brain, liver and kidney tissues. Apoptotic characteristics could be seen in group BF1-2. The positive rates of bcl-2 and bax protein expression of each group by immunohistochemical staining were 10.0%, 10.0%, 20.0%, 10.0% and 20.0%; 90.0%, 80.0%, 80.0%, 40.0% and 30.0%, respectively. Loss of expression of bcl-2 mRNA in each group was to be found and the density of bax mRNA was increased progressively with increase of dose of bufalin by RT-PCR.

Conclusion: Bufalin has significant anti-tumor activities in the orthotopic transplantation tumor model of human hepatocellular carcinoma in nude mice with no marked toxicity and was able to induce apoptosis of transplanted tumor cells. This apoptosis may be mediated mainly via up-regulating the expression of apoptosis-regulated gene bax, which may be involved in its anti-tumor mechanism of bufalin.