[The significance of blood group-related antigen A in a pancreatic cell line (PGHAM-1) in hamsters. With special reference to cell proliferation]

Re-expression of reduced VEGF activity in liver metastases of experimental pancreatic cancer

PURPOSE

Vascular endothelial growth factor (VEGF) is thought to play a crucial role in the process of cancer growth and metastasis. In this study, the expression of VEGF in liver metastases of pancreatic cancer was investigated using an established hamster model.

METHODS

Pancreatic cancer cells (PGHAM-1, 1 x 10(6)) derived from N-nitrosobis (2-oxopropyl) amine (BOP)-induced pancreatic tumors in Syrian golden hamsters were transplanted into the pancreas of female hamsters. All hamsters were sacrificed at 21 days after transplantation and used for the histopathological examination of pancreatic and metastatic lesions (primary transplantation model). The metastatic liver tumors were minced with scissors and 1 mm(3) tumors were retransplanted into the pancreas of a second hamster. All hamsters were sacrificed 21 days after retransplantation, and the pancreatic tumors were removed (back transplantation model). Immunohistochemical analyses using antibody against VEGF were performed for all pancreatic and liver tumors. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to examine the expression of VEGF mRNA in the tumors. In addition, we investigated the proliferation of each tumor using Ag-NOR staining.

RESULTS

In the primary transplantation models, VEGF expression in the pancreatic tumors was positive, but that in the liver metastases was only weakly positive or negative. On the other hand, VEGF expression in the pancreatic tumors that had developed from the retransplantation of the liver tumors (back transplantation model) was strongly positive. VEGF mRNA was expressed in the pancreatic tumors of both primary and back transplantation models. In the metastatic liver tumors of the primary transplantation model, VEGF mRNA was expressed in all cases, although the immunohistochemical staining pattern was weakly positive or negative. Similarly, in the metastatic liver tumor of the back transplantation model, VEGF mRNA was expressed in all cases, although the immunohistochemical staining pattern was weakly positive or negative. No significant differences in Ag-NOR scores were found between the models.

CONCLUSION

Our results suggest that VEGF expression usually occurs in PGHAM-1 cells but that VEGF expression is reduced during the process of liver metastasis and revived by retransplantation. Thus, the interrelationship between cancer cells and the organ environment might play an important role in VEGF expression.

Anti-tumor effect of N-[3,4-dimethoxycinnamoyl]-anthranilic acid (tranilast) on experimental pancreatic cancer

The anti-tumor effect of N- [3,4-dimethoxycinnamoyl] -anthranilic acid (tranilast) was examined in experimental pancreatic cancer. Proliferation of PGHAM-1 cells was inhibited by tranilast in a dose-dependent manner, showing a significant difference at a concentration of 25 microgram/ml (p<0.05). In colony formation, tranilast reduced the number of colonies at a concentration of 25 microgram/ml (p<0.01). DNA synthesis for 12 hours was attenuated dose-dependently and a significant difference was observed at concentrations of greater than 50 microgram/ml (p<0.05). From cell cycle analysis, a dose-dependent increase in the distribution of G0-G1 phase was observed. In the dorsal air sac model, the mean angiogenesis indices in PGHAM-1 chambers were 4.17 +/- 0.22 (control group) and 2.33 +/- 0.84 (treatment group), and in VEGF chambers they were 3.60 +/- 0.67 (control group) and 1.92 +/- 0.42 (treatment group), In the peritoneal dissemination model, the quantity of sanguineous ascites, the number and the size of diaphragmatic nodules and the microvessel density (MVD) of the metastatic site were reduced by tranilast significantly. In conclusion, the anti-tumor effect of tranilast on proliferation and on tumor-angiogenesis was confirmed in experimental pancreatic cancer.

Effect of angiostatin on liver metastasis of pancreatic cancer in hamsters

The liver is the most common site of metastasis in pancreatic cancer, and there are no promising strategies to treat it. Angiostatin, a kringle-containing fragment of plasminogen, is a potent inhibitor of angiogenesis. The effect of angiostatin on liver metastasis in pancreatic cancer was investigated by using our established hamster model of liver metastasis. Pancreatic cancer cells (PGHAM-1, 1 x 10(6)) derived from N-nitrosobis(2-oxopropyl)amine (BOP)-induced pancreatic tumor in Syrian golden hamsters were transplanted into the spleen of female hamsters, and the animals were subcutaneously injected with angiostatin and saline. Subsequently, the macroscopic appearance of liver surface metastases was evaluated. In addition, histological sections of the liver metastases were analyzed for neovascularization, proliferation, and apoptosis on the basis of von Willebrand factor, argyrophilic nucleolar organizer region (Ag-NOR), and TdT-mediated dUTP-biotin nick end labeling (TUNEL) staining, respectively. The results showed significant tumor growth retardation and inhibition of angiogenesis in metastatic liver tumors in response to treatment with angiostatin. Moreover, the metastases remained in a nearly dormant state due to a balance between apoptosis and proliferation of the tumor, with no detectable side effects. This is the first experimental trial of angiostatin on pancreatic cancer and liver metastasis. The results suggest that angiostatin therapy could be effective against liver metastases of pancreatic cancer.

Two types of peritoneal dissemination of pancreatic cancer cells in a hamster model

Peritoneal dissemination has an unfavorable impact on the prognosis of pancreatic cancer, and a peritoneal dissemination model was created in hamsters by using an experimental pancreatic cancer to clarify its pathological characteristics. PGHAM-1, a cancer cell line we established from BOP induced pancreatic cancer in Syrian golden hamsters, was inoculated into the abdominal cavity of Syrian golden hamsters. After inoculation, sequential changes in the diaphragm, omentum, and parietal peritoneum, and the metastatic patterns of the PGHAM-1 cells were morphologically investigated by macroscopical, microscopical, and ultrastructural observation. The cancer cells were easily absorbed at the stomata in the diaphragm and milky spots in the omentum, which were absorptive lymphatic structures, and lymphatic metastasis occurred 4 days after inoculation. In the parietal peritoneum, however, the cancer cells attached to and proliferated on the parietal peritoneum where mesothelial cells had exfoliated and the basement membrane was exposed. This process was comparatively time-consuming, and metastasis occurred in the parietal peritoneum at 7 days after inoculation. This study suggested that there might be two patterns of peritoneal dissemination of hamster pancreatic cancer. One route is lymphatic metastasis via stomata in the diaphragm and milky spots in the omentum, and the other is direct metastasis on the parietal peritoneum; each metastasis forms independently.