摘要：

In this study, we investigated the effect of bombesin/GRP antagonist RC-3095 on the growth of CFPAC-1 human pancreatic cancer cells transplanted to nude mice or cultured in vitro. Nude mice bearing xenografts of the CFPAC-1 cell line received s.c. injections of RC-3095 (10/tg twice a day) or the vehicle (control) for 25 days. Chronic administration of RC3095 inhibited the growth of CFPAC-1 tumors in nude mice as shown by a significant decrease in tumor volume throughout the period of treatment. Tumor volume doubling time was prolonged by RC-3095 treatment from 7.2 days to 10 days, and the tumor growth rate was decreased by 49%. In mice treated with RC-3095, the tumor growth delay time was 5.8 days. ~I~reatment with RC-3095 decreased the final tumor weight by 37% and reduced DNA and protein contents in tumor tissues by 44 and 39.9%, respectively, compared to the controls. In cultures of the CFPAC-I cell line, the addition of bombesin(1-14) (1 p~a-0.1 pM) to the medium induced a dose-dependent increase in cell number. RC-3095 at 1 nM concentration effectively inhibited the bombesin-stimulated growth of CFPAC-I cells in cultures. In the presence of 1 btM RC-3095 in the culture medium, the bombesin-induced growth of CFPAC-1 cells was totally suppressed. Bombesin was also shown to stimulate the DNA synthesis in CFPAC-1 cells in vitro as based on [3H]thymidine incorporation assay. When the cells were cultured in the presence of 1-100 nM bombesin, the uptake of [3H]thymidine by the cells was increased by 89-131%. RC-3095 inhibited both the basal and bombesin-stimulated DNA synthesis of CFPAC-1 cells. Addition of RC-3095 (10-100 nM) alone to the cultures caused a 39-40% decrease in the [3H]thymidine incorporation by the cells. Concomitant addition of RC-3095 (1 p~) and bombesin (1-100 nM) to the cultures induced a significant reduction in the uptake of [aH]thymidine by the cells compared to the values obtained with bombesin alone. Receptor binding assays showed the presence of two classes of specific binding sites for bombesin on CFPAC-1 cells, one with high affinity (Ka = 4.25 _+ 0.77 n~a) and low capacity (B,,ox = 0.268 +_ 0.052 pmol/106 cells) and the other with low affinity (K,t -" 321.70 + 68.46 nM) and high capacity (B .... 3.991 +_ 0.374 pmoi/106 cells). Antagonist RC-3095 inhibited the binding of ~2SI-Tyr 4bombesin to CFPAC-1 cell membranes in a dose-dependent manner. These observations suggest that bombesin acts as a growth factor and stimulates proliferation of CFPAC-1 human pancreatic cancer through specific receptors for bombesin/GRP present on the cells. RC-3095 appears to inhibit the growth of CFPAC-1 cells by blocking the interaction of bombesin with its receptors. Bombesin/GRP receptor antagonist RC-3095 could be considered for the development of new approaches for treatment of human pancreatic cancers. I N T R O D U C T I O N Pancreatic cancer is one of the greatest challenges for oncologists (1-5). Carcinoma of the exocrine pancreas is the fifth leading cause of death from cancer in the United States (1). Most of pancreatic cancers are histologically ductal cell carcinomas, which constitute about 8090% of the cases (2). In the past two decades, great efforts have been made to improve the therapies for pancreatic cancers. However, the overall prognosis of patients with pancreatic cancer is still very poor, and the 5-year survival rate is only 2-5% (2-4). Less than 15-20% of pancreatic tumors are resectable, mostly due to the difficulties in early diagnosis and the frequent occurrence of local or distal metastases, and fewer than 5% of the patients can survive for over 5 years postoperatively (3-5). Radiotherapy and chemotherapy are usually ineffective (2-5). Therefore, an urgent need exists to develop a new and effective therapy for treatment of patients with pancreatic cancers. Recently, various investigations have demonstrated that gastrointestinal hormones and growth factors may play important roles in the regulation of growth of normal and malignant exocrine pancreas (510). In vitro studies have shown that g

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