The nude mouse as a model for the study of human pancreatic cancer

Abstract

The purpose of this study was to characterize an in vivo model of human pancreatic cancer suitable for chemotherapy and immunotherapy studies. In this study we report a 2-year experience in growing the MIA PaCa-2 (CRL 1420) human pancreatic cancer cell line in 92 adult (8 weeks old) and 256 young (3–6 weeks old) nude mice. Ten million tumor cells were transplanted into orthotopic (duodenal lobe of the pancreas) and/or heterotopic positions (hepatic and subcutaneous) and data on operative mortality, effect of total body irradiation (TBI), tumor growth kinetics, and survival are presented comparing the two age groups. Operative mortality was due to anesthetic intolerance which was higher in the young mouse population (13.4% versus 5.7%). Adult mice withstood TBI (500 rad) without mortality but young mice were highly sensitive to radiation damage and their maximum tolerated dose (LD 50) was 425–450 rad. Subcutaneous tumors grew significantly more often in young compared to adult animals (97.9% versus 69%) and this finding was not affected by TBI (96.9% versus 75%), though tumors did appear more quickly after TBI. An average of 14.7 ± 2.8 days was required for the subcutaneous tumors to become macroscopically apparent in the adult population compared with 3.1 ± 0.8 days in the young mice. The largest subcutaneous tumor diameter 28 days following tumor implant averaged 9.3 ± 0.6 mm in the young animals and 5.5 ± 1.7 mm in the adult population ( P < 0.01). Treatment of young mice with human recombinant interleukin-2 (IL-2) (10,000 Units twice a day for 28 days) produced a 27% decrease in tumor growth. This effect was abolished by prior irradiation of the young mice with 375 rad TBI. Pancreatic tumor growth also occurred more consistently in young than in adult animals (91.2% versus 64.3%) and irradiation did not affect pancreatic tumor take in either group. Occasionally intrapancreatic tumor growth was associated with liver metastases in animals that were killed after 28 days (17.8% in young and 22.2% in adult animals). However, when more than 45 days elapsed before sacrificing the animals, the incidence of hepatic metastases increased to 57.1%. This was slightly less than the incidence of hepatic lesions found after direct injection of cancer cells into the liver by portal vein injection (71.4%). Direct extension of tumor into surrounding tissues was common with frequent involvement of the duodenum (83.7%), kidneys (30.6%), and other intraabdominal organs (43.9%). Survival was significantly longer in adult compared to young mice. All young mice that grew intrapancreatic tumors died within 3 months from the injection of tumor cells, while about 50% of the adult animals with documented pancreatic tumors survived up to 5 months. The model is an efficient means for the in vivo study of human pancreatic cancer and the autologous anti-tumor response can be controlled by the use of young and irradiated nude mice by methods described in this paper.