Locoregional IL-2 therapy in the treatment of colon cancer. Cell-induced lesions of a murine model

Abstract. Background: Local therapy with IL-2 may be very effective in the treatment of different forms of cancer. The aim of this study was to determine the effectiveness of IL-2 locoregional application in the treatment of colon cancer. Materials and Methods: Twenty eight syngenic BDIX rats were utilized in this study. The rats were divided into two groups of fourteen animals: group T (treatment) and group C ( control). All rats of both groups were injected, under the splenic capsule, with T 10 7 DHD/K12/ TRb neoplastic cells. Then, within and around the site of the previous inoculation, the T group was injected with 1 ml of glucosate solutions + 0.1% albumin (BSA) containing 2.5x10 6 IU of IL-2 ( Proleukin-Chiron), whereas the C group was injected with 1 ml of BSA alone. After three weeks, rats were sacrificed and the liver and spleen were removed. The following parameters were considered: volume and weight, neoplastic–non neoplastic tissue index of the spleen, mitotic index and vascular density of splenic and hepatic lesions. Results: All the studied parameters showed statistically significant differences in treated and untreated animals. Conclusion: This study of a murine model demonstrated that IL-2 locoregional therapy may be effective in the treatment of colon cancer. Surgical treatment is the primary therapy for solid tumors. However, a complementary therapy to surgery I necessary, particularly in an advanced tumor stage. Among complementary therapies, immunotherapy with interleukin (IL-2) seems to be the more promising. IL-2 as a therapeutic agent has been used in animal models as well as in human cancer therapy (1-6). IL-2, the main growth factor of CD8+ lymphocytes and natural killer (NK) cells, has been evaluated in patients with metastatic colorectal carcinoma but the results have not been conclusive (5). Den Otter et al. reported in a letter that, while they had no experience with IL-2 local treatment in colorectal cancer, they believed that at least a proportion of patients with colorectal cancer could benefit from local IL-2 therapy (7). Since then, other studies have been published demonstrating the effectiveness of IL-2 therapy in gastrointestinal tumors (8-11). The aim of this study in a murine model was to evaluate the effectiveness of IL-2 as an antiproliferative agent and in prevention of hepatic metastases when injected in sites that were previously inoculated with colorectal cancer cells. Materials and Methods Twenty eight syngenic BDIX rats (Charles River Laboratoires, Lecco, Italy) were utilized for the study, carried out according to international principles for Biomedical Research on Animals (US Department of Health and Human Science, National Institutes of Health, 1985). Two groups, T (treatment) and C (control), of 14 rats each were formed. Under intraperitoneal anesthesia with Nathiopental 1.25% at 40 mg/kg, a short midline laparotomy was performed in each rat of both groups and 0.5 ml of phosphate buffered saline (PBS) solution containing 10 7 DHD/K12/TRb neoplastic cells was injected under the spleen capsule, according to the technique used by Karube et al. (12). Rats in the T group were injected with 1 ml of glucosate solution +0.1% albumin (BSA) containing 2.5x10 6 IU of IL-2 (Proleukin, Chiron) within and around the previously inoculated site; rats in the C group were injected with 1 ml of BSA alone as placebo. After three weeks, rats were sacrificed and the liver and spleen were removed, weighed and fixed in formalin to evaluate the number, dimension and size (volume) of the cancerous lesions in the two groups and to perform a histological study. The following parameters were considered: weight, size, volume and neoplastic–non neoplastic tissue index of the spleen; spleen and hepatic mitotic index; peritoneal cancer index (PCI) according to a modified Sugarbaker's score (1= lesion of 1 mm; 2= from 1 to 5 mm; 3= up to 5 mm or confluent); vascular density (13). The vascular density of the lesions developed in treated and untreated rats was analyzed in sections of spleen stained for factor