CpG-Oligonukleotide hemmen das Wachstum orthotoper Pankreaskarzinome auch im immundefizienten Mausmodell

Abstract

Background/Aim: Significant inhibitory effects on tumor growth have been demonstrated for modified oligodeoxynucleotides (ODN) in preclinical systems. This was also shown for CpG-ODN in an immune competent subcutaneous tumor model. The object was now to investigate whether these effects were also reproducible for pancreatic cancer in an orthotopic immune deficient model. Methodology: For in vitro analysis in PancTul cells, DNA synthesis was assessed by [³H]-thymidine-incorporation, a colorimetric cell viability assay (easy4you™-Assay) was employed, and DNA fragmentation as an indicator for cell death was analysed (JAM-[³H]-thymidine-incorporation assay). Cell cycle analysis was carried out by PI-FACS-analysis. In vivo testing was done in an orthotopic pancreatic xenotransplantation model using SCID beige as well as nude mice. ODN employed were CpG-1826 and a random control ODN which were applied intraperito-neally. Results: In vitro, CpG-1826 and control-ODN induced an inhibition of DNA synthesis by about 40%, but did not alter cell viability in Panc-Tul cells. Incubation of tumor cells with conditioned medium from human dermal fibroblasts, treated with CpG-ODN lead to a further reduction of DNA-synthesis. In vivo CpG-1826 proved to have a significant growth inhibitory effect (up to 50%) when compared to controls treated by saline or control-ODN. This was accompanied with a seven fold splenomegaly and hepatomegaly of 50%. The reduction of tumor weight by CpG-1826 was only slightly more pronounced in nude compared to SCID beige mice. Conclusion: CpG-1826 induced significant growth inhibitory effects on orthotopic xenotransplanted pancreatic tumours in immune deficient mice. Since in vitro results indicate an effect of conditioned media of fibroblasts on tumor cells and since relevant immunological effector cells are lacking in the animal models employed, our data suggest that tumor-stroma-interactions might be involved in CpG-induced therapeutic effects on solid tumours in immune deficient mice.