Effects of immunomodulatory oligonucleotides on pancreatic cell lines

Background. Pancreatic cancer is a devastating malignancy with a mortality rate almost identical with its incidence. Thus, the development of new therapeutic strategies for treating this cancer is absolutely required. A potential novel strategy is targeted immunotherapy. The recent discovery of Toll-like receptors (TLRs) provides new targets to specifically activate this immunity. Among TLRs, TLR9 is expressed by various normal and tumor cells and its activation by DNA containing unmethylated CpG motifs leads to a cascade of molecular events that culminate in the induction of several inflammatory mediators, such as cytokines and nitric oxide (NO). Aim. The study was performed to demonstrate the presence of TLR9 in four human pancreatic carcinoma cell lines (PCCs: PP78, PP109, PP161, and PP117) and to investigate whether its activation by selected oligodeoxynucleotides containing CpG motifs (CpG ODNs) could affect the in vitro characteristics of PCCs. Methods. TLR9 expression was assessed by using molecular (RT-PCR and/or real-time PCR, and DNA sequencing), and immunological assays (immunofluorescence and Western Blot analysis). Cell viability and cell cycle parameters were checked by trypan blue exclusion and FACS analysis, respectively. NO production was measured by the Griess reagent and cytokine production profiles were evaluated using commercial ELISA kits. Results. TLR9 mRNA and protein were both expressed at basal levels in all PCCs. CpG ODNs treatment of PP78 and PP109 PCCs increased the TLR9 expression, and it reduced significantly the cell proliferation. CpG ODNs also induced a delay in S-phase followed by a G0/G1 arrest and decreased the basal level of interleukin (IL)-8 in PP78 cells. In addition, a significant enhancement in NO production was observed in CpG-ODN treated cells. Conclusions. Our results indicate that TLR9 ligands produce an evident anti-proliferative effect in PCCs; such an effect might depend on the CpG-DNA induced modulation of endogenous mediators such as IL-8 and NO.