Molecular Targeting Of Toll-Like Receptor 9 With Cpg Oligodeoxynucleotides (Odn) For Enhancement Of Tumor Radioresponse

CpG oligodeoxynucleotides (ODNs) are synthetic DNA sequences containing unmethylated cytosine-guanine motifs having potent immunomodulatory and anti-tumor effects. Via Toll-like receptor 9-agonism of dendritic cells and B-cells, CpG ODNs induce cytokines, activate natural killer cells, and elicit vigorous T-cell responses that lead to significant anti-tumor effects. Based on known CpG (ODN) mechanisms and on previously demonstrated in vivo radiopotentiation by bacterial immunotherapeutic agents, we tested CpG ODN-1826 for its ability to enhance tumor response to radiotherapy. We have already shown that this highly innovative new approach to combined modality therapy dramatically improves tumor response to single dose radiotherapy, enhancing tumor growth delay of a mouse fibrosarcoma by a factor of about 2.6 and reducing the TCD50 (radiation dose required to cure 50% of treated tumors) by a factor of 1.93 (L Milas et al, Cancer Res., 2004). The present investigation extends these in vivo preclinical findings to more clinically relevant fractionated radiotherapy treatment protocols in combination with CpG ODN. C3Hf/Kam/Law mice bearing a syngeneic immunogenic sarcoma (FSa) received single dose or fractionated irradiation to the tumor bearing leg with or without CpG (ODN). A control ODN with no CpG motif was used as an inactive control. CpG (ODN) was given sc peritumorally 3 x 100 microgram per mouse at: 6mm diameter, at 8mm diameter when tumors were irradiated, and 7 days later. Tumor growth delay (TGD) and tumor cure were treatment endpoints. A single radiation dose of 20 Gy or 20 Gy in 2 Gy-fractions were used. Fractionated irradiation was delivered twice daily (6–7 h apart) for 10 doses in 5 days. CpG (ODN) strongly enhanced the effect of single and fractionated radiation by factors of 2.49 and 6.91, respectively (Table). Importantly, neither CpG (ODN) nor radiation alone produced tumor cure whereas the combined treatment cured 60% for single dose and 44% for fractionated treatment. Based on these promising results we initiated full radiation dose response studies covering a range of 1–9 Gy to more accurately quantify the TCD50 (dose required to cure 50% of the tumors) in combination with CpG (ODN). Overall, results showed that CpG (ODN) strongly enhanced radioresponse measured by both TGD and tumor cure. Therefore, CpG (ODNs) may have strong potential to improve the efficacy of clinical radiotherapy.