Dose response of CpG ODN1826 and its combination effect with X-ray irradiation on Lewis lung cancer in mice

Objective: To explore the combination effect of unmethylated cytosine-phosphate-guanine oligodeoxynucleotide (CpG ODN) 1826 and X-rays on Lewis lung cancer in mouse and the dose response of CpG ODN. Methods: The tumor-bearing mouse model was established by injecting Lewis lung cancer cells into the right infra-axillary dermis of mouse.Sixty-four C57BL /6 J mice were evenly randomized into eight groups with 8 mice each: control group, IR group, CpG OND1826 0.15 mg group, CpG OND1826 0.3 mg group, CpG OND1826 0.45 mg group, CpG OND1826 0.15 mg + IR group, CpG OND1826 0.30 mg + IR group, and CpG OND1826 0.45 mg + IR group. On the 1st, 2nd, and 9th days, CpG ODN was injected into mouse. After 3 hours of injection, the mice were start to irradiate with X-rays once a day on the 2nd-6th days, and the total dose was 12.50 Gy. Tumor growth and TGD were measured, and the apoptosis of tumor cells were examined with TUNEL. Results: The Lewis lung cancer-bearing model was successfully established in all mice. Under the treatments of CpG OND1826 and irradiation, the tumor volumes were smaller than that of control group, and the tumor volumes of CpG OND1826 0.45 mg + IR group was the smallest. TUNEL results revealed that the apoptosis rate were (2.40 ± 0.51)% in control group, (5.62 ±0.50)% in IR, (7.13±0.83)% in CpG OND1826 0.15 mg, (11.63±1.06)% in CpG OND1826 0.3 mg, (19.13 ±0.83)% in CpG OND1826 0.45 rag, (12.88±0.83)% in CpG OND1826 0.15 mg + IR,(20.57±2.37)% in CpG OND1826 0.3 mg + IR, and (28.17 ±3.31)% in CpG OND1826 0.45 mg + IR group, and thus the apoptosis rate of every therapy group was higher than that in control (t=11.15, 7.91, 17.82, 39.48, 24.73, 16.61 and 17.05, P<0.05). The apoptosis rates of CpG ODN1826 plus X-ray irradiation group were significantly higher than those in IR alone (t=13.78, 15.08 and 17.47, P<0.05) or CpG ODN group (t=18.53, 9.66 and 7.51, P<0.05). Conclusions: CpG ODN1826 can dramatically increase the efficiency of radiotherapy by inhibiting tumor growth and promoting tumor apoptosis. (authors)