Abstract: Objective To observe the effect of astaxanthin on radiotherapy sensitivity of lung cancer A549 cells transplanted in nude mice. Methods Twenty BALB/c nude mice were divided into four groups: control group (mice were gavaged with pure water containing with 10% DMSO), astaxanthin group (mice were gavaged with astaxanthin suspension containing with 10% DMSO, astaxanthin was given to mice with the dose of 50 mg/kg on the first day, and every other day in the following days with a total of 7 times), radiotherapy group (mice were gavaged with pure water containing with 10% DMSO, the tumor site was given local radiotherapy with a dose of 5 Gy per time and the total dose was 15 Gy) and combination group (mice were given 50 mg/kg astaxanthin and radiotherapy with 15 Gy total irradiated dose). When the minor axis of the tumor reached 5 mm we began experiment. Tumor growth curve was measured by detecting the line of apsides every other day. Mice were killed on the second day after the last time of astaxanthin administration. Weights of tumor were measured by a balance and then tumor mass was processed into paraffin sections. Expressions of proliferating tumor cell antigen Ki-67, phosphorylated-signal transducers and activators of transcription (p-STAT3), and cell apoptosis (measured by terminal deoxynucleotidyl transferase mediated dUTP nick- end labeling, Tunnel) were detected by immunohistochemistry. Results Compared with control group, the transplanted tumor growth rate slowed down in other three groups (P < 0.05), and tumor growth was the most slowly in the combination group. Tumor weight, Ki-67 and p-STAT3 expressions were decreased gradually in turn in control group, astaxanthin group, radiotherapy group and combination group. The anti- tumor rate and percentage of cell apoptosis were increased gradually in turn. There was significant difference between groups by multiple comparison statistics(P < 0.05). Conclusion Astaxanthin enhances radiotherapy sensitivity of human lung cancer A549 cells in nude mice by down-regulating the expression of p-STAT3.

Key words: lung neoplasms, carcinoma, radiation tolerance, radiotherapy, mice, nude, Astaxanthin, lung cancer A549 cell