Abstract: Objective: To observe the anti-tumor effect of different doses of ¹²⁵I seed implantation in the human breast cancer bearing nude mice, and to explore the mechanism. Methods: The healthy BALB/c nude mice were selected,and the human breast cancer HMLER90hi cells were transplanted into the fourth breast fat pad to establish the tumor-bearing models of nude mice. After successful modeling, 40 nude mice were randomly divided into:blank control group and low, middle and high doses of ¹²⁵I particle groups,and there were 10 rats in each group. The mice in blank control group were only implanted with one blank particle (without radioactive elements); the mice in low, middle and high doses of ¹²⁵I particle groups were implanted with 1.48×10^-7, 2.22×10^-7 and 2.96×10^-7 Bq ¹²⁵I particles, respectively, according to the Paris system principle. The volumes and weights of tumor of the mice in various groups were detected,and the inhibitory rates of growth of tumor of the mice in various groups were calculated.The levels of telomerase protein in tumor tissue of the mice in various groups were determined by ELISA method,the expression levels of CD90 and granulocyte-macrophage colony stimulating factor (GM-CSF)mRNAin the HMLER90hi cells of the mice in various groups were detected by qRT-PCR method. Results: At 7, 14 and 28 d after implantation of ¹²⁵I particles, the weights and volumes of tumor of the mice in different doses of ¹²⁵I particle groups were decreased compared with blank control group(P<0.05 or P<0.01), and the inhibitory rates of growth of tumor of the mice were significantly increased (P<0.05 or P<0.01);the ELISA results showed that compared with blank control group, the levels of telomerase protein in tumor tissue of the mice in different doses of ¹²⁵I particle groups were significantly decreased(P<0.05 or P<0.01);the qRT-PCR results showed that compared with blank control group, the expression levels of CD90 and GM-CSF mRNA in the HMLER90hi cells of the mice in different doses of ¹²⁵I particle groups were significantly decreased(P<0.05 or P<0.01). Conclusion: Different doses of ¹²⁵I particles can inhibit the proliferation of breast cancer in the nude mice, and its mechanism may be related to the inhibition of expressions of CD90 and GM-CSF mRNA in tumor-bearing tissue.

Key words: ¹²⁵I particle, HMLER90hi cells, granulocyte-macrophage colony stimulating factor, CD90