Luciferase Reporter Cell Line - EO771

The tumor immune microenvironment (TIME) generated by tumor-infiltrating immune cells plays a crucial role in promoting or inhibiting breast cancer progression. However, it remains unclear whether steroid receptor coactivator 3 (SRC-3) promotes breast cancer progression by regulating TIME. Here, researchers used a homologous immunointact mouse breast cancer model to evaluate whether SRC-3 generates a tumor-promoting TIME in breast tumors. SI-2 inhibition of SRC-3 significantly suppressed the progression of breast cancer cells (E0771 and 4T1) to breast cancer in immunointact homologous female mice. Compared with parental cells, SRC-3 knockdown E0771 and 4T1 breast cancer cells did not form well-developed tumors in immunointact homologous female mice, but in immunodeficient host mice, SRC-3 knockdown breast cancer cells developed well. Compared to the vector control group, the inhibitory effects of SI-2 and SRC-3 KD on SRC-3 effectively increased the number of cytotoxic immune cells (such as CD4+ and CD8+ T cells and CD56+ NK cells) and interferon-γ (IFN-γ) in breast cancer tissue. However, compared to the vector control group, SI-2 treatment reduced the number of tumor-infiltrating CD4+/Foxp3+ regulatory T (Treg) cells. Therefore, SRC-3 is a key immunomodulatory factor in breast cancer, generating a pro-tumor immune microenvironment. The inhibitory effects of SI-2 or SRC-3 KD on SRC-3 can activate the Cxcl9/Cxcr3 axis in breast tumors, enhance the anti-tumor immune microenvironment, and thus inhibit the progression of breast cancer.

Here, researchers constructed luciferase-labeled E0771 cells for non-invasive assessment of tumor growth in mice. Comparative analysis of luciferase activity images showed that E0771 cells formed stable mammary tumors in syngeneic C57BL/6J mice treated with the vector (Figure 1A, B). However, SI-2 treatment significantly reduced luciferase activity in E0771 mammary tumors compared to vector-treated tumors (Figure 1A, B). Therefore, SI-2 treatment effectively inhibited the growth of E0771 mammary tumors in immunocompetent syngeneic C57BL/6J mice. All E0771 breast cancer-bearing mice treated with the vector were sacrificed 35 days after cancer cell injection, as the tumors had reached their maximum volume (diameter > 20 mm) at this time (Figure 1C, D). However, compared to the vector control group, the SI-2 (2.5 mg/kg) treatment group had smaller tumors, but the tumor diameter did not reach its maximum value (< 10 mm) on day 35 after cancer cell injection (Figure 1C, D). Hematoxylin and eosin (H&E) staining showed that the tumor cell density in the SI-2 treatment group was lower than that in the vector control group because no ordered structures were detected in the tumor tissue of the SI-2 treatment group (Figure 1E). In summary, these results confirm that SI-2 treatment can effectively inhibit the growth of E0771 mammary tumors in immune-intact C57BL/6J mice compared with the vector control group.

Figure 1. SI-2 suppresses the growth of E0771 mammary gland tumors in C57BL/6J mice. (Han S J, et al., 2022)