Author:
Han Sang Jun,Sung Nuri,Wang Jin,O’Malley Bert W.,Lonard David M.
Abstract
AbstractBackgroundThe tumor immune microenvironment (TIME) generated by cancer-infiltrating immune cells has a crucial role in promoting or suppressing breast cancer progression. However, whether the steroid receptor coactivator-3 (SRC-3) modulates TIME to progress breast cancer is unclear. Therefore, the present study evaluates whether SRC-3 generates a tumor-promoting TIME in breast tumors using a syngeneic immune-intact mouse model of breast cancer.MethodsWe employed E0771 and 4T1 breast cancer in immune-intact syngeneic female C57BL/6 and BALB/c mice, respectively. SI-2, a specific small-molecule inhibitor of SRC-3, was administered daily (2.5 mg/kg) to E0771 and 4T1 breast tumor-bearing immune-intact mice. In addition, SRC-3 knockdown (KD)-E0771 and SRC-3 KD-4T1 cells and their parental breast cancer cells were injected into their syngeneic immune-intact female mice versus immune-deficiency mice to validate that the host immune system is required for breast tumor suppression by SRC-3 KD in immune-intact mice. Furthermore, tumor-infiltrating immune cells (such as CD4+, CD8+, CD56+, and Foxp3+ cells) in E0771 and 4T1 breast cancers treated with SI-2 and in SRC-3 KD E0771 and 4T1 breast cancers were determined by immunohistochemistry. Additionally, cytokine levels in SI-2-treated and SRC-3 KD E0771 breast tumors and their control cancers were defined with a Mouse Cytokine Array.ResultsSRC-3 inhibition by SI-2 significantly suppressed the progression of breast cancer cells (E0771 and 4T1) into breast cancers in immune-intact syngeneic female mice. SRC-3 KD-E0771 and -4T1 breast cancer cells did not produce well-developed tumors in immune-intact syngeneic female mice compared to their parental cells, but SRC-3 KD breast cancers were well developed in immune-defective host mice. SRC-3 inhibition by SI-2 and SRC-3 KD effectively increased the numbers of cytotoxic immune cells, such as CD4+ and CD8+ T cells and CD56+ NK cells, and Interferon γ (Ifng) in breast cancers compared to vehicle. However, SI-2 treatment reduced the number of tumor-infiltrating CD4+/Foxp3+ regulatory T (Treg) cells compared to vehicle treatment. In addition, SRC-3 inhibition by SI-2 and SRC-3 KD increased C-X-C motif chemokine ligand 9 (Cxcl9) expression in breast cancer to recruit C-X-C motif chemokine receptor 3 (Cxcr3)-expressing cytotoxic immune cells into breast tumors.ConclusionsSRC-3 is a critical immunomodulator in breast cancer, generating a protumor immune microenvironment. SRC-3 inhibition by SI-2 or SRC-3 KD activates the Cxcl9/Cxcr3 axis in breast tumors and enhances the antitumor immune microenvironment to suppress breast cancer progression.
Funder
National Cancer Institute
Eunice Kennedy Shriver National Institute of Child Health and Human Development
Publisher
Springer Science and Business Media LLC
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