Abstract 5067: Suppression of tumorigenicity and metastasis of triple-negative breast cancer (TNBC) by c-Jun N-Terminal Kinase (JNK) inhibitor via reversing immunosuppressive tumor microenvironment (TME)
Authors: Semba Takashi , Xie Xuemei , Cohen Evan N. , Reuben James M. , Dalby Kevin N. , Wang Xiaoping , Ueno Naoto T. 
Published: September 2020

Immune checkpoint inhibitors (ICIs) is now a standard of care for metastatic TNBC, the most aggressive subtype of breast cancer. However, rates of tumor response to ICIs are low. Evidence suggests that an immunosuppressive TME weakens the efficacy of ICIs. We previously showed that JNKs can regulate migration, invasion, and stemness of TNBC, and JNKs are known to mediate inflammatory signaling. However, the role of JNK signaling in the immunosuppressive TME of TNBC is unclear. We studied the role of JNK signaling in modulating the immunosuppressive TME of TNBC by treating syngeneic TNBC mice with a JNK inhibitor and determining the chemokine profiles related to the aggressive nature of TNBC.

Method: The effect of JNK inhibitor, JNK-IN-8, on TNBC tumor growth and lung metastasis was measured in 4T1.2 syngeneic mouse model. Cytokine expression in tumor tissues from vehicle- and JNK-IN-8-treated mice was measured by antibody array and qPCR. Tumor-infiltrating immune cells were measured by flow cytometry. For a rescue experiment, 4T1.2 mice were treated with JNK-IN-8 and administered either PBS or recombinant mouse CCL2 via an osmotic pump. In addition, CCL2 levels were measured in sera of 46 TNBC patients by Luminex assay.

Results: JNK-IN-8 treatment significantly reduced tumor growth (p = 0.0065), lung metastasis (p = 0.0364), and tumor-infiltrating leukocytes, including regulatory T cells (Tregs) (p = 0.0469) and myeloid-derived suppressor cells (MDSCs) (p = 0.0143), while increasing infiltration of CD8+ T cells (p = 0.0152). JNK-IN-8 also reduced levels of chemokines, including CCL2, CCL11, CCL19, CCL21, CCL22, and CXCL1, and increased levels of cytokines involved in T cell activation and effector function, including IL-2 and IFN-γ. CCL2 is involved in attracting Tregs, MDSCs, and other cells. Indeed, systemic CCL2 administration mitigated the inhibitory effect of JNK-IN-8 on tumor-infiltrating Tregs and MDSCs, TNBC tumor growth, and lung metastasis in the 4T1.2 mouse model. Indeed, in patient serum, the median CCL2 level was significantly higher in patients with metastatic TNBC than in patients with non-metastatic TNBC (988.72 pg/mL vs 414.86 pg/mL, p = 0.0053), and a higher CCL2 level was associated with poor progression-free and overall survival (univariate Cox, p = 0.004 and p = 0.008).

Conclusion: We have determined that the CCL2 is one of the important critical cytokines contributing to the immunosuppressive TME of TNBC. Our data suggest that JNK inhibition can improve an immunosuppressive TME through CCL2 reduction and may have the potential to boost the efficacy of ICIs. Studies of the therapeutic efficacy of JNK inhibitor-ICI combination treatment in syngeneic mouse models are in progress.

Citation Format: Takashi Semba, Xuemei Xie, Evan N. Cohen, James M. Reuben, Kevin N. Dalby, Xiaoping Wang, Naoto T. Ueno. Suppression of tumorigenicity and metastasis of triple-negative breast cancer (TNBC) by c-Jun N-Terminal Kinase (JNK) inhibitor via reversing immunosuppressive tumor microenvironment (TME) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5067.