Abstract 1484: SCD-1 blockade sensitizes triple negative breast cancer to immune checkpoint inhibition
Authors: Vivekanandhan Sneha , Trynda Justyna , Marlow Laura A. , shreeder Barath , Miller James L. , Kase Adam M. , Tan Winston , Knutson Keith L. , Copland John A. 
Published: July 2021

The increase in fatty acid metabolism is a hallmark of cancer. Stearoyl CoA desaturase (SCD) is an endoplasmic reticulum (ER) enzyme that catalyzes D9 cis désaturation of fatty acyl-CoA substrates. One of its isoforms, SCD1, is overexpressed in several cancers including breast cancer. The higher expression of SCD1 in breast cancer patients correlates with significantly shorter relapse-free and overall survival rates, indicating that SCD1 may be a therapeutic target. We have previously developed and published a novel SCD1 inhibitor, SSI4. Metabolic reprogramming facilitates tumor growth by promoting immune suppression in tumors. Fundamental metabolic processes like fatty acid (FA) metabolism are involved in T cell activation and differentiation and their modulation can differentially affect the development of T helper cell lineages. FA synthesis and oxidation are essential for the development and functioning of CD8+ T memory cells and are contributing factors that influence CD4+ T effector and Treg cell development. These associations between metabolism and immune cells lead us to our hypothesis that aberrant de novo lipogenesis is linked to immune suppression. Thus, SCD1 inhibitors should increase anti-tumor immunity. We evaluated the effect of SSI4-mediated SCD1 inhibition in two mouse triple negative breast cancer cell lines. The data showed that SSI4 stimulates calreticulin (CRT) translocation to cell membrane. CRT is an ER resident protein that translocates to the cell surface under ER stress conditions. Cell surface expression of CRT is known to induce immune responses including phagocytosis, translocation of cancer antigen to the cell surface, and apoptosis. We are currently studying the effect of CRT translocation in our model. A major focus of our project is to assess the efficacy of combination treatment of SSI4 and an immune checkpoint blockade. To this end, this combination therapy synergistically blocked E0771 tumor growth in vivo. Further, to understand the immune responses generated, we performed immunohistochemical analysis of the tumors (day 20 post-treatment) indicating that the combination therapy resulted in higher membrane localized CRT, supporting our rationale that CRT translocation is involved in mediating the anti-tumor responses. Flow cytometry analysis indicated that the combination treatment increased immune cell infiltration. Specifically, SSI4 treatment induced infiltration of double negative T cells, natural killer cells and macrophages, suggesting that it promoted a pro-inflammatory immune response. SSI4 treatment down regulated immune suppressive cells including Tregs, dendritic cells and mesenchymal derived stem cells. The response of cancers with low and intermediate tumor mutational burden such as breast cancer to immune checkpoint inhibition is limited. Our data indicates that combination treatment of SSI4 and anti PD1 is a promising therapeutic strategy.

Citation Format: Sneha Vivekanandhan, Justyna Trynda, Laura A. Marlow, Barath shreeder, James L. Miller, Adam M. Kase, Winston Tan, Keith L. Knutson, John A. Copland. SCD-1 blockade sensitizes triple negative breast cancer to immune checkpoint inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1484.