Abstract 2700: Sulindac reverses an immunosuppressive tumor microenvironment associated with metastatic mammary tumors in obese mice
Authors: McDonell Shannon B. , Eisenbeis Lydia K. , Walens Andrea N. , Cozzo Alyssa J. , Hursting Stephen D. 
Published: July 2021

Abstract
Obesity is an established risk factor for several breast cancer (BC) subtypes. Obese BC patients also show poorer response to therapy, increased metastases, and increased mortality. While high levels of inflammation are thought to be a driver for BC metastasis, it is unknown how chronic exposure to low levels of obesity-associated inflammation contributes to BC progression and metastasis. We previously showed that treatment with the non-steroidal anti-inflammatory drug (NSAID) Sulindac (140 ppm mixed into control [10% kcal/fat] or diet induced obesity [DIO, 60% kcal/fat] diets) offset both the pro-growth and pro-metastatic effects of obesity on BC using three different mouse models of metastatic BC - basal-like E0771, and claudin-low metM-Wntlung and metM-Wntliver. To determine the effect of Sulindac treatment on the tumor microenvironment, we conducted gene expression microarray analysis on tumors from mice in all four diet groups (Control, Control+Sulindac, DIO, and DIO+Sulindac). Ingenuity Pathway Analysis revealed significant decreases (q&lt;0.01) in several pathways relating to immune function in DIO tumors that was restored in DIO+Sulindac tumors. Specifically, CD28 signaling and dendritic cell activation were significantly downregulated in DIO tumors compared to all other diet groups, while markers of T cell exhaustion were up in DIO tumors. To further explore Sulindac-associated effects on immune and cancer cell gene expression, we performed single-cell RNA-seq on E0771 tumors. Preliminary analyses showed marked differences in both tumor and immune populations between control, DIO, and DIO+Sulindac mice. Of the top 10 significant (q&lt;0.01) genes upregulated in DIO vs Control tumor cells, 7 have been previously shown to be drivers of breast cancer progression or metastasis. Similarly, 7 of the top 10 genes upregulated in DIO+Sulindac compared to DIO tumor cells have been previously shown to have tumor suppressive functions or limit progression of cancer. Immune analyses showed fewer immune cells in DIO tumors, specifically myeloid (CD11b+) and CD8+ T cells, which were both partially restored in the DIO+Sulindac tumors. Finally, T cell receptor (TCR) analysis showed decreased TCR diversity in DIO T cells compared to control that was restored in DIO+Sulindac T cells. Taken together, these preclinical findings indicate that obesity-driven mammary tumor progression and metastatic burden are associated with an immunosuppressive tumor microenvironment that is largely reversed by Sulindac treatment. This suggests treatment with NSAIDs like Sulindac should be further assessed as a possible strategy for decreasing immunosuppression and improving outcomes in obese breast cancer patients.
This research was supported by R35CA197627 to S.D. Hursting and T32LM012420 and F30CA225142 to S.B. McDonell.
Citation Format: Shannon B. McDonell, Lydia K. Eisenbeis, Andrea N. Walens, Alyssa J. Cozzo, Stephen D. Hursting. Sulindac reverses an immunosuppressive tumor microenvironment associated with metastatic mammary tumors in obese mice [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 2700.