Abstract 2680: Knockout on enhancer of zeste homolog 2 in triple-negative breast cancer model alters immune signaling and decreases tumor progression and lung metastasis

Abstract Triple-negative breast cancer (TNBC) is an aggressive and highly metastatic subtype of breast cancer. Lack of known targets, patient-to-patient variations of target antigens and resistance to immune checkpoint inhibitors make TNBC one of the most challenging cancers to treat. TNBC is enriched in tumor-infiltrating neutrophils (TINs). TINs are key contributors to pro-tumorigenic processes linked to “immunologically cold” tumors, in part by preventing recruitment of T-lymphocytes (TILs). Prior studies identified the Enhancer of zeste homolog 2 (EZH2) as a prominent methyltransferase expressed in primary and metastatic TNBC cells. EZH2 is an upstream regulator of the stimulator of interferon genes (STING), a critical innate sensor mediating anti-tumor responses that is inhibited in cold tumors. To date, EZH2/STING signaling in TINs is relatively unknown. Here, we hypothesized that EZH2 inhibition and subsequent STING activation could exert anti-tumor activity by modulating TINs. We derived EZH2-knockout (KO) and EZH2-overexpressed (OX) cell lines from the well-established 4T1 TNBC mouse cell line. We demonstrate a 10-fold decrease in lung metastasis and significant reduction of 4T1 EZH2 KO tumor growth compared to the parent 4T1 cell line. Concomitantly, the TIN: TIL ratio was significantly reduced in 4T1 EZH2 KO vs. control tumors. Overexpression of EZH2 in 4T1 TNBC cells did not affect the primary tumor growth or lung metastasis. A therapeutic study using the repeated injection of the STING agonist MSA-2 after tumor engraftment in vivo also demonstrated a decrease in lung metastasis and tumor growth in MSA-2 vs. vehicle injection with both 4T1 parent and EZH2 KO cell lines. Together, our findings suggest a key role for STING pathway modulation and TIN/TIL poise in primary TNBC progression and lung metastasis. Citation Format: Lenore Monterroza, Maria Parrilla, Sarah Samaranayake, Dormarie Rivera, Brian Dobosh, Periasamy Selvaraj, Rabindra M. Tirouvanziam. Knockout on enhancer of zeste homolog 2 in triple-negative breast cancer model alters immune signaling and decreases tumor progression and lung metastasis abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2680.