Abstract 2989: PIM1 contributes to tumor progression, immune evasion and metastasis of triple-negative breast cancer

Abstract Triple-negative breast cancer (TNBC), which is characterized by the absence of expression of estrogen, progesterone and HER2/Neu receptors, is the most aggressive subtype of breast cancer and associated with poor prognosis. Due to the absence of definitive molecular targets, chemotherapies are commonly used to treat TNBC, but these patients eventually develop resistance to chemotherapies. Therefore, there is a critical need to develop novel targeted therapies for TNBC. Analysis of the TCGA gene expression datasets and CCLE breast cancer cell line database revealed that PIM1 expression is significantly elevated in TNBC patients and TNBC cell lines. We also observed increased levels of PIM1 expression in metastatic breast cancer patients. Furthermore, high expression of PIM1 is associated with poor survival in TNBC patients. PIM1 belongs to the PIM family of serine/threonine kinase that controls cell growth and survival. Depletion of PIM1 by shRNA-mediated knockdown or CRISPR/Cas9-mediated genome editing significantly reduced the proliferation, migration, invasion and 3D tumor sphere formation of TNBC cells. To study the in vivo roles of PIM1 in breast cancer progression and metastasis, we crossed the MMTV-PyMT metastatic breast cancer mouse model with Pim1 knockout mice. Genetic ablation of Pim1 significantly inhibited breast tumor growth and reduced lung metastasis in these mice. Treatment of TP-3654, a novel second generation PIM1 kinase inhibitor, also significantly reduced proliferation, migration, invasion and tumor sphere formation in TNBC cells, and reduced breast tumor growth and lung metastasis in MMTV-PyMT mice. Genetic deletion or pharmacologic inhibition of Pim1 also resulted in a significant reduction of tumor-associated macrophages (TAMs) and cancer stem cells (CSC) while increased the infiltration of cytotoxic and helper T cells in the mammary tumors of MMTV-PyMT mice, suggesting a role of Pim1 in the maintenance of tumor microenvironment and immune evasion. Mechanistically, we show that deletion or inhibition of PIM1 significantly inhibited the activation of mTORC1 signaling pathway and reduced the expression of Slug, Vimentin and c-Met in TNBC cells. Additionally, we performed RNA-sequencing analysis on MDA-231 TNBC cells without or with PIM1 deletion or TP-3654 treatment to identify which pathways were affected by PIM1 deletion or inhibition. Gene Set Enrichment Analysis (GSEA) revealed significant downregulation of genes related to cell proliferation, translation, EMT and metastasis in PIM1-deleted or TP-3654-treated TNBC cells compared to control TNBC cells. Collectively, our results suggest that PIM1 plays an important role in tumor progression, immune evasion and metastasis of TNBC, and inhibition of PIM1 with TP-3654 might be potentially useful for treatment of TNBC. Citation Format: Chandrajeet Singh, Patrick Faughnan, Wasif A. Mohi, Bao Le, Jason M. Foulks, Golam Mohi. PIM1 contributes to tumor progression, immune evasion and metastasis of triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2989.