Abstract 149: The roles of PIM1 and PIM2 kinases in the progression and metastasis of triple negative breast cancer

Abstract Breast cancers are often evaluated by their expression of estrogen, progesterone and HER2/Neu receptors. Triple negative breast cancers (TNBC), which do not have upregulation of any of these receptors, lack directed therapies and therefore, are associated with a worse prognosis. The lack of directed therapies for TNBC and high incidence of relapse and drug resistance found in all breast cancers underscores the need for identification of additional therapeutic targets. The analysis of gene expression data revealed that PIM1 and PIM2 kinases are upregulated in triple negative breast cancer. PIM kinases are a family of serine/threonine kinases that activate cell division, promote cell growth, and inhibit apoptosis. Due to PIM1/2’s effect on these cellular processes and PIM1/2 being upregulated in TNBC, we hypothesized that PIM1/2 play an important role in progression of triple negative breast cancer. Knockdown of PIM1 significantly inhibited the proliferation, migration, and invasion of TNBC cells, including MDA-231, BT-20, HCC-1806, and MDA-468 cells. To study the in vivo roles of PIM1/2 in breast cancer progression and metastasis, we crossed the highly metastatic MMTV-PyMT breast cancer mouse model with PIM1/2 knockout mice. Deletion of PIM1 or PIM2 alone significantly inhibited tumor growth and reduced lung metastasis in these mice. Dual deletion of PIM1 and PIM2 significantly reduced tumor growth and almost completely blocked lung metastasis in these mice. A major advantage of the MMTV-PyMT model over xenograft models is that the immune system is intact in these mice, and that enabled us to perform immune cell profiling on the tumors. Tumor associated macrophages (TAMs) have been shown to promote tumor metastasis and are a poor prognostic marker for TNBC. Deletion of PIM1 alone and combined PIM1 and PIM2 deletion resulted in a significant reduction in the number of TAMs, indicating PIM1/2 play a significant role in regulating the immune milieu of these tumors. To understand the underlying mechanism by which PIM1 and PIM2 contribute to these processes, we performed biochemical analysis. Western blot analysis of PIM1 knockdown in MDA-231 cells showed a decrease in phosphorylation of CXCR4, S6 ribosomal protein, and 4EBP1 and increased expression of cell cycle regulator p27. Additionally, we performed RNA-seq analysis to identify which pathways were affected by PIM1/2 deletion in MMTV-PyMT tumors. GSEA analysis showed a significant enrichment of genes related to inflammatory response, extracellular matrix, EMT and metastasis in PyMT tumors and those were significantly reduced in PIM1/2 double knockout tumors. These results suggest that PIM1 and PIM2 play a significant role in the progression and metastasis of triple negative breast cancer and indicate that PIM1/2 inhibition could be a useful therapeutic approach for TNBC. Citation Format: Patrick Faughnan, Golam Mohi, Chandrajeet Singh. The roles of PIM1 and PIM2 kinases in the progression and metastasis of triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 149.