Targeting the nuclear LSD1 axis reduces stem-like mesenchymal signatures and reinvigorates dysfunctional T cells in triple-negative breast cancer

Abstract

Lysine specific demethylase 1 (LSD1) is a key eraser enzyme critical in breast cancer metastasis and recurrence. We have recently shown that nuclear LSD1 phosphorylated at serine 111 (nLSD1p) is critical for the development of breast cancer stem cells (CSCs), a subpopulation of malignant cells implicated in metastasis and therapeutic resistance. In addition, we have previously shown that the highly selective catalytic inhibitors GSK2879552 (GSK) and ORY-1001 (Oryzon) target LSD1 exclusively via the flavin adenine dinucleotide (FAD) domain. To date, these FAD-specific inhibitors have shown disappointing efficacy in the clinical treatment of solid tumours such as triple-negative breast cancer (TNBC). In this thesis, we propose that GSK and Oryzon have limited therapeutic impact because they target the FAD domain alone. Given the importance of nLSD1p in metastatic breast cancer, we suggest that selectively targeting the nuclear domain of LSD1 is required to improve clinical responses in TNBC patients. We show that circulating tumour cells (CTCs) isolated from immunotherapy-resistant metastatic melanoma patients express high levels of nLSD1p compared to responding metastatic melanoma patients, and furthermore that nLSD1p is associated with increased co-expression of critical stem-like, mesenchymal markers. For the first time, we show that targeting nLSD1p with our novel selective nLSD1 inhibitors better inhibits stem-like mesenchymal signatures and cell viability in TNBC and immunotherapy-resistant cancer cell lines compared to traditional FAD-specific or dual nuclear LSD1 catalytic inhibitors such as GSK and phenelzine. In addition, nLSD1p inhibition significantly reduces CSC signatures in primary tumours and infiltrating tumour cells in 4T1 tumour-bearing mice. Furthermore, we show that targeting LSD1p via the nuclear axis induces interferon-γ, tumour necrosis factor-α-expressing CD8+ T cell infiltration and globally reinvigorates immune transcription pathways in 4T1 immunotherapy-resistant mice, pathways which are conserved in control HIV-infected patients. For the first time we discover that nLSD1 inhibition establishes transcriptional memory responses in a human metastatic breast cancer CD8+ T cell model and an in vitro model of T cell memory. Overall, dual inhibition using immunotherapy combined with LSD1 epigenetic inhibitors that specifically target the nLSD1p axis is required to reduce metastatic CSC signatures and reinvigorate dysfunctional T cell responses in TNBC

Date of Award	2020
Original language	English
Supervisor	Sudha Rao (Supervisor) & Rachel DAVEY (Supervisor)