LSD1 inhibition exerts its antileukemic effect by recommissioning PU.1- and C/EBPα-dependent enhancers in AML

Abstract

Epigenetic regulators are recurrently mutated and aberrantly expressed in acute myeloid leukemia (AML). Targeted therapies designed to inhibit these chromatin-modifying enzymes, such as the histone demethylase lysine-specific demethylase 1 (LSD1) and the histone methyltransferase DOT1L, have been developed as novel treatment modalities for these often refractory diseases. A common feature of many of these targeted agents is their ability to induce myeloid differentiation, suggesting that multiple paths toward a myeloid gene expression program can be engaged to relieve the differentiation blockade that is uniformly seen in AML. We performed a comparative assessment of chromatin dynamics during the treatment of mixed lineage leukemia (MLL)-AF9-driven murine leukemias and MLL-rearranged patient-derived xenografts using 2 distinct but effective differentiation-inducing targeted epigenetic therapies, the LSD1 inhibitor GSK-LSD1 and the DOT1L inhibitor EPZ4777. Intriguingly, GSK-LSD1 treatment caused global gains in chromatin accessibility, whereas treatment with EPZ4777 caused global losses in accessibility. We captured PU.1 and C/EBPα motif signatures at LSD1 inhibitor-induced dynamic sites and chromatin immunoprecipitation coupled with high-throughput sequencing revealed co-occupancy of these myeloid transcription factors at these sites. Functionally, we confirmed that diminished expression of PU.1 or genetic deletion of C/EBPα in MLL-AF9 cells generates resistance of these leukemias to LSD1 inhibition. These findings reveal that pharmacologic inhibition of LSD1 represents a unique path to overcome the differentiation block in AML for therapeutic benefit.

LSD1/KDM1A, a Gate-Keeper of Cancer Stemness and a Promising Therapeutic Target

“…Interestingly, LSD1 pharmacological inhibition phenocopied the knockdown effects in human patient AML cells and murine models, and it also prevented the establishment of the disease, upon murine MLL-AF9 AML cell transplantation into sub-lethally irradiated CD45.1 + congenic mice [84]. In line with these results, a recent work by Cusan et al showed that LSD1 inhibition induced global accessibility onto dynamic sites of chromatin and occupancy by the myeloid transcription factors PU.1 and C/EBPα in murine MLL-F9 cells, leading to premature developmental arrest at the stage of granulocyte-macrophage progenitor [85]. Both of these studies [84,85] underlined the fact that LSD1 attenuation released LSCs from this "premature" differentiation arrest and sensitized them to anti-cancer treatments with promising results.…”

Phase I, Open-Label, Dose-Escalation Study of the Safety, Pharmacokinetics, Pharmacodynamics, and Efficacy of GSK2879552 in Relapsed/Refractory SCLC

“…[12][13][14] KDM1A is overexpressed in primary SCLC, 15 and its inhibition in acute myeloid leukemia (AML) has been shown to relieve the differentiation block, thereby exerting an antileukemic effect and sensitizing AML cells to anticancer therapy. 16,17 Furthermore, inhibition of KDM1A provided an antileukemic effect in secondary engraftment models, indicating an effect on the leukemiainitiating cell population and further suggesting a role for KDM1A in the self-renewal of cancer stem cells. 18 Both SCLC and AML are poorly differentiated tumors 19,20 ; thus, inhibition of KDM1A may invoke a similar differentiation mechanism in SCLC.…”

Leukemia cell of origin influences apoptotic priming and sensitivity to LSD1 inhibition

“…One well-characterized consequence of LSD1 inhibition is induction of myeloid maturation or differentiation, which is associated with cell surface upregulation of the type I transmembrane protein, CD86 11,37-40 . To determine if perturbation of the p53 pathway affects LSD1 inhibitor-mediated upregulation of cell surface CD86 expression, we treated GMP-MLL-AF9 cells expressing shRNAs targeting either p53 or Renilla with IMG-7289 and measured cell surface induction of CD86.…”