Epigenetic Regulation of Langerhans Cell Histiocytosis Pathophysiology and Microenvironment by HDAC3

PROJECT SUMMARY/ABSTRACT Langerhans cell histiocytosis (LCH) is a rare inflammatory myeloid neoplasm with a wide range of clinical manifestations and severity caused by mutations that constitutively activate mitogen-activated protein kinase (MAPK) signaling in myeloid lineage cells- most commonly BRAFV600E. Constitutive MAPK activation endows

pathological histiocytes with a senescence associated secretory phenotype (SASP)- leading to resistance to apoptosis, increased inflammatory cytokine and matrix metalloproteinase expression, and decreased ability to migrate to lymph nodes. These features allow LCH cells to persist in tissues and reshape the microenvironment

leading to the characteristic granulomatous lesions harboring CD207+ cells. However, little is known about tissue- specific and time-dependent features of the LCH microenvironment (LCH-ME). Treatment of LCH remains unacceptable due to significant drug-induced toxicity and inability of current treatment strategies to eliminate LCH precursor cells leading to high-rates of disease recurrence. Recurrence

often leads to life-threatening sequalae. Drugs targeting both development and homeostasis of LCH cells could revolutionize treatment for patients with LCH. Our lab showed histone deacetylase 3 (HDAC3) regulates multiple facets of myeloid cell biology, including development and homeostasis. This F30 proposal seeks to define the

therapeutic potential of targeting HDAC3 to ameliorate LCH. Collectively, the data presented will further our understanding of the epigenetic regulation of pathological myeloid cells, provide novel insights to the LCH-ME, and provide preclinical data for HDAC3 inhibition (HDAC3i) as a treatment for LCH.

In Aim1, we will us a mouse model of LCH to define tissue-specific and time-dependent features of the LCH-ME. Using flow cytometry, single-cell RNA sequencing, and imaging mass cytometry we will compare the composition, gene expression, and spatial organization of lung and liver LCH lesions over time.

In Aim2, the efficacy of HDAC3i will be evaluated in a mouse model of severe-multifocal LCH. Using genetic ablation and pharmacological inhibition, we will test how HDAC3i influences development, homeostasis, and SASP properties of LCH cells, and the LCH-ME. These studies will address a major gap in our

understanding of LCH disease development and define a potential new therapeutic that could be translated to treat LCH and other MAPK-driven histiocytic disorders. The training plan outlined in this proposal will be performed between Henry Ford Health System, Wayne State University School of Medicine, and Karmanos Cancer Institute, which presents a unique opportunity to

leverage the advantages and expertise at all three institutions providing a robust clinical and research training. Executing this training plan in such a vibrant multi-institutional environment, with the guidance of dedicated sponsors, collaborators, and mentors with expertise in immunology, epigenomics, cancer biology, and

hematology, will provide an unparalleled training for a successful career as a physician-scientist.