Transcriptomic analysis of early Craniopharyngioma tumourigenesis

Abstract

Craniopharyngiomas are clinically challenging pituitary tumours that disrupt pituitaryhypothalamic function causing severe long-term morbidities. There are two histologically and pathologically distinct subtypes. Adamantinomatous Craniopharyngioma (ACP) presents during childhood and 70% of cases are driven by activating mutations of CTNNB1 in pituitary stem/progenitor cells (PSCs). It is histologically characterized by clusters of tumour initiating PSCs with accumulated β-catenin (β-catenin clusters) that secrete paracrine factors thought to drive tumourigenesis. Papillary Craniopharyngiomas (PCPs) present mainly during adulthood and are driven by activating BRAFV600E mutations. The molecular aetiology of these tumours is poorly understood, and both subtypes are treated surgically. Neither yet has licensed pharmaceutical treatments and this thesis represents an exploratory transcriptomic analysis of early tumour development in the pursuit of novel therapeutic targets. To evaluate early ACP tumourigenesis, a fluorescent lineage tracer was used to isolate Sox2-positive murine PSCs and a Wnt/β-catenin signalling reporter enabled separation of the tumour initiating subpopulation from those PSCs refractory to transformation by oncogenic β-catenin. Transcriptomic analysis of ACP-mutant PSCs, and intra-subpopulation variability revealed increased expression of secreted paracrine factors and increased MAPK signalling. Tumour initiating PSCs showed a marked pro-inflammatory gene signature, with upregulation of the IL6-Jak-stat3 and Tnf-NFkB signalling pathways as well as secreted chemokines and cytokines. This led to increased immune cell infiltration centred around tumour initiating β-catenin clusters. Immunophenotyping by flow cytometry identified tumour-associated macrophages as the predominant cell population, highlighting their potential role in the early stages of ACP tumourigenesis and candidacy as targets for future therapeutic strategies. For PCP, a novel adult-onset mouse model was generated and characterized. Transcriptional analysis of PSCs after BrafV600E activation revealed changes in genes associated with an epithelial to mesenchymal transition and metabolism. This metabolic shift was profiled in vitro revealing an increased reliance on respiration in BrafV600E mutant PSCs, which may represent a therapeutic vulnerability of stem cells in BrafV600E driven pituitary tumours.