Targeting non-canonical NF-κB signalling in CYLD defective tumours

Abstract

CYLD cutaneous syndrome (CCS) is a rare, autosomal dominant, hair follicle tumour predisposition syndrome where non-surgical therapeutics are needed. In this thesis I delineate non-canonical NF-κB signalling in CYLD defective tumours and evaluate the utility of targeting this pathway with novel small molecule IKKα inhibitors. Such information may underpin the potential development of non-surgical approaches for CCS. First, I sought to establish the genetic landscape of tumours in CCS. Using whole genome sequencing, I showed that biallelic mutation of the cylindromatosis gene (CYLD) was present in almost all tumours studied. In addition, I discovered that a subset of tumours had mutations in epigenetic modifiers that modulate Wnt signalling, a known oncogenic dependency in these tumour cells. CCS has not been successfully modelled in mice, limiting mechanistic insight into how truncating mutations in CYLD result in a skin tumour phenotype. To overcome this, I explored both the canonical and non-canonical NF-κB signalling pathways in CCS whole tumour tissue. I also developed a patient-derived tumour spheroid model that recapitulated in vivo deregulation of both NF-κB signalling pathways. In the non-canonical pathway, I showed processing of the p52 precursor p100 was altered in CCS tumour tissue and spheroids. Given non-canonical NF-κB signalling is targetable by inhibiting IKKα, I inhibited IKKα in CCS spheroids with a novel compound, designated Compound Z, and showed reduction in viability following treatment. To determine the impact of biallelic CYLD truncating mutations on the transcriptome, I used a CD45 depletion method to isolate CD45- CCS tumour keratinocytes by FACS. RNA-sequencing of tumour keratinocytes identified the ectodysplasin a receptor EDAR as highly differentially expressed. Measurement of gene expression after treatment with Compound Z confirmed that EDAR overexpression is IKKα-dependent in CCS spheroids. In summary, I have highlighted the oncogenic dependency of CCS tumour cells on non-canonical NF-κB signalling and demonstrate the effectiveness of targeting IKKα for the treatment of CYLD cutaneous syndrome.