Activation of Cilia-Independent Hedgehog/GLI1 Signaling as a Novel Concept for Neuroblastoma Therapy

Abstract

Although being rare in absolute numbers, neuroblastoma (NB) represents the most frequent solid tumor in infants and young children. Therapy options and prognosis are comparably good for NB patients except for the high risk stage 4 class. Particularly in adolescent patients with certain genetic alterations, 5-year survival rates can drop below 30%, necessitating the development of novel therapy approaches. The developmentally important Hedgehog (Hh) pathway is involved in neural crest differentiation, the cell type being causal in the etiology of NB. However, and in contrast to its function in some other cancer types, Hedgehog signaling and its transcription factor GLI1 exert tumor-suppressive functions in NB, rendering GLI1 an interesting new candidate for anti-NB therapy. Unfortunately, the therapeutic concept of pharmacological Hh/GLI1 pathway activation is difficult to implement as NB cells have lost primary cilia, essential organelles for Hh perception and activation. In order to bypass this bottleneck, we have identified a GLI1-activating small molecule which stimulates endogenous GLI1 production without the need for upstream Hh pathway elements such as Smoothened or primary cilia. This isoxazole compound potently abrogates NB cell proliferation and might serve as a starting point for the development of a novel class of NB-suppressive molecules.

Tumor-suppressive disruption of cancer subtype-associated super enhancer circuits by small molecule treatment

“…In addition to the reported MES markers, ISX transcriptionally upregulated also pro-differentiating neurotrophin genes ( NGF, NT3 ) as well as the p75 NGF receptor ( NGFR ) in IMR32 cells ( Supplementary Figure S4A–C ). Noteworthy, NGF , NT3 and NGFR transcripts were found to be elevated in MES/NC versus ADRN samples ( Supplementary Figure S4D–F ), as was that of the Hedgehog target gene GLI1 ( Supplementary Figure S4G ), which we previously reported to be induced by ISX ( 28 ).…”

“…As chromatin accessibility is considered a defining feature of cell fate ( 35 , 36 ), this observation is perfectly in line with the drug-mediated modulation of CRCs and the resulting subtype switch. Specifically, ISX-treated cells adopted a de novo accessibility landscape associated with low-risk NB, a feature which might be supported by the inherent property of ISX to increase histone acetylation by indirectly blocking class I HDACs (this study and ( 28 )). In fact, pharmacological HDAC inhibition has previously been reported to drive NB differentiation ( 52 ).…”

“…Next, we were interested to shed more light on the underlying molecular mechanism of ISX. We recently reported on ISX as a Hedgehog/GLI1-inducing substance and its impact on histone acetylation ( 28 ). In addition, MYC (or N-MYC, which is regulated by ISX) had previously been shown to be a major positive regulator of histone acetylation ( 34 ).…”

“…Kaplan-Meier curves, gene expression analyses, PCAs, gene correlations from public datasets were done using the R2: Genomics Analysis and Visualization Platform ( http://r2.amc.nl ). Data can be accessed through Array Express: RNAseq: E-MTAB-10249 (IMR32; previously published in: ( 28 )); E-MTAB-11915 (SH-SY5Y). ChIPseq: E-MTAB-12344 (IMR32); ATACseq: E-MTAB-11633 (IMR32).…”

Analysis of Primary Cilium Expression and Hedgehog Pathway Activation in Mesothelioma Throws Back Its Complex Biology

“…PC is lost in a group of developmental genetic disorders, collectively known as ciliopathies, and in a variety of human neoplasms [ 5 ], leading to the hypothesis that PC is a tumor-suppressor organelle [ 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. However, different cancers retain PC, such as basal cell carcinomas (BCC), pleomorphic adenomas, neuroblastoma, colorectal tumors, craniopharyngioma, a subset of medulloblastoma and gastrointestinal stromal tumors [ 13 , 14 , 15 , 16 , 17 , 18 ], supporting the recent hypothesis that PC has tissue- and cancer-specific roles.…”