Investigating the role the PI3K pathway plays in ependymoma pathogenesis

Estranero, Jasper (2019) Investigating the role the PI3K pathway plays in ependymoma pathogenesis. PhD thesis, University of Nottingham.

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Introduction: Ependymoma is the second most common malignancy of the central nervous system in paediatric cohorts, accounting for 6-12% of all cases of childhood brain tumours. Its clinical management remains a challenge at present, generally manifesting poor patient prognoses with a paucity of effective treatments. It was previously found that the PI3K signalling pathway, a cell survival cascade implicated in many cancers, was activated in 72% of primary ependymomas which suggests a significant role in disease pathogenesis. The PI3K pathway regulates a range of cellular processes that support tumourigenesis and its targeting has yielded therapeutic benefits in many malignancies. This study investigated the impact of signalling through the PI3K pathway in ependymoma survival and its prospect as an alternative target to treat these tumours.

Methods: The pan-PI3K inhibitor BKM120 was used to treat a panel of patient-derived ependymoma cell lines. Functional assays determined whether inhibition of the PI3K pathway conferred a cytostatic or cytotoxic response in ependymoma. Whole transcriptome analysis was used to elucidate the downstream effects of suppressing PI3K signalling on gene expression profiles. Based on this work, a proposed molecular mechanism for the instigation of the anti-tumourigenic effects of BKM120 treatment in ependymoma was functionally validated. Chemotherapeutic drugs which were predicted to work synergistically with PI3K pathway inhibition were subsequently investigated to evaluate their prospect as a treatment approach in ependymoma.

Results: Monotherapeutic treatment of ependymoma cells with BKM120 resulted in a significant decrease in cell viability at concentrations that have been shown to be achieved clinically. However, BKM120 treatment only resulted in a G1/S phase cell cycle arrest, highlighting the induction of a cytostatic rather than a cytotoxic response. Gene expression analysis of BKM120-treated ependymoma cells identified a transcriptional profile consistent with a cell cycle arrest as well as a reduction in cellular responses that contribute towards tumourigenesis including regulation of DNA repair systems. A mechanism of G1/S arrest induced FOXO1 control of Rb/E2F1 was proposed. Inhibition of the PI3K pathway resulted in a loss of FOXO1 and Rb phosphorylation. However, in experiments so far, no decrease in E2F-mediated luciferase reporter activity was found. Combining PI3K inhibition with gemcitabine, but not paclitaxel or cisplatin, resulted in a synergistic effect in ependymoma. Indications of potential resistance to BKM120-mediated PI3K inhibition in ependymoma have also been identified from the gene expression data through the positive regulation of the MAPK signalling pathway and reactivation of the PI3K pathway.

Conclusion: BKM120-mediated inhibition of the PI3K pathway in ependymoma impedes survival and viability, making it an attractive chemotherapeutic target to treat these tumours. However, it was only found to induce a cytostatic response as a single therapy thus highlighting its suitability for disease stabilisation instead of being used as a first-line of treatment. Clinical efficiency of PI3K pathway inhibitors in ependymoma might be more appreciated when administered as part of a combination treatment.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Grundy, Richard
Rogers, Hazel
Keywords: Ependymoma; Pathogenesis; Cellular processes; PI3K pathway inhibitors; BKM120
Subjects: W Medicine and related subjects (NLM Classification) > WL Nervous system
Faculties/Schools: UK Campuses > Faculty of Medicine and Health Sciences > School of Medicine
Item ID: 56824
Depositing User: Estranero, Jasper
Date Deposited: 15 Sep 2023 10:44
Last Modified: 15 Sep 2023 10:44

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