Author: Manam Inushi De Silva
De Silva, Manam Inushi, 2024 Glioblastoma plasticity and therapeutic sensitivity in the human brain microenvironment, Flinders University, College of Medicine and Public Health
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Glioblastoma (GBM) is the most malignant tumour of the central nervous system. Despite advancements in treatment, the prognosis remains poor due to tumour plasticity, where cells shift their identity to endure sudden microenvironmental changes. Understanding this plasticity, the relationship of tumour cells with their microenvironment, and accurately modelling these features in preclinical trials is essential for effective treatment. This thesis explores these aspects in four parts.
In Chapter 2 I discuss the development and plasticity of GBM. GBM consists of multifaceted tumour cells, originating from aberrant neuronal cells, that develop along known neuronal trajectories. In the event of microenvironmental disruption, such as through therapeutics, GBM tumour cells utilise injury response pathways to change their identity and endure cellular stresses. In this chapter, I deconstruct the genetic, epigenetic, transcriptomic, and phenotypic dispositions of GBM cells and contrast these factors with that of typical neurodevelopment. Inducing tumour cell differentiation along known neurodevelopmental pathways can help restrict tumour plasticity and enhance therapeutic efficacy.
In Chapter 3 I explore how cerebrospinal fluid (CSF) shapes the identity and plasticity of GBM. CSF is a major component of the brain providing buoyancy, nutrients to brain cells, and removing waste. GBM tumours near the ventricles or tumour cells remaining following surgical resection are, therefore, going to be exposed to CSF. However, the influence of CSF on GBM is unknown. Here, we find that CSF alters GBM cellular morphology, decreases cell proliferation, and increases resistance to temozolomide chemotherapy and irradiation. Transcriptomic analyses reveal that the ferroptosis inhibitor, nuclear protein 1 (NUPR1), is upregulated upon exposure to CSF and drives resistance to standard treatment. Treating GBM cells with the anti-psychotic trifluoperazine (TFP), effectively targets this treatment resistance, while being safe for healthy, human, pluripotent stem cell (hPSC)-derived neurons and glia.
In Chapter 4, I highlight how TFP can be repurposed to restrict tumour plasticity and minimise treatment resistance. Trifluoperazine (TFP) is an anti-psychotic used for schizophrenia or anxiety through the inhibition of dopamine receptors. In Chapter 3, we show that TFP also inhibits NUPR1 and alleviates CSF-induced resistance to chemoradiotherapy. TFP, therefore, is a potential therapeutic for GBM. However, for translation into the clinic the exact mechanisms of action of TFP and its distribution throughout the body need to be investigated. Here, I show that TFP prevents transition to a stem cell state, modulates cell cycle, autophagy and drug-resistance pathways to decrease tumour growth, induce apoptosis and enhance sensitivity to chemotherapeutics.
In Chapter 5, I explore how well hPSC-derived neuronal cultures can recapitulate the transcriptomic diversity of the adult human brain. Accurate modelling of GBM and its microenvironments is vital to understand the tumour biology as well as the safety and efficacy of therapeutics. hPSC-derived neuronal cultures enable high-throughput modelling of the brain while preserving patient genetics. However, whether these cultures capture the molecular diversity and complexity of the human brain is yet unknown. In this chapter, I show that hPSC-derived cortical neuronal cultures encompass a wide-variety of neuronal and glial cell types and recapitulate 55 of the 69 known neuronal transcriptomic types of the adult cortex. Accordingly, hPSC-derived neuronal cultures can be used in conjunction with patient-derived GBM models to assess safety and efficacy of GBM therapeutics and model GBM-brain interactions.
Overall, this PhD project expands the current understanding of GBM development and plasticity in human brain environments. The work suggests TFP as a therapeutic to counteract plasticity-induced therapeutic resistance and presents hPSC-derived neuronal cultures as a valuable addition to preclinical models of GBM.
Keywords: glioblastoma, brain cancer, glioma, treatment resistance, cerebrospinal fluid, plasticity, brain environment, transcriptomics, induced pluripotent stem cells, neurons
Subject: Neuroscience thesis
Thesis type: Doctor of Philosophy
Completed: 2024
School: College of Medicine and Public Health
Supervisor: Professor Cedric Bardy