Characterisation of novel genetic determinants of Craniopharyngioma tumours

Adamantinomatous craniopharyngiomas (aCPs) are pituitary tumours which mainly affect children. The pituitary gland is situated at the base of the brain and controls vital body functions such as growth, fertility, metabolism, water balance, stress responses and lactation. The pituitary is controlled by a region of the brain known as the hypothalamus and together they form the hypothalamic-pituitary axis (HP-axis). When the HP-axis is disrupted by aCP tumours, the consequences are devastating and include suboptimal growth, infertility, impaired metabolism, inability of the body to respond to stress, morbid obesity and other hormone disturbances. These tumours can also invade surrounding brain structures causing blindness and impaired intellectual function. As a consequence, these children are in need of lifelong medical care and their development, education and quality of life are severely affected. No drug therapies are available for aCPs and the most common current treatment is a combination of surgery and radiotherapy. Unfortunately, these treatments can have severe side effects due to damage to nearby brain regions. Often, surgeons do not remove the whole tumour to avoid extensive damage to the HP- axis. Additionally, there is a great variability in patient outcome with some patients having a significantly worse prognosis than others despite the same treatment. More personalised treatment will be provided if we can diagnose these tumours more accurately, specifically in terms of their genetic signature. There is an urgent need to understand how these tumours form and to be able to correlate tumour characteristics (molecular signatures) with progression of the disease.

We have identified that a large proportion of aCP tumours have a genetic defect (mutation) in a sequence of DNA which encodes a protein known as B-catenin, but these tumours also harbour mutations in other important genes (RNF43, APC and TCFL2) that could have an effect on the disease progression and account for the variable clinical outcomes. However, the role of these genes during early pituitary development and how they lead to tumour formation later in life is not yet known. Understanding the role of these genes and determining if they can predict a patient's clinical outcome would confer an immediate benefit to patients. My overall aim is to understand how these mutated genes (RNF43, APC and TCFL2) either alone or in combination with B-catenin affect tumour development and if there is a correlation between these mutations and the patient's clinical outcomes. In order to achieve this aim I will work on the proposed following objectives:

1. To analyse if the mutations in the identified genes RNF43, APC and TCFL2 affect the protein produced and its function within the cell.

2. Using animal modelling I will delete the production of proteins by the two most highly mutated genes (RNF43 and APC) to understand their role during pituitary development and tumour formation.

3. To investigate if the identified mutations in the genes correlate with the clinical outcomes of the aCP patients.

This proposal will advance our knowledge of the development and behaviour of aCPs and will have important clinical implications. We will be able to advise our patients about their prognosis more accurately and tailor their treatment accordingly. For those tumours that confer a better prognosis, less aggressive treatments could be considered, which would spare important brain areas. Successful conservative treatment could lead to less morbidity and mortality and an improved quality of life for children with aCPs.

Adamantinomatous Craniopharyngiomas (aCPs) lead to severe endocrine dysfunction and other sequelae, due to their effect on local structures such as the hypothalamus, optic and cranial nerves. Treatment is currently limited to surgery and radiotherapy, which are associated with significant morbidity. There is an urgent need to understand the molecular basis leading to formation and progression of aCPs to allow improved and personalised clinical management.
My group's preliminary work has identified that 70% of aCPs carry mutations in B-catenin and these tumours have a high frequency of mutations in important negative regulators of the Wnt/B-catenin pathway. The group has identified that negative regulators of the the Wnt/B-catenin pathway are also mutated in the aCP-B-catenin-negative tumours, suggesting these genes could contribute to the development of aCPs independently of B-catenin. Importantly the identified mutational heterogeneity of aCPs tumours could confer variability in tumour phenotype, which may explain the variable clinical outcomes of aCPs.

My project aims to understand the role of mutations in negative regulators of WNT signalling in the aetiology of aCPs 1) functional characterisation of the identified mutations 2) transgenic in vivo modelling of the identified mutations 3) clinical phenotype correlation of aCP patients with mutations identified.
To achieve these objectives I will use well established lab techniques to determine the role of identified mutations on their protein function. I will use transgenic modelling to genetically ablate, within the pituitary, the two most commonly mutated genes and study the role of these genes in pituitary development and tumour formation. Finally, in collaboration with a tumour bio-informatician and cancer statistician, I will use correlation studies to understand if the variable clinical phenotype in aCP cohort is due to mutational heterogeneity within these tumours.

My research aims to understand the role of genetic mutations in components of the Wnt/B-catenin pathway in aCP tumour progression. This research will benefit the following groups:

1. The most important people to benefit from long-term outcomes of this research will be patients with aCP and their families. Some aCPs have infiltrative behaviour affecting the hypothalamus, visuals tracts and cranial nerves causing significant morbidity and mortality. Current treatment options are limited by the risk of damaging local structures. Total surgical resection is not recommended due to inevitable hypothalamic damage. Subtotal resection followed by radiotherapy is utilised if the aCP has already invaded the cavernous sinus or hypothalamus in order to preserve hypothalamic and cranial nerve function. aCPs often have a propensity to reoccur and patients may require multiple neurosurgical interventions during their lifetime, with increasing surgical complexity and morbidity with successive surgical interventions. Identification of gene mutations that correlate with time to first recurrence will benefit patients by providing greater prognostic information at the time of diagnosis. This may take away some of the uncertainty facing patients and families and allow for more informed treatment choices.
2. In addition to helping patients, health professionals directly managing patients diagnosed with aCPs (such as endocrinologists, neurosurgeons, pathologists and ophthalmologists) will all benefit from this research. The most significant benefit to clinicians is the correlation of mutations identified through our Next Generation Sequencing in the Wnt/B-catenin pathway components with clinical outcomes. Currently, no biomarkers or specific tumour mutations are available that predict aCP tumour progression. If I am able to identify genetic variants that predict clinical outcomes, such as time to recurrence, this would allow clinicians to have better prognostic information at time of diagnosis. Greater prognostic information could allow for more individualised treatment strategies, such as timing of interventions and duration and intensity of follow-up. Correlation studies between the four mutated genes, hypothalamic infiltrative behaviour and size of tumour will also give important information to clinicians to help determine the likely progression of the tumour. This again could help shape treatment strategies for patients in the future. This research has the potential to change clinical practice by giving the treating clinical team greater prognostic information and could lead to personalised clinical management of each patient based on the molecular signature of their tumour.

3. This project will generate several mouse transgenic lines and reagents to understand the role of RNF43 and APC both in normal pituitary development and in the pathogenesis of aCP. These genetic tools will be important for other researchers working on hypothalamic-pituitary development. Transgenic lines, protocols and reagents will be made available which will directly impact other researchers working in related fields.

4. The project will provide information on mutations in key negative regulators of the Wnt/B-catenin pathway which are currently unknown. Since the Wnt/B-catenin pathway has a pleiotropic effect on stem cells and cancer, the knowledge of the functional role of the mutations will directly benefit researchers in tumour biology, specifically Wnt/B-catenin mediated tumours such as hepatoblastomas, neuroblastomas and colon cancer.