Pre-clinical investigation of the effect of combining the cytotoxic agent Temozolomide with a dual mTORC2 inhibitor for the treatment of glioblastoma and establishment of an imageable surgical resection model of glioblastoma
Glioblastoma is the most common primary brain tumour. It is an incurable disease and is commonly referred to as the worst of the “incurable cancers” by neurosurgeons and neuro-oncologists. It is heterogeneous on a cellular and genetic level. The genetic mutations that occur in glioblastoma lead to dysregulation of several principal pathways, the most commonly dysregulated pathways involve mTOR. mTOR is involved in the control of several cellular processes including autophagy and apoptosis. Despite maximal treatment, median survival remains abysmal ranging from 15 to 16 months. Current standard of care consists of two phases. The first phase involves maximal safe surgical resection. This intervention reduces the tumour burden and improves the efficacy of the second phase. This second phase involves chemotherapy and radiotherapy commonly referred to as the “Stupp protocol”. This phase employs a common strategy of inducing apoptosis in an attempt to control the residual disease. Within this thesis we explore both phases of treatment for glioblastoma.
Firstly, we established the in vitro efficacy of the mTOR inhibitor, AZD 8055 using the glioblastoma cell line U87MG, and glioblastoma tissue derived from a patient in Norway referred to as patient 3. We then assessed the in vivo efficacy of AZD 8055 in combination with temozolomide, using the patient derived glioblastoma tumour material from patient 3, in an orthotopic bioluminescence murine model. We demonstrated that although AZD 8055 is a strong inhibitor of the mTOR pathway when used as a monotherapy or combined with temozolomide, this did not translate into either increased survival or a reduction in tumour growth in vivo. By interrogating the points of crosstalk between autophagy and apoptotic pathways, we hypothesized that mTOR inhibition induced a protective autophagy which antagonised the apoptosis induced by temozolomide. Secondly, we validated a novel animal model of surgical resection. We established that orthotopic implantation of glioblastoma cells can be safely resected, and that the residual tumour, which has invaded the surrounding brain parenchyma, can be reliability imaged in vivo. We advocated the use of this model for the investigation of local delivery of novel therapies into the surgical resection cavity or in the assessment of systemic therapeutic agents targeting residual tumour that has migrated into the normal brain parenchyma.