In search for new therapeutic approaches for glioblastoma multiforme

Abstract

Glioblastoma Multiforme (GBM) is a very aggressive type of primary brain cancer with poor prognosis. According to the WHO classification of CNS tumours, GBM is a high-grade infiltrating glioma (grade IV). The introduction of “Stupp protocol” in 2005 was a majormilestone towards improving quality of life and clinical outcome for GBM patients. However,
since then and up until now, the expanding knowledge about the molecular basis of the
disease has only led to small advancement in the therapy and prognosis of GBM, which
remains abysmal. This is mainly due to the tremendous heterogeneity of molecular
abnormalities between GBM and within GBM. Non-conventional therapeutic approaches,
such as photodynamic therapy (PDT) and drug repurposing, could help to speed up the
progress in our fight against this deadly disease. PDT is the concept of using a molecule, a
photosensitizer (PS) that is not inherently toxic, to induce toxicity selectively on cancer cells
after illumination. Drug repurposing is defined as the use of an existing approved drugs for
treatment of other diseases than the indicated target disease. Six different primary human
GBM cell lines were used in the project and normal rat astrocytes served as a reference. In
the first part of the project, the molecular heterogeneity of my GBM cohort was evaluated by Sanger sequencing. RNA samples were extracted from all 6 GBM cell lines, followed by reverse transcription for cDNA synthesis. Next, PCR was done using primers for 4 commonly mutated genes implicated in gliomagenesis, including IDH-1, p53, PTEN, and EGFR. In the second part, the feasibility and efficiency of utilizing Tetramethylrhodamine methyl ester (TMRM), as a novel PS was assessed. TMRM was originally develop as dye to assess mitochondrial membrane potential. The properties of TMRM as a PS, and the efficacy of TMRM-PDT were evaluated. Possible synergy with other pharmacological agents was also examined. Finally, based on pre-existing literature, efficacy of antidepressants (AD) for treatment of GBM was re-evaluated. ADs were assessed for their toxicity towards GBM cells, and their effect on some cellular biological functions.

Different molecular prints were documented among the 6 GBM cell lines, including mutations in p53 and EGFR genes. Future work should include functional gene studies to correlate these molecular profiling of GBM with their sensitivity to different therapeutic iii models. TMRM-PDT showed promising results on GBM cell lines. Future modification of treatment protocol should aim to enhance efficacy and selectivity of this treatment modality. Finally, ADs were effective in inducing GBM death, however, the required concentrations for this effect were high and poor selectivity towards cancer cells vs normal astrocytes was noted. This effect was associated with mitochondrial depolarization rather than cAMP activation, contrary to some previous reports.

Date of Award	12 Jul 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Sergey Kasparov (Supervisor) & Anja G Teschemacher (Supervisor)