Targeting an immortalization mutation to control glioblastoma
Glioblastoma multiforme (GBM), the most aggressive primary brain tumor, is a very heterogeneous tumor, but its standard treatment of temozolomide and radiation therapy has not changed for the past thirty years. However, over 80% of GBM tumors have a telomerase reverse transcriptase (TERT) promoter mutation, or TPM. This makes the mutation an attractive target in glioma cells. TERT is the catalytic subunit of telomerase, an enzyme residing in the nucleus that regulates the length of telomeres, a specific sequence of nucleotides located at the end of chromosomes. TERT is often overexpressed in malignant cancers to prevent cells from senescence and to promote rapid and unchecked cellular division, and it is rarely expressed in somatic cells with the exception of stem cells. Targeting the TPM with the pharmacological chaperone RG1534, a small molecule inhibitor, stabilizes the G4 structure in the promoter and the resultant transcription of the protein. Glioblastoma cells were plated, lysed, treated, and their RNA was extracted, reverse transcribed, and amplified in RT-qPCR to determine the effect of TPM inhibition. Biological replicates of TPM inhibition were also plated for western blots to validate the fold gene expression change calculated in qPCR. Both a decrease in TERT mRNA and protein expression was determined, coinciding with high levels of apoptosis. Additionally, western blots were conducted on sub-cellular fractions of different glioblastoma cell lines to show TERT and its expression outside the nucleus. In the preliminary investigation of the functional effects of a normalized TPM, TERT was revealed to be present in the cytosol and mitochondria, prompting that it has non-canonical functions outside of the nucleus. Stabilizing the TPM therefore warrants further study of the functional effects of this mutation’s inhibition. Since the standard of care for this cancer has not changed, the TPM is a specific, viable therapeutic target in GBM patients.