Cairncross, John GregoryYuan, Alice2019-05-162019-05-162019-05-15Yuan, A. (2019). Preventing the Emergence of Temozolomide Resistance in Glioblastoma by PARP Inhibition (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.http://hdl.handle.net/1880/110364Temozolomide (TMZ) is active against the subset of glioblastomas (GBMs) in which the O6-methylguanine DNA-methyltransferase (MGMT) gene is silenced by promoter methylation. Unfortunately, virtually all MGMT-methylated tumors acquire TMZ resistance and regrow in patients. In a preliminary study, we showed that inhibition of the DNA repair enzymes poly (ADP-ribose) polymerase-1 and -2 (collectively, ‘PARP’) reverses TMZ resistance in patient-derived GBM and oligodendroglioma cell lines (Chapter 3). While this suggests that PARP inhibitors may be useful for treating TMZ-resistant cases, we predict that greater clinical benefit can be derived from their use in TMZ-sensitive cases, where inhibition may prevent the emergence of TMZ-resistant cell populations. To test this hypothesis, we developed a model of acquired TMZ resistance in the MGMT- methylated GBM cell line U251N (Chapter 4). In this system, prolonged treatment of U251N with TMZ induces TMZ-resistant colonies of cells that frequently harbor mutations in and reduced expression of DNA mismatch repair genes, and less frequently re-express MGMT. In Chapter 5, we observed that co-treatment of the parent U251N line with TMZ and the PARP inhibitor ABT-888 prevents such resistant colonies from emerging. Moreover, co-treatment causes established resistant colonies to regress and may also enhance cell kill in TMZ-sensitive cellular subpopulations. For some colonies, however, sensitivity to PARP inhibition diminishes with increasing exposure to TMZ. Collectively, these observations suggest that PARP inhibitors may be optimally used early in newly-diagnosed, MGMT-methylated GBMs to prevent or delay progression to a TMZ-refractory disease state by targeting both TMZ-resistant and sensitive tumour subpopulations.University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.Oncologymaster thesis10.11575/PRISM/36536