LAUSR

Glioblastoma multiforme (GBM) is one of the most aggressive and invasive types of brain cancer, but targeted treatment options remain elusive. The standard of care (surgery chemotherapy and radiation) falls far short of where it should be with two-year survival rates less than 10%. Using stem cell isolates from GBM patients, we found that perturbing PHF5A, a component of the spliceosome machinery, was lethal and caused hundreds of genes to be mis-spliced. These mis-splicing events included both exon skipping and intron inclusions. In contrast, similar levels of PHF5A suppression in normal control stem cells and astrocytes failed to induce cell death and mis-splicing, indicating that PHF5A plays a specific role in the cancer biology. Moreover, when normal astrocytes were transformed with the Myc oncogene, they became sensitive to PHF5A perturbation. Taken together, these results suggested that specifically inhibiting PHF5A would be an effective therapy for glioblastoma and other Myc-driven cancers. Specifically targeting PHF5A would also likely result in reduced side-effects seen with general spliceosome inhibitors. Unfortunately, there are currently no known inhibitors that target PHF5A. In order to discovery novel PHF5A inhibitors, we created a mini-gene mis-splicing reporter assay that was sensitive to both general spliceosome inhibitors and PHF5A perturbation. In a 96-well assay format, the assay was robust with a 200-fold assay window and Z’ values over 0.8. Following miniaturization to a 1536-well format, we conducted a high throughput screening (HTS) campaign testing 450,000 small molecule compounds. The initial hits were retested and counter-screened yielding 381 confirmed actives and we are further interrogating these actives in secondary and tertiary assays. Future efforts will focus on developing an SAR of the lead and backup series and identifying potential liabilities that will be addressed, if necessary, in further lead optimization efforts. We are enthusiastic about the potential of developing a targeted PHF5A inhibitor as a novel and effective therapy for patients and their families fighting GBM and other Myc-driven cancers. Citation Format: Andrew J. Mhyre, Shanon Turnbaugh, Shelli M. Morris, Hu Xin, Patrick J. Paddison, Marc Ferrer, James M. Olson. Targeting PHF5A for the treatment of glioblastoma and other Myc-driven cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3200. doi:10.1158/1538-7445.AM2017-3200