AB067. New drug development for the use of PARP1-E2F1 transcriptional inhibitors in the treatment of glioblastoma

Background: Glioblastoma (GBM) is the most malignant brain tumor and ranks among the most lethal of all human cancers, without improvements in survival over the last 30 years. Data obtained in our group suggest that PARP1, a well-known DNA-repairing protein, could also play a key role in the regulation of cell cycle through its interaction with the transcription factor E2F1. Therefore, considering that most oncogenic processes are associated with cell cycle deregulation, we hypothesized that disruption of PARP1-E2F1 interaction would provide a novel therapeutic approach to different types of cancer.

Methods: The identification of novel compounds disrupting PARP1-E2F1 interaction was carried out by combining in silico and in vitro screening, using a rational drug design. The virtual screen was performed using a molecular library of several million compounds at the selected target site, using AtomNet^® (Atomwise, San Francisco, CA, USA), the first deep learning neural network for structure-based drug design and discovery. Since there is no complete structural information of the PARP1-E2F1 protein-protein interaction, a homologous structure of the BRCT domain of BRCA1 complex with the phospho-peptide (PDBID: 1T2V) was used to identify the potential binding interface of BRCT domain of PARP-1 (PDBID: 2COK) and the E2F1 protein. Top scoring compounds were clustered and filtered to obtain a final subset of 83 compounds that were incorporated to our in vitro screening, which included both transcriptional E2F1 activity and survival studies. Complete culture medium supplemented with the compounds selected in the in silico screening (10 μM) were added and incubated for 24 hours. E2F1 activity was observed by measuring luminescence. For the viability assay, the fluorescence reading was performed (excitation 544 nm and emission 590 nm).

Results: The in silico and in vitro screening resulted in 12 compounds that inhibited E2F1 transcriptional activity and significantly reduced cell number. The highest inhibition of both E2F1 transcriptional activity and cell growth was observed with compound 3797, which was selected for further studies.

Conclusions: Both in silico and in vitro results indicate that inhibition of PARP1-E2F1 transcriptional activity may provide a new rationale for designing novel therapeutic approaches for the treatment of GBM.

Keywords: Glioblastoma (GBM); PARP1; E2F1