Design and synthesis of RAD51-BRCA2 disruptors that trigger synthetic lethality in pancreatic cancer in combination with Olaparib

My PhD research project has been finalized to the discovery of potential RAD51-BRCA2 protein-protein interaction (PPI) disruptors, able to trigger synthetic lethality (SL) in pancreatic cancer in combination with PARP inhibitor Olaparib. SL has been validated clinically, as anticancer therapeutic strategy, through the efficacy of Olaparib in BRCA2-defective cancers. In this context, we proposed to trigger a fully small-molecule-induced SL, combining RAD51-BRCA2 PPI disruptor with Olaparib to target pancreatic cancer. RAD51-BRCA2 PPI is essential in homologous recombination (HR) for DNA repair and it is mediated by two critical “hotspots” on RAD51 surface, Zone I and Zone II, suitable sites to design small molecule disruptors. This thesis reports the application of two distinct hit identification strategies to identify potential RAD51-BRCA2 PPI disruptors. In the first part of this project, an approach of structure-based design was applied, which exploited Virtual Screening (VS) campaign as hit identification strategy, followed by chemical modifications and SAR studies. Two VS, targeting separately Zone I and Zone II, led to the discovery of two classes of potential RAD51-BRCA2 PPI disruptors. In particular, VS targeting Zone II identified the dihydroquinolone pyrazoline 19 as hit compound. The optimization of a general synthetic strategy gave access to a series of analogs for SAR investigation, leading to compound 47 with the desired biological profile. Indeed, 47 inhibited RAD51-BRCA2 PPI, reduced cell HR and triggered cell death in combination with Olaparib in BxPC-3 cells, fully reproducing the paradigm of SL. The second part of this thesis was devoted to a second hit identification strategy. During the six-month placement at HIPS in Prof. A. K. H. Hirsch’s group, I applied a technique of target directed dynamic combinatorial chemistry (tdDCC) on RAD51. This approach allowed the identification of N-acylhydrazone-based compounds, which proved to inhibit RAD51-BRCA2 PPI at micromolar range in the preliminary biochemical assay.