Dihydroquinoline pyrazoline-based compound as a new RAD51-BRCA2 protein-protein disruptor to trigger synthetic lethality in pancreatic cancer

Synthetic lethality is an innovative framework for the discovery of new anticancer drugs. Cancer cells are strictly dependent on efficient DNA repair pathways due to their pervasive genomic instability. Targeting different DNA repair pathways provides the opportunity to apply the synthetic lethality as a novel anticancer therapeutic strategy.[1] In this context, we proposed to trigger a fully small-molecule-induced synthetic lethality, combining a RAD51-BRCA2 protein-protein interaction (PPI) disruptor with Olaparib, a known PARP inhibitor, to target pancreatic cancer, one of the major unmet oncological needs. RAD51-BRCA2 PPI is essential to repair DNA double strand breaks (DSBs) through the homologous recombination (HR). According to our working hypothesis, a RAD51-BRCA2 PPI inhibitor would chemically mimic the enhanced sensitivity to Olaparib observed in BRCA2-defective tumors, leading to a synthetic lethal effect (Figure 1A).[1] The RAD51-BRCA2 complex is mediated by two critical “hotspots” on RAD51 surface, zone I and II, which lodge eight highly conserved BRCA2 motifs.[2] These two pockets make the RAD51-BRCA2 interaction suitable for a structure based design of PPI small molecule disruptors. Herein, we focused on zone II, which has proved to be crucial in RAD51’s mechanism of action.[2] To date no inhibitors targeting zone II have been reported. Through a virtual screening campaign, we identified a dihydroquinolone pyrazoline-based molecule 1 as promising hit compound, which showed an inhibitory activity of RAD51-BRCA2 PPI in the competitive ELISA assay (EC50= 16 ± 4 μM).[1] To discover more effective compounds and depict general structure-activity relationship (SAR) studies, we explored the chemical space around 1 by optimizing a general synthetic strategy and building a library that contains a variety of aromatic substitutions (green region) in combination with modifications of the acyl chain moiety (red region) (Figure 1B).[1] SAR efforts yielded 2 with the desired biological profile. As expected, 2 proved to disrupt the RAD51 BRCA2 PPI, inhibiting HR in pancreatic cancer cell line BxPC-3 and reproducing the paradigm of synthetic lethality in combination with Olaparib (Figure 1B).