Exploring the effect of RAD51/BRCA2 inhibition to pursue synthetic lethality with PARPi in in-vitro models of pancreatic cancer

Synthetic lethality (SL) is an innovative framework for discovering novel anticancer treatments for personalized targeted therapies. Two genes are synthetically lethal if the inhibition of either gene alone has no effect on cell viability, but their simultaneous impairment leads to cell death. In this context, the Food and Drug Administration approved in 2014 the PARP inhibitor (PARPi) olaparib for oncology patients with BRCA1/2 mutations. My Ph.D. research project is focused on pancreatic cancer, an oncological need. It is aimed at exploiting a new paradigm, dubbed “fully small-molecule-induced synthetic lethality”, which was already presented in previous studies by the research group of Professors A. Cavalli (Italian Institute of Technology) and M. Roberti (University of Bologna). It is based on the possibility of triggering SL by using only small molecules: a PARPi and a RAD51/BRCA2 disruptor that mimics the BRCA2-defective condition. RAD51 and BRCA2 are two key proteins in the homologous recombination (HR) pathway. Their interaction is mediated by eight motifs of BRCA2, among which the fourth (BRC4) has the highest affinity for RAD51. The first section of this thesis describes the effects on cell cultures of a synthetic BRC4 peptide, which reproduced the expected outcomes of HR pathway inhibition, such as the reduction of RAD51 nuclear foci following DNA damage and the increased response to chemotherapeutic agents. A subsequent proteomic study in BRC4-exposed cultures led to identify a statistically significant downregulation of three proteins (FANCI, FANCD2, RPA3) involved in the DNA damage response. The second section of the thesis is focused on the biological characterization of compound 46, a RAD51/BRCA2 inhibitor identified by IIT colleagues. 46 was studied on both 2D and 3D pancreatic cancer models in combination with the PARPi talazoparib. Taken together, the obtained results suggested that the talazoparib-46 combination is a potential inducer of SL.