2nd Edition of Pharma R&D and Drug Discovery World Conference 2026

Abstract

The interaction between RAD51 and BRCA2 is central to homologous recombination (HR), a high-fidelity DNA repair pathway essential for genome stability and cancer cell survival. Disrupting this interaction represents an attractive therapeutic strategy to sensitise tumours to DNA-damaging agents. Here, we report the rational design and functional characterisation of single-stranded RNA and DNA aptamers engineered to bind RAD51 and selectively modulate its activity.

Using the catRAPID computational framework, we identified candidate oligonucleotides predicted to interact with high affinity and specificity with RAD51. The lead aptamer binds RAD51 at the BRCA2 interaction interface, effectively competing with BRCA2 in vitro. This interaction was validated by biolayer interferometry (BLI), demonstrating strong binding kinetics, and further confirmed by fluorescence lifetime imaging microscopy (FLIM), supporting direct molecular engagement.

The aptamer alters stress-induced nuclear recruitment of RAD51 through BRCA2, thereby compromising RAD51 foci formation and reducing DNA repair capacity. As a consequence, treated cells accumulate unrepaired DNA damage, consistent with defective HR.

Given the central role of HR in mediating resistance to PARP inhibition, we next assessed combinatorial effects with the clinically approved PARP inhibitor olaparib. Aptamer targeting RAD51 synergises with olaparib in a dose-dependent manner, inducing synthetic lethality in pancreatic cancer cells. In addition, the effect is observed also in 3D spheroid models, supporting the robustness of the mechanism in more physiologically relevant tumour contexts.

Together, these findings demonstrate that aptamers can be rationally engineered to disrupt critical protein-protein interactions within the DNA repair machinery. Targeting the RAD51-BRCA2 axis represents a powerful strategy to exploit synthetic lethality and enhance the efficacy of PARP inhibition in cancer cells. The lead aptamer is currently being further developed to advance its mechanistic characterisation and therapeutic potential.