Fig. 3.

Principle of synthetic lethality reached with PARP inhibitors (PARPi) used in homologous recombination deficient (HRD) cells. a In standard conditions, PARP proteins repair single-stand breaks (SSB). b In homologous recombination repair (HRR)-competent cells, the use of PARPi prevents SSB from repairing. Though replication, this converts SSB into double-strand breaks (DSB), and cells survive using HRR. c In HRD cells with PARPi, neither SSB nor DSB could be repaired. This leads to cell death, through a synergy between PARPi and HRD called synthetic lethality