Targeting Replication Fork Processing Synergizes with PARP Inhibition to Potentiate Lethality in Homologous...

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Synthetic lethality in homologous recombination (HR)-deficient cancers treated with Poly (ADP-ribose) polymerase inhibitors (PARPi) is increasingly linked to replication processes rather than solely DNA repair.
• Targeting replication fork processing alongside HR-downregulation offers a strategy for HR-proficient and PARPi-resistant tumors.
• Stilbenes, like resveratrol, are known to modulate replication and RAD51 expression.

Purpose of the Study:

• To identify novel agents that downregulate RAD51 expression and homologous recombination (HR) repair.
• To evaluate the efficacy of combining a novel stilbene, trans-4,4 -dihydroxystilbene (DHS), with a PARPi in ovarian cancer models.
• To elucidate the underlying mechanisms of action for the combination therapy.

Main Methods:

• Screening of a stilbene library to identify compounds affecting RAD51 expression and HR repair using a GFP-reporter assay.
• Combination treatment of ovarian cancer cells with DHS and talazoparib (PARPi).
• Assessment of replication stress, single-stranded DNA (ssDNA) gaps, poly-ADP-ribosylation (PARylation), and DNA double-strand breaks.
• In vivo studies using ovarian tumor xenografts in SCID mice to evaluate therapeutic efficacy and toxicity.

Main Results:

• Trans-4,4 -dihydroxystilbene (DHS) was identified as a potent natural agent that downregulates RAD51 expression and HR repair.
• DHS synergistically enhanced cell death in ovarian cancers when combined with talazoparib (PARPi).
• Mechanistically, DHS induced replication stress by impeding replication fork progression and speed, leading to ssDNA gaps and PARylation, which were potentiated by PARPi to cause lethal double-strand breaks.
• The combination therapy significantly inhibited ovarian tumor xenograft growth with minimal observed tissue toxicity.

Conclusions:

• Trans-4,4 -dihydroxystilbene (DHS) is a potent natural agent that induces replication stress and downregulates HR repair.
• The combination of DHS and talazoparib (PARPi) demonstrates significant synergistic efficacy in ovarian cancer treatment, targeting both HR-proficient and potentially PARPi-resistant tumors.
• This combination therapy warrants further investigation as a novel therapeutic strategy for ovarian cancer, showing promising efficacy and a favorable toxicity profile.