PARPi triggers the STING-dependent immune response and enhances the therapeutic efficacy of immune checkpoint blockade independent of BRCAness

Poly-(ADP-ribose) polymerase (PARP) inhibitors (PARPi) have shown remarkable therapeutic efficacy against BRCA1/2 mutant cancers through a synthetic lethal interaction. PARPi exert their therapeutic effects mainly through the blockade of single-stranded DNA damage repair, which leads to the accumulation of toxic DNA double-strand breaks specifically in cancer cells with DNA repair deficiency (BCRAness), including those harboring BRCA1/2 mutations. Here we show that PARPi-mediated modulation of the immune response contributes to their therapeutic effects independently of BRCA1/2 mutations. PARPi promoted accumulation of cytosolic DNA fragments due to unresolved DNA lesions, which in turn activated the DNA sensing cGAS-STING pathway and stimulated production of type I interferons to induce antitumor immunity independent of BRCAness. These effects of PARPi were further enhanced by immune checkpoint blockade. Overall, these results provide a mechanistic rationale for using PARPi as immunomodulatory agents to harness the therapeutic efficacy of immune checkpoint blockade.

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