Li Zhu

Sequential treatment with PARPi and WEE1i enhances antitumor immune responses in preclinical models of ovarian cancer

The antitumor activity demonstrated by DNA damage response inhibitors (DDRis) can be partially attributed to their capacity to enhance immune responses. However, the toxicity of DDRis to lymphocytes, particularly when a DDRi is combined with other treatments targeting cell cycle checkpoint kinases, indicates a need for the development of different DDRi treatment schedules. Here, we systematically assessed changes to the tumor immune microenvironment (TIME) in response to DDRis across various treatment timelines in ovarian cancer. Using single-cell analysis, we found that the sequential treatment with an inhibitor of poly(ADP-ribose) polymerase (PARPi), followed by an inhibitor of the cell cycle checkpoint kinase WEE1 (WEE1i), resulted in more effective cancer eradication and stronger antitumor immune responses in vivo, compared with mono- and concurrent therapy. Both sequential and concurrent treatment schedules could induce lethal DNA damage and activate the cGAS-STING pathway in cancer cells, but T cell viability was greater under sequential treatment. Proteomic analysis showed that T cells more quickly recovered from DNA damage after DDRi treatment compared with cancer cells. Both immune checkpoint therapy and CAR T cells were more effective when combined with sequential treatment compared with monotherapy treatment in a syngeneic high-grade serous ovarian cancer mouse model and in a treatment-resistant ovarian cancer patient-derived xenograft model. Our study demonstrated that sequential treatment with PARPi and WEE1i spared T cells from severe DNA damage and activated the cGAS-STING pathway in cancer cells, suggesting that antitumor immunity and control of tumor growth can be optimized through changes in treatment schedules.

Mitigating T cell DNA damage during PARP inhibitor treatment enhances antitumor efficacy

Poly(ADP-ribose) polymerase inhibitors (PARPis) are a class of agents targeting DNA damage repair that have become standard therapy for epithelial ovarian cancer (EOC) and multiple other solid tumors. In addition to targeting DNA damage repair, PARPis actively modulate antitumor immune responses, with efficacy being partially dependent on T cell activity. Here, we found that patient T cells sustain DNA damage during PARPi treatment, which reduces treatment efficacy. Leveraging paired pre- and posttreatment tumor samples from a clinical trial of patients with EOC treated with neoadjuvant niraparib as monotherapy, we showed that the PARPi caused DNA damage, slowed proliferation, and increased apoptosis in T cells, which we validated both in vitro and in mouse models. A genome-wide CRISPR (clustered regularly interspaced short palindromic repeats) knockout screen in primary human T cells identified PARP1 as the principal mediator of PARPi-induced T cell death. T cell–specific deletion of PARP1 or mutating Parp1 at its binding sites in transgenic mice led to reduced T cell DNA damage during PARPi treatment, resulting in improved efficacy of PARPis, alone or in combination with immune checkpoint inhibition. We then engineered PARPi-tolerant CAR T cells using cytosine base editing, which decreased PARPi-induced PARP1 trapping and led to reduced PARPi-induced DNA damage, resulting in superior antitumor efficacy in xenograft models compared with parental CAR T cells. This study highlights the relevance of PARPi-induced DNA damage to T cells and suggests opportunities to improve the efficacy of PARPis as monotherapy or in combination with immunotherapy.