Inhibiting Mitochondria Potentiates PARPi-Triggered, STING-Dependent Immune Response in Pre-Clinical Models of Epithelial Ovarian Cancer
Recommended Citation
Speak A, Hijaz M, Singh H, Udumula M, Miller M, Munkarah A, and Rattan R. Inhibiting mitochondria potentiates PARPi-triggered, STING-dependent immune response in pre-clinical models of epithelial ovarian cancer. Gynecol Oncol 2024; 190:S233-S234.
Document Type
Conference Proceeding
Publication Date
11-1-2024
Publication Title
Gynecol Oncol
Abstract
OBJECTIVES: In ovarian cancer patients with hereditary or somatic BRCA1/2 mutations, PARP inhibitors (PARPi) have altered the treatment landscape. DNA damage caused by PARPi in conjunction with DNA repair errors due to mutations in BRCA1/2 initiates immunologic signaling via the cGAS/STING pathway. Studies have shown that therapy with a STING agonist can boost the efficacy of olaparib in BRCA-mutated ovarian cancer cells. Current research suggests that the activity of almost all immune cells is regulated by their cellular metabolism, especially energy metabolism. We have previously shown that inhibiting mitochondria by metformin augmented the therapeutic efficacy of PARPi in BRCA-intact pre-clinical ovarian cancer models. This study examined whether mitochondrial inhibition could increase STING pathway activation by olaparib in BRCA1/2-mutated and wild-type ovarian cancer cells and mouse models.
METHODS: ID8 p53+/+, ID8 p53-/-, ID8 p53-/-, BRCA1-/-, and ID8 p53-/-, BRCA2-/- mouse ovarian cancer cells were treated with olaparib (5mm) or metformin (2.5mM) or a combination of both; 2′,3′-Cyclic GAMP was measured by ELISA. DNA damage (gH2AX) was evaluated by flow cytometry. Mitochondrial function was assessed by an XF seahorse analyzer. Treated cells were co-cultured with naïve CD8 T cells and profiled by flow cytometry. All cell lines were used to validate the response in vivo.
RESULTS: Olaparib increased γH2AX (P < 0.001) in the ID8 p53-/-, BRCA2-/- cells relative to ID8 p53-/-, BRCA1-/- and wild-types, and metformin further augmented this effect (P < 0.0001); while the lowest DNA damage was induced in BRCA and p53 intact ID8 p53+/+ (P < 0.001) cells. Increased DNA damage in ID8 p53-/-, BRCA2-/- cells correlated with elevated STING by olaparib, which was further exacerbated by the addition of metformin (P < 0.0001). When co-cultured with naïve splenic CD8 T cells, all cell lines activated CD8 effector and cytotoxic function (CD8+IFNg+, P < 0.0001; CD8+perforin+, P < 0.001; CD8+granzyme B+, P < 0.001) and STING response (CD8+STING+, P < 0.000; CD8+TBK+, P < 0.001). The effector activity and STING were highly elevated in CD8 T cells when co-cultured with olaparib-treated ID8 p53-/-, BRCA2-/- compared to ID8 p53-/-, BRCA1-/- and wild-type ID8 cells; this effect was further enhanced by the addition of metformin. Metabolic phenotyping revealed that CD8 T cells treated with olaparib and metformin exhibited an increase in glycolysis linked with a greater STING response. Similar results were replicated by CPI-613, another mitochondrial inhibitor.
CONCLUSIONS: Olaparib activates cGAS/STING differently in ovarian cancer cells with BRCA1 and BRCA2 mutations. Mitochondrial inhibition promotes DNA damage and STING pathway activation induced by olaparib. Overall, the combination of metabolic modulators with PARPi may offer a possible therapeutic strategy for boosting the immunomodulatory effect of PARPi.
Volume
190
Issue
Supplement 1
First Page
S233
Last Page
S234
