PGG Enhances Olaparib Efficacy via cGAS-STING Signaling and Sensitizes Triple-Negative Breast Cancer to PD- L1 Blockade

Triple-negative breast cancer (TNBC) is a highly aggressive malignancy and options for targeted therapy are limited. Although PARP inhibitors (PARPi) like olaparib (Ola) leverage synthetic lethality, their clinical utility is severely impeded by drug resistance and low frequency of BRCA mutations. In this study, 1,2,3,4,6-penta-O-galloyl-{beta}-D-glucose (PGG), a natural polyphenolic compound, can induce a state of homologous recombination deficiency (HRD) in TNBC cells by inhibiting the PALB2-BRCA2 interaction. PGG potentiated the inhibitory effects of Ola on the in vitro proliferation, clonogenic potential, migration, and invasion of TNBC cells. Mechanistically, the dual therapy triggered severe oxidative stress and mitochondrial collapse, which accelerated the classical apoptosis cascade and promoted the emission of immunogenic cell death (ICD)-associated DAMPs. The accumulated cytosolic double-stranded DNA activated the innate immune cGAS-STING pathway, thereby promoting robust intra-tumoral infiltration of CD8+ T cells. Furthermore, since cGAS-STING hyperactivation drives compensatory PD-L1 upregulation on TNBC cells, incorporating anti-PD-L1 antibody into the combination regimen further reversed the immunosuppressive barrier, achieving near-complete tumor eradication and maximum infiltration of cytotoxic T cells in vivo. Bioinformatics analyses further suggested a potential network of PGG targets associated with extracellular matrix organization, offering a bioinformatics-derived hypothesis for its theoretical involvement in modulating stromal tension and vascular homeostasis. Collectively, this study establishes PGG as a multi-functional therapeutic agent integrating intracellular synthetic lethality and innate immune sensing, while providing a preliminary bioinformatic rationale for prospective microenvironmental investigation. This study also shows PGG as a multi-functional therapeutic agent that integrates intracellular synthetic lethality, innate immune sensing, and microenvironmental remodeling to convert immunologically "cold" TNBC into "hot" tumors.