Targeting GRP75 by natural compound polyphyllin II triggers mitochondrial calcium overload and pyroptosis to potentiate cancer immunotherapy
Yuting Wang, Jingwen Dong, Yu Long, Liping Li, Cuicui Sun, Ruoqi Li, Jiayu Zhang, Yichen Liu, Zipeng Yao, Shuqi Wang, Ke Li, Mingxiao Yin, Xinbo Zhou, Na Zhang, Hongbin DengBackground
Immune checkpoint blockade (ICB) therapy has emerged as a pivotal cancer treatment by activating antitumor immunity. However, its clinical efficacy remains limited in many patients, highlighting the need for combination strategies to overcome resistance. Inducing immunogenic cell death (ICD) represents a promising approach to remodel the immunosuppressive tumor microenvironment and improve ICB efficacy.
Methods
A high-throughput screen of a natural compound library identified potent ICD inducers. Polyphyllin II (PPII), a bioactive component from Paris polyphylla , was selected for further investigation. Its effects on ICD markers, tumor growth, and immune activation were evaluated in vitro and in vivo. Limited proteolysis-mass spectrometry was employed to identify the direct target of PPII, followed by mechanistic studies using molecular and immunological assays.
Results
PPII was identified as a potent ICD inducer, stimulating the release of high mobility group box 1, ATP, and calreticulin from tumor cells. PPII suppressed tumor growth and enhanced antitumor immunity by promoting dendritic cell maturation and antigen cross-presentation, leading to CD8 + T-cell activation. Mechanistically, PPII directly bound to glucose-regulated protein 75 (GRP75), enhancing endoplasmic reticulum-mitochondrial tethering, provoking endoplasmic reticulum stress and mitochondrial calcium overload, and promoting cytochrome c release and caspase-3 activation. This cascade ultimately triggered gasdermin E (GSDME)-mediated pyroptosis. Furthermore, PPII synergized with anti-programmed cell death protein 1 therapy by reprogramming the tumor immune microenvironment and promoting systemic antitumor immunity.
Conclusion
Our findings identify GRP75 as a novel therapeutic target for cancer immunotherapy and highlight PPII-driven immune reprogramming as a translatable strategy to potentiate ICB efficacy through the induction of immunogenic pyroptosis.