Isoliensinine inhibits mitophagy and sensitizes T cell malignancies for STING-mediated NK clearance

Mitochondrial DNA (mtDNA) damage and accumulation activate the cGAS-STING DNA-sensing pathway, which promotes immune clearance of tumor cells. Maintenance of the cytosolic level of mtDNA is key to sustain immune activation. T cell malignancies (T-CMs) are a general name of diseases with abnormal clonal proliferation of T lymphocytes at various stages. Immunotherapy of T-CMs is challenged by the lack of specific antigens to discriminate T-CMs from normal T cells. As intrinsic STING activation can promote the clearance of T-CMs by immune cells, we herein explored whether isoliensinine (IsoL), a natural compound from Nelumbinis Plumula could enhance NK clearance by mtDNA-mediated immune responses in tumor cells. To investigate whether IsoL modulated immune recognition and clearance of T-CMs, we pre-treated three T-CM cell lines (Jurkat, Molt4 and Hut102) with IsoL then co-cultured with NK-92MI cells. We showed that IsoL pre-treatment promoted cytosolic mtDNA accumulation by inducing ROS-dependent mitochondrial damage and inhibiting mitophagy via peroxiredoxin 1 (PRDX1), an antioxidant enzyme. Loss of PRDX1 in T-CMs also induced ROS-dependent mitochondrial DNA damage, and blocked mitophagy by preventing accumulation of mature PINK1, which was required to initiate mitophagy via recruiting Parkin to the damaged mitochondria. Remarkably, IsoL could induce expression of activating ligands in vitro, enhance NK cell infiltrations, and increase apoptosis of T-CMs. Moreover, we demonstrated that IsoL could sensitize T-CMs for NK clearance in vitro and in vivo. These results suggest that IsoL could be a potential therapeutic agent to enhance immune therapy of T-CMs.