AML Stem Cell Clearance By Inhibiting Selenoprotein Biosynthesis That Causes Cgas-Sting Activation and Ferroptosis

Background: Despite the intense drug development focus on immunotherapy and mutation-targeted therapies, most patients with acute myeloid leukemia (AML) are not cured and still rely on traditional cytotoxic multi-agent chemotherapy. Metabolic alteration is one of the hallmark characteristics distinguishing malignant cells from normal cells, especially following the extreme metabolic stress from chemotherapy. We hypothesized that this metabolic stress would reveal unique vulnerabilities in the persisting AML cells.

Results: Using a comprehensive genome-wide CRISPR-Cas9 knockout (KO) screen in a HoxB8-ER model of myeloid neoplasia, we identified a critical dependency on phosphoseryl-tRNA kinase (PSTK), an atypical kinase essential for the biosynthesis of all selenoproteins. Selenoproteins are a group of evolutionarily conserved proteins essential for maintaining cellular antioxidant capacity and redox homeostasis. They contain the 21^st amino acid selenocysteine (Sec). Among them is Glutathione peroxidase 4 (GPX4), a master regulator of ferroptosis.

In vivo, PSTK inhibition (PSTKi) significantly impeded the growth of AML cell lines and primary mouse and human AML cells. PSTKi impaired the self-renewal capacity of leukemic stem cells. Notably, timed pharmacological inhibition of PSTK exhibited potent efficacy in targeting and even eradicating AML, particularly in chemo-resistant forms of the disease, within murine and patient-derived xenograft models. PSTKi showed a pronounced selectivity for malignant cells over normal hematopoietic cells, suggesting a possible therapeutic window.

Mechanistically, PSTKi resulted in the induction of reactive oxygen species (ROS), which in turn triggered the release of mitochondrial DNA into cytosol. This event activated the cGAS-STING pathway, a critical component of the innate immune response. Activation of the cGAS-STING pathway altered iron metabolism, leading to increased ROS production and enhanced ferroptosis. This creates a self-amplifying PSTK-cGAS-STING-ROS feedback loop that precipitates an oxidative crisis and ferroptotic cell death in leukemic cells.

Conclusions and discussion: Our findings elucidate a novel PSTK-cGAS-STING-ROS signaling cascade that induces ferroptosis in leukemia. Inhibition of PSTK enhances leukemia cell death across various genotypic backgrounds, presenting a potential strategy to sensitize chemoresistant leukemic stem cells to therapy. These results highlight the promise of leveraging timed metabolic interventions to augment existing cancer chemotherapies and reduce AML relapse. Moreover, the cooperative effects of PSTK inhibition and cGAS-STING activation promote cell-intrinsic oxidative death and may foster an inflammatory tumor microenvironment, thereby enhancing immune activation. Targeting PSTK could thus represent a dual approach, combining direct anti-tumor effects with immune system engagement.

Sykes:Clear Creek Bio: Consultancy, Current equity holder in private company. Scadden:Editas Medicine: Membership on an entity's Board of Directors or advisory committees; Lightning Biotherapeutics: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees; Sonata Therapeutics: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees; VCanBio: Consultancy; Clear Creek Bio: Current holder of stock options in a privately-held company; Garuda Therapeutics: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees; Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Carisma Therapeutics: Membership on an entity's Board of Directors or advisory committees.