Targeting ferritinophagy to iron out Tet2-mutant cells Free

In this issue of Blood, Loke et al¹ show that ferritinophagy, a selective autophagic process mediated by the cargo receptor Ncoa4, supports the expansion of Tet2-mutant hematopoietic stem and progenitor cells (HSPCs) by maintaining mitochondrial iron availability and oxidative metabolism. This work identifies a novel metabolic dependency in Tet2-deficient clonal hematopoiesis (CH) and reveals a promising therapeutic target for early intervention.

CH occurs when somatic mutations in long-lived HSPCs confer a competitive advantage, leading to the expansion of mutant clones over time.² Although initially asymptomatic, CH is associated with an increased risk of both hematologic malignancies and nonhematologic diseases, particularly cardiovascular disease.^3,TET2 is mutated in approximately one-third of CH cases and encodes a dioxygenase involved in active DNA demethylation.⁴ Although Tet2-deficient HSPCs exhibit enhanced self-renewal and long-term repopulation capacity in murine models,⁵ the molecular mechanisms that maintain their clonal advantage remain incompletely understood.

To address this gap, Loke et al developed a barcoded lentiviral CRISPR-Cas9 screening platform to induce and clonally track targeted gene perturbations in vivo. Applying this system to competitive transplantation assays in mouse models, the authors identified Ncoa4 as a selective genetic vulnerability in Tet2 knockout (KO) HSPCs (see figure). Genetic deletion of Ncoa4 impaired the long-term fitness of Tet2-deficient cells without affecting wild-type HSPCs, in both primary and secondary transplants. These results establish ferritinophagy as a critical dependency of Tet2-mutant hematopoiesis. Notably, these findings are consistent with recent reports identifying ferritinophagy as a critical dependency of leukemic stem cells in patient-derived xenograft models of acute myeloid leukemia,⁶ suggesting that NCOA4-mediated iron mobilization may be a common metabolic feature of both preleukemic and leukemic stem cells.

To assess therapeutic relevance, the authors used ironomycin, a lysosome-targeting compound that functionally sequesters iron and inhibits its lysosomal release.⁷ Ironomycin treatment phenocopied the effects of Ncoa4 deletion by selectively impairing the expansion of Tet2 KO HSPCs in vivo, with a pronounced effect on the myeloid lineage. These findings position ironomycin as a potential therapeutic strategy to target dysregulated iron metabolism in malignancies driven by aberrant ferritinophagy, including those associated with TET2 mutations.

A particularly compelling aspect of the study is the mechanistic link between ferritinophagy, mitochondrial iron availability, and cellular bioenergetics. Tet2-deficient HSPCs exhibited increased mitochondrial mass, cristae density, and oxidative phosphorylation (OXPHOS) compared to wild-type cells. These features were reversed by genetic or pharmacological disruption of ferritinophagy, implicating iron-dependent mitochondrial reprogramming as a key driver of Tet2-mutant cell fitness.

These results parallel recent findings in Dnmt3a R878H mutant HSPCs (the murine equivalent of human DNMT3A R882H), which also depend on elevated OXPHOS for their competitive advantage.⁸ In this context, treatment with metformin, a mitochondrial complex I inhibitor, attenuated the expansion of mutant clones in both murine and human models. Together, these studies highlight enhanced mitochondrial metabolism as a hallmark of CH and suggest that metabolic vulnerabilities may be therapeutically exploitable to prevent or delay malignant progression.

This work raises several important questions: is ferritinophagy similarly required for the fitness of other CH-associated mutations, such as DNMT3A or ASXL1, or is this dependence unique to TET2 deficiency? Comparative studies across different CH genotypes will be critical to determine whether shared or mutation-specific metabolic programs support clonal expansion. Furthermore, validation of these findings in aged human HSPCs, particularly from individuals with TET2-mutant CH, will be essential to confirm clinical relevance.

In conclusion, this study reveals a novel link between iron metabolism, mitochondrial bioenergetics, and clonal expansion in Tet2-mutant hematopoiesis. It provides mechanistic insight into CH and establishes the rationale for targeting metabolic vulnerabilities as a strategy to intercept preleukemic evolution. As the field of CH continues to expand, studies such as this will be key to translating molecular discoveries into interventions that may alter the disease trajectory at its earliest stages.

Conflict-of-interest disclosure: The authors declare no competing financial interests.