Activation of a promyelocytic leukemia-tumor protein 53 axis underlies acute promyelocytic leukemia cure

Acute promyelocytic leukemia (APL) is driven by the promyelocytic leukemia (PML)-retinoic acid receptor-a (PML-RARA) fusion protein, which interferes with nuclear receptor signaling and PML nuclear body (NB) assembly. APL is the only malignancy definitively cured by targeted therapies: retinoic acid (RA) and/or arsenic trioxide, which both trigger PML-RARA degradation through nonoverlapping pathways. Yet, the cellular and molecular determinants of treatment efficacy remain disputed. We demonstrate that a functional Pml-transformation-related protein 53 (Trp53) axis is required to eradicate leukemia-initiating cells in a mouse model of APL. Upon RA-induced PML-RARA degradation, normal Pml elicits NB reformation and induces a Trp53 response exhibiting features of senescence but not apoptosis, ultimately abrogating APL-initiating activity. Apart from triggering PML-RARA degradation, arsenic trioxide also targets normal PML to enhance NB reformation, which may explain its clinical potency, alone or with RA. This Pml-Trp53 checkpoint initiated by therapy-triggered NB restoration is specific for PML-RARA-driven APL, but not the RA-resistant promyelocytic leukemia zinc finger (PLZF)-RARA variant. Yet, as NB biogenesis is druggable, it could be therapeutically exploited in non-APL malignancies.