BACH2‐mediated FOS confers cytarabine resistance via stromal microenvironment alterations in pediatric ALL

Acute lymphoblastic leukemia (ALL) is an aggressive hematological cancer that mainly affects children. Relapse and chemoresistance result in treatment failure, underlining the need for improved therapies. BTB and CNC homology 2 (BACH2) is a lymphoid‐specific transcription repressor recognized as a tumor suppressor in lymphomas, but little is known about its function and regulatory network in pediatric ALL (p‐ALL). Herein, we found aberrant BACH2 expression at new diagnosis not only facilitated risk stratification of p‐ALL but also served as a sensitive predictor of early treatment response and clinical outcome. Silencing BACH2 in ALL cells increased cell proliferation and accelerated cell cycle progression. BACH2 blockade also promoted cell adhesion to bone marrow stromal cells and conferred cytarabine (Ara‐C)–resistant properties to leukemia cells by altering stromal microenvironment. Strikingly, we identified FOS, a transcriptional activator competing with BACH2, as a novel downstream target repressed by BACH2. Blocking FOS by chemical compounds enhanced the effect of Ara‐C treatment in both primary p‐ALL cells and pre‐B‐ALL–driven leukemia xenografts and prolonged the survival of tumor‐bearing mice. These data highlight an interconnected network of BACH2‐FOS, disruption of which could render current chemotherapies more effective and offer a promising therapeutic strategy to overcome Ara‐C resistance in p‐ALL.