The Dysregulation of the Integrated Stress Response in Leukemic Stem Cells as a Marker of Treatment Sensitivity in Acute Myeloid Leukemia.

Acute myeloid leukemia (AML) persistence is sustained by leukemic stem cells (LSCs) that survive metabolic deprivation, oxidative stress, hypoxia, proteotoxic burden, and therapeutic pressure. The integrated stress response (ISR) has emerged as a central adaptive network in this process. Through phosphorylation of a subunit of eukaryotic initiation factor 2 (eIF2α) and selective translation of activating transcription factor 4 (ATF4), the ISR coordinates stress-responsive transcriptional programs that may either preserve cellular fitness or promote apoptotic commitment, depending on the intensity, duration, and biological context of activation. In AML, ATF4 occupies a critical position at the interface between stemness, metabolic adaptation, redox control, ferroptosis resistance, and treatment response. In primitive leukemic compartments, ISR-ATF4 signaling appears to support stress tolerance, amino acid metabolism, serine biosynthesis, autophagy, and leukemic persistence. At the same time, pharmacologic or sustained ISR activation may lower the apoptotic threshold by inducing pro-apoptotic mediators such as CHOP, PUMA, and NOXA, thereby modulating MCL-1 dependency and enhancing sensitivity to venetoclax-based strategies. Conversely, adaptive ISR signaling may promote resistance through mechanisms such as ATP-binding cassette subfamily B member 1 (ABCB1) enhancer activation and mitochondrial stress tolerance. This duality creates a therapeutic paradox: ISR-ATF4 signaling may need to be inhibited in adaptive, resistance-promoting states but amplified in apoptosis-permissive contexts. This review discusses the biological and therapeutic relevance of ISR-ATF4 dysregulation in AML and highlights the need for biomarkers capable of distinguishing adaptive ATF4 dependency from inducible apoptotic vulnerability.