Abstract 4758: MYC-BCL6 state transition drives metabolomic cycling and leukemia-initiating capacity in B-ALL

Abstract Background and significance: Stemness in AML is defined by a rare leukemia-initiating cell (LIC) population, but analogous LICs in B-ALL have remained elusive (Kelly 2007, Le Viseur 2008, Rehe 2013). Given that LICs in AML are drug-resistant and initiate relapses, identifying an LIC population in B-ALL would be consequential. Results: Time-lapse studies of patient-derived B-ALL cells revealed that most B-ALL cells were continuously proliferating, while subpopulations underwent periodic transitions between quiescent and proliferative states. Gene expression studies identified MYC as the top-ranking gene in ‘proliferative’ and BCL6 in ‘quiescent’ B-ALL cells. To dissect MYC-BCL6 dynamics, we knocked in dual reporters with mNeonGreen fused to MYC and mScarlet fused to BCL6 in patient-derived B-ALL (PDX). Time-lapse imaging revealed proliferative cells expressed MYC with no detectable BCL6, whereas PDX also included ‘alternating’ cells that underwent repeated transitions between MYC+ BCL6− and MYC− BCL6+ states. Approximately 30% of BCR-ABL1 B-ALL and 50% of RAS-pathway B-ALL consisted of ‘alternating’ cells. Transitions occurred independently of the ∼36-hour cell-division cycle, with ∼3-hour MYC phases and ∼6-hour BCL6 phases. Integrated ChIP-seq, RNA-seq, and metabolomics showed that MYC-high cells are much larger and activate glycolysis and protein-synthesis programs, whereas BCL6-high cells are small and enriched for phosphatidylethanolamine (PtdEtn) synthesis, essential for autophagosome formation. To directly link MYC-BCL6 dynamics with growth, we combined quantitative phase microscopy and time-lapse fluorescence to measure single-cell dry mass. MYC-high cells accumulated biomass at twice the rate of BCL6-high cells (0.018 vs 0.009 pg/min), producing stepwise trajectories aligned with each MYC/BCL6 state transition. To experimentally induce transitions, we engineered PDX with MYC-dTAG knock-in alleles and employed the BCL6 PROTAC ARV-393. Acute MYC degradation caused rapid shrinkage and reduced dry mass, whereas BCL6 degradation decreased autophagy and increased biomass, confirming opposing MYC-driven anabolic and BCL6-driven catabolic programs. To functionally study ‘steady’ (MYC-only) and ‘alternating’ (MYC/BCL6) B-ALL populations, we developed a cell-sorting strategy that enriched each of the two populations to a purity of 85% as confirmed by subsequent time-lapse imaging. Extreme limiting dilution and series transplantation experiments revealed MYC-BCL6 alternating B-ALL cells significantly enriched for LIC (1 in 124) compared to MYC-only population (1 in 574) and initiated fatal leukemia after short latency. Conclusion: These findings reveal a MYC-BCL6 state-transition program in B-ALL that coordinates quiescence-proliferation cycling, anabolic-catabolic metabolism, and leukemia-initiating potential. Citation Format: Zhangliang Cheng, Ruoyi Shi, Kohei Kume, Mark Robinson, Richard Kim, Kadriye Nehir Cosgun, Yujin Bao, Siyi Chen, Mina Xu, Joerg Bewersdorf, Markus Muschen, . MYC-BCL6 state transition drives metabolomic cycling and leukemia-initiating capacity in B-ALL abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4758.