Identification of the Energy Stress Sensor AMPK As Therapeutic Target in Acute Lymphoblastic Leukemia

Background and Hypothesis: While often transformed by the same oncogenes, biological and clinical characteristics of B-cell lineage and myeloid leukemias markedly differ. For instance, BCR-ABL1 tyrosine kinase drives both chronic myeloid leukemia (CML) and B cell lineage Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ ALL). While the majority of CML patients achieve long-term disease-free survival under treatment, Ph⁺ ALL patients invariably relapse within months after initial remission. Here, we investigated whether the distinct characteristics of Ph⁺ ALL and CML have a metabolic basis and identified the metabolic sensor LKB1 and its substrate AMPK as novel therapeutic targets in pre-B ALL.

Results: Metabolic measurements revealed strikingly higher AMP:ATP ratios with concomitant decreases in ATP production in patient-derived Ph⁺ ALL cells when compared to CML cells. These findings indicate a state of chronic energy depletion in pre-B ALL cells. Energy deficit activates the LKB1-AMPK energy sensor pathway to stimulate glucose uptake to restore ATP levels. Notably, LKB1 levels and activity of its substrate AMPKα were higher in patient-derived Ph⁺ ALL cells compared to CML cells. To study the consequences of inducible deletion of Lkb1, murine BCR-ABL1-driven myeloid lineage (CML) and B cell precursor (Ph⁺ ALL) Lkb1^fl/fl leukemia cells were generated. We found that Lkb1-deletion increased glycolysis, ATP levels and proliferation in myeloid leukemia, consistent with the common notion that LKB1 is an established tumor suppressor. On the contrary, loss of Lkb1 function resulted in diminished glycolytic activity, impaired mitochondrial functions and cell death in pre-B ALL cells. C/EBPa-mediated reprogramming of B-cell into myeloid identity reversed the detrimental effects of Lkb1-deletion, restoring glycolysis, energy levels and survival of B→ myeloid reprogrammed cells. To study Lkb1 early in B cell lineage in vivo, Lkb1^fl/fl mice were crossed with Mb1-Cre^tg/+ mice. Loss of Lkb1 function strikingly eradicated early B cell progenitor cells in vivo. Reduced survival fitness upon Lkb1 deletion in pre-B ALL cells was largely rescued by metabolites that can enter the TCA cycle and thus provide ATP. Importantly, we found that inducible deletion of Lkb1 delayed onset of pre-B ALL and prolonged survival of transplant recipient mice in vivo. Similar to observations made with deletion of Lkb1 in murine BCR-ABL1 pre-B ALL cells, both loss of Ampka function and small molecule inhibition of AMPK (BML-275) resulted in cell death as well as reduced glycolytic activity and mitochondrial function in BCR-ABL1 pre-B ALL cells. Moreover, prolonged overall survival was observed in transplant recipient mice injected with Ampka-deficient pre-B ALL cells. Finally, BML-275 synergized with glucocorticoids, a central component of all main therapy regimen in pre-B ALL, in eradicating patient-derived pre-B ALL cells.

Conclusions: Taken together, our findings showed that B-cell lineage leukemia, unlike myeloid leukemia, critically depend on LKB1/AMPK signaling for survival. Our findings also showed that LKB1/AMPK can be leveraged to provide a novel therapeutic avenue in pre-B ALL.