Year: 2025
Type: conference-abstract
Abstract: Background and Significance: Oncogenic tyrosine kinases activate STAT5a and STAT5b to promote survival and proliferation in acute lymphoblastic leukemia (B-ALL). Counterintuitively, we found that high expression levels of negative STAT5-regulators (CISH and SOCS-family proteins) predict poor clinical outcomes for B-ALL patients. Likewise, our experiments based on genetic deletion of SOCS2 and SOCS3 showed that impaired STAT5 feedback inhibition resulted in loss of colony formation and cell death in B-ALL. While STAT5 functions as oncogenic driver in B-ALL, these results highlight a previously unrecognized role of STAT5-feedback inhibition in leukemia cells and suggest a “Goldilocks zone” to maintain optimal STAT5 signaling strength. Results: To assess STAT5 signaling thresholds in vivo, we modeled modest increases and decreases of STAT5-activity based on Stat5a gain- (GOF) and loss-of-function (LOF) point mutations. Stat5aGOF B-ALL cells showed increased cell mass, glycolysis (ECAR, lactate production) and accelerated proliferation. However, increased ER-stress and cellular senescence subverted colony formation and leukemia-initiation capacity of Stat5aGOF B-ALL cells. In contrast, Stat5aLOF leukemia cells were small and quiescent with 3.5-fold increased colony formation and a 21-fold increased the frequency of leukemia-initiating cells in transplant recipients. Studying Stat5aGOF- and Stat5aLOF-dependent transcriptional programs, we identified MYC- and BCL6-target genes as top-ranking gene sets. Metabolomic analyses revealed that Stat5aGOF increased 60 MYC-dependent metabolites across glycolysis, TCA cycle and amino acid metabolism pathways. In contrast, metabolomic and lipidomic analyses revealed that Stat5aLOF promoted BCL6-dependent phosphatidylethanolamine (PtdEtn) production, which is essential for autophagosome biogenesis. Stat5aLOF not only promoted PtdEtn synthesis but also increased autophagy (LC3B puncta formation and flux). Interestingly, defective autophagy, ER-stress, and senescence in Stat5aGOF B-ALL cells were largely mitigated by supplementation of PtdEtn. To leverage MYC and BCL6 as biomarker of increased and decreased STAT5-activity, respectively, we engineered patient-derived B-ALL xenografts (PDX) with N-terminal mNeonGreen-MYC and mScarlet-BCL6 fusion knockin-alleles by CRISPR and HDRT. Single-cell time-lapse experiments over 24 hours revealed that B-ALL cells with mutant JAK2 and BCR-ABL1 autonomously transitioned between cell states of high (MYC) and low (BCL6) STAT5-activity, with a period of four hours. Interestingly, inhibitors of JAK2 (ruxolitinib) and BCR-ABL1 (imatinib) suppressed STAT5 (MYC) activity and forced transition to a quiescent BCL6+ cell state. Conversely, treatment of B-ALL PDX carrying MYC- and BCL6-knockin fusions with the STAT5-agonist ABBV-CLS-484 had the opposite effect of imatinib, strongly activated STAT5 and forced transition of BCL6+ quiescent B-ALL cells into a MYC+ proliferative cell state. To assess potential therapeutic benefit of targeted STAT5-hyperactivation, we treated NSG mice bearing patient-derived BCR-ABL1 B-ALL xenografts with daily injections of 40 mg/kg ABBV-CLS-484 i.p. for two weeks. Recapitulating the effects of Stat5aGOF in murine B-ALL, ABBV-CLS-484 treatment subverted leukemia-initiation capacity and substantially prolonged survival of transplant recipient mice. Conclusions: The tyrosine kinase inhibition paradigm is based on the dependency of B-ALL cells on high-level STAT5-signaling and activation of MYC. Our findings reveal a previously unrecognized dependency of human B-ALL cells on negative STAT5-feedback regulation by CISH and SOCS and activation of BCL6. Every four hours, B-ALL cells transition between cell-states of higher (MYC) and lower (BCL6) STAT5 activity. While traditional tyrosine kinase inhibitors target the MYC-dependent cell proliferation, our findings support a rationale for targeting BCL6-dependent quiescence. The small molecule STAT5-agonist ABBV-CLS-484 was recently introduced in Phase 2 clinical trials as immunotherapy adjuvant to increase STAT5-activity in T-cells for enhanced T-cell antitumor immunity in patients with solid tumors (NCT04777994). Since ABBV-CLS-484 showed favorable safety and desirable activation of T-cell antitumor immunity, targeted STAT5-hyperactivation is amenable to near-term evaluation in patients with refractory B-ALL.
Source: Blood
Institutions: Yale University, National Institutes of Health, National Heart, Lung, and Blood Institute, Zhejiang University, University of California, San Francisco, University of Eastern Finland, University of California, Los Angeles, University of Washington, St. Jude Children's Research Hospital, Walter and Eliza Hall Institute of Medical Research, Harvard University, University of Turin, European Institute of Oncology
Language: English
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W4417001906
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