SYK inhibition targets acute myeloid leukemia stem cells by blocking their oxidative metabolism

Spleen tyrosine kinase (SYK) is an important oncogene and signaling mediator activated by cell surface receptors crucial for acute myeloid leukemia (AML) maintenance and progression. Genetic or pharmacologic inhibition of SYK in AML cells leads to increased differentiation, reduced proliferation, and cellular apoptosis. Herein, we addressed the consequences of SYK inhibition to leukemia stem-cell (LSC) function and assessed SYK-associated pathways in AML cell biology. Using gain-of-function MEK kinase mutant and constitutively active STAT5A, we demonstrate that R406, the active metabolite of a small-molecule SYK inhibitor fostamatinib, induces differentiation and blocks clonogenic potential of AML cells through the MEK/ERK1/2 pathway and STAT5A transcription factor, respectively. Pharmacological inhibition of SYK with R406 reduced LSC compartment defined as CD34+CD38-CD123+ and CD34+CD38-CD25+ in vitro, and decreased viability of LSCs identified by a low abundance of reactive oxygen species. Primary leukemic blasts treated ex vivo with R406 exhibited lower engraftment potential when xenotransplanted to immunodeficient NSG/J mice. Mechanistically, these effects are mediated by disturbed mitochondrial biogenesis and suppression of oxidative metabolism (OXPHOS) in LSCs. These mechanisms appear to be partially dependent on inhibition of STAT5 and its target gene MYC, a well-defined inducer of mitochondrial biogenesis. In addition, inhibition of SYK increases the sensitivity of LSCs to cytarabine (AraC), a standard of AML induction therapy. Taken together, our findings indicate that SYK fosters OXPHOS and participates in metabolic reprogramming of AML LSCs in a mechanism that at least partially involves STAT5, and that SYK inhibition targets LSCs in AML. Since active SYK is expressed in a majority of AML patients and confers inferior prognosis, the combination of SYK inhibitors with standard chemotherapeutics such as AraC constitutes a new therapeutic modality that should be evaluated in future clinical trials

Management and outcome of patients with chronic myeloid leukemia in blast phase in the tyrosine kinase inhibitor era – analysis of the European LeukemiaNet Blast Phase Registry

Blast phase (BP) of chronic myeloid leukemia (CML) still represents an unmet clinical need with a dismal prognosis. Due to the rarity of the condition and the heterogeneity of the biology and clinical presentation, prospective trials and concise treatment recommendations are lacking. Here we present the analysis of the European LeukemiaNet Blast Phase Registry, an international collection of the clinical presentation, treatment and outcome of blast phases which had been diagnosed in CML patients after 2015. Data reveal the expected heterogeneity of the entity, lacking a clear treatment standard. Outcomes remain dismal, with a median overall survival of 23.8 months (median follow up 27.8 months). Allogeneic stem cell transplantation (alloSCT) increases the rate of deep molecular responses. De novo BP and BP evolving from a previous CML do show slightly different features, suggesting a different biology between the two entities. Data show that outside clinical trials and in a real-world setting treatment of blast phase is individualized according to disease- and patient-related characteristics, with the aim of blast clearance prior to allogeneic stem cell transplantation. AlloSCT should be offered to all patients eligible for this procedure

Phase 3 Trial of Gilteritinib Plus Azacitidine Vs Azacitidine for Newly Diagnosed FLT3mut+ AML Ineligible for Intensive Chemotherapy.

Treatment results for patients with newly diagnosed FMS-like tyrosine kinase 3 (FLT3)-mutated (FLT3mut+) acute myeloid leukemia (AML) ineligible for intensive chemotherapy are disappointing. This multicenter, open-label, phase 3 trial randomized (2:1) untreated adults with FLT3mut+ AML ineligible for intensive induction chemotherapy to gilteritinib (120 mg/day orally) and azacitidine (GIL+AZA) or azacitidine (AZA) alone. The primary endpoint was overall survival (OS). At the interim analysis (26 August 2020), 123 patients were randomized (GIL+AZA, n=74; AZA, n=49). Subsequent AML therapy, including FLT3 inhibitors, was received by 20.3% (GIL+AZA) and 44.9% (AZA) of patients. Median OS was 9.82 (GIL+AZA) and 8.87 (AZA) months (HR 0.916 [95% CI: 0.529, 1.585]; P=0.753). The study was closed based on the protocol-specified boundary for futility. Median event-free survival (EFS) was 0.03 months in both arms. EFS defined using composite CR (CRc) was 4.53 (GIL+AZA) and 0.03 (AZA) months (HR 0.686 [95% CI: 0.433, 1.087]; P=0.156). CRc rates were 58.1% (GIL+AZA) and 26.5% (AZA; difference 31.4% [95% CI: 13.1, 49.7]; P<0.001). Adverse event (AE) rates were similar for GIL+AZA (100%) and AZA (95.7%) and grade ≥3 AEs were 95.9% and 89.4%, respectively. Common AEs with GIL+AZA included pyrexia (47.9%) and diarrhea (38.4%). Gilteritinib steady state trough concentrations were no different between GIL+AZA and gilteritinib. GIL+AZA resulted in significantly higher CRc rates although similar OS versus AZA. Results support the safety/tolerability and clinical activity of upfront therapy with GIL+AZA in older/unfit patients with FLT3mut+ AML. Clinical Trial # NCT02752035

Targeting the thioredoxin system as a novel strategy against B cell acute lymphoblastic leukemia.

B cell precursor acute lymphoblastic leukemia (BCP-ALL) is a genetically heterogeneous blood cancer characterized by abnormal expansion of immature B cells. Although intensive chemotherapy provides high cure rates in a majority of patients, subtypes harboring certain genetic lesions, such as MLL rearrangements or BCR-ABL1 fusion, remain clinically challenging, necessitating a search for other therapeutic approaches. Herein, we aimed to validate antioxidant enzymes of the thioredoxin system as potential therapeutic targets in BCP-ALL. We observed oxidative stress along with aberrant expression of the enzymes associated with the activity of thioredoxin antioxidant system in BCP-ALL cells. Moreover, we found that auranofin and adenanthin, inhibitors of the thioredoxin system antioxidant enzymes, effectively kill BCP-ALL cell lines and pediatric and adult BCP-ALL primary cells, including primary cells co-cultured with bone marrow-derived stem cells. Furthermore, auranofin delayed the progression of leukemia in MLL-rearranged patient-derived xenograft model and prolonged the survival of leukemic NSG mice. Our results unveil the thioredoxin system as a novel target for BCP-ALL therapy, and indicate that further studies assessing the anticancer efficacy of combinations of thioredoxin system inhibitors with conventional anti BCP-ALL drugs should be continued