The Combination of Lanraplenib, a Selective SYK Inhibitor, and Gilteritinib, a FLT3 Inhibitor, Targets Aberrant Proliferation and Differentiation Blockade in Acute Myeloid Leukemia
Authors: Carvajal Luis A. , McKeown Michael R. , Hood Tressa , Guo Linlin , Lin Charles Y. , DiMartino Jorge F. 
Published: December 2023

Background:
Acute myeloid leukemia (AML) is an aggressive disease characterized by uncontrolled clonal proliferation of poorly differentiated myeloid progenitor cells in the bone marrow and blood. Deregulated spleen tyrosine kinase (SYK) impairs myeloid differentiation and has been implicated in the pathogenesis of AML driven by FMS-like tyrosine kinase 3 (FLT3) internal tandem duplication (ITD) mutation (FLT3-ITD). While SYK is rarely mutated, it is highly activated in FLT3-ITD-mutated AML and directly phosphorylates FLT3-ITD, resulting in aberrant expression of multiple oncogenic pathways. Lanraplenib (LANRA) is a selective, next-generation, SYK inhibitor that has shown favorable PK, PD, and safety in healthy volunteers and patients with autoimmune diseases. LANRA is currently being evaluated in combination with gilteritinib, a FLT3 inhibitor, in patients with relapsed or refractory (R/R) FLT3-mutated AML (NCT05028751). By jointly inhibiting the leukemogenic network created by SYK and mutant FLT3, LANRA and gilteritinib potentially provide a new treatment regimen in a patient population with few treatment options.
Method:
AML cell viability in response to LANRA, gilteritinib or their combination was assessed by CellTiter Glo (CTG) at 5 days. Apoptosis was evaluated by measuring Annexin V and propidium iodide staining by flow cytometry. Myeloid differentiation was assessed by flow cytometry using CD11b and CD14 cell surface markers and/or immunohistochemistry. In addition, RNA-seq was performed to evaluate differential changes in gene expression in response to LANRA. Gene set enrichment analysis (GSEA) was performed to evaluate perturbation in leukemogenic signaling pathways. In vivo studies were conducted using the MV4;11 cell line-derived xenograft model. LANRA was administered twice daily at a dose of 75 mg/kg via subcutaneous injections, either alone or in combination with gilteritinib at a dose of 2 mg/kg dosed once daily by oral gavage, for 28 days.
Results:
Treatment of FLT3-ITD mutated AML cells with LANRA results in dose- and time-dependent increase in myeloid differentiation and reductions in leukemic cell viability. RNA-seq analysis of MV4;11 cells revealed that LANRA abrogates multiple downstream FLT3-ITD leukemogenic signaling pathways including JAK/STAT3/5, MAPK, mTOR and OXPHOS. Combined pharmacologic inhibition of SYK with LANRA and FLT3-ITD with gilteritinib results in robust antileukemic effects in preclinical models of FLT3 ITD-driven AML. Additionally, the combination of LANRA and gilteritinib demonstrated increased differentiation and apoptosis induction in vitro. LANRA in combination with gilteritinib showed significant tumor growth inhibition compared to either single agent in a subcutaneous FLT3-ITD AML cell line-derived xenograft mouse model. In line with these observations, a retrospective analysis of bone marrow-engrafted AML cells from a disseminated FLT3-ITD AML patient-derived xenograft mouse model showed evidence of increased myeloid differentiation and inhibition of cell proliferation.
Conclusion:
In preclinical models, LANRA demonstrates compelling anti-leukemic activity in combination with gilteritinib. By jointly targeting hyperproliferation and differentiation blockade, LANRA and gilteritinib may provide a new therapeutic approach that can be exploited in AML. Additionally, LANRA disrupts downstream signaling of key pathways often associated with resistance to gilteritinib, providing additional mechanistic support for continued testing of LANRA in combination with gilteritinib in FLT3-ITD-mutated AML patients. These studies helped motivate the ongoing clinical combination with gilteritinib in patients with (R/R) FLT3-mutated AML (NCT05028751).