Molecular Targeting of AXL-Receptor Tyrosine Kinase in the subtypes of Acute Myeloid Leukemia (AML)

Abstract

Leukemia refers to the cancer of white blood cells (WBCs) in which aberrant proliferation of immature blasts is seen due to the differentiation blockage, hence effecting the production of normal WBCs. Acute myeloid leukemia (AML), the most common form of acute leukemia, is a malignant disorder that is identified due to the aberrant growth and differentiation of hematopoietic stem cells (HSCs), leading to the accumulation of immature myeloid precursors (myeloblasts) in the bone marrow and peripheral blood. AML is a heterogeneous disease consisting of various combinations of genetic aberrations, two of them are t(15;17) and t(6;9) that results in the formation of chimeric genes encoding leukemia associated fusion proteins (LAFP); PML/RARα associated with AML subtype acute promyelocytic leukemia (APL) that has good prognosis and DEK/CAN associated with subtype high risk AML that has poor prognosis. PML/RARα is involved in the stabilization and up regulation of β-catenin through activation of Wnt pathway and hence involved in the leukemogenesis of APL. The current therapy for PML/RARα-positive AML is ATRA and Arsenic trioxide. Both ATRA and arsenic trioxide target PML/RARα fusion protein. ATRA induces differentiation, resulting in differentiation syndrome while arsenic trioxide induces apoptosis and promote differentiation. But due to resistance development, differentiation induction and poisoning by ATO, it is important to explore such therapies and targets that are less toxic and can overcome the resistance to the current therapies. Currently no therapy other than standard chemotherapy is available for DEK/CAN positive AML. So there is a need for effective targeted therapy for DEK/CAN-positive AML. AXL receptor tyrosine kinase belongs to TAM family of receptors that are known for their active role in developing resistance to therapy. R428 is the first specific AXL-RTK inhibitor to enter the clinical trials. So the current study aims to explore xxAbstract the therapeutic potential of AXL-RTK by targeting with R428. ATRA resistant PML/RARα- positive NB4 cell line was developed to study the role of AXL-RTK in resistance development. Upregulation of AXL-RTK was found in R-NB4. We showed that pharmacological targeting of AXL receptor strongly interfered with leukemogenic potential of PML/RARα- and DEK/CAN-positive AML (p<0.05). Furthermore resistance to ATRA was also overcome by targeting AXL receptor with R428 in APL (p <0.05). The anti- proliferative effects of targeting AXL-RTK were related to down regulation of target genes including c-myc (p < 0.001), Axin2 (p < 0.001), and Hif-1 alpha (p < 0.001 and < 0.01). Hence AXL-RTK might be a suitable therapeutic target for PML/RARα-positive and DEK/CAN- positive AML. Further studies of this receptor and its inhibitor on LSCs and clinical samples may pave the way in proposing an effective therapy for AML without differentiation induction in PML/RARα-positive APL and especially for DEK/CAN-positive high risk AML that currently lacks an effective therapy.