SLIT2 modulates leukaemic cell proliferation and stromal support in acute myeloid leukaemia models

Acute myeloid leukaemia (AML) is supported by leukaemic stem cells (LSCs), whose continued existence and growth are dependent upon signals derived from their bone marrow (BM) microenvironment. Although the highly conserved glycoprotein slit guidance ligand 2 (SLIT2), implicated in axon guidance, has been proposed to support normal haematopoietic stem cell (HSC) function, its role in AML pathogenesis remains poorly defined. Here, we show that SLIT2 is downregulated in mesenchymal stem cells (MSCs) from AML patients. Patients with higher-than-normal SLIT2 protein levels had better outcomes, independently of classical risk factors. Functionally, knocking down (KD) SLIT2 in MSCs caused a reprogramming of the microenvironment. Specifically, SLIT2-KD in MSCs resulted in increased expression of LSC-supporting genes including C-X-C motif chemokne ligand 12 (CXCL12) and KIT proto-oncogene, receptor tyrosine kinase (KIT), and co-culture of primary AML cells on SLIT2-KD stromal cells prevented myeloid differentiation. Conversely, the addition of recombinant SLIT2 had cytostatic effects on AML cells, resulting in reduced proliferation and reduced clonogenicity in all tested models. Furthermore, in human xenograft models, systemic administration of recombinant SLIT2 resulted in a decrease in leukaemic burden in BM and spleen, delayed disease progression and improved survival. Overall, these data demonstrate that SLIT2 may act as a tumour suppressor, while SLIT2 loss impairs myeloid terminal differentiation, suggesting that SLIT2 signalling could serve as a potential therapeutic axis in AML.