Abstract
Neutrophil elastase (ELANE) mutations are the most common cause of cyclic (CyN) and congenital neutropenia (SCN), two autosomal dominant disorders causing recurrent infections due to impaired neutrophil production. Granulocyte colony-stimulating factor (G-CSF) corrects neutropenia but has adverse effects, including bone pain and in some cases, an increased risk of myelodysplasia (MDS) and acute myeloid leukemia (AML). Hematopoietic stem cell transplantation is an alternative but is limited by its complications and donor availability. Alternative therapies are needed, particularly for patients with poor responses to G-CSF and those at higher risk of MDS/AML. We previously reported that cell-permeable neutrophil elastase (NE) inhibitors are a potential treatment for ELANE neutropenia, based on studies using HL-60 cells. Our hypothesis was that mutant NE was not properly stored to the neutrophil granules and thereby caused cytoplasmic damage, activation of apoptotic pathways and neutropenia. We have extended this work using CD34+ cells from patients with ELANE mutations and several selective NE inhibitors, i.e., MK0339, sivelestat, BAY-678, and GW311616, as well as the DDP1 inhibitor, brensocatib. Only MK0339 restored neutrophil differentiation with an increase in the proportion of neutrophil marker-positive cells (CD66b+/CD14+ and CD11b+/CD15+). In contrast, other NE inhibitors, i.e., sivelestat, BAY-678, and GW311616 and the DPP1 inhibitor, brensocatib, showed no effect on neutrophil differentiation. Molecular docking studies showed that MK0339 binds to an alternative site on the NE protein compared to other inhibitors with greater inhibitor-NE protein stability, suggesting a unique mechanism of action and supporting further investigation of MK0339 as a therapy for ELANE associated neutropenia.