Flavopiridol Restores Granulopoiesis in an Experimental Model of Severe Congenital Neutropenia

Severe congenital neutropenia (CN) patients require life-long treatment with recombinant human granulocyte colony-stimulating factor (rhG-CSF), but some show no response. We sought to establish a therapy for CN that targets signaling pathways that cause maturation arrest of granulocytic progenitors. The largest group of CN patients harbors autosomal dominant ELANE mutations (ELANE-CN).

We developed an isogenic induced pluripotent stem cell (iPSC) in vitro model of ELANE-CN and identified signaling pathways deregulated by ELANE mutations in iPSC-derived hematopoietic stem and progenitor cells, potentially leading to defective granulopoiesis. We further performed an in silico drug repurposing analysis of the transcriptomics data and selected flavopiridol, an FDA-approved pan-cyclin-dependent kinase inhibitor, as a potential therapeutic.

We found that treatment with low-dose flavopiridol (up to 10-fold lower than that usually used to treat cancer patients) rescued defective granulopoiesis in primary CD34⁺ cells of CN patients with different inherited gene mutations, including ELANE, HAX1, SRP54 and JAGN1, in vitro and in two zebrafish CN models in vivo (hax1-CN and jagn1b-CN) without any toxic effects on hematopoietic stem cells or granulocytes and leading to fully functional granulocytes.

We have previously shown that the expression levels of the transcription factor CEBPA are severely reduced in hematopoietic cells and myeloid progenitors of CN patients. Rescue of defective granulopoiesis by transduction of CD34⁺ cells from CN patients with CEBPA further supports its key role in the pathogenesis of CN. CEBPA is known to counteract CDK2 and CDK4 activity to induce granulopoiesis and we found that flavopiridol restored granulopoiesis caused by reduced CEBPA expression in vitro and in zebrafish embryos in vivo. These data provide insight into the mechanism of action of flavopiridol in rescuing defective granulopoiesis in CN.

Thus, we described for the first time a therapy for CN with flavopiridol that could be potentially used to treat patients with different types of neutropenia.

No relevant conflicts of interest to declare.