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Pyrimido-Indole Derivatives Are Novel Agonists of Human Cord Blood Hematopoietic Stem Cell Self-Renewal

Iman Fares, Jalila Chagaroui, Yves Gareau, Stéphane Gingras, Nadine Mayotte, Elizabeth Csaszar, Hans-Peter Kiem, Norman N. Iscove, R. Keith Humphries, Connie J. Eaves, Sandra Cohen, Anne Marinier, Peter W. Zandstra and Guy Sauvageau

Abstract

The widespread use of cord blood (CB) unit in transplantation is limited with low number of long-term hematopoietic stem cells (LT-HSCs) and progenitors. Several approaches have been developed to expand HSC ex vivo such as automated and continuous medium delivery (fed-batch), notch delta ligand and SR1 (antagonist of aryl hydrocarbon receptor (AhR)). Concurrent with these studies, we hypothesized that small molecule with potent LT-HSC stimulating activity might be identified and potentiated in fed-batch culture system. Accordingly, we tested a library of more than 5000 small molecules for their in vitro expansion of CD34+CD45RA- cells. Most of the identified hits, except one (UM729) synthesized in our institute, suppress AhR pathway. Structure activity relationship was performed on UM729 to generate a more potent analog named UM171. This optimized molecule was 10-20 times more potent with an effective concentration of 15-20 nM when tested for its ability to expand CD34+CD45RA- cells. When compared to SR1, UM171 delivered in a fed-batch system for 12 and 16 days showed a better expansion of HSC phenotypes and lower apoptotic cell number compared to SR1 or DMSO controls. Also, UM171-expaned cultures showed higher number in multipotent progenitors (CFU-GEMM) and long term initiating cells (LTC-IC) compared to DMSO controls. Further studies showed the UM171 did not affect division rate, and its effect in expanding HSC phenotype was reversible. When combined with SR1, UM171 showed a better suppression of differentiation and led to a higher CFU-GEMM expansion compared to the single treatment of the compounds or DMOS controls. These observations suggest that UM171+SR1 cooperate to enhance ex vivo expansion of progenitor cells and suppress differentiation. To determine the in vivo activity of the expanded CD34+ CB cells, we transplanted fresh (un-manipulated) and 12-day cultured cells in NSG mice and monitored the human hematopoietic reconstitution after 20 and 30 weeks post-transplantation. Frequencies of day0 equivalent LT-HSCs were 13-fold higher in UM171 expanded cultures compared to fresh or fed-batch cultures supplemented with DMSO or SR1. Secondary experiments indicated that UM171 ex vivo treatment did not appear to affect the capability of LT-HSC to expand in primary recipients and hence similarly reconstituted secondary animals for at least 18 more weeks. This suggests that UM171 expands LT-HSC ex vivo without losing their engraftment potential. To further investigate UM171 mechanism of action, RNA- Seq expression profiling was performed. Unlike SR1 or DMSO controls, UM171 treatment was accompanied by a marked suppression of transcripts associated with erythroid and megakaryocytic differentiation and up-regulation of membrane protein transcripts such as EPCR and TEMEM 183a. In summery, UM171 is the first molecule identified so far that enables a robust ex vivo expansion of human CD34+ CB cells that sustain their in vivo activity independent of AhR suppression. Conversely, AhR suppression was limited to expand cells with less durable self-renewal potential. This study could enhance the use of small yet well HLA-matched CB units to become a prioritized source for stem cells transplantation.

Disclosures No relevant conflicts of interest to declare.

  • * Asterisk with author names denotes non-ASH members.