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Hematopoietic stem cells (HSC), known for their ability to multipotent and self-renew, are often used in HSC transplantation for the treatment of hematological diseases and malignancies. Umbilical cord blood (UCB) and mobilized peripheral blood (mPB), which are alternatives to bone marrow (BM) for HSC transplantation, have reduced HSC. To address this restriction, the ex vivo expansion of HSCs is a highly promising therapeutic approach rather than the use of a double-cord blood unit that induces delays in hematopoietic recovery. We have previously shown that knockout of HSC quiescence genes could increase the HSC pool in vivo. Thus, we thought that targeting HSC quiescence regulators using small molecules could be used for ex vivo expansion of both mPB and UCB-HSC. The goal was to identify novel hematopoietic small molecules (HSMs) and their combinations, and to enhance performance of human HSC expansion medium. We identified and analyzed 35 possible HSMs targeting HSC quiescence factors. We assessed their impact on human HSPC activity, including expansion, quiescence, multilineage capacity, cycling capability and metabolism. We have also investigated their cytotoxic and genotoxic effects on human HSPCs. On the other hand, a transplantation study was performed on immunocompromised mice for the evaluation of the repopulation and engraftment capacities of the expanded cells. We observed that BML-260 and TAME molecules robustly increased both the mPB and UCB-HSPC content and activated the re-entry of HSCs into the cell cycle. Colony Forming Unit (CFU) assay confirmed their improved multilineage capacity. BML-260 proved safer for the viability of expanded cells based on cytotoxicity and genotoxicity assays. In addition, gene expression analysis showed that BML-260 and TAME molecules contributed to HSC expansion by modulating cell cycle kinetics, including p27, Skp2 and Cdh1. In conjunction with these in vitro results, we have observed that BML-260-expanded HSCs had a strong hematopoietic reconstitution capacity. After the determination of the most effective molecule as BML-260, a comparative study of chemically defined media, including various supplements, was analyzed in addition to the BML-260 molecule. These results from in vitro and xenotransplantation experiments have shown that BML-260 molecules can be used therapeutically for human HSC expansion and regulation of HSC activity. In addition, the medium composition found may be a novel platform for human HSC expansion to used in clinical trials. |
