StemRegenin 1 (SR1)

StemRegenin 1 (SR1), a purine derivative, is a potent small molecule inhibitor of aryl hydrocarbon receptor (AhR) that potently antagonizes AhR with a value of 50% inhibition concentration IC₅₀ of 127 nM in CD34⁺ cells. SR1 has been found to promote the ex vivo expansion of CD34⁺ cells. Recent study results have suggested that culture of hematopoietic stem cells (HSC) with SR1 increases cells expressing CD34 by fifty-fold and increases cells retaining the ability to engraft immunodeficient mice by 17-fold. SR1 has also been found to induce the ex vivo differentiation of pDCs, BDCA1⁺ and BDCA3⁺ mDCs as well as the generation of high numbers of all these DC subsets.

Reference

Thordardottir S, Hangalapura BN, Hutten T, Cossu M, Spanholtz J, Schaap N, Radstake TR, Vandervoort R, Dolstra H. The aryl hydrocarbon receptor antagonist StemRegenin 1 promotes human plasmacytoid and myeloid dendritic cell development from CD34+ hematopoietic progenitor cells. Stem Cells Dev. 2013 Dec 10. [Epub ahead of print]

Boitano AE, Wang J, Romeo R, Bouchez LC, Parker AE, Sutton SE, Walker JR, Flaveny CA, Perdew GH, Denison MS, Schultz PG, Cooke MP. Aryl hydrocarbon receptor antagonists promote the expansion of human hematopoietic stem cells. Science. 2010 Sep 10;329(5997):1345-8. doi: 10.1126/science.1191536. Epub 2010 Aug 5.

Aryl hydrocarbon receptor-dependent enrichment of a megakaryocytic precursor with a high potential to produce proplatelets.[Pubmed:26966088]

Blood. 2016 May 5;127(18):2231-40.

The mechanisms regulating megakaryopoiesis and platelet production (thrombopoiesis) are still incompletely understood. Identification of a progenitor with enhanced thrombopoietic capacity would be useful to decipher these mechanisms and to improve our capacity to produce platelets in vitro. Differentiation of peripheral blood CD34(+) cells in the presence of bone marrow-human mesenchymal stromal cells (MSCs) enhanced the production of proplatelet-bearing megakaryocytes (MKs) and platelet-like elements. This was accompanied by enrichment in a MK precursor population exhibiting an intermediate level of CD41 positivity while maintaining its expression of CD34. Following sorting and subculture with MSCs, this CD34(+)CD41(low) population was able to efficiently generate proplatelet-bearing MKs and platelet-like particles. Similarly, StemRegenin 1 (SR1), an antagonist of the aryl hydrocarbon receptor (AhR) transcription factor known to maintain CD34 expression of progenitor cells, led to an enriched CD34(+)CD41(low) fraction and to an increased capacity to generate proplatelet-producing MKs and platelet-like elements ultrastructurally and functionally similar to circulating platelets. The effect of MSCs, like that of SR1, appeared to be mediated by an AhR-dependent mechanism because both culture conditions resulted in repression of its downstream effector CYP1B1. This newly described isolation of a precursor exhibiting strong MK potential could be exploited to study normal and abnormal thrombopoiesis and for in vitro platelet production.

The aryl hydrocarbon receptor antagonist StemRegenin 1 promotes human plasmacytoid and myeloid dendritic cell development from CD34+ hematopoietic progenitor cells.[Pubmed:24325394]

Stem Cells Dev. 2014 May 1;23(9):955-67.

The superiority of dendritic cells (DCs) as antigen-presenting cells has been exploited in numerous clinical trials, where generally monocyte-derived DCs (Mo-DCs) are injected to induce immunity in patients with cancer or infectious diseases. Despite promising expansion of antigen-specific T cells, the clinical responses following vaccination have been limited, indicating that further improvements of DC vaccine potency are necessary. Pre-clinical studies suggest that vaccination with combination of primary DC subsets, such as myeloid and plasmacytoid blood DCs (mDCs and pDCs, respectively), may result in stronger clinical responses. However, it is a challenge to obtain high enough numbers of primary DCs for immunotherapy, since their frequency in blood is very low. We therefore explored the possibility to generate them from hematopoietic progenitor cells (HPCs). Here, we show that by inhibiting the aryl hydrocarbon receptor with its antagonist StemRegenin 1 (SR1), clinical-scale numbers of functional BDCA2(+)BDCA4(+) pDCs, BDCA1(+) mDCs, and BDCA3(+)DNGR1(+) mDCs can be efficiently generated from human CD34(+) HPCs. The ex vivo-generated DCs were phenotypically and functionally comparable to peripheral blood DCs. They secreted high levels of pro-inflammatory cytokines such as interferon (IFN)-alpha, interleukin (IL)-12, and tumor necrosis factor (TNF)-alpha and upregulated co-stimulatory molecules and maturation markers following stimulation with Toll-like receptor (TLR) ligands. Further, they induced potent allogeneic T-cell responses and activated antigen-experienced T cells. These findings demonstrate that SR1 can be exploited to generate high numbers of functional pDCs and mDCs from CD34(+) HPCs, providing an alternative option to Mo-DCs for immunotherapy of patients with cancer or infections.

Aryl Hydrocarbon Receptor Antagonist StemRegenin 1 Promotes the Expansion of Human Promyelocytic Leukemia Cell Line, NB4.[Pubmed:27354634]

Anticancer Res. 2016 Jul;36(7):3635-43.

BACKGROUND/AIM: StemRegenin 1 (SR1), an antagonist of aryl hydrocarbon receptor (AHR), reportedly promotes expansion of hematopoietic stem cells but its effect on leukemia cells is unclear. This study focused on the role of SR1 in leukemia cell proliferation. MATERIALS AND METHODS: AHR expression was compared in the cell lines Jurkat, Kasumi-1, NB4 and K562, using real-time polymerase chain reaction. Highly AHR-expressing NB4 cells were cultured with SR1 for 2 and 4 days, and evaluated for viability and gene expression. DNA microarray was also performed. RESULTS: The viability of NB4 cells treated with 1.5 muM SR1 increased at day 4. Expression of B-cell CLL/lymphoma 2 (BCL2) was up-regulated, while that of BCL2 associated X protein (BAX) was down-regulated at day 2. Increased cyclin D1 (CCND1), CCND2 and v-myc avian myelocytomatosis viral oncogene homolog (MYC) expressions were observed at day 4. Global gene expression profiles showed up-regulation of splice variant-related genes and down-regulation of inflammation-related genes. CONCLUSION: SR1 promotes the expansion of NB4 cells in vitro, implying the need for caution regarding in vivo use of R1.

Biomodification of PCL Scaffolds with Matrigel, HA, and SR1 Enhances De Novo Ectopic Bone Marrow Formation Induced by rhBMP-2.[Pubmed:26309805]

Biores Open Access. 2015 Jun 1;4(1):298-306.

The de novo formation of ectopic bone marrow was induced using 1.2-mm-thin polycaprolactone (PCL) scaffolds biomodified with several different biomaterials. In vivo investigations of de novo bone and bone marrow formation indicated that subcutaneous implantation of PCL scaffolds coated with recombinant human bone morphogenetic protein-2 (rhBMP-2) plus Matrigel, hydroxyapatite (HA), or StemRegenin 1 (SR1) improved formation of bone and hematopoietic bone marrow as determined by microcomputed tomography, and histological and hematopoietic characterizations. Our study provides evidence that thin PCL scaffolds biomodified with Matrigel, HA, and SR1 mimic the environments of real bone and bone marrow, thereby enhancing the de novo ectopic bone marrow formation induced by rhBMP-2. This ectopic bone marrow model will serve as a unique and essential tool for basic research and for clinical applications of postnatal tissue engineering and organ regeneration.

The Aryl Hydrocarbon Receptor Antagonist StemRegenin1 Improves In Vitro Generation of Highly Functional Natural Killer Cells from CD34(+) Hematopoietic Stem and Progenitor Cells.[Pubmed:26414401]

Stem Cells Dev. 2015 Dec 15;24(24):2886-98.

Early natural killer (NK)-cell repopulation after allogeneic stem cell transplantation (allo-SCT) has been associated with reduced relapse rates without an increased risk of graft-versus-host disease, indicating that donor NK cells have specific antileukemic activity. Therefore, adoptive transfer of donor NK cells is an attractive strategy to reduce relapse rates after allo-SCT. Since NK cells of donor origin will not be rejected, multiple NK-cell infusions could be administered in this setting. However, isolation of high numbers of functional NK cells from transplant donors is challenging. Hence, we developed a cytokine-based ex vivo culture protocol to generate high numbers of functional NK cells from granulocyte colony-stimulating factor (G-CSF)-mobilized CD34(+) hematopoietic stem and progenitor cells (HSPCs). In this study, we demonstrate that addition of aryl hydrocarbon receptor antagonist StemRegenin1 (SR1) to our culture protocol potently enhances expansion of CD34(+) HSPCs and induces expression of NK-cell-associated transcription factors promoting NK-cell differentiation. As a result, high numbers of NK cells with an active phenotype can be generated using this culture protocol. These SR1-generated NK cells exert efficient cytolytic activity and interferon-gamma production toward acute myeloid leukemia and multiple myeloma cells. Importantly, we observed that NK-cell proliferation and function are not inhibited by cyclosporin A, an immunosuppressive drug often used after allo-SCT. These findings demonstrate that SR1 can be exploited to generate high numbers of functional NK cells from G-CSF-mobilized CD34(+) HSPCs, providing great promise for effective NK-cell-based immunotherapy after allo-SCT.