Effects of JAK1/2 inhibition on bone marrow stromal cells of myeloproliferative neoplasm (MPN) patients and healthy individuals

Bone Marrow Niches and Tumour Cells: Lights and Shadows of a Mutual Relationship

The bone marrow (BM) niche is the spatial structure within the intra-trabecular spaces of spongious bones and of the cavity of long bones where adult haematopoietic stem cells (HSCs) maintain their undifferentiated and cellular self-renewal state through the intervention of vascular and nervous networks, metabolic pathways, transcriptional and epigenetic regulators, and humoral signals. Within the niche, HSCs interact with various cell types such as osteoblasts, endothelial cells, macrophages, and mesenchymal stromal cells (MSCs), which maintain HSCs in a quiescent state or sustain their proliferation, differentiation, and trafficking, depending on body needs. In physiological conditions, the BM niche permits the daily production of all the blood and immune cells and their admittance/ingress/progression into the bloodstream. However, disruption of this delicate microenvironment promotes the initiation and progression of malignancies such as those included in the spectrum of myeloid neoplasms, also favouring resistance to pharmacological therapies. Alterations in the MSC population and in the crosstalk with HSCs owing to tumour-derived factors contribute to the formation of a malignant niche. On the other hand, cells of the BM microenvironment cooperate in creating a unique milieu favouring metastasization of distant tumours into the bone. In this framework, the pro-tumorigenic role of MSCs is well-documented, and few evidence suggest also an anti-tumorigenic effect. Here we will review recent advances regarding the BM niche composition and functionality in normal and in malignant conditions, as well as the therapeutic implications of the interplay between its diverse cellular components and malignant cells.

Bone marrow morphological features and therapy in patients with Philadelphia-negative neoplasms

Introduction Chronic myeloproliferative neoplasm (MPNs) are clonal malignant bone marrow (BM) diseases, arising from a hematopoietic stem cell. All therapies for these neoplasms have peculiar effects on the bone marrow, but little evidence has been described in the literature.Areas covered This review examines BM morphological changes following the main treatments in Philadelphia-negative MPNs. Hydroxyurea can reduce the cellularity of the erythroid and megakaryocyte lineages but has minimal impact on fibrotic evolution. There is general agreement on its dysplastic effects, with a high incidence of acute myeloid leukemia and myelodysplastic syndrome. Interferon treatment can reduce or normalize BM cellularity, improve erythropoiesis, and reduce the number and atypicality of megakaryocytes. Most data describe reduction or complete resolution of marrow fibrosis; dysplastic effects are not reported. Anagrelide may induce an increase in the number of BM megakaryocytes, especially immature megakaryocytes or precursors, and a worsening of marrow fibrosis or increased transformation of essential thrombocythemia into myelofibrosis. Ruxolitinib can improve or stabilize BM fibrosis and reduces the frequency and dense clustering of megakaryocytes.Expert opinion Since previous therapy can modify BM features, it is essential to obtain information on previous or current therapies and to collect complete clinical information.

Proliferative activity is disturbed in myeloproliferative neoplasms (MPN), myelodysplastic syndrome (MDS), and MDS/MPN diseases. Differences between MDS and MDS/MPN

The proliferation marker Ki-67 is widely used within the field of diagnostic histopathology as a prognostic marker for solid cancers. However, Ki-67 is hardly used for prognostic and diagnostic purposes in flow cytometric analyses of hematologic neoplasms. In the present study, we investigated to what extent the proliferative activity, as determined by Ki-67 expression, is disturbed in myeloproliferative neoplasms (MPN), myelodysplastic syndrome (MDS), and MDS/MPN diseases. Bone marrow aspirates from 74 patients suffering from MPN, MDS, or MDS/MPN, and aspirates from 50 non-malignant cases were analyzed by flow cytometry for Ki-67 expression in the erythro-, myelo-, and monopoiesis. Ki-67 expression was used to investigate the proliferative activity during the various maturation steps within these hematopoietic cell lineages. In the MPN patient cohort, the proliferative activity of all cell lineages is significantly higher during almost all maturation stages compared to those of the benign control cohort. In the MDS and MDS/MPN cohort, a significantly lower proliferative activity is observed in the early maturation stages. In the MDS/MPN patient cohort, increased proliferative activity is seen in the later stages of the maturation. MDS and MDS/MPN display a distinct pattern in the proliferating fraction of maturing hematopoietic cells. This could become of added value in order to classify these malignancies based on their biological background and behavior, as well as in gaining a better understanding into the pathobiology of these malignancies.

The potential of JAK/STAT pathway inhibition by ruxolitinib in the treatment of COVID-19

Ruxolitinib is the first approved JAK1 and JAK2 inhibitor, and is known to interfere with the JAK / STAT signaling pathway, one of the critical cellular signaling pathways involved in the inflammatory response. This review presents an overview of SARS-CoV-2 and the COVID-19 pandemic, and then focuses on the potential efficacy of ruxolitinib in this infection. The potential targets of ruxolitinib were determined by using genetic alterations that have been reported in COVID-19 patients. The potential effectiveness of ruxolitinib is suggested by evaluating the interactions of these potential targets with ruxolitinib or JAK/STAT pathway.

Stem cell library screen identified ruxolitinib as regulator of osteoblastic differentiation of human skeletal stem cells

Background

Better understanding of the signaling pathways that regulate human bone marrow stromal stem cell (hBMSC) differentiation into bone-forming osteoblasts is crucial for their clinical use in regenerative medicine. Chemical biology approaches using small molecules targeting specific signaling pathways are increasingly employed to manipulate stem cell differentiation fate.

Methods

We employed alkaline phosphatase activity and staining assays to assess osteoblast differentiation and Alizarin R staining to assess mineralized matrix formation of cultured hBMSCs. Changes in gene expression were assessed using an Agilent microarray platform, and data normalization and bioinformatics were performed using GeneSpring software. For in vivo ectopic bone formation experiments, hMSCs were mixed with hydroxyapatite–tricalcium phosphate granules and implanted subcutaneously into the dorsal surface of 8-week-old female nude mice. Hematoxylin and eosin staining and Sirius Red staining were used to detect bone formation in vivo.

Results

We identified several compounds which inhibited osteoblastic differentiation of hMSCs. In particular, we identified ruxolitinib (INCB018424) (3 μM), an inhibitor of JAK-STAT signaling that inhibited osteoblastic differentiation and matrix mineralization of hMSCs in vitro and reduced ectopic bone formation in vivo. Global gene expression profiling of ruxolitinib-treated cells identified 847 upregulated and 822 downregulated mRNA transcripts, compared to vehicle-treated control cells. Bioinformatic analysis revealed differential regulation of multiple genetic pathways, including TGFβ and insulin signaling, endochondral ossification, and focal adhesion.

Conclusions

We identified ruxolitinib as an important regulator of osteoblast differentiation of hMSCs. It is plausible that inhibition of osteoblast differentiation by ruxolitinib may represent a novel therapeutic strategy for the treatment of pathological conditions caused by accelerated osteoblast differentiation and mineralization.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1068-x) contains supplementary material, which is available to authorized users.