Tasquinimod Improves Erythropoiesis and Mitigates Bone Loss in Myelodysplastic Mice

Myelodysplastic neoplasms (MDS) are characterized by ineffective hematopoiesis, peripheral cytopenia, and a risk of transforming into acute myeloid leukemia (AML). Interestingly, MDS is also associated with an increased prevalence of osteoporosis. Studies have suggested that dysregulated innate immune responses and a proinflammatory bone marrow (BM) microenvironment play significant roles in the pathogenesis of MDS. Targeting inflammatory pathways, especially in low-risk MDS patients, presents a potential strategy to modulate the progression of the disease. One such candidate is Tasquinimod (TASQ, ABR-215050, Active Biotech AB), a small-molecule oral inhibitor and second-generation quinoline-3-carboxamide compound. TASQ binds to the inflammatory protein S100A9 and inhibits its interaction with the proinflammatory toll-like receptor 4, thereby displaying both immunomodulatory and antitumor properties. Our in vitro data provided evidence for a rescuing effect of TASQ on inflammatory signal-primed MDS stromal cells, leading to enhanced hematopoietic support.

This study aims to validate these findings using a transgenic MDS mouse model expressing the NUP98/HOXD13 (NHD13) fusion protein in hematopoietic cells. NHD13 mice, generated on a C57BL/6J background, were obtained from Jackson Laboratory. TASQ was administered orally by adding it to the drinking water at a dose of 30 mg/kg. Both transgenic and littermate control (WT) mice (12 weeks old, n=5-10 per group) were treated with or without TASQ for 12 weeks.

Throughout the experiment, peripheral blood cell counts were measured every 4 weeks using Sysmex analysis. In the final analysis, primary BM cells were isolated from the femora, and the number of lineage-negative, sca-1-positive, and c-kit-positive (LSK) cells, as well as erythroid differentiation, were assessed using flow cytometry. Additionally, bone volume, trabecular number, and thickness were analyzed in femora using µCT.

Transgenic NHD13 mice displayed MDS-like characteristics, including peripheral cytopenias, dysplasia in blood and BM cells, and microstructural abnormalities in the bone microenvironment.

As expected, hemoglobin levels (Hb) and red blood cell (RBC) counts were lower in NHD13 mice compared to WT mice [Hb: 8.9 vs. 9.5 mmol/L; RBC: 9.5 vs. 10.3x1012/L] and showed a consistent decrease in the untreated group from 12 to 24 weeks. Notably, treatment with TASQ significantly improved red blood cell counts in NHD13 mice [+14%; p<0.01] after 24 weeks, while having no effect on WT mice. White blood cells were significantly decreased in WT mice after 4 weeks of TASQ treatment [-19%; p<0.001] until the end of the experiment [-36%; p<0.001]. In contrast, in transgenic mice, the lower white blood cell counts [-76%; p<0.001] were not further diminished. Interestingly, TASQ led to an elevation in neutrophil counts. The platelet count was not affected by the treatment in both transgenic and WT mice.

Using flow cytometry, an increase in the total number of LSK cells was detected in the BM of WT mice after TASQ treatment. However, no increase was observed in NHD13 mice, which already had lower LSK numbers compared to WT controls. Late-stage erythropoiesis was slightly increased in both WT and transgenic mice after TASQ treatment, whereas early erythroid differentiation was unaffected or even decreased by TASQ. Moreover, BM cells were used for colony-forming assays ex vivo. NHD13 mice had a lower erythroid differentiation potential compared to WT mice, which was improved after TASQ treatment.

To assess the potential influence of the microenvironment, adherent BM cells were assayed for their CFU-F forming capacity. BM cells of transgenic mice exhibited a slightly lower CFU-F forming capacity compared to WT mice, which was partially reversed by TASQ treatment.

Finally, the bone microarchitecture was analyzed. NHD13 mice showed a lower bone volume [-43%; p<0.01] compared to WT mice. Notably, treatment with TASQ abolished the bone loss in NHD13 mice by increasing the trabecular number [+35% p<0.001], whereas the trabecular thickness was not affected.

In conclusion, this study provides the first evidence for an in vivo effect of TASQ in a murine model of MDS, suggesting improved erythropoiesis and positive effects on the bone phenotype. These results warrant further investigations of TASQ in human trials, particularly in MDS patients in whom anemia and bone loss often coexist.