Tasquinimod Targets Immunosuppressive Myeloid Cells, Increases Osteogenesis and Has Direct Anti-Myeloma Effects By Inhibiting c-Myc Expression in Vitro and In Vivo

Introduction

Immunotherapy has revolutionized cancer treatment and significantly affected the management of Multiple Myeloma (MM) patients. Unfortunately, these immunotherapeutic approaches are hampered by the presence of a suppressive bone marrow microenvironment including myeloid derived suppressor cells and tumor associated macrophages. Tasquinimod (TasQ), an immunomodulatory compound, is currently in phase Ib/IIa for relapsed/refractory MM patients (NCT04405167). TasQ blocks the interaction between S100A9 and its receptors, which is associated with reduced MDSC accumulation. In this study, we investigated TasQ-mediated direct and indirect effects on MM cell growth, bone disease and immunomodulation in vitro and in vivo using human myeloma cell lines and the immunocompetent 5TMM models.

Material and methods

In vitro, murine (5T33vt, 5TGM1) and human (JJN3, LP1, OPM2, and RPMI8226) MM cell lines were cultured at different concentrations of TasQ. Cell proliferation was assessed by BrdU staining using flow cytometry. C-Myc and pSTAT3 expression were analyzed by western blot. In vitro T cell proliferation experiments were performed using MACS-sorted CD11b ⁺ cells and CFSE-labeled T cells from naïve mice. Cells were cocultured for 72h in the presence of MM conditioned medium (5T33MMvt CM) with CD3/CD28 microbeads, followed by flow cytometry to assess T cell proliferation. For in vivo experiments, we used the 5T33 (aggressive) and 5TGM1 (moderate) MM models. On the second day after tumor cell injection, the mice were randomly assigned to the treatment group and the control group. The treatment group received 30 mg/kg of TasQ in drinking water for 35 days (5TGM1) and 21 days (5T33). Anti-tumor and immunomodulating effects were analyzed by flow cytometry (e.g. tumor cells, myeloid subsets, CD4/CD8 ⁺ T cells), qRT-PCR, western blot and serum ELISA (interferon-gamma). Effects on osteogenesis in the 5TGM1 model was investigated by Micro-CT. Statistical differences were assessed by Mann-Whitney U test and One-way ANOVA with p<0.05 considered as statistically significant.

Results

TasQ-treatment of murine and human myeloma cell lines (HMCL), at concentrations of 10-25uM, significantly reduced MM cell proliferation after 24h and 48h in vitro (n=3, p<0.05). In addition, a downregulation in c-Myc expression could be observed 6h after treatment of human MM cell lines (n=3). In vitro, TasQ significantly increased T cell proliferation in co-culture experiments with T cells and myeloid cells in 5T33MMvt CM (n=3, p<0.05).

Using the immunocompetent 5TGM1 and 5T33MM model, we investigated direct and indirect anti-tumor effects of TasQ. We found that TasQ significantly reduced tumor load in the bone marrow of 5TGM1 (n=10/group, p=0.0012) and 5T33MM mice (n=10/group, p=0.0106) compared to vehicle-treated control mice. Using flow cytometry, we could not observe a difference in the percentage of CD4 ⁺ and CD8 ⁺ T cells. However, a significant upregulation in serum interferon-gamma could be observed in the 5T33MM mice (p=0.0284). While the percentage of CD11b ⁺ cells in the TasQ-treated group was significantly increased (p<0.05), the percentage of monocytic myeloid cells (CD11b ⁺Ly6G ^-) was significantly reduced in both models (p<0.05). qRT-PCR results showed that the expression of IL-10 was downregulated in purified CD11b ⁺ myeloid cells (p<0.05). Consistent with the in vitro data, we observed a decrease in the protein expression of c-Myc in purified MM cells obtained from TasQ-treated mice compared to control mice. Micro-CT analysis of femurs demonstrated a significant increase in the percentage BV/TV (ratio of bone material volume over tissue volume) and trabeculae number (p<0.0001) in TasQ-treated 5TGM1 mice compared to untreated mice.

Conclusion

TasQ has pleiotropic effects on the MM cells and its surrounding bone marrow microenvironment. It affects MM cell growth by decreasing c-Myc expression. In addition, TasQ targets the immunosuppressive monocytic myeloid cell population and increases serum interferon-gamma levels, indicative for immune cell activation. Moreover, it stimulates osteogenesis in vivo. Taken together, all these data provide evidence for the therapeutic benefits of TasQ as an anti-MM therapy for patients.