A Novel Agent Tasquinimod Demonstrates a Potent Anti-Tumor Activity in Pre-Clinical Models of Multiple Myeloma
Authors: Ramachandran Indu R , Lin Cindy , Chase Tess , Gabrilovich Dmitry , Nefedova Yulia 
Published: October 2019

Abstract
Multiple myeloma (MM) is a devastating bone marrow (BM) cancer characterized by clonal proliferation of plasma cells. Despite the emergence of novel therapeutics MM remains a fatal disease. The tumor microenvironment plays a critical role in promoting MM growth. We have recently demonstrated that a population of BM myeloid-derived suppressor cells is involved in regulation of MM progression. These cells abundantly produce the pro-inflammatory protein S100A9. Tasquinimod (ABR-215050, Active Biotech/IPSEN) is a quinoline-3-carboxamide derivative that binds to S100A9 and blocks its interaction with receptors TLR4, RAGE, and CD147. Here we investigated whether pharmacological inhibition of S100A9 with tasquinimod inhibits MM progression.
A panel of MM murine (DP42) and human (RPMI-8226, H929, and U266) cell lines was cultured in the presence of tasquinimod or vehicle control and cell viability was determined using MTT assay. Treatment with tasquinimod did not affect MM cell viability.
We then evaluated the anti-tumor effect of tasquinimod in vivo in a MM syngeneic model. In this model, murine MM DP42 cells are injected i.v., home to the BM, and grow as MM that closely resembles the human disease. On day 2 after tumor cell injection mice were randomly assigned to the treatment or control groups. Treatment group received tasquinimod at a dose of 30 mg/kg/day in drinking water for 28 days. We found that tasquinimod significantly improved survival of MM-bearing mice (p<0.005).
To exclude a B and T-cell driven mechanism for tasquinimod’s pro-survival effect, we tested whether this compound has an anti-tumor effect in immunodeficient mice. A xenograft model of H929 human MM cells was established in SCID-beige mice. Treatment with tasquinimod significantly (p<0.0001) reduced tumor growth in this model. Similar results were obtained for RPMI-8226 human MM tumor. We next tested whether the anti-tumor effect of tasquinimod is indeed mediated through inhibition of S100A9. MM DP42 tumors were established in syngeneic S100A9 knockout (KO) mice. Treatment of S100A9KO mice with tasquinimod did not improve their survival from MM.These data suggest that the anti-MM effect of tasqunimod is indeed mediated through inhibition of S100A9.
BM angiogenesis plays a critical role in MM progression. We evaluated whether inhibition of S100A9 with tasquinimod would block angiogenesis in MM. Immunohistochemical staining with anti-CD31 antibody demonstrated increased angiogenesis in the BM of MM-bearing mice as compared with control tumor-free mice, and treatment with tasquinimod significantly reduced angiogenesis (p<0.005). Serum collected from tasquinimod or vehicle control treated MM DP42-bearing mice two weeks after tumor cell inoculation, was subjected to Mouse Angiogenesis Proteome Profiler Antibody Array (R&D). A significant decrease in serum levels of pro-angiogenic factors including VEGF, FGF2, tissue factor, and endoglin was detected in tasquinimod-treated mice.
Taken together, our data indicate that targeting S100A9 with tasquinimod results in strong anti-tumor effect in preclinical models of MM. This effect is associated with a reduced angiogenesis in the BM. Therefore, tasquinimod could be therapeutically beneficial for patients with MM.

Disclosures
No relevant conflicts of interest to declare.