Tasquinimod

While investigating the SAR associated with tasquinimod, whose anticancer activity is primarily derived from inhibition of S100A9 and HDAC4, we designed and prepared several analogues. We identified a potent hit (FB2) that showed cytotoxicity against several cancer cells with IC₅₀s between 0.3 and 2.0 μM. Surprisingly, FB2 appeared to halt cells during mitosis. To better define the relevance of FB2's unanticipated action, we further explored its mechanism and found that it significantly alters microtubule dynamics. KT-1 exposed to FB2 showed an elongated cellular morphology with condensed chromosomes and mitotic spindles. FB2 also reduced the rate of microtubule regrowth in cells; however, we are unable to conclude whether this is due to direct binding to tubulin or to some indirect mechanism involving initial interaction with some other target sites. These effects on tubulin dynamics are likely responsible for defects in spindle structure, mitotic arrest, and the observed robust killing of cancer cells.

The alarmins, S100A8 (A8) and S100A9 (A9), are low molecular weight proteins belonging to the S100 protein family. A8 and A9 are secreted into the extracellular space and plasma, in which they interact with Toll-like receptor 4, receptor for advanced glycation end products, and CD33. In these studies, we determined the preclinical efficacy of tasquinimod (TQ) against advanced myeloproliferative neoplasm (MPN) cell lines and patient-derived (PD) CD34+ blastic phase (BP; >5% blasts in the peripheral blood) MPN cells. TQ induced loss of viability in cell lines and PD MPN-BP cells, but not in normal CD34+ progenitor cells. In TQ-treated PD MPN–acute myeloid leukemia (AML) cells, RNA-sequencing analysis showed negative enrichment of the gene sets of MYC and E2F targets, interleukin-6–JAK-STAT3 signaling, and of inflammatory response. In phenotypically defined, PD CD34+ MPN-BP stem progenitor cells, cytometry by time-of-flight analysis showed that TQ reduced expression of proteins including A8, A9, and myeloperoxidase, while increasing expression of Growth Factor Independence 1 (GFI1), p21, and cleaved Poly(ADP-ribose) polymerase (PARP). Cotreatment with TQ and ruxolitinib or Bromodomain and extraterminal domain (BET) inhibitor induced synergistic lethality in advanced MPN-BP cells. Monotherapy with TQ significantly improved survival of immune-depleted NOD scid gamma (NSG) mice engrafted with PD xenograft (PDX) cells of MPN-AML. Notably, cotreatment with TQ and ruxolitinib or OTX015 induced significantly greater survival than treatment with single agents in the NSG mice engrafted with the PDX cells. These findings clearly demonstrate the preclinical efficacy of TQ in advanced MPN-BP cells and create the rationale to further interrogate the efficacy of TQ-based combinations with the current, frontline therapies or novel agents in advanced MPNs with excess blasts.