OTS514

OTS514, a thieno[2,3-c]quinolone compound, is a highly potent TOPK inhibitor with an IC50 value of 2.6 nM. The compound can inhibit TOPK kinase activity. TOPK (T-lymphokine-activated killer cell-originated protein kinase) is a protein that is found in a wide range of human cancers and is believed to work as an oncogene, promoting tumor growth.

It has been reported that OTS514 strongly inhibited the growth of the TOPK-positive cancer cell lines with low IC50 values ranging from 1.5 to 14 nM. While in HT29 cells, in which TOPK expression was little detectable, the IC50 value was 170 nM. Intravenous administration of free OTS514 at 1, 2.5, and 5mg/kg once a day for 2 weeks resulted in tumor growth Inhibition（TGI）of 5.7, 43.3, and 65.3% on day 15, respectively, without anybody weight loss. However, this inhibition also cause dysfunction in the differentiation process of hematopoietic stemcells (HSCs) to WBCs and RBCs but may enhance the differentiation of HSCs to megakaryocytes and platelets.

The antitumor effect of OTS514 in lung cancer xenograft model of LU-99 cells has also been investigated. OTS514 was administered to mice bearing LU-99 cancer cells after the tumor size reached about 200mm3. Intravenous administration of OTS514 (5 mg/kg) once a day for 2 weeks achieved good growth-suppressive effect with TGI of 104% without any body weight loss. However, the antitumor effect of OTS514 against LU-99 xenograft caused a significant reduction of WBCs.

References:
1. Matsuo Y, Park JH2, Miyamoto T, et al. TOPK inhibitor induces complete tumor regression in xenograft models of human cancer through inhibition of cytokinesis. ci Transl Med. 2014 Oct 22;6(259):259ra145.
2. Y. Nakamura, Y. Matsuo, S. Hisada, et al. Tricyclic compounds and PBK inhibitors containing the same. Patent WO/2011/123419 (2011)

T-LAK Cell-Originated Protein Kinase (TOPK) as a Prognostic Factor and a Potential Therapeutic Target in Ovarian Cancer.[Pubmed:27334838]

Clin Cancer Res. 2016 Dec 15;22(24):6110-6117.

BACKGROUND: We aimed to clarify the clinical significance of TOPK (T-lymphokine-activated killer cell-originated protein kinase) expression in ovarian cancer and evaluate the possible effect of TOPK inhibitors, OTS514 and OTS964, on ovarian cancer cells. METHODS: TOPK expression was examined by immunohistochemistry using 163 samples with epithelial ovarian cancer (EOC). TOPK protein level and FOXM1 transcriptional level in ovarian cancer cell lines were examined by Western blot and RT-PCR, respectively. Half-maximum inhibitory concentration (IC50) values against TOPK inhibitors were examined by the MTT assay. Using the peritoneal dissemination model of ES-2 ovarian cancer cells, we examined the in vivo efficacy of OTS514. In addition, the cytotoxic effect of OTS514 and OTS964 on 31 patient-derived primary ovarian cancer cells was examined. RESULTS: TOPK was expressed very highly in 84 (52%) of 163 EOC tissues, and high TOPK expression was significantly associated with poor progression-free survival and overall survival in early-stage cases of EOC (P = 0.008 and 0.006, respectively). Both OTS514 and OTS964 showed significant growth-inhibitory effect on ovarian cancer cell lines with IC50 values of 3.0 to 46 nmol/L and 14 to 110 nmol/L, respectively. TOPK protein and transcriptional levels of FOXM1 were reduced by TOPK inhibitor treatment. Oral administration of OTS514 significantly elongated overall survival in the ES-2 abdominal dissemination xenograft model, compared with vehicle control (P < 0.001). Two drugs showed strong growth-inhibitory effect on primary ovarian cancer cells regardless of tumor sites or histological subtypes. CONCLUSIONS: Our results demonstrated the clinical significance of high TOPK expression and potential of TOPK inhibitors to treat ovarian cancer. Clin Cancer Res; 22(24); 6110-7. (c)2016 AACR.

Oncogenic roles of TOPK and MELK, and effective growth suppression by small molecular inhibitors in kidney cancer cells.[Pubmed:26933922]

Oncotarget. 2016 Apr 5;7(14):17652-64.

T-lymphokine-activated killer cell-originated protein kinase (TOPK) and maternal embryonic leucine zipper kinase (MELK) have been reported to play critical roles in cancer cell proliferation and maintenance of stemness. In this study, we investigated possible roles of TOPK and MELK in kidney cancer cells and found their growth promotive effect as well as some feedback mechanism between these two molecules. Interestingly, the blockade of either of these two kinases effectively caused downregulation of forkhead box protein M1 (FOXM1) activity which is known as an oncogenic transcriptional factor in various types of cancer cells. Small molecular compound inhibitors against TOPK (OTS514) and MELK (OTS167) effectively suppressed the kidney cancer cell growth, and the combination of these two compounds additively worked and showed the very strong growth suppressive effect on kidney cancer cells. Collectively, our results suggest that both TOPK and MELK are promising molecular targets for kidney cancer treatment and that dual blockade of OTS514 and OTS167 may bring additive anti-tumor effects with low risk of side effects.

T-LAK cell-originated protein kinase presents a novel therapeutic target in FLT3-ITD mutated acute myeloid leukemia.[Pubmed:26450903]

Oncotarget. 2015 Oct 20;6(32):33410-25.

Gain-of-function mutations of FLT3 (FLT3-ITD), comprises up to 30% of normal karyotype acute myeloid leukemia (AML) and is associated with an adverse prognosis. Current FLT3 kinase inhibitors have been tested extensively, but have not yet resulted in a survival benefit and novel therapies are awaited. Here we show that T-LAK cell-originated protein kinase (TOPK), a mitotic kinase highly expressed in and correlated with more aggressive phenotype in several types of cancer, is expressed in AML but not in normal CD34+ cells and that TOPK knockdown decreased cell viability and induced apoptosis. Treatment of AML cells with TOPK inhibitor (OTS514) resulted in a dose-dependent decrease in cell viability with lower IC50 in FLT3-mutated cells, including blasts obtained from patients relapsed after FLT3-inhibitor treatment. Using a MV4-11-engrafted mouse model, we found that mice treated with 7.5 mg/kg IV daily for 3 weeks survived significantly longer than vehicle treated mice (median survival 46 vs 29 days, P < 0.001). Importantly, we identified TOPK as a FLT3-ITD and CEBPA regulated kinase, and that modulating TOPK expression or activity resulted in significant decrease of FLT3 expression and CEBPA phosphorylation. Thus, targeting TOPK in FLT3-ITD AML represents a novel therapeutic approach for this adverse risk subset of AML.

TOPK (T-LAK cell-originated protein kinase) inhibitor exhibits growth suppressive effect on small cell lung cancer.[Pubmed:28075524]

Cancer Sci. 2017 Mar;108(3):488-496.

T-lymphokine-activated killer cell-originated protein kinase (TOPK) plays critical roles in cancer cell proliferation as well as maintenance of cancer stem cells (CSC). Small cell lung cancer (SCLC) has highly aggressive phenotype, reveals early spread to distant sites, and results in dismal prognosis with little effective treatment. In this study, we demonstrate that TOPK expression was highly upregulated in both SCLC cell lines and primary tumors. Similar to siRNA-mediated TOPK knockdown effects, treatment with a potent TOPK inhibitor, OTS514, effectively suppressed growth of SCLC cell lines (IC50 ; 0.4-42.6 nM) and led to their apoptotic cell death. TOPK inhibition caused cell morphologic changes in SCLC cells, elongation of intercellular bridges caused by cytokinesis defects or neuronal protrusions induced by neuronal differentiation in a subset of CSC-like SCLC cells. Treatment with OTS514 suppressed forkhead box protein M1 (FOXM1) activity, which was involved in stemness of CSC. Furthermore, OTS514 treatment reduced CD90-positive SCLC cells and showed higher cytotoxic effect against lung sphere-derived CSC-like SCLC cells. Collectively, our results suggest that targeting TOPK is a promising approach for SCLC therapy.