Pharmacologic, Pharmacodynamic Action Of Melk Kinase Inhibitor Ots167 In Cancer Cells

Proceedings: AACR 107th Annual Meeting 2016; April 16-20, 2016; New Orleans, LACancer is the second most common cause of death in US in 2015 and has been the leading cause of death in Japan since 1981. Despite of improved therapeutic strategies in cancer, only limited treatment options can still be available to a subset of patients. Many efforts have been made to develop molecular targeted drugs, but the success rate did not reach to patients’ expectation. Unlike the conventional chemotherapy, the use of maximum tolerated dose (MTD) and the measurement of bulk tumor volume are not always appropriate for the clinical evaluation of molecular targeted drugs. To optimize and personalize the dosing for targeted agents, detailed molecular pathway and biomarkers that are affected by the drug should be elucidated. OTS167 was developed as a novel and potent MELK kinase inhibitor that we previously reported. The expression of MELK is elevated in various human cancers both in solid and hematological tumor and MELK is known to be associated with cancer progression and poor prognosis. Because MELK is indicated its critical roles in cancer stem cell proliferation as well, targeting MELK is an attractive and promising therapeutic strategy for cancer patient.Here, we report the molecular mechanism of action of OTS167 in preclinical model. OTS167 suppressed MELK activity and promoted MELK protein degradation by inhibition of autophosphorylation. OTS167-treated cells showed drastic morphological transformation with the induction of p53 and p21 expression. We also investigated the expression of stem cell markers to elucidate whether OTS167 suppresses cancer stem-like properties through inhibition of MELK. Furthermore, we evaluated antitumor activity of OTS167 using human xenograft model and molecular changes in tumor tissue. The expression of MELK and downstream molecules were decreased in OTS167-treated xenograft tumor tissues by IHC. The change of expression and pharmacological effect were well correlated. Our data provide the evidence for the concept that OTS167 suppresses tumor growth through the inhibition of MELK signaling pathway and suggest the possibility of biomarkers for the assessment of clinical efficacy.Citation Format: Suyoun Chung, Kyoko Kijima, Yosuke Harada, Naofumi Takamatsu, Takashi Miyamoto, Yo Matsuo, Yusuke Nakamura. Pharmacologic, pharmacodynamic action of MELK kinase inhibitor OTS167 in cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2158.