Abstract 3073: Potential predictive biomarkers of clinical responses for a novel CDC7-selective inhibitor TAK-931
Authors: Iwai Kenichi , Nambu Tadahiro , Kurasawa Osamu , Uchiyama Noriko , Dairiki Ryo , Yamamoto Yukiko , Nishizawa Satoru , Zhang Mengkun , Ishii Yuko , Niu Huifeng , Ohashi Akihiro 
Published: July 2017

Abstract
Cell division cycle 7 (CDC7) is a serine/threonine kinase, which plays important roles in initiation of DNA replication by phosphorylating MCM2. Kinase activity of CDC7 is controlled by its binding protein DBF4 in a cell-cycle dependent manner. Here we developed a potent CDC7 inhibitor TAK-931 (IC50&lt; 0.3 nM) as a cancer therapeutic drug candidate, which exhibits a time-dependent ATP-competitive kinetics to its ATP-binding pocket. The selectivity studies using the 308 kinases revealed &gt;120-fold selectivity of TAK-931 for CDC7 kinase inhibition compared to other kinase inhibitions. Treatment with TAK-931 suppressed the cellular MCM2 phosphorylation at Ser40, resulting in a delayed S phase progression, checkpoint activation, apoptosis, and potent growth suppression in various cancer cell lines. Furthermore, oral administration of TAK-931 as a single agent caused a significant antitumor activity in multiple xenograft models which include both cell line-based xenografts and patient-derived xenograft (PDX) models. These results demonstrate that TAK-931 is a highly potent and selective inhibitor of CDC7 kinase, and causes a potent antiproliferation both in vitro and in vivo studies using various cancer cells. Next, to identify potential predictive biomarkers to guide patient-selection strategies, in vitro cell panel screening of TAK-931 using was tested for its ability to antiproliferation in 246 cell lines, which includes both solid and hematological cancer cells. TAK-931 inhibited proliferation of multiple cancer cell lines, with mean concentration producing a half-maximal response (EC50) values ranging from 29.1 nM to &gt; 30 μM (median = 554.5 nM). While the wide range of TAK-931 antiproliferative spectrum was observed, neither doubling speed nor CDC7 expression profile did predict tTAK-931 sensitivity in cancer cell lines. A correlative study of the tumor genetic mutations in relation to antiproliferative activity that KRAS mutant cancer cells were more sensitive to TAK-931 compared to KRAS non-mutant cell lines (p&lt;0.05). We also confirmed this KRAS-associated antiproliferative effect of TAK-931 in the SW48 isogenic cell lines of KRAS mutations (G12V, G13D). The ectopic expressions of G12V- and G13D-KRAS mutations increased the TAK-931 sensitivity compared to the KRAS-wild parental SW48 cell line. Given that KRAS mutations are frequently detected in clinical pancreatic tumors, we next conducted in vivo efficacy studies using pancreatic PDX models. Consistent to our hypothesis from in vitro studies, KRAS-mutant pancreatic PDX tumors were more sensitive to TAK-931 than the KRAS-wild pancreatic tumors; all KRAS-mutant pancreatic PDX models we tested exhibited &gt;60% TGI. Our findings suggest that the KRAS-mutant pancreatic tumors could be the potential candidate for the TAK-931 target indication.
Citation Format: Kenichi Iwai, Tadahiro Nambu, Osamu Kurasawa, Noriko Uchiyama, Ryo Dairiki, Yukiko Yamamoto, Satoru Nishizawa, Mengkun Zhang, Yuko Ishii, Huifeng Niu, Akihiro Ohashi. Potential predictive biomarkers of clinical responses for a novel CDC7-selective inhibitor TAK-931 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3073. doi:10.1158/1538-7445.AM2017-3073