Discovery of Imidazo[1,2‑b]pyridazine Derivatives: Selective and Orally Available
Mps1 (TTK)
Kinase Inhibitors Exhibiting Remarkable Antiproliferative Activity

Genta Tadano (1648051); Hiroshi Hashizume (188480); Hiroshi Yoshida (169925); Keiji Dohi (1648054); Ken-ichi Kusakabe (1648057); Kenichi Higashino (1557556); Kohei Nozu (1648045); Makiko Inoue (1648063); Masahiro Maeda (140901); Masayo Higaki (1648084); Motofumi Iguchi (1648081); Nobuyuki Ide (1648066); Sachie Tagashira (1648060); Shigeru Ando (1648069); Shingo Sakamoto (1648087); Takahiko Yamamoto (1648078); Takayuki Kanazawa (42579); Takeshi Itoh (2974); Yasuto Kido (1648075); Yataro Daigo (224938); Yoshiyasu Baba (1648072); Yousuke Okano (1648048); Yuji Sato (81706); Yukichi Ishioka (1648090); Yusuke Nakamura (25445)

Discovery of Imidazo[1,2‑b]pyridazine Derivatives: Selective and Orally Available Mps1 (TTK) Kinase Inhibitors Exhibiting Remarkable Antiproliferative Activity

Abstract

Monopolar spindle 1 (Mps1) is an attractive oncology target due to its high expression level in cancer cells as well as the correlation of its expression levels with histological grades of cancers. An imidazo[1,2-a]pyrazine 10a was identified during an HTS campaign. Although 10a exhibited good biochemical activity, its moderate cellular as well as antiproliferative activities needed to be improved. The cocrystal structure of an analogue of 10a guided our lead optimization to introduce substituents at the 6-position of the scaffold, giving the 6-aryl substituted 21b which had improved cellular activity but no oral bioavailability in rat. Property-based optimization at the 6-position and a scaffold change led to the discovery of the imidazo[1,2-b]pyridazine-based 27f, an extremely potent (cellular Mps1 IC50 = 0.70 nM, A549 IC50 = 6.0 nM), selective Mps1 inhibitor over 192 kinases, which could be orally administered and was active in vivo. This 27f demonstrated remarkable antiproliferative activity in the nanomolar range against various tissue cancer cell lines