J. Med. Chem. 2008, 51, 2879–2882
2879
Letters
Discovery and Optimization of
Triazolopyridazines as Potent and Selective
Inhibitors of the c-Met Kinase†
Brian K. Albrecht,*,‡ Jean-Christophe Harmange,‡
David Bauer,‡ Loren Berry,‡ Christiane Bode,‡
Alessandro A. Boezio,‡ April Chen,‡ Deborah Choquette,‡
Isabelle Dussault,§ Cary Fridrich,‡ Satoko Hirai,‡
Doug Hoffman,§ Jay F. Larrow,‡ Paula Kaplan-Lefko,§
Jasmine Lin,‡ Julia Lohman,‡ Alexander M. Long,‡
Jodi Moriguchi,§ Anne O’Connor,‡ Michele H. Potashman,‡
Monica Reese,§ Karen Rex,§ Aaron Siegmund,§
Kavita Shah,‡ Roman Shimanovich,‡ Stephanie K. Springer,‡
Yohannes Teffera,‡ Yajing Yang,§ Yihong Zhang,§ and
Steven F. Bellon‡
Figure 1. Reported c-Met inhibitors.
Amgen Inc., One Kendall Square, Building 1000, Cambridge,
Massachusetts 02139, and Amgen Inc., One Amgen Center DriVe,
Thousand Oaks, California 91320
ReceiVed January 17, 2008
Abstract: Tumorigenesis is a multistep process in which oncogenes
play a key role in tumor formation, growth, and maintenance. MET
was discovered as an oncogene that is activated by its ligand, hepatocyte
growth factor. Deregulated signaling in the c-Met pathway has been
observed in multiple tumor types. Herein we report the discovery of
potent and selective triazolopyridazine small molecules that inhibit
c-Met activity.
Figure 2. Analogues of triazolotriazine 2.
aim of the present work was to develop a potent, selective, ATP-
competitive orally bioavailable small molecule inhibitor of
c-Met.6
The receptor tyrosine kinase, c-Met, and its natural ligand,
hepatocyte growth factor (HGFa), are involved in cell prolifera-
tion, migration, and invasion and are essential for normal
embryonic development.1 However, when deregulated, the
c-Met/HGF pathway leads to tumorigenesis and metastasis.2 The
overexpression of c-Met and/or HGF, the amplification of
the MET gene, and mutations in the c-Met kinase domain have
been linked to human cancers.3 Recently it has been shown that
MET amplification occurs as a resistance mechanism in some
lung cancer patients that were initially responsive to gefitinib.4
Inhibition of c-Met activity in cell lines that reproduce this
resistance mechanism restored sensitivity to gefitinib. For these
reasons, c-Met small molecule kinase inhibitors have been
sought for therapeutic intervention.
Recently, we disclosed the structure of pyrimidinone 1 as a
potent (IC50 ) 10 nM) c-Met inhibitor (Figure 1).7 In an ongoing
effort to design novel inhibitors of the c-Met enzyme, we were
intrigued by a report from Sugen in which they showed that a
series of triazolotriazines of low molecular weight were potent
c-Met inhibitors.8 They reported that a representative example,
triazolotriazine 2, was shown to inhibit c-Met activity with an
IC50 of 6 nM.
Intrigued by the low molecular weight and unknown binding
mode of triazolotriazine 2 to c-Met, three structurally relevant
novel compounds were prepared and evaluated for their potency
against the c-Met enzyme (Figure 2). Since triazolopyridazine
3a had the greatest activity and was exquisitely selective against
other kinases,9 it was investigated further.
The cocrystal structure of 3a bound to the unphosphorylated
c-Met kinase domain revealed a bent “U-shaped” binding mode
with the inhibitor wrapped around Met1211 (Figure 3). A direct
hydrogen bond is formed between the backbone NH of Met1160
(linker) and the phenol-O with a distance of 3.0 Å. A second
hydrogen bond is mediated by a water molecule and bridges
the backbone carbonyl of Met1160 and the phenol-H. Other
notable interactions include a π-stacking interaction between
the triazolopyridazine core and Tyr1230 and a hydrogen bonding
interaction between N1 of the inhibitor and the backbone NH
of Asp1222.
Inhibition of the tyrosine kinase activity by an ATP-
competitive small molecule is a pharmacologically attractive
method that has been demonstrated for other tyrosine kinases.5
One limitation to small molecule kinase inhibitors is the
difficulty of obtaining specificity for the desired enzyme. The
†
Cocrystal structures of c-Met with 3a and 4 have been deposited in
the Protein Data Bank with access codes 3CCN and 3CD8, respectively.
* To whom correspondence should be addressed. Phone: 617-444-5166.
Fax: 617-577-9822. E-mail: brian.albrecht@amgen.com.
‡
Amgen Inc., MA.
Amgen Inc., CA.
§
a Abbreviations: ATP, adenosine triphosphate; HGF, hepatocyte growth
factor; Met1211/1260, methionine 1211/1260; Tyr1230, tyrosine 1230;
Asp1222, aspartic acid 1222; NADPH, nicotinamide adenine dinucleotide
phosphate; HATU, N,N,N′,N′-tetramethyl-O-(7-azabenzotriazol-1-yl)uro-
nium hexafluorophosphate.
Our previous crystallographic analysis of pyrimidinone 1
revealed a strikingly different mode of binding to the c-Met
active site (Figure 4). Instead of an overall bent shape,
10.1021/jm800043g CCC: $40.75
2008 American Chemical Society
Published on Web 04/22/2008