J. Med. Chem. 2009, 52, 6193–6196 6193
DOI: 10.1021/jm901108b
neitherCa2þ nor DAG. Several isotypes of PKC playa central
role in T cell signaling pathways which translate the engage-
ment of the T cell receptor (TCR) and the coreceptor CD28
into amplification of IL-2 expression and T cell activation.3
Thus, blockade of PKC is expected to inhibit T lymphocyte
activation and to offer opportunities for novel T cell immu-
nomodulators.
Discovery of 3-(1H-Indol-3-yl)-4-
[2-(4-methylpiperazin-1-yl)quinazolin-4-yl]-
pyrrole-2,5-dione (AEB071), a Potent and
Selective Inhibitor of Protein Kinase C Isotypes†
€
Jurgen Wagner,* Peter von Matt,* Richard Sedrani,
In this communication, we report on our project aimed at
finding novel, low-molecular weight inhibitors of T cell
activation acting via inhibition of classical and novel PKC
isotypes. We describe the optimization of inhibitory potency
and pharmacokinetic properties of a new class of maleimides.
These efforts led to the identification of AEB071 (1, INN,
sotrastaurin; for short, STN; Figure 1),4 a representative of a
new class of potent and selective PKC inhibitors based on a
heteroarylindolylmaleimide scaffold. 1 is currently in phase II
clinical trials for the inhibition of solid organ allograft rejec-
tion.
Rainer Albert, Nigel Cooke, Claus Ehrhardt, Martin Geiser,
Gabriele Rummel, Wilhelm Stark, Andre Strauss,
Sandra W. Cowan-Jacob, Christian Beerli,
Gisbert Weckbecker, Jean-Pierre Evenou, Gerhard Zenke,
and Sylvain Cottens
Novartis Institutes for BioMedical Research, Basel CH-4002,
Switzerland
Received July 27, 2009
Abstract: A series of novel maleimide-based inhibitors of protein
kinase C (PKC) were designed, synthesized, and evaluated. AEB071
(1) was found to be a potent, selective inhibitor of classical and novel
PKC isotypes. 1 is a highly efficient immunomodulator, acting via
inhibition of early T cell activation. The binding mode of malei-
mides to PKCs, proposed by molecular modeling, was confirmed by
X-ray analysis of 1 bound in the active site of PKCR.
Solid organ allotransplantation has become a common
medical procedure with considerable impact on extending
and improving the quality of life of patients with end stage
renal, cardiac, hepatic, or pulmonary failure.1 Currently
known immunosuppressants can effectively modulate the
immune system and induce acceptance of transplanted or-
gans, but their use is limited by side effects. This challenge is
addressed in clinical protocols by the use of drug combination
treatments, which commonly consist of a calcineurin inhibitor
(CNI,a cyclosporine A (CsA), or FK506) inhibiting T cell
activation together with a T cell proliferation inhibitor (e.g.,
mycophenolic acid-based compounds or mTOR inhibitors)
and steroids. However, as mechanism-based side effects limit
the useof CNIs, a highmedical need exists for safe and specific
inhibitors of early T cell activation with a novel mechanism of
action.
The protein kinase C (PKC) family of serine/threonine
kinases consists of 10 isotypes that share sequence and
structural homology and that are grouped into three cate-
gories based on their cofactor requirements.2 Classical PKC
isotypes R, β, and γ require Ca2þ and diacylglycerol (DAG) as
cofactors. Novel isotypes δ, ε, η, and θ require DAG but are
Ca2þ independent, and atypical isotypes ζ and ι/λ require
Figure 1. Structure of 1.
At the outset of the project, typical maleimide-based PKC
inhibitors contained two indole moieties at the C3 and C4
positions of the maleimide, with one of these indoles carrying
a chain with a basic amine group (e.g., 2,5 Table 1).6 Aiming to
expand the structural diversity of the maleimide substituents,
we tested the replacement of one of the two indoles with
alternative (hetero)aromatic moieties. We first explored the
possibility of replacing the unsubstituted indole (Table 1). The
inhibitory potency on classical and novel PKC isotypes was
determined by scintillation proximity assay (SPA) technol-
ogy.7 Results from these assays indicated that neither the
1-naphthyl (3),8 2-azaindol-3-yl (4),9 nor the benzothiophen-
3-yl (5)8 moieties were suitable replacements of the indolyl, as
these derivatives showed modest inhibitory activity on PKC
(Table 1).
These disappointing results prompted us to refocus our
efforts on the other indole and to design compounds in which
the basic side chain was appended to a new (hetero)aromatic
ring. This derivation strategy turned out to be successful, as it
yielded novel, highlypotent, and very selectivePKC inhibitors
(Table 2). The straightforward syntheses of the corresponding
phenyl-, naphthyl-, and quinazolinyl-containing maleimide
derivatives are described in Schemes 1-3 and are all based
on the known base-mediated maleimide formation using a
primary amide and a 2-oxoacetic acid ester derivative.10
The first compound (9) of this series, which contained a
3-(2-dimethylaminoethoxy)phenyl moiety, displayed promis-
ing nanomolar inhibitory activity in the biochemical assays on
all PKC isoforms tested (Table 2). The docking of 9 into
a homology model of PKCθ suggested that the active site
could accommodate the extension of the phenyl ring to the
†The atomic coordinates of the X-ray crystal structure of 1 bound
PKCR have been deposited with the Protein Data Bank: PDB code
3IW4.
*To whom correspondence should be addressed. For J.W.: phone,
þ41 61 69 62 385; fax, þ41 61 69 62 455; e-mail, juergen.wagner@
novartis.com. For P.v.M.: phone, þ41 61 32 49 713; fax, þ41 61 32 46
121; e-mail, peter.von_matt@novartis.com.
a Abbreviations: CNI, calcineurin inhibitor; CsA, cyclosporine A;
DAG, diacylglycerol; GvH, rat graft-versus-host model; IL-2, interleu-
kin 2; INN, international nonproprietary name; MLR, mixed lympho-
cyte reaction; pan-PKC inhibition, simultaneous inhibition of both
classical and novel protein kinase C isotypes; PKC, protein kinase C;
SPA, scintillation proximity assay; TCR, T cell receptor.
r
2009 American Chemical Society
Published on Web 09/18/2009
pubs.acs.org/jmc
Wagner, Jürgen
