Novel carboxamide-based allosteric MEK inhibitors: Discovery and optimization efforts toward XL518 (GDC-0973)

Article abstract of DOI:10.1021/ml300049d

The ERK/MAP kinase cascade is a key mechanism subject to dysregulation in cancer and is constitutively activated or highly upregulated in many tumor types. Mutations associated with upstream pathway components RAS and Raf occur frequently and contribute to the oncogenic phenotype through activation of MEK and then ERK. Inhibitors of MEK have been shown to effectively block upregulated ERK/MAPK signaling in a range of cancer cell lines and have further demonstrated early evidence of efficacy in the clinic for the treatment of cancer. Guided by structural insight, a strategy aimed at the identification of an optimal diphenylamine-based MEK inhibitor with an improved metabolism and safety profile versus PD-0325901 led to the discovery of development candidate 1-({3,4-difluoro-2-[(2-fluoro-4-iodophenyl)amino]phenyl}carbonyl)-3-[(2S) -piperidin-2-yl]azetidin-3-ol (XL518, GDC-0973) (1). XL518 exhibits robust in vitro and in vivo potency and efficacy in preclinical models with sustained duration of action and is currently in early stage clinical trials.

Full text of DOI:10.1021/ml300049d

Letter
pubs.acs.org/acsmedchemlett
Novel Carboxamide-Based Allosteric MEK Inhibitors: Discovery and
Optimization Efforts toward XL518 (GDC-0973)
Kenneth D. Rice,* Naing Aay, Neel K. Anand, Charles M. Blazey, Owen J. Bowles, Joerg Bussenius,
Simona Costanzo, Jeffry K. Curtis, Steven C. Defina, Larisa Dubenko, Stefan Engst, Anagha A. Joshi,
Abigail R. Kennedy, Angie I. Kim, Elena S. Koltun, Julie C. Lougheed, Jean-Claire L. Manalo,
Jean-Francois Martini, John M. Nuss, Csaba J. Peto, Tsze H. Tsang, Peiwen Yu, and Stuart Johnston
Exelixis Inc., 210 East Grand Avenue, South San Francisco, California 94080, United States
S
* Supporting Information
ABSTRACT: The ERK/MAP kinase cascade is a key mechanism subject to dysregulation in cancer
and is constitutively activated or highly upregulated in many tumor types. Mutations associated with
upstream pathway components RAS and Raf occur frequently and contribute to the oncogenic
phenotype through activation of MEK and then ERK. Inhibitors of MEK have been shown to
effectively block upregulated ERK/MAPK signaling in a range of cancer cell lines and have further
demonstrated early evidence of efficacy in the clinic for the treatment of cancer. Guided by
structural insight, a strategy aimed at the identification of an optimal diphenylamine-based MEK
inhibitor with an improved metabolism and safety profile versus PD-0325901 led to the discovery of
development candidate 1-({3,4-difluoro-2-[(2-fluoro-4-iodophenyl)amino]phenyl}carbonyl)-3-
[(2S)-piperidin-2-yl]azetidin-3-ol (XL518, GDC-0973) (1). XL518 exhibits robust in vitro and in vivo potency and efficacy
in preclinical models with sustained duration of action and is currently in early stage clinical trials.
KEYWORDS: MAPK pathway, MEK, cancer, kinase inhibitor, XL518, GDC-0973
he MAPK cascade, or mitogen-activated protein kinase
signal transduction pathway, is a mechanism commonly
Our goal at the outset was the identification of a potent and
selective MEK inhibitor with sustained duration of efficacy
suitable for qd dosing and an optimized safety profile relative to
clinical precursors. The diphenylamine series disclosed by the
Pfizer/Warner Lambert groups served as a starting point for
our effort. A key aspect that served as a guide post for the
optimization process included elimination of the hydroxamate
ester, which demonstrated metabolic instability in the CI-1040
series.12 Potentially neurological side effects associated with
ataxia, confusion, and syncope were also observed in patients
during early trials involving PD-0325901 (2), possibly
associated with BBB penetration and MAPK pathway
suppression in brain tissue by parent or active metabolite (4),
and we sought to minimize this activity as well.13
T
subject to dysregulation in cancer, and constitutive or highly
upregulated signaling is a frequent hallmark of oncogenic
transformation and progression. Controlled by activation of
RAS at the cell surface interior, the subsequent stimulation of
Raf and then MEK and ERK serves to regulate a range of key
intracellular effectors associated with cell proliferation,1
invasion,2 angiogenesis,3 and apoptotic resistance.4 Mutated
RAS is associated with almost one-third of human cancers, and
a majority of malignant melanomas and papillary thyroid
cancers harbor B-Raf mutations.5,6 Inhibitors of MEK have
demonstrated efficacy against malignant tumors characterized
by mutations in either RAS or Raf in preclinical models, and
early development candidates including GSK1120212,7
AZD6244,8 and PD0325901 (2)9 have further demonstrated
evidence of activity in the clinical setting as well.
In some tumors, activation of both the RAS driven ERK/
MAPK cascade and the PI3K-Akt pathway is observed,
resulting in degenerate and convergent oncogenic signals, and
upregulation or constitutive PI3K pathway activation is
associated with resistance to MEK inhibitor single agent
treatment.10 Several combination approaches using inhibitors of
mTor, PI3K, Akt, and Raf have more recently been validated in
preclinical models and are being pursued clinically. Herein, the
discovery of XL518 (GDC-0973) (1), a potent and selective
MEK inhibitor, is described. XL518 is currently in early stage
clinical testing as both a single agent and in combination with
the class I PI3K inhibitor GDC-0941.11
Received: February 27, 2012
Accepted: April 9, 2012
Published: April 9, 2012
© 2012 American Chemical Society
416
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ACS Medicinal Chemistry Letters
Letter
Guided by structural insight, our approach focused on
replacement of the hydroxamate ester with a carboxamide.
Binding of the hydroxamate group in 2 is defined by a network
of hydrogen bond contacts involving the C2 and C3 hydroxyl
groups with the γ-phosphate of bound ATP (Figure 1). The
adenocarcinoma cells, selected for the expression of both K-
RAS G13D and B-RAF G464V mutations.
Preliminary results were not encouraging, and weak activity
was generally observed for early amides, exemplified by 4-
aminobutane-1,2-diol carboxamide (3), which was 103-fold less
potent than PD-0325901. The azetidin-3-ol analogue (7) stood
out as the most promising starting point for further
optimization efforts with a biochemical IC50 of 44 nM and
similar potency in the cellular assay. Increasing the ring size of
the carboxamide to pyrrolidine or piperidine analogues resulted
in a dramatic loss of activity. Oral exposure in the rat was rather
poor for (7), the result of low oral availability (19%) and high
clearance, and suggested that both absorption and metabolism
liabilities need to be addressed going forward (Table 2).
Metabolic instability was also reflected in relatively high rat liver
microsomal instability observed in vitro. The lipophilic
character (cLog P = 4.3, PSA = 52.6 Å2) of 7 suggested
further that an improvement in aqueous solubility may also
serve to optimize oral exposure.
The hydroxyl group at the 3-position of the azetidine was
important for biochemical potency, and deletion in the case of
6 was poorly tolerated. The cocrystal structure of azetidinol (7)
in adenosine 5′-(β,γ-methylenetriphosphonate) (AMP-PCP)
bound MEK1 was solved and provided structural insight
(Figure 1). The azetidine hydroxyl projects efficiently into the
catalytic loop region, forming two hydrogen bonds with
residues Asp190 and Asn195 with the diphenylamine core
binding in a manner entirely consistent with that of PD-
0325901. Azetidin-3-ol interaction with catalytic loop was
initially unanticipated and left open the prospect for
introduction of additional contacts with bound phosphate
and served as the strategic basis for follow up SAR.
On the basis of structural guidance and for pragmatic
reasons, our attention was directed primarily to substitution of
the azetidine ring 3-position for follow up SAR. We set out to
prepare key analogues bearing additional hydrophilic sub-
stitutions that could serve to interact with bound ATP
phosphate and further enhance aqueous solubility. The
introduction of a basic aminomethylene at the 3-position (8)
highlighted this effort and led to a significant 6-fold
improvement in biochemical activity. Deletion of the basic
amine as in the case of 9 resulted in a greater than 10-fold
reduction in potency, and nonbasic analogues (10 and 11)
failed to improve activity beyond that of 7. The crystal structure
of AMP-PCP bound MEK1 with 8 was solved and revealed that
the amine does engage the γ-phosphate (Figure 2). The amine
appears to induce reorganization of the phosphate chain and
brings the groups into close proximity. This shift also allows the
alcohol to bridge and engage both Asp190 and the γ-phosphate,
resulting in the formation of a more complex network of
contacts. Gratifyingly, compound 8 also demonstrated
improved oral exposure in the rat relative to 7. Compound 8
was found to have an oral bioavailability of 77% in the rat and a
significantly lower clearance, resulting in a dramatic improve-
ment in oral AUC and half-life.
Figure 1. Overlay of MEK1:AMP-PCP complex X-ray cocrystal
structures for PD0325901 (2) in blue and azetidinol (7) in green.
Dashed lines indicate key contacts and distances for the hydroxamate
and carboxamide.
diphenylamine core binds in the manner reported for early
analogues in the CI-1040 series.14 Initial efforts focused on the
synthesis and evaluation of simple cyclic and acyclic
carboxamide derivatives of (4) that feature polar substituents
including alcohols (Scheme 1). The set of amide derivatives
(6−19) featured in Table 1 were evaluated for MEK
biochemical inhibitory activity in a c-Raf-1/MEK1/ERK triple
coupled assay using an AlphaScreen chemiluminescense
readout and for cellular activity in MDA-MB-231T breast
Table 1. In Vitro Activity for MEK Inhibitors
a
b
compd
MEK1 IC50 (nM)
MD-MBA-231T IC50 (nM)
1
2
0.9
0.6
0.2
0.9
128
102
111
29
3
801
19.5
535
44
4
6
7
8
6.6
57
9
82
51
10
11
12
13
14
15
16
17
18
19
27
29
220
7.2
81
6.9
3.7
11
1.8
4.8
Compound 8 was examined in a duration of action MDA-
MB-231T xenograft PD study that included measurement of
BBB penetration and p-ERK inhibition in brain tissue (Table
3). Samples were taken at 2 and 24 h, and at both time points,
the concentration of metabolite 4 was measured. At an oral
dose of 30 mg/kg, mean plasma and tumor levels of 2.4 and
7.36 μM were observed at 2 h, and some brain tissue exposure
was apparent. At 24 h, plasma exposure diminished markedly,
5.1
14
7.6
50
1708
5.2
331
46
16
164
a
b
Biochemical activity c-Raf/MEK1/ERK (T202/Y204). Cellular
inhibition assay p-ERK (T202/Y204).
417
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ACS Medicinal Chemistry Letters
Letter
Figure 2. MEK1:AMP-PCP ternary complex cocrystal structures for 8 (A) and 1 (XL518) (B). Dashed lines indicate key contacts for the
carboxamide and aminoethanol fragments.
duration of PD response was encouraging and consistent with
sustained tumor exposure, the level of brain tissue activity and
an ED50 >30 mg/kg was considered less than ideal for moving
forward.
Table 2. In Vitro ADME and PK Parameters for Lead MEK
Inhibitors
a
rat PK parameters
oral
Going forward, we reasoned that the aminoethanol fragment
embedded in 8 should be conserved since it affords optimal
contact with ATP γ-phosphate and Asp190. The influence of
substitution at the aminomethylene terminus was then
explored. A broad set of N-substituted derivatives highlighted
by 12−17 were readily synthesized using the same general
coupling approach employed for the synthesis of earlier
analogues. The required azetidines were prepared straightfor-
wardly from 3-azetidinol (20) (Scheme 2). Mono- and
disubstitution of the amine was well tolerated for small groups,
and significantly improved cellular activity as well was observed
in the case of 12 and 13, although morpholine 17 demonstrated
a clear limit to the SAR. Structural studies revealed that
nitrogen substitution alters binding by rotation of the amine
away from the γ-phosphate to significantly favor interaction
with the catalytic loop, presumably driven by steric effects. Rat
pharmacokinetic studies revealed relatively poor oral exposure
for the series characterized by high clearance and reduced half-
life associated in part with metabolic degradation back to parent
8 and correlated well with increased rat microsomal instability
Cl
RLM HLM (mL/h/kg)
t1/2
AUC/
d
b
c
c
compd MDCK
(h)
F %
dose
7
8
399
43
80.1
16.2
31.5
40.5
−4.5
22.4
30.8
8324
755
1.5
9.1
19
78
0.05
1.57
0.85
0.25
1.03
0.35
12
13
18
1
207
210
99
46.3
35.8
2.6
2101
5958
800
5.4
101
86
4.9
11.4
6.1
58
105
13.8
3565
77
a
Compounds were prepared as amorphous solids and dosed at 5 mg/
b
c
kg in female CD rats. Cell permeability Papp nm/s. % Conversion in
the presence of rat and human liver microsomes at 0.5 mg/mL
microsomal concentration supplemented with NADPH and at 15 μM
substrate concentration at 37 °C for 30 min. Oral AUC (0−t)
normalized to dose (μM h/mg/kg).
d
and tumor accumulation was observed while brain levels
remained relatively unchanged. Minimal 4 was detected in
plasma only at 24 h time point and could not be detected in
tumor or brain tissue. Overall, the inhibition of p-ERK was
modest and apparent in both tumor and brain tissue. While the
Table 3. PD Activity for Lead MEK Inhibitor (8) and XL518 (1)
b
b
tumor
brain
b
plasma
2 h
p-ERK (%)
27
24 h
p-ERK (%)
2 h
p-ERK (%)
23
24 h
p-ERK (%)
a
compd
dose
concn 2 h
concn 24 h
concn
concn
concn
concn
8
30
2.4
0.03
0.21
<LQ
0.1
7.36
26.85
<LQ
0.53
44
0.73
1.24
<LQ
<LQ
<LQ
<LQ
0.22
17
c
4
0.01
<LQ
<LQ
1
1
1
1
5
10
16
45
75
87
8
7
2
0
1.99
20
0.1
3.59
100
0.12
22.85
a
b
Single oral dosage in MDA-MB-231T tumor bearing mice in mg/kg. Parent drug and metabolite (4) concentrations given in units of μM. p-ERK
c
(T202/Y204) reported as % inhibition. Metabolite (4) measured on administration of parent (8).
418
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ACS Medicinal Chemistry Letters
Letter
a
Scheme 1. General Synthesis of Carboxamide MEK Inhibitors
a
Reagents and conditions: (a) Compound 1, cyanuric fluoride, DCM, pyr. 0 °C. (b) Compound 5, DMF, DIPEA, RT. (c) Compound 4, PyBOP,
DMF, DIPEA, RT.
a
Scheme 2. General Synthesis of Azetidine Precursors for Compounds 12−19
a
+
Reagents and conditions: (a) BOC2O, aqueous dioxane, NaHCO3. (b) (COCl)2, DMSO, DCM, −78 °C. (c) RCH2P(Ph)3 Br−, t-BuOK, Et2O, 35
°C. (d) m-CPBA, CHCl3. (e) R1R2NH, THF. (f) TFA. (g) AD-mix-β, MeSO2NH2, aqueous t-BuOH. (h) (i) HCl, MeOH; (ii) CbzCl, aqueous
dioxane, NaHCO3. (i) SOCl2, pyr., DCM, 0 °C. (j) RuCl3, NaIO4, aqueous ACN. (k) NaN3, DMF, 60 °C. (l) PPh3, aqueous THF, 70 °C. (m)
BOC2O, THF. (n) Pd/C (10%), H2, MeOH, 1 atm.
in vitro. Methylene substitution was explored by preparation of
the individual α-methyl enantiomers (18 and 19). The requisite
azetidine precursors were prepared from ethylidine (22) using
Sharpless dihydroxylation methodology followed by diol
sulfation and regioselective azide ring opening.15 Subsequent
azide reduction and protecting group manipulation afforded the
desired chiral azetidines (26 and 27). Methylation was well
tolerated and the (S)-enantiomer (18) exhibited 3-fold
improved potency over the (R)-isomer. Substitution with
progressively larger alkyl groups or gem-dialkylation proved
unproductive. Compound 18 demonstrated cellular activity and
oral exposure analogous to that of the parent methylene 8 and
offered no advantage.
The strategy for final optimization recognized the oppor-
tunity to combine the tolerance for N-alkylation and α-
methylene substitution. Ultimately, the ideal balance of optimal
cellular potency and oral exposure was achieved by linking the
methylene and terminal nitrogen through an alicyclic ring. A
piperidine ring was found to be optimal and on the laboratory
scale was isolated in chiral form by resolution of 28, prepared
according to the published method of Peter Beak (Scheme 3).16
The piperidin-2-yl (S)-isomer (1) (XL518, GDC- 0973) was
found to be over 10-fold more potent than the (R)-isomer and
exhibits subnanomolar biochemical and cellular activity. The
cocrystal structure of XL518 in AMP-PCP bound MEK1 was
solved and revealed the formation of a highly complex network
Scheme 3. Resolution of Piperdines for the Synthesis of
XL518
a
a
Reagents and conditions: (a) (i) (R)-(−)-α-Methoxy-α-trifluorome-
thylphenylacetyl chloride, DMAP, DCM, 0 °C; (ii) Silica gel
chromatography. (b) Aqueous NaOH, MeOH. (c) Pd/C (10%), H2,
MeOH, 1 atm.
of interactions involving the embedded aminoethanol terminus
with both the catalytic loop Asp190 and the γ-phosphate
(Figure 2). Introduction of the cyclic constraint repositions the
amine closer to the catalytic loop and allows for engagement of
both γ-phosphate and Asp190. Acceptable oral exposure in the
rat was observed with half-life and clearance values intermediate
that of the N-substituted derivative (13) and parent (8), which
translated into potent PD activity as well (Table 3). In a dose
ranging duration of action PD study, limited brain exposure was
observed at the 100 mg/kg dose, and no metabolite (4) could
be detected. An ED90 of 39.7 mg/kg for p-ERK inhibition in
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ACS Medicinal Chemistry Letters
Letter
Activation of the MAPK Pathway. Mol. Cancer Res. 2011, 9 (8), 1018−
1029.
(2) Anand, M.; Meter, T. E.; Fillmore, H. L. Epidermal growth factor
induces matrix metalloproteinase-1 (MMP-1) expression and invasion
in glioma cell lines via the MAPK pathway. J. Neuro-Oncol. 2011, 104
(3), 679−687.
(3) Romon, R.; Adriaenssens, E.; Lagadec, C.; Germain, E.;
Hondermarck, H.; Le Bourhis, X. Nerve growth factor promotes
breast cancer angiogenesis by activating multiple pathways. Mol.
Cancer 2010, 9, 157.
(4) Kloster, M. M.; Naderi, E. H.; Carlsen, H.; Blomhoff, H. K.;
Naderi, S. Hyperactivation of NF-κ B via the MEK signaling is
indispensable for the inhibitory effect of cAMP on DNA damage-
induced cell death. Mol. Cancer 2011, 10, 45.
tumor tissue at 24 h was measured and provided support for an
improved safety profile of 1 in terms of minimizing MAPK
pathway inhibition in brain tissue within an effective therapeutic
dose range. In an MDA-MB-231T efficacy study, XL518
demonstrated tumor growth inhibition values of 60 and 93% at
1 and 3 mg/kg, respectively, and statistically significant tumor
regression was observed at higher doses.17 Overall, predicted
ED50 and ED90 values based on this study are 0.6 and
approximately 3 mg/kg/day, respectively, in the latter case
corresponding to peak circulating plasma levels in the range of
130 nM. Intermediate serum protein binding in the range of
94−96% across species as well as a disproportionate
accumulation of XL518 into the tumor tissue in xenograft
studies affords a disconnect between effective drug concen-
trations under serum-free conditions in vitro with those in vivo.
XL518 demonstrated no mutagenicity in Ames testing and was
well tolerated in subchronic oral dosing studies in rats with
minimal effects on plasma clinical chemistry and hematology
parameters.
In summary, a series of highly potent and selective MEK
inhibitors based on the diphenylamine core have been
identified. This novel series makes use of a metabolically stable
azetidinyl carboxamide linkage that exploits unique and efficient
contacts with bound ATP γ-phosphate and Asp190 in the
catalytic loop region. Efforts to optimize the potency and
pharmacokinetic profile of this series culminated in the
discovery of the XL518 (GDC-0973). XL518 demonstrates
excellent pharmacokinetics in preclinical species and minimal
BBB penetration by parent or active metabolite (4) that
translates into sustained tumor tissue selective inhibition of the
ERK/MAPK pathway in PD studies. Potent in vivo efficacy in
tumor xenograft models using a qd dosing regimen compares
favorably with PD-0325901. Early preclinical safety assessments
indicate that XL518 is well tolerated when dosed subchronically
to achieve efficacious circulating concentrations and is currently
in early clinical development as both a single agent and in
combination with the class I PI3K inhibitor GDC-0941.
(5) Fernandez-Medarde, A.; Santos, E. Ras in cancer and
developmental diseases. Genes Cancer 2011, 2 (3), 344−358.
(6) Matallanas, D.; Birtwistle, M.; Romano, D.; Zebisch, A.; Rauch, J.;
von Kriegsheim, A.; Kolch, W. Raf family kinases: Old dogs have
learned new tricks. Genes Cancer 2011, 2 (3), 232−260.
(7) Gilmartin, A. G.; Bleam, M. R.; Groy, A.; Moss, K. G.; Minthorn,
E. A.; Kulkarni, S. G.; Rominger, C. M.; Erskine, S.; Fisher, K. E.; Yang,
J.; Zappacosta, F.; Annan, R.; Sutton, D.; Laquerre, S. G.
GSK1120212 (JTP-74057) is an inhibitor of MEK activity and
activation with favorable pharmacokinetic properties for sustained in
vivo pathway inhibition. Clin. Cancer Res. 2011, 17 (5), 989−1000.
(8) Bennouna, J.; Lang, I.; Valladares-Ayerbes, M.; Boer, K.; Adenis,
A.; Escudero, P.; Kim, T.-Y.; Pover, G. M.; Morris, C. D.; Douillard, J.-
Y. A Phase II, open-label, randomised study to assess the efficacy and
safety of the MEK1/2 inhibitor AZD6244 (ARRY-142886) versus
capecitabine monotherapy in patients with colorectal cancer who have
failed one or two prior chemotherapeutic regimens. Invest. New Drugs
2011, 29 (5), 1021−1028.
(9) Barrett, S. D.; Bridges, A. J.; Dudley, D. T.; Saltiel, A. R.; Fergus,
J. H.; Flamme, C. M.; Delaney, A. M.; Kaufman, M.; LePage, S.;
Leopold, W. R.; Przybranowski, S. A.; Sebolt-Leopold, J.; Van
Becelaere, K.; Doherty, A. M.; Kennedy, R. M.; Marston, D.;
Howard, W. A., Jr.; Smith, Y.; Warmus, J. S. Tecle Haile The
discovery of the benzhydroxamate MEK inhibitors CI-1040 and PD-
0325901. Bioorg. Med. Chem. Lett. 2008, 18 (24), 6501−6504.
(10) Mirzoeva, O. K.; Das, D; Heiser, L. M. Basal subtype and
MAPK/ERK kinase (MEK)-phosphoinositide 3-kinase feedback
signaling determine susceptibility of breast cancer cells to MEK
inhibition. Cancer Res. 2009, 69 (2), 565−572.
ASSOCIATED CONTENT
* Supporting Information
■
S
(11) Hoeflich, K. P.; Merchant, M.; Orr, C.; Chan, J.; Den Otter, D.;
Berry, L.; Kasman, I.; Koeppen, H.; Rice, K.; Yang, N. Y.; Engst, S.;
Johnston, S.; Friedman, L. S.; Belvin, M. Intermittent administration of
MEK inhibitor GDC-0973 plus PI3K inhibitor GDC-0941 triggers
robust apoptosis and tumor growth inhibition. Cancer Res. 2012, 72
(1), 210−219.
Experimental procedures for the synthesis and characterization
of 1 and 6−19, MEK1 cocrystal structure determinations,
kinase selectivity data for XL518, and details for key in vitro
and in vivo studies. This material is available free of charge via
the Internet at http://pubs.acs.org.
(12) Wabnitz, P. A.; Mitchell, D.; Wabnitz, D. A. M. In Vitro and In
Vivo Metabolism of the Anti-Cancer Agent CI-1040, a MEK Inhibitor,
in Rat, Monkey, and Human. Pharm. Res. 2004, 21 (9), 1670−1679.
(13) Haura, E. B.; Ricart, A. D.; Larson, T. G.; Stella, P. J.;
Bazhenova, L.; Miller, V. A.; Cohen, R. B.; Eisenberg, P. D.; Selaru, P.;
Wilner, K. D.; Gadgeel, S. M. A Phase II Study of PD-0325901, an
Oral MEK Inhibitor, in Previously Treated Patients with Advanced
Non-Small Cell Lung Cancer. Clin. Cancer Res. 2010, 16 (8), 2450−
2457.
(14) Ohren, J. F.; Chen, H.; Pavlovsky, A.; Whitehead, C.; Zhang, E.;
Kuffa, P.; Yan, C.; McConnel, P.; Spressard, C.; Banotai, C.; Mueller,
W. T.; Delaney, A.; Omer, C.; Sebolt-Leopold, J.; Dudley, D.; Leung,
I.; Flamme, C.; Warmus, J. S.; Kaufman, M.; Barrett, S.; Tecle, H.;
Hasemann, C. Nat. Struct. Mol. Biol. 2004, 11, 1192.
AUTHOR INFORMATION
Corresponding Author
*Tel: 650-837-7063. E-mail: krice@exelixis.com.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank John Woolfrey, Lester Bornheim, and Jae Lee for
project team support, Paul Foster for structural and graphics
support, Siamak Dailami for analytical and instrumentation
support, and Tom Von Geldern and Stuart McCombie for
helpful discussions.
(15) Sharpless, K. B.; Amberg, W.; Bennani, Y. L.; Crispino, G. A.;
Hartung, J.; Jeong, K.-S.; Kwong, H.-L.; Morikawa, K.; Wang, Z.-M.;
Xu, D.; Zhang, X.-L. The osmium-catalyzed asymmetric dihydrox-
ylation: A new ligand class and a process improvement. J. Org. Chem.
1992, 57, 2768.
REFERENCES
■
(1) Luo, X.; Ruhland, M. K.; Pazolli, E.; Lind, A. C.; Stewart, S. A
Osteopontin Stimulates Preneoplastic Cellular Proliferation Through
420
dx.doi.org/10.1021/ml300049d | ACS Med. Chem. Lett. 2012, 3, 416−421

ACS Medicinal Chemistry Letters
Letter
(16) Beak, P.; Lee, W. K. α-Lithioamine synthetic equivalents:
syntheses of diastereoisomers from the Boc-piperidines. J. Org. Chem.
1990, 55 (9), 2578−80.
(17) Johnston, S. XL518, a potent selective orally bioavailable MEK1
inhibitor, downregulates the RAS/Raf/MEK/ERK pathway in vivo,
resulting in tumor growth inhibition and regression in pre-clinical
models. AACR-NCI-EORTC International Conference on Molecular
Targets and Cancer Therapeutics. Oct. 22−26, 2007, San Francisco, CA.
421
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