Therapeutic targeting of oncogenic K-ras by a covalent catalytic site inhibitor

Article abstract of DOI:10.1002/anie.201307387

We report the synthesis of a GDP analogue, SML-8-73-1, and a prodrug derivative, SML-10-70-1, which are selective, direct-acting covalent inhibitors of the K-Ras G12C mutant relative to wild-type Ras. Biochemical and biophysical measurements suggest that modification of K-Ras with SML-8-73-1 renders the protein in an inactive state. These first-in-class covalent K-Ras inhibitors demonstrate that irreversible targeting of the K-Ras guanine-nucleotide binding site is potentially a viable therapeutic strategy for inhibition of Ras signaling. Putting a stop to Ras: Two new selective, direct-acting covalent inhibitors of the K-Ras G12C mutant are reported. Studies suggest that the modification of K-Ras with SML-8-73-1 renders the protein inactive. These novel covalent inhibitors demonstrate that irreversible targeting of the K-Ras guanine-nucleotide binding site is potentially a viable therapeutic strategy for inhibition of Ras signaling. Copyright

Full text of DOI:10.1002/anie.201307387

Angewandte
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DOI: 10.1002/anie.201307387
Drug Design
Hot Paper
Therapeutic Targeting of Oncogenic K-Ras by a Covalent Catalytic Site
Inhibitor**
Sang Min Lim, Kenneth D. Westover, Scott B. Ficarro, Rane A. Harrison, Hwan Geun Choi,
Michael E. Pacold, Martin Carrasco, John Hunter, Nam Doo Kim, Ting Xie, Taebo Sim,
Pasi A. Jꢀnne, Matthew Meyerson, Jarrod A. Marto, John R. Engen, and Nathanael S. Gray*
Abstract: We report the synthesis of a GDP analogue, SML-8-
73-1, and a prodrug derivative, SML-10-70-1, which are
selective, direct-acting covalent inhibitors of the K-Ras G12C
mutant relative to wild-type Ras. Biochemical and biophysical
measurements suggest that modification of K-Ras with SML-8-
73-1 renders the protein in an inactive state. These first-in-class
covalent K-Ras inhibitors demonstrate that irreversible target-
ing of the K-Ras guanine-nucleotide binding site is potentially
a viable therapeutic strategy for inhibition of Ras signaling.
signaling pathways,[5] thus leading to deregulated cell growth,
inhibition of cell death, invasiveness, and induction of angio-
genesis. About 30% of all human cancers harbor activating
Ras mutations, making them one of the most common known
genetic causes of cancer.[6,7] Moreover, cancers with a high
prevalence of K-Ras mutations, such as lung cancer and
pancreatic cancer, are difficult to treat and clinical outcomes
are poor even with aggressive and toxic medical interventions.
Despite more than 20 years of effort in industry and
academia, Ras has proven highly difficult to drug and no
effective targeted therapy currently exists.[8–10] Small mole-
cules targeting the guanine nucleotide (GN) binding site of
GTPases like Ras have been largely ignored because both
GTP and GDP bind to Ras with sub-nanomolar affinity and
their intracellular concentrations are very high, leading to the
widely held conclusion that the development of GN-binding-
site-directed inhibitors is not possible.
R
as proteins are members of a large family of GTPase
enzymes that are essential to transducing extracellular signals
into diverse cellular responses, such as proliferation, apopto-
sis, and differentiation.[1] Ras operates as a molecular switch
that is activated when growth factors bind to extracellular
receptors, which induce nucleotide exchange from GDP to
GTP.[2–4] Wild-type Ras proteins possess a slow intrinsic
GTPase activity for hydrolysis of GTP to GDP, a reaction
enhanced by GTPase-activating proteins (GAPs), which halt
Ras signaling by switching Ras into an inactive GDP-bound
signaling state. Mutations that diminish the GTPase activity
or induce GAP insensitivity result in constitutively activated
In light of the difficulties with GTPase inhibitor develop-
ment, we reasoned that a covalent approach targeting one of
the more potent Ras oncogenic mutants may be feasible. Of
the oncogenic Ras family members (H, K, N), K-Ras is
frequently mutated with most cancer causing mutations at
[*] Dr. S. M. Lim,[+] Dr. S. B. Ficarro, Dr. H. G. Choi, Dr. M. E. Pacold,
T. Xie, Dr. J. A. Marto, Dr. N. S. Gray
Dr. N. D. Kim
New Drug Development Center, Daegu-Gyeongbuk Medical Inno-
vation Foundation, Daegu, 706-010 (South Korea)
Department of Cancer Biology, Dana-Farber Cancer Institute
450 Brookline Avenue, Boston, MA 02215 (USA)
E-mail: Nathanael_Gray@dfci.harvard.edu
Dr. S. M. Lim,[+] Dr. H. G. Choi, T. Xie, Dr. N. S. Gray
Department of Biological Chemistry & Molecular Pharmacology,
Harvard Medical School, 250 Longwood Avenue
Boston, MA 02115 (USA)
Dr. K. D. Westover,[+] Dr. M. Carrasco, Dr. J. Hunter
Departments of Biochemistry and Radiation Oncology, The Uni-
versity of Texas, Southwestern Medical Center
Dr. T. Sim
Chemical Kinomics Research Center, Korea Institute of Science and
Technology, Seoul, 130-650 (South Korea)
Dr. P. A. Jꢀnne, Dr. M. Meyerson
Department of Medical Oncology, Dana-Farber Cancer Institute
450 Brookline Avenue, Boston, MA 02115 (USA)
Dr. M. Meyerson
Broad Institute of Harvard and MIT
320 Charles St., Cambridge, MA 02141 (USA)
and
5323 Harry Hines Blvd., Dallas, TX 75390 (USA)
R. A. Harrison, Dr. J. R. Engen
Department of Chemistry and Chemical Biology, Northeastern
Department of Pathology, Harvard Medical School
77 Avenue Louis Pasteur, Boston, MA 02115 (USA)
[+] These authors contributed equally to this work.
University, 360 Huntington Avenue, Boston, MA 02115 (USA)
Dr. S. M. Lim,[+] T. Xie
Department of Chemistry and Chemical Biology, Harvard University
12 Oxford Street, Cambridge, MA 02138 (USA)
[**] This work was supported by CPRIT (R1207), The Welch Foundation
(I1829), NIH P01NS047572, the Strategic Research Initiative at the
Dana Farber Cancer Institute (J.A.M.), the Dana Farber Cancer
Institute/Northeastern University Joint Program in Cancer Drug
Development, NIH GM101135 (J.R.E.), a research collaboration
with the Waters Corp (J.R.E.), Sally Gordon Fellowship of the Damon
Runyon Cancer Research Foundation (DRG 112-12) (M.E.P.), DOD
Breast Cancer Research Program Postdoctoral Fellowship
(BC120208) (M.E.P.).
Dr. S. B. Ficarro, Dr. J. A. Marto
Blais Proteomics Center, Dana-Farber Cancer Institute
450 Brookline Avenue, Boston, MA 02115 (USA)
Dr. M. E. Pacold
Whitehead Institute for Biomedical Research
9 Cambridge Center, Cambridge, MA 02139 (USA)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201307387.
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codons 12, 13, and 61.[6,7] G12C is a naturally occurring
activating K-Ras mutation present in roughly 10–20% of all
Ras-driven cancers, and roughly 50% of Ras-driven lung
adenocarcinomas.[11–13] This mutation places a solvent-acces-
sible cysteine adjacent to the active site, near the usual
position of the gamma-phosphate of the native GTP and
constitutively activates K-Ras (Figure 1). We hypothesized
that small molecules could be developed to selectively target
this activating mutation. Our group has successfully devel-
oped selective covalent kinase inhibitors,[14–16] which irrever-
sibly occupy the ATP binding site and prevent ATP load-
ing.[17] We envisioned that a GN-based molecule, which could
covalently modify the GN binding site of Ras, would over-
come challenges in targeting K-Ras for the following reasons:
a) the guanine nucleotide scaffold would preserve many of
the non-covalent interactions with Ras and b) covalent bond
formation in the GN binding site could overcome the problem
of high competing nucleotide concentration by preventing
further exchange upon covalent addition. As a proof of
concept, we herein present our efforts to develop a selective,
covalent Ras inhibitor that targets the GN binding site
directly, and overcomes the high intracellular concentrations
of GDP and GTP that would preclude binding of a non-
covalent inhibitor.
We presumed that structures utilizing a GDP scaffold
would induce an inactive K-Ras conformation, and designed
several diphosphate compounds by varying the identity of
electrophile and linker length between the b-phosphate and
electrophile. Molecular docking studies using a homology
model of K-Ras G12C that was adapted from a K-Ras crystal
structure (PDB ID: 3GFT) allowed the design of promising
candidates which were prioritized for synthesis. SML-8-73-
1 (1) appeared to have favorable geometric properties for
reaction with the cysteine in position 12 (Supporting Infor-
mation, Figure S1). The synthesis of SML-8-73-1 was ach-
ieved by reacting monophosphate intermediate 2 with
guanosine monophosphate morpholidate 3, followed by the
incorporation of an electrophile (Scheme 1). Monophosphate
2 was prepared by tetrazole-facilitated coupling of N-Boc
(Boc = tert-butoxycarbonyl) ethanolamine with dibenzyl N,N-
diisopropylphosphoramidite at ambient temperature, fol-
lowed by oxidation with meta-chloroperoxybenzoic acid
(mCPBA). The resulting dibenzyl phosphate ester was
subjected to hydrogenolysis in the presence of triethylamine
(TEA) to provide monophosphate 2 as a TEA salt. Diphos-
Figure 1. Model of K-Ras G12C bound to GDP (sticks). Cysteine 12 is
located in the P-loop opposite the catalytic magnesium (magenta ball)
and switches 1 (green) and 2 (pink). Model based on PDB: 4EPR.
Scheme 1. Synthesis of SML-8-73-1. Bn=benzyl, Boc=tert-butoxycarbonyl, mCPBA=meta-chloroperoxybenzoic acid, DIPEA=diisopropylethyl-
amine, DMF=N,N-dimethylformamide, TEA=triethylamine, TFA=trifluoroacetic acid.
2
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phate 4 was prepared by the reaction of 2 and 3 in the
presence of 5-(ethylthio)-1H-tetrazole. We noticed that the
free acid form of 2 is insoluble in pyridine and did not react
with 3 to produce 4, which suggests that utilization of the TEA
salt of 2 is critical to achieve good solubility of the mono-
phosphate. Deprotection of the Boc group and subsequent
formation of a-chloroacetamide completed the synthesis of
SML-8-73-1 (1), which was purified by preparative reverse-
phase HPLC.
It is possible that the high concentrations of GTP and
GDP within cells may prevent compounds like SML-8-73-
1 from making productive interactions with K-Ras G12C. To
investigate this, we simulated cellular conditions by repeating
the above experiment with the addition of 1 mm GDP and
1 mm GTP. We found that under identical incubation
conditions K-Ras G12C is more than 95% labeled within
2 h, which is similar to what we observe in the absence of
competing nucleotides (Figure S3).
To determine if SML-8-73-1 could covalently modify K-
Ras G12C, we incubated purified recombinant K-Ras at
a concentration of 50 mm for 2 h at 378C in phosphate buffer
solution (PBS) with the inhibitor at a concentration of
2.5 mm. Electrospray ionization mass spectrometry revealed
no addition of SML-8-73-1 to the wild-type protein (Fig-
ure 2a,b). In contrast, a single adduct was detected when K-
Ras G12C was incubated with SML-8-73-1 (Figure 2c,d).
Under these conditions, a molar ratio of 1:10 (K-Ras G12C/
SML-8-73-1) was required for complete incorporation of the
compound (Figure S2). Proteolytic digestion and analysis of
the resulting peptides by nano LC/MS demonstrated the
exclusive covalent labeling of the GN-site of K-Ras G12C
(cysteine residue 12; Figure 2e).
To investigate whether covalent labeling of K-Ras G12C
by SML-8-73-1 stabilizes the active or inactive conformation
of the protein, we used hydrogen exchange (HX) mass
spectrometry (MS). HX-MS provides a means to assess
protein conformational dynamics by measuring the rate of
hydrogen exchange of backbone amide hydrogens.[18] We
performed HX-MS on K-Ras G12C bound to a non-hydro-
lyzable GTP mimic (GMPPNP), GDP, or SML-8-73-1.
Hydrogen exchange into each species was compared by
monitoring the deuteration of over 40 peptides that were
produced after labeling and proteolytic digestion. In most of
the protein, there was no difference in deuterium incorpo-
ration between all three states (Figure S4). The regions that
did show differences are summarized in Figure 3.
Residues 7–20 showed significantly more deuterium
incorporation in the active conformation (GMPPNP-bound)
compared to the other conformation (Figure 3a, top) whereas
residues 114–120 showed slightly higher deuterium incorpo-
ration in the active state than in other states (Figure 3a,
bottom). Both of the regions with significant differences in
deuteration comprise portions of the nucleotide binding
pocket (Figure 3b), with residues 7–20 in close proximity to
Figure 3. Summary of differences in deuterium exchange in K-Ras
G12C bound to GMPPNP, GDP, and SML-8-73-1. Hydrogen–deuterium
exchange suggests that SML-8-73-1 places K-Ras G12C in the inactive
state. a) Relative deuterium uptake curves for two key peptides (top:
residues 7–20, VVVGACGVGKSALT; bottom: residues 114–120,
VGNKCDL) showing differences in deuterium incorporation. These are
representative data; each data point is the average of duplicate mass
determinations from one of three triplicates of the entire experimental
measurement (see the Supporting Information). b) Location of the two
regions from (a), on PDB file 4Q21. GDP is shown in brown, residues
7–20 in blue, and residues 114–120 in red.
Figure 2. SML-8-73-1 reacts quantitatively with K-Ras G12C, but does
not label WT K-Ras. Deconvoluted electrospray mass spectra obtained
for: a,b) WT K-Ras and c,d) K-Ras G12C before (a,c) and after (b,d)
incubation with SML-8-73-1 (2.5 mm). A mass increase of 526 Da
(compound-HCl) was observed only after treatment of K-Ras G12C,
thus indicating covalent labeling of the protein. e) HCD MS/MS
spectrum of SML-8-73-1 modified K-Ras G12C peptide (residues 6–16).
Ions of type b and y are shown in blue and red, respectively, and
localize the modification to C12. GDP=guanosine diphosphate,
*=loss of GDP.
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the phosphate groups and residues 114–120 adjacent to the
guanosine moiety. When K-Ras G12C was bound to covalent
inhibitor SML-8-73-1, the deuterium incorporation in resi-
dues 7–20 and 114–120 mimicked that observed in the GDP-
bound state (Figure 3a), which suggests that the compound
likely stabilizes an inactive form of K-Ras G12C.
To corroborate that SML-8-73-1 stabilizes K-Ras G12C in
an inactive state, we designed a functional biochemical assay
using AlphaScreen (PerkinElmer) technology to measure the
affinity of K-Ras/nucleotide complexes for the Ras binding
domain (RBD) of the Raf protein kinase. K-Ras preferen-
tially binds the Raf RBD in its active, GTP-bound state.[19–21]
Examination of a homology model of the RBD/K-Ras
complex (based on PDB ID 1C1Y) reveals that a solvent-
exposed cysteine (cys95) sits on the face of RBD opposite the
K-Ras binding side. We coupled biotin to this cysteine in
purified RBD[22,23] using maleimide chemistry (Thermo
Scientific), which resulted in the covalent addition of one
biotin per RBD molecule, as verified by HABA/Avidin assay
(Figure S5). N-terminally FLAG tagged K-Ras G12C pre-
loaded with the GTP analogue GNPPNP was incubated with
biotinylated Raf-RBD to form complexes. We performed
a competition assay by adding untagged K-Ras G12C, which
had been preloaded with various test molecules, over a range
of concentrations. The assay was developed with Alpha
donator and acceptor beads directed against the FLAG tag or
biotin respectively. We tested multiple nucleotides for their
ability to induce K-Ras G12C/Raf binding. The GDP/K-Ras
G12C complex had a lower affinity for RBD (EC50 of 22.6 nm;
95% CI, 17.5-32.0 nm), than the GTP/K-Ras G12C complex
(EC50 of 6.6 nm; 95% CI, 5.1–8.5 nm). Labeling of K-Ras
G12C with SML-8-73-1 at a 1:10 molar ratio to K-Ras
G12C prior to the assay yields a curve that is super-
imposable with that obtained when K-Ras G12C is
treated with GDP, a result which is consistent with the
notion that the compound stabilizes an inactive con-
formation of K-Ras G12C (Figure 4).
Figure 4. Alpha assay confirms that modification with SML-8-73-1 ren-
ders K-Ras G12C biochemically inactive. Untagged GMPPNP-loaded K-
Ras G12C was incubated with a 10-fold molar excess of GDP (red),
SML-8-73-1 (green) or buffer (blue). Under these conditions, K-Ras
G12C becomes completely labeled by SML-8-73-1, or loaded with GDP
or GMPPNP. These K-Ras G12C preparations were then added at the
indicated concentrations to compete for binding with Alpha-tagged K-
Ras G12C/Raf-RBD (donor/acceptor) complexes that had been pre-
formed. SML-8-73-1 bound K-Ras G12C (green) resembles GDP-bound
K-Ras G12C (red), with respect to affinity for Raf-RBD.
hydrolysis of the phosphate ester. However, we were able to
modify the beta phosphate as an alanine ester phosphorami-
date, thus resulting in a partially-caged version of SML-8-73-
1, SML-10-70-1 (Figure 5; see also Scheme S2). This phos-
phoramidate has been previously used to cage phosphates,
and intracellular hydrolysis of the lipophilic ester is reported
to result in regeneration of the phosphate group.[25]
We next investigated whether SML-10-70-1 is capable of
penetrating cell membranes and covalently engaging K-Ras
G12C. We designed a cellular “target engagement” assay,
where we measured the ability of SML-10-70-1 to protect K-
We further confirmed the results of the Alpha assay
using an FP variant of the K-Ras-RBD binding assay
wherein the RBD was labeled with the fluorescent dye
Oregon Green (Figure S6) and the protein-binding-
dependent FP signal was measured. GDP-bound K-Ras
G12C mimicked the SML-8-73-1 labeled protein, and
both possessed a lower affinity for K-Ras G12C bound
to the GTP analogue GMPPNP (Figure S7). Wild-type
K-Ras behaved similarly in this assay, which suggests
that the G12C mutation does not significantly affect the
interaction between K-Ras and RBD, or between K-
Ras and the nucleotides GTP and GDP (Figure S8).
SML-8-73-1 cannot pass through the cell membrane
because it contains two negatively charged phosphate
groups. “Caging” is a method whereby charged ions can
be chemically modified to mask the charged group and
thereby allow for passive cellular uptake.[24] The caging
moiety is typically designed to be removed intracellu-
larly, as a consequence of enzymatic cleavage. Caged
bisphosphates, where both phosphates are modified,
have not been reported, and indeed we discovered that
Figure 5. The caged analogue SML-10-70-1 is cell permeable and disrupts Ras
signaling. a) Chemical structures of caged SML-10-70-1 and the unreactive
negative control, SML-10-57-1. b) Treatment of H358 cells with SML-10-70-
1 (100 mm) prior to probing with desthiobiotin-GTP decreases the amount of K-
Ras that can be pulled down with streptavidin, as compared to cells treated
with unreactive control, which suggests that SML-10-70-1 penetrates into cells
and accesses the active site of K-Ras-G12C. c) Treatment of H358 cells with
SML-10-70-1 decreases levels of pErk and pAkt, as compared to treatment with
negative control (SML-10-57-1), which suggests a compound-dependent effect
these compounds were unstable as a consequence of on K-Ras signaling.
4
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Ras G12C from subsequent labeling with desthiobiotin-GTP
in lysates. Desthiobiotin-GTP is able to react with a conserved
lysine in the K-Ras GTP site such that K-Ras becomes
covalently biotinylated.[26] The K-Ras G12C expressing H358
cells were treated with SML-10-70-1 or a negative control
containing no electrophile (SML-10-57-1) for 6 h prior to
lysis. Lysates were incubated with desthiobiotin-GTP and the
biotinylated proteins were recovered using streptavidin
beads. Treatment of cells with SML-10-70-1 decreased the
recovery of biotinylated Ras, which suggests that SML-10-70-
1 is able to penetrate into cells and effectively compete for the
GTP binding pocket (Figure 5b). We investigated the effects
of SML-10-70-1 on signaling to Erk and Akt, two key K-Ras
effector pathways. SML-10-70-1, but not the non-covalent
SML-10-57-1, was able to attenuate Akt and Erk phosphor-
ylation, albeit only at a high concentration of 100 mm.
We further tested for the antiproliferative activity of
SML-10-70-1 in H23, H358, and A549 cells. H23 and H358
cells express the K-Ras G12C mutation and are considered K-
Ras dependent (for growth), whereas A549 cells have a G12S
mutation and are considered K-Ras independent.[27] Upon
treatment with SML-10-70-1, antiproliferative effects were
seen in all lines with an EC50 of 43.8 mm, 47.6 mm, and 26.6 mm
for A549, H23, and H358 cells, respectively.
Efforts to directly target Ras proteins have largely proven
unsuccessful. Targeting farnesyl transferase (FT), which adds
an isoprenyl group to the C-terminus of Ras and is essential
for Ras signaling, appeared promising in preclinical studies,
but did not progress beyond early phase trials because of
toxicity and lack of efficacy; this is likely because of
compensatory geranylgeranyl transferase, or other isoprenyl
transferase, activity for K-Ras and N-Ras.[28] Peptides have
been used to disrupt protein–protein interactions between
Ras and downstream signaling molecules, but this approach
has not produced clinically useful agents because the peptides
had poor drug-like properties. Along similar lines, small-
molecule ligands that bind to the surface of K-Ras are also in
the early stages of development.[10] Antisense oligonucleo-
tides directed against K-Ras have demonstrated efficacy in
cell culture, but have not been advanced to clinical inves-
tigation.[9] Notably, recent work targeting the prenyl-bindng
pocket of phosphodiesterase 6 (PDE6) delta subunit (PDEd)
has shown promise as a means of disrupting oncogenic
signaling by K-Ras.[29] PDEd regulates the spatial distribution
of the Ras family of proteins by solubilizing depalmitoylated
Ras proteins and facilitating diffusion to the Golgi for
palmitoylation. Downregulation of PDEd or the disruption
of Ras/PDEd interaction by small-molecule inhibitors mod-
ulates oncogenic Ras signaling and results in an antiprolifer-
ative effect on Ras-transformed cells.[30]
50% of Ras-driven lung adenocarcinomas). Labeling with
SML-8-73-1 stabilizes an inactive form of K-Ras G12C, as
assessed by biochemical and biophysical means. This work
demonstrates that specific GN-directed covalent inhibitors of
K-Ras G12C can be prepared and can compete with GTP and
GDP for active-site binding in a cellular context. Extending
this paradigm to other Ras forms may be possible by
specifically targeting other active-site side chains such as
lysine. SML-8-73-1 possesses two negative charges and
appears to be cell impermeable. A caged version of SML-8-
73-1 is able to penetrate into cells, but only at high
concentrations where it likely shows limited target selectivity,
as evidenced by the general cytotoxicity independent of K-
Ras G12C status in lung cancer cell lines. Future efforts will
explore cellular delivery strategies, including alternative
prodrugs, non-charged phosphate bioisosteres, and encapsu-
lation strategies that will be required to assess the potential of
this pharmacological approach in cellular and in vivo models
of K-Ras driven cancer.
Received: August 22, 2013
Published online: && &&, &&&&
Keywords: cancer · covalent inhibitors · drug design · K-Ras
.
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In summary, as another potential approach to directly
targeting oncogenic Ras, we have synthesized a GDP ana-
logue, SML-8-73-1, which contains an electrophilic chloroa-
cetamide attached to the beta phosphate, that can covalently
modify cysteine 12 of K-Ras G12C. The covalent modifica-
tion is specific to mutant K-Ras G12C when compared to the
wild-type protein, and would therefore specifically target
those Ras-driven cancers in which the K-Ras G12C mutation
is present (10-20% of all Ras-driven cancers and roughly
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K. K. Wong, M. J. Eck, N. S. Gray, P. A. Jꢂnne, Nature 2009, 462,
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6
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These are not the final page numbers!

Angewandte
Chemie
Communications
Drug Design
S. M. Lim, K. D. Westover, S. B. Ficarro,
R. A. Harrison, H. G. Choi, M. E. Pacold,
M. Carrasco, J. Hunter, N. D. Kim, T. Xie,
T. Sim, P. A. Jꢁnne, M. Meyerson,
J. A. Marto, J. R. Engen,
N. S. Gray*
&&&& — &&&&
Putting a stop to Ras: Two new selective,
direct-acting covalent inhibitors of the K-
Ras G12C mutant are reported. Studies
suggest that the modification of K-Ras
with SML-8-73-1 renders the protein
inactive. These novel covalent inhibitors
demonstrate that irreversible targeting of
the K-Ras guanine-nucleotide binding site
is potentially a viable therapeutic strategy
for inhibition of Ras signaling.
Therapeutic Targeting of Oncogenic K-
Ras by a Covalent Catalytic Site Inhibitor
Angew. Chem. Int. Ed. 2013, 52, 1 – 7
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
7
These are not the final page numbers!