New Scaffold for Angiogenesis Inhibitors Discovered by Targeted Chemical Transformations of Wondonin Natural Products

Article abstract of DOI:10.1021/acsmedchemlett.7b00281

The structure of wondonin marine natural products was renovated to attain new drug-like scaffolds. Wondonins have novel antiangiogenic properties without overt cytotoxicity. However, the chemical instability and synthetic complexity of wondonins have hindered their development as a new type of antiangiogenesis agent. Using a structure-based bioisosterism, the benzodioxole moiety was changed to benzothiazole, and the imidazole moiety was replaced by 1,2,3-triazole. Our efforts resulted in a new scaffold with enhanced antiangiogenic activity and minimized cytotoxicity. One compound with this scaffold effectively inhibited hyaloid vessel formation in diabetic retinopathy mimic zebrafish model. The biological findings together suggested the potential of the scaffold as a lead structure for development of antiangiogenic drugs with novel functions and as a probe to elucidate new biological mechanisms associated with angiogenesis.

Full text of DOI:10.1021/acsmedchemlett.7b00281

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Letter
New Scaffold for Angiogenesis Inhibitors Discovered by Targeted
Chemical Transformations of Wondonin Natural Products
Shuai Yu, Jedo Oh, Feng Li, Yongseok Kwon, Hyunkyung
Cho, Jongheon Shin, Sang Kook Lee, and Sanghee Kim
ACS Med. Chem. Lett., Just Accepted Manuscript • Publication Date (Web): 12 Sep 2017
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New Scaffold for Angiogenesis Inhibitors Discovered by Targeted
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†
Shuai Yu, Jedo Oh, Feng Li, Yongseok Kwon, Hyunkyung Cho, Jongheon Shin, Sang Kook Lee,*
Sanghee Kim*
College of Pharmacy, Seoul National University, 1 Gwanakꢀro, Gwanakꢀgu, Seoul, 08826, Korea
KEYWORDS: Angiogenesis, Diabetic retinopathy, Drug design, VEGF/VEGFR2 pathway, Wondonins
ABSTRACT: The structure of wondonin marine natural products was renovated to attain new drugꢀlike scaffolds. Wondonins have
novel antiꢀangiogenic properties without overt cytotoxicity. However, the chemical instability and synthetic complexity of wondonꢀ
ins have hindered their development as a new type of antiꢀangiogenesis agent. Using a structureꢀbased bioisosterism, the benzodiꢀ
oxole moiety was changed to benzothiazole, and the imidazole moiety was replaced by 1,2,3ꢀtriazole. Our efforts resulted in a new
scaffold with enhanced antiꢀangiogenic activity and minimized cytotoxicity. One compound with this scaffold effectively inhibited
hyaloid vessel formation in diabetic retinopathy mimic zebrafish model. The biological findings together suggested the potential of
the scaffold as a lead structure for development of antiꢀangiogenic drugs with novel functions and as a probe to elucidate new bioꢀ
logical mechanisms associated with angiogenesis.
Nature has provided an immense array of bioactive
chemical entities across structurally diverse scaffolds. Some
differ in the configuration of the styryl double bond. We
previously defined the relative and absolute stereochemistries
of isowondonins via the asymmetric synthesis and electronic
1
scaffolds are suitable for direct employment as templates in
the generation of compounds with drugꢀlike properties, but
other scaffolds are not directly suitable for use in drug
development, mostly due to unfavorable physicochemical
properties. In the latter case, transformative structural
renovations are desirable to extract new scaffolds that are
more relevant for drug discovery.
4
circular dichroism calculations.
The family of wondonins has notable antiꢀangiogenic
5
properties by suppressing the expression of HIFꢀ1ɑ and
vascular endothelial growth factor (VEGF) in endothelial
cells. In contrast to other antiꢀangiogenesis agents, a
remarkable biological property of wondonins is that they
2,3,5
inhibit
angiogenesis
without
overt
cytotoxicity.
Angiogenesis is the formation of new blood vessels from preꢀ
existing ones, which occurs under normal physiological
conditions such as embryonic vascular development and
6
wound healing. Aberrant angiogenesis is observed in disease
processes including diabetic ocular neovascularization,
7
duodenal ulcers, arthritis, and cancer. VEGF is one of the
8
most important factors regulating angiogenesis. VEGF is
enriched in the endothelial cells for new blood vessels and
plays roles in vascular permeability, vascular network growth,
8
and vessel cell survival. Therefore, the modulation of the
VEGFꢀmediated angiogenic pathway is considered an
important target in drug discovery programs for diseases
9
,10
associated with the overꢀactivation of angiogenesis.
Several VEGFꢀsignaling pathway inhibitors are on the
9–11
market for the treatment of cancer or are in clinical trials.
A
large array of compounds are also currently in preꢀclinical
development. Most studies of VEGF pathway inhibitors have
focused on the identification of compounds with high
inhibitory effects on human umbilical vascular endothelial cell
(HUVEC) proliferation that could be used for the treatment of
Figure 1. Chemical structures of wondonins and analogues.
9–11
cancer.
In addition to their use as antiꢀcancer drugs, VEGF
Wondonins and isowondonins (1 and 2, Figure 1) are
structurally unique marine alkaloids that were identified from
an association of the sponges Poecillatra wondoensis and
pathway inhibitors have been proposed as potential therapeutic
12ꢀ14
agents for obesity and diabetic retinopathy.
However, few
2,3
drugs that specifically inhibit the pathways for such diseases
are available.
We conceived that the relevant biological properties of
novel antiꢀangiogenesis agents targeting the VEGF pathway,
Jaspis sp. These marine natural products possess an unusual
skeleton with a fiveꢀmembered acetal ring. Attached vinyl
sulfate and histamine moieties distinguish wondonins from
other natural products. Wondonins 1 and isowondonins 2
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especially for the treatment of diabetic retinopathy, should synthetic details in the Supporting Information). Its antiꢀ
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include minimized cytotoxicity or no cytotoxicity to avoid side
effects in normal cells. In this regard, we consider structurally
angiogenic activity was assessed by measuring its effects on
VEGFꢀinduced tube formation and growth of HUVECs in
comparison with those of natural wondonin A (1a) (see Figure
unique wondonins
a promising starting point for the
18
generation of a new lead compound. However, the wondonin
family presents challenges due to their chemical instability.
The fiveꢀmembered acetal ring and the vinyl sulfate moiety
are unstable, particularly under acidic conditions. In our
laboratory, wondonins readily decompose unless stored at
freezer temperatures and remain free of acid or base
contaminants. Another concern is their difficult synthesis. In
our total synthesis, installation of the vinyl sulfate and
S1 in the Supporting Information). The effect on tube
formation was determined by counting the intact tube number
under a microscope, and the IC50 of the compound was
calculated by comparison with the control group. The effect on
cell growth was measured in the MTT assay. As shown in
Figure 2, the triazole analogue 3 was 1.5ꢀfold more potent than
the parent natural product 1a in the tube formation assay and
was nearly as inactive as the parent 1a in inhibiting the growth
of HUVECs. Furthermore, analogue 3 did not show overt
cytotoxicity against various cancer cell lines (see Table S1 in
the Supporting Information), similar to wondonin A. These
results suggested that the triazole and ethyl moieties in 3 could
serve as bioisosteric replacements for the imidazole and vinyl
sulfate moieties in wondonins.
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histamine moieties was not trivial. In addition, the burdens
associated with the introduction of two stereocenters are
significant. Therefore, our primary aim in this study was to
discover a new scaffold from the structures of wondonins that
is chemically stable and easily accessible with drugꢀlike
properties. In this study, a series of wondonin analogues were
designed, synthesized, and evaluated. Our efforts resulted in
structurally distinct drugꢀlike scaffolds with more potent antiꢀ
angiogenic activity without overt cytotoxicity to HUVECs.
As an initial structural modification of wondonins, the
imidazole moiety was replaced by its bioisostere, 1,2,3ꢀ
triazole. This replacement was made because the
regioselective Nꢀalkylation of a substitutedꢀ1Hꢀimidazole is
The next replacement was implemented in the fiveꢀ
membered acetal ring. With the aim of eliminating the
stereocenter at C1 and endowing stability, the benzodioxole
ring of
3
was replaced with several benzoꢀfused
heteroaromatics, including benzofuran, benzothiazole, and
benzoxazole (Figures 1 and 2). The benzofuran analogue 4
displayed considerably improved potency in the inhibition of
tube formation (Figure 2) and was approximately 7 and 5
times more potent than the natural product 1a and
benzodioxole analogue 3, respectively. In contrast to 1a and 3,
benzofuran 4 exhibited a moderate inhibitory effect on the
VEGFꢀinduced growth of HUVECs. The benzoxazole
analogue 5 did not show notable activity against tube
formation. By contrast, the benzothiazole analogue 6 was
approximately 2 times more potent than the benzofuran
analogue 4 and less cytotoxic to cells. Based on the selectivity
index of the ratio of the IC50 for tube formation to the IC50 for
cell growth, the benzothiazole analogue 6 had more desirable
biological properties than the other heteroaromatic analogues.
Thus, benzothiazole 6 was used as a new lead scaffold for
4,15
difficult due to the rapid tautomeric equilibrium.
In
addition, the preparation of a wide range of suitably
16
substitutedꢀ1Hꢀimidazoles is not trivial. By contrast, a 1,4ꢀ
disubstituted 1,2,3ꢀtriazole moiety can be easily introduced via
a
Cu(I)ꢀcatalyzed azideꢀalkyne 1,3ꢀdipolar cycloaddition
17
(CuAAC) reaction. Given the instability and synthetic
difficulty, the vinyl sulfate moiety of wondonins was
substituted for a simple ethyl group, which is neither
significantly electron donating nor withdrawing. Although
ethyl might not be an optimal substituent for activity, it is a
good starting point for further optimization due to its unbiased
physicochemical properties. Such structural modifications
resulted in analogue 3 (Figures 1 and 2).
1
9
The designed analogue 3 was prepared as a mixture of
diastereomers that were inseparable (see Scheme S1 and
further
structural
modification.
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Figure 2. Chemical structures of wondonin A (1a), analogues 3–12, and sunitinib and measurement of their effects on the VEGFꢀinduced
tube formation and cell growth of HUVECs. Tube formation was determined by counting the number of intact tubes after treatment with
each compound in the absence or presence of VEGF (50 ng/mL) for 8 h. The value represents the mean IC50 in triplicate experiments
against VEGFꢀinduced tube formation by HUVECs. Cell growth was measured by the MTT assay after treatment with each compound in
the presence of VEGF (50 ng/mL) for 24 h. The value represents the mean IC50 in triplicate experiments against VEGFꢀinduced cell
growth in HUVECs. The fold change was calculated as the ratio of the IC50 values of tube formation and cell growth. For the values of
IC50 ± SD, see Table S2 in the Supporting Information.
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2
To assess the importance of the catechol unit in the
biological activity of benzothiazole analogue 6, two catecholic
hydroxyl groups were replaced with a methoxy group (Figure
permeability and angiogenesis. The activation of FAK is also
an important contributor to markedly involved in endothelial
2
3
cell migration, proliferation and adherens junction integrity.
2
). The methoxy analogue 7 was approximately 2–3 times less
Therefore, the present data suggest that the inhibition of cell
migration and neovascular tube formation by compound 12 is
partly associated with modulation of the signaling axis of
VEGFR2ꢀmediated PI3K/AKT/eNOS and the SRC/FAK
signaling pathway in HUVECs.
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potent than the parent 6 both in the tube formation assay and
the cell growth inhibition assay, and thus the selectivity index
remained nearly unchanged. Because replacement with a
methoxy group did not cause a significant decrease in activity,
a vicinal dimethoxyꢀsubstituted benzene ring was used in
further structural modifications instead of the metabolically
and chemically vulnerable catechol unit.
Recent findings suggest the existence of crossꢀactivation
between
angiogenesis.
betaꢀ3ꢀintegrin
and
VEGFRꢀ2
during
24,25
In particular, integrin is associated with
The next structural modification involved the N,Nꢀdimethyl
amino group of 7. Typical results are shown in Figure 2. The
inhibitory effects on both tube formation and cell growth were
sensitive to amino group modifications. All compounds with
different amino groups (8–12) exhibited increased tube
formation inhibition together with an increase in cell growth
inhibition. However, the degrees of inhibition differed,
indicating that these two effects were not correlated. For
example, while compound 9, with a cyclopentylamino group,
was approximately 8 times more potent than compound 7 in
tube formation inhibition and 5 times more potent in cell
growth inhibition, compound 12, with a piperidine moiety,
was approximately 13 times more potent in tube formation
inhibition but showed only a twoꢀfold increase in cell growth
inhibition. Of the analogues examined in this study, 12
exhibited the highest selectivity index, up to 75, with
pronounced inhibitory activity (IC50 = 0.631 ꢁM) against tube
formation. The selectivity index of the typical antiꢀangiogenic
stimulation of the migration of endothelial cells. Although we
did not directly detect the effect of wondonin analogues on
integrin expression, we found that SRC/FAK activation, which
is downstream of the integrin signaling pathway and correlated
with cell migration, was suppressed by compound 12. This
finding suggests that compound 12 is also able to affect
integrin signaling indirectly.
To further determine whether compound 12 directly affects
the activity of kinases that are closely associated with
angiogenic processes, compound 12 was evaluated at 10 ꢁM
TM
using KINOMEscan (DiscoverX Co., Fremont, CA, USA)
against a panel of 30 kinases, including VEGFR2. Kinase
activity was determined based on the binding capacity
between the each kinase and the corresponding ligand.
Compound 12 did not significantly inhibit the kinase activities
tested (see Table S3 in the Supporting Information) and
weakly inhibited only three kinases, namely CSNK1A1,
PRKCl, and MEK1 (over 40% inhibition at 10 ꢀM).
Therefore, the antiꢀangiogenic activity of compound 12 might
be more relevant in the regulation of VEGF/VEGFR2 axis
suppression than in the direct inhibition of angiogenesisꢀ
associated kinase activity.
2
0
tyrosine kinase inhibitor sunitinib was also determined in our
evaluation system, although its mechanism of action could
differ from those of wondonins and the synthesized analogues.
Sunitinib exhibited a much lower selectivity index of 18
compared to compound 12; it showed a similar level of
inhibitory potency (IC50 = 0.546 ꢁM) against tube formation as
Since diabetic retinopathy (DR) is associated with the
26
angiogenic processes, we evaluated the effects of compound
12 on neovascular formation in a DRꢀmimic animal model. In
general, DR leads to progressive vascular occlusions,
ultimately resulting in blindness with pericyte loss and vessel
1
2 but a 4.8ꢀfold higher inhibitory effect on the cell growth of
HUVECs.
Further biological studies were performed with compound
2
7
1
2 to understand the molecular mechanisms of the new
thickening. DR also increases vascular permeability, which
28
benzothiazole scaffold. The enhancement of endothelial cell
migration and tube formation capacity by VEGF was
effectively inhibited by 12 in a concentrationꢀdependent
manner (Figures 3A and 3B). Biomarker analysis revealed that
treatment of HUVECs with VEGF (50 ng/mL) for 20 min led
to the activation of PI3K (pꢀPI3K), AKT (pꢀAKT) and eNOS
(pꢀeNOS), whereas pretreatment with 12 for 30 min
significantly suppressed the activation processes in endothelial
cells (Figure 3C). In addition, the levels of VEGFR2 (pꢀ
VEGFR2) activated by VEGF were also suppressed by 12,
which subsequently inhibited the activation of SRC (pꢀ
SRC)/FAK (pꢀFAK) in VEGFꢀstimulated HUVECs. The
phosphorylation of VEGFR2 (Tyr1175) affects the activation
of PI3K signaling, and this event leads to an increase in
leads to macula edema. Zebrafish larvae treated with high
levels of glucose (HG) were employed as a mimic of
29
mammalian DR models. Transgenic zebrafish (flk:EGFP)
embryos (3 dpf) were treated with 130 mM glucose for 3 days
to induced DRꢀmimic hyaloid vessels in the larval eye lenses.
As shown in Figure 3D, HGꢀtreated zebrafish larvae exhibited
significantly increased hyaloid vessel diameters in isolated eye
lenses. However, treatment with 12 effectively suppressed the
increase in hyaloid vessel diameters induced by HG in a
30
concentrationꢀdependent manner. In particular, treatment
with 2.5 ꢁM compound 12 markedly reduced the hyaloid
vessel diameters in the optic disc area. These results suggest
that the reduction in HGꢀinduced hyaloid vessel diameters by
12 might also be associated with antiꢀangiogenic activity in
the in vivo animal model.
2
1
vascular permeability. In the VEGF signaling pathway, SRC
kinases are downstream of VEGFR2 and regulate vascular
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Figure 3. Antiꢀangiogenic activities of 12. A, Aꢀ1) Inhibition of vascular tube formation in HUVECs by compound 12. The capillary strucꢀ
tures were photographed, and the total tube length was quantified. The length of the capillary tubes formed were compared with that obꢀ
tained for the VEGFꢀtreated control groups. B, Bꢀ1) Inhibition of cell migration in HUVECs by compound 12. The migrated cells were
counted and compared with the VEGFꢀtreated control groups. C) Effects of compound 12 on the VEGFR2 signaling pathway. The cells
were treated with various concentrations of compound 12 for 30 min and then stimulated with VEGF (50 ng/mL) for 20 min. βꢀactin was
used as a loading control. D) Inhibition of hyaloid vessels in HGꢀtreated zebrafish larvae by compound 12. The hyaloid vessel diameters
were measured at a position near the optic disc (red circle) using ImageJ software (scale bar = 50 ꢁm). Quantification of the number of
primary vessel branches compared with that in the HGꢀtreated control groups. A, B, D) P values were calculated by ANOVA using Tukꢀ
#
#
#
#
#
ey’s test
(
P
<
0.001,
P
<
0.01; *P
<
0.05, **P
<
0.01; ***P
<
0.001, n=3)
To evaluate pharmaceutical properties of compound 12, the
aqueous solubility, permeability, plasma stability, and
metabolic stability were examined (Table 1). A notable
property of 12 is its high plasma stability that is important for
the achievement of in vivo activity. Compound 12 showed
plasma stability of 95% remaining intact after 30 min
incubation with human plasma. In the metabolic stability study
using human liver microsomes, a modest microsomal stability
was observed. Compound 12 exhibited high MDCK cell
permeability but low aqueous solubility (Biopharmaceutics
Classification System Class 2), probably due to its high
lipophilicity. Our theoretical calculations indicated that the
physicochemical properties of 12 were in compliance with
Lipinski’s rule of five and Veber’s rule for druglikeness
except a logP value (5.955) (see Table S4 in the Supporting
Information). Functional group modifications of 12 are in
progress in our laboratory, such as replacement of a methoxy
group with a more polar bioisosteric moiety, to improve
solubility and metabolic stability by lowering the lipophilicity.
percentage of parent compound remaining after 30 min incubation
in human plasma. The percentage of parent compound remaining
after 30 min incubation in human liver microsomes.
d
In summary, using the structure of wondonin marine natural
products, we created a novel lead scaffold for the development
of a new type of antiꢀangiogenesis agent that possesses potent
antiꢀangiogenic activity with minimized cytotoxicity to avoid
side effects. The analogues with benzothiazole and 1,2,3ꢀ
triazole rings, in place of benzodioxole and imidazole
moieties, respectively, displayed the desired biological
properties. The representative compound 12, which was more
easily synthesized than the parent natural product, exhibited an
excellent selectivity index with pronounced inhibitory activity.
The in vivo antiꢀangiogenic activity was also assessed using
DRꢀmimic zebrafish, which demonstrated the high potential of
the new scaffold for the treatment of diseases requiring antiꢀ
angiogenesis agents with minimized cytotoxicity. The precise
target of this new class of compounds remains unclear. Further
elucidation of the specific molecular target of compound 12
are in progress. In addition, we are currently investigating the
structureꢀactivity relationship in this series of compounds in
more detail to elucidate the minimal pharmacophore required
for the selectivity between antiꢀangiogenic activity and
cytotoxicity to HUVECs. The results of these efforts will be
reported in due course.
Table 1. Preliminary ADME Study of 12
soluba MDCK Papp,A B
plasma
stability (%)
microsomal
d
‑
pK
a
c
ꢀ6
b
(
mM)
(10 cm/s)
stability (%)
9
.24
0.024
11
95
31
a
b
Measured by the CheqSol method at 25 °C. Apparent permeꢀ
ASSOCIATED CONTENT
c
ability coefficients (Papp,A‑B) across MDCK cell monolayers. The
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Supporting Information. Synthetic Scheme S1 and S2, experiꢀ
(9) Ferrara, N.; Kerbel, R. S. Angiogenesis as a therapeutic target.
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endothelial growth factor (VEGF) receptors: drugs and new
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(12) Gariano, R. F.; Gardner, T. W. Retinal angiogenesis in develꢀ
opment and disease. Nature 2005, 438, 960–966.
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mental procedures and spectroscopic data for all new compounds,
supplementary Tables S1–S4, Figure S1 and S2, and HPLC analyꢀ
sis of biologically tested compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
(
(
AUTHOR INFORMATION
Corresponding Author
(
13) Salam, A.; Mathew, R.; Sivaprasad, S. Treatment of proliferaꢀ
tive diabetic retinopathy with antiꢀVEGF agents. Acta. Ophthalmol.
011, 89, 405–411.
14) Park, B. Y.; Lee, H.; Woo, S.; Yoon, M.; Kim, J.; Hong, Y.;
*S.K.L., Eꢀmail: sklee61@snu.ac.kr.
*S.K., Eꢀmail: pennkim@snu.ac.kr.
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ORCID
Lee, H. S.; Park, E. H.; Hahm, J. C.; Kim, J. W.; Shin, S. S.; Kim, M.
Y.; Yoon, M. Reduction of adipose tissue mass by the angiogenesis
inhibitor ALSꢀL1023 from Melissa officinalis. PLoS One 2015, 10,
e0141612.
Sang Kook Lee: 0000ꢀ0002ꢀ4306ꢀ7024
Sanghee Kim: 0000ꢀ0001ꢀ9125ꢀ9541
Author Contributions
(
15) Allin, S. M.; Bowman, W. R.; Elsegood, M. R. J.; McKee, V.;
Karim, R.; Rahman, S. S. Synthetic applications of aryl radical buildꢀ
ing blocks for cyclisation onto azoles. Tetrahedron 2005, 61, 2689–
†S.Y. and J.O. contributed equally to this work. All authors have
given approval to the final version of the manuscript.
2
696.
16) Kamijo, S.; Yamamoto, Y. Recent progress in the catalytic
(
Notes
synthesis of imidazoles. Chem. Asian J. 2007, 2, 568–578.
(17) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Click chemistry:
diverse chemical function from a few good reactions. Angew. Chem.
Int. Ed. 2001, 40, 2004–2021.
The authors declare no conflict of interest.
Funding
(18) Wondonin suppresses VEGF expression under hypoxia condiꢀ
This work was supported by the MidꢀCareer Researcher Program
5
tions. In the present study, the analogues were evaluated using a
(NRFꢀ2016R1A2A1A05005375) of the National Research
VEGFꢀinduced angiogenesis model rather than under hypoxia condiꢀ
tions because we hypothesized that evaluation under hypoxia condiꢀ
tions is more relevant to cancer.
(19) Similarly to wondonin, compound 6 suppresses HIFꢀ1α and
downstream targets under hypoxia conditions (see Figure S2 in the
Supporting Information). These data suggest that the mechanisms
involved in the antiꢀangiogenic activity of wondonin and its analogues
are similar.
Foundation (NRF) grant funded by the Korea government
(MSIP). This work was also supported by NRF (Grant 2009ꢀ
0
083533) grant funded by the Korean Government (MEST).
ABBREVIATIONS
ADME, absorption distribution metabolism excretion; AKT,
protein kinase B; CSNK1A1, casein kinase 1 isoform alpha;
EGMꢀ2, endothelial cell growth mediumꢀ2; eNOS, endothelial
NOS; FAK, focal adhesion kinase; FBS, fetal bovine serum; HIFꢀ
(
20) Roskoski Jr, R. Sunitinib: A VEGF and PDGF receptor proꢀ
tein kinase and angiogenesis inhibitor. Biochem. Biophys. Res. Com-
mun. 2007, 356, 323–328.
1
ɑ, hypoxia inducible factor 1ꢀalpha; MDCK, madinꢀdarby canine
(
21) Olsson, A. K.; Dimberg, A.; Kreuger, J.; ClaessonꢀWelsh, L.
kidney; MEK1, mitogenꢀactivated protein kinase 1; MTT, 3ꢀ(4,5ꢀ
Dimethylthiazolꢀ2ꢀyl)ꢀ2,5ꢀdiphenyltetrazolium bromide; PI3K,
phosphoinositide 3ꢀkinase; PRKCl, protein kinase C iota; PVDF,
polyvinylidene difluoride; qPCR, quantitative PCR; VEGFR,
vascular endothelial growth factor receptor.
VEGF receptor signalling ꢀ in control of vascular function. Nat. Rev.
Mol. Cell Biol. 2006, 7, 359–371.
(
22) Eliceiri, B. P.; Paul, R.; Schwartzberg, P. L.; Hood, J. D.;
Leng, J.; Cheresh, D. A. Selective requirement for Src kinases during
VEGFꢀinduced angiogenesis and vascular permeability. Mol. Cell
1
999, 4, 915–924.
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New Scaffold for Angiogenesis Inhibitors Discovered by Targeted Chem-
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†
Shuai Yu, Jedo Oh, Feng Li, Yongseok Kwon, Hyunkyung Cho, Jongheon Shin, Sang Kook Lee,*
Sanghee Kim*
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