Chalcone–benzoxaborole hybrids as novel anticancer agents

Article abstract of DOI:10.1016/j.bmcl.2016.10.024

In this study, we report the synthesis of a series of chalcone–benzoxaborole hybrid molecules and the evaluation of their anticancer activity. Their anticancer potency and toxicity were tested on three human cancer cell lines and two normal cell lines. The 4-fluoro compound 15 was found to be the most potent compound with an IC₅₀value of 1.4 μM on SKOV3 cells. The 4-iodo compound 18 and 3-methyloxy-4-amino compound 47 showed good potency on SKOV3 cells while exhibiting low toxicity on normal cells. This work extended the application of benzoxaboroles to the field of anticancer research.

Full text of DOI:10.1016/j.bmcl.2016.10.024

Accepted Manuscript
Chalcone-Benzoxaborole Hybrids as Novel Anticancer Agents
Jiong Zhang, Fei Yang, Zhitao Qiao, Mingyan Zhu, Huchen Zhou
PII:
S0960-894X(16)31052-6
DOI:
http://dx.doi.org/10.1016/j.bmcl.2016.10.024
BMCL 24327
Reference:
Bioorganic & Medicinal Chemistry Letters
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Received Date:
Revised Date:
Accepted Date:
18 May 2016
20 September 2016
10 October 2016
Please cite this article as: Zhang, J., Yang, F., Qiao, Z., Zhu, M., Zhou, H., Chalcone-Benzoxaborole Hybrids as
Novel Anticancer Agents, Bioorganic & Medicinal Chemistry Letters (2016), doi: http://dx.doi.org/10.1016/j.bmcl.
2016.10.024
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Chalcone-Benzoxaborole Hybrids as Novel Anticancer Agents
Jiong Zhang,a Fei Yang,a Zhitao Qiao,a Mingyan Zhu,a Huchen Zhou∗a,b
aState Key Laboratory of Microbial Metabolism, School of Pharmacy, Shanghai Jiao Tong University, Shanghai, China
bChemical Biology Division of Shanghai Universities E-Institutes, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education,
Shanghai Jiao Tong University School of Medicine, Shanghai, China
ARTICLE INFO
ABSTRACT
Article history:
Received
In this study, we report the synthesis of a series of chalcone-benzoxaborole hybrid molecules
and the evaluation of their anticancer activity. Their anticancer potency and toxicity were tested
on three human cancer cell lines and two normal cell lines. The 4-fluoro compound 15 was
found to be the most potent compound with an IC50 value of 1.4 µM on SKOV3 cells. The 4-
Iodo compound 18 and 3-methyloxy-4-amino compound 47 showed good potency on SKOV3
cells while exhibiting low toxicity on normal cells. This work extended the application of
benzoxaboroles to the field of anticancer research.
Revised
Accepted
Available online
Keywords:
2016 Elsevier Ltd. All rights reserved.
Drug discovery
Anticancer
Structure-activity relationship
Benzoxaborole
Cancer, as one of the major causes of death, seriously
endangers human health.1 In 2015 alone, an estimated 2.8 and 0.6
million cancer deaths occurred in China2 and United States,3
respectively. While chemotherapy remains the main treatment,
clinically used anticancer drugs are generally limited by toxicity,
side effects, and resistance.4,5 Consequently, it remains urgent to
develop novel anti-cancer agents. During the past decade, boron-
containing compounds has started to attract much attention from
medicinal chemists.6,7 The boronic acid-containing drug
bortezomib (Velcade) (Figure 1), a proteasome inhibitor,8 was
approved in 2003 to treat multiple myeloma.9 An interesting class
of cyclic boron-containing compounds, benzoxaboroles, were
first synthesized in 195710 while its medicinal usage had
remained unexplored for fifty years until tavaborole (Kerydin)
(Figure 1) was approved in 2014 for the treatment of fungal
infection of the toenails.11,12 To date, benzoxaboroles have been
investigated for their antifungal, antibacterial, anti-parasite,
antiviral, and anti-inflammatory properties.11-19 However, an
investigation of their anticancer activity has been lacking.
Although Kunar and coworkers tested a few benzoxaboroles
against cancer cell line, their compounds failed to show any
significant inhibitory activity.20 Li and coworkers reported
benzoxaborole-containing phenylalanine analogues which have
potential applications in boron neutron capture therapy (BNCT),
but subsequent study was not reported.21
Figure 1. Structures of bortezomib and tavaborole.
benzoxaboroles against three human cancer cell lines, SKOV3
(ovarian carcinoma), MDA-MB231 (breast cancer), and HCT116
(colon colorectal carcinoma), and two human normal cell lines,
MCF-10A (human mammary epithelial cells) and WI-38 (lung
fibroblast) by MTT assay.22 The chalcone-benzoxaborole hybrid
molecule 8 showed inhibitory activity against SKOV3, MDA-
MB231, and HCT116 cell lines with IC50 value of 3.4, 2.3, and
6.1 µM, respectively. It also showed an 8-fold selectivity
between human cancer cells (MDA-MB231) and normal cells
(WI-38). Further investigation of the derivatives of compound 8
led to the discovery of anticancer agents with IC50 value as low as
1.4 µM (compound 15) and compounds 18 and 47 which possess
both high potency and good selectivity.
The compounds were synthesized according to our previously
reported methods.23 As shown in Scheme 1, 2,6-
dimethylbromobenzene (1) was oxidized to 2-bromoterephthalic
acid 2 which was subsequently converted to methyl ester 3.
Reduction of ester 3 gave benzyl alcohol 4 which underwent
protection and treatment with n-BuLi and triisopropyl borate,
followed by deprotection and cyclization in 6 M HCl to give
In order to develop novel anticancer agents and extend the
range of application of benzoxaboroles, we screened a series of
———
∗Corresponding author. Tel.: +86-21-3420-6721; e-mail: hczhou@sjtu.edu.cn.

Cisplatin
benzoxaborole 6. Oxidation of alcohol 6 gave aldehyde 7 which
underwent aldol condensation to give compounds 8-45.
Compound 46 was obtained by alkali hydrolysis from ester 27.
Compound 47 was obtained from nitro compound 45 by SnCl2
reduction.
12.8
41.8
21.7
11.0
>100
a IC50 indicates compound concentration required to inhibit cell viability by
50%. Values are expressed as the mean of triplicate experiments.
N-methyl-pyrrolyl compound 14 showed completely diminished
activity. Therefore, we next continued to investigate the
substituted phenyl compounds for their anticancer activity.
Br
HOOC
Br
MeOOC
Br
a
b, c
d
COOH
COOMe
1
2
3
As shown in Table 2, the anticancer activity of para-
substituted phenyl compounds is discussed. Compared to
unsubstituted phenyl compound 8, p-fluoro compound 15 showed
a 2-fold increase of potency, while p-chloro, -bromo, and –iodo
compounds 16-18 showed moderately decreased potency. It is
worth mentioning that the p-iodo compound 18 showed more
than 25-fold of selectivity between cancerous cells (SKOV3) and
normal cells (MCF-10A and WI-38). The p-methyl, -ethyl, -
methylthio, and -benzyloxy compounds 19-22 showed moderate
decrease of activity. Introduction of hydrogen bond donors,
including hydroxyl (23) and amino (24), gave significantly
reduced potency. Electron withdrawing groups, including
trifluoromethyl (25), nitro (26), and ester (27) resulted in
moderate decrease of potency, while the carboxylic acid 46
completely lost inhibitory potency.
OH
OTHP
OH
e
f, g
h
Br
Br
B
HO
O
OH
OTHP
4
5
6
O
R
OH
O
i or j
OH
OHC
B
B
R
O
O
7
8-45
Scheme 1. Reagents and conditions: (a) KMnO4, t-BuOH,
H2O, 70 °C; (b) SOCl2, reflux; (c) MeOH, Et3N; (d) LiBH4,
MeOH, THF; (e) DHP, p-TsOH, DMF; (f) n-BuLi, B(i-PrO)3,
THF, -78 °C; (g) 6 M HCl; (h) PCC, Celite, DCM; (i) NaOH,
EtOH, H2O; (j) CH3COCl, EtOH.
Table 2. The effect of different para-substitutions.
a IC50 (µM)
Compound
R
MDA-
MB231
SKOV3
1.4
HCT116 MCF-10A WI-38
15
16
17
18
1.6
7.9
9.5
2.8
9.3
9.9
11.8
12.1
27.8
7.6
24.7
36.7
Scheme 2. Reagents and conditions: (a) NaOH, EtOH, H2O;
(b) SnCl2·2H2O, EtOH.
3.7
4.5
First, we explored the effect of different aromatic rings on
anticancer activity. As shown in Table 1, bulky aromatic rings
such as naphthyl (9) and biphenyl (10) showed activity
comparable to compound 8. However, heterocycles including
furanyl (11), thiophenyl (12), and pyridinyl (13) gave
significantly reduced inhibitory activity. In addition, the
4.2
3.7
4.4
4.1
14.9
6.5
9.8
9.8
11.6
10.5
10.9
10.3
>100
8.3
>100
22.2
20.6
54.3
19
20
21
Table 1. The effect of different aromatic A rings.
8.8
7.4
22
23
24
a IC50 (µM)
6.0
13.0
20.2
3.7
5.3
25.6
25.8
9.2
12.1
24.1
26.1
6.3
23.3
24.8
19.9
22.3
>100
>100
25.4
22.6
Compound
R
MDA-
MB231
MCF-
10A
SKOV3
3.4
HCT116
WI-38
19.1
8
2.3
3.6
6.1
15.9
9
2.7
4.9
5.0
9.5
13.4
18.8
18.3
25
10
26
27
46
6.4
20.7
7.9
7.1
11.2
13.0
>100
9.1
7.6
17.5
12.9
>100
39.3
47.2
>100
11
12
20.7
10.4
7.3
4.6
24.1
14.2
7.4
59.0
26.0
13.8
>100
>100
a IC50 indicates compound concentration required to inhibit cell viability
by 50%. Values are expressed as the mean of triplicate experiments.
13
14
18.5
11.4
20.5
34.4
76.2
93.6
0.42
>100
0.07
>100
0.31
>100
0.06
>100
9.0
We also explored more substitution patterns on the phenyl
group as shown in Table 3. The o- and m-fluoro compounds 28-
29, dichloro compound 30, and methyl compounds 31-32 showed
Doxorubicin

potency comparable to parent compound 8. Although the phenols
23 and 33-34 all showed significantly decreased or even
abolished activity, the m-OH compound 35 showed activity
comparable to compound 8. Similarly, the m-NH2 compound 36
also showed good activity although its p-NH2 analog 24 gave
poor activity. Introduction of single methoxy group (37-38) gave
inhibitory activity comparable to compound 8, while multiple
methoxy or alkoxy groups gave moderately reduced activity (39-
44). Introduction of an electron withdrawing group and an
electron donating group simultaneously (45) gave good
inhibitory potency against SKOV3 cells (IC50 = 1.7 µM),
however it also exhibited strong toxicity to human normal MCF-
10A cells (IC50 = 3.6 µM). However, its amino analog 47 retained
the high anticancer activity while showed low toxicity on human
normal WI-38 cells.
47
1.7
24.3
27.9
17.6
>100
a IC50 indicates compound concentration required to inhibit cell viability by
50%. Values are expressed as the mean of triplicates experiments.
In summary, we reported the anticancer activity of a series of
chalcone-benzoxaborole hybrid compounds. We have shown that
the terminal phenyl group can tolerate bulky aromatic rings, and
it is sensitive to the substitution pattern and the electronic
properties of the substituents. Iodo- and amino-groups are
beneficial for selectivity between cancerous and normal cells.
Compound 15 showed both high potency on cancer cells and
high toxicity on normal cells. Compounds 18 and 47 showed
high potency on cancer cells with low toxicity on normal cells.
This structure-activity relationship provided a basis for further
optimization. To date, despite of their application in antifungal,
antibacterial, antiviral, and antiparasitic research, benzoxaboroles
have not been reported for any significant anticancer activity.
This work showed that bezoxaboroles may serve as a potentially
useful class of anticancer agents. However, their mechanism of
action remains to be elucidated. In previous reports, their
biological activities were mainly assessed by phenotypic
screening while the cellular targets remained unknown. Much
effort has been made to reveal their cellular targets, such as the
successful identification of an antifungal target leucyl-tRNA
synthetases (LeuRS).12 Although LeuRS was also suggested as an
anticancer target24 our chalcone-benzoxaboroles did not show
any significant inhibition of it. In addition, it has been reported
that specific benzoxaboroles inhibited β-lactamases15 and HCV
NS3 protease.18 But these targets are not involved in anticancer
activity. We are currently making efforts to investigate the
cellular targets of these molecules in cancer cells and will report
our progress in due time.
Table 3. The effect of different phenyl substitutions.
a IC50 (µM)
Compound
R
MDA-
MB231
SKOV3
3.7
HCT116 MCF-10A WI-38
28
2.2
4.2
25.4
23.6
29
30
4.8
1.8
3.0
3.4
6.7
3.2
15.8
14.9
26.7
12.5
31
32
2.9
1.9
4.5
5.3
6.7
6.1
15.9
4.7
16.7
22.0
33
48.8
16.9
67.6
77.9
53.7
>100
>100
Acknowledgements
34
35
36
>100
>100
>100
We thank National Science Foundation of China (81222042;
81573264; 21402118) for financial support of this work.
3.8
7.4
2.7
3.2
6.5
4.5
25.3
19.6
26.4
25.3
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2.6
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21.7
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86.3
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Graphical Abstract
Chalcone-Benzoxaborole Hybrids as Novel
Anticancer Agents
Leave this area blank for abstract info.
Jiong Zhang, Fei Yang, Zhitao Qiao, Mingyan Zhu, Huchen Zhou
O
O
O
OH
OH
OH
O
B
B
B
O
R
O
O
H2N
I
47
18
IC50(SKOV3):
IC50 (WI-38):
4.2 µM
1.7 µM
> 100 µM
> 100 µM