Discovery of vanadium complexes bearing tridentate schiff base ligands as novel LSD1 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2018.10.004

Lysine specific demethylase (LSD1) plays a pivotal role in epigenetic modulation of gene expression. Abberrant expression of LSD1 was associated with the progress and oncogenesis of multiple human cancers. Herein, we report the preliminary anti-LSD1 evalu

Full text of DOI:10.1016/j.bmcl.2018.10.004

Accepted Manuscript
Discovery of vanadium complexes bearing tridentate shiff base ligands as novel
LSD1 inhibitors
Ling-Pan Lu, Jin-Hai Liu, Shi-Hong Cen, Ya-Ling Jiang, Guo-Qiang Hu
PII:
S0960-894X(18)30784-4
https://doi.org/10.1016/j.bmcl.2018.10.004
BMCL 26063
DOI:
Reference:
Bioorganic & Medicinal Chemistry Letters
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Revised Date:
Accepted Date:
27 July 2018
7 September 2018
1 October 2018
Please cite this article as: Lu, L-P., Liu, J-H., Cen, S-H., Jiang, Y-L., Hu, G-Q., Discovery of vanadium complexes
bearing tridentate shiff base ligands as novel LSD1 inhibitors, Bioorganic & Medicinal Chemistry Letters (2018),
doi: https://doi.org/10.1016/j.bmcl.2018.10.004
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Discovery of vanadium complexes bearing tridentate shiff base ligands
as novel LSD1 inhibitors
Ling-Pan Lu, Jin-Hai Liu, Shi-Hong Cen,Ya-Ling Jiang, Guo-Qiang, Hu*
School of Pharmaceutical Sciences, Zhengzhou University of Industrial Technology,
Zhengzhou,451199, PR China
*Corresponding Author
E-mail address: hgqxy@sina.com
Abstract: Lysine specific demethylase (LSD1) plays a pivotal role in epigenetic
modulation of gene expression. Abberrant expression of LSD1 was associated with
the progress and oncogenesis of multiple human cancers. Herein, we report the
preliminary anti-LSD1 evaluation of the synthetic vanadium (V) complexes. Among
them, complex 2 showed a moderate inhibitory effect against LSD1 with IC50 value of
19.0 μM, as well as good selectivity over MAO-A/B. Complex 2 is the first vanadium
based LSD1 inhibitor, which provides a novel scaffold for the development of LSD1
inhibitor.
Keywords: Vanadium complex, LSD1, MAO, anticancer
The methylation modificaton of histone lysine has long been considered to be an
irreversible and stable protein mark, until the discovery of lysine specific demethylase
1 (LSD1) in 2004.1 LSD1 can catalize the demethylation of mono- and dimethlyated
K4/K9 of histone H3 (H3K4/K9) via flavin adenine dinucleotide (FAD) dependent
amine oxidation to regulate downstream gene expression.2, 3 Aside from histone,
LSD1 can also eliminate methyl from modified lysine of nonhistone proteins such as
p53, E2F transcription factor, DNA methyltransferases (DNMTs) to modulate their
downstream cellular fuction.4-8 In addition, there have been increasing reports that
aberrant expression of LSD1 is associated with multiple kinds of diseases, especially
malignant cancers,9 and inactivation of LSD1 holds a promising potential for cancer

therapy.
To date, multiple structurally diverse small molecular LSD1 inhibitors were well
developed since the discovery of LSD1 as an attractive molecular target for cancer
therapy.10 Among them, mechanism-based tranylcypromine (TCP)-derived
irreversible LSD1 inhibitors have attracted extensive interests from researchers (Fig.
1), and made a greater progress than other reversible kinds of LSD1 inhibitors.11
Indeed, several TCP-based LSD1 inhibitors, such as ORY-1001, GSK2879552, and
INCB059872 are under clinical assessments for the treatment of acute myeloid
leukemia (AML) and non-small-cell lung carcinoma (NSLCL).11-13 Even that, there
are currently no LSD1-targeted drugs approved by the US Food and Drug
Administration (FDA) for the clinical use for cancer treatment. Therefore, it is of
great urgency to develop more efficient LSD1 inhibitors of different chemotypes for
use in cancer treatment.
In addition to conventional organic molecules, organometallic complexes have also
attracted particular attention due to their antitumor potential in recent years.14-17
Oranometallic complexes poss unique structural benefits relying on the oxadation
state of metal center and variation of ligands, making them to be promising scaffolds
for therapeutic agent development.18 Most recently, rhodium (III) based coordination
complex 1 (Fig. 1) was firstly identifed to possess inhibitory ability towards LSD1,
which inhibited LSD1 selectively over related enzymes, KDM2b, KDM7 and
MAOs.17 Our group has been dedicated to the study of vanadium-based complexes as
well as their biological function.19 In the present study, we report herein the synthesis
and preliminary investigation of vanadium complexes bearing tridentate shiff base
ligands on their inhibitory activities against LSD1. To our knowledge, complex 2 (Fig.
1) is the first vanadium metal-based LSD1 inhibitor reported in the literature, which is
believed to be a useful scaffold for further development of novel and potent LSD1
inhibitors.

Fig. 1. Chemical structures of tranylcypromine, rhodium (III) complex 1, and vanadium complexs
2-4.
The synthetic route for complex 2 was illustrated in Scheme 1. The tridentate
salicylaldiminato chelating ligand was prepared by reaction of 3,5-di-tert-butyl
salicylaldehyde with 2-(methylthio)aniline, and V(N-2,6-Me2C6H3)Cl3 was prepared
from VOCl3 with 2,6-dimethylphenyl isocyanate in octane under heating.20 The
desired complex 2 was obtained by reacting V(N-2,6-Me2C6H3)Cl3 with the
[ONS]-type ligand in the presence of triethylamine in tetrahydrofuran, which was
51
identified by 1H, 13C, V NMR spectra and elemental analysis. The single resonance
assigned to –SCH3 in the 1H NMR spectra shifts from 2.48 ppm in ligand 2' (Fig. 3a)
to 2.86 ppm in complex 2, which indicates that the sulphur atom coordinates to the
metal center. In addition, crystals of 2 suitable for X-ray crystal analysis were grown
from the chilled concentrated THF and hexane mixture solution. As shown in Fig. 2,
two chlorine atoms, the oxygen atom with the sulphur atom of the tridentate
salicylaldiminato chelating ligand are coordinated at the equatorial positions.

Meanwhile, the imido nitrogen and the imino nitrogen occupy the axial positions. The
Cl(1)-V-Cl(2) bond angle is 162.28(7)°, indicating that two chlorine atoms are
situated in trans position. Thus it can be seen that complex 2 adopts a six-coordinate,
distorted octahedral geometry around the vanadium center. The V-S bond length is
2.4896(19) Å, indicating the formation of coordinate bond between sulfur atom and
the vanadium center. All these data show that the desired complex is formed by
reaction of the [ONS]-type multidentate ligand with V(N-2,6-Me2C6H3)Cl3. The
distance between V and O(1) is 1.834(4) Å, indicating that O atom coordinates to
vanadium as a σ-donor. In addition, the V-N(1) (imido nitrogen) bond length is
1.689(4) Å, apparently shorter than the V-N(2) (imino nitrogen) bond distance
(2.197(4) Å), and the C(1)-N(1)-V bond angle is 171.1(4)º， indicating the linear
nature of the imido group as well as a π-bond between the imido nitrogen and V
atom.21 The crystallographic data together with the collection and refinement
parameters are summarized in Table S1. d nd dis an s ) and angles
(degree) of complex 2 are summarized in Table S2.
Scheme 1. Synthesis of vanadium complex 2.

Fig. 2. Molecular structure of complex 2, with thermal elipsoids at 50% probability.
The complex 2 was biochemically tested for their inhibitory activity against LSD1,17
and TCP was chosen as the reference compound (IC50 = 26.1 μM ). Additionally,
both synthesized complexes 3 and 4 were also examined for their LSD1 inhibition,19
with the aim to have an preliminary understanding of structure-activity relationship of
the vanadium complexes. As shown in Fig. 3b, complex 3 and 4 had around 28% and
44% of inhibition rate at 30 μM, respectively, indicating that sulfur atom in aniline
ring made a positive contribution for the inhibition against LSD1. The introduction of
tertiary butyl to the salicylaldiminato ligands in complex 2 led to an improved activity
of anti-LSD1, with the inhibitory rate of about 70% at the same concentration.
Besides, the shiff-base ligands 2'-4' (Fig. 3a) were also tested for their LSD1
inhibitory activity, and there was no significant inhibitory response observed. These
results indicated that the vanadium (V) center played an important role in arranging
the ligands around to shape a suitable active conformation for binding to the active
site in LSD1 pocket. With these inhibitory results at 30 μM single concentration, the
most active complex 2 was chosen for further evaluation to give the IC50 value of 19.0
μM (Fig. 3c), slightly more active than TCP. Furthermore, the inhibition of
monoamine oxidases (MAOs) by complex 2 was also examined, since LSD1 shares

similar amine acid sequence with MAOs.22 As indicated in Fig. 3d, complex 2
exhibited very weak inhibition of MAO-A/B at indicated concentrations, indicating
that complex 2 was selective for LSD1 over its homologues MAOs.
Fig. 3. (a) Structures of ligands 2'-4'; (b) Inhibitory evaluation of complexes against LSD1 at a
concentration of 30 μM; (c) IC50 curves of complex 2 and TCP; (d) Inhibitory activity of complex
2 against LSD1 and MAO-A/B at indicated concentrations. Data are mean ± SD. All experiments
were independently carried out at least three times.
In conclusion, a small-size block of vanadium complexes was screened for their
inhibitory ability against LSD1. The preliminary results showed that complex 2
showed a moderate inhibitory effect with an IC50 value of 19.0 μM, comparable with
TCP (IC50 = 26.1 μM). Besides, complex 2 displayed no activity toward MAOs,
showing a good selectivity for LSD1. Therefore, vanadium complexes may represent
a novel chemotype of LSD1 inhibitors, and could be considered as a useful scaffold
for the development of more potent LSD1 inhibitors.

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Highlights
 A novel vanadium complex bearing tridentate schiff base ligand was prepared and
fully characterized.


Complex 2 showed a moderate inhibitory effect against LSD1 with IC50 value of
19.0 μM.
Complex 2 displayed good selectivity for LSD1 with no inhibition of MAO-A/B
at indicated concentrations.

Graphic abstract