AROMATIC THIOSEMICARBAZONES ARE INHIBITORS
OF TRYPTOPHAN 2,3-DIOXYGENASE (TDO),
AN EMERGING TARGET FOR CANCER TREATMENT
Eduard Dolušić,a Sara Modaffari,a Pierre Larrieu,b Christelle Vancraeynest,a Luc Pilotte,b Didier Colau,b
Vincent Stroobant,b Johan Wouters,a Bernard Masereel,a Benoît Van den Eyndeb and Raphaël Frédéricka
bLudwig
aDrug Design and Discovery Center, University of Namur, 61 Rue de Bruxelles, 5000 Namur, Belgium ;
Institute for Cancer Research, Université Catholique de Louvain, 74 Avenue Hippocrate, 1200 Brussels, Belgium
edolusic@fundp.ac.be
Introduction and aim of the work. Indoleamine 2,3-dioxygenase (IDO; EC 1.13.11.52) is a heme dioxygenase that
catalyzes the first and rate-limiting step of the kynurenine pathway of tryptophan catabolism. The resulting local
tryptophan depletion and catabolite formation are important causes of peripheral immune tolerance contributing to
tumoral immune resistance. IDO inhibition is thus an active area of research in drug development. 1
Recently, our group has shown that tryptophan 2,3-dioxygenase (TDO; EC 1.13.11.11), a structurally unrelated hepatic
enzyme catalyzing the same reaction, is also expressed in many tumors. This expression similarly prevents tumor
rejection.2 Very recently, we published a structure-activity study on a series of 3-ethenylindoles as TDO inhibitors.3
LM10 (58),
The best compound, LM10 (58), was chosen for preclinical evaluation in mice in order to decipher the exact role of
IC50 = 2 mM
TDO in cancer immunosuppression.
in a cellular
Thiosemicarbazones are pharmacologically interesting compounds exhibiting a spectrum of biological activities. 4
TDO assay3
Compounds of this class, such as marboran (an antiviral used against pox viruses) and triapine (a ribonucleotide
reductase inhibitor used in anti-cancer treatment), have been advanced into clinical trials. Their biological actions
have generally been attributed to metal chelating properties5. We set out to synthesize a range of
thiosemicarbazones and investigate their inhibitory potencies on IDO and TDO in cellular assays.
Synthesis. The compounds were
synthesized by a condensation of an
appropriate (hetero)aromatic
aldehyde with the corresponding
thiosemicarbazide in ethanol, either
by conventional6,7 or microwave
heating. If the required aldehyde
was not commercially available, it
was prepared by a Vilsmeier-Haack
formylation of the parent
heterocycle. The double bond
geometry in the final products was
assumed to be (E), as suggested
both by literature7 and our own
NOESY experiments.
TDO
IDO
%inh. @
30 mM
%inh. @
30 mM
Biological
evaluation
1
20
0
2
6
3
0
4
Table 1
(Het)Ar =
(Het)Ar =
IDO
TDO %inh.
%inh. @
@ 30 mM
30 mM
TDO
IDO
entry
R3
%inh. @
30 mM
%inh. @
30 mM
entry
R
R1
R2
R3
10
1-Me
1
0
1
H
H
H
H
20
0
7
11
4-Me
3
0
15
H
H
H
5-F
15
0
0
12
5-Me
toxic
0
16
H
H
H
6-F
55
0
toxic
toxic
13
7-Me
5
0
20
H
Me
H
6-F
16
1
5
0
0
14
4-F
15
0
21
H
f
H
6-F
14
3
6
0
0
15
5-F
15
0
22
Me
H
H
H
2
0
7
1
11
16
6-F
55
0
23
H
H
Me
5-F
49
39
R = R1 = R2
entry
=H
(Het)Ar
R = R1 = R2
=H
8
0
0
17
7-F
4
6
9
0
0
18
6-Cl
toxic
toxic
19
6-CO2Me
3
toxic
Table 2
Table 3
24
H
H
Me
H
25
H
H
Me
6-F
60
IC50 = 20.0 mM
89
IC50 = 2.5 mM
10
14
References. [1] (a) Uyttenhove, C. et al, Nat. Med. 2003, 9, 1269-1274; (b) Macchiarulo, A. et al, Amino Acids 2009, 37, 219-229; (c) Röhrig, U. et al, J. Med. Chem. 2010, 53, 11721189; (d) Dolušić, E. et al, Bioorg. Med. Chem. 2011, 19, 1550-1561; (e), Dolušić, E. et al, Eur. J. Med. Chem. 2011, 46, 3058-3065. [2] Van den Eynde, B. et al, 2010, WO2010008427.
[3] Dolušić, E. et al, J. Med. Chem. 2011, doi: 10.1021/jm2006782. [4] (a) Beraldo, H. et al, Mini-Rev. Med. Chem. 2004, 4, 31–39; (b) Duffy, K.J. et al, J. Med. Chem. 2002, 45, 35733575. [5] Yu, Y. et al, J. Med. Chem. 2009, 52, 5271-5294. [6] Husain, K. et al, Eur. J. Med. Chem. 2008, 43, 2016-2028. [7] Rizal, R. M. et al, Acta Cryst. 2008, E64, o919–o920. [8]
Madge et al, Bioorg. Med. Chem. Lett. 1996, 6, 857-860. This work was supported by FNRS-Télévie 7.4.543.07 and by the Walloon Region (grant ‘CANTOL’ n° 5678).