Synthesis and antiproliferative activity of 2-aryl-4-oxo-thiazolidin-3-yl- amides for prostate cancer

Article abstract of DOI:10.1016/j.bmcl.2004.08.029

We have previously described serine amide phosphates (SAPs) as a novel class of cytotoxic agents for prostate cancer. Several of them showed potent cytotoxicity against human prostate cancer cell lines, but were not selective in non-tumor cells. To improv

Full text of DOI:10.1016/j.bmcl.2004.08.029

Bioorganic & Medicinal Chemistry Letters 14 (2004) 5289–5293
Synthesis and antiproliferative activity of
2-aryl-4-oxo-thiazolidin-3-yl-amides for prostate cancerI
Veeresa Gududuru,a Eunju Hurh,b James T. Daltonb and Duane D. Millera,*
aDepartment of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis,
TN 38163, USA
bDivision of Pharmaceutics, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA
Received 22 July 2004; revised 11 August 2004; accepted 11 August 2004
Available online 17 September 2004
Abstract—We have previously described serine amide phosphates (SAPs) as a novel class of cytotoxic agents for prostate cancer.
Several of them showed potent cytotoxicity against human prostate cancer cell lines, but were not selective in non-tumor cells.
To improve the selectivity and further enhance the potency, we designed a new series of 2-aryl-4-oxo-thiazolidin-3-yl amides.
The current work describes synthesis, SAR, and biological evaluation of these compounds for their ability to inhibit the growth
of prostate cancer cells. The antiproliferative effects of synthesized compounds were examined in five human prostate cancer cell
lines (DU-145, PC-3, LNCaP, PPC-1, and TSU), and in RH7777 cells (negative controls). From this study, three potent compounds
(8, 20, and 21) have been detected, which are effective in killing prostate cancer cells with improved selectivity compared to SAPs.
Ó 2004 Published by Elsevier Ltd.
Prostate cancer accounts for 33% of all newly diagnosed
malignancies among men in the United States.1 Accord-
ing to the American Cancer Society,2 an estimated
230,110 men will be diagnosed with prostate cancer in
2004, and 29,900 men will die of it. The incidence of
prostate cancer varies worldwide, with the highest rates
found in the United States, Canada, and Scandinavia,
and the lowest rates found in China and other parts of
Asia.3,4 These differences are caused by genetic suscepti-
bility, exposure to unknown external risk factor, or dif-
ferences in health care and cancer registration, or even a
combination of these factors.4
confined to the prostate, it can be successfully controlled
by surgery or radiation, but in metastatic disease, few
options are available beyond androgen ablation,8 the
mainstay of treatment in the case of lymph node
involvement or disseminated loci. Once tumor cells have
become hormone refractory, the standard cytotoxic
agents are marginally effective in slowing disease pro-
gression, although they do provide some degree of palli-
ative relief. Current chemotherapeutic regimens,
typically two or more agents, afford response rates in
the range of only 20–30%.9,10
We have endeavored to address the need for improved
antitumor therapy by means of a novel approach, and
a recent report from our laboratory details the develop-
ment of serine amide phosphates (SAPs), derivatives of
lysophosphatidic acid (LPA) as effective cytotoxic
agents against human prostate cancer cell lines.11 We
showed that SAP derivatives represent a class of anti-
cancer agents for the treatment of prostate cancer and
several of these were potent inhibitors of prostate tumor
cell proliferation at low micromolar concentrations.11
Despite their high cytotoxicity, the same compounds
were not selective against non-tumor CHO cells and
LPA receptor negative RH7777 cells. We also hypothe-
size that the phosphate group in SAPs is susceptible
to hydrolysis, as the phosphate moiety is readily
hydrolyzed by the action of lipid phosphate
Cancer of the prostate is multifocal and it is commonly
observed that the cancerous gland contains multiple
independent lesions, suggesting the heterogeneity of
the disease.5 Determinants responsible for the patho-
logic growth of the prostate remain poorly understood,
although steroidal androgens and peptide growth fac-
tors have been implicated.6,7 As long as the cancer is
Keywords: Prostate cancer; Lysophosphatidic acid; Phosphate mimics;
Thiazolidinones; Antiproliferative effect.
q This work was presented at the 31st MALTO Meeting, Memphis,
TN, May 16–18, 2004.
*
Corresponding author. Tel.: +1 901 448 6026; fax: +1 901 448
3446; e-mail: dmiller@utmem.edu
0960-894X/$ - see front matter Ó 2004 Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2004.08.029

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V. Gududuru et al. / Bioorg. Med. Chem. Lett. 14 (2004) 5289–5293
O
O
O
O
P
OH
O
P
O
HO
O
O
(CH2)nCH3
HO
O
N
H
(CH2)nCH3
N
S
O-
+NH3
N
H
R1
OH
R
LPA
I
SAP
Figure 1.
O
O
O
N
O
O
O
c or d
a,b
HS
+
ClH.H2N
+ R CHO
N
S
S
OMe
OH
OH
R1
R
R
2
3
1
5 - 12
4a - 4e
Scheme 1. Reagents: (a) toluene, Dean–Stark; (b) NaOH, MeOH; (c) CH3(CH2)nNH2, EDC, HOBt, CH2Cl2; (d) (COCl)2, benzene, NH3, MeOH.
phosphatases.12–14 The biomimetic replacement of phos-
phate group by a hydrolytically more stable pharmaco-
phore would be expected to prolong biological activity
by altering pharmacokinetics and metabolism.
O
O
O
O
a
N
N
S
S
OH
N
H
R
4a
Scheme 2. Reagents: (a) R–NCO, DMAP, CH2Cl2.
13 - 17
Andres et al. have postulated that 4-thiazolidinones may
be recognized as phosphate mimics, and using this scaf-
fold they synthesized and evaluated some 4-thiazolidi-
nones for their ability to inhibit the bacterial enzyme
MurB.15 Based on this hypothesis, we decided to explore
the 4-thiazolidinone pharmacophore as a biomimetic
replacement for the phosphate group. This strategic
modification would be expected to enhance the physio-
chemical, pharmacokinetic, and antiproliferative prop-
erties and result in highly potent and selective
anticancer agents for prostate cancer. To this end, we
designed a new series of thiazolidinone derivatives as
shown in Figure 1. In this paper we report the synthesis,
structure–activity relationship, and antiproliferative
activity of type I compounds (Fig. 1) in five human pros-
tate cancer cell lines (DU-145, PC-3, LNCaP, PPC-1,
and TSU).
acid, glycine methyl ester, and aromatic aldehydes in a
one-pot reaction, followed by basic hydrolysis of the es-
ter. Thiazolidinone amides were obtained by the treat-
ment with appropriate amines in the presence of EDC/
HOBt under standard conditions. Compound 5 that
has no side chain was synthesized from the correspond-
ing acid as shown in Scheme 1. Thiazolidinone amides
13–17 were synthesized by a simple and direct method,17
which involves reaction of the acid 4a with different iso-
cyanates in the presence of a catalytic amount of DMAP
(Scheme 2). Exhaustive reduction of 8 using BH3ÆTHF
under reflux conditions gave 19 (Scheme 3). Oxidation
of 8 using H2O2 and with KMnO4 afforded sulfoxide
(20) and sulfone (21), respectively, as shown in Scheme
The synthesis of thiazolidinone derivatives (5–12) uti-
lized straightforward chemistry as shown in Scheme 1.
Various 4-thiazolidinones were synthesized following a
reported procedure16 of condensing mercaptoacetic
3. All compounds18 were characterized by H and 13C
NMR, mass spectroscopy and, in certain cases, elemen-
tal analysis.
1
O
O
O
O
O
N
S
N
H
C18H37
N
S
b
a
N
S
N
H
C18H37
N
H
C18H37
O
8
19
21
c
O
O
N
S
N
C18H37
O
H
20
Scheme 3. Reagents: (a) KMnO4, AcOH; (b) BH3ÆTHF; (c) H2O2, AcOH.

V. Gududuru et al. / Bioorg. Med. Chem. Lett. 14 (2004) 5289–5293
Table 1. Antiproliferative effects of compounds 4a–b and 5–18
5291
O
O
R1
N
S
R
Compd
IC50 (lM)
R
R1
RH 7777a
DU-145b
PC-3b
LNCaPb
PPC-1b
TSUb
4a
4b
5
Ph
OH
OH
ND
>50>5>050>5>050
Biphenyl
Ph
Ph
>100
>100
20.0
16.4
39.6
>100
>100
>100
>100
20.3
13.5
11.1
>100
>100
14.1
14.1
9.3
>100
>100
15.8
10.1
7.1
>100
>100
NH2
6
NHC10H21
NHC14H29
NHC18H37
NHC18H37
22.4
19.7
7
Ph
Ph
19.6
12.6
13.4
8.5
8
9
Biphenyl
>50>50>>550>0>5050
10
11
NHC18H37
>50>50>>550>0>5050
N
NHC18H37
31.1
14.8
12.6
11.8
10.7
17.5
OMe
Cl
Cl
12
13
NHC18H37
>50>50>>550>0>5050
70.9
F
Ph
Ph
Ph
69.0
74.1
18.1
24.1
14.5
46.2
13.1
53.2
16.1
HN
F
CF3
HN
HN
14
15
25.4
34.9
16.2
CF3
Cl
24.028.6
13.2 .5
2017.2
Cl
HN
MeO
16
17
Ph
Ph
>100
>100
>100
>100
>100
82.5
31.4
>100
>100
60.8
69.9
OMe
NH
>100
>100
OMe
MeO
18
Ph
>100
ND
>100
>100
>100
>100
HN
5-FU
11.9
12.04.9
6.4
3.6
a Control cell line.
b Prostate cancer cell lines.

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V. Gududuru et al. / Bioorg. Med. Chem. Lett. 14 (2004) 5289–5293
Table 2. Antiproliferative effects of compounds 19–21
Compd
IC50 (lM)
DU-145b
Structure
RH 7777a
>2015.8
PC-3b
LNCaPb
PPC-1b
TSUb
19
>21026.01
N
S
N
H
C18H37
Ph
O
O
20
11.5
11.2
6.5
7.9
5.4
6.4
9.3
N
S
N
C
18H37
O
H
Ph
O
O
O
O
21
22.1
ND
15.5
11.9
8.5
10.9
5.5
N
S
N
H
C18H37
Ph
5-FU
12.04.9
6.4
3.6
a Control cell line.
b Prostate cancer cell lines.
The antiproliferative activity of all the synthesized com-
pounds has been evaluated against five human prostate
cancer cell lines and in RH7777 cells (negative control)
using the sulforhodamine B (SRB) assay.19 5-Fluoroura-
cil (5-FU) was used as reference drug. As shown in Table
1, 4-thiazolidinone carboxylic acids (4a and 4b) were
unable to inhibit the growth of any of the five prostate
cancer cells below 50lM. However, the corresponding
amides (6–8) showed higher activities. It was observed
that an increase in the alkyl chain length [6 (C10), 7
(C14), and 8 (C18)] enhances the antiproliferative activ-
ity of these analogs in prostate cancer cells. Interestingly,
the simple amide 5 without any long alkyl chain is not
cytotoxic below 100lM, which indicates that the absence
of an alkyl side chain causes a considerable decrease in
antiproliferative effect. On the other hand, replacement
of the alkyl chain with various aryl side chains (13–18)
reduced the biological activity. Among this series, 13 is
moderately cytotoxic, where as analogs 16–18 displayed
poor cytotoxicity in several prostate cancer cell lines.
However, it is noteworthy to mention that thiazolidinone
amides (14 and 15), with electron-withdrawing substitu-
ents on the aryl ring showed cytotoxicity in the range of
13–29lM against all five prostate cancer cell lines.
In summary, starting with the SAPs, we identified a ser-
ies of novel and cytotoxic 4-thiazolidinone amides based
on a 4-thiazolidinone scaffold. Among this series, we
synthesized and carried out detailed structure activity
relationship studies of type I compounds (Fig. 1) and
evaluated their antipropliferative activity against five
prostate cancer cell lines and RH7777 cells (negative
controls). The cytotoxicity study shows that the antipro-
liferative activity is sensitive to 2-aryl ring substitutions,
the length of the alkyl side chain, and the removal or
replacements of the lipophilic alkyl side chain. Sulfur
oxidation is well tolerated as compounds 20 and 21
showed significant cytotoxicity compared to 5-FU. This
study resulted in the discovery of potent cytotoxic 4-thi-
azolidinones 8, 20, and 21, which inhibit the growth of
all five human prostate cancer cell lines (DU-145, PC-
3, LNCaP, PPC-1, and TSU) with 2–5-fold lower selec-
tivity compared to RH7777 cell line. These 4-thiazolidi-
none derivatives are a significant improvement on the
SAP moiety in that they are less cytotoxic but demon-
strated improved selectivity in non-tumor cells. How-
ever, further investigations are required to increase the
potency and selectivity.
Thiazolidinone derivatives (9 and 10) with bulky biphe-
nyl or naphthalene groups demonstrated low cytotoxic-
ity compared to 8 (Table 1). We synthesized compounds
11 and 12 to understand the effects of aromatic ring sub-
stitution in 8. It was observed that electron-donating
substituents maintained good activity while the ortho
electron-withdrawing substituents substantially decrease
the antiproliferative activity of these derivatives (Table
1). Compound 19, which has no amide groups, showed
significantly good potency in all five prostate cancer cell
lines. Notably, 20 and 21 bearing sulfoxide or sulfone
moiety displayed higher cytotoxic potency comparable
to that of the reference drug 5-FU against both PC-3
and PPC-1 cell lines (Table 2).
Acknowledgements
This research was supported by a grant from the
Department of Defense (DAMD17-01-1-083).
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243.
18. Compounds were obtained as mixtures of diastereomers
and were used as such for the biological studies. Charac-
teristic data for some compounds are given below.
Compound 8: 1H NMR (300MHz, CDCl3): d 0.89 (t,
J = 6.0Hz, 3H), 1.26 (br s, 30H), 1.46 (m, 2H), 3.16–3.29
(m, 3H), 3.82 (d, J = 1.5Hz, 2H), 4.20(s, 0.5H), 4.25 (s,
0.5H), 5.83–5.85 (m, 2H), 7.27–7.41 (m, 5H); 13C NMR
(300MHz, CDCl3): d 13.55, 22.13, 26.30, 28.69, 28.80,
28.88, 28.99, 29.03, 29.10, 29.14, 31.37, 32.13, 39.08, 45.88,
63.67, 127.05, 128.58, 128.96, 137.61, 166.30, 171.61; MS
(ESI) m/z 511 [M+Na]. Anal. Calcd for C29H48N2O2S: C,
71.26; H, 9.90; N, 5.73. Found: C, 71.18; H, 10.03; N, 5.79.
Compound 11: 1H NMR (300MHz, CDCl3): d 0.89 (t,
J = 6.0Hz, 3H), 1.26 (br s, 30H), 1.33 (s, 2H), 3.16–3.19
(m, 1H), 3.2–3.29 (m, 2H), 3.80(d, J = 0.9Hz, 2H), 3.83 (s,
3H), 4.16 (s, 0.5H), 4.21 (s, 0.47H), 5.82 (s, 1H), 6.9 (dd,
J = 1.8Hz, 2H), 7.29 (dd, J = 1.5Hz, 2H); 13C NMR
(300MHz, CDCl3): d 13.53, 22.12, 26.31, 28.70, 28.74,
28.79, 28.89, 28.99, 29.03, 29.09, 29.13, 31.36, 32.23, 39.06,
45.74, 54.79, 63.44, 128.64, 129.11, 159.97, 166.41, 171.47;
MS (ESI) m/z 541 [M+Na]. Anal. Calcd for C30H50N2O3S:
C, 69.45; H, 9.71; N, 5.40. Found: C, 69.30; H, 9.86; N,
1
5.43. Compound 12: H NMR (300MHz, CDCl3): d 3.54
(d, J = 15.3Hz, 1H), 3.87 (s, 2H), 4.25 (d, J = 15.3Hz,
1H), 5.88 (s, 1H), 7.10(t, J = 1.8Hz, 1H), 7.36–7.43 (m,
7H), 8.29 (s, 1H); 13C NMR (300MHz, CDCl3): d 32.35,
46.73, 64.40, 117.37, 123.85, 127.29, 128.74, 129.32,
134.59, 136.87, 138.61, 165.14, 172.60; MS (ESI) m/z 403
[M+Na]. Anal. Calcd for C17H14Cl2N2O2S: C, 53.55; H,
3.70; N, 7.35. Found: C, 53.39; H, 3.47; N, 7.36.
Compound 21: 1H NMR (300MHz, CDCl3): d 0.89 (t,
J = 6.0Hz, 3H), 1.26 (br s, 32H), 3.19–3.34 (m, 3H), 3.88–
4.03 (dd, J = 16.5Hz, 2H), 4.66 (s, 0.5H), 4.72 (s, 0.5H),
5.67 (br s, 1H), 5.95 (s, 1H), 7.38 (m, 2H), 7.50–7.53 (m,
3H); 13C NMR (300MHz, CDCl3): d 13.54, 22.12, 26.26,
28.66, 28.79, 28.96, 29.02, 29.09, 29.14, 31.36, 39.30, 44.35,
49.85, 81.32, 125.77, 128.43, 128.91, 130.55, 163.23,
165.30; MS (ESI) m/z 519 [MÀH]. Anal. Calcd for
C29H48N2O4S: C, 66.88; H, 9.29; N, 5.38. Found: C,
66.68; H, 9.27; N, 5.41.
19. Thiazolidinone derivatives were dissolved in dimethyl
sulfoxide (DMSO) and serially diluted in complete growth
medium to desired final concentrations at DMSO concen-
trations of less than 0.5%. Cells were exposed to a wide
range of concentrations (0–100lM) of the particular
compound for 96h in 96 well plates. Cells were fixed with
10% trichloroacetic acid and washed five times with water.
The plates were air dried overnight and fixed cells were
stained with SRB solution. The cellular protein-bound
SRB was measured at 540nm using a plate reader. Cell
numbers at the end of the treatment were measured. IC50
(i.e., concentration that inhibited cell growth by 50% of
untreated control) values were obtained by nonlinear
regression analysis using WinNonlin.