Antitrypanosomal activities and cytotoxicity of some novel imidosubstituted 1,4-naphthoquinone derivatives

Article abstract of DOI:10.1007/s12272-012-0103-1

The antitrypanosomal activities, cytotoxicity, and selectivity indices of eleven imido-substituted 1,4-naphthoquinone derivatives and nifurtimox have been studied. Compared to nifurtimox (IC₅₀ = 10.67 μM), all the imido-naphthoquinone analogs (

Full text of DOI:10.1007/s12272-012-0103-1

Arch Pharm Res Vol 35, No 1, 27-33, 2012
DOI 10.1007/s12272-012-0103-1
Antitrypanosomal Activities and Cytotoxicity of Some Novel Imido-
substituted 1,4-Naphthoquinone Derivatives
Mozna H. Khraiwesh1, Clarence M. Lee1, Yakini Brandy2, Emmanuel S. Akinboye2, Solomon Berhe2, Genelle
Gittens2, Muneer M. Abbas3, Franklin R. Ampy1, Mohammad Ashraf4,and Oladapo Bakare2
2
1Department of Biology, Howard University, Washington DC 20059, USA, Department of Chemistry, Howard Univer-
3
sity, Washington DC 20059, USA, College of Medicine, The National Human Genome Center, Howard University,
4
Washington DC 20059, USA, and Department of Comprehensive Sciences, Howard University, Washington DC 20059,
USA
(Received October 1, 2010/Revised July 26, 2011/Accepted July 26, 2011)
The antitrypanosomal activities, cytotoxicity, and selectivity indices of eleven imido-substi-
tuted 1,4-naphthoquinone derivatives and nifurtimox have been studied. Compared to nifur-
timox (IC50 = 10.67
µ
M), all the imido-naphthoquinone analogs (IMDNQ1
-
IMDNQ11) are
more potent on Trypanosoma cruzi with IC50 values ranging from 0.7
µ
M to 6.1
µ
M ( < 0.05).
p
Studies of the cytotoxic activities of these compounds on a Balb/C 3T3 mouse fibroblast cell
line revealed that four of these compounds, IMDNQ1, IMDNQ2, IMDNQ3, and IMDNQ10 dis-
played selectivity indices of 60.25, 53.97, 31.83, and 275.3, respectively, rendering them signif-
icantly (p < 0.05) more selective in inhibiting the parasite growth than nifurtimox (selectivity
index = 10.86).
Key words: Imido-substituted 1,4-naphthoquinone, Trypanosoma cruzi, Cytotoxicity, Chagas
disease, Epimastigotes, Fibroblasts
pomastigotes) are detectable in the peripheral blood
(Andrade et al., 2004; Schofield and Kabayo, 2008).
Selected by Editors
Both drugs have gastrointestinal and neurological
side effects which may worsen as the patient ages
(Nagel and Nepomnaschy, 1983; Ferreira and Ferreira,
INTRODUCTION
Chagas disease is a tropical disease caused by the 1986; Melo and Ferreira, 1990; Coura and de Castro,
protozoan Trypanosoma cruzi and transmitted by 2002). Consequently, alternative drugs with a more
triatomine bugs. It commonly occurs in poor and rural selective mode of action are being investigated. Sev-
areas of Central and South America. Chagas disease eral classes of drug-like molecules have been studied
is expanding beyond its endemic area as a result of for their antitrypanosomal activity. One of the most
migration from and to the endemic countries (Hanford interesting is the quinone family of compounds. This
et al., 2007; Hotez, 2008; Schofield and Kabayo, 2008). class of compounds incorporates several diverse struc-
American trypanosomiasis therapy mostly depends on tural types including the naphthoquinones, which are
drugs that were developed decades ago, requires long known to possess a number of useful biological activi-
term administration, and is not available to all pati- ties including antiviral, antifungal, antineoplastic,
ents due to its high cost. Two drugs, Nifurtimox and antihypoxic, anti-ischemic, antiplatelet, anti-inflam-
Benznidazole (Fig. 1), are currently used to treat only matory, and antiallergic activities (Kartoflitskaya
the acute phase of the infection where parasites (try- et al., 1997; Huang et al., 1998; Tandon et al., 2004;
Copeland et al., 2007). For instance, the naturally
occurring naphthoquinone, lapachol (Fig. 1), and some
of its derivatives have been found to show trypano-
cidal activity against T. cruzi (Salas et al., 2008). Also,
some naphthofuranquinones synthesized from 2-
Correspondence to: Oladapo Bakare, Department of Chemistry,
Howard University, Washington DC 20059, USA
Tel: 1-202-806-6888, Fax: 1-202-806-5442
E-mail: obakare@howard.edu
27

28
M. H. Khraiwesh et al.
stituted 1,4-naphthoquione (IMDNQ) derivatives (Fig.
2) have been identified as a new class of anti-try-
panosomal agent. This new class of naphthoquinones
has not been previously investigated as an antitry-
panosomal agent. The present research reports on the
in vitro antitrypanosomal activities of eleven imido-
substituted 1,4-naphthoquinone analogs on T. cruzi
epimastigotes.
MATERIALS AND METHODS
Fig. 1. Structures of nifurtimox, benznidazole and the nat-
urally occurring naphthoquinone compound lapachol
Chemical compounds
Eleven imido-substituted 1, 4-naphthoquinones
(Fig. 2) were used in this study.
hydroxy-3-allyl-1,4-naphthoquinone were found to be
active against epimastigote and trypomastigote forms
of T. cruzi (Silva et al., 2006). In a recent study, a
Chemistry
The succinimidyl (IMDNQ1), phthalimidyl (IMDNQ2),
series of naphthoquinones were assessed for their try- and dibutytryl (IMDNQ3) derivatives were synthesiz-
panocidal activity and 2,3-diphenyl-1,4-naphthoquin- ed from 2-amino-3-chloro-1,4-naphthoquinone and the
one (DPNQ) was found to be effective against T. cruzi appropriate acid chloride as previously described
epimastigotes at a low micromolar concentration (LD50 (Bakare et al., 2003; Berhe et al., 2008). The morpholine
= 2.5 µM) by inhibiting T. cruzi lipoamide dehydro- dione analog (IMDNQ4) was synthesized by microwave
genase (TcLipDH) (Ramos et al., 2009). Previously, irradiation of a mixture of 2-amino-3-chloro-1,4-na-
Bakare et al. (2003) and Berhe et al. (2008) reported a phthoquinone and diglycolyl chloride as depicted in
series of imido-substituted 1,4-naphthoquinones as a scheme 1 (Berhe et al., 2008). On the other hand, the
unique class of mitogen activated protein kinase kinase bis-(chloroacetyl)-derivative (IMDNQ11) was prepared
1 (MEK1) inhibitors with a number of them showing by heating 2-amino-3-chloro-1,4-naphthoquinone in
anticancer activities. In pursuit of potent and more excess 2-chloroacetyl chloride at high temperatures as
selective antitrypanosomal agents, several imido-sub- shown in scheme 1 (Bakare et al., 2003; Berhe et al.,
Fig. 2. Structures of imido–substituted 1,4-naphthoquinone derivatives

Antitrypanosomal Studies of Imidonaphthoquinones
29
2008). The diarylimido-substituted naphthoquinones twice to remove traces of chemical compounds. IMEM
IMDNQ5 to IMDNQ10 were synthesized via sodium without phenol containing 10% (v/v) of 3 mg/mL MTT
hydride facilitated bis-acylation of 2-amino-3-chloro- was added to each well. The plates were incubated for
1,4-naphthoquinone or 2-amino-3-bromo-1,4-naphtho- 4 h at 37oC followed by aspiration. The plates were
quinone as shown in scheme 2. All reactions were dried for 1 h in a 37oC incubator. 100
µL of 0.04 N HCl
carried out using laboratory grade materials and solv- in isopropanol was added to each well and incubated
ents. Melting points were determined in open capillary at room temperature (27oC) in the dark for 2 h to
tubes on a Mel-Temp melting point apparatus and are dissolve the formazan crystals. The absorbance was
uncorrected. The IR spectra were recorded on a Perkin measured spectrophotometrically at 570 nm in a plate
Elmer PE 100 spectrometer with an Attenuated Total reader. The concentration that reduces cell viability
Reflectance (ATR) window. The 1H- and 13C-NMR spec- by 50% (IC50) was calculated for each compound. The
tra were obtained on a Bruker Avance 400 MHz spec- toxicity for mammalian cells and the activity against
trometer in deuterated chloroform (CDCl3). Chemical T. cruzi were compared by calculating the selectivity
shifts are in ä units (ppm) with TMS (0.00 ppm) or index (SI), which is the ratio of IC50 for fibroblast cells/
1
CHCl3 (7.26 ppm), as the internal standard for H- IC50 for parasites.
NMR, and CDCl3 (77.00 ppm) for 13C-NMR. Electro-
spray ionization mass spectrometry was recorded on
a Thermo LTQ Orbitrap XL mass spectrometer and
Statistical analysis
All experiments were carried out in triplicate, and
compounds dissolved in acetonitrile containing 0.1% the means and standard errors (S.E.) were determin-
formic acid. The known intermediates were prepared ed. Data were analyzed by one way ANOVA and Tukey’s
according to procedures that are reported in the multiple comparison test using GraphPad PRISM soft-
literature. 2-Amino-3-bromo-1,4-naphthoquinone was ware version 5.00.
prepared by refluxing commercially available 2,3-di-
p < 0.05 was considered significant.
bromo-1,4-naphthoquinone with ammonia/ammonium
hydroxide mixture in ethanol.
General procedure for the synthesis of arylim-
ido-substituted naphthoquinones (IMDNQ5 –
IMDNQ10)
2-Amino-3-chloro-1,4-naphthoquinone (1.47 mmol)
Antitrypanosomal activity assay
T. cruzi epimastigotes (Tulahuen CL98 strain) were or the 3-bromo-analog was dissolved in THF (15 mL).
cultured in liver infusion trypose (LIT) medium sup- NaH (3.08 mmol) was added and the mixture was
plemented with 10% fetal bovine serum (FBS) at 28oC, stirred at room temperature for 15 min. Appropriate
with an inoculum of 1
trations ranging from 0.39-100
×
105 cells/mL. Different concen- acid chloride (3.08 mmol) was added drop wise, and
µM of the chemical the resulting mixture was stirred at room temperature
compounds were added. All assays were carried out in for 24 h. The THF was then evaporated under vacuum
triplicate. Parasites were counted after 48 h using and ice-cooled water added to the residual mixture.
hemocytometers and the concentration that inhibits The resulting aqueous mixture was extracted with
the parasite’s proliferation by 50% (IC50) was calculat- CH2Cl2 (2
ed for each compound. Nifurtimox (one of two com- was washed with water (3
mercial drugs for Chagas disease) was used as a refer- solution (15 mL) and dried over anhydrous MgSO4. The
×
30 mL) and the combined organic phase
×
15 mL) and saturated NaCl
ence drug.
crude product was purified by triturating in hot
ethanol followed by recrystallization in ethyl acetate
and/or column chromatography on silica gel.
Cytotoxicity assay
The cytotoxic effects of the imido-substituted 1, 4-
naphthoquinones on Balb/C 3T3 mouse fibroblasts
N-(3-Bromo-1,4-dioxo-1,4-dihydronaphthalen-2-yl)-
(clone A31) were quantitatively assessed using a 3- 4-fluoro-N-(4-fluorobenzoyl)-benzamide (IMDNQ 5)
(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bro- Yellow solid (66%); m.p. 170-172oC; IR (cm-1) 1719.23,
1
mide (MTT) colorimetric assay. MTT is a yellow tetra- 1670.56, 1596.69, 1505.57; H-NMR (CDCl3) 7.05 (t,
zolium salt that is reduced to purple formazan crys- 4H,
J = 12.0 Hz), 7.77-7.88 (m, 6H), 8.08-8.15 (m, 1H),
tals by metabolically active cells. Cells (2.2
×
104 cells/ 8.21-8.27 (m, 1H); 13C-NMR (CDCl3) 115.57, 115.79,
well) were seeded in a 96-well plate in Improved 127.4, 127.71, 130.18, 130.30, 130.33, 130.85, 131.35,
Minimum Essential Medium (IMEM). Serial dilutions 131.44, 134.46, 134.50, 138.52, 146.90, 165.03, 169.91,
(0.39-100 µ
M) of the compounds were added. After 48 176.96, 177.97; ESI MS m/z 517.9785 ([M+Na]+ calcd
h incubation at 37oC in the presence 5% CO2, the 517.9815).
medium was aspirated and the cells were washed

30
M. H. Khraiwesh et al.
N-(3-Bromo-1,4-dioxo-1,4-dihydronaphthalen-2-yl)- 126.93, 127.60, 127.80, 129.69, 130.54, 130.85, 131.37,
2-chloro-N-(2-chlorobenzoyl)-benzamide (IMDNQ 6) 132.36, 132.52, 132.56, 132.75, 134.14, 134.75, 134.91,
Yellow crystal (34%); m.p. 232-234oC; IR (cm−1) 1728.78, 142.65, 144.43, 177.13, 178.22; ESI MS m/z 505.9741
1
1688.76, 1671.10, 1588.22, 1468.70; H-NMR (CDCl3) ([M+Na]+ calcd 505.9730).
7.13 (d, 2H,
J
= 7.9 Hz), 7.21 (dd, 2H,
J = 1.6, 7.9 Hz),
7.28 (dd, 2H,
J
= 1.3, 7.5 Hz), 7.78-7.86 (m, 2H), 7.94 N-(3-Chloro-1,4-dioxo-1,4-dihydronaphthalen-2-yl)-
(d, 2H, 5.2 Hz), 8.15-8.21 (m, 1H), 8.22-8.28 (m, 2H); 4-fluoro-N-(4-fluorobenzoyl)-benzamide (IMDNQ
13C-NMR (CDCl3) 126.65, 127.66, 128.08, 129.63, 130.49, 9)
130.81, 131.23, 132.25, 134.68, 134.80, 140.78, 145.81, Yellow solid (56%); m.p. 284-286oC; IR (cm-1) 3074.94,
1
167.57, 177.26, 177.81; ESI MS m/z 549.9240 ([M+Na]+ 1719.61, 1689.97, 1672.75, 1591.10; H-NMR (CDCl3)
calcd 549.9224).
7.00-7.06 (m, 1H), 7.75-7.85 (m, 1H), 8.10-8.12 (m, 6H),
8.20-8.22 (m, 4H); 13C-NMR (CDCl3) 115.97, 116.19,
4-Chloro- -(4-chlorobenzoyl)-
N
N-(3-chloro-1,4-dioxo- 116.41, 126.65, 126.96, 127.67, 127.77, 130.53, 130.57,
1,4-dihydronaphthalen-2-yl)-benzamide (IMDNQ 130.58, 131.35, 131.62, 131.71, 132.75, 134.88, 142.42,
7)
144.13, 164.14, 166.68, 170.33, 177.13, 178.63; ESI
Yellow solid (27%); m.p. 212-2130C; IR (cm-1) 1737.38, MS m/z 474.034 ([M+Na]+ calcd 474.032).
1714.75, 1696.91, 1673.62, 1589.20, 1571.10; 1H-NMR
(CDCl3) 7.33-7.36 (m, 4H), 7.68-7.72 (m, 4H), 7.79-7.85 3-Chloro-N-(3-chlorobenzoyl)-N-(3-chloro-1,4-dioxo-
(m, 2H), 8 09-8.11 (m, 1H), 8.20-8.22 (m, 1H); 13C- 1,4-dihydronaphthalen-2-yl)-benzamide (IMDNQ
NMR (CDCl3) 127.72, 127.80, 129.18, 130.34, 130.50, 10)
131.32, 132.52, 134.92, 134.95, 139.67, 142.46, 143.87, Yellow solid (31%); m.p. 258-260oC; IR (cm-1) 3075.36,
170.40, 177.05, 178.59; ESI MS m/z 505.975 ([M+Na]+ 1713.64, 1698.11, 1672.50, 1591.48, 1571.31; 1H-NMR
calcd 505.973).
(CDCl3) 7.27-7.31 (t,
= 1.03, 2.09, 8.07 Hz, 2H), 7.60-7.63 (td,
2-Chloro-N-(2-chlorobenzoyl)-N-(3-chloro-1,4-dioxo- 7.68 Hz, 2H), 7.70-7.71 (t, = 1.82 Hz, 2H), 7.80-7.85
1,4-dihydronaphthalen-2-yl)-benzamide (IMDNQ (m, 2H), 8.11-8.14 (m, 1H), 8.21-8.23 (m, 1H); 13C-
J
= 7.85 Hz, 2H), 7.42-7.45 (ddd,
J
J
= 1.07,
J
8)
NMR (CDCl3) 127.02, 127.93, 128.03, 129.34, 130.21,
Yellow solid (49%); m.p. 217-2180C; IR (cm-1) 1720.19, 130.75, 131.55, 133.29, 135.14, 135.21, 136.06, 143.00,
1681.22, 1618.00, 1588.02; 1H-NMR (CDCl3) 7.10-7.16 143.84, 170.20, 177.25, 178.66; ESI MS m/z 505.9741
(m, 2H), 7.21-7.31 (m, 4H), 7.79-7.89 (m, 4H), 8.17-8.20 ([M+Na]+ calcd 505.9730).
(m, 1H), 8.20-8.26 (m, 1H); 13C-NMR (CDCl3) 126.76,
Scheme 1. Synthesis of imido-substituted naphthoquinone derivatives IMDNQ4 and IMDNQ11
Scheme 2. Synthesis of diaryimido-naphthoquinone derivatives IMDNQ5 to IMDNQ10

Antitrypanosomal Studies of Imidonaphthoquinones
31
IMDNQ11) studied are significantly more potent on T.
RESULTS AND DISCUSSION
cruzi with IC50 values ranging from 0.7
µM to 6.1 µM
The antitrypanocidal activities, cytotoxicity, and
(p < 0.05, Fig. 3). A cytotoxicity study on a Balb/C 3T3
selectivity indices of the eleven imido-substituted 1,4- mouse fibroblast cell line showed that three of the com-
naphthoquinones and nifurtimox are summarized pounds, IMDNQ1, IMDNQ2, IMDNQ10, are consider-
in Table I. Compared to nifurtimox (IC50 = 10.67 µM), ably less cytotoxic than nifurtimox (Fig. 4). As shown
all the imido-naphthoquinone analogs (IMDNQ1 – in Fig. 5, these three analogs (IMDNQ1, IMDNQ2,
IMDNQ10) and the more cytotoxic IMDNQ3 displayed
Table I. Trypanocidal activity, cytotoxicity, and selecti-
selectivity indices of 60.25, 53.97, 275.30, and 31.83,
vity indices of the chemical compounds
respectively, rendering them significantly more selective
in inhibiting the parasite’s growth than nifurtimox
(selectivity index = 10.86).
Antitrypanocidal
activity
S e l e c t i v i t y i n d e x
(Cytotoxicity/
Activity)
Cytotoxicity
IC50 M)
(
µ
IC50 (µM)
In the pursuit of novel selective antitrypanosomal
agents with little or no toxicity to mammalian cells,
eleven imido-substituted 1,4-naphthoquione analogs
were developed as a new class of antitrypanosomal
agent. The study of these cyclic and acyclic imido-sub-
stituted 1,4-naphthoquinone derivatives on T. cruzi
revealed potent antitrypanosomal properties against
T. cruzi by inhibiting their proliferation in vitro. All
the eleven imido-substituted 1,4-naphthoquinone dis-
played more potent antitrypanosomal activities than
the clinically used nifurtimox. Further, comparison of
the antitryponosomal activities with cytotoxicity on a
Balb/C 3T3 mouse fibroblast cell line revealed that
four of these compounds, IMDNQ1, IMDNQ2, IMDNQ3,
and IMDNQ10 show considerably better selectivity
Nifurtimox
IMDNQ1
IMDNQ2
IMDNQ3
IMDNQ4
IMDNQ5
IMDNQ6
IMDNQ7
IMDNQ8
IMDNQ9
IMDNQ10
IMDNQ11
10.67 ± 1.01 114.0 ± 11.03 10.86 ± 10.93
2.77 ± 0.15 165.9 ± 11.24 60.25 ± 12.79
4.83 ± 0.60 253.7 ± 11.87 53.97 ± 15.95
0.70 ± 0.10 21.67 ± 11.45 31.83 ± 13.17
4.93 ± 0.64 35.50 ± 11.76
2.27 ± 0.15 12.83 ± 10.73
1.51 ± 0.01 14.17 ± 11.42
7.43 ± 10.97
5.70 ± 10.06
9.43 ±1 0.94
1.27 ± 0.15 17.83 ± 12.21 14.23 ± 11.62
2.67 ± 0.33 26.50 ± 11.61 10.17 ± 10.97
4.07 ± 0.23 21.83 ± 11.88
2.23 ± 0.15 610.9 ± 10.27 275.3 ± 13.73
6.10 ± 0.38 19.67 ± 13.71 3.20 ± 10.44
5.43 ±1 0.69
Each value represents the mean ± S.E. of three experiments.
Fig. 3. Trypanocidal effects of the imido-substituted 1, 4-
naphthoquinones on T. cruzi. Results are expressed as the
Fig. 4. Cytotoxicity of the imido-substituted 1, 4-na-phth-
oquinones on Balb/C 3T3 mouse fibroblasts. Results are
means ± S.E. of three experiments. *
p
< 0.05, **
p
< 0.01,
expressed as the means ± S.E. of three experiments. ***
p <
*** < 0.001 compared with Nifurtimox
p
0.0001 compared with Nifurtimox

32
M. H. Khraiwesh et al.
a diaryl imido analog with meta-chloro-substituent on
each of the imide aryl groups and thus significantly
differs from the two cyclic imido-derivatives IMDNQ1
and IMDNQ2. The other cyclic imido-analog IMDNQ4
is also potent against T. cruzi with an IC50 value of
4.93
µ
M, but is more cytotoxic in the mouse fibroblast
cell (IC50 = 35.50
µM). This greater cytotoxicity could
be due to the presence of the oxygen atom in the cyclic
imide moiety which could facilitate further hydrogen-
bonding to molecular targets in the mouse fibroblast
cell, rendering it more susceptible to the cytotoxic
activity of compound IMDNQ4. Comparison of all the
diaryl imido derivatives (IMDNQ5 to IMDNQ10) showed
that, with the exception of compound IMDNQ10, all the
other diarylimido compounds (IMDNQ5 to IMDNQ9)
are reasonably cytotoxic to the mouse fibroblast cells
and consequently show poorer selectivity indices (Table
I, Fig. 5). The non-cytotoxic diarylimido naphthoquin-
one IMDNQ10 possess a chloro group in the meta-
position of each aryl group in the diarylimido-moiety,
while the other analogs possess a chloro or fluoro
group in either a para- or ortho-position. The reason
for the observed difference in cytotoxicity between a
chloro group in a meta- (IMDNQ10), para- (IMDNQ7)
or ortho- (IMDNQ8) position in these compounds is
not immediately apparent; however, it could be sug-
Fig. 5. Selectivity indices of the imido-substituted 1, 4-na-
phthoquinones. Results are expressed as the means ± S.E. of
three experiments. **p < 0.01, ***p < 0.0001 compared with
Nifurtimox
gested that the presence of the chloro group in a meta
-
than nifurtimox as seen from the selectivity indices position could have distorted the interaction of com-
values (Table I and Fig. 5). Of the compounds studied, pound IMDNQ10 with a potential binding site neces-
the structure-activity relationship revealed that dibu- sary for cytotoxicity in the mouse fibroblast cells. The
tyrylamino derivative (IMDNQ3) is the most potent replacement of the 3-chloro group on the 1,4-naphtho-
with an IC50 value of 0.7
this compound is among the most cytotoxic to the affect the activities and selectivity indices of these com-
mouse fibroblast cells (IC50 = 21.67 M) in this study, pounds, as can be seen in the activity and selectivity
µM against T. cruzi. However, quinone ring with a 3-bromo group did not drastically
µ
and as shown in previous reports of the cytotoxicity of of compound IMDNQ6 versus IMDNQ8 and also com-
compound IMDNQ3 on different human cancer cell pound IMDNQ5 versus IMDNQ9 (Table I, Fig. 2).
lines (Bakare et al., 2003; Berhe et al., 2008). The potent There appears to be a slight increase in antitrypano-
activity in the antitrypanosomal study nevertheless somal activity when the 3-chloro group is substituted
provided IMDNQ3 with a good selectivity index of with a 3-bromo group as seen in compounds IMDNQ9
31.83. On the other hand, two of the cyclic imido-na- (IC50 = 4.07
phthoquinone analogs, IMDNQ1 and IMDNQ2, while can also be seen when the activity of compound
showing potent antitrypanosomal activities (IC50 IMDNQ8 (IC50 = 2.67 M) is compared with that of
2.77 M for IMDNQ1 and 4.89 M for IMDNQ2), are IMDNQ6 (IC50 = 1.51 M). Similarly, there is a cor-
relatively non-toxic to the mouse fibroblast cell (IC50 responding slight increase in cytotoxicity on the Balb/
values of 165.9 M for IMDNQ1 and 253.7 M for C 3T3 mouse fibroblast cell line when the 3-chloro
IMDNQ2). This selectivity means that the two com- group is substituted with a 3-bromo group, as again
pounds are of greater value and interest than the most can be seen in compound IMDNQ9 (IC50 = 21.83 M) vs
potent antitrypanosomal compound, IMDNQ3. Of great- IMDNQ5 (IC50 = 12.83 M) and in compound IMDNQ8
er interest is the selectivity of IMDNQ10 (selectivity (IC50 = 26.50 M) vs IMDNQ6 (IC50 = 14.17 M). Com-
index of 275.3), which showed potent antitrypanoso- parison of compounds IMDNQ7 and IMDNQ9 reveal-
mal activity with an IC50 value of 2.23 M against T. ed that substituting the para-chloro group in the
cruzi, while being non-cytotoxic to the mouse fibroblast diarylimido moiety of IMDNQ7 with the smaller and
cell (IC50 value of 610.9 M). Compound IMDNQ10 is more electronegative fluoro group in IMDNQ9 slightly
µM) and IMDNQ5 (IC50 = 2.27 µM). This
=
µ
µ
µ
µ
µ
µ
µ
µ
µ
µ
µ
µ

Antitrypanosomal Studies of Imidonaphthoquinones
33
27, 1537-1546 (2007).
reduced both the antitrypanosomal and cytotoxic acti-
vities (Table I). The bis-chloroacetylamino derivative
IMDNQ11 is the least potent antitrypanosomal imido
naphthoquinone in this study with an IC50 value of
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5,8-dimethoxy-1,4-naphthoquinone and related compounds.
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6.10
µM. This compound is also the least selective
analog with a selectivity index of 3.20 (Table I, Fig. 5).
All the imido-substituted naphthoquinones studied
are more potent antitrypanosomal agents than the cli-
nically used nifurtimox; however, only four compounds,
IMDNQ1, IMDNQ2, IMDNQ3 and IMDNQ10 with
selectivity indices of 60.25, 53.97, 31.83, and 275.3, re-
spectively, are significantly more selective than nifur-
timox (selectivity index of 10.86). Further, three of
these compounds are relatively non-cytotoxic to the
Balb/C 3T3 mouse fibroblast cell line with IC50 values
of significantly more than 100 µM. These compounds
thus represent a novel class of selective antitrypano-
somal agents for further drug development. We are
currently studying the mechanism of antitrypano-
somal activity of this imidonaphthoquinone class of
compounds.
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ACKNOWLEDGEMENTS
This work was supported in part by the WBHR-
LSAMP Program, NSF#0401723 and by an NIH grant
from the Research Centers in Minority Institutions
(RCMI) Program of the Division of Research Infra-
structure, National Center for Research Resources
(RCMI-NIH 2G12RR003048).
Ramos, E. I., Garza, K. M., Krauth-Siegel, R. L., Bader, J.,
Martinez, L. E., and Maldonado, R. A., 2,3-diphenyl-1,4-
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