Cytotoxicity and reversal of multidrug resistance by tryptanthrin-derived indoloquinazolines

Article abstract of DOI:10.1038/aps.2009.198

Aim: To evaluate the effects and elucidate the mechanisms of a series of indoloquinazolines as novel anticancer agents. Methods: Condensation of the substituted isatoic anhydride with the substituted isatin was performed to prepare compounds 1-4, followed by adding malononitrile to prepare compounds 5-7. Cytotoxicity was measured by MTT assays. Apoptosis induction was evaluated using DNA fragmentation, cell cycle assay, caspase 3/7 activity and Western blot. Results: Compounds 3, 4, and 5 display cytotoxicity against MCF-7, HeLa, SKOV3, and A498 cancer cells. DNA ladders appear in cells treated with compounds 3, 4, and 5. Within those, compound 4 exhibits the greatest activity in regards to sub-G 1 accumulations in the cell cycle and the activation of caspase-3/7. Furthermore, Fas and Fas ligand levels are elevated by compound 4, implying that the apoptosis is in part mediated through the signals. On the other hand, compounds 1 and 7 display chemosensitizing activity since cytotoxicity of doxorubicine and etoposide is enhanced in combination with compound 1 and 7, respectively, in MCF-7/adr (doxorubicin-resistant) and MCF-7/vp (etoposide-resistant). Conclusion: The cytotoxicity of indoloquinazolines is structure-dependent rather than cell type-dependent due to the similar degree of cytotoxicity induced by the individual compounds in all four cell lines. Further modification of the tryptanthrin skeleton is important to develop novel anticancer agents bearing either cytotoxicity against MCF-7 cells or drug resistance reversal in MCF-7/adr and MCF-7/vp.

Full text of DOI:10.1038/aps.2009.198

Acta Pharmacologica Sinica (2010) 31: 259–264
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Original Article
Cytotoxicity and reversal of multidrug resistance
by tryptanthrin-derived indoloquinazolines
Sung-tsai YU1, Ji-wang CHERN1, Tzer-ming CHEN3, Yi-fan CHIU1, Hui-ting CHEN1, Yen-hui CHEN1,2,
*
1Graduate Institute of Pharmaceutical Sciences and 2Graduate Institute of Clinical Pharmacy, Nation Taiwan University, No 1 Sec 1,
Jen-Ai Road, Taipei 10051, Taiwan, China; 3Department of Obstetrics and Gynecology, Nation Taiwan University Hospital, No 7 Chung
San South Road, Taipei 10051, Taiwan, China
Aim: To evaluate the effects and elucidate the mechanisms of a series of indoloquinazolines as novel anticancer agents.
Methods: Condensation of the substituted isatoic anhydride with the substituted isatin was performed to prepare compounds 1–4, fol-
lowed by adding malononitrile to prepare compounds 5–7. Cytotoxicity was measured by MTT assays. Apoptosis induction was evalu-
ated using DNA fragmentation, cell cycle assay, caspase 3/7 activity and Western blot.
Results: Compounds 3, 4, and 5 display cytotoxicity against MCF-7, HeLa, SKOV3, and A498 cancer cells. DNA ladders appear in cells
treated with compounds 3, 4, and 5. Within those, compound 4 exhibits the greatest activity in regards to sub-G1 accumulations in the
cell cycle and the activation of caspase-3/7. Furthermore, Fas and Fas ligand levels are elevated by compound 4, implying that the
apoptosis is in part mediated through the signals. On the other hand, compounds 1 and 7 display chemosensitizing activity since cyto-
toxicity of doxorubicine and etoposide is enhanced in combination with compound 1 and 7, respectively, in MCF-7/adr (doxorubicin-
resistant) and MCF-7/vp (etoposide-resistant).
Conclusion: The cytotoxicity of indoloquinazolines is structure-dependent rather than cell type-dependent due to the similar degree of
cytotoxicity induced by the individual compounds in all four cell lines. Further modification of the tryptanthrin skeleton is important to
develop novel anticancer agents bearing either cytotoxicity against MCF-7 cells or drug resistance reversal in MCF-7/adr and MCF-7/
vp.
Keywords: apoptosis, cytotoxicity, drug resistance, MCF-7, tryptanthrin
Acta Pharmacologica Sinica (2010) 31: 259–264; doi: 10.1038/aps.2009.198
cate a number of central mediators of apoptosis[2]. The cell
Introduction
In the last decade, basic cancer research has produced remark- surface molecule Fas (APO-1/CD95) transduces the intracellu-
able advances in our understanding of cancer biology and lar apoptotic death signaling upon stimulation by Fas ligand[3].
cancer genetics. Among the most important advances is that Fas plays a dominant role in various physiological cell death
apoptosis and the genes that regulate it have a profound effect and disease states, leading to the caspase 8-dependent activa-
on the malignant phenotype. For example, it is now clear that tion of effector caspases, such as caspase 3[4, 5]. Among cas-
some oncogenic mutations interrupt apoptosis, leading to pases, an essential role of caspase 3 in Fas-mediated apoptosis
tumor initiation, progression or metastasis. Finally, it is now has been reported[6]. Caspase 3 exists in the cytoplasm of
well documented that most cytotoxic anticancer agents induce intact cells as a proenzyme form and is activated by prote-
apoptosis, raisingthe possibility in apoptotic programs.
olysis induced by the stimulation of Fas[7]. Caspase 3 is the
Apoptosis is a form of programmed cell death that plays a essential factor in Fas-initiated death signaling, since it directly
fundamental role in many normal biological processes as well induces the activation of DNA fragmentation factor[8].
as several disease states. Apoptosis can be induced by various
Multidrug resistance (MDR) is recognized as the most com-
stimuli that all produce the same end result: systematic and mon cause of failure of cancer chemotherapy. MDR is an
deliberate cell death[1]. Recent developments strongly impli- overall phenomenon resulting from cross-resistance to a vari-
ety of structurally and functionally unrelated natural products
such as anthracyclines, Vinca alkaloids, epipodophyllotoxins
and taxanes. Chemotherapeutic agents such as doxorubicin
can select for mutations leading to increased expression of
*
To whom correspondence should be addressed.
E-mail tcyhchen@ntu.edu.tw
Received 2009-06-04 Accepted 2009-12-22

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Scheme 1: Preparation of tryptanthrins. (Compounds 1–4)
P-glycoprotein and the phenotype of MDR in tissue culture
models[9]. Development of adjuvant agents to overcome mul-
tidrug resistance (MDR) becomes a new trend in cancer che-
motherapy.
Indigo plants have been a familiar and important source of
dye for Asians since ancient times. Honda et al first isolated
an indoloquinazoline, tryptanthrin, from Indigo plant Strobi-
lanthes cusia[10]. Tryptanthrin with chemical name indolo[2,1-b]
quinazolin-6,12-dione was reported to carry anti-microbial
activity against a variety of microorganisms including bacte-
ria, yeasts, dermatophytes and phytopathogens[10, 11]. Recently,
tryptanthrin has been paid much attention as an aryl hydro-
carbon receptor agonist[12], anti-inflammatory agent[13], inducer
of caspase-3/Fas mediated apoptosis[14], cytostatic agent[15]
and drug resistance reversal agent[16]. In this study, a series
of tryptanthrin derivatives were synthesized and designated
as compounds 1–7. Anticancer and chemosensitizing activi-
ties were examined in MCF-7 cells. Results showed that
compounds 3, 4, and 5 exhibited cytotoxicity at micromolar
or lower concentrations. DNA fragmentation and cell cycle
progression were determined by treating with compounds 3,
4, and 5. Changes in Fas/Fas ligand and casepase-3/7 activi-
ties reveal the anticancer mechanisms involving Fas-mediated
apoptosis pathway. On the other hand, compounds 1 and 7
which are not (or mild) cytotoxic are capable of sensitizing
drug-resistant MCF-7 cells.
Scheme 2: Preparation of 6,12-dihydro-6-(dicyanomethylene)-12-oxoindolo
[2,1-b] quinazoline derivatives. (Compounds 5–7)
Figure 1. The synthetic strategy depicted in Schemes 1 and 2 to synthe-
size the tryptanthrin derivatives.
bad, CA) at 37 °C in 5% CO2. MCF-7/adr and MCF-7/vp cells
were grown in the presence of 0.1 μmol/L of doxorubicin or
etoposide that was removed from the medium 1 week before
each assay.
Cell survivability assay
To detect growth inhibition by the series of compounds, cells
were seeded onto 96-well plates at a density of 5×103/well
before compound treatment. Cytotoxicity of the series of
compounds in a variety of cell lines was determined using the
MTT assay after incubation of cells with these compounds at
various concentrations for 3 d. IC50 (the concentration of 50%
inhibition of cell growth) was determined by interpolation of
the dose-response curves.
Materials and methods
Chemicals
Synthesis of 6,12-dihydro-6,12-dioxoindolo-[2,1-b]qinazoline
(tryptanthrin) and its analogues were as described with modi-
fications[15, 17]. As outlined in Scheme 1, compounds 1–4 were
prepared by condensation of the substituted isatoic anhydride
with the substituted isatin in N-methylmorpholine, N,N’-
diisopropyl carbodiimide and pyridine. The solution of N,N’-
diisopropyl carbodiimide in anhydrous pyridine was added
with N-methylmorpholine to increase solubility. The resulting
solution was added with the substituted isatoic anhydride and
substituted isatin, then subjected to reflux at 120–130 °C for
6 h. Compounds 5–7 containing dicyanomethylene substitu-
ent were made as showed in Scheme 2 by treating substituted
tryptanthrin with malononitrile in DMSO or NaH/THF,
and then stirring for 5 h. The structures of tryptanthrin and
DNA fragmentation
MCF-7/wt cells were plated at 4×105 cells/well onto each of
6-well plates. After overnight growth, cells were treated with
tryptanthrins for various time periods. DNA was extracted by
a Wizard® Genomic DNA Purification Kit (Promega, Madison,
WI) and then dissolved in TE buffer. The purified DNA was
quantified and equally loaded onto a 2% agarose gel for elec-
trophoresis. The resulting bands were stained with ethidium
bromide and visualized under UV light.
1
its analogues were determined by H and 13C NMR spectra
Cell cycle analysis
Cells were treated with various concentrations of tryptanthrin
derivatives for 1 d, and then harvested by 0.25% trypsin and
washed with PBS. Cells (2×105) were fixed in 70% ice-cold
EtOH/PBS for 20 min on ice, and then washed with PBS and
incubated in PI solution (69 mmol/L PI, 388 mmol/L sodium
citrate, 100 μg/mL RNase A). Then the cells were analyzed
immediately using a FACS Caliber (Beckton Dickinson, USA).
(Bruker AX-400, AX-300 spectrometer, Billerica, MA). The
substituents of the tryptanthrin skeleton were systematically
modified as in Schemes 1 and 2 (Figure 1), and tabulated in
Table 1.
Cell lines and cell culture
MCF-7/wt, MCF-7/adr and MCF-7/vp cell lines were pro-
vided by Dr Chih-hsin YANG (National Taiwan University
Hospital, Taiwan, China). HeLa, A498, and SKOV3 cell lines
were purchased from ATCC (http://www.atcc.org). Cells
were maintained in DMEM medium with 10% fetal calf serum
and 100 ng/mL penicillin and streptomycin (Invitrogen, Carls-
Caspase 3/7 assay
Caspase 3/7 activity was measured using the Caspase-glo
3/7 assay kit (Promega, Madison, WI). After treatment with
tryptanthrins at different time points, the cells were incubated
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Table 1. Structures and anticancer activities of tryptanthrin derivatives.
with Caspase-glo reagent for 1 h in the dark, and the lumines-
cence was measured using a luminometer (Berthold Technolo-
gies, Bad Wildbad, Germany). Equal amount of cells were
analyzed by counting a parallel set of cells and determining
the total cell number for each sample.
Western blot analysis
Com-
Growth inhibition (%)a
The MCF-7 cells were treated with 10-6 mol/L tryptanthrins for
various time periods. At the end of each treatment, the cells
were trypsinized from the subconfluent monolayers, and their
proteins were extracted using CelLyticTM M Cell Lysis Reagent
(Sigma-Aldrich, St Louis, MO). The protein concentration of
each sample was determined using a Bio-rad protein assay kit
(Bio-Rad Laboratories, Hercules, CA). Total cellular proteins
(80 μg/lane) were electrophoresized on 10% SDS-polyacryl-
amide gels and transferred to a PVDF membrane (GE Health-
care, Little Chalfont, Buckinghamshire, UK). Proteins were
labeled with primary antibody: anti-Fas B-10 and anti-Fas
Ligand (Santa Cruz, Santa Cruz, CA). Immunoreactive bands
were detected by anti-mouse HRP or anti-rabbit peroxidase-
conjugated secondary antibody (Chemicon, Temecula, CA).
pound R1
R2
H
X
R3
R4
Y
MCF-7 HeLa A498 SKOV3
1
H
C
C
C
N
C
C
C
H
H
I
H
H
H
H
H
H
H
H
H
H
H
O
O
O
O
Ab
Ab
Ab
26
0
24
12
48
46
49
3
17
-8
68
78
45
-5
8
6
47
50
46
8
2
OMe OMe
3
4
5
6
7
H
H
H
H
H
H
40
77
41
17
5
OMe OMe
Cl
H
10
95
10
84
17
86
Doxo-
rubicin
95
a
Growth inhibition was calculated as the ratio of cell viability of the
treated cells over the untreated cells. Data are representative of
three independent experiments. The compounds tested were at the
Proteins were visualized via enhanced chemiluminescence concentration of 1 μmol/L.
b A=
(ECL detection kit, GE Healthcare, Buckinghamshire, UK).
Statistical analysis
Data are presented as mean±SD for the indicated number of
separate experiments. Comparisons between groups were
analyzed via Student’s t-tests. Probability values of P<0.05 are
considered statistically significant.
Table 2. The IC50 of compounds 3–5 (μmol/L).
Cell line
Doxorubicin
3
4
5
MCF-7
HeLa
SKOV3
A498
0.14±0.03
0.59±0.02
0.33±0.03
0.58±0.04
1.50±0.28
1.86±0.21
1.20±0.29
0.65±0.04
0.39±0.31
2.34±0.36
2.00±0.39
0.31±0.02
1.40±0.12
1.26±0.17
8.51±0.23
1.48±0.13
Results
Effect of tryptanthrin derivatives on inhibition of proliferation in
several cancer cell lines
Tryptanthrin-derived indoloquinazolines were synthesized by
condensation. Compounds 1–4 were prepared via Scheme 1
and compounds 5–7 containing dicyanomethylene substituent
were made via Scheme 2. Growth inhibition of the series of
compounds at 1 μmol/L was measured in MCF-7, HeLa, A498,
and SKOV3 cells (Table 1). Compounds 3–5 demonstrate
higher than 40% inhibition of proliferation in four cell lines.
The IC50 of compounds 3–5 is lower than 1×10-6 mol/L in four
cell lines among which A498 and MCF-7 are more sensitive to
the compounds. Compound 4 is the most potent tryptanthrin
derivative presenting cytotoxic activity. The IC50 is 3.10×10-7
mol/L in A498 and 3.9×10-7 mol/L in MCF-7, respectively
(Table 2).
Cell viability was determined using the MTT assay. Data are presented as
mean±SD of triplicate determinations.
(Figure 2A). A delayed appearance (up to 40–44 h) of the
DNA ladders was shown in cells treated compounds 3 or 5.
Cell cycle analysis of MCF-7 cells was performed after 24 h
of incubation with compounds 3, 4, or 5 at 10-6 mol/L. As
compared to the untreated cells, compounds 3 and 5 did not
induce considerable cell cycle arrest, while an important sub-
G1 peak appeared in cells treated with compound 4 at 10-6
mol/L for 24 h (Figure 2B).
Activity of caspase-3/7 which is essential for apoptosis was
determined in MCF-7 cells treated with compounds 3, 4, and
5. After exposure to compound 4 at 10-6 mol/L for 36 h, cas-
pase-3/7 activity was elevated about five folds, compared to
the control (Figure 2C). Only a slight increase in caspase-3/7
activity was observed in cells with compound 3 or 5.
Apoptotic biomarkers in MCF-7 cells treated with compounds
3–5
DNA fragmentation is a characteristic feature of apoptosis.
Fragmented DNA, subjected to electrophoresis on an agarose
gel, is in a manner of ladders, suggesting the formation of
nucleosomes in apoptosis progress. When MCF-7 cells were
treated with compound 4 at 10-6 mol/L for 6 h, DNA ladders
appeared. The intensity of the ladders significantly increased
after the cells were longer exposed to compound 4 up to 9 h
Changes in Fas and Fas ligand levels in MCF-7 cells treated with
compound 4
To verify if compound 4-induced apoptosis was mediated
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4. Immunoblots against anti-Fas B-10 and anti-Fas Ligand
showed that Fas level was raised within 2 h after cells treated
with compound 4 and followed by an increase in Fas ligand
level in cells after 4 h exposure to compound 4. The promptly
elevated Fas did not sustain since a drop of Fas levels was
detected in cells with 4–8 h exposure to compound 4 (Figure
3).
Figure 3. Fas and Fas ligand levels increased by compound 4. MCF-7
cells were treated with 10-6 mol/L 4 for different periods of time. Proteins
from whole-cell extracts were electrophoresed and Western blots were
performed as described in Methods. α-tubulin was used as the loading
controls. Data are representative of three independent experiments.
Effect of tryptanthrin and its derivatives in drug-resistant MCF-7
cells
Instead of compouds 3–5 bearing cytotoxicity through activa-
tion of apoptosis process, the rest tryptanthrin derivatives,
compounds 1, 2, 6, and 7, were not as potent as to inhibit cell
proliferation. The IC50 of compound 1 was 8.23 μmol/L and
compounds 2, 6, and 7 existed greater than 10 μmol/L of IC50
in MCF-7 cells, compared to doxorubicin of which the IC50 was
0.14 μmol/L in MCF-7 cells. In terms of non-cytotoxic agents,
compounds 1, 2, 6, and 7 did not or slightly show growth inhi-
bition in neither MCF-7 nor MCF-7/adr cells (Table 3). How-
ever, in combination with doxorubicin, compounds 1 and 7 at
10-6 mol/L enhanced growth inhibition activity of doxorubicin
in MCF-7/adr cells from 19% to 63% and 53%, respectively.
Table 3. MTT assays of tryptanthrin derivatives in MCF-7 and MCF-7/adr
cells.
Figure 2. Apoptotic biomarkers induced by compounds 3, 4, and 5 in
MCF-7 cells. (A) DNA fragmentation in MCF-7 cells treated with com-
pounds 3, 4, and 5. DNA extracts from the cells treated with the com-
pounds for various time periods as indicated were electrophoresed on
a 2% agarose gel and stained with ethidium bromide. (B) The cell cycle
analysis of MCF-7 cells with compounds 3, 4, and 5. DNA contents of
MCF-7 cells were analyzed by flow cytometry. (C) Caspase 3/7 activity
assays. MCF-7 cells were exposed to 10-6 mol/L compound 3 (●), 4 (○),
or 5 (▼) for 0–36 h and subjected to casepase 3/7 assay. Assays were
performed in triplicates for each treatment.
Growth inhibition
IC50 (μmol/L)
Compounds
Compounds+Dox
Com-
pound
MCF-7
MCF-7/ MCF-7 MCF-7/ MCF-7 MCF-7/
adr
adr
adr
1
2
6
7
Dox
8.23±0.37
>100
5.63±0.53 26%
>100
>10
18%
0%
1%
95%
99%
97%
92%
63%
25%
12%
53%
0%
17%
5%
>10
>100
>100
0%
0.14±0.03
9.13±0.51
95%
19%
10-6 mol/L tryptanthrin derivatives and 10-6 mol/L doxorubicin were
used for growth inhibition assays. Data are from three independent
experiments.
through Fas/Fas ligand pathway, Fas and Fas ligand pro-
teins were determined in MCF-7 cells treated with compound
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Etoposide which is also a cytotoxic agent is capable of enhances the cytotoxicity, except the dimethoxy substitution in
inducing drug resistance in MCF-7 cells, named MCF-7/vp. A ring. Nitrogen-containing A ring seems to be important to
MCF-7/vp cells were still viable when the cells were treated increase cytotoxicity. The cytotoxicity is structure-dependent
with compound 1, 7, or etoposide, while the cells turned out rather than cell line-dependent because a compound presents
to be sensitive to the combination of either compound 1 plus similar degree of cytotoxicity in all four cell lines. Tryptan-
etoposide or compound 7 plus etoposide at concentrations thrin derivatives exhibited double-stranded DNA binding
of 1 μmol/L of each (Figure 4). Compound 7 raised a higher activity[17], which may in part account for structure-dependent
chemosensitizing activity than compound 1 in MCF-7/vp cytotoxicity.
cells. On the contrary, MCF-7/adr cells are more susceptible
to compound 1 for enhancing cytotoxicity of doxorubicin.
Although the tryptanthrin derivatives are not as potent as
doxorubicin to kill the cancer cells, compounds 3–5 exhibit
growth inhibition (40%–77%) activity in MCF-7, HeLa, A498,
and SKOV3 cells. The apoptotic biomarkers, including DNA
fragmentation, elevated sub-G1 accumulation and an increase
in caspase 3/7 activity, appear in the cells treated with com-
pounds 3–5 with various intensities. Among them, compound
4 is of most importance. Mechanisms other than apoptosis
may be involved in cell growth inhibition by compounds 3
and 5. The MCF-7 cell line which has been described to be
Fas-sensitive[18] undergoes apoptosis through Fas/Fas ligand
activation. The Fas/Fas ligand system is a key signaling trans-
duction pathway of apoptosis in cells and tissues. Engage-
ment of Fas by a Fas-ligand lead to the formation of a protein
complex known as death-inducing signaling complex and
permit acute execution of apoptosis by caspase-8 activation[19]
.
Figure 4. Effect of compounds 1 and 7 on sensitizing drug-resistant cells
to doxorubicin or etoposide. Cells were treated with 10-6 mol/L doxoru-
bicin (D), 10-6 mol/L etoposide (E), 10-5 mol/L verapamil (V), 10-6 mol/L
compound 1 (1) or 7 (7), either alone or in combination as indicated for 5 d.
The percentage of cell viability of MCF-7 (□), MCF-7/adr (■), and MCF-7/vp
(■) was determined by the MTT assay. Data are presented as mean±SD
of triplicate determinations.
Reimer et al[20] reported that the selection process leading to
highly aggressive breast tumor variants might be enhanced
by Fas ligand-mediated tumor fratricide, eventually a possible
target for novel therapeutic strategies. Our results show the
consistent elevation of Fas ligand levels by treating compound
4 in different time periods (4 and 8 h), in spite of the various
levels of Fas with time. Elevation of Fas ligand levels may be
important to engage Fas and activate the Fas/Fas ligand-medi-
Similar to compounds 1 and 7, a known MDR revers- ated apoptosis afterwards. Results may suggest that com-
ing agent verapamil at 10-5 mol/L did not exist cytotoxicity pound 4 resents cytotoxicity in part through Fas/Fas ligand
though, it enhanced cytotoxicity of doxorubincin and etopo- pathway. It is possible of crosstalk between extrinsic pathway
side in MCF-7/adr and MCF-7/vp, respectively, with various and intrinsic pathway through mitochondria. It would be
degrees.
worth examining if tryptanthrin derivatives induce mitochon-
dria-related signals such as cytochrome c, caspase 9, etc. To
differentiate activity of caspase 8 from caspase 9 enables us to
Disscussion
Tryptanthrin and its derivatives have been reported to exhibit confirm which pathway induced by compound 4. It would be
anticancer effects[15, 17]. In this study, we synthesized a series of interesting to check this issue in the future experiments.
tryptanthrin-derived indoloquinazolines, designated as com-
Resistance to chemotherapy has been remaining a major
pounds 1–7 and screened for anticancer activity. Compouds cause of treatment failure in cancer patients. Development of
1–4 were prepared by condensation as shown in Scheme 1 and adjuvant agents to circumvent MDR becomes a new trend in
compounds 5–7 containing dicyanomethylene substituents cancer chemotherapy. Many attempts, such as inhibition of
were made via Scheme 2. Among those, either compound 3 MDR-related genes, to overcome MDR have been proposed[21]
.
bearing an iodine substituent at R3 or compound 4 with nitro- Inhibition of MDR1 gene function, either by blocking P-gp
gen containing A ring demonstrated effective growth inhibi- function or inhibiting MDR1 gene expression, has been one
tion activity. The oxygen or dicyanomethylene substitution at of the most extensive studies[22, 23]. In this report, compounds
Y was indifferent to the cytotoxicity in four cell lines. In fact, 1 and 7 in combination with cytotoxic agents such as doxo-
the malononitrile derivatives, including compounds 5–7 with rubicin and etoposide enhance cytotoxicity of the cytotoxic
dicyanomethylene substitution at Y, exhibited various degree agents against drug-resistant MCF-7 cells. It suggests that
of cytotoxicity. Methoxy group at R1 and R2 or chlorine at compounds 1 and 7 can sensitize drug-resistant cells to the
R1 did not influence the growth inhibition activity. Accord- cytotoxic agents, which may contribute to reverse multidrug
ing to structure-activity relationship analysis, modification resistance. It is still unclear the mechanisms involved in MDR
of tryptanthrin skeleton with substituents in A ring or D ring reversal. As compound 1 largely sensitizes MCF-7/adr rather
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MDR1 gene or its function. Nevertheless, compound 7 sensi-
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Acknowledgements
This work was supported by National Science Council grant
NSC 89-2320-B-002-232. We thank Dr Chih-hsin YANG for
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Author contribution
Yen-hui CHEN designed and corresponded to the study.
Ji-wang CHERN and Hui-ting CHEN synthesized a series
of indoloquinazoline compounds. Sung-tsai YU and Yi-fan
CHIU performed the experiments. Sung-tsai YU, Tzer-ming
CHEN, and Yen-hui CHEN analyzed data and prepared the
manuscript.
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Acta Pharmacologica Sinica