Exploration of quinolone and quinoline derivatives as potential anticancer agents

Article abstract of DOI:10.1007/s40199-019-00290-3

Background: Among the different types of cancers, breast cancer, bone cancer and cervical cancer are the most common gender specific cancer types that are affecting the women worldwide. Currently, many enzymatic and cellular pathways are known as drug targets for the treatment of cancer. Even though many improvements have been made in the therapy of various types of cancer, but the major disadvantage of available anti-cancer drugs is their non-selective behavior towards cancer cells as well as normal cells. Objectives: In the light of this fact, the searching of new compounds with selective behavior only towards cancer cells is critically important. Previously, we have identified several series of compounds as the potential inhibitors of these families. Methods: Herein, we investigate quinolones and quinolines for their anti-cancer activity against breast cancer cells (MCF–7), bone marrow cancer cells (K–562) and cervical cancer cells (HeLa) by MTT assay. The most effective derivatives were further subjected to flow cytometry analysis followed by fluorescence microscopic analysis by using 4′,6-diamidine-2′-phenylindole (DAPI) and propidium staining (PI) staining. Results: All the tested compounds were found selective only towards cancer cells. The identified compounds also induced either G2 or S-phase cell cycle arrest within the respective cancer cell line, chromatin condensation and the nuclear fragmentation, as well as maximum interaction with DNA. Conclusions: These results provide evidence that the characteristic chemical features of attached groups are the key factors for their anticancer effects and play a useful role in revealing the mechanisms of action in relation to the known compounds in future research programs. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s40199-019-00290-3

DARU Journal of Pharmaceutical Sciences
https://doi.org/10.1007/s40199-019-00290-3
RESEARCH ARTICLE
Exploration of quinolone and quinoline derivatives as potential
anticancer agents
Jamshed Iqbal1 & Syeda Abida Ejaz1 & Imtiaz Khan2 & Elina Ausekle3 & Mariia Miliutina3 & Peter Langer3,4
Received: 18 February 2019 /Accepted: 10 July 2019
#
Springer Nature Switzerland AG 2019
Abstract
Background Among the different types of cancers, breast cancer, bone cancer and cervical cancer are the most common gender
specific cancer types that are affecting the women worldwide. Currently, many enzymatic and cellular pathways are known as drug
targets for the treatment of cancer. Even though many improvements have been made in the therapy of various types of cancer, but
the major disadvantage of available anti-cancer drugs is their non-selective behavior towards cancer cells as well as normal cells.
Objectives In the light of this fact, the searching of new compounds with selective behavior only towards cancer cells is critically
important. Previously, we have identified several series of compounds as the potential inhibitors of these families.
Methods Herein, we investigate quinolones and quinolines for their anti-cancer activity against breast cancer cells (MCF–7),
bone marrow cancer cells (K–562) and cervical cancer cells (HeLa) by MTT assay. The most effective derivatives were further
subjected to flow cytometry analysis followed by fluorescence microscopic analysis by using 4´,6-diamidine-2´-phenylindole
(DAPI) and propidium staining (PI) staining.
Results All the tested compounds were found selective only towards cancer cells. The identified compounds also induced either
G2 or S-phase cell cycle arrest within the respective cancer cell line, chromatin condensation and the nuclear fragmentation, as
well as maximum interaction with DNA.
Conclusions These results provide evidence that the characteristic chemical features of attached groups are the key factors for
their anticancer effects and play a useful role in revealing the mechanisms of action in relation to the known compounds in future
research programs.
.
.
.
.
.
Keywords Quinolones Quinolines Breast cancer cells (MCF–7) Bone marrow cells (K–562) Cervical cancer cells (HeLa)
Cell-cycle
Introduction
in molecular events including uncontrolled cell proliferation
[1], cellular transformation, improper regulation of cell cycle
[2], angiogenesis and increased invasion ensuing metastases
[3]. Moreover, a variety of factors are known to contribute
towards cancer; many cellular/enzymatic pathways have been
discovered as an important drug targets for the treatment of
cancer [4]. Although many anticancer agents are known, but
most of them are cytotoxic not only to the cancerous cells but
also to the normal cells [5]. As a result, they cause severe side
effects including nausea, hair loss, weight loss, fatigue, skin
rashes and loss of appetite [6]. In the light of this fact, the
search for novel chemotherapeutic agents is a motivating
and continually sprouting field in cancer research. Still there
is a need of developing more effective and less toxic agents
that may lead as best anticancer effects with defined molecular
targets.
Now a days, cancer is one of the most leading cause of death
worldwide. It is characterized by disturbances and alterations
* Jamshed Iqbal
drjamshed@ciit.net.pk
1
Centre for Advanced Drug Research, COMSATS University
Islamabad, Abbottabad Campus, Abbottabad 22060, Pakistan
2
Department of Chemistry, Quaid-i-Azam University, -45320,
Islamabad, Pakistan
3
Institut für Chemie, Universität Rostock, Albert Einstein Str. 3a,
18059 Rostock, Germany
4
Institut für Chemie, Universität Rostock, Albert Einstein Str. 3a,
18059 Rostock, Germany

DARU J Pharm Sci
In the course of identifying various chemical substances
which may serve as leads for designing novel antitumor
agents, many classes of organic compounds have been tested
[7], with special attention being paid to quinolones and quin-
olines. These are the most common condensed heterocyclic
aromatic compounds, containing nitrogen in their structure
and are known for their diverse therapeutic potential [8].
Moreover, the quinolone and quinoline nucleus occurs in sev-
eral natural compounds and pharmacologically active sub-
stances where they are responsible for broad spectrum of bio-
logical activity [9]. Previously we have identified several quin-
olones and quinolines derivatives; isoquinoline derivatives
(4a-p), quinoline–4–carboxylic acid derivatives (3a-j) and 4–
quinolone derivatives (2a-7d) as potent and selective inhibitors
of alkaline phosphatases (specifically tissue non-specific alka-
line phosphatase; TNAP) and NPPs (NPP1; ecto-nucleotide
pyrophosphatases/phosphodiesterases1) with lower micromo-
lar potency [10–12]. These members of ecto-nucleotidases
possesses different enzymatic and cellular expression proper-
ties [13]. Moreover, they are involved in regulation of various
signalling pathways especially purinergic signalling pathway
though which they are responsible for the maintenance of nu-
cleotide and nucleoside level [14]. The abberrant level of these
ecto-nucleotidases is associated with various types of cancers,
especially breast cancer as its associated malagnancies.
Therefore, the inhibitors of these ecto-nucleotidases could play
a promising role in the treatment of cancer [15].
and 4–quinolone derivatives (2a-7d) have been reported in our
previous work [10–12], respectively.
Cell lines and cell cultures
Two cancer cell lines breast adenocarcinoma (MCF–7) cell line
(ATCC® HTB–22™) human cervical cancer (HeLa) cell line
(ATCC–USA) were kept in DMEM media [having heat–
inactivated fetal bovine serum (10%), 100 U/mL penicillin
and 100 μg/mL streptomycin] and bone marrow lymphoblast
(K–562) cell line (ATCC® CCL–243™) was kept in RPMI–
1640 [having heat–inactivated fetal bovine serum (15%), 100 U/
mL penicillin and 100 μg/mL streptomycin] in T–75 cm2 sterile
tissue culture flasks in a 5% CO2 incubator at 37 °C. For cell
viability assay, these cell lines were grown in different 96–well
plates by inoculating 2.5 × 103 cells/100 μL/well at 37 °C for
24 h in a CO2 (5%) incubator and then treated with selected
compounds (10 μL). For cell cycle analysis and microscopic
experiments, these cell lines (2.5 × 105 cells/mL) were incubated
at 37 °C overnight in 6–well plate and then were treated with the
most potent cytotoxic compounds (according to GI50 values)
and positive control, i.e., carboplatin [16].
Anticancer assays
Cell viability assays (MTT assay)
Herein we performed extensive studies to investigate anti-
cancer potential of quinolones and quinolines derivatives;
isoquinoline derivatives (4a-p), quinoline–4–carboxylic acid
derivatives (3a-j) and 4–quinolone derivatives (2a-7d) against
different cancer cell lines i.e., breast cancer cells (MCF–7),
bone-marrow cancer cells (K–562) and cervical cancer cells
(HeLa) by using the flow cytometry, fluorescence microscopy
and DNA-binding studies. The screening of compounds
against healthy baby hamster kidney cells (BHK-21) was also
performed. The results were found significant as they showed
selective cytotoxicity against cancerous cells only. Moreover,
the data obtained from both studies suggested that quinolone
and quinoline derivatives, synthesized from different strate-
gies could be beneficial for the treatment of various types of
cancer. Further investigations may help researchers to synthe-
size such types of compounds with minimum toxicity.
The cytotoxic potentials of the test compounds were evaluated
in human breast adenocarcinoma cells (MCF-7), human mye-
logenous leukemia cells (K-562), human cervical adenocarci-
noma cells (HeLa) by MTT (Dimethyl–2–thiazolyl–2,5–
diphenyl–2H–tetrazolium bromide)–based cell viability assay
as described earlier [17–19]. The effect of these derivatives
was also examined against normal cells i.e., baby hamster kid-
ney cells (BHK–21). Briefly, the cells (2.5 × 104/mL) were cul-
tured in a volume of 90 μL in each well of a 96-well flat-bottom
culture plate and kept in 5% CO2 incubator at 37 °C. After an
overnight incubation, the cells were treated with the test com-
pounds (100 μM) and incubated for 24 h. The media was
poured out and 10 μL MTT reagent (5 mg/mL) was added to
each well to crystallize the viable cells. The plate was incubated
for 4 h at 37 °C and 5% CO2, followed by the addition of
100 μL of the reagent (1:1 solution of 50% isopropanol and
10% sodium dodecyl sulfate). The plate was further incubated
for 30 min at room temperature and the optical density was
observed at 570 nm wavelength by subtracting the absorbance
at 630 nm, using microplate reader (Bio-Tek ELx 800™,
Winooski, USA). The percent growth inhibition values of the
each compound was calculated in reference to the negative
control (blank) with the mean of three independent values
( SEM). The experiment was carried out in triplicate and de-
rivatives exhibited equal to or more than 50% inhibition were
further evaluated for their growth inhibitory (GI50) values.
Material and methods
Synthesis of Isoquinoline, Quinoline–4–carboxylic
acid and 4–quinolone compounds
The general procedure for the synthesis of isoquinoline deriv-
atives (4a-p), quinoline–4–carboxylic acid derivatives (3a-j)

DARU J Pharm Sci
Cell cycle analysis assay
accurate binding interactions. The best pose was then selected
and visualized through Discovery Studio [25].
The treated cells were subjected to cell cycle analysis by fow
cytometry (BD Accuri™, United States), using the method as
reported earlier [19, 20]. Initially, the cells (25 × 104 cells/mL)
were treated with the most potent derivatives obtained from
MTT assay from the selected series and incubated over night
at 37 °C. Then the pallets of cells were attained by centrifu-
gation at 4000 g (for 5 min) and after that the pallet was
resuspended in 3% FBS solution (200 μL) that contained
5 μL of propidium iodide (20 μg/mL), 0.1% (v/v) Triton X-
100 and ribonuclease A (10 μL, 10 mg/mL). The samples
were analyzed by BD accuri flow cytometry as described ear-
lier [21].
Results
Chemistry
Synthesis of Isoquinoline derivatives
Isoquinoline ring system was synthesized in one–pot reaction
by initially forming C–N bonds using catalyst–free
defluorination of 1–bromo–2–(2,2–difluorovinyl)benzenes 1
in reaction with various N–H heterocycles 2. The α,α–
dihetaryl substituted alkene intermediate 3 was then subjected
to Pd(OAC)2 catalyzed intramolecular C2 arylation to give
nitrogen–fused isoquinoline derivatives 4 as given in
Scheme 1 [10].
Microscopic analysis of apoptosis
The microscopic analysis of most potent derivatives was car-
ried out to support the flow cytometry results as discussed
previously [21, 22]. The confluent cells (2.5 × 105 cells/well)
were treated with the compound and kept in incubator (5%
CO2) at 37 °C. After 24 h, culture medium was removed
and cells were washed thrice with cold PBS. The cells were
further treated with 4% formalin and 0.1% Triton X–100.
Finally, after 5 min incubation at room temperature, 10 μL
(0.1 mg/mL) of 4′,6-diamidino-2-phenylindole (DAPI) or
propidium iodide (PI) dye was mixed to stain the nuclear
material and images were captured by using the fluorescence
microscope ((Nikon ECLIPSE Ni–U), Japan) at excitation/
emission wavelength of 350/460 nm and 493/632 for DAPI
and PI, respectively.
Synthesis of Quinoline–4–carboxylic Acid derivatives
Quinoline–4–carboxylic acid derivatives (3a–j) were synthe-
sized by the reaction of 5–chloro–isatin 1 with corresponding
aryl substituted acetophenones (2a–j) in the presence of po-
tassium hydroxide followed by acidification as given in
Scheme 2 [11].
Synthesis of 4–Quinolone derivatives
The synthesis pathway of 4-quinolones is depicted in
Schemes 3 and 4. Nucleophilicity of the unsubstituted
C–3 atom in a quinolone molecule 1 gave an option for
an expanding of the molecule complexity. This could be
demonstrated by a good reactivity with electrophilic
agents. For example, utility of the N–bromsuccinimide
resulted in products 2 brominated at their C–3 position.
In this manner we obtained 3–bromoquinolones 2 as a
platform for further functionalization (Schemes 3 & 4)
[12].
DNA interaction and docking studies
To determine the mechanism of inhibition of the most potent
compounds as well as to support the above results, the DNA
interaction studies were performed according to the previously
reported method [21, 23]. Briefly, the concentration of mam-
malian DNA was estimated at 260 nm wavelength using
FLUOstar Omega (BMG Labtech, Germany). The test com-
pound (100 μM) was treated with different concentrations of
DNA from 0 μM to 340 μM, whereas the same concentrations
of DNA were used in respective reference solutions. After an
incubation for 10 min, the absorption spectra were recorded in
96 well plates with the path length of 5.5 mm.
The DNA docking studies were performed by Molecular
Operating Environment (MOE, version 2014) software [24] as
reported by our group, previously [21]. Firstly, the binding
pockets in the DNA (minor and major groves) and the inter-
calating sites in the DNAwere determined by the known com-
pounds. Then, the 3D structures of compounds and 3D struc-
ture of DNAwere further processed as discussed previously. A
total 100 poses for each compound were generated to get
Biological results
Cytotoxic potential of Compounds by MTT assay
Isoquinoline derivatives The cytotoxic potential of different
isoquinoline derivatives (4a-p) is illustrated in Table 1 as a
percent growth reduction. The study was carried out by using
three cancer cell lines (HeLa, MCF–7 and K–562) and one
normal cell line (BHK–21). The cell viability was evaluated
by treating the different cells with 100 μM of each derivative
for 24 h. In addition, it was found from the results that these
derivatives remained inactive against normal cell line and pos-
sessed promising anticancer effects (Table 1).

DARU J Pharm Sci
Scheme 1 One–pot two–step synthesis of N–fused isoquinolines. (Reaction conditions: 1) difluoroalkene1, heterocycle 2 (2 equiv.), K3PO4 (4 equiv.), in
DMF (5 mL), 100 °C, 12 h; 2) Pd(OAc)2 (5 mol%), PPh3 (10 mol%), 140 °C) [10]
The potent derivatives were further evaluated for the deter-
mination of growth inhibitory values (GI50) values towards
MCF–7, K–562 and HeLa cells, respectively (Table 2).
Microscopic analysis (using DAPI & PI)
MCF-7, K-562 and HeLa cells were treated for with their
respective potent derivatives from all selected series as men-
tioned above. The images were captured after 24 h, illustrating
the cell death mechanism. DAPI and its counter stained PI
were used for staining the nuclear material (Fig. 3).
Quinoline–4–carboxylic derivatives The cytotoxic potential of
Quinoline–4–carboxylic acid derivatives (3a-j) are depicted in
Table 3.
The growth inhibitory concentrations (GI50) of the most
potent derivatives were further evaluated in the respective cell
lines that are given in Table 4.
DNA interaction studies
The most potent derivatives against MCF–7 cells (4p, 3j and
3a), K–562 cells (4 l, 3j and 2b) and HeLa cells (4i, 3b and 5a)
were further evaluated to determine their mechanism of action
by interacting with HS–DNA in UV–visible range (Figs. 4
and 5).
4–quinolone derivatives The 4–quinolone derivatives (2a-c,
3a-g, 4a, 5a-g, 6a, 7c-d) exhibited moderate to excellent cy-
totoxic behavior against different cell lines as compared to
normal BHK–21 cells, as depicted in Table 5.
The most potent compounds were further evaluated for the
determination of GI50 values against MCF–7, K–562 and
HeLa cells (Table 6).
Discussion
Cell cycle analysis and detection of apoptosis by flow
cytometry
The isoquinoline ring system is highly active pharmacophore
and is responsible for various pharmaccological activities. The
were synthesized in one-pot reaction by N-vinylation and Pd-
catalysed C-H arylation reactions. Different N-H heterocycles
were used and different functional groups were allowed,
which resulted in wide range of products (4a-p) as previously
reported earlier by us [10]. The quinoline–4–carboxylic deriv-
atives (3a–3j) were synthesized by the reaction of 5-chloro-
isatin 1 with corresponding aryl substituted acetophenones in
the presence of potassium hydroxide followed by acidification
as reported earlier by our group [11]. The 4-quinolone deriv-
atives were synthesized via sequential derivatization methods
The most effective cytotoxic derivatives from quino-
lones and quinoline series were selected for flow cytom-
etry analysis to further investigate their effect on cell
cycle progression and apoptosis in the three mentioned
cell lines i.e., HeLa, K-562 and MCF–7. Figs. 1 and 2
showed the DNA content within the dividing cells as
estimated by propidium iodide staining, whereas the
percent cell population within the cell cycle phases
i.e., Go – G1, S, and G2/ M phases.
Scheme 2 Synthesis of quinoline–4–carboxylic acids (3a–j) (Reaction
conditions: 1) 5-chloro-isatin (1.0 mmol), corresponding aryl substituted
acetophenones (1.1 mmol), KOH (3.0 mmol), in ethanol (5 mL), mixture
was refluxed for 24 h, acidified with 2 M aqueous hydrochloric acid,
recrystallized from ethanol to get compunds (3a-j) [11]

DARU J Pharm Sci
Scheme 3 Modification
strategies at the C–3 position in
the 4–quinolinones. (Reagents
and conditions: (i) 1.45 equiv. of
NBS, CH3COOH, 20 °C, 1.5 h;
(ii) 1.2 equiv. of aryl boronic acid,
0.1 equiv. of Pd(PPh3)4 10 equiv.
K2CO3 in 5.5 mL of toluene with
1 mL of H2O and 1.5 mL of
MeOH at 90 °C for 4 h; (iii)
CF3COONa 4 equiv., CuI 8
equiv., DMA, 120 °C 6 h) [12]
in order to get C-1, C-3 and C-6 substituted 4-quinolone (2a-c,
3a-g, 4a, 5a-g, 6a, 7c-d) as reported earlier by us [12].
derivatives were found to inhibit the only cencerous cell lines
selectively. None of the derivative exhibited cytotoxic effect
towards the normal cell line. Different functional groups at-
tached to the ring are responsible for such variable effect on cell
lines. Moreover, it can be suggested from the detailed structure–
activity relationship of derivative 9-Fluoro-6-(6-fluoro-1H-
indol-1-yl)-[1,3]dioxolo[4,5-g]indolo[2,1-a]isoquinoline (4 l)
and 6-(4-Oxo-4,5,6,7-tetrahydro-1H-indol-1-yl)-9,10-
dihydroindolo[2,1-a]isoquinolin-11(8H)-one (4p), that the pres-
ence of pyrol, pyrolo–pyridine rings as well as fluorine substi-
tution in case of 6-(4-Oxo-4,5,6,7-tetrahydro-1H-indol-1-yl)-
9,10-dihydroindolo[2,1-a]isoquinolin-11(8H)-one (4p) might
be responsible for this maximum anticancer potential towards
MCF–7 and K–562 cell lines, respectively. Another quinolone
derivative i.e., 2,3-Dimethoxy-12-methyl-6-(3-methyl-1H-
indol-1-yl)indolo[2,1-a]isoquinoline (4i), showed maximum in-
hibitory response towards HeLa cell which is in accordance with
its significant inhibitory effects on h–NPP1 [10]. The potent
derivatives were further evaluated for the determination of
growth inhibitory values (GI50) values towards MCF–7, K–
562 and HeLa cells, respectively (Table 2).
Biological results
Cytotoxic potential by MTT assay
The derivatives from three different series showed different
behavior as discussed below:
Isoquinoline derivatives The cytotoxic potential of different
isoquinoline derivatives (4a-p) is illustrated in Table 1 as a per-
cent growth reduction. Among all derivatives, derivatives 6-(4-
Oxo-4,5,6,7-tetrahydro-1H-indol-1-yl)-9,10-dihydroindolo[2,1-
a]isoquinolin-11(8H)-one (4p), 9-Fluoro-6-(6-fluoro-1H-indol-
1-yl)-[1,3]dioxolo[4,5-g]indolo[2,1- a]isoquinoline (4 l) and
2,3-Dimethoxy-12-methyl-6-(3-methyl-1H-indol-1-
yl)indolo[2,1-a]isoquinoline (4i), induced an approximately
95%, 97% and 70% inhibition in the growth of breast cancer
cells (MCF–7), bone–marrow cancer cell line (K–562) and hu-
man cervical cancer cell line (HeLa) cells, respectively. All the
Scheme 4 Functionalization of 2, 3 and 4 derivatives. (Reagents and conditions: (i) CF3COOH, reflux 2–10 h; (ii) Methanol: AcOH 1:1, 0.1 equiv. Pd/C
(10%), H2, 2–3 h; (iii) Methanol, 0.1 equiv. Pd/C (10%), H2, 5 h) [12]

DARU J Pharm Sci
Table 1 Cytotoxic potential of isoquinoline derivatives (4a-p) against cancerous and normal cell lines
Codes
Structure
R1, R2, R3
H, H, H
Me, H, H
H, OMe, H
H, CN, H
H, H, F
Me, H, H
H, CN, H
H, H, F
Me, H, H
H, CN, H
H, H, F
–
Cytotoxic Potential (% Growth Reduction SEM)
MCF–7
51.7 2.01
51.3 1.98
55.6 1.76
44.8 0.97
50.3 1.39
24.3 0.73
46.1 1.59
57.3 2.03
47.8 1.01
10.1 0.09
57.5 1.93
53.3 0.99
57.3 2.31
47.6 1.24
52.2 1.48
95.6 2.95
K–562
HeLa
58.3 1.74
60.3 2.5
BHK–21
85.7 4.02
79.8 3.05
86.9 2.83
91.7 1.87
75.1 2.16
80.9 3.01
82.1 2.97
86.9 1.49
54.1 1.69
92.4 3.29
88.1 2.53
96.6 2.96
75.1 3.14
86.9 0.99
63.1 2.18
88.1 3.5
21.8 0.69
24.5 1.03
8.82 0.01
28.7 0.63
22.1 0.12
35.2 0.74
29.1 0.81
13.6 0.09
14.8 0.1
13.7 0.17
17.9 0.02
16.1 0.3
7.34 0.06
12.9 0.05
20.1 0.72
12.9 0.42
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
57.7 0.87
47.7 2.04
42.4 1.36
45.7 0.69
35.9 0.72
51.5 2.15
69.7 0.84
63.5 1.57
64.9 2.31
63.7 2.06
26.5 0.73
59.5 0.78
32.1 1.07
39.8 0.94
–
–
–
–
90.7 3.08
82.8 2.67
85.2 2.98
18.4 2.67
Carboplatin
The cytotoxic potential of tested compounds was measured at the final concentration of 100 μM. Results represented here as the mean (S.E.M) of three
independent determinations
Table 2 Growth inhibitory values GI50 SEM (μM) of compounds 4i,
4 l and 4p against respective cell lines
Quinoline–4–carboxylic acid derivatives The results showed
(Table 3) that these derivatives possessed variable degree of
inhibition against the different cell lines (HeLa, MCF–7, K–
562) as compared to normal cells. These derivatives were also
found selective only towards cancer cell lines. Considering the
breast cancer cells (MCF–7), the compound 6-Chloro-2-(4-
hydroxy-3-methoxyphenyl)quinoline-4-carboxylic acid (3j)
displayed 82.9% reduction in cellular growth under favorable
conditions. These results here support the enzymatic inhibito-
ry potential (alkaline phosphatase) of same compound i.e.,
6-Chloro-2-(4-hydroxy-3-methoxyphenyl)quinoline-4-car-
boxylic acid (3j) which has been discussed in our previous
data [11]. The potent inhibitor of h–TNAP, displayed the
Code
MCF–7
K–562
HeLa
GI50 SEM (μM)
4i
>100
17.1 2.66
10.9 1.04
13.6 1.78
4.11 0.78
1.43 0.26
7.19 0.78
>100
4 l
7.25 0.86
0.49 0.02
3.91 0.32
4p
Carboplatin
5.13 0.45
GI50 denotes compound concentrations that result in a 50% decrease in
the cell number compared to non–treated controls and were derived after
24 h treatment
The bold entries in the Table represent the GI50 SEM (μM) for the
potent compounds among the series against each cell line

DARU J Pharm Sci
Table 3 Cytotoxic potential of quinoline-4-carboxylic acid derivatives (3a-j) against cancerous and normal cell lines
Cytotoxic Potential (% Growth Reduction SEM)
Substituent
Compound
R
MCF–7
K–562
HeLa
BHK–21
2–Br
3–Br
3a
3b
3c
3d
3e
3f
61.7 2.41
57.9 1.32
64.4 2.38
66.8 2.48
56.2 1.59
63.4 1.64
59.2 1.49
65.9 2.37
53.3 0.94
82.9 2.06
90.7 3.08
46.2 1.37
48.7 2.07
30.8 1.65
46.2 1.49
53.9 0.95
71.8 3.02
48.7 1.36
76.9 3.07
71.8 1.74
82.1 3.29
82.8 2.67
62.4 2.17
75.9 3.10
46.3 0.94
51.9 1.80
67.5 2.38
59.6 2.38
60.2 1.84
56.4 1.79
43.3 0.21
43.1 2.07
85.2 2.98
20.7 0.83
10.9 0.42
21.6 0.62
14.6 0.43
30.9 1.07
18.1 0.78
12.5 0.58
39.1 1.02
1 5.7 0.29
13.6 0.43
18.4 2.67
3–F
3–Me
4–OMe
4–I
3g
3h
3i
3–F–4–OMe
3–I–4–OMe
2, 4–diOMe
4–OH–3–OMe
3j
Carboplatin
The cytotoxic potential of tested compounds was measured at the final concentration of 100 μM. Results represented here as the mean (SEM) of three
independent determinations
maximum growth reduction of breast cancer cell line (MCF–
7). The detailed study of this derivative structure suggested
that the maximum activity might be due to the presence of
electron donating methyl group at position 3 (Tables 3 and
4). Against MCF–7 cells, the other derivatives also exhibited
significant growth inhibition, suggesting the effectiveness of
these derivatives against breast cancer.
These derivatives showed moderate sensitivity towards the
bone marrow lymphoblast K–562 cells and HeLa cells by
exhibiting % growth reduction values in range of 53% to 76%
and 51% to 68%, respectively. Five derivatives (3a, 3b, 3c, 3d,
3 g) remained inactive against K–562 while two derivatives
2-(3-Bromophenyl)-6-chloroquinoline-4-carboxylic acid (3b)
and 6-Chloro-2-(2,4-dimethoxyphenyl)quinoline-4-carboxylic
acid (3i) showed minimum response against HeLa cells.
Table 4 Growth inhibitory values GI50 SEM (μM) for compounds 3b
and 3j against respective cell lines
4–quinolone derivatives The 4–quinolone derivatives (2a-
7d) exhibited moderate to excellent cytotoxic behavior
against different cell lines, as depicted in Table 5.
Overall, many derivatives were found selective inhibitor
of K–562 as compared to MCF–7 cells. The compound
3-(4-Ethylphenyl)-1-(4-methoxybenzyl)-6-nitro-2-p-
tolylquinolin-4(1H)-one (3a) exhibited maximum inhibi-
tory activity against MCF–7 cells while other com-
pounds 3-Bromo-6-nitro-1-(1-phenylethyl)-2-p-
tolylquinolin-4(1H)-one (2b) and 6-Nitro-2-p-
tolylquinolin-4(1H)-one (5a) were more active against
Code
MCF–7
K–562
HeLa
GI50 SEM (μM)
3b
4.11 0.99
0.54 0.05
3.91 0.32
>100
1.15 0.65
>100
3j
25.8 0.79
4.11 0.78
Carboplatin
5.13 0.45
GI50 denotes compound concentrations that result in a 50% decrease in
the cell number compared to non–treated controls and were derived after
24 h treatment
The bold entries in the Table represent the GI50 SEM (μM) for the
potent compounds among the series against each cell line

DARU J Pharm Sci
Table 5 Cytotoxic potential of 4-quinolone derivatives (2a-c, 3a-g, 4a, 5a-g, 6a, 7c,d) against cancerous and normal cell lines
Cytotoxic Potential (% Growth Reduction SEM)
Substituent
Compound
R1, R2, R3
MCF–7
58.9 1.85
57.1 2.43
57.3 1.73
81.1 3.37
52.1 2.53
50.8 2.05
56.5 1.49
63.2 1.84
52.6 2.01
52.3 1.64
56.6 2.09
51.3 1.76
55.8 2.43
49.8 1.68
49.5 2.16
70.9 1.59
61.9 2.17
90.7 3.08
K–562
HeLa
BHK–21
14.7 0.53
24.7 1.01
2.56 0.002
37.8 0.73
41.9 0.39
7.86 0.06
28.7 1.00
24.7 0.76
18.7 0.59
9.78 0.08
15.4 0.72
19.6 0.58
14.8 0.32
5.76 0.02
18.5 0.70
31.7 1.23
5.85 0.06
18.4 2.67
4-OCH3Bn, p–tolyl, Br
Ph-ethyl, p–tolyl, , Br
4-OCH3Bn, n-Pent, -Br
4-OCH3Bn, p–tolyl, 4-ethyl-Ph
4-OCH3Bn , p–tolyl, 3,5-di-CH3-Ph
4-OCH3Bn, p–tolyl, 4-CF3-Ph
4-OCH3Bn , p–tolyl, 4-OCH3Ph
4-OCH3Bn , p–tolyl, p–tolyl
4-OCH3Bn, p–tolyl, 2-formyl-Ph
4-OCH3Bn , p– tolyl, CF3
H, p–tolyl, H
2a
2b
2c
3a
3b
3c
3d
3e
3f
84.6 3.07
97.4 3.69
74.3 2.27
69.2 1.93
66.7 0.96
38.5 1.17
71.8 3.19
74.4 2.59
65.8 1.76
35.9 0.84
33.3 1.08
7.69 0.03
92.3 3.79
74.4 2.53
30.8 1.02
51.3 2.37
84.6 3.59
82.8 2.67
64.3 1.95
62.8 1.76
56.3 2.18
51.9 1.39
62.1 2.51
65.4 0.92
66.1 1.84
63.6 2.62
68.4 1.93
62.1 1.86
72.5 2.24
40.2 1.75
50.3 2.19
54.4 1.27
60.6 2.18
57.9 0.99
59.8 2.03
85.2 2.98
4a
5a
5c
5d
5f
H, p–tolyl, Br
H, n-Pent, Br
H, p–tolyl, 4-CF3-Ph
4-OCH3Bn, p-tolyl
6a
7c
7d
H, 4-OCH3Ph
H, p-tolyl
Carboplatin
The cytotoxic potential of tested compounds was measured at the final concentration of 100 μM. Results represented here as the mean (SEM) of three
independent determinations
K–562 and HeLa cells, respectively. Additionally, the
growth inhibitory activity of these compounds against
cancer cells also showed that these compounds are more
sensitive towards cancer cells and are less sensitive to-
wards normal cells. From Table 5, it was found that the
cytotoxicity effect of these derivatives against MCF–7

DARU J Pharm Sci
Table 6 Growth inhibitory values GI50 SEM (μM) for compounds
2b, 3a and 5a against respective cell lines
much potential to inhibit growth of breast cancer cells.
B r i e f l y, c o m p o u n d 3 - ( 4 - e t h y l p h e n y l ) - 1 - ( 4 -
methoxybenzyl)-6-nitro-2-p-tolylquinolin-4(1H)-one (3a)
from 4–quinolone showed maximum apoptosis (54.4%)
in comparison to 6-(4-oxo-4,5,6,7-tetrahydro-1H-indol-1-
yl)-9,10-dihydroindolo[2,1-a]isoquinolin-11(8H)-one (4p)
from isoquinoline and 6-chloro-2-(4-hydroxy-3-
methoxyphenyl)quinoline-4-carboxylic acid (3j) from
quinoline–4–carboxylic acid. Both derivatives induced
maximum apoptotic potential such as 51.4% and
51.9%, respectively, within the respective series and re-
sulted in equipotent apoptosis as that of positive control
i.e., carboplatin (50.1%). The cell cycle analysis sug-
gested the possible interference and inhibition of mitotic
spindling that finally resulted in DNA disruption and
cell arrest in G2 phase. Therefore, these derivatives re-
sulted in amassing of cells at G2 phase. Among these
potent derivatives (3a, 4p, 3j), the compound 3-(4-
ethylphenyl)-1-(4-methoxybenzyl)-6-nitro-2-p-
tolylquinolin-4(1H)-one (3a) from 4–quinolone and 6-
chloro-2-(4-hydroxy-3-methoxyphenyl)quinoline-4-car-
boxylic acid (3j) from quinoline–4–carboxylic acid
depicted the higher apoptotic cell death i.e., 19.7%
and 22.5%, respectively, within G2 phase. Fig. 1
showed the percentage apoptosis within different cell
cycle phases i.e., Go– G1, S, and G2/ M, of these
potent derivatives (4p, 3j and 3a). When the effect
Code
MCF–7
K–562
HeLa
GI50 SEM (μM)
2b
6.22 0.77
0.61 0.02
6.45 0.87
3.91 0.32
7.91 0.62
13.5 1.67
>100
7.65 0.97
9.88 1.23
2.02 0.11
5.13 0.45
3a
5a
Carboplatin
4.11 0.78
GI50 denotes compound concentrations that result in a 50% decrease in
the cell number compared to non–treated controls and were derived after
24 h treatment
The bold entries in the Table represent the GI50 SEM (μM) for the
potent compounds among the series against each cell line
was moderate except 3-(4-Ethylphenyl)-1-(4-
methoxybenzyl)-6-nitro-2-p-tolylquinolin-4(1H)-one
(3a). The structure activity relationship (SAR) of these
derivatives clearly demonstrated the effect of different
functional groups at R1, R2 and R3 position affects
the cytotoxic potential.
Flow cytometric analysis of cell cycle
The most potent derivatives from quinolones and quin-
oline series displayed promising cytotoxic behavior on
the MCF–7 cells, suggesting that these derivatives have
Fig. 1 Flow cytometric analysis of cell cycle using propidium iodide (PI)
staining. (a) untreated MCF–7 cells (b-e) MCF–7 cells treated with
carboplatin, 4p, 3j and 3a, respectively. (f) untreated K–562 cells (g-j)
K–562 cells treated with carboplatin, 4 l, 3j and 2b, respectively. (k)
untreated HeLa cells (l-o) HeLa cells treated with carboplatin, 4i, 3b and
5a, respectively

DARU J Pharm Sci
Fig. 2 Cell cycle profile by the most potent derivatives against respective
cell lines (a) MCF–7 cells treated with compound 4p, 3j and 3a (b) K–
562 cells treated with compound 4 l, 3j and 2b (c) HeLa cells treated with
compound 4i, 3b and 5a. Data were analyzed by one way analysis of
variance (ANOVA) using Graphpad PRISM® 5 (GraphPad, San Diego,
California, USA). The mean of three experiments S.D. is shown and
statistical differences between the groups was found significant
***p < 0.0001
was observed against K–562 cells, the potent derivatives
from each series (4 l, 3j, 2b) exhibited promising and
comparable apoptosis as that of positive control,
carboplatin.
Against K–562 cells, the compound 9-fluoro-6-(6-
fluoro-1H-indol-1-yl)-[1,3]dioxolo[4,5-g]indolo[2,1-
a]isoquinoline (4 l) from isoquinolines, 6-chloro-2-(4-
hydroxy-3-methoxyphenyl)quinoline-4-carboxylic acid
(3j) from quinoline–4–carboxylic acid and 3-bromo-6-
nitro-1-(1-phenylethyl)-2-p-tolylquinolin-4(1H)-one (2b)
from 4–quinolone exhibited percentage apoptotic value
i.e., 54.3%, 51.1% and 57.9%, respectively. The positive
control, carboplatin induced 58.1% apoptosis against K–
562 cells. Compound compound 9-fluoro-6-(6-fluoro-
1H-indol-1-yl)-[1,3]dioxolo[4,5-g]indolo[2,1-
a]isoquinoline (4 l) from isoquinolines exhibited higher
S phase apoptotic cell death (approx. 24%) among all
derivatives but its overall apoptosis (54.3%) is slightly
less than other derivative 3-bromo-6-nitro-1-(1-
phenylethyl)-2-p-tolylquinolin-4(1H)-one (2b) from 4–
quinolone. In S phase, these derivatives intercalated
with DNA molecule and undergone programmed cell
death (apoptosis). The cell cycle analysis suggested that
these derivatives are every effective with respect to S
Fig. 3 Cell apoptosis observed under fluorescence microscope using
DAPI (a) and PI (b) staining respectively. In both (a) and (b), (A)
untreated MCF–7 cells (B-E) MCF–7 cells treated with carboplatin,
4p 3j and 3a, respectively. (F) untreated K–562 cells (G-J) K–562 cells
treated with carboplatin, 4 l, 3j and 2b, respectively. (K) untreated HeLa
cells (L-O) HeLa cells treated with carboplatin, 4i, 3b and 5a,
respectively

DARU J Pharm Sci
phase and ultimately more cell death occurred in this
phase as compared to other phases (Figs. 1 and 2).
While using the HeLa cells, among 4–quinolones de-
rivatives, the compound 6-nitro-2-p-tolylquinolin-4(1H)-
one (5a) showed maximum apoptotic percentage
(41.8%). While, 2-(3-bromophenyl)-6-chloroquinoline-4-
carboxylic acid; 3b (35.1%) and 2,3-dimethoxy-12-
methyl-6-(3-methyl-1H-indol-1-yl)indolo[2,1-a-
]isoquinoline; 4i (22.8%) of quinoline–4–carboxylic acid
and isoquinoline derivatives, respectively, caused maxi-
mum apoptotic potential within their series. These po-
tent derivatives intercalated with DNA molecule during
S phase and resulted in programmed cell death (apopto-
sis). The compound 5a resulted in significant S phase
apoptotic cells arrest as well as their accumulation as
compared to other derivatives 2-(3-bromophenyl)-6-
chloroquinoline-4-carboxylic acid (3b) from quinoline–
4–carboxylic acid and 2,3-dimethoxy-12-methyl-6-(3-
methyl-1H-indol-1-yl)indolo[2,1-a]isoquinoline (4i) from
isoquinoline. Figure 2 represented the percentage cell
apoptosis of potent compounds 2,3-dimethoxy-12-meth-
yl-6-(3-methyl-1H-indol-1-yl)indolo[2,1-a]isoquinoline
(4i) from isoquinoline, 2-(3-bromophenyl)-6-
chloroquinoline-4-carboxylic acid (3b) and compound
6-nitro-2-p-tolylquinolin-4(1H)-one (5a) during different
cell cycle phase (Go– G1, S, and G2/ M). Hence, the
apoptotic cell death with respect to the total cell count
indicated the compound 6-nitro-2-p-tolylquinolin-4(1H)-
one (5a) from 4–quinolones as most potent derivative
possessing higher pro–apoptotic activity than 2,3-
dimethoxy-12-methyl-6-(3-methyl-1H-indol-1-
yl)indolo[2,1-a]isoquinoline (4i) from isoquinoline and
2-(3-bromophenyl)-6-chloroquinoline-4-carboxylic acid
(3b) from quinoline–4–carboxylic acid, which are in re-
lation with the results obtained from MTT assay,
discussed earlier.
The scattering of cell cycle phases as Go – G1, S, and G2 -
M in the MCF-7 cells by carboplatin (11.1%, 16.9% and
18.5%) and compounds 4p, 3j and 3a indicated prominent
increase in DNA content in G2 - M phase and resultant
a
h
a
h
a
h
a
b
Fig. 4 Absorption spectra of 40 μM of (a) isoquinoline (4p (A), 4 l (B)
and 4i (C)) and (b) 4–quinolone derivatives (3a (A), 2b (B) and 5a (C))
in absence and presence of increasing concentration of DNA (indicated
with arrow). The graph within the figure is the plot of A°/ (A–A°) vs
1/[DNA] plot for the determination of Gibb’s free energy as well as the
binding constant for the tested derivatives

DARU J Pharm Sci
a
h
a
h
Fig. 5 Absorption spectra of 40 μM of quinoline–4–carboxylic acid
derivatives (3j (A) and 3b (B)) in absence and presence of in absence
and presence of increasing concentration of DNA (indicated with arrow).
The graph within the figure is the plot of A°/ (A–A°) vs 1/[DNA] plot for
the determination of Gibb’s free energy as well as the binding constant for
the tested derivatives
decrease in G0 - G1 phase as compared to the untreated
cells. However, in K-562 cells, most prominent changes
in Go – G1, S and G2 - M phases were shown by carboplatin
(7.0%, 13.6% and 20.9%). Furthermore, the cell cycle pro-
gression of the HeLa cells (when treated with carboplatin
(28.1%, 23.6% and 22.1%) and compounds 4i, 3b and 5a)
was particularly promoted the transition of G1/S phase and
entry to the S phase (Fig. 1) and the distributions of DNA
content was observed.
membrane allows the permeability of PI with resultant image
of red nuclei in front of black background (Fig. 3b). The
potent derivatives (3a, 2b and 5a) from 4–quinolone series
resulted in higher apoptosis in their respective cell lines, as
represented by DAPI and PI stained images, with relation to
positive control, carboplatin.
DNA interaction studies
It was found from Figs. 4 and 5 that with the increase in HS–
DNA concentration there is increase in absorbance with resul-
tant no shift of band positions. Hence this hyperchromic effect
exhibited the non–covalent interaction of various derivatives
with HS–DNA. Against MCF–7 cells, the derivative 3a
showed maximum inhibitory activity along with higher DNA
interactions having Gibbs free energy Δ–18.19 KJ/mol.
Moreover, compound 3-bromo-6-nitro-1-(1-phenylethyl)-2-p-
tolylquinolin-4(1H)-one (2b) from 4–quinolone exhibited
higher inhibitory potential as compared to other derivatives
(9-fluoro-6-(6-fluoro-1H-indol-1-yl)-[1,3]dioxolo[4,5-
g]indolo[2,1-a]isoquinoline (4 l) from isoquinolines, 6-chloro-
2-(4-hydroxy-3-methoxyphenyl)quinoline-4-carboxylic acid
(3j)) against K–562 with Gibbs free energy Δ–18.09 KJ/mol.
Among the potent derivatives of HeLa cells (4i, 3b and 5a),
2-(3-bromophenyl)-6-chloroquinoline-4-carboxylic acid (3b)
resulted in maximum interactions with HS-DNA with Gibbs
free energy Δ–18.20 KJ/mol. Except the potent derivatives,
Microscopic analysis (using DAPI & PI)
The findings from the morphological analysis were in
close agreement with the anti-proliferative assay as well
as flow cytometry results. After 24 h of incubation, the
images under fluorescent microscope exhibited the apo-
ptotic changes within the cells like fragmented and con-
densed nuclei. In apoptotic cells, there is shrinkage and
fragmentations of nuclei occur whereas in viable cells,
the nuclear material is regular, oval shape with homo-
geneous chromatin. The images containing cells treated
with DAPI staining (Fig. 3a) revealed bluish intact nuclei in
the control whereas bright fragmented nuclei in treated cells
with different derivatives (4p, 3j, 3a, 4 l, 2b, 3b and 5a).
Similarly, PI treated viable cells revealed nuclei without stain-
ing because PI is impermeable to nuclear membrane.
However, in case of dead cells, the compromised nuclear

DARU J Pharm Sci
other derivatives were also studied for DNA binding interaction
and concluded that few of them resulted in higher interaction.
From the docking studies, the results were in agreement
with the experimental data. Furthermore, it was evident
that the potent compounds from all three series indicat-
ed strong hydrogen bond interactions with the minor
groove of DNA (Figs. 4 and 5).
It was revealed from the above analysis that few com-
pounds from isoquinolines, quinoline–4–carboxylic acid
and 4–quinolone, which were found potent and selective
inhibitors of APs and NPPs [10–12], are found here with
strong anticancer potential. The cytotoxic results obtained
from MTT assay confirmed that these compounds are se-
lective towards cancerous cells only. Anitcancer mecha-
nisms; cell cycle arrest and apoptosis induced by the iden-
tified compounds were confirmed by flow cytometry using
PI staining and by fluorescence microscopy using two nu-
cleus staining dyes, i.e., DAPI and PI. Furthermore, the
mechanism of cytotoxic compound was further determined
by DNA interaction studies and it was found that the most
potent inhibitors exhibited the non–covalent mode of inter-
action with the herring sperm –DNA.
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interests.

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