Ferrocene incorporated selenoureas as anticancer agents

Article abstract of DOI:10.1016/j.jphotobiol.2015.04.024

For a compound to be a best chemopreventive agent it should be a descent DNA binder and at the same time should be active against any of the three stages of carcinogenesis i.e. cancer initiation, cancer propagation and tumor growth. Most of the problems a

Full text of DOI:10.1016/j.jphotobiol.2015.04.024

Accepted Manuscript
Ferrocene incorporated selenoureas as anticancer agents
Raja Azadar Hussain, Amin Badshah, John M. Pezzuto, Nadeem Ahmed,
Tamara P. Kondratyuk, Eun-Jung Park
PII:
S1011-1344(15)00147-5
DOI:
http://dx.doi.org/10.1016/j.jphotobiol.2015.04.024
JPB 10021
Reference:
To appear in:
Journal of Photochemistry and Photobiology B: Bi-
ology
Received Date:
Revised Date:
Accepted Date:
26 February 2015
17 April 2015
20 April 2015
Please cite this article as: R.A. Hussain, A. Badshah, J.M. Pezzuto, N. Ahmed, T.P. Kondratyuk, E-J. Park, Ferrocene
incorporated selenoureas as anticancer agents, Journal of Photochemistry and Photobiology B: Biology (2015), doi:
http://dx.doi.org/10.1016/j.jphotobiol.2015.04.024
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Ferrocene incorporated selenoureas as anticancer agents
*1
1
2
2,3
Raja Azadar Hussain , Amin Badshah , John M. Pezzuto , Nadeem Ahmed , Tamara P.
2
2
Kondratyuk and Eun-Jung Park
1
. Co-ordination Chemistry Laboratory, Department of Chemistry, Quaid-i-Azam
University 45320, Islamabad, Pakistan.
2
3
. University of Hawaii at Hilo.
. Phytoharmone Laboratory, Department of Plant Sciences, Quaid-i-Azam University
4
5320, Islamabad, Pakistan.
Abstract
For a compound to be a best chemopreventive agent it should be a descent DNA binder and at
the same time should be active against any of the three stages of carcinogenesis i.e. cancer
initiation, cancer propagation and tumor growth. Most of the problems associated with
chemotherapy can be overcome if the chemopreventive agent is active against all the three stages
of cancer development. Cancer may be initiated by higher concentration of free radicals,
inflammating agents and phase I enzymes (Cytochrome P450) in the body. Cancer propagation
can be very efficiently controlled by inducing the phase II enzymes (glutathione S-transferases
(
GSTs), UDP-glucuronosyl transferases, and quinone reductases) in the body and cancer
termination depends on the killing of the faulty cells i.e. cytotoxic actions. This article reports
comprehensively the comparative DNA binding studies (with, cyclic voltammetry, UV-vis
spectroscopy and viscometry), antioxidant activities (DPPH scavenging), anti-inflammatory
activities (nitrite inhibition), phase I enzyme inhibition activities (aromatase inhibition), phase II
enzyme induction studies (quinone reductase induction) and cytotoxic studies against
1

neuroblastoma (MYCN2 and SK-N-SH), liver cancer (Hepa 1c1c7) and breast cancer (MCF-7)
of seventeen ferrocene incorporated selenoureas.
Key Words: Ferrocene incorporated selenoureas, enzyme inhibition and induction, antioxidant,
anti-inflammatory, anticancer.
1
. Introduction
Selenoureas are known for their free radical scavenging [1-6], enzyme inhibition [7-9],
anticancer activities, and DNA binding potencies [10-14]. Historically, scientific community was
reluctant of their use in bioorganic chemistry due to the presence of selenium which was
considered to be an absolute biological poison those days [15]. It is evident from the fact that
acylselenoureas were synthesized way back in 1937 [16] but the interest in their bioinorganic
chemistry developed after the findings that selenium is present in the bacterial enzymes formate
dehydrogenase and glycine reductase in 1971 [17]. Until now selenium derivatives have been
evaluated for their applications as anti-infective drugs (antifungal, antibacterial and antiviral),
photochemotherapeutic agents, antitumor agents, cytokine inducers/immunomodulators, enzyme
inhibition (nitric oxide synthase inhibitors, inosine monophosphate dehydrogenase inhibitors,
lipoxygenase inhibitors, urdpase and thymidylate synthase inhibitors, and tyrosine kinase and
iodothyronine deiodinase inhibitors), antioxidant defense enzymes (reduction of hydroperoxides-
GPx mimics, reduction of peroxinitriles, and lipid peroxidation), antihypertensive and
cardiotonic agents [18]. But there are no reports available for the systematic anticancer studies of
selenoureas which should start from activities against cancer initiation (antioxidant and anti-
inflammatory activities with phase I enzyme inhibition), and end up with activities against cancer
propagation (phase II enzyme induction) and tumors (cytotoxicity against cancer cell lines).
2

On the other end, ferrocene derivatives have shown their importance in the drug
development. Earlier attempts on ferrocene derivatives for their biological applications were
individualistic in nature and it was known in 1978 (compound 1) that they are active against
lymphocytic leukemia P-388 [19] (Chart 1, compound 1-10). Other similar type of findings have
shown the activity of ferrocene derivatives against lungs carcinoma (compound 2) [20], 70%
tumor growth inhibition (compound 3) against Ca-755 cell lines [21] and 100% inhibition of
solid (compound 4) tumor [22]. But detail studies have opened new horizons of research on
ferrocene. Following are some important developments in this regard:
•
Illudin M (compound 5a) (derived from mashroom) is active against prostate, ovarian,
pancreatic, renal and breast cancer. Ferrocene incorporated Illudin M (compound 5b) has
shown less toxicity for nonmalignant fibroblasts while more cancer selectivity and more
cell line specificity than parent Illudin M. This improvement was partially attributed to
the shielding of enone group by ferrocene due to the attack of glutathione [23].
Ferrocene incorporated tamoxifen (compound 6b) has shown better activities than simple
tamoxifen (compound 6a) against breast cancer cell line MCF-7 at a concentration of 1
µM [23-27].
•
•
Ferrocene incorporated nilutamides (compound 7b) derivatives have shown enhanced
activities than simple nilutamides (compound 7a) towards prostate cancer. Moreover this
work suggested that the introduction of ferrocene has very similar effect, which was
obtained by the introduction of an aromatic ring [28, 29].
•
Raloxifens (compound 8a) have shown activities against ovarian, cervical, lung, colon
and breast cancer cell lines. Incorporation of ferrocene to raloxifens (compound 8b) has
3

been reported to improve their cytotoxicity and one of the compounds have shown the
activity which is even better than cis-platin [30].
•
Ferrocene incorporated testosterone (compound 9b) and dihydrotestosterone (compound
1
0b) derivatives have shown better activities than simple testosterone (compound 9a)
and dihydrotestosterone (compound 10a) depending upon the position at which ferrocene
has been incorporated [26].
•
For the research work presented in this article, introduction of ferrocene moiety was also
necessary because of following reasons:
o Ferrocene is a beautiful electrochemical and spectroscopic marker which enabled
us to evaluate its biological applications (specially the DNA binding studies with
cyclic voltammetry and UV-vis spectroscopy [1, 11-14, 31, 32]).
o Because of its lipophilic character it can cross the blood brain barrier and several
activities inside the cells can be performed very easily.
o Moreover, it is nontoxic for the living organisms and its incorporation does not
have any negative impact inside the living organisms.
Cancer may simply be defined as, uncontrolled proliferation of the cells which may be
initiated by a change in the genetic makeup or DNA repair mechanism, propagated by the
growing of the mutated cells and finally ends up with tumor growth [33]. A chemopreventive
agent is any chemical compound which can prevent, block or reverse any of the three above
mentioned stages of carcinogenesis. One of the most preliminary criterion for any anticancer
agent is that, it should bind/interact with DNA [1]. Different compounds with different
functionalities can bind with the DNA differently. Drug-DNA interactions are mainly of two
types:
4

•
•
Covalent binding
Noncovalent binding
Covalent binding is generally exhibited by alkylating agents and intrastrand crosslinkers and
is characterized by irreversible nature of interaction, complete inhibition of the cellular processes
and cell death [34]. Noncovalent interactions are subdivided into external binding, intercalation
and groove binding. They are generally reversible and only cause the conformational changes to
interfere with normal DNA functions [35]. Different techniques are used for DNA binding
studies which include cyclic voltammetry (CV), UV-vis spectroscopy, fluorimetry, laser light
scattering and viscometry etc [31]. We have used CV for DNA binding studies of synthesized
FIS, mainly because of their best electrochemical signals due to the presence of ferrocene. The
results obtained from CV have been verified with UV-vis spectroscopy and viscometry.
Aerobically respirating organisms produce free radicals (superoxide, hydroxide,
peroxynitrile etc.) during metabolism processes mainly in mitochondria which are considered
responsible for Alzheimer’s disease, myocardial infarction, atherosclerosis, Parkinson’s disease,
autoimmune diseases, radiation injury, emphysema, sunburns and cancer initiation [1]. In case of
endotoxin shock these free radicals can kill the host but body has a self defense system in the
form of superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase, vitamins and
biological dyes to neutralize the damage of free radicals. In cancer patients however these free
radicals are produced in comparatively larger amounts therefore, if a compound which is aimed
for the treatment of cancer has free radical scavenging activity, then its value increases.
Lower NO levels are important to protect the body organs from damage. Ischemic
damage for example, is a condition in which blood supply to the tissue is restricted which causes
5

the shortage of the glucose levels and oxygen to disturb the metabolism. NO can also contribute
to the reperfusion injury i.e. after ischemic stress high levels of NO are produced which then
react with superoxide radicals to produce peroxynitrile radical. Although NO is an important
signaling molecule [36] but its higher levels have been related to obesity, cancer and diabetes. It
is also established that cancerous cells have higher concentrations of NO than the normal cells
[
37].
In this article we have combined the two functionalities i.e. ferrocene and selenoureas in a
new class of compounds called ferrocene incorporated selenoureas (FIS). We have discussed the
synthesis and chemical characterization (FT-IR, multinuclear NMR, and elemental analysis) of
six new compounds with comparative DNA binding (with cyclic voltammetry, UV-vis
spectroscopy and viscometry), antioxidant studies (DPPH scavenging activity), anti-
inflammatory activities (nitrite inhibition), phase I enzyme inhibition activities (aromatase
inhibition), phase II enzyme induction studies (quinone reductase induction) and cytotoxic
studies against neuroblastoma (MYCN2 and SK-N-SH), liver cancer (Hepa 1c1c7) and breast
cancer (MCF-7) of seventeen FIS.
2
. Material and Methods
Melting points were determined in a capillary tube using Gallenkamp (U.K) electrothermal
melting point apparatus. Infrared spectrum was taken on Thermoscientific NICOLET 6700 FTIR
-1
1
13
between 4000-400 cm . H and C spectra were recorded between 0-13 ppm and 0-210 ppm
respectively on Jeol JNM-LA 500 FT-NMR. Si(CH was used as internal reference. The
3 4
)
elemental analysis was performed using a LECO-932 CHNS analyzer while the Fe
6

concentrations were determined on an Atomic Absorption Spectrophotometer Perkin Elmer
380.
2
Commercial salmon DNA was solubalized in doubly distilled water to prepare a stock
-4
solution of 5.88 x 10 M from which working concentrations of DNA were prepared.
Concentration of stock solution was measured by UV absorbance at 260 nm using an epsilon
-1
-1
value of 6600 M cm . This DNA was protein free because A260/A280 > 1.8. Working solutions
for DNA binding studies were prepared by our previously reported method [13].
In CV studies a three electrode system was used consisting of working (platinum disc
2
electrode with a geometric area of 0.071 cm ) reference (Ag/AgCl) and auxiliary electrodes
(
platinum electrode with geometric area much greater than working electrode). Changes in peak
current and peak potential provided the information about drug-DNA binding constant and mode
of interaction respectively. The changes in peak current of the free drug (test compounds in
absence of DNA) by the addition of varying concentrations of DNA was used to evaluate the
drug-DNA binding constant with the help of following equation [38]:
log (1/[DNA]) = log K + log (I/I
ₒ
- I)
Eq 1
Where K is the binding constant and I
drug respectively.
ₒ
and I are the peak currents of free drug and DNA bound
For the measurement of binding site size (s) following equation was used [39]:
b
C /C
f
= K[(free base pairs)/s]
Eq 2
Where s is the binding site size in terms of base pair, K is the binding constant, C
f
is the
concentration of free species and C
b
represents concentration of drug-DNA bound species.
7

Considering the concentration of DNA in terms of nucleotide phosphate, the concentration of
DNA base pair will be taken as [DNA base pair]/2 and Eq 2.4 will be written as [31]:
b
C /C
f
= K[(DNA base pair)/2s]
Eq 3
The value of C
b
/C
f
is equal to (I - I/I) which are the values of experimental peak currents.
ₒ
For the determination of diffusion coefficient of free and DNA bound drug following form of
Randles-Sevcik Equation was used [32]:
5
3/2
*
1/2 1/2
I
pa = 2.69 x 10 n A C
ₒ
D
ₒ
ʋ
Eq 4
*
-3
Where Ipa is the anodic peak current in ampere, C
ₒ
is the reductants’s concentration in molcm ,
-1
2
ʋ is the scan rate in volts , A is the geometric area of the electrode in cm , n is the number of
2
-1
electrons involved in the process and D is the diffusion coefficient in cm s . Same procedure
ₒ
was followed for the interaction of surfactants with FIS.
Absorption spectra were recorded on Shimadzu 1800 spectrophotometer. First the spectra
for the solution of pure compounds were recorded between 220-800 nm in the absence of DNA
and then in the presence of different concentration of DNA. Equal amount of DNA was added to
both reference and sample cells in order to avoid the appearance of its peak at 260 nm.
The Ubbelohde viscometer was used for viscosity measurements at room temperature (25
±
1 °C). Flow time was measured with a digital stopwatch. Flow time measurements were made
in triplicate for the measurement of average flow time. Data were presented as relative specific
viscosity (η/ η₀), vs. binding ratio ([compound]/[DNA]) where η is the viscosity of DNA in the
presence of complex and η₀ is the viscosity of DNA alone.
8

Reducing abilities of all the FIS were determined by monitoring the decrease in the
absorbance (with micropipette reader or UV-vis spectrophotometer) at 517 nm of 1,1-
diphenylpicrylhydrazyl radical to form 1,1-diphenylpicrylhydrazine. Scavenging activity values
were calculated by following equation:
Scavenging activity (%) = Aₒ-A/Aₒ x 100
Eq 5
Where Aₒ is the absorbance of DPPH alone and A is the absorbance of DPPH with different FIS.
Nitrite inhibition assay was performed according to a previously reported method [33].
4
According to this method, inside a 96-well plate, 10 x 10 cells/plate of RAW 264.7 cells
(
murine leukemia) were seeded in 10% FBS containing DMEM (Dulbecco's Modified Eagle
Medium) for 24 h. Then the media was replaced with 1% FBS-containing (190 µL) phenol red
free DMEM and the cultured cells were treated with 10 µL of test samples in 10% DMSO for 15
-1
min. Then each plate was treated with 1 µgmL of LPS for 20 h. Quantitative estimation of
nitrite (which is the major oxidation product of NO) was carried out by reacting the incubation
media with Griess reagent (90 µL of 1% sulfanilamide in 5% phosphoric acid, and 90 µL of N-
(
1-Naphthyl)ethylenediamine). Absorbance was scanned at 540 nm according to Eq 5 for
percentage inhibition values.
For aromatase inhibition activity [33], test samples of synthesized compounds were
preincubated with NADPH generating system at 37 °C for 10 min. Further incubation for 30 min
at 37 °C was carried out before quenching with NaOH after adding the enzyme and substrate to
the plates which contained NADPH generating system. The addition of NaOH terminates the
reaction and after complete termination the plates were incubated for further 2 h to improve the
signal to noise ratio. Fluorescence measurement was carried out at 485 and 530 nm for triplicate
readings of five different concentrations of the test samples using Letrozole as a positive control.
9

QR (quinone reductase) assay was carried out with hepa 1c1c7 (murine hepatoma) cells
4
which were plated with 200 µL per well with a cell density of 0.5 x 10 cells/mL in MEM-α
(
minimum essential medium) without ribonucleosides or deoxyribonucleosides, supplemented
with antimycotic/antibiotic and 10% FBS for 24 h in a carbon dioxide incubator. After 24 h
medium was replaced with 190 µL of fresh medium and 10 µL of test samples were added for a
final concentration of 4 ppm. After 48 h of incubation, cell membrane was permeabilized with
digitonin and enzyme activity was measured by the reduction of 3-(4,5-dimethylthiazo-2-yl)-2,5-
diphenyltetrazolium bromide (MTT) to a blue formazan. 4-bromoflavone was used as a positive
control and production was measured by absorption at 595 nm [40] with a total protein assay
using crystal violet staining run, in parallel [41]. Test samples with an induction ratio > 2 were
tested in a 5 fold serial dilutions to determine the CD values [33].
The cytotoxic activities of the test compounds were carried out against neuroblastoma
cell lines MYCN-2 and SK-N-SH, hepa 1c1c7 liver carcinoma cell line, human breast cancer cell
line MCF-7. Briefly, 10 µL of test compounds in all the three series were filled in 96-well plate
4
using 10% DMSO in phosphate buffered saline along with 190 µL of cells (5 x 10 cells/mL) and
incubated at 37 °C for 72 h in a carbon dioxide incubator. After quenching the incubation with
5
0 µL of cold 20% trichloroacetic acid, the cells were washed, air dried and stained with 0.4%
SRB in 1% acetic acid for 30 min at room temperature. Wells were then washed 4 times with 1%
acetic acid solution and plates were dried for 12 h. Bound dye was solubalized in trisbase (200
µL, 10 mM, pH 10) for 10 min on gyratory shaker. For the measurement of optical density at 515
nm, microplate reader (bio-tek) was used which gave information about percent survival. Zero
day control was performed in each case with all the procedure mentioned above [33].
10

Ferrocene, anilines, sodium nitrite, diethyl ether, acetone, DMSO, Pd-charcoal,
carboxylic acid chlorides and hydrazine were purchased from Sigma Aldrich. Ferrocenyl anilines
were synthesized by a procedure reported by our group previously [42].
3
3
. Experimental
.1 General procedure
For the synthesis of FIS, respective carboxylic acid chloride was reacted with potassium
selenocyanate in 1:1 using dried acetone as a solvent inside a two necked round bottom flask
under constant magnetic stirring. This resulted in the formation of white precipitates of
potassium chloride with yellow isoselenocyanate in the solution. The reaction was carried out for
3
h to completion and then respective ferrocenylphenylaniline was added (1:1 with acid chloride
and KSeCN) (Scheme 1). The reaction took almost 4 h for completion and the progress of
reaction was monitored with the help of thin layer chromatography. The resulting orange colored
solution was mixed with cold water under constant magnetic stirring. This removed the
potassium chloride suspension and precipitated the product which was then filtered, dried and
washed with n-hexane and methanol [1, 10-14, 43-46].
3
.1.1 1-(2-methylbenzoyl)-3-(4-ferrocenylphenyl)selenourea (A-1)
-1
Yield: 63%; Decomposition temperature: 130-132 °C; FT-IR (cm ): 3400-3200 (NH
stretching broad), 3013 (Aromatic-H stretching), 2968 (Aliphatic-H), 1666 (C=O stretching),
1
597, 1525, 1511 (C=C stretching of aromatic ring), 1365 (CH bending) 1229 (C=Se
3
1
stretching); H-NMR (300 MHz, Benzene, δ (ppm): 13.41 (s, 1H, CSeNH), 9.10 (s, 1H, CONH),
7
.98-6.67 (m, 8H, Aromatic), 4.55 (t, 2H, J 1.8 Hz, Cp-Ph), 4.23 (t, 2H, J 1.8 Hz, Cp-Ph), 4.00
1
3
(
s, 5H, Cp), 2.37 (s, 3H, CH ); C-NMR (75 MHz, Benzene, δ (ppm): 178.0 (1C), 169.0 (1C),
3
11

1
1
38.5 (1C), 133.4 (1C), 126.1 (2C), 126.0 (2C), 125.5 (1C), 125.1 (1C), 123.5 (1C), 122.0 (1C),
21.7 (1C), 121.3 (1C), 84.6 (1C), 69.9 (5C), 69.7 (2C), 66.3 (2C), 19.9 (1C); Anal. Calcd. for
C
25
H
22
2
N OFeSe: C 59.88, N 5.51, H 4.39, Fe 11.17; Found: C 59.58, N 5.29, H 3.99, Fe
1
0.99%.
3
.1.2 1-(3-methylbenzoyl)-3-(4-ferrocenylphenyl)selenourea (A-2)
-1
Yield: 77%; Decomposition temperature: 141-143 °C; FT-IR (cm ): 3400-3200 (NH
stretching broad), 3010 (Aromatic-H stretching), 2968 (Aliphatic-H), 1664 (C=O stretching),
1
592, 1527, 1490 (C=C stretching of aromatic ring), 1367 (CH bending), 1231 (C=Se
3
1
stretching); H-NMR (300 MHz, Benzene, δ (ppm): 13.08 (s, 1H, CSeNH), 10.30 (s, 1H,
CONH), 7.52-6.14 (m, 8H, Aromatic), 4.55 (t, 2H, J 2.1 Hz, Cp-Ph), 4.23 (t, 2H, J 1.8 Hz, Cp-
1
3
Ph), 4.21 (s, 5H, Cp), 2.29 (s, 3H, CH
3
); C-NMR (75 MHz, Benzene, δ (ppm): 179.2 (1C),
63.6 (1C), 136.5 (1C), 134.1 (1C), 127.0 (1C) 126.9 (1C) 126.7 (2C), 126.1 (2C), 125.6 (1C),
23.9 (1C), 122.0 (1C) 114.4 (1C), 84.0 (1C), 69.8 (5C), 69.7 (2C), 66.6 (2C), 20.1 (1C); Anal.
1
1
Calcd. for C25
Fe 11.08%.
H
22
2
N OFeSe: C 59.88, N 5.51, H 4.39, Fe 11.17; Found: C 59.33, N 5.41, H 4.32,
3
.1.3 1-(4-methylbenzoyl)-3-(4-ferrocenylphenyl)selenourea (A-3)
-1
Yield: 83%; Decomposition temperature: 151-153 °C; FT-IR (cm ): 3400-3200 (NH
stretching broad), 3012 (Aromatic-H stretching), 2967 (Aliphatic-H), 1680 (C=O stretching),
1
594, 1530, 1493 (C=C stretching of aromatic ring), 1365 (CH bending), 1241 (C=Se
3
1
stretching); H-NMR (300 MHz, Benzene, δ (ppm): 13.31 (s, 1H, CSeNH), 9.47 (s, 1H, CONH),
8
.02-7.32 (m, 8H, Aromatic), 4.78 (t, 2H, J 1.8 Hz, Cp-Ph), 4.35 (t, 2H, J 2.1 Hz, Cp-Ph), 4.04
1
3
(
s, 5H, Cp) 2.41 (s, 3H, CH ); C-NMR (75 MHz, DMSO, δ (ppm): 178.1 (1C), 167.7 (1C),
3
12

1
8
5
36.0 (1C), 135.7 (1C), 131.1 (1C), 128.3 (2C), 125.2 (2C), 122.6 (2C), 120.9 (1C), 114.0 (2C),
4.4 (1C), 69.4 (5C), 69.3 (2C), 66.0 (2C), 20.6 (1C); Anal. Calcd. for C25
H
22
2
N OFeSe: C
9.88, N 5.51, H 4.39, Fe 11.17; Found: C 59.73, N 5.43, H 4.01, Fe 11.00%.
3
.1.4 1-(2-chlorobenzoyl)-3-(4-ferrocenylphenyl)selenourea (A-4)
-1
Yield: 64%; Decomposition temperature: 134-136 °C; FT-IR (cm ): 3400-3200 (NH
stretching broad), 3009 (Aromatic-H stretching), 1662 (C=O stretching), 1598, 1526, 1500 (C=C
1
stretching of aromatic ring), 1246 (C=Se stretching); H-NMR (300 MHz, Acetone, δ (ppm):
1
2.92 (s, 1H, CSeNH), 10.01 (s, 1H, CONH), 8.01-7.15 (m, 8H, Aromatic), 4.54 (t, 2H, J 2.1 Hz,
1
3
Cp-Ph), 4.30 (t, 2H, J 1.8 Hz, Cp-Ph), 4.17 (s, 5H, Cp); C-NMR (75 MHz, Acetone, δ (ppm):
1
1
78.0 (1C), 167.6 (1C), 136.5 (1C), 136.0 (1C), 134.1 (1C), 133.8 (1C), 133.0 (1C), 132.0 (1C),
26.9 (2C), 126.0 (2C), 123.4 (1C), 118.6 (1C), 84.5 (1C), 69.7 (5C), 69.0 (2C), 66.1 (2C); Anal.
Calcd. for C24
H
19
2
N OFeSeCl: C 55.25, N 5.37, H 3.64, Fe 10.70; Found: C 55.21, N 5.02, H
3
.51, Fe 10.63%.
.1.5 1-(3-chlorobenzoyl)-3-(4-ferrocenylphenyl)selenourea (A-5)
3
-1
Yield: 79%; Decomposition temperature: 136-137 °C; FT-IR (cm ): 3400-3200 (NH
stretching broad), 3002 (Aromatic-H stretching), 1662 (C=O stretching), 1598, 1528, 1513 (C=C
1
stretching of aromatic ring), 1242 (C=Se stretching); H-NMR (300 MHz, Acetone, δ (ppm):
1
3.29 (s, 1H, CSeNH), 9.16 (s, 1H, CONH), 7.97-6.58 (m, 8H, Aromatic), 4.56 (t, 2H, J 1.8 Hz,
1
3
Cp-Ph), 4.24 (t, 2H, J 1.5 Hz, Cp-Ph), 4.01 (s, 5H, Cp); C-NMR (75 MHz, Acetone, δ (ppm):
1
1
79.1 (1C), 165.1 (1C), 138.7 (1C), 134.6 (1C), 133.0 (1C) 130.1 (2C), 129.2 (1C), 126.9 (1C),
26.8 (1C), 125.1 (2C), 123.2 (1C), 120.9 (1C), 84.5 (1C), 69.2 (5C), 68.8 (2C), 66.7 (2C); Anal.
13

Calcd. for C24
H
19
2
N OFeSeCl: C 55.25, N 5.37, H 3.64, Fe 10.70; Found: C 54.89, N 5.19, H
3
.55, Fe 10.54%.
3
.1.6 1-(4-chlorobenzoyl)-3-(4-ferrocenylphenyl)selenourea (A-6)
-1
Yield: 81%; Decomposition temperature: 159-160 °C; FT-IR (cm ): 3400-3200 (NH
stretching broad), 3021 (Aromatic-H stretching), 1678 (C=O stretching), 1598, 1540, 1505 (C=C
1
stretching of aromatic ring), 1268 (C=Se stretching); H-NMR (300 MHz, Acetone, δ (ppm):
1
2.89 (s, 1H, CSeNH), 11.94 (s, 1H, CONH), 8.05-7.52 (m, 8H, Aromatic), 4.75 (t, 2H, J 1.8 Hz,
1
3
Cp-Ph), 4.33 (t, 2H, J 1.8 Hz, Cp-Ph), 4.02 (s, 5H, Cp); C-NMR (75 MHz, Acetone, δ (ppm):
1
1
78.4 (1C), 169.0 (1C), 136.4 (1C), 136.0 (1C), 131.4 (1C) 130.7 (2C), 129.3 (2C), 126.3 (2C),
26.0 (2C), 125.8 (1C), 84.3 (1C), 69.3 (5C), 69.2 (2C), 69.0 (2C); Anal. Calcd. for
C
24
H
19
2
N OFeSeCl: C 55.25, N 5.37, H 3.64, Fe 10.70; Found: C 54.88, N 5.29, H 3.39, Fe
1
0.41%.
4
. Results and Discussion
1
All the compounds are orange in color and were synthesized in solid state. In H NMR spectra
(
Figure S-1) there are three different types of protons i.e. –NH protons, aromatic protons and
protons of the ferrocene ring in all the compounds. Maximum downfield protons are the ones
which are between the phenyl ring and C=Se groups and provides a singlet at ~ 13 ppm in all the
compounds because of the intramolecular hydrogen bonding. The protons between the carbonyl
and C=Se in all the compounds are comparatively less deshielded and appears at ~ 10 ppm as a
singlet. Aromatic protons are available between 7-8 ppm whereas five protons of unsubstituted
cylopentadienyl (Cp) moiety give a singlet at 4.11 ppm for both the compounds. Substituted Cp
ring provides two triplets with a coupling constant value of 1.8 Hz downfield from the singlet of
14

1
3
unsubstituted Cp in all the compounds [1, 10-14, 43-46]. In C NMR (Figure S-2) maximum
downfield carbon is the carbon attached with selenium and appears as a weak signal at ~ 179
ppm whereas carbonyl carbon is available at ~ 162 ppm. Aromatic carbons give their peaks
between 120-140 ppm and unsubstituted Cp gives a singlet at ~ 66 ppm. In all the compounds
substituted carbon of the Cp ring gives a peak at ~ 84 ppm whereas four other carbons of the
substituted Cp ring give two peaks at ~ 69 ppm [1, 10-14, 43-46].
-1
In FT-IR all the compounds provide broad peaks between 3200-3400 cm owing to the
-1
intramolecular hydrogen bonding. Aromatic-H provide their signals slightly above 3000 cm
-1
whereas carbonyl carbons are available at ~ 1660 cm for all the compounds. Aromatic rings
-1
yield their peak in their respective region and C=Se is present at ~ 1200 cm for all the
compounds [1, 10-14, 43-46].
Calculated and found percentages of carbon, hydrogen, nitrogen and iron are in close
agreement with each other which confirms the purity of the synthesized compounds. We have
already published the single crystal XRD structures of a few FIS (Figure 1) in our previous
publications [12, 13] but details cancer studies are the main concern in this manuscript.
4
4
.1 Carcinogenesis
.1.1 DNA binding studies
In CV all the synthesized FIS provide couple of well defined redox peaks between 0-1V in a
00% reversible electrochemical process (Figure 2a) by using 1mL of 1.5 M KCl as supporting
1
electrolyte.
The reversibility of the process was evident by:
15

•
•
•
Absence of a shift in peak potentials with a variation in scan rate.
∆E = Epc - Epa for one electron system gives a value of almost 59 mV.
p
Anodic and cathodic peak current ratios (Ipa/Ipc) of about one [13].
DNA binding study of a representative compound A-3 is explained here with CV. In CV
A-3 provides couple of well defined redox peaks which show 100% reversibility according to the
criteria described above (Figure 2a). By the addition of DNA to the free A-1 (by keeping the
dilution constant) there is a negative shift in the peak potential of A-3-2 µMDNA adduct relative
to the free A-3 (Figure 2b). This negative shift in the peak potential represents the electrostatic
mode of interaction between the negatively charged phosphate backbone of the DNA and A-3
which makes the oxidation of A-3 easy. Decrease in the current is attributed to the slow diffusion
of A-3-DNA adducts relative to free A-3 which was also confirmed by the low diffusion
coefficient of adducts relative to the free A-3 (Figure 2c). This uniform decrease in the current
with different DNA concentrations was scanned for the determination of A-3-DNA binding
constant according to the Eq. 1 above (Figure 2d). Lower values of the binding site (Eq. 2) also
confirm the electrostatic mode of interaction (Figure 2e). Similar type of electrostatic interaction
was confirmed by hyperchromism in the absorbance of DNA solution by the addition of different
concentrations of A-3 to it in UV-vis spectroscopy. Same amounts of A-3 were also added in the
blanks to avoid its absorbance in the same region. This hyperchromism is attributed to the
neutralization of charges on the phosphate backbone of the DNA which causes the unwinding of
DNA double helix to cause the conformational changes (Figure 3a). Moreover decrease in the
relative viscosity of the DNA also confirms the electrostatic mode of interaction (Figure 3b) [1,
1
0-14]. Data for all other compounds have been presented in Table 1 which reveals that, para
substituted derivatives generally show higher DNA binding constants than that of meta and ortho
16

substituted derivatives. Diffusion coefficients of drug-DNA adducts for all the compounds are
lower than the free drugs and lower values of binding site sizes are also in favor of electrostatic
interactions. Magnitude of DNA binding constants reported in this paper are better than
ferrocene [31], nitrophenyl ferrocene [32], ferrocene incorporated thioureas [47], cis-platin [48]
and most of the closely related platinum, copper, nickel and zinc complexes [49] but are inferior
than the universal intercalators like ethidium [50] and proflavin [51]. These DNA binding studies
provided us very good preliminary information about possible chemopreventive nature of FIS.
4
.1.2 DPPH scavenging activity
Here we present the results for DPPH scavenging activities by synthesized FIS, using ascorbic
acid as a positive control. Figure 4 displays the results for antioxidant effects of FIS to convert
the DPPH to 1,1-diphenylpicryl hydrazine. Generally, the compounds which have electron
withdrawing groups attached to them are more active than those which have electron donating
groups because the free radical formed are more stabilized by the electron withdrawing groups.
This uniform behavior originates because of the antioxidant effect of the –NH groups present in
the structures of the synthesized FIS, however there are two –NH groups and both of them
compete with each other to cause the discrepancies in the structure and activity relationship
(
Chart 2). Discrepancy in case of 4-methylphenyl and 2-methylphenyl derivatives may be
because of the special role played by the Se atom. FIS which show more than 50% inhibition of
DPPH were scanned for IC50 values (Figure 5a) with the help of UV-vis spectroscopy (Figure
5
b).
4
.1.3 Nitrite inhibition activity
17

Raw 264.7 (tumor tissue of male mouse with murine leukemia) cells were used to determine the
NO inhibition of synthesized FIS using LNMMA (L-N-monomethyl arginine citrate) as a
positive control. Figure 6 shows the NO inhibition activity of the synthesized FIS which is even
better than the positive control for more than 10 compounds. The compounds which presented
more than 50% inhibition were scanned for IC50 values as well (Figure 7a). Although a
generalization cannot be developed on the basis of structure but higher activity of ortho
substituted derivatives (2-fluorophenyl, 2-chlorophenyl, 2-bromophenyl and 2-methoxyphenyl)
may be due to the formation of more active byproduct presented in Figure 7b. Whereas higher
activity of toulyl substituted derivatives may be because of their higher permeability through the
cell membrane but conformation to this hypothesis needs more detail study by the biochemists
and biotechnologists.
4
.1.4 Enzymatic activities
In terms of carcinogenesis, those compounds are good anticancer agents who can inhibit phase I
enzymes (cytochrome P450) and induce the phase II enzymes (glutathione S-transferases (GSTs),
UDP-glucuronosyl transferases, and quinone reductases). The reason behind is that phase I
enzymes favor the production of reactive oxygen species (ROS) which are initiator of the cancers
whereas phase II enzymes detoxify the ROS and effects caused by them to stop the propagation
of the cancer. Phase I (aromatase inhibition) and phase II (quinone reductase induction) activities
of the synthesized FIS have been presented below to have the glimpse about their
chemopreventive nature.
4
.1.4.1 Aromatase inhibition activity
Aromatase is the enzyme which controls a key step in the biosynthesis of estrogen. Lower
concentrations of estrogen are required to fight the breast cancer, ovarian cancer and lungs
18

cancer. Recent investigations have shown that aromatase inhibitors are even better than the
tamoxifen for the treatment of breast cancer [52].
Figure 8a puts on show the aromatase inhibition activities of the synthesized FIS.
Although the synthesized FIS inhibit aromatase but their activity is inferior to the positive
control however some activities are better than cis-platin. The best activity in this regard was
presented by the precursor aniline (paraferrocenylphenylaniline) which shows 100% inhibition of
aromatase (even more than the positive control). The compounds which show more than 50%
inhibition of aromatase have been evaluated for IC50 values (Figure 8b).
4
.1.4.2 Quinone reductase induction activity
Quinone reductase induction activity was carried out inside hepa 1c1c7 (murine hepatoma) cells.
For this activity induction ration of QR1 (IR of QR1) are the values which represent the specific
enzyme activity of agent treated cells compared with a DMSO treated control. And the
compounds which have an induction ratio of more than 2 are further evaluated for concentration
dose (CD) experimentation. CD is the concentration of a chemical under investigation which
doubles the QR activity. Figure 9 presents the results of QR induction for the synthesized
compounds and it is evident from the results that most the compounds have an induction ratio of
greater than 2 which makes them a very good candidate for CD experimentation.
CD (µM) (Figure 10) values reveal that most of the compounds have better activities than
previously reported unsymmetrical diphenyl selenourea and all of them are better than
unsymmetrical dimethyl selenourea [1] (Chart 3). Both the aromatase inhibition and quinone
reductase induction activities prove that the synthesized FIS have the ability to stop the cancer
initiation and cancer propagation [53]. In terms of enzymology these compounds are even better
19

than cis-platin, in a way that cis-platin only kills the cancerous cells by covalent binding with
DNA (because of its cytotoxic effect) and does not have any importance to stop the initiation of
the cancer or to equip the body with the enzymes which can themselves fight the cancer.
4
.1.5 Activities against the cancer cell lines
Cytotoxic activities have been carried out against four cancerous cell lines namely
neuroblastoma cell lines (MYCN2 and SK-N-SH), lungs cancer cell line (hepa 1c1c7) and breast
cancer cell line MCF-7 to further investigate the chemopreventive nature of the synthesized FIS.
4
.4.5.1 Neuroblastoma
Neuroblastoma is a type of malignant extracranial cancer of the childhood between the age of 1-
years [54]. There are 650 cases/year in USA and 100 cases/year in UK. This cancer is caused
by the over expression of a protein called NMYc which is controlled by a gene called MYCN
neuroblastoma myelocytomatosis). This protein has an important function in the transfer of the
5
(
genetic information by binding with the DNA. It is believed that if over expression of NMYc is
controlled by inhibiting MYCN then neuroblastoma will be controlled [55]. Table 2 displays the
data for the compounds scanned against MYCN. The data very clearly presents that synthesized
FIS can kill up to 70-90% of cancerous cells. Although few exceptions are there but mostly ortho
substituted derivatives have shown the highest activities.
Another neuroblastoma cell line SK-N-SH was also scanned for cytotoxic activities with
the help of the synthesized FIS but data for only the most active compounds have been presented
in Table 2. The activity against this cell lines is comparatively too much inferior than MYCN2.
4
.4.5.2 Cytotoxicity against hepa 1c1c7 and liver cancer
20

th
Liver cancer is the 5 most diagnosed cancer of the world and is mostly caused by hepatitis B
and hepatitis C. The synthesized FIS have shown 27-37% cell killings against this cancer cell
line hepa1c1c7. Table 2 presents data for the most active FIS.
4
.4.5.3 Cytotoxicity against MCF-7 and breast cancer
Breast cancer is 22.7% of all the cancers in the world and in 2008 13.7% of cancer deaths were
caused because of this cancer. It is 100 time more common in females than in males [56]. Table
2
presents the data for the synthesized FIS against breast cancerous cell line MCF-7. Ortho
substituted derivatives once again have shown the highest activities as was observed against
neuroblastoma.
Conclusions
We have successfully reported the chemopreventive nature of ferrocene incorporated selenoureas
(
FIS) against cancer initiation, cancer propagation and cancer termination. We found that FIS are
good DPPH scavengers in comparison with ascorbic acid although their IC50 values are slightly
inferior. Anti-inflammatory action of some FIS is even better than the positive control (L-
NMMA). FIS reported in this article can inhibit aromatase (phase I enzyme) and can induce the
quinone reductase (phase II enzyme) in the body and these two enzymatic potencies are even
better than cis-platin. Cancer termination of the FIS is proved by their cytotoxic activities against
neuroblastoma, hepa 1c1c7 and MCF-7 cancerous cell lines. Mostly those FIS which had ortho
substitution on the phenyl ring attached with the carbonyl carbon were found the most active.
Corresponding Author
Prof. Amin Badshah: aminbadshah@yahoo.com, +923009780374.
21

Acknowledgements
I am thankful to the Higher Education Commission, H-9, Islamabad, Pakistan for research
funding.
22

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