IN VITRO ANTIPROLIFERATIVE AND IN SILICO ACTIVITY OF RUBIADIN ISOLATED FROM ROOTS OF Rubia Cordifolia

Abstract

Background: Rubia cordifolia Linn.[ Rubiaceae], commonly known as Indian Maddar and Manjistha, is used as medicine for treatment of various ailments in Traditional System of Medicine of India. Purpose: To isolate rubiadin and evaluate in vitro antiproliferative activity and in silico method. Material and Methods: Rubiadin was isolated from the roots of R.cordifolia. Rubiadin was characterized by IR, 1H-NMR, 13C-NMR and Mass spectrum. Standardization of rubiadin was done also by HPLC fingerprinting. In vitro antiproliferative activity was done using HeLa cell lines by MTT assay at different concentrations ranging from 20-100 μg/ml in triplicate and in silico docking studies using enzyme EGFR tyrosine kinase. Results: Fingerprinting of isolated rubiadin were done by HPLC method. The IC50 value was found to be 56.63 ± 0.025 μg/ml in in vitro antiproliferative activity in HeLa cell lines. Rubiadin was subjected to molecular docking studies for the inhibition of the enzyme EGFR tyrosine kinase, which is one of the targets for inhibition of cancer cells. It has shown -7.07 kJ mol-1 binding and -7.12 kJ mol-1 docking energy with two hydrogen bonds. Conclusion: Rubiadin has shown to possess in vitro antiproliferative activity and in silico studies.

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IN VITRO ANTIPROLIFERATIVE AND IN SILICO ACTIVITY OF RUBIADIN ISOLATED
FROM ROOTS OF Rubia Cordifolia
PADMAA M PAARAKH*1, DILEEP CHANDRA SREERAM2, SHRUTHI SD3, SUJAN GANAPATHY PS4,
VEDAMURTHY AB5
1Dept of Pharmacognosy, The Oxford College of Pharmacy, Hongasandra, Bangalore, Karnataka.2R & D[Phytochemistry], Natural
Remedies Private limited, Bangalore.3Microbiology and Cell Biology Department, Indian Institute of Science, Bangalore, Karnataka.4
Research and Development Centre, Olive Life Sciences Pvt. Ltd., Neelamangala, Bangalore, Karnataka.5 P.G. Department of Studies
in Biotechnology and Microbiology, Karnataka University,Dharwad, Karnataka.Email:padmaparas@hotmail.com
Received - 05.12.2015; Reviewed and accepted -18.12.2015
ABSTRACT
Background: Rubia cordifolia Linn.[ Rubiaceae], commonly known as Indian Maddar and Manjistha, is used as medicine for treatment of various ailments in Traditional
System of Medicine of India. Purpose: To isolate rubiadin and evaluate in vitro antiproliferative activity and in silico method. Material and Methods: Rubiadin was isolated
from the roots of R.cordifolia. Rubiadin was characterized by IR, 1H-NMR, 13C-NMR and Mass spectrum. Standardization of rubiadin was done also by HPLC fingerprinting.
In vitro antiproliferative activity was done using HeLa cell lines by MTT assay at different concentrations ranging from 20-100 µg/ml in triplicate and in silico docking studies
using enzyme EGFR tyrosine kinase. Results: Fingerprinting of isolated rubiadin were done by HPLC method. The IC50 value was found to be 56.63 ± 0.025 µg/ml in in vitro
antiproliferative activity in HeLa cell lines. Rubiadin was subjected to molecular docking studies for the inhibition of the enzyme EGFR tyrosine kinase, which is one of the
targets for inhibition of cancer cells. It has shown -7.07 kJ mol-1 binding and -7.12 kJ mol-1 docking energy with two hydrogen bonds. Conclusion: Rubiadin has shown to
possess in vitro antiproliferative activity and in silico studies.
Key words: In vitro antiproliferative activity; in silico docking studies; Isolation; Rubiadin; Rubia cordifolia.
INTRODUCTION
Cancer is one of the highest impacting diseases worldwide with
significant morbidity and mortality rates. The current known
therapies are based on radio and chemotherapies and although
in many cases, the patients have their health re-established, the
treatment is very painful since their immunological system is
severely compromised, because these procedures are not cells
selective [1].Substantial advances have been made in
understanding the key roles of receptor tyrosine kinase (RTK) in
the signalling pathways that govern fundamental cellular
processes, such as proliferation, migration, metabolism,
differentiation and survival. In the normal cells RTK activity is
tightly controlled. When they are mutated or structurally altered,
they become potent oncoproteins which leads to abnormal
activation of RTKs in transformed cells has been shown to be
causally involved in the development and progression of many
human cancers [2,3].
The cost of treatment is very high and with lot of side effects. In
order to find new natural sources that are biologically active
substances from plants have acquired immense attention. A
number of studies have been carried out on various plants,
vegetables and fruits because they are rich sources of
phytoconstituents which prevent free radical damage thereby
reducing risk of chronic diseases viz., cancer, cardiovascular
diseases etc. This beneficial role of plants has led to increase in
the search for newer plant based sources for the treatment of
diseases like cancer. One such plant is Rubia cordifolia Linn.
Rubia cordifolia Linn.[ Rubiaceae], commonly known as Indian
Maddar and Manjistha, is used as medicine for treatment of
various ailments in Traditional System of Medicine fairly
throughout the greater part of India. Traditionally the plant has
been recommended as it is useful as bitter, acrid, astringent,
thermogenic, antidysenteric, antiinflammatory, antipyretic,
analgesic, anodyne, anthelmintic, antiseptic, constipating,
diuretic, galactopurifier, febrifuge, rejuvenating and tonic [4]. It is
scientifically proved to be used as antiacne,
anticancer,antidiabetic, antimicrobial,anticonvulsant, anti-
inflammatory,wound healing, antiulcer, antiviral, antioxidant,
antistress, antiplatelet activating activity, gastroprotective,
hepatoprotective, immunomodulatory and radioprotection
activities[5].
The tyrosine kinases inhibitor activity of rubiadin is not studied
till date.The aim of the present study is to isolate rubiadin from
dried roots of Rubia cordifolia and perform in silico activity and
in vitro MTT assay to prove its antiproliferative activity.
MATERIAL AND METHODS
Drugs and Chemicals
DMEM medium (GIBCO), heat-inactivated fetal bovine serum
(FBS), trypsin, ethylene-diaminetetraacetic acid (EDTA),PBS
and MTT were purchased from Hi media and Sigma Chemicals.
All chemicals and reagents used in this study were at least of
analytical grade.
Plant Material
The dried roots of Rubia cordifolia were collected, identified and
authenticated by Botanist from Natural Remedies Private
Limited, Bengaluru, Karnataka. A voucher specimen was
deposited in the Herbarium of Department of Pharmacognosy,
The Oxford College of Pharmacy, Bangalore. The roots were
dried under normal environmental conditions. The dried roots
were powdered and stored in a closed container for further use.
Extraction and Isolation Procedure
Extract the dried roots of R.cardifolia (3 kg) with methanol (4 l)
by refluxing for 1 h. Filter and repeat the process of reflux by
adding methanol (4 l) to the marc and filter. Distill the combined
filtered methanol extract to remove the solvent and dry the
concentrate under vacuum to get a thick green paste (250 g).
Carry out liquid-liquid partitioning with ethyl acetate and water
(1:1) three times. Concentrate the ethyl acetate layer under
vacuum and dissolve the extractive (110 g) in 100 ml methanol
and adsorb over 100 g of silica gel (60-120 mesh grade). Dry
the adsorbed material in vacuum oven at temperature not more
than 70o to remove solvent. Charge the adsorbed material on a
silica column (~1 kg; 60-120 mesh grades). Elute the column by
gradient elution using n-hexane with increasing percentage of
ethyl acetate. Monitor the elution with TLC and combine the
fractions eluted with 25-30 % ethyl acetate in n-hexane and
concentrate under vacuum (35g). Adsorb the fraction over flash
grade silica (230-400 mesh grade) and

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subject to flash chromatography by using flash grade silica
column (40 g) with mixture of n-hexane and ethyl acetate as the
eluting solvents. Collect the fractions eluted with ethyl acetate:n-
hexane (1.5:8.5) and concentrate under vacuum to get a
enriched fraction of rubiadin (1.2 g). Crystallize the fraction in
methanol to get rubiadin (350 mg). Store in airtight container in
a cool and dry place.
Characterization of Rubiadin
The structure of rubiadin was characterized by UV, IR, NMR,
Mass spectrum. HPLC fingerprinting was done to confirm the
presence and purity of rubiadin.
HPLC Chromatogram of the Rubiadin
Weigh 10 mg of reference standard and isolated rubiadin were
mixed with 50 ml of the mobile phase respectively. 1 ml of each
solution was diluted with 200 ml of mobile phase and filter with
syringe filter and kept ready for injection. The column used was
ODS silica column[5 µm; 20cm X 4.6 mm]; mobile phase used
was methanol: water :: 80:20 V/V with flow rate of 1.0 ml/min
with UV detection at 300 nm. 10 µl of the standard was injected
and the chromatogram was run in triplicate to get retention time
for standard. Similarly sample was also injected triplicate and
run the chromatogram. The percentage purity of the sample was
calculated.
In vitro antiproliferative activity using HeLA cell lines by
MTT assay
Cell culture
HeLa cell line was maintained in DMEM medium (GIBCO)
supplemented with 10% (v/v) heat-inactivated fetal bovine
serum (FBS) and 1% antibiotic solution (penicillin 100U/ml and
streptomycin 100µg/ml) at 37”o”C in a humidified atmosphere of
95% air/5% CO2. The medium was changed every second day,
and cells were subcultured when confluency reach to 95% by
0.25% trypsin containing 0.02% ethylene-diaminetetraacetic
acid (EDTA) in PBS for 3 min at 37”o”C.
MTT Assay
The MTT assay was carried out as described previously to
measure cell viability [6]. Ten thousand cells in 100μl of DMEM
media were seeded in the wells of a 96-well plate. After 24 h,
existing media was removed and 100 μl of various
concentrations of compound [20 to 100 µg/ml] were added and
incubated for 48 h at 37”o”C in a CO2 incubator. Control cells
were supplemented with 0.05% DMSO vehicle. At the 48th hour
of incubation, MTT (3-(4,5-dimethylthaizol-2-yl)-2,5-
diphenyltetrazolium bromide- supplied from Sigma, 10μl of 5
mg/ml) was added to the plate. The contents of the plate were
pipetted out carefully, the formazan crystals formed were
dissolved in 100 μl of DMSO, and the absorbance was
measured at 550 nm in a microplate reader (Tecan, infinite
F200 Pro). Experiments were performed in triplicate [3 times x 3
wells each time /group] and the results were expressed as
mean of percentage inhibition. A graph of the concentration
versus percentage growth inhibition was plotted, and the
concentration at which 50% cell death occurred was considered
as the IC50 value. Before adding MTT, bright field images
(Olympus 1X81, cellSens Dimension software) were taken for
visualizing the cell death.
In silico activity: Molecular Docking studies
The three dimensional structure of target protein EGFR tyrosine
kinase(PDB ID:2J5F) was downloaded from PDB
(www.rcsb.org/pdb) structural database. This file was then
opened in SPDB viewer edited by removing the heteroatoms,
adding C terminal oxygen. The active pockets on target protein
molecule were found out using CASTp server [7]. The ligands
were drawn using ChemDraw Ultra 6.0 and assigned with
proper 2D orientation (ChemOffice package). 3D coordinates
were prepared using PRODRG server [8]. Autodock V3.0 was
used to perform Automated Molecular Docking in AMD Athlon
(TM)2x2 215 at 2.70 GHz, with 1.75 GB of RAM. AutoDock 3.0
was compiled and run under Microsoft Windows XP service
pack 3. For docking, grid map is required in AutoDock, the size
of the grid box was set at 102, 126 and 118 Å (R, G, and B),
and grid center -58.865, -8.115, -24.556 for x, y, and z-
coordinates. All torsions were allowed to rotate during docking.
The Lamarckian genetic algorithm and the pseudo-Solis and
Wets methods were applied for minimization, using default
parameters [9].
RESULTS
The Characterization of the Rubiadin [Fig 1]
Fig 1: Structure of Rubiadin
Physical data
Rubiadin is Yellow needles, m.p. 303 -304 ºC (lit.6 302 ºC).
Molecular formula: C15H10O4. ; Molecular weight: 254
Spectral Data
UV-VIS spectrum shows absorption at nm: 245, 279, 412. The
UV-VIS spectrum indicates the presence of chromophoric
system in the molecule. The IR spectrum of rubiadin showed
characteristic peaks at 3393(OH str.), 2361.9(alkyl CH str.),
1661.75 (unchelated C=O) and 1624 cm-1(chelated C=O).
Superimposible IR was done with reference standard and
isolated compound and was found to be exactly the same as
reference standard.
1H NMR spectrum (DMSO-d6-500 MHz): The signal at δ 13.25
(S, Cl-OH), 8.21-8.26 (2H, m, C5-Hand C8-H), 7.80-7.87 (2H,
m, C6-H and C7-H), 7.30 (1H, s, C4-H). The δ values were
comparable with that of reported 1H NMR Rubiadin [10].
13C NMR spectrum (CD3OD -300 MHz): the signals at 
109.6,116,126.9,127,133,133.4,133.9,
134,134.2,161.7,164.1,182 and 186.7. The δ values were
comparable with that of reported 13C NMR rubiadin [10].
Mass spectrum of rubiadin showed molecular ion peak of
aglycone at (m/z) 254 which further confirmed the molecular
formula as C15H10O4.
The HPLC chromatogram showed peak with retention time of
25.07 minutes with 99.0 % purity which confirmed the presence
of rubiadin in comparison with reference standard.
In vitro antiproliferative activity on HeLa Cell Lines
The MTT values obtained demonstrated that rubiadin has
antiproliferative effect as the IC50 value was found to be 56.63 ±
0.025 µg/ml. Microscopy images representing the cell death
caused by the compounds are as seen in Fig No.2. It is very
clear that it is antiproliferative agent when compared to control
cell with vehicle alone.
Fig 2: Percentage inhibition of cell growth at different
concentrations of rubiadin compound. Data are Mean±SE
(n=3).
O
O
OH
CH3
OH

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Fig 3: Anticancer activity of rubiadin showing cell death, A-control; B-treated.
Fig 4: 3D structure of EGFR tyrosine kinase from PDB (A); Interacting amino acids as
predicted from the ligplot (B).
Fig 5: Enfolding of rubiadin in the active pocket.
In silico molecular docking studies
The tyrosine kinase receptors have multidomain extracellular
Ligands for specific Ligand, a signal pass transmembrane
hydrophobic helix and tyrosine kinase domain. The receptor
tyrosine kinases are not only cell surfaces transmembrane
receptors, but are also enzymes having kinase activity[11].In
cancer, angiogenesis is an important step in which new
capillaries develop for supplying a vasculature to provide
nutrient and removing waste material. So tyrosine kinase
inhibitor as an anti-angiogenic agent is new cancer therapy.
Developing natural drugs and prodrugs as inhibitor is today’s
trend. Low molecular weight substances, which inhibit tyrosine
kinase phosphorylation block signaling pathway, initiated in the
extracellular part of receptor[12,13].Since, the type I receptor
tyrosine kinase is a major regulator of several distinct and
diverse cellular pathways we have evaluated it as a target.
Rubiadin was taken and docked to get the best conformer.
Results were compared for the binding energy, docking energy
and number of hydrogen bonds formed. According to the
docking results (Table No.1), it has -7.07 kJ mol-1 binding and -
7.12 kJ mol-1 docking energy with two hydrogen bonds.
Molecular docking with EGFR tyrosine kinase domain revealed
that, our compound has inhibitory capability and thereby
exhibiting interactions with one or the other amino acids in the
active pockets as shown in Fig No.3a and 3b. The topology of
the active site of EGFR tyrosine kinase was similar in all
synthesized molecules, which is lined by interacting amino acids
as predicted from the ligplot (Fig No.3a and 3b).In in vitro
studies the molecule emerged to be active against the cell line
used in inhibiting the cell growth.

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Table1: Molecular docking results of rubiadin with EGFR tyrosine kinase.
Molecule
Binding
energy
Docking
energy
Inhibitory
constant
Intermol
energy
H- bonds
Bonding
RD
-7.07
-7.12
6.54e-006
-7.07
2
RD::DRG:HAU:TK:A:LEU777:O
RD::DRG:OAO:TK:A:LEU703:HN
CONCLUSION
Rubiadin has shown to possess in vitro antiproliferative activity
and in silico studies. The IC50 value was found to be 56.63 ±
0.025 µg/ml and in silico studies, it has more number of
hydrogen bonds with minimum binding and docking energy and
may be considered as inhibitor of EGFR tyrosine kinase. More
experiments are required to understand the exact mechanism
by which the cells are affected. It is important to correlate the
structure of these compounds with their biological effect, which
will be valuable to propose new lead compounds with better
cytotoxic potential.
ACKNOWLEDGEMENT
The authors are grateful to the Chairman and Executive
director, Children’s Education Society and Department of
Pharmacognosy, The Oxford College of Pharmacy, Bangalore,
for providing the facilities for carrying out the entire experiment.
ETHICAL ISSUES
There is none to be applied
CONFLICT OF INTEREST
None to be declared
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