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This study aimed to
determine the anti-proliferative properties of different solvent extracts
obtained from various parts of Rhododendron
luteum. In order to investigate anti-cancer activity, non-transformed and
transformed cell lines were treated by various organic extracts (ethyl acetate,
hexane and methanol) obtained from different flower parts of R. luteum or DMSO for 48 h in in vitro conditions. Cytotoxic activity
measurement was achieved by the MTT method. The results obtained from this
study showed that ethyl acetate extracts derived from the sepals, petals and
buds illustrated significant anti-proliferative effects on the HT29 colorectal
cancer cell line. The IC50 values that were determined for sepal,
petal and bud ethyl acetate extracts were 133.2 μg/ml, 459.3 μg/ml and 159.94
μg/ml, respectively in comparison to the ARPE-19 IC50 values which
were 266.6 μg/mL, 800 μg/ml and 366.65 μg/ml, respectively. The difference
between the non-transformed ARPE-19 and transformed HT-29 cell lines was
statistically significant (p<0.05). In consequence, the results from this
study suggest that different organic extracts from R. luteum may have selective effects on different cancer cells and
offer a potential for usage as anticancer agents for colorectal cancer. For
determination of this potential, further studies are needed to assess the
activity of the compound/compounds that may mediate selective effects on
different types of cancer cells.
Keywords: R. luteum, Cancer, Cytotoxicity, MTT, HT-29, HeLa, A549, ARPE-19
INTRODUCTION
Cancer is a growing global public health
problem that leads to significant morbidity and mortality every year[1-3].
Cancer is a systemic disease which emerges when changes occur in normal cells
and spreads into the surrounding normal tissue or throughout the whole body.
Therefore, it is thought that chemotherapy is the most effective treatment.
However, the fact that drugs that are used in chemotherapy are also effective
on normal cells and, more importantly, the ability of cancer cells to develop
resistance to these drugs over time [4-6] have led scientists to investigate
new anticancer agents.
Natural products have been used traditionally
for more than 5.000 years and even today more than 60% of the world’s
population depends on medicinal plants as their primary source of healthcare [7,8].
Among herbal and plant medicines, Rhododendrons (Ericaceae) have gained prominence
in recent years for their secondary metabolites [9-14] and anti-carcinogenic
potential [15,16]. Rhododendron is one of the largest genera of plants; it is a
small, woody, evergreen shrub, mainly distributed on the Northern hemisphere
and have been widely used for traditional medicine in China and Korea [17].
The first written reference about
Rhododendron dates back as far as 401 B.C. and records the toxicity of
rhododendron honey [18]. Some Rhododendron
spp. still known to cause intoxication, mainly due to grayanotoxin-contaminated
honey [19,20]. To the best of our knowledge, biological research on the genus
goes back to 1960. Rhododendron spp.
are a rich source of secondary metabolites and some of these induce various
kinds of bioactivities [9] which promise therapeutic potential. Recently,
antimicrobial [14], anti-
MATERIALS AND METHODS
Reagents
All chemicals and
reagents were procured from certified suppliers. DMSO (dimethyl sulfoxide), MTT
(3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), Taxol, D-PBS
and trypan blue (0.4%) were purchased from Sigma Aldrich. RPMI-1640 (Hyclone), fetal
bovine serum (FBS), antibiotics (100 µg/ml streptomycin + 100 U/mL penicillin),
0.25% trypsin-EDTA and Dulbecco’s modified Eagle’s medium (DMEM) were obtained
from GIBCO. The ethyl acetate was supplied by Sigma-Aldrich (St. Louis, MO,
USA), while methanol and hexane that were used for the exractions were obtained
from Merck KGaA, Darmstandt, Germany).
Cell lines and cell culture
Adenocarcinomic
human alveolar basal epithelial cell line A-549 and human cervical cancer
epithelial cell line (HeLa) were kindly provided by Prof. Fikrettin Sahin
(Yeditepe University, Istanbul, Turkey), human endometrial adenocarcinoma cell
line CRL-2923 was a gift from Prof. Bedia Agachan Cakmaoglu (Istanbul
University, Istanbul; Turkey) and diploid ARPE-19 retinal pigment epithelial
cell line was kindly provided by Dr. MuradiyeAcar (Turgut Ozal University,
Ankara, Turkey). Human colon adenocarcinoma cell line HT-29 was obtained from
the American Type Culture Collection (ATCC). The cell lines were maintained in
RPMI-1640 or DMEM with 10% fetal bovine serum (FBS) and antibiotics (100 μg/mL
streptomycin + 100 U/mL penicillin) in T25 flasks at 37°C in a humidified
atmosphere of 5% CO2. At 70-80% confluency, the cells were passaged
enzymatically with 0.25% trypsin and sub-cultured in 25 cm2 plastic
flasks for further maintenance. The culture media were replaced every 2 days.
Samples and extraction
The flowers of R.
luteum were collected from Ayder in Rize, Turkey in the month of April
2016. The plant species was identified by Prof. Vagif Atamov, at the Department
of Biology, Recep Tayyip Erdogan University in Rize, Turkey. After
identification, R. luteum flowers were separated into their
parts (sepals, petals, buds) and the freshly collected specimens were stored at
(-20°C) at the Microbiology Cell Culture Laboratory. Extractions were performed
with the maceration method. In summary, the frozen samples of R. luteum were weighed
(10-20 g) and ground into powder. Crude extracts were prepared by suspending
the powders in 100 mL of, ethyl acetate (EtOAc), hexane and methanol (MeOH) and macerated in a shaker for 48 h at room temperature. Thereafter, the extracts were filtered
through a Whatman paper and the filtrates were then concentrated using a rotary
evaporator (LabTech.EV311) at 40°C. First of all, stock solutions of the extracts (50-200
mg/mL) were prepared in DMSO and all the
extracts were stored at –20°C for further anti-proliferative activity testing. For all
the experiments, the working solutions were prepared by diluting
the stocks of R. luteum extracts in
complete media to the desired concentrations immediately before use. The final
DMSO (as a negative control) concentration during the assays was kept below
0.4%.
Morphological studies
Morphological studies were performed as
described earlier by Eksi et al. [23]. Briefly, different volumes of each
extract were added to the complete media in order to generate working
solutions. Transformed (Hela, HT-29, A549, CRL2923) (1 × 104 cells/ml)
and non-transformed ARPE cells (2 × 104 cells/ml) were seeded into
24-well culture plates with 1000 μL of growth media. After overnight
cultivation, various concentrations of the test samples or solely the
corresponding DMSO (max. 0.4%) alone were added to the plate wells. Taxol (5
nM) was used as a positive control. The cultures were cultivated at 37°C for 24
h in an atmosphere of 5% CO2 and 95% air in an incubator.
Afterwards, cellular morphology was viewed an under inverted microscope using a
10X magnification (Olympus CKX410). The changes in cellular morphology were
photographed using a digital microscope camera (Olympus SC30).
Cytotoxic studies using MTT assay
Cytotoxic activity
was evaluated based on the method described by Mosmann [24], with minor
modifications. Briefly, after trypsinization, for the transformed cells, 1 × 103 cells/well
were seeded into a flat-bottom 96-well microtiter plates in 100 µL of growth
medium in duplicatse and allowed to adhere overnight. On the other hand, the
cell count for the non-transformed diploid cells was adjusted to 2 × 103 cells/well.
The next day, varying concentrations of extracts from the stocks were added to
the microtiter plate wells in duplicates per concentrations, and serial
dilutions ranging from (800 µg/mL to 15.6 µg/mL) were made in the plates. The
negative control received the corresponding amount of DMSO alone, and all
plates were incubated for 48 h at 37°C in 5% CO2. After the exposure
time, 10 µl of (5 mg/ml in water) filtered, sterilized MTT solution was added
to each well and the cells were incubated for an additional 4 h at 37°C.
Afterwards, the medium was removed, and the formazan crystals that formed in
the viable cells during the MTT treatment were dissolved by adding 100 µl of
DMSO per well. The plates were incubated at 37°C for 20 more minutes to allow
complete solubilization. Absorbance was then measured at 570 nm using an ELISA
microplate reader (Thermo, Multiskan Go). All experiments were performed in
duplicates and repeated at least three times. Growth inhibition was calculated using
the following formula: % Growth inhibition = [(negative control OD–Sample
OD)/Negative control ODl] × 100.
The cytotoxic
concentrations of the extracts (IC50) were calculated from the
dose-response curve, which inhibited cell growth by 50%. The selective index
(SI) was calculated from the ratio of the IC50 of the normal cells
over the cancer cells. Extracts with SI values close to 3 were considered to
have better biological activity against tumor cells than the normal cells in in vitro conditions [25].
Apoptosis studies
Gel electrophoresis: DNA fragmentation analysis was
performed as follows: Transformed (Hela, HT-29, A549, CRL2923) (1 × 104 cells/ml)
and non-transformed ARPE-19 cells (2 × 104 cells/ml) were seeded
into 6-well culture plates in 2000 μl of growth medium. After incubation
overnight, various concentrations of test samples or the solely the
corresponding DMSO (max. 0.4%) alone were added to the wells. Taxol (5 nM) was
used as a positive control as it induces DNA fragmentation. The treated and
untreated cultures were incubated at 37°C for 48 h in an atmosphere of 5% CO2
and 95% air in an incubator. After trypsinization, the cells were counted
and centrifuged at 2000 rpm for 5 min. The harvested cells were rinsed twice in
cold phosphate-buffered saline (PBS, pH 7.4). The supernatants were discarded
and the pellets were used for genomic DNA isolation. DNA extraction was
performed according to the manufacturer’s instructions from a Wizard Genomic
DNA Purification Kit (Promega, A1120) and stored at 20°C until needed. The DNA
samples that were obtained from the cells and Thermo 1 Kb DNA molecular weight
marker were size-fractionated in 1% agarose gel and visualized by ethidium
bromide (EtBr) staining. The scanned images were processed using Bio-Imaging
Systems (MiniLumi).
Hoechst (H33342) staining: Transformed (1 × 104 cells/ml) and non-transformed cells (2 × 104 cells/ml) were seeded into 6-well culture plates in 2000 μl of growth medium. After 24 h extract and controls treatment, the cells were trypsinized, washed with cold 1x PBS two times and fixed in cold (-20°C) MeOH for 5 min. A staining solution of Hoechst (H33342) was prepared immediately before use. The cells were then incubated with Hoechst (2 µg/ml) for 10 min and washed with cold 1x PBS two times. The nuclear morphology of the cells was viewed under a microscope using a 20x magnification (Leica fluorescence DM4000) and the results were photographed using a digital microscope camera (Leica DFC425).
STATISTICAL ANALYSIS
All experiments
were performed at least three times and growth inhibition was calculated in
terms of percentage by the formula: % Growth inhibition = [(negative control OD
– Sample OD)/Negative control ODl] × 100. The statistical analysis of all data
was performing using an unpaired t-test.
A level of p<0.05 denoted significance in all cases.
RESULTS
Cytotoxicity
Cytotoxicity of sepal extracts (Hexane, MeOH, EtOAc): To evaluate the
growth inhibition on non-transformed and transformed cell lines induced by the
exracts from R. luteum sepals, cells
were incubated in six different concentrations of hexane extract (between 300
and 9.3 μg/ml) or a carrier DMSO (negative control) alone in in vitro conditions. Following a 48 h
treatment with the extract, cytotoxicity was determined by an MTT assay. As
shown in Figure 1A, the hexane
extract from the sepals had a dose-dependent antiproliferative effect on all
the cell lines and there was no statistically significant difference between
non-transformed and transformed cells in the terms of cytotoxicity.
The addition of
various concentrations (between 400 and 35 μg/ml) of the sepal MeOH extract to
the cell culture media exhibited no anti-proliferative effects on
non-transformed ARPE-19 cells following 48 h treatment (Figure 1B) in in vitro
conditions. Meanwhile, it was found to be more prominent in HeLa and HT-29
cancer cells in comparison to A549 and CRL-2923 cancer cell lines. It was
determined that 400 μg/mL of the MeOH extract induced >60% and 52% cell
death in the HeLa and HT-29 cell lines, respectively. In terms of cytotoxicity,
the ARPE-19 cells were significantly less sensitive than the HT-29 and HeLa
cells as represented by the calculated P values of P=0.025 and P=0.05,
respectively.
Furthermore, the
anticancer properties of the EtOAc extract obtained from the sepals of R. luteum were investigated. An MTT
assay was performed with various concentrations (between 600 and 79 μg/ml) of
the EtOAc extract with an exposure time of 48 h in in vitro conditions. As shown in Figure 1C, at high concentrations (³ 400 μg/ml), the
extract was highly cytotoxic and led to >60% cell growth inhibition in all
the cells. However, as the concentrations of the extract gradually decreased to
177.7 μg/ml and 118.5 μg/ml), the transformed HT-29 cell line was more
sensitive to the treatment by the EtOAc extract. In terms of cytotoxicity, the
non-transformed ARPE-19 cells were significantly less sensitive than the HT-29
colorectal cancer cells (p<0.05). Additionally, the IC50 of EtOAc
extract was determined to be 266.6 μg/ml for the non-transformed ARPE-19 cells.
On the other hand, the lowest IC50 value (133 μg/ml) was calculated
for HT-29 cells suggesting that the extract may have selective cytotoxic
activity against the HT-29 colon cancer cells.
Cytotoxicity of petal extracts (Hexane, EtOAc): The hexane and EtOAc extracts from R. luteum petals were
studied for their anti-proliferative effects on the growth of the
non-transformed and the transformed cell lines. All the cell lines were treated
by various concentrations of the hexane extract ranging from (500 to 15.6
μg/ml), EtOAc extract ranging from (800 to 105.3 μg ml) or consisting of the
corresponding DMSO (max. 0.4%) in in
vitro for 48 h conditions.
As shown in Figure 2A, exposure
of non-transformed and transformed cell lines to decreasing concentrations of
petal hexane extract caused dose-dependent inhibition of cell growth. On the
other hand, the anti-proliferative effects of the extract on the HeLa cells
were more evident at the 500 μg/ml and 250 μg/ml concentrations, causing growth
inhibition by 58.7% and 46.4%, respectively, in comparison to the other cancer
cell lines that were used in the study. Higher cytotoxic values indicated that
the HeLa (cervical cancer) cells were the most sensitive cancer cells to the
petal hexane extract as in comparison to the other three cancer cell lines
(A549, HT-29, CRL2923). Nevertheless, the results revealed that there was no
statistically significant difference between ARPE-19 and any other cancer cell
line.
Treatment of the non-transformed and the transformed cell lines with
various concentrations of the EtOAc extract from the petals of R. luteum for 48 h in in vitro conditions resulted in a
concentration-dependent decline in cell viability (Figure 2B). The IC50 values were calculated as 800
μg/ml, 644.4 μg/ml, 622.1 μg/ml, 459.3 μg/ml and 800 μg/ml for ARPE, HeLa,
A549, HT-29 and CRL2923, respectively. Additionally, we found that the EtOAc
extract from the petals at the concentrations of 533.5 μg/ml and 355.5 μg/ml
induced the highest cytotoxic effects on HT-29 and showed growth inhibition by
65.67% and 41.99%, respectively (Figure 2B).
The same concentrations of the extract decreased cell viability by 20.2% and
6.29% in ARPE-19 cells, respectively. In terms of the cytotoxicity, the
statistical analysis revealed that the difference between the ARPE-19 and HT-29
cells was significant (p<0.05). However, there was no significant difference
between ARPE-19 and the other transformed cell lines. To summarize, the
findings provided evidence that the EtOAc extract from R. luteum petals might have some compound/compounds that may induce
specific anti-proliferative effects on HT-29 colorectal cancer cell line.
Cytotoxicity of bud extracts (Hexane,
MeOH, EtOAc): The non-transformed and
the transformed cell lines were treated with various concentrations of the
hexane, MeOH and EtOAc extracts obtained from the buds of R. luteum. As it can be seen in Figure 3A, the exposure of the cell lines to decreasing
concentrations (500 μg/ml to -15.62 μg/ml) of bud hexane extract was found to
be not effective on the ARPE-19, HT-29 and A549 cell lines. On the other hand,
the extract induced mild anti-proliferative effects in both HeLa and CRL2923
cancer cells. Since both cell lines originated from human uterus tissues, the
data may suggest that the extract may have selective anticancer activity
against uterus tissues originated cancer cells. It is also interesting to note
that the hexane extract of buds significantly enhanced the proliferation of
non-transformed ARPE-19 cells especially at higher concentrations (500 μg/ml to
-125 μg/ml). In the light of this information, it brings in mind that this
extract has some components that might have a mitogen activity on
non-transformed cells.
Figure 3B shows the anticancer activity of the MeOH extract of buds on normal human
cell line (ARPE-19) and four cancer cell lines (ARPE, HeLa, A549, HT-29,
CRL2923). The effect of the extract on human cell lines was tested at
concentrations ranging from 400 to 52.6 μg/ml or DMSO (control) alone for 48 h
in in vitro conditions. The results
showed that the MeOH extract of R. luteum
buds exhibited a dose-dependent cytotoxic effect for all the cancer cell
lines that were evaluated. The extract at the concentrations of 400 μg/mL
exhibited moderate cytotoxic effects on ARPE-19 cells by killing only 21.3% of
the cells. However the same concentration of the extract showed higher
cytotoxic activity against the cancer cell lines of HeLa, A549 and HT-29 with
growth inhibition by 42.2% 47.3% and 60.2%, respectively (Figure 3B). In addition to this, the difference between the
ARPE-19 and transformed cell lines (A549, HT-29, HeLa) was found to be
statistically significant (p<0.05).
Finally, we evaluated anti-proliferative effects of the EtOAc extract of R. luteum buds. It was determined that,
at the concentrations of 400 μg/ml, the extract was highly cytotoxic and led to
³ 70% cell death in all
the cell lines that were evaluated. However, as the concentrations were reduced
gradually to 177.7 and 118.5 μg/ml, there were statistically significant
differences the between non-transformed ARPE-19 and transformed cell lines
(A549, HT-29, HeLa). As it can be seen in Figure
3C, the treatment of the cells with the 177.7 μg/ml concentration of the
extract induced 74.28% cell death in the HT-29 cell while produced only 6.45%
growth inhibition in normal ARPE-19 cell line. The IC50 values were
found to be 366.6, 231.1, 222.1, 159.94 and 333.5 μg/ml for ARPE-19, HeLa,
A549, HT-29 and CRL2923, respectively. Additionally, the results revealed that
the extract was more potent and more selective against the HT-29 colon cancer
cells showing the highest SI (selectivity index) as 2.29.
Morphological changes
To observe the morphological changes, the cells (ARPE-19, A549, HT-29,
HeLa) were treated with 300 μg/ml of R. luteum
EtOAc extract from the
sepals, Taxol, media or DMSO alone. After 24 h of incubation, the cells were
examined under an inverted microscope. As shown in Figure 4A, no morphological changes were observed in the cells
treated with negative controls (DMSO or media). However, Taxol (5 nM) was used
as a positive control, which caused rounding and detachment of the transformed
cells (Figure 4A). Meanwhile,
exposure of the diploid ARPE-19 cells to the EtOAc extract (300 μg/ml) for 24 h caused no apparent morphological
alterations in these cells. However, similar to Taxol, the EtOAc extract was
found to cause cellular death in the HT-29 and HeLa cell lines by breaking the
cells from the surface (Figure 4A).
Additionally, among the transformed cell lines, the least morphologically
affected one was the A549 cell line.
Apoptotic activity analysis
In recent years, there has been considerable interest in treatment-induced
apoptosis. Formation of DNA fragmentation is one of the characteristic features
of apoptosis [26]. Therefore, the controls and EtOAc induced apoptosis were
performed by the DNA fragmentation assay using agarose gel electrophoresis and
Hoechst (H33342) staining.
Hoechst staining and electrophroretic analysis of DNA showed that exposure
of the cells to R. luteum EtOAc
extract (400 µg/ml) for 48 h did not result in a characteristic chromatin
condensation or DNA laddering pattern (Figures
4B and 4C). Since these two are the biochemical hallmarks of apoptosis,
these data may suggest that the EtOAc extract might promote different signals
to mediate cancer cell death. Over the past few years the role of autophagy in
cancer has been reported in various studies [27-29]. Others showed that some
anticancer agents [30] or some plant extracts [31,32] can promote necroptosis
in cancer cells.
DISCUSSION
Thousands of years ago, human beings found the power of plants for
treatment [7-33]. In the past few years, the use of some remedies has attracted
a great deal of attention for alternative cancer therapies and some of them
have been reported to inhibit the growth of human cancer cell lines [34-37].
Rhododendron is one of the largest genera of plants [17] and R. luteum is a well-known poisonous plant that widely grows and is
distributed in the Black Sea region of Turkey [38]. Very limited information is
available regarding the biological activity of R. luteum. However, among herbal and plant-base
medicines, Rhododendrons have
gained prominence in recent years for their bioactive compounds and their
anti-carcinogenic potential [14]. Previously,
it was reported that the some species of the Rhododendron genus contain high levels of essential
oils [39] and flavonoid [40,41] compounds in their chemical composition. It was
also, documented that both the essential oils [39] and flavonoids may display
anti-carcinogenic activity against different cancer cell lines [42,43].
Additionally, another study reported that flavonoids may increase
susceptibility of cancer cells to chemotherapy [44]. Therefore, Rhododendron species may have prominence due to their anti-carcinogenic
potential.
The goal of this study was to understand whether or not R. luteum is a medicinal herbal plant.
Therefore, extracts were prepared
using R. luteum flower parts (sepals,
petals) and buds in different solvents including MeOH, EtOAc and hexane. All
extracts were tested for their anticancer activity using non-transformed
(ARPE-19) and transformed (HeLa, A549, HT-29 and CRL2923 cell lines. The
cytotoxic activities of the extracts were determined by MTT assay and
morphological alterations.
First of all, MeOH extract of the sepals was found to have no anti-proliferative
effect on non-transformed ARPE-19 cells, whereas the extract was more prominent
in the HeLa and HT-29 cells in comparison to A549 and CRL-2923 (Figure 1A). MeOH extract from the buds
caused moderate cytotoxicity on ARPE-19 cells, while extract showed a
dose-dependent cytotoxic effect on all the cancer cells (Figure 3B). These findings suggest that MeOH extract of R. luteum exhibit cytotoxic effect
against broader range of the cancer cell lines. Therefore, the extract might
have antitumor potential against cancer that originated from the different
tissues.
Next, we tested the anti-proliferative effects of hexane extracts that
were obtained from R. luteum. Even though,
administration of the sepal hexane extract on non-transformed and transformed
cells caused dose-dependent death of the cells (Figure 1A), the petal and bud hexane extracts gave rise to
consistently higher cytotoxic effect on HeLa cervical cancer cells at high
concentrations (Figures 2A and 3A).
Our results here indicated a surprising finding that the hexanic extract from
the buds had no harming effects on non-transformed ARPE-19 cells, while it
actually significantly enhanced the proliferation of the ARPE-19 cells
especially at high concentrations (Figure
3A). One possible reason for the finding might be that, despite its anti-proliferative
activity on some cancer cell lines, the extract may play a role as a mitogen on
non-dividing or slow-dividing cells. This needs to be further studied to be
verify the possible mitogenic activity of the bioactive compounds that might
present in the hexane extract.
This study also focused on the anti-proliferative effects of the EtOAc
extracts obtained from different parts of the flowers (sepal, petal) and the
buds of R. luteum. As shown in Figures 1C, 2C and 3C at high
concentrations all the extracts were shown to possess high cytotoxicity against
all the cells lines that were used in the study. However, as the concentrations
of the extracts were gradually reduced, the results revealed that extracts from
the sepals, buds or petals were more potent and more selective against HT-29
colon cancer cells showing higher SI (selectivity index) values as 2.0, 2.3 and
1.7, respectively, in comparison other cancer cell lines. This finding might be
important since it was reported that, if a compound has a SI value above 3 that
compound may potentially be used to develop anticancer agents [25]. Given that
the samples assayed in the study were not purified compounds, the extracts may
have so many compounds with different biological activities. These results
provide a possible lead towards further studies to find out the chemical
composition of the extracts including the individual compounds which may
mediate selective activity against HT-29 colon cancer cells.
Although there is a limited number of studies regarding the anti-proliferative
activities of R. luteum in in vitro conditions, our results
reported above were consistent with those of Selim Demir et al. [45] which
indicated that extracts from R. luteum
had specific cytotoxicity against WiDr colon cancer cell line. In a study
conducted in 2011, three different components (Ferruginenes A, B, C) obtained
from the leaves of R. ferrugineum were tested for their
cytotoxic effects on the transformed (HT-60, HeLa, S3, MCF-7) and
non-transformed (HEK-293) cell lines. As a result they reported that
Ferruginenes (A, B, C) were the most effective against HL-60 human cell line
[46]. In another study, the researchers showed that essential oils obtained
from the leaves and flowers of R. antropogoni
induced more cytotoxic activity on Cervix A-143 cells in comparison to other human
adenocarcinoma cell lines (Ovarian-2008, LoLo-colon) [39]. In related studies, Way et al. [47,48] showed that
components that were obtained from R.
formosanum leaves enhanced cell death in non-small-cell lung carcinoma
cells. Our results agreed with the reports above on that extracts from Rhododendron spp. may have different
anti-proliferative properties in different cancer cell lines.
CONCLUSION
In conclusion, identifying differential cytotoxicity is important for
developing potential anticancer agents. The overall findings of this study
indicated that the hexane extracts derived from R. luteum showed selective anti-proliferative activity more against
the HeLa cervical cancer cells, whereas the MeOH extracts from R. luteum affected a broader range of the
cancer cell lines similarly. The encouraging result obtained from this study
was that HT-29 cells were particularly susceptible to EtOAc extracts of R. luteum, which may finally lead us to
think that these extracts may have some specific compounds that are responsible
for the anti-proliferative activity on these cells. This suggests that further
studies are needed to better understand the mechanisms behind these inhibitory
effects that lead to cell death in HT-29 cell line. Therefore, we will pursue
isolation and characterization of the specific compounds responsible for this
biological activity and investigate its detailed molecular mechanism.
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