Nutraceuticals as new treatment approaches for oral cancer – i

Review
Nutraceuticals as new treatment approaches for oral cancer – I: Curcumin
Ayelet Zlotogorski
a
, Aliza Dayan
b
, Dan Dayan
f,
⇑
, Gavriel Chaushu
a,c
, Tuula Salo
d,e
, Marilena Vered
f,g
a
Department of Oral and Maxillofacial Surgery, Rabin Medical Center, Beilinson Campus, Petah Tikva, Israel
b
Tiltan College, Natural Health Science, Tel Aviv, Israel
c
Department of Oral and Maxillofacial Surgery, School of Dentistry, Tel Aviv University, Tel Aviv, Israel
d
Department of Diagnostics and Oral Medicine, Institute of Dentistry, University of Oulu, Oulu, Finland
e
Institute of Dentistry, University of Helsinki, Helsinki, Finland
f
Department of Oral Pathology and Oral Medicine, School of Dentistry, Tel Aviv University, Tel Aviv, Israel
g
Institute of Pathology, The Chaim Sheba Medical Center, Tel Hashomer, Israel
article info
Article history:

Received 16 August 2012
Accepted 22 September 2012
Available online 30 October 2012
Keywords:
Oral cancer
Curcumin
Nutraceuticals
Anti-cancer activity
Nuclear Factor-
j
B (NF-
j
B)
Bioavailability
Radiotherapy
Chemotherapy
summary
Oral squamous cell carcinoma (OSCC) is a growing global public health problem for which standard ther-
apeutic strategies have failed to contribute significantly to improve the survival rates that have remained
around 50% over the past three decades. Therefore, there is a pressing need for new therapeutic strate-
gies. Curcumin is a natural dietary compound with known anti-neoplastic activities, hence its classifica-
tion as a nutraceutical agent. This review presents the current in vitro and in vivo studies in which
curcumin has been examined for its anti-cancer potential in treating OSCC. Its mechanisms of action
are also beginning to become unveiled. The available studies have been focusing on the impact of curcu-
min on epithelial malignant cells, but overlooking the components of the tumor microenvironment. Cur-
cumin has been emerging as a promising therapeutic agent in oral cancer, either alone or in combination
with standard therapeutic agents, and will probably become of practical use once its route of administra-
tion has overcome its poor bioavailability.
Ó 2012 Elsevier Ltd. All rights reserved.
Introduction

Oral and oropharyngeal cancers, the vast majority of which are
comprised of squamous cell carcinomas (SCCs), are among the 10
most common cancers worldwide.
1
The American Cancer Society
estimated 40,250 new cases of these cancers for 2012 in the United
States alone, with oral SCC (OSCC) constituting more than half of
them.
2
Tobacco use and alcohol consumption are regarded as the
main risk factors for OSCC, while human papilloma virus (HPV)
infection is emerging as the leading risk factor in cancers of the
oropharynx.
3
In view of the difference in etiopathogenesis, there
are also different trends in morbidity and mortality between OSCC
and oropharyngeal cancers.
3
In spite of extensive treatment (surgery, radiotherapy and/or
chemotherapy), OSCC is associated with recurrence and second pri-
mary tumors that are responsible for poor overall survival rates
($50%) that have not improved significantly over the past three
decades.
4
This can be attributed, in part, to genetic predisposition,
which can be a key issue in oral cancer pathogenesis, since tumors
often develop within pre-neoplastic fields of genetically altered
cells.
5
In addition, components of the tumor microenvironment that

are in continuous molecular crosstalk with the cancer cells have
been shown to further facilitate the invasion and spread of the tu-
mor and, therefore, they play a crucial role in the poor prognosis
of OSCC patients.
6–8
OSCC patients who have been apparently suc-
cessfully treated haveto contend with serious side effects, especially
following radiotherapy.
9
As a consequence, there have been con-
certed efforts to find alternative therapies which encompass more
favorable clinical results and less morbidity among those patients.
‘‘Nutraceutical’’ (a combination of the words ‘‘nutrition’’ and
‘‘pharmaceutical’’) refers to any substance considered to be a food
or a food ingredient that provides medical and health benefits. A
number of nutraceuticals have been identified during the past
decade.
10
The present review will focus on one of the more prom-
ising and more extensively investigated nutraceuticals, curcumin.
Curcumin is one of the components of curry and a popular dietary
spice worldwide. It is the primary active constituent of turmeric, a
botanical agent derived from the rhizome (root) of the Curcuma
longa, a perennial herb belonging to the ginger family that is
broadly cultivated in south and south-east Asia. Turmeric is com-
prised of a group of three curcuminoids, i.e., curcumin (difer-
uloylmethane), demethoxycurcumin, and bisdemethoxycurcumin,
as well as volatile oils, sugars, proteins and resins. Curcumin is a
1368-8375/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
/>⇑

Corresponding author. Address: Department of Oral Pathology and Oral
Medicine, School of Dentistry, Tel Aviv University, Tel Aviv 69978, Israel. Tel.:
+972 3 6409305; fax: +972 3 6409250.
E-mail address: (D. Dayan).
Oral Oncology 49 (2013) 187–191
Contents lists available at SciVerse ScienceDirect
Oral Oncology
journal homepage: www.elsevier.com/locate/oraloncology
hydrophobic polyphenol that is nearly insoluble in water. Impor-
tantly, it has limited systemic bioavailability due to its rapid
metabolism, largely through conjugation to sulfates and glucuron-
ides.
11,12
In humans, this metabolism presumably occurs in the
gastrointestinal tract rather than in the liver.
13
Curcumin has been used for thousands of years in traditional
oriental medicine as a healing agent for a variety of illnesses, such
as biliary disorders, anorexia, cough, diabetic wounds, hepatic dis-
orders, rheumatism, and sinusitis.
12
Epidemiologic data have sug-
gested a correlation between the widespread use of dietary
curcumin and the low incidence of gastrointestinal mucosal can-
cers in south-east Asia.
14
Paradoxically, OSCC has the highest inci-
dence rates in the same geographical areas, with apparently no
benefit from the popular consumption of curcumin.
4

These results
may be attributed to the concomitant excessive habitual use of to-
bacco, alcohol and other carcinogenic substances. Curcumin has
been considered pharmacologically safe, based on the fact that it
has been consumed for centuries as a dietary spice at doses up to
100 mg/day.
15
Moreover, its safety and tolerability became evident
in phase I studies when it was administered at doses as high as 8 g
per day.
16
Curcumin has been studied in various in vitro and in vivo models
of OSCC with encouraging results. The present paper summarizes
the current literature on the potential therapeutic and chemopre-
ventive qualities of this nutraceutical in the treatment of OSCC.
The focus of this review is on the in vitro studies that employed
cancer cell lines from the oral cavity per se as well as on the
in vivo animal studies in which tumors were induced in the oral
cavity or oral tumors were implanted subcutaneously. Some of
these studies were performed some years ago, before oral cancer
had been differentiated from oropharyngeal cancer. We are aware
that some of the reviewed studies included cells or tumors from
both locations and that clear-cut separation between them was
not always feasible. Therefore, whenever the cell line origin was
specifically mentioned as being from the oral cavity, it will be re-
ferred to as an OSCC cell line, and the rest will be referred to as
head and neck squamous carcinoma (HNSCC) cell lines.
In vitro studies
Extensive in vitro and in vivo studies have indicated that nuclear
factor-

j
B (NF-
j
B) activation, one of the ‘‘masters’’ of inflammation,
has a promoting role in most cancers. It is involved in most aspects
of tumorigenesis, and many of its important activities are exerted
through components of the tumor microenvironment.
17
NF-
j
Bis
activated by a broad range of agents, including various carcinogens,
inflammatory cytokines (e.g., interleukin-1 [IL-1] and tumor necro-
sis factor [TNF]), and extracellular stress (e.g., ultraviolet light and
cigarette smoke), most of which play an important role in OSCC.
17,18
Activation of NF-
j
B has been implicated in cellular transformation,
tumor promotion, angiogenesis, and tumor invasion and metasta-
sis.
17
One mechanism that may play a role in the anticancer proper-
ties of curcumin may be related to the down-regulation of NF-
j
B.
Aggarwal et al.
18
demonstrated that HNSCC cell lines expressed
constitutively active NF-

j
B and I
j
B
a
kinase (IKK), and that treat-
ment with curcumin inhibited NF-
j
B activation through abrogation
of IKK. This led to the suppression of expression of various cell sur-
vival and cell proliferative gene products, i.e., Bcl-2, cyclin D1, IL-6,
COX-2, and MMP-9, cell cycle arrest in the G1/S phase, and to the
activation of upstream- and downstream-caspases and PARP cleav-
age. It has been demonstrated that curcumin down-regulates
smokeless tobacco-induced NF-
j
B activation and COX-2 expression
in oral premalignant and malignant cells.
19
Furthermore, exposure
to curcumin led to reduced nuclear expression of NF-
j
B and conse-
quently to a dose-dependent growth inhibition of HNSCC cell
lines,
20
which was followed by a dose-dependent inhibition of IL-
6 and IL-8.
21
Compared to other HNSCC cell lines, OSCC cells had

significantly higher I
j
B kinase levels and required considerably
higher doses of curcumin for the inhibition of IL-6 and IL-8.
21
Wang
et al.
22
showed that curcumin was able to inhibit NF-
j
B through an
AKT-independent mechanism in an UM-SCC1 cell line. Kim et al.
23
collected saliva before and after subjects chewed curcumin tablets:
treatment of an UM-SCC1 cell line with curcumin as well as with a
post-curcumin salivary supernatant showed a reduction of their
IKKb kinase activity. It has also been suggested that antitumor
activity of curcumin is mediated through a novel mechanism
involving inactivation of Notch-1 and NF-
j
B signaling pathways,
24
since curcumin treatment in CAL-27 cell lines significantly reduced
cell viability in association with down-regulation of Notch-1 and
NF-
j
B. In addition, it was proposed that the inhibitory effect of cur-
cumin on the motility of the highly invasive human YD-10B OSCC
cell line could result from its potential to inhibit the activation
of MAP kinases (especially ERK) and NF-

j
B that consequently
down-regulate the mRNA expressions and activities of proteolytic
enzymes, such as urokinase-type plasminogen activator (uPA) and
matrix metalloproteinase (MMP)-2/9.
25
The oncogenic significance of activated signal-transducer-and-
activator-of-transcription-3 (STAT3) molecules stems from their ef-
fects on the development and progression of malignancy.
26
Studies
have shown that STAT3 is often constitutively activated in HNSCC
27
and mediated by IL-6.
28
It has been implicated in the induction of
resistance to apoptosis.
29
Chakravarti et al.
30
demonstrated thatcur-
cumin is a potent inhibitor of constitutive and IL-6-induced STAT3
phosphorylation and, as a result, it has the ability to suppress prolif-
eration of HNSCC cell lines. Abuzeid et al.
31
recently demonstrated
that a novel curcumin analog (FLLL32) inhibited the active form of
STAT3 in HNSCC cells and induced a potent antitumor effect. Chak-
ravarti et al.
32

showed thatcurcumin inhibitedthe growth of immor-
talized oral mucosa epithelial cells, leukoplakia cells and HNSCC cell
lines, but had only a minimal effect on the growth of normal oral epi-
thelial cells.In theabnormal andcancerous cells, however, curcumin
inhibited cap-dependent translation by suppressing the phosphory-
lation and/or total levels of mTOR-related factors (4E-BP1, eIF4G,
eIF4B, eIF4E and Mnk1). The inhibition of p4E-BP1 and eIF4E was
associated with a reduction in cyclin D1, which could explain the
inhibitory effect of curcumin on cell proliferation.
Rinaldi et al.
33
reported that curcumin increased the expression
and function of cytochrome P450 (CYP) 1A1 and/or CYP1B1 in
OSCC of the tongue cells, indicating that it has chemopreventive
properties mediated by the inhibition of carcinogen bioactivation.
A more recent study also revealed that curcumin is a potent inhib-
itor of CYP 1B1in OSCC.
34
Insulin-like growth factors (IGFs) that bind high affinity IGF
receptors (IGFRs) play important roles in regulating cell pheno-
types, including proliferation, differentiation, migration and apop-
tosis. The binding of IGF binding proteins (IGFBPs) to IGF prolongs
the half-life of the latter and limits the bioavailability of free IGF to
bind to IGFRs. Down-regulation of IGFBP-5 was recently shown to
increase tumorigenesis of OSCC cells.
35
The results of another cur-
rent study further indicated that the inhibitory effects of curcumin
on the tumorigenesis of an SAS cell line of OSCC origin were prob-
ably exerted by up-regulating IGFBP-5.

36
That latter study also re-
vealed that up-regulation by curcumin of CCAAT/enhancer-binding
protein
a
(C/EBP
a
), another tumor suppressor for HNSCC, underlies
the up-regulation of IGFBP-5.
In vivo studies
Curcumin as a single therapeutic agent or combined with others
has been currently tested in OSCC models in rats and hamsters.
188 A. Zlotogorski et al. / Oral Oncology 49 (2013) 187–191
Tanaka et al.
37
found that curcumin inhibited rat oral carcinogen-
esis initiated with 4-nitroquinoline 1-oxide (4-NQO). Azuine and
Bhide
38
showed inhibition of oral mucosa tumors in hamsters fol-
lowing the administration of dietary turmeric. In another study,
curcumin administered both alone and in combination with green
tea had inhibitory effects against oral carcinogenesis in hamsters,
which the authors described as being related to the suppression
of cell proliferation, induction of apoptosis and inhibition of angi-
ogenesis.
39
Inhibition of tumor growth was observed in nude mice
xenografts from a HNSCC cell line following the application of cur-
cumin as a topical paste.

20
Manoharan et al.
40
induced OSCC in the
buccal pouch of hamsters by painting them with 7,12-dimethyl-
benz[a]anthracene (DMBA). Oral administration of curcumin and
piperine to the DMBA-painted hamsters on alternate days to DMBA
painting completely prevented the formation of oral tumors, prob-
ably due to their antioxidant properties. It has been previously ob-
served that the combination of curcumin with piperine (an
inhibitor of hepatic and intestinal glucuronidation) resulted in
higher curcumin concentrations in serum and substantially im-
proved the bioavailability of curcumin in healthy human volun-
teers.
41
Lin et al.
42
showed significant inhibitory effects of
curcumin on the proliferation and the growth of a human OSCC cell
line (SAS) inoculated subcutaneously to mice. The cytotoxic effect
of curcumin was mainly at the G2/M phase of the cell cycle.
Intravenous liposomal curcumin has been studied in xenograft
tumors of an HNSCC cell line in nude mice and it was found to
be both nontoxic as well as effective at suppressing tumor growth;
in addition, it was found that curcumin’s growth suppressive ef-
fects are related to the suppression of NF-
j
B in an AKT-indepen-
dent pathway, thus supporting the in vitro findings.
22

Clark
et al.
43
showed that curcumin was highly effective in suppressing
the growth of HNSCC cell xenografts in mice, and that its activity
was associated with modulation of the MTOR downstream target
pS6. In addition, the authors showed that curcumin suppressed
carcinogenesis via inhibition of the AKT/MTOR pathway. In another
study, Chang et al.
36
demonstrated that curcumin-induced IGFBP-5
expression was associated with the suppression of xenograft
tumorigenesis in mice. Those authors suggested that curcumin
activates p38, which, in turn, activates the C/EBPa transactivator
by interacting with binding elements in the IGFBP-5 promoter.
The consequent up-regulation of C/EBPa and IGFBP-5 by curcumin
is crucial to the suppression of oral carcinogenesis.
In vitro and in vivo therapeutic potential of curcumin combined
with standard anti-neoplastic treatment modalities
In addition to its holding considerable therapeutic promise as a
single agent, much interest has been shown in the administration
of curcumin as an adjuvant agent combined with different thera-
peutic modalities. Elattar and Virji
44
concluded that curcumin
has a significant dose-dependent inhibitory effect on growth and
proliferation of OSCC cells, but that it was 5-fold less potent than
cisplatin. Duarte et al.
45
showed enhanced growth suppression of

HNSCC cell lines in vitro and in vivo, using combinations of these
two agents. According to their report, the suppressive effect of
Figure 1 Curcumin acts on oral squamous cell carcinoma (OSCC) cells through multiple pathways. Curcumin’s anti-cancer effect consists of inhibiting the NF-
j
B pathway,
thereby holding back the downstream NF-
j
B-related factors (e.g., cyclin D1, Bcl-2, IL-6, IL-8, MMP-9 and COX2). Curcumin also acts through epithelial growth factor receptors
(EGFRs) to inhibit two downstream pathways, STAT3 and AKT-mTOR. These pathways participate in cancer cell proliferation, have an anti-apoptotic effect, and are involved in
cancer cell-tumor microenvironment crosstalk related to extra-cellular matrix degradation and angiogenesis. Unlike these pathways, curcumin activates the C/EBPa
transactivator by interacting with binding elements in the IGFBP-5 promoter. The resultant up-regulation of C/EBPa and IGFBP-5 by curcumin is crucial to the suppression of
oral carcinogenesis.
A. Zlotogorski et al. / Oral Oncology 49 (2013) 187–191
189
curcumin was mediated through the inhibition of cytoplasmic and
nuclear IKKb, resulting in the inhibition of NF-
j
B activity. Concom-
itantly, they demonstrated that cisplatin acts through the nuclear
p53 protein to control NF-
j
B transactivation with the resultant re-
duced expression of NF-
j
B-regulated proteins. As a result, the anti-
neoplastic cytotoxic effect of cisplatin should be enhanced by the
addition of curcumin, necessitating lower, less toxic doses of cis-
platin. Furthermore, Abuzeid et al.
31
recently found that the novel

curcumin analog FLLL32 sensitized cisplatin-resistant cancer cells,
achieving an equivalent tumor kill with a 4-fold lower dose of
cisplatin.
Recent studies have also investigated the radiosensitization ef-
fect of curcumin upon irradiated OSCC. HNSCC cell lines and ortho-
topic mouse models of SCC-1 tumors were treated with curcumin,
irradiation, or their combination. The combination of curcumin and
irradiation exerted an additive effect. In one study, curcumin treat-
ment of SCC-1 cell lines resulted in diminished COX-2 expression
and inhibition of EGFR phosphorylation.
46
In another study, curcu-
min administration to OSCC cells (PE/CA-PJ15), which were ex-
posed to different doses of irradiation (1, 2.5 and 5 Gy), resulted
in enhanced cytotoxic activity in the OSCC cells.
47
Javvadi et al.
48
reported that an inhibitory activity of curcumin on the anti-oxi-
dant enzyme thioredoxin reductase-1 (TxnRd1) is required for cur-
cumin-mediated radiosensitization of squamous carcinoma cells.
Tuttle et al.
49
examined curcumin-induced irradiation sensitization
in HNSCC cell lines with differing HPV status and expressing differ-
ent levels of TxnRd1 and found that all HPV (À) cell lines expressed
high levels of TxnRd1 and exhibited higher intrinsic resistance to
irradiation. While curcumin was effective in increasing the irradi-
ation response of the resistant HPV (À) cell lines, it had no effect
on the HPV (+) cells.

49
Bioavailability of curcumin in clinical trials
Although curcumin has multiple pathways of action that lead to
enhanced therapeutic effects, the main disadvantages associated
with its oral administration are the high metabolic instability and
poor aqueous solubility that limit its systemic bioavailability.
11,12
In addition, significant side effects and low patient compliance
may preclude the use of oral curcumin at the high doses
(>8 g/day) needed to achieve a therapeutic effect.
50
In order to over-
come these difficulties, new strategies for effective delivery of cur-
cumin are being investigated.
51
Among these methods, there are
liposomal curcumin formulations and encapsulation in diverse
polymeric nanoparticles.
14,22,51
Lin et al.
52
tested the effect of
microemulsions carrying a concentration of curcumin as high as
15
l
M together with low-frequency ultrasound on two OSCC cell
lines (OSCC-4 and OSCC-25). The ultrasound-enhanced delivery of
curcumin as a cytotoxic agent for OSCC was found to be favorable:
the microemulsion could be ingested orally and the concentration
could be adjusted so as to have minimal effect on healthy tissues

in the absence of the ultrasound releasing trigger. Those authors
found that the addition of ultrasound strongly enhanced the cyto-
toxic effect of curcumin-containing microemulsions, especially on
OSCC-25 cells.
Role of curcumin in modulation of the tumor
microenvironment
Recent studies have shown that curcumin possesses anti-tumor
action through modulation of some essential components of the
tumor microenvironment that regulates tumor progression.
53,54
There are emerging lines of evidence that curcumin alters fibro-
blast cell behavior, such as proliferation, migration and apopto-
sis.
55
Furthermore, curcumin modifies immune cells and
inflammatory processes by enhancing the cytotoxicity of CD8(+)
T cells toward tumors.
56
Tumor suppression via regulation of the
tumor microenvironment represents a new attractive way for the
therapeutic usage of curcumin in malignant diseases. More re-
search is required to confirm those beneficial properties of curcu-
min in OSCC as well. The main routes of action of curcumin on
the malignant cells as well as on the components of the tumor
microenvironment are schematically illustrated in Fig. 1.
Concluding remarks and future perspectives
Various scientific investigations have confirmed that curcumin
possesses diverse and multiple molecular pathways of action in-
volved in carcinogenesis and tumor formation. Experimental
in vitro and in vivo studies have demonstrated the anti-tumor ef-

fects of curcumin on OSCC as a single agent as well as in combina-
tion with currently available conventional therapies. It should be
noted that the in vitro studies are actually a mixture of oral and
oropharyngeal cell lines and so future studies should take into con-
sideration the essential differences between SCC of the oropharynx
and SCC of the oral cavity in terms of etiopathogenesis, morbidity
and mortality, and investigate each of them separately. A variety of
strategies and delivery systems have been developed to improve
the bioavailability of curcumin and to refine its therapeutic effi-
cacy, including liposomal formulations or encapsulation in poly-
meric nanoparticles. Further preclinical and clinical studies are
required in order to establish their bioavailability and their chemo-
preventive and therapeutic effects on OSCC. Further research is
also required to confirm the antitumor effect of curcumin in mod-
ulating the tumor microenvironment in OSCC.
Conflict of interest statement
None declared.
Acknowledgments
The authors would like to thank Ms. Esther Eshkol for editorial
assistance.
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