Cannabidiol as a novel inhibitor of Id-1 gene expression in aggressive breast cancer cells

Cannabidiol as a novel inhibitor of Id-1 gene expressionin aggressive breast cancer cells

Sean D. McAllister, Rigel T. Christian,
Maxx P. Horowitz, Amaia Garcia,
and Pierre-Yves Desprez
California Pacific Medical Center, Research Institute,
San Francisco, California
Abstract
Invasion and metastasis of aggressive breast cancer cells
is the final and fatal step during cancer progression, and
is the least understood genetically. Clinically, there are still
limited therapeutic interventions for aggressive and metastatic breast cancers available. Clearly, effective and nontoxic therapies are urgently required. Id-1, an inhibitor of
basic helix-loop-helix transcription factors, has recently
been shown to be a key regulator of the metastatic
potential of breast and additional cancers. Using a mouse
model, we previously determined that metastatic breast
cancer cells became significantly less invasive in vitro and
less metastatic in vivo when Id-1 was down-regulated by
stable transduction with antisense Id-1. It is not possible
at this point, however, to use antisense technology to
reduce Id-1 expression in patients with metastatic breast
cancer. Here, we report that cannabidiol (CBD), a cannabinoid with a low-toxicity profile, could down-regulate
Id-1 expression in aggressive human breast cancer cells.
The CBD concentrations effective at inhibiting Id-1 expression correlated with those used to inhibit the proliferative
and invasive phenotype of breast cancer cells. CBD was
able to inhibit Id-1 expression at the mRNA and protein
level in a concentration-dependent fashion. These effects
seemed to occur as the result of an inhibition of the
Id-1 gene at the promoter level. Importantly, CBD did
not inhibit invasiveness in cells that ectopically expressed
Id-1. In conclusion, CBD represents the first nontoxic
exogenous agent that can significantly decrease Id-1
expression in metastatic breast cancer cells leading to the
down-regulation of tumor aggressiveness. [Mol Cancer
Ther 2007;6(11):2921–7]
Introduction
The development of breast cancer and its spread to other
parts of the body requires several genotypic and phenotypic changes in the cells leading to de-differentiation,
uncontrolled proliferation, and invasion. Invasion and
metastasis to the other tissues of the body is the final and
fatal step during cancer progression and is the least
understood genetically (1). Despite all currently available
treatments, breast cancer is most often incurable once
clinically apparent metastases develops.
Id helix-loop-helix proteins are negative regulators of
basic helix-loop-helix transcription factors (2). Strong evidence now suggests that the Id family of helix-loop-helix
proteins control cellular processes related to tumor progression (3). We found that reducing Id-1 using antisense
technology led to significant reductions in breast cancer
cell proliferation and invasiveness in vitro and metastasis
in vivo in mice (4). Furthermore, Id-1 overexpression in
breast cancer cells was also found to be one of the most
significant genes within a gene signature set that is correlated with the propensity of primary human breast cancer cells to metastasize to the lung (5).
Reducing Id-1 expression could provide a rational
therapeutic strategy for the treatment of aggressive human
breast cancers. It is not possible at this point, however,
to use antisense technology to reduce Id-1 expression in
humans with metastatic breast cancer. In our search for a
nontoxic exogenous compound that could inhibit Id-1 expression, a potential candidate agent, cannabidiol (CBD),
was discovered.
The endocannabinoid system was discovered through
research focusing on the primary psychoactive component
of Cannabis sativa, D
9
-tetrahydrocannabinol (D
9
-THC), and
other synthetic cannabinoids (6). D
9
-THC and additional
cannabinoid agonists have been shown to interact with two
G protein – coupled receptors named CB1 and CB2 (6). More
recent studies have shown that CB1 and CB2 receptor
agonists show promise as tumor inhibitors (7, 8). The
psychotropic effects of D
9
-THC and additional cannabinoid
agonists, mediated through the CB1
receptor, limit their
clinical utility. In addition to D
9
-THC, CBD is also present
in significant quantities in C. sativa (9). CBD does not have
appreciable affinity for CB1 or CB2 receptors and does not
have psychotropic activities (10). CBD has been shown to
inhibit breast cancer metastasis in vivo in mice (11).
However, modulation of a distinct signaling pathway that
would explain the inhibitory action of CBD on breast
cancer metastasis has not been elucidated.
Received 6/4/07; revised 9/5/07; accepted 9/20/07.
Grant support: NIH (CA102412, CA111723, DA09978, and CA82548),
the Department of Defense (PC041013), the California Breast Cancer
Research Program (12IB-0116), and the Research Institute at California
Pacific Medical Center.
The costs of publication of this article were defrayed in part by the
payment of page charges. This article must therefore be hereby marked
advertisement in accordance with 18U.S.C. Section 1734 solely to
indicate this fact.
Requests for reprints: Sean D. McAllister, California Pacific Medical
Center, Research Institute, 475 Brannan Street, San Francisco, CA
94107. Phone: 415-600-5926; Fax: 415-600-1725.
E-mail: mcallis@cpmcri.org
Copyright C 2007 American Association for Cancer Research.
doi:10.1158/1535-7163.MCT-07-0371
2921
Mol Cancer Ther 2007;6(11). November 2007Our data presented here show that CBD represents the
first exogenous agent that can down-regulate Id-1 expression in aggressive hormone-independent breast cancer
cells. We suggest that CBD down-regulation of Id-1 and
corresponding inhibition of human breast cancer cell
proliferation and invasiveness provides a potential mechanism for the antimetastatic activity of the compound.
Materials and Methods
Cell Culture and Treatments
We used the human breast cancer cells lines MDA-MB231
and MDA-MB436 obtained from American Type Culture
Collection. To prepare the MDA-MB231-Id-1 cells, cells
were infected with a pLXSN-Id-1 sense expression vector.
In all experiments, the different cell populations were first
cultured in RPMI medium containing 10% fetal bovine
serum. On the first day of treatment, the medium was
replaced with vehicle control or drug in RPMI and 0.1%
fetal bovine serum as previously reported (12). The media
with the appropriate compounds were replaced every 24 h.
D
9
-THC, CBN, CBD, CBG, and CP55,940 were obtained
from the NIH through the National Institute of Drug
Abuse. WIN55,212-2 was purchased from Sigma-RBI.
MTT Assay
To quantify cell proliferation, the MTT assay was used
(Chemicon). Cells were seeded in 96-well plates. Upon
completion of the drug treatments, cells were incubated at
37jC with MTT for 4 h, and then isopropanol with 0.04 N
HCl was added and the absorbance was read after 1 h in
a plate reader with a test wavelength of 570 nm. The
absorbance of the medium alone at 570 nm was subtracted,
and percentage control was calculated as the absorbance
of the treated cells/control cells 100.
Boyden Chamber Invasion Assay
Assays were done in modified Boyden chambers (BD
Biosciences) as previously described (4). Cells at 1.5 10
4
per well were added to the upper chamber in 500 AL of
serum-free medium supplemented with insulin (5 Ag/mL).
The lower chamber was filled with 500 AL of conditioned
medium from fibroblasts. After a 20-h incubation, cells
were fixed and stained as previously described (4). Cells
that remained in the Matrigel or attached to the upper side
of the filter were removed with cotton tips. Invasive breast
cancer cells on the lower side of the filter were counted
using a light microscope.
QuantitativeWestern Analysis
Proteins were separated by SDS-PAGE, blotted on Immobilon membrane, and probed with anti – Id-1 and the
appropriate secondary antibody as previously described
(4, 13). Band intensity values were obtained directly from the
blot using AlphaeaseFC software or from film using Image-J
(NIH). As a normalization control for loading, blots were
stripped and reprobed with mouse alpha-tubulin (Abcam).
PCR
Total cellular RNA was isolated from breast cancer
cells treated with vehicle control or with CBD. Transcripts
for Id-1 and for h-actin were reverse-transcribed using
Superscript II Reverse Transcriptase II (Life Technologies),
and PCR was done. The 5¶ and 3¶ PCR primers were
AGGTGGTGCGCTGTCTGTCT and TAATTCCTCTTGCCCCCTGG for Id-1; and GCGGGAAATCGTGCGTGACATT
and GATGGAGTTGAAGGTAGTTTCGTG for h-actin.
PCR was done in buffer containing 1 Amol/L of each of
the 5¶ and 3¶ PCR primers and 0.5 units of Taq polymerase
using 25 cycles for amplification of Id-1 and h-actin cDNAs.
The cycle conditions were 45 s denaturation at 94jC, 45 s
annealing at 55jC, and 1 min extension at 72jC.
Id-1Promoter Reporter Assays
A SacI-BspHI fragment of 2.2 kb corresponding to the
5¶ upstream region of human Id-1 gene and driving a
luciferase gene in a PGL-3 vector (Promega) has already
been described (Id-1-sbsluc; ref. 13). Cells were plated in
six-well dishes in medium supplemented with 10% fetal
bovine serum and 5 Ag/mL insulin. After 24 h, cells were
cotransfected with 6 Ag of luciferase reporter plasmids and
2 Ag of pCMVh (Clontech) using Superfect reagent
(Qiagen). pCMVh contained bacterial h-galactosidase and
served to control for variation in transfection efficiency.
Three hours after transfection, the cells were rinsed twice
with PBS and were cultured in the absence or presence
of CBD for 48 to 72h. Cell pellets were lysed in 80 AL of
reporter lysis buffer (Promega) for 10 min at room temperature. Lysed cells were centrifuged and supernatants
harvested. Luciferase and h-gal assays were done using
Luciferase assay system (Promega), h-Gal assay kit (Clontech), and a 2010 luminometer (PharMingen).
Statistical Analysis
The IC50 values with corresponding 95% confidence
limits were compared by analysis of logged data (GraphPad Prism). When only the confidence limits of the IC50
Table 1. Antiproliferative potencies of cannabinoids during a
3-d treatment of MDA-MB231 and MDA-MB436 breast cancer
cells
Compound MDA-MB231 MDA-MB436
O
H3
C
H3
C
OH
CH3
CH3
D9
-THC 1.2(1.0 – 1.4) 2.5 (1.8 – 3.4)
H3
C
H3
C
OH
CH3
O CH3
CBN 1.2(0.9 – 1.5) 2.6 (1.8 – 3.7)
N CH3
O
O
N(CH2
CH2
)
2
0
WIN55,212-2 1.7 (1.5 – 2.2) 2.4 (1.6 – 3.4)
H3
C
OH
OH
OH
CH3
CH3
CP55,940 2.5 (1.5 – 4.1) 1.3 (0.7 – 1.6)
H3
C
H2
C
OH
HO CH3
CH3
CBD 1.3 (1.0 – 1.9) 1.6 (1.1 – 2.2)
H3C
CH3
CH3
HO
OH
CH3
CBG 2.3 (2.1 – 2.5) 2.1 (1.5 – 3.0)
NOTE: Cells were treated with cannabinoid compounds for 3 d and the
IC50 values for the antiproliferative effects of the compounds were
calculated. Data are the means and corresponding 95% confidence limits
of at least three experiments. IC50 values are reported in Amol/L.
2922 Cannabidiol and Id-1 in Breast Cancer
Mol Cancer Ther 2007;6(11). November 2007values overlapped, significant differences were determined
using unpaired Student’s t test. Significant differences were
also determined (Prism) using ANOVA or the unpaired
Student’s t test, where suitable. Bonferroni-Dunn post
hoc analyses were conducted when appropriate. P < 0.05
values defined statistical significance.
Results
Cannabinoids Reduce the Growth of Aggressive Human Breast Cancer Cells
In order to test their antiproliferative activities, three
groups of cannabinoid compounds were chosen: (a)
natural cannabis constituents that have affinity for CB1
and CB2
receptors, D
9
-THC and CBN; (b) synthetic
cannabinoid analogues that have high affinity for CB1
and CB2 receptors, WIN55,212-2 and CP55,940; and (c)
natural cannabis constituents that do not have appreciable affinity for CB1 and CB2 receptors, CBD and CBG.
Breast cancer cells were treated for 3 days and IC50
values were calculated (Table 1). The rank order of
potencies for the antiproliferative effects of the cannabinoids in MDA-MB231 cells was: CBD = D
9
-THC = CBN >
WIN55,212-2 > CBG = CP55,940. The rank order of
potencies for the antiproliferative effects of the cannabinoids in MDA-MB436 cells was: CBD = CP55,940 > CBG =
WIN55,212-2 = D
9
-THC = CBN. Overall, the data showed
that CBD was the most effective inhibitor of human breast
cancer cell proliferation.
Cannabinoids Reduce Breast Cancer Cell Invasiveness
Invasion is an important step towards breast cancer
cell metastasis. Therefore, we next determined the effects of
several cannabinoids on the ability of the most aggressive
human breast cancer cell line, MDA-MB231, to migrate and
invade a reconstituted basement membrane in a Boyden
chamber. All three compounds tested, i.e., CBD, D
9
-THC,
and WIN55,212-2, significantly reduced the invasion of
MDA-MB231 cells (Fig. 1A). Again, as was observed with
the cell proliferation experiments, the most potent inhibitor
of invasion was CBD.
Figure 1. CBD is the most effective inhibitor of invasiveness and Id-1 expression in MDA-MD231 cells. A, the Boyden chamber invasion assay was used
to determine the effects of cannabinoids on the invasiveness of aggressive human breast cancer MDA-MB231 cells. Compounds were added at
concentrations of 0.1, 1.0, or 1.5 Amol/L. Data are presented as relative invasiveness of the cells through the Matrigel, where the respective controls are
set as 100%. B, proteins from MDA-MB231 cells treated with vehicle (control), 0.1, 1.0, or 1.5 Amol/L of CBD for 3 d were extracted and analyzed for
Id-1 by Western blot analysis as described in Materials and Methods. C, proteins from MDA-MB231 cells treated with additional cannabinoids for 3 d
were extracted and analyzed for Id-1 by Western blot analysis. Normalization was carried out by stripping the blots and reprobing with a monoclonal
antitubulin antibody. Densitometry readings of the blots were taken and the percentage of relative expression was calculated as the expression of Id-1 in
the treated cells / vehicle cells 100. D, the inhibitory effect of 1.5 Amol/L of CBD on Id-1 expression was compared over a time course of 1, 2, and 3 d.
Columns, mean of at least three replicates; bars, SE. Data were compared using a one-way ANOVA with a corresponding Dunnett’s post hoc test.
*, P < 0.05, statistically significant differences from control.
Molecular Cancer Therapeutics 2923
Mol Cancer Ther 2007;6(11). November 2007CBD Down-regulates Id-1Expression
We predicted that CBD, the most potent inhibitor of
breast cancer cell proliferation and invasion tested, would
regulate the expression of key genes that control breast
cancer cell proliferation and invasiveness. A potential
candidate protein that could mediate the effects of CBD
on both phenotypes was the helix-loop-helix protein Id-1.
We determined that treatment of MDA-MB231 cells with
CBD led to a concentration-dependent inhibition of Id-1
protein expression (Fig. 1B and C). The inhibitory effect of
CBD on Id-1 expression occurred at concentrations as low
as 100 nmol/L. CBD was significantly more effective at
reducing Id-1 protein expression compared with other cannabinoid compounds (Fig. 1C). The CBD concentrations
effective at inhibiting Id-1 expression correlated with those
used to inhibit the proliferative and invasive phenotype of
MDA-MB231 cells. Furthermore, the down-regulation of
Id-1 protein in the presence of CBD seemed to precede,
and not follow, the inhibitory effects of CBD on the
proliferation and invasiveness of MDA-MB231 cells
(Fig. 1D), suggesting that Id-1 down-regulation represents
a cause rather than a consequence of a decrease in breast
cancer cell aggressiveness.
The Effects of CBD on Invasion and Id-1 Protein Expression Can Be Reproduced in an Additional Breast
Cancer Cell Line
Based on the data presented in Table 1, CBD could also
decrease cell proliferation in another breast cancer cell
line other than MDA-MB231, the MDA-MB436 cells. The
metastatic cell line MDA-MB436 is able to invade
through the peritoneum and colonize visceral organs
when injected in athymic nude mice (14). However, these
cells are less metastatic than the MDA-MB231 cell line.
Using the MDA-MB436 cells, we confirmed the effects of
CBD on a decrease of cell invasion (Fig. 2A) associated
with a down-regulation of Id-1 protein expression
(Fig. 2B and C). These data suggest that the effects of
CBD on breast cancer cell phenotypes, potentially
through a decrease in Id-1 expression, are not restricted
to one particular cell line but could represent a more
general phenomenon.
CBD Inhibits theTranscription of the Id-1Gene
In order to determine if CBD modulated Id-1 at the
gene expression level, we investigated if Id-1 mRNA
was down-regulated by CBD. As shown in Fig. 3A using
reverse transcription-PCR, Id-1 mRNA expression was
significantly reduced upon treatment with CBD in MDAMB231 cells. To determine if this effect was due to the
inhibition of transcription, a construct was used that
contained the Id-1 promoter fused to a luciferase reporter
in a PGL-3 basic vector. This construct was transiently
transfected, and 24 h after transfection, MDA-MB231-Id-
1-luc cells were treated with CBD for 2or 3 days and
luciferase activity was measured. Transfection efficiency
and analysis of equal amounts of total protein were
controlled by cotransfection of the cells with pCMVB
containing h-galactosidase. Treatment with CBD resulted
in a significant inhibition of luciferase activity, with the
greatest inhibition occurring on day 3 (Fig. 3B and C).
The effect on the down-regulation of Id-1 mRNA and
promoter expression could also be reproduced in the
MDA-MB436 cell line (Fig. 3D and E). Overall, all these
findings correlated with the inhibition of Id-1 expression
as assessed by Western analysis.
CBD Does Not Inhibit Cell Invasiveness in Cells that
Ectopically Express Id-1
To determine if Id-1 represented a key mediator of
CBD effects in highly aggressive breast cancer cells, Id-1
was constitutively expressed into MDA-MB231 cells (+Id-
1 as described in Fig. 4). The ectopic Id-1 gene, which is
not under the control of the endogenous promoter, was
introduced in the cells using the pLXSN retroviral vector.
Figure 2. CBD reduces invasion as well as Id-1 expression in MDA-MD436 cells. A, the Boyden chamber invasion assay was used to determine the
effects of CBD on the invasiveness of human breast cancer MDA-MB436 cells. Data are presented as relative invasiveness of the cells through the Matrigel,
where the respective controls are set as 100%. B, proteins from MDA-MB436 cells treated with vehicle (control) or 2.0 Amol/L of CBD for 3 d were
extracted and analyzed for Id-1 by Western blot analysis. Normalization was carried out by stripping the blots and reprobing with a monoclonal antitubulin
antibody. C, densitometry readings of the blots were taken from three independent experiments and the percentage of relative expression was calculated
as the expression of Id-1 in the treated cells / vehicle cells 100. *, P < 0.05, statistically significant differences from control.
2924 Cannabidiol and Id-1 in Breast Cancer
Mol Cancer Ther 2007;6(11). November 2007As a control, cells were infected with an empty pLXSN
vector ( Id-1). Ectopic Id-1 expression increased invasion
in MDA-MB231 cells in agreement with our previous
studies (13, 15). However, the difference in invasion
between cells that ectopically expressed Id-1, or the
control vector lacking Id-1, was not reflected in Fig. 3A
because the data was represented as relative invasiveness
(with all the control cells set at 100%). In cells expressing
the control vector, treatment with CBD led to a significant reduction in cell invasiveness (Fig. 4A). Western
blotting confirmed the down-regulation of Id-1 expression in this cell population (Fig. 4B). Importantly, and in
contrast with the results in control cells, CBD did not
inhibit cell invasiveness (Fig. 4A) or Id-1 expression
(Fig. 4B) in MDA-MB231+Id-1 cells that ectopically
expressed Id-1.
Discussion
Metastasis is the final and fatal step in the progression of
breast cancer. Currently available therapeutic strategies at
this stage of cancer progression are often nonspecific, have
only marginal efficacy, and are highly toxic. This is in part
due to the lack of knowledge about the molecular mechanisms regulating the development of aggressive cancers.
Therapeutic approaches targeting only specific mechanisms involved in the development of aggressive breast
cancers are urgently need. The expectation would be that
this strategy would reduce unwanted toxicities associated
with the therapy itself.
We previously showed that the helix-loop-helix protein
Id-1, an inhibitor of basic helix-loop-helix transcription factors, plays a crucial role during breast cancer progression
(4). Id-1 stimulated proliferation, migration, and invasion
in breast cancer cells (13, 16). Moreover, targeting Id-1
expression partially in breast cancer cells reduced invasion
in vitro and breast cancer metastasis in preclinical animal
models (4, 5). Based on these data, we hypothesized that
Id-1 could be a promising candidate for future therapy
approaches, and that inhibiting Id-1 expression and/or
activity might be of benefit for patients with breast cancer. This approach may be highly effective and safe in
advanced breast cancer patients, given (a) the relationship
between high Id-1 expression levels and aggressive breast
Figure 3. CBD inhibits the expression of Id-1 gene at the mRNA and promoter levels in MDA-MB231 and MDA-MB436 cells. A, the inhibition of the Id-1
gene product (434 bp) by CBD was investigated in MDA-MB231 cells using reverse transcription-PCR. Expression of the h-actin gene product (232 bp) was
used as a control. B, luciferase activity in MDA-MB231 cells transiently transfected with Id-1-sbsluc was determined in the presence of vehicle (control) or
1.5 Amol/L of CBD. Cells were treated for 2 d and luciferase activity was measured. C, cells were treated for 3 d. For both B and C, all values were
normalized for the amount of h-gal activity present in the cell extracts. Columns, mean of at least three replicates; bars, SE. The data are represented as
percentage of activity of the treated cells / vehicle cells 100. Data were compared using the unpaired Student’s t test. *, P < 0.05, statistically
significant differences from control. D, the inhibition of the Id-1 gene product by CBD was investigated in MDA-MB436 cells using reverse transcriptionPCR. Expression of the h-actin gene product was used as a control. E, luciferase activity in MDA-MB436 cells transiently transfected with Id-1-sbsluc was
determined in the presence of vehicle (control) or 2 Amol/L of CBD. Cells were treated for 2 d and luciferase activity was measured.
Molecular Cancer Therapeutics 2925
Mol Cancer Ther 2007;6(11). November 2007cancer cell behaviors; (b) partial reduction in Id-1 activity
can achieve significant outcomes; and (c) Id-1 expression is
low in normal adult tissues, thereby eliminating unwanted
toxicities generally associated with currently available therapeutic modalities.
However, approaches targeting Id-1 expression, including gene therapy using antisense oligonucleotide, short
interfering RNA, and nonviral or viral plasmid – based
strategies, are not yet routinely used in the clinic. Therefore,
the development of new strategies to modulate Id-1
expression/functional activity is needed. A range of small
molecules that target the molecular pathology of cancer are
now being developed, and a significant number of them are
being tested in ongoing human clinical trials (17). We
propose that the use of CBD, as an inhibitor of Id-1,
represents a novel strategy to treat breast cancer. A wide
range of cannabinoid compounds were tested and CBD,
a nonpsychoactive cannabinoid constituent, was the most
potent inhibitor of human breast cancer cell aggressiveness
through Id-1 mRNA and protein down-regulation.
Cannabinoid agonists working through CB1 and CB2
receptors have been shown to act as tumor inhibitors in a
variety of cancer models (7, 8). Present evidence also shows
that the cannabinoid constituent CBD, which has negligible
affinity for CB1 and CB2 receptors, also has antitumor
activity (18 – 20). Specifically, Ligresti et al. have recently
shown that CBD inhibits the metastasis of aggressive
human breast cancer cancers in vivo (11). However, the
primary molecular pathways involved in CBD inhibition of
invasion and metastasis remain to be clarified. Overall, the
IC50 values, even being within the range observed by other
laboratories (21, 22), were lower than those reported by
Ligresti et al. (11). This difference is likely due to the fact
that we did the experiments in lower serum concentrations,
which have been shown to improve the antiproliferative
activity of cannabinoids (23).
Here, we report that CBD acting as a potent Id-1 inhibitor
might effectively inhibit genotypic and phenotypic changes
that allow aggressive breast cancers to invade and metastasize. Most importantly, ectopic expression of Id-1 in MDAMB231 breast cancer cells abolished the effects of CBD on cell
invasion. Cells were infected with an Id-1 gene (pLXSN
vector) that is not under the control of the endogenous Id-1
promoter. As presented in Fig. 3, CBD seems to act by downregulating endogenous Id-1 gene expression at the promoter
level, not as a result of mRNA and/or protein destabilization. Therefore, CBD should not have any effect on the Id-1
expression from the pLXSN vector. Indeed, ectopic expression of Id-1 in MDA-MB231 breast cancer cells was able to
abolish the effects of CBD.
These data indicate that Id-1 is a key factor whose
expression needs to be down-regulated in order to observe
the beneficial effects of CBD on the reduction of breast
cancer cell aggressiveness. Based on previous findings
(reviewed in ref. 15), we suggest that a decrease in Id-1
protein upon CBD treatment might consequently lead to a
down-regulation of growth-promoting genes such as
Zfp289 as well as to a down-regulation of invasionpromoting genes such as the membrane type matrix
metalloproteinase (MT1-MMP).
Plant cannabinoids are stable compounds with lowtoxicity profiles that are well tolerated by animals and
humans during chronic administration (24, 25). A formulation including a 1:1 ratio of THC and CBD has recently
been used in a clinical trial for the treatment of multiple
sclerosis (26). The few side effects reported were related to
the psychoactivity of D
9
-THC. If CBD shows efficacy for
treatment of metastatic breast cancer in humans, the low
toxicity of the compound would make it an ideal candidate
for chronic administration.
Because CBD inhibits Id-1 expression in aggressive
breast cancer cells, a rational drug design strategy could
be used to potentially create more potent and efficacious
analogues. Moreover, reducing Id-1 expression with
cannabinoids could also provide a therapeutic strategy
for the treatment of additional aggressive cancers because
Id-1 expression was found to be up-regulated during
the progression of almost all types of solid tumors
investigated (27).
Acknowledgments
The authors thank Dr. Mary Abood for helpful scientific discussions and
the critical reading of the manuscript.
Figure 4. Ectopic expression of Id-1 blocks the effect of CBD on MDAMB231 invasiveness. A, data are presented as relative invasiveness of
control MDA-MB231 cells ( Id-1) and of MDA-MB231 cells that
ectopically expressed Id-1 (+Id-1) after a 2-d treatment with vehicle
(control) or 1.5 Amol/L of CBD (CBD), and then an overnight invasion
assay. The respective controls are set as 100%; columns, mean of at
least three replicates; bars, SE. Data were compared using the unpaired
Student’s t test. *, P < 0.05, statistically significant differences from
control. B, the inhibitory effect of CBD on Id-1 expression in Id-1 and
+Id-1 MDA-MB231 cells was compared using Western analysis. Equal
loading was confirmed by stripping the blots and reprobing with a
monoclonal antitubulin antibody.
2926 Cannabidiol and Id-1 in Breast Cancer
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