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Department of Urology, Robert C. Byrd Health Science Center West Virginia University, Morgantown, WV 26506-9251
2To whom correspondence should be addressed. E-mail: Dlamm{at}wvuhsc1.hsc.wvu.edu.
ABSTRACT
Of the many beneficial actions of garlic, inhibition of the growth of
cancer is perhaps the most remarkable. Our previous animal studies
demonstrated that aged garlic extract was highly effective, and unlike
the approved immunotherapy for human bladder cancer, bacillus
Calmette-Guérin (BCG), garlic was effective when added to the
diet. To elucidate the mechanism of this antitumor effect, the
literature describing antitumor and immune-enhancing effects of
garlic is reviewed. Garlic can detoxify carcinogens by stimulation of
cytochrome P450 enzymes, antioxidant activity or sulfur
compound binding. Studies demonstrate a direct toxic effect of garlic
to sarcoma and gastric, colon, bladder and prostate cancer cells in
tissue culture, but these effects cannot explain the inhibition of
growth of transplanted cancer in animal models. The most likely
explanation of this effect is immune stimulation. Comparison of the
effects of garlic to BCG immunotherapy reveals many similarities. Both
stimulate proliferation of lymphocytes and macrophage phagocytosis,
induce the infiltration of macrophages and lymphocytes in transplanted
tumors, induce splenic hypertrophy, stimulate release of interleukin-2,
tumor necrosis factor-
and interferon-
, enhance natural killer
cell, killer cell and lymphokine-activated killer cell activity.
These activities represent effective stimulation of the immune
response. Studies suggest that garlic may be useful in preventing the
suppression of immune response that is associated with increased risk
of malignancy. Data suggest that maintenance of immune stimulation can
significantly reduce the risk of cancer. Clinical trials should be
initiated to test the hypothesis that the immune stimulation and other
beneficial effects of garlic are able to reduce the incidence of
cancer.
KEY WORDS: • immunocopetence • garlic • cancer • bladder • mouse
\E
Transitional cell carcinoma of the bladder is highly susceptible
to immunotherapy and is one of a very few human malignancies for which
immunotherapy is the current treatment of choice. Immunotherapy with
bacillus Calmette-Guérin
(BCG)3
is superior to chemotherapy in the treatment of carcinoma in situ of
the bladder; unlike chemotherapy, it provides long-term protection
from tumor recurrence and disease progression. Clinical efficacy in the
treatment of bladder cancer has also been reported with other
immunotherapies, including Keyhole limpet hemocyanin (KLH),
interleukin-2 (IL-2), interferon- (INF-) and the interferon
inducer, bropirimine.
Previous studies have demonstrated that BCG immunotherapy is superior
to chemotherapy with thiotepa, doxorubicin or mitomycin in clinical
trials, and laboratory studies have suggested the superiority of BCG
over alternative immunotherapies. We were, therefore, surprised by the
report of Lau et al. (1990)
that intralesional aged
garlic extract (AGE) was more effective than BCG in the treatment of
transplanted transitional cell carcinoma in the mouse model. In an
effort to develop improved treatments for bladder cancer, we evaluated
AGE in the murine model. These results and the data that suggest that
the antitumor activity of garlic may be related at least in part to
immune stimulation will be reviewed.
Antitumor activity of garlic
The recorded use of garlic in the treatment of tumors dates all
the way back to 1550 BC when ancient Egyptians administered
it orally and topically; the modern era, however, begins in the 1950s
when Weisberger and Pensky (1958)
demonstrated in vitro
and in vivo that thiosulfinate extracts of garlic inhibited the growth
of malignant cells and prevented growth of sarcoma 180 ascites tumor.
Since that time, garlic has been demonstrated in epidemiologic studies
to be associated with a reduced risk of stomach cancer (You et al. 1989
) and, in animal models, to have antitumor activity in
sarcoma, mammary carcinoma, hepatoma, colon cancer, and squamous cell
carcinoma of the skin and esophagus (Lau et al. 1990
).
These effects appear to be mediated by various mechanisms. Prevention
of malignant transformation after the administration of chemical
carcinogens may result from inhibition of the activation of
procarcinogens by garlic’s effect on cytochrome
P450 enzymes (Dion and Milner 1997
), antioxidant activity, or detoxification by binding to
sulfur compounds in garlic (Abdullah et al. 1988
).
Direct inhibition of cancer cell growth in tissue culture has been
documented in sarcoma as well as gastric, colon, bladder and prostate
carcinoma cell lines (Knowles and Milner 1997
,
Pan et al. 1985
, Weisberger and Pensky 1958
). The mechanism of direct tumor cell inhibition has not
yet been determined. Perhaps the most important action of garlic in the
inhibition of cancer and the topic of this review is potentiation of
the immune system.
Aged garlic extract as an immunotherapy for bladder cancer
Lau et al. (1986)
compared intralesional and
intraperitoneal garlic extract therapy with effective immunotherapies
for bladder cancer, BCG, Corynebacterium parvum (CP) and KLH
in the transplantable murine bladder tumor model MBT2. These
experiments demonstrated that intralesional immunotherapy with each of
these agents significantly inhibited tumor growth (P < 0.05). Maximal inhibition of tumor growth was seen with CP (250
µg) and garlic extract (25 mg). Significant reduction in
tumor growth was observed with intraperitoneal CP treatment.
Intraperitoneal garlic appeared to reduce tumor growth, although not to
the level of statistical significance, and intraperitoneal BCG had no
effect.
Examination of hematoxylin and eosin–stained sections of the transplanted tumors demonstrated necrosis and infiltration with macrophages and lymphocytes. Intralesional BCG and CP induced granuloma formation as well, but no granuloma were seen after treatment with garlic extract. Intraperitoneal garlic treatment produced tumor necrosis and infiltration with macrophages and small lymphocytes, suggesting an immune response.
This group (Marsh et al. 1987
) evaluated these same
treatments intravesically after intravesical tumor transplantation. The
efficacy of CP, garlic and BCG, but not KLH, was confirmed. Maximal
inhibition of tumor growth was again observed with CP and garlic.
Comparing treatment schedules of 1, 6, or both 1 and 6 d after
tumor transplantation, only garlic treatment achieved statistical
significance when given as a single treatment 6 d after
transplantation.
Microscopic examination of the bladders revealed infiltration of macrophages and small lymphocytes in animals treated with CP, BCG and, to a lesser extent, KLH. Topical garlic treatment resulted in extensive macrophage and neutrophil infiltration, with few lymphocytes. Splenic weights were significantly increased in all treatment groups relative to untreated controls. Splenic phagocytic function and natural killer (NK) cell cytotoxicity were reported to be significantly increased with both CP and garlic immunotherapy.
These experiments suggested that garlic treatment effectively inhibited growth of transitional cell carcinoma in vivo. In view of the recognized toxicity of BCG therapy and the absence of observed toxicity with garlic treatment in these studies, garlic therapy could be an effective treatment alternative for patients with bladder cancer. Data suggested that immune mechanisms might be responsible for the observed beneficial response to garlic.
To further establish garlic as a safe and effective treatment for
bladder cancer, we evaluated intralesional and oral AGE treatment of
transitional cell carcinoma in the murine model (Riggs et al. 1997
). We confirmed that intralesional garlic extract was
highly effective in the treatment of subcutaneously transplanted MBT2
bladder cancer. Inhibition of tumor growth was highly significant
(P < 0.001) and similar to that of BCG (Table 1
). Unfortunately, in contrast to the previous investigators, we observed
that repeated intralesional garlic injection was toxic, resulting in
death of up to 42% of treated mice. Reduction in the dose and
frequency of intralesional garlic injection reduced the toxicity, but
our enthusiasm for a clinical trial of intravesical garlic was
diminished in view of the newly discovered risk. Because oral garlic
has been used for thousands of years, we sought to evaluate oral garlic
in the treatment of transplanted bladder cancer. Remarkably, oral AGE
when added to drinking water in doses of 5, 50 and 500 mg/100 mL
inhibited the growth of transitional cell carcinoma in a
dose-dependent manner (Table 2
). Significant inhibition of tumor growth was seen at the 50 and 500
mg/mL dose (P = 0.023 and P < 0.001,
respectively), and significant improvement in survival (10 of 20, 50%
vs. 4 of 20, 20% control, P = 0.048) was seen with the
500 mg/mL dose. No adverse effect of oral garlic administration was
seen. Animal weights did not differ among groups and water intake was
highest in the group with the highest concentration of AGE. Because no
toxicity was observed and antitumor effect was highest in the group
with the highest oral garlic intake, it is possible that higher doses
may be even more effective. Studies to identify the optimal oral dose
of garlic in the treatment of bladder cancer are in progress.
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Evidence for immunologic antitumor action of garlic
We observed that garlic has direct dose-dependent toxicity to
cultured transitional cell carcinoma cells, but only at doses 
15
mg/mL, concentrations that are not practical with systemic
administration (Riggs et al. 1997
). The remarkable
efficacy of oral, intravesical and intralesional AGE is therefore
clearly not related to direct cytotoxicity alone. The alternative
antitumor mechanisms of detoxification of carcinogens, antioxidant
activity and inhibition of procarcinogens similarly cannot explain the
inhibition of growth of transplanted cancer. Of the currently
recognized effects of garlic, only immune stimulation can logically
explain the observed inhibition of growth of transplanted cancer.
What evidence supports immune stimulation as an important antitumor effect of garlic? One approach to answer this question is to compare the reported effects of garlic with a recognized, Food and Drug Administration–approved, clinically useful cancer immunotherapy such as BCG.
The effects of garlic on murine transitional cell carcinoma are remarkably similar to those of BCG. Both inhibit tumor growth, and microscopic examination of the site of tumor transplantation reveals infiltration with macrophages and lymphocytes. BCG, but not garlic, induces granuloma formation. In animal models, both BCG and garlic induce hypertrophy of the reticuloendothelial system as measured by splenic hypertrophy. Garlic, like BCG, increases NK cell activity.
Intravesical BCG administration results in the release of cytokines in
the urine, and elevation of urinary cytokines, particularly IL-2, tumor
necrosis factor- (TNF-), and INF-, is associated with
antitumor activity. In animal studies, AGE is reported to induce the
release of IL-2, TNF-, and INF- (Kyo et al. 1998
).
Enhanced phagocytosis, one of the first immunostimulatory actions
reported with BCG, is seen with garlic administration (Kyo et al. 1998
). Additional activities seen with both BCG and garlic
include enhanced killer cell activity and immunoproliferation of
lymphocytes in response to mitogen stimulation (Kyo et al. 1998
). These effects, particularly the pattern of cytokine
release, suggest that garlic, like BCG, stimulates a Th1 cellular
immune response that is characteristic of effective antitumor
immunotherapies.
The component in garlic that is responsible for the effective immune
stimulation is not known conclusively, and it is likely that multiple
ingredients are immunologically active. A protein fraction from garlic
is known to augment in vitro macrophage cytotoxicity and phagocytosis
as well as stimulate lymphocyte proliferation (Hirao et al. 1987
). The protein fraction 4 (F4) from garlic has been
demonstrated to enhance the cytotoxicity of human peripheral blood
lymphocytes against NK-sensitive (K562) and NK-resistant (M14)
cell lines (Morioka et al. 1993
). These effects were
markedly augmented by the addition of low doses of IL-2. The
combination was also more effective in inducing
lymphokine-activated killer cell activity. F4 enhanced IL-2 or
conconavalin A–induced proliferation of lymphocytes and IL-2 receptor
expression. The enhanced cytotoxicity induced by F4 and F4 plus IL-2
was abolished by anti-IL-2 antibody, suggesting that the activity of F4
is mediated by IL-2 (Morioka et al. 1993
). These data
suggest that the F4 fraction of garlic is an efficient
immunopotentiator that may be effective in cancer immunotherapy.
Although the F4 fraction of garlic is clearly an immune stimulant, it
is not the only immunologically active ingredient in garlic. Therefore,
F4 may not be entirely responsible for the observed beneficial response
in transplanted tumors. In studies of the effect of diallyl disulfide
on the growth of transplanted human colon carcinoma cell lines in
immunologically compromised nude mice, Sundaram and Milner (1996)
found diallyl disulfide to be as effective as
5-fluorouracil (5-FU) in inhibiting tumor growth. Combining the diallyl
disulfide and 5-FU did not increase the effect, but concurrent diallyl
disulfide treatment did significantly reduce the depression of
leukocyte counts and splenic weight associated with chemotherapy
administration (Sundaram and Milner 1996
). In another
study, Geng et al. (1997)
examined the effects of
S-allyl cysteine, a water-soluble constituent of garlic
that inhibits chemical carcinogen-induced colon and mammary tumors
in animals and inhibits the growth of neuroblastoma and melanoma in
vitro. In studies of human T cells, S-allyl cysteine was
found to inhibit activation of the nuclear protein of the Rel oncogene
family (nuclear factor-
B). This protein, which is induced by TNF-
or H2O2, regulates immune
function, inflammation and cellular growth (Geng et al. 1997
). These studies suggest that low-molecular-weight
compounds as well as proteins found in garlic have antitumor and immune
effects.
Prevention of immune suppression
Immune surveillance offers protection from cancer and from
impairment of immune defenses, as occurs with conditions ranging from
abnormalities such as acquired immunodeficiency syndrome (AIDS) to the
normal aging process. In addition to enhancing NK function in AIDS
patients, garlic is reported to improve age-related deterioration
of learning behavior and impairment of immune response in a mouse model
(Zhang et al. 1997
). The most common carcinogen,
ultraviolet irradiation, appears to be inhibited by garlic. UV
irradiation damages DNA and induces a specific defect in T-cell
immunity, impairing the recognition of UV-induced malignancy. Most
interestingly, oral garlic administration is found to protect from
photoimmunosuppression (Reeve et al. 1997
). Induction of
an impaired immune response by the tumor itself is an effective means
to escape destruction by host surveillance mechanisms. It is not known
whether garlic can reduce the inhibition of immune response induced by
tumor, but the observed responses are certainly compatible with this
hypothesis. Protection from immune suppression is potentially an
important mechanism in preventing the development of malignancy. For
example, in our experience with maintenance BCG immunotherapy in
patients with superficial bladder cancer, stimulation of the immune
system for a period of 3 y not only protects from recurrence of
bladder cancer, but significantly reduces the incidence of other
malignancies as well (Lamm et al. 1999
). Additional
evidence that garlic potentiates immune responses is provided from
other studies as well. In a study of the effect of garlic on the
neuroendocrine and immunomodulation network, Zhang et al. (1997)
reported that AGE improves age-related deterioration
of learning behavior as well as impaired immune response in a mouse
model. Garlic increased not only lymphocyte proliferation, as seen in
other studies, but antibody production as well (Zhang et al. 1997
).
Further study will be required to identify the active ingredients in
garlic that are responsible for the observed antitumor activity and
immune stimulation. Data now suggest that low-molecular-weight sulfur
compounds and F4 have immune-stimulating properties and also that
garlic can detoxify chemical carcinogens to prevent carcinogenesis and
directly inhibit the growth of cancer cells. Garlic appears to
stimulate immunity including macrophage activity, NK and killer cells,
and lymphokine activated killer cells, and it increases production of
IL-2,TNF, and INF-. These cytokines are associated with the
beneficial Th1 antitumor response, which is characteristic of effective
cancer immunotherapies. Like BCG, garlic stimulates proliferation of
macrophages and lymphocytes, and also protects against suppression of
immunity by chemotherapy and UV radiation. Garlic is clearly not a
panacea for cancer, but its broad range of beneficial effects warrants
serious consideration in clinical trials for the prevention and
treatment of cancer.
FOOTNOTES
1 Presented at the conference "Recent Advances
on the Nutritional Benefits Accompanying the Use of Garlic as a
Supplement" held November 15–17, 1998 in Newport Beach, CA. The
conference was supported by educational grants from Pennsylvania State
University, Wakunaga of America, Ltd. and the National Cancer
Institute. The proceedings of this conference are published as a
supplement to The Journal of Nutrition. Guest editors:
John Milner, The Pennsylvania State University, University Park, PA and
Richard Rivlin, Weill Medical College of Cornell University and
Memorial Sloan-Kettering Cancer Center, New York, NY. 
3 Abbreviations: AGE, aged garlic extract; AIDS,
acquired immunodeficiency syndrome; BCG, bacillus
Calmette-Guérin; CP, Corynebacterium parvum; F4,
protein fraction 4; 5-FU, 5-fluorouracil; IL-2, interleukin-2; INF,
interferon; KLH, Keyhole limpet hemocyanin; TNF-, tumor necrosis
factor-.
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