LE Magazine February 2003
Cancer/vitamins
Inhibition of cigarette smoke-related
DNA adducts in rat tissues by indole-3-carbinol.
Indole-3-carbinol (I3C) found in various cruciferous
vegetables has been shown to exert anti-carcinogenic activity
in several target organs. In this study, we have investigated
the effects of I3C on cigarette smoke-related lipophilic DNA
adduct formation, potentially a key step in chemical
carcinogenesis. Female Sprague-Dawley rats were exposed to
sidestream cigarette smoke in a whole-body exposure chamber
for six h per day, seven days a week for four weeks. Control
animals received only vehicle while the intervention groups
received I3C (1. 36 or 3.40 mmol/kg, b.wt.) daily by gavage
starting from one week prior to smoke initiation until the end
of the experiment. Analysis of tissue DNA by nuclease
P1-mediated 32P-postlabeling showed one major and several
minor smoke-related adducts in lung, trachea, heart and
bladder. The high dose of I3C significantly inhibited the
major adducts in lung (#5) and trachea (#3) by 55% each; minor
adducts were slightly inhibited (20% to 40%). The low dose of
I3C showed lesser degree of inhibition (30% to 40%) in both
lung and trachea; however, it was found statistically
significant in lung only. The major smoke-related adduct in
bladder (#2) was strongly inhibited (>65%) by high dose of
I3C approaching adduct levels achieved in sham-exposed rats. A
small but statistically significant decrease in the
smoke-related DNA adduct (#5) in heart tissue was also
observed by intervention with high dose I3C. Low levels (30 to
50 adducts/10(10) nucleotides) of I3C-derived DNA adducts were
also found in all the tissues examined although their
significance remains unknown. These data show significant
inhibition of cigarette smoke-related DNA adducts by I3C,
particularly in the lung, trachea and bladder.
Mutat Res 2000 Jul 20;452(1):11-8
Placebo-controlled trial of
indole-3-carbinol in the treatment of CIN.
OBJECTIVE: Most precancerous lesions of the cervix are
treated with surgery or ablative therapy. Chemoprevention,
using natural and synthetic compounds, may intervene in the
early precancerous stages of carcinogenesis and prevent the
development of invasive disease. Our trial used
indole-3-carbinol (I-3-C) administered orally to treat women
with CIN as a therapeutic for cervical CIN. METHODS: Thirty
patients with biopsy proven CIN II-III were randomized to
receive placebo or 200, or 400 mg/day I-3-C administered
orally for 12 weeks. If persistent CIN was diagnosed by
cervical biopsy at the end of the trial, loop electrocautery
excision procedure of the transformation zone was performed.
HPV status was assessed in all patients. RESULTS: None (0 of
10) of the patients in the placebo group had complete
regression of CIN. In contrast four of eight patients in the
200 mg/day arm and four of nine patients in the 400 mg/day arm
had complete regression based on their 12-week biopsy. This
protective effect of I-3-C is shown by a relative risk (RR) of
0.50 ((95% CI, 0. 25 to 0.99) P = 0.023) for the 200 mg/day
group and a RR of 0.55 ((95% CI, 0.31 to 0.99) P = 0.032) for
the 400 mg/day group. HPV was detected in seven of 10 placebo
patients, in seven of eight in the 200 mg/day group, and in
eight of nine in the 400 mg/day group. CONCLUSIONS: There was
a statistically significant regression of CIN in patients
treated with I-3-C orally compared with placebo. The 2/16
alpha-hydroxyestrone ratio changed in a dose-dependent
fashion.
Gynecol Oncol 2000
Aug;78(2):123-9
Fraction of prostate cancer incidence
attributed to diet in Athens, Greece.
Diet appears to be a major determinant in the incidence of
prostate cancer. In a case-control study conducted in Athens,
Greece, we found that dairy products, butter and seed oils
were positively associated with risk of prostate cancer,
whereas cooked and raw tomatoes were inversely associated. We
utilized the data from this study to calculate the population
attributable fractions under alternative assumptions of
feasible dietary changes. For each subject, a dietary score
was calculated and categorized into approximately quintiles,
representing increasing levels of prostate cancer risk as a
function of the intake of the five discriminatory food groups
or items. Population attributable fractions in terms of this
dietary score were calculated taking into account multivariate
adjustment. We observed that, if all individuals were shifted
to the baseline category, the incidence of prostate cancer in
this study population would be reduced by 41% (95% confidence
interval 23% to 59%). However, if all individuals were shifted
to the adjacent lower risk quintile, the expected incidence
reduction would be a more modest 19%. The incidence of
prostate cancer in Greece could be reduced by about two-fifths
if the population increased the consumption of tomatoes and
reduced the intake of dairy products, and substituted olive
oil for other added lipids.
Eur J Cancer Prev 2000
Apr;9(2):119-23
Flavonoids apigenin and quercetin
inhibit melanoma growth and metastatic potential.
Flavonoids are a class of polyphenolic compounds widely
distributed in the plant kingdom, which display a variety of
biological activities, including chemoprevention and tumor
growth inhibition. Our aim was to investigate the effects of
several polyphenols on the growth and metastatic potential of
B16-BL6 melanoma cells in vivo. Intraperitoneal administration
of quercetin, apigenin, (-)-epigallocathechin-3-gallate
(EGCG), resveratrol and the anti-estrogen tamoxifen, at the
time of i.m. injection of B16-BL6 cells into syngeneic mice,
resulted in a significant, dose-dependent delay of tumor
growth, without toxicity. The relative descending order of
potency was EGCG > apigenin = quercetin = tamoxifen >
resveratrol > control. Furthermore, polyphenols
significantly potentiated the inhibitory effect of a non-toxic
dose of cisplatin. When tested for the ability to inhibit lung
colonization, quercetin, apigenin and tamoxifen (but not EGCG
or resveratrol) significantly decreased the number of B16-BL6
colonies in the lungs in a dose-dependent manner, with
quercetin and apigenin being more effective than tamoxifen.
Interestingly, quercetin, apigenin and tamoxifen (but not EGCG
or resveratrol) significantly decreased the invasion of
B16-BL6 cells in vitro, with quercetin and apigenin being more
effective than tamoxifen. This suggests that anti-invasive
activity is one of the mechanisms underlying inhibition of
lung colonization by quercetin and apigenin. In conclusion,
quercetin and apigenin inhibit melanoma growth and invasive
and metastatic potential; therefore, they may constitute a
valuable tool in the combination therapy of metastatic
melanoma.
Int J Cancer 2000 Aug
15;87(4):595-600
Excessive intake of zinc impairs
immune responses.
The effect of administration of large amounts of zinc on
immune response and serum lipoproteins was examined. Eleven
healthy adult men ingested 150 mg of elemental zinc twice a
day for six weeks. This was associated with a reduction in
lymphocyte stimulation response to phytohemagglutinin as well
as chemotaxis and phagocytosis of bacteria by
polymorphonuclear leukocytes. Serum high-density lipoprotein
concentration decreased significantly and low-density
lipoprotein level increased slightly. The common food fad of
zinc supplementation with resultant excessive intake could
have deleterious effects in healthy persons.
JAMA 1984 Sep 21;252(11):1443-6
Flavonoids (apigenin, tangeretin)
counteract tumor promoter-induced inhibition of intercellular
communication of rat liver epithelial cells.
We have shown previously that two flavonoids, apigenin and
tangeretin, enhance gap junctional intercellular communication
(GJIC) in rat liver epithelial cells, named REL cells. Here,
we show that these two flavones also antagonize the inhibition
of GJIC induced by tumor promoters like
12-O-tetradecanoyl-phorbol-acetate (TPA) and
3,5,di-tertio-butyl-4-hydroxytoluene (BHT). Their preventive
effect is rapid. It does not seem to involve any change of the
amount of the connexin expressed in REL cells, connexin 43 (Cx
43), and in its phosphorylation state. Other flavonoids tested
including naringenin, myricetin, catechin and chrysin did not
enhance GJIC nor counteract TPA-induced inhibition of
GJIC.
Cancer Lett 1997 Mar
19;114(1-2):207-10
Review article: cyclooxygenase?a
target for colon cancer prevention.
Use of nonsteroidal anti-inflammatory drugs such as
aspirin, which are known to inhibit cyclooxygenase activity,
reduces the relative risk of colorectal cancer in humans by
40% to 50%. Animal and human studies have shown a 50% to 80%
reduction in tumour multiplicity following treatment with a
variety of nonsteroidal anti-inflammatory drugs. Two isoforms
of cyclooxygenase have been described, cyclooxygenase-1
(COX-1) and cyclooxygenase-2 (COX-2). In 85% of colorectal
adenocarcinomas taken from humans. COX-2 levels are two to
50-fold higher than levels in adjacent normal intestinal
mucosa, while COX-1 levels are unchanged. These observations
raise the question: Does COX-1 or COX-2 provide a useful
target for prevention or treatment of colorectal cancer?
Aliment Pharmacol Ther 2000 Apr;14
Suppl 1:64-7
Chlorophyllin
Chlorophyllin protects cells from the
cytostatic and cytotoxic effects of quinacrine mustard but not
of nitrogen mustard.
Chlorophyllin (CHL), the sodium and copper salt of
chlorophyll, is capable of inhibiting the mutagenic activity
of many chemical compounds. Several mechanisms have been
advanced to explain the antimutagenic activity of CHL,
including its antioxidant properties and its ability to form
complexes with mutagens. The present study was designed to
reveal whether the heterocyclic aromatic nature of a potential
mutagen is essential to its sensitivity to CHL. Toward this
end, the inhibitory effect of CHL on two compounds of similar
chemical reactivity (mustards), that either embodied an
aromatic structure (quinacrine mustard; QM) or did not
(nitrogen mustard; NM), were compared. Human leukemic HL-60
and breast carcinoma MCF-7 cells were treated with QM or NM in
the absence or presence of various concentrations of CHL. Both
QM and NM when administered for one to two h at micromolar
concentrations exerted similar effects; both arrested cells in
G2 phase of the cell cycle, induced apoptosis and reduced the
clonogenicity of MCF-7 cells. The simultaneous addition of
0.22 M CHL to cultures receiving QM virtually abolished the
QM-induced inhibition of cell growth and clonogenicity. In
contrast, CHL had no effect on reducing the cytostatic or
cytotoxic activity of NM. CHL alone, at a concentration of
0.22 M, had minimal effect on growth of HL-60 cells slightly
perturbing their progression through G2. The results are
consistent with the model that explains the inhibition of the
activity of mutagens or antitumor drugs with aromatic
structures by CHL as mediated by its ability to sequester
these molecules within heterologous mutagen:CHL complexes that
are maintained by stacking interactions. Therefore, excess of
chlorophyll in the diet, by sequestering aromatic mutagens (or
antitumor drugs with a heterocyclic structure, if taken
orally), may inhibit their accessibility to cells, thereby
reducing their activity.
Int J Oncol 2001 Apr;18(4):849-53
Chemopreventive effect of
chlorophyllin on mutagenicity and cytotoxicity of
6-sulfooxymethylbenzo[a]pyrene.
The chemopreventive activity of chlorophyllin (CHL) was
monitored by using 6-sulfooxymethylbenzo[a]pyrene (SMBP) which
is an ultimate metabolite of benzo[a]pyrene (B[a]P). CHL was
quite effective in reducing both cytotoxicity and mutagenicity
for SMBP in dose dependent manner up to 12.5 mM CHL in Chinese
hamster V79 cells. The inhibitory patterns of CHL for SMBP
were also confirmed in Salmonella typhimurium strains TA98 and
TA100. Mutation frequency caused by SMBP was diminished almost
to a control level at a 50 nmol CHL. A similar but less
effective prevention of CHL was indicated in the mammalian and
the bacterial mutagenicity assays with
6-hydroxymethylbenzo[a]pyrene (HMBP). The inhibitory effect of
CHL against assault of SMBP on V79 cells was found to be
related to the reduced cellular uptake of SMBP and further the
remarkably lowered DNA adducts.
Cancer Lett 1996 Oct
22;107(2):223-8
Early detection and prevention of
colorectal cancer (review).
Colorectal cancer is a leading cause of cancer-related
deaths, and the two most important considerations for
avoidance of this disease are early detection and prevention.
If metastasis has occurred to distant sites, such as the liver
and lung, the five-year survival rate for colorectal cancer is
below 10%, but this increases to greater than 90% when the
cancer is found early. Early detection can be facilitated by
use of the digital rectal exam, fecal occult blood test,
sigmoidoscopy, and colonoscopy, but these methods might be
supplemented in the future by other screening assays using
intermediate biomarkers. One interesting biomarker, the
aberrant crypt focus (ACF), has been observed in resected
human colons, and is the earliest detectable morphological
change in the colons of experimental animals treated with
carcinogens such as the cooked meat heterocyclic amines. The
ACF can also be used as an end-point to screen for potential
inhibitors of colorectal cancer; using this approach, we
identified conjugated linoleic acids, indole-3-carbinol,
chlorophyllin, and tea polyphenols as promising inhibitors in
the colon. These compounds can be added to a growing list of
natural and synthetic agents that might be effective against
colorectal cancer, including selenium, calcium and
nonsteroidal anti-inflammatory agents. However, results from
human clinical trials with several of these compounds have
highlighted the need for detailed mechanism data before
recommendations can be made for wide-scale use in humans. In
the meantime, the best approach to reducing the risk of
colorectal cancer would be to increase the dietary intake of
fruits, vegetables and cereals, while reducing the overall
intake of fat, particularly from animal sources.
Oncol Rep 1999
Mar-Apr;6(2):277-81
Study of the forces of stabilizing
complexes between chlorophylls and heterocyclic amine
mutagens.
Chlorophyllin (CHL), a water-soluble derivative of
chlorophyll, forms molecular complexes with heterocyclic amine
mutagens in vitro. In a previous study [Dashwood and Guo
(1993): Environ Mol Mutagen, 22:164-171], we observed an
inverse correlation between the binding constants of several
mutagen-CHL complexes and the antimutagenic potency of CHL in
the Salmonella assay. The present investigation utilized
molecular mechanics methods of energy minimization and
spectrophotometric titration to examine structural features of
chlorophylls, chlorins, and porphyrins that might be important
for complex formation with heterocyclic amines. The exocyclic
amine group of the mutagen aligned consistently with acid
groups in CHL, suggesting that H-bond or electrostatic
interactions facilitate complex formation. Replacement of the
exocyclic amine with a nitro group abrogated this specific
orientation and raised the minimized energies of the
complexes. No relationship was found between complex strength
and the specific positions of amine or methyl groups on the
mutagen. However, the presence of methyl groups increased the
minimized energies and lowered the binding constants of the
complexes, perhaps due to partial disruption of pi-pi
interaction by steric effects. All of the compounds examined,
including chlorophyll a, required the presence of pi-pi
interactions to form stable complexes with the heterocyclic
amines. In general, the present results were in agreement with
the inhibitory potency of each compound in the Salmonella
assay, and they provide further support for the hypothesis
that chlorophylls in the diet might act as interceptor
molecules of food-borne carcinogens and mutagens.
Environ Mol Mutagen
1996;27(3):211-8
Chlorophyllin intervention reduces
aflatoxin-DNA adducts in individuals at high risk for liver
cancer.
Residents of Qidong, People's Republic of China, are at
high risk for development of hepatocellular carcinoma, in part
from consumption of foods contaminated with aflatoxins.
Chlorophyllin, a mixture of semisynthetic, water-soluble
derivatives of chlorophyll that is used as a food colorant and
over-the-counter medicine, has been shown to be an effective
inhibitor of aflatoxin hepatocarcinogenesis in animal models
by blocking carcinogen bioavailability. In a randomized,
double-blind, placebo-controlled chemoprevention trial, we
tested whether chlorophyllin could alter the disposition of
aflatoxin. One hundred and eighty healthy adults from Qidong
were randomly assigned to ingest 100 mg of chlorophyllin or a
placebo three times a day for four months. The primary
endpoint was modulation of levels of aflatoxin-N(7)-guanine
adducts in urine samples collected three months into the
intervention measured by using sequential immunoaffinity
chromatography and liquid chromatography-electrospray mass
spectrometry. This aflatoxin-DNA adduct excretion product
serves as a biomarker of the biologically effective dose of
aflatoxin, and elevated levels are associated with increased
risk of liver cancer. Adherence to the study protocol was
outstanding, and no adverse events were reported.
Aflatoxin-N(7)-guanine could be detected in 105 of 169
available samples. Chlorophyllin consumption at each meal led
to an overall 55% reduction (P = 0.036) in median urinary
levels of this aflatoxin biomarker compared with those taking
placebo. Thus, prophylactic interventions with chlorophyllin
or supplementation of diets with foods rich in chlorophylls
may represent practical means to prevent the development of
hepatocellular carcinoma or other environmentally induced
cancers.
Proc Natl Acad Sci U S A 2001 Dec
4;98(25):14601-6
Protection by chlorophyllin and
indole-3-carbinol against
2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced
DNA adducts and colonic aberrant crypts in the F344 rat.
The most abundant heterocyclic amine in fried ground beef,
2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP),
induces colon carcinomas in the male F344 rat. The potential
chemopreventive effects of two compounds, namely, the
'interceptor molecule' chlorophyllin (CHL) and a modulator of
carcinogen activation, indole-3-carbinol (I3C), were examined
in a PhIP colon carcinogenesis model. During weeks three and
four of a 16-week study, F344 rats were given PhIP by oral
gavage (50 mg/kg body weight, alternating days). Inhibitors
were given either before and during PhIP exposure, after PhIP
treatment, or continuously for 16 weeks. Treatment of rats
with 0.1% CHL in the drinking water inhibited the formation of
aberrant crypt foci (ACF) with > or = 4 crypts/focus, from
1.4 +/- 0.9 in controls to 0.7 +/- 0.3 following
post-initiation CHL treatment, and to 0.3 +/- 0.5 in rats
given CHL continuously for 16 weeks (mean +/- SD; P <
0.05). Potent inhibition of PhIP-induced ACF occurred
following initiation, post-initiation and continuous exposure
to 0.1% I3C in the diet. Using the initiation protocol, I3C
completely inhibited the induction of the ACF with > or = 4
crypts/focus. In a separate experiment, rats were given 0.1%
CHL in the drinking water or 0.1% I3C in the diet for four
weeks. At the end of week three, animals received 50 mg
PhIP/kg body weight by single oral gavage and PhIP-DNA adducts
were quantified in the colon and several other tissues by
32P-postlabeling analysis. In addition, the urine and feces
were collected to study the effects of inhibitor treatment on
PhIP metabolism and excretion. No significant protection
against PhIP-DNA adduct formation was detected in the colon
after CHL dosing, nor was a consistent pattern of CHL
inhibition observed in several other tissues. In contrast, I3C
shifted the time-course of adducts in all tissue; compared
with controls, adducts were increased by I3C at six h but
decreased at 24 h and seven days following PhIP treatment.
Analysis of urine metabolites revealed that I3C and CHL
decreased the excretion of unmetabolized PhIP and 4'-hydroxy-
< PhIP but increased the phase II detoxification
products PhIP-4'-O-glucuronide and PhIP-4'- sulfate. In the
feces, the elimination of unmetabolized PhIP was increased
from 54.5% in controls to approximately 67% in CHL-treated
rats and decreased to 28% in rats given I3C (P < 0.05).
These results support a protective role for CHL and I3C
against PhIP-induced colon carcinogenesis through mechanisms
which alter the uptake or metabolism of the carcinogen, and by
suppression in the post-initiation phase.
Carcinogenesis 1995
Dec;16(12):2931-7
Inhibition of radiation-induced DNA
damage in plasmid pBR322 by chlorophyllin and possible
mechanism(s) of action.
Naturally occurring compounds capable of protecting DNA
against ionizing radiation and chemical mutagens have
considerable potential for prevention of mutation-based health
impairment including cancer and other degenerative diseases.
Chlorophyllin (CHL), a water-soluble derivative of
chlorophyll, has been examined for its ability to protect DNA
against radiation induced strand breaks using an in vitro
plasmid DNA system. Gamma-radiation, up to a dose of 6 Gy
(dose rate 1.25 Gy/min), induced a dose-dependent increase in
single-strand breaks (ssbs) in plasmid pBR322 DNA. CHL per se
did not induce, but inhibited radiation-induced ssbs in a
concentration-dependent manner; 500 microM giving about 90%
protection. The protection afforded by CHL was comparatively
less than that of trolox, a water-soluble analogue of
alpha-tocopherol. To elucidate the underlying mechanism(s),
reaction of CHL with the radiation-derived hydroxyl radical
(OH) and deoxyribose peroxyl radical (ROO) was studied by
pulse radiolysis. CHL exhibited a rate constant of
6.1+/-0.4x109 M-1 s-1 with OH and 5.0+/-1.3x107 M-1 s-1 with
ROO. To our knowledge, this is the first report providing
direct evidence of free radical-scavenging properties of CHL.
The results showed that CHL, effectively protects plasmid DNA
against ionizing radiation, in an in vitro system independent
of DNA repair or other cellular defense mechanisms. The
ability of CHL to scavenge OH and ROO, may contribute to its
protective effects against radiation induced DNA damage in the
pBR322 system.
Mutat Res 1999 Mar 10;425(1):71-9
Scavenging of reactive oxygen species
by chlorophyllin: an ESR study.
The antioxidant effects of chlorophyllin (CHL), a
water-soluble analog of the green plant pigment chlorophyll,
on different reactive oxygen species (ROS) were investigated
by electron spin resonance (ESR) spectroscopy. As a standard,
we have used the ability of CHL to scavenge the stable
1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. CHL inhibits the
formation of 5,5-dimethyl-1-pyrroline-N-oxide adduct with
hydroxyl radical (DMPO-.OH adduct) generated by
gamma-radiation in a dose-dependent manner. At a concentration
of 1 mM, CHL caused more than 90% inhibition of ESR signal
intensity of this adduct. However, the results obtained with
the Fenton reaction were different. We also found evidence for
the inhibition of 1O2-dependent formation of the
2,2,6,6-tetramethyl-piperidine oxide (TEMPO) radical during
photosensitization of methylene blue with visible light. CHL
was also able to inhibit hydrogen peroxide induced oxidation
of phenol red. The rate constant of the reaction of CHL with
H2O2 was found to be 2.7 x 10(6) M-1 s-1. In conclusion, CHL
has potent antioxidant ability involving scavenging of various
physiologically important ROS.
Free Radic Res 2001
Nov;35(5):563-74
Effect of chemopreventive agents on
DNA adduction induced by the potent mammary carcinogen
dibenzo[a,l]pyrene in the human breast cells MCF-7.
Over 1500 structurally diverse chemicals have been
identified which have potential cancer chemopreventive
properties. The efficacy and mechanisms of this growing list
of chemoprotective agents may be studied using short-term
bioassays that employ relevant end-points of the carcinogenic
process. In this study, we have examined the effects of eight
potential chemopreventive agents, N-acetylcysteine (NAC),
benzylisocyanate (BIC), chlorophyllin, curcumin,
1,2-dithiole-3-thione (D3T), ellagic acid, genistein, and
oltipraz, on DNA adduction of the potent mammary carcinogen
dibenzo[a,l]pyrene (DBP) using the human breast cell line
MCF-7. Bioactivation of DBP by MCF-7 cells resulted in the
formation of one predominant (55%) dA-derived and several
other dA- or dG-derived DNA adducts. Three test agents,
oltipraz, D3T, and chlorophyllin substantially (>65%)
inhibited DBP-DNA adduction at the highest dose tested (30
microM). These agents also significantly inhibited DBP adduct
levels at a lower dose of 15 microM, while oltipraz was
effective even at the lowest dose of 5 microM. Two other
agents, genistein and ellagic acid were moderate (45%) DBP-DNA
adduct inhibitors at the highest dose tested, while NAC,
curcumin, and BIC were ineffective. These studies indicate
that the MCF-7 cell line is an applicable model to study the
efficacy of cancer chemopreventive agents in a human setting.
Moreover, this model may also provide information regarding
the effect of the test agents on carcinogen bioactivation and
detoxification enzymes.
Mutat Res 2001 Sep
1;480-481:97-108
Nutrients
Progress in cancer chemoprevention:
development of diet-derived chemopreventive agents.
Because of their safety and the fact that they are not
perceived as "medicine," food-derived products are highly
interesting for development as chemopreventive agents that may
find widespread, long-term use in populations at normal risk.
Numerous diet-derived agents are included among the >40
promising agents and agent combinations that are being
evaluated clinically as chemopreventive agents for major
cancer targets including breast, prostate, colon and lung.
Examples include green and black tea polyphenols, soy
isoflavones, Bowman-Birk soy protease inhibitor, curcumin,
phenethyl isothiocyanate, sulforaphane, lycopene,
indole-3-carbinol, perillyl alcohol, vitamin D, vitamin E,
selenium and calcium. Many food-derived agents are extracts,
containing multiple compounds or classes of compounds. For
developing such agents, the National Cancer Institute (NCI)
has advocated codevelopment of a single or a few putative
active compounds that are contained in the food-derived agent.
The active compounds provide mechanistic and pharmacologic
data that may be used to characterize the chemopreventive
potential of the extract, and these compounds may find use as
chemopreventives in higher risk subjects (patients with
precancers or previous cancers). Other critical aspects to
developing the food-derived products are careful analysis and
definition of the extract to ensure reproducibility (e.g.,
growth conditions, chromatographic characteristics or
composition), and basic science studies to confirm
epidemiologic findings associating the food product with
cancer prevention.
J Nutr 2000 Feb;130(2S
Suppl):467S-471S
Sulforaphane, a naturally occurring
isothiocyanate, induces cell cycle arrest and apoptosis in
HT29 human colon cancer cells.
Sulforaphane is an isothiocyanate that is present naturally
in widely consumed vegetables and has a particularly high
concentration in broccoli. This compound has been shown to
block the formation of tumors initiated by chemicals in the
rat. Although sulforaphane has been proposed to modulate the
metabolism of carcinogens, its mechanism of action remains
poorly understood. We have previously demonstrated that
sulforaphane inhibits the reinitiation of growth and decreases
the cellular viability of quiescent human colon carcinoma
cells (HT29). Moreover, the weak effect observed on
differentiated CaCo2 cells suggests a specific anticancer
activity for this compound. Here we investigated the effect of
sulforaphane on the growth and viability of HT29 cells during
their exponentially growing phase. We observed that
sulforaphane induced a cell cycle arrest in a dose-dependent
manner, followed by cell death. This sulforaphane-induced cell
cycle arrest was correlated with an increased expression of
cyclins A and B1. Moreover, we clearly demonstrated that
sulforaphane induced cell death via an apoptotic process.
Indeed, a large proportion of treated cells display the
following: (a) translocation of phosphatidylserine from the
inner layer to the outer layer of the plasma membrane; (b)
typical chromatin condensation; and (c) ultrastructural
modifications related to apoptotic cell death. We also showed
that the expression of p53 was not changed in
sulforaphane-treated cells. In contrast, whereas bcl-2 was not
detected, we observed increased expression of the proapoptotic
protein bax, the release of cytochrome c from the mitochondria
to the cytosol, and the proteolytic cleavage of
poly(ADP-ribose) polymerase. In conclusion, our results
strongly suggest that in addition to the activation of
detoxifying enzymes, induction of apoptosis is also involved
in the sulforaphane-associated chemoprevention of cancer.
Cancer Res 2000 Mar
1;60(5):1426-33
Vitamin D and vitamin D analogs in
cancer treatment.
The secosteroid hormone 1,25-dihydroxyvitamin D3
(1,25-(OH)2D3) is a key player in the regulation of bone
mineralization and calcium homeostasis. In addition,
1,25-(OH)2D3 has antiproliferative and prodifferentiation
effects on various cells in vitro and in vivo. The
growth-inhibitory properties of 1,25-(OH)2D3 could be
harnessed in the treatment of cancer. However, its use as an
anti-cancer drug is limited because of the calcemic effects of
pharmacological doses. In an attempt to dissociate the
antiproliferative and calcemic effects, numerous vitamin D3
analogs were developed. The mechanisms by which 1,25-(OH)2D3
and 1,25-(OH)2D3 analogs exert their growth-inhibitory effects
are not clear but include effects on cell differentiation,
apoptosis, cell cycle regulation, metastases, and
angiogenesis. In the current review aspects involved in the
tumor suppressive activity of 1,25-(OH)2D3 and 1,25-(OH)2D3
analogs will be addressed. The use of vitamin D3 compounds,
alone or in combination with other drugs, in cancer treatment
and the potential drawbacks will also be discussed.
Curr Drug Targets 2002
Feb;3(1):85-94
Se-methylselenocysteine induces
apoptosis through caspase activation and Bax cleavage mediated
by calpain in SKOV-3 ovarian cancer cells.
Se-methylselenocysteine (Se-MSC) is a potent
chemopreventive agent in many test systems and has been shown
to inhibit tumor promotion and induce apoptosis, but its
mechanism of action is still not well understood. The present
study was designed to assess the mechanism of Se-MSC on the
induction of apoptosis in SKOV-3 ovarian cancer cells. Se-MSC
displayed strong inhibitory effects on cell proliferation and
viability of SKOV-3 cells in dose and time dependent manners
and induced apoptosis. Investigation of the mechanism of
Se-MSC-induced apoptosis revealed that treatment with Se-MSC
produced morphological features of apoptosis and DNA
fragmentation. This was associated with caspase-3 activation
and cleavage of poly(ADP-ribose) polymerase and phospholipase
C-gamma1 proteins. However, SKOV-3 cells treated with Se-MSC
did not demonstrate cytochrome c accumulation in the cytosol
during apoptosis induction. Pretreatment of cells with the
caspase inhibitors (z-VAD-fmk and DEVD-CHO) prevented
Se-MSC-induced apoptosis. These results suggested that Se-MSC
induces apoptosis through cytochrome c-independent caspase-3
activation in SKOV-3 cells. In late stage of apoptosis, p18kDa
fragment of Bax was generated with the down-regulation of the
expressions of survivin, X-linked inhibitor of apoptosis
protein, and human inhibitor of apoptosis protein 1 following
Se-MSC treatment, suggesting that the modulation of Bax and
IAP (inhibitors of apoptosis) family proteins play some role
in Se-MSC-mediated apoptosis. Pre-treatments of z-VAD-fmk and
the calpain inhibitor, calpeptin inhibited Bax cleavage. These
results suggested that Bax cleavage is mediated by calpain,
and calpain activation may be a caspase-dependent one. Taken
together, the chemopreventive effects of Se-MSC may be related
in part to the caspase-3 activation, the down-regulation of
IAP family proteins, and Bax cleavage mediated by
caspase-dependent calpain activation.
Cancer Lett 2002 Aug
8;182(1):83-92
Se-methylselenocysteine induces
apoptosis mediated by reactive oxygen species in HL-60
cells.
Recent studies have implicated apoptosis as one of the most
plausible mechanisms of the chemopreventive effects of
selenium compounds, and reactive oxygen species (ROS) as
important mediators in apoptosis induced by various stimuli.
In the present study, we demonstrate that
Se-methylselenocysteine (MSC), one of the most effective
selenium compounds at chemoprevention, induced apoptosis in
HL-60 cells and that ROS plays a crucial role in MSC-induced
apoptosis. The uptake of MSC by HL-60 cells occurred quite
early, reaching the maximum within 1 h. The dose-dependent
decrease in cell viability was observed by MSC treatment and
was coincident with increased DNA fragmentation and sub-G(1)
population. 50 microM of MSC was able to induce apoptosis in
48% of cell population at a 24 h time point. Moreover, the
release of cytochrome c from mitochondria and the activation
of caspase-3 and caspase-9 were also observed. The measurement
of ROS by dichlorofluorescein fluorescence revealed that dose-
and time-dependent increase in ROS was induced by MSC.
N-acetylcysteine, glutathione, and deferoxamine blocked cell
death, DNA fragmentation, and ROS generation induced by MSC.
Moreover, N-acetylcysteine effectively blocked caspase-3
activation and the increase of the sub-G(1) population induced
by MSC. These results imply that ROS is a critical mediator of
the MSC-induced apoptosis in HL-60 cells.
Free Radic Biol Med 2001 Aug
15;31(4):479-89
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