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Pentagenic Pharmaceuticals, Inc., Diamond Bar, California 91765 [Z. Y., S. L., X. C., H. C., M. H.], and the Department of Pathology, University of Southern California School of Medicine, Los Angeles, California 90033 [J. Z.]
| ABSTRACT |
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40 days. Our results showed
that 13-MTD could effectively inhibit the growth of orthotopic tumor
implants of both cell lines compared with control groups. The average
inhibition rate was 84.6% for DU 145 and 65.2% for LCI-D35
(P < 0.01). LD50 test
results showed that mice could well sustain the oral feeding of 5
g/kg/day without observable anomaly. Our preliminary data demonstrated
that 13-MTD could effectively inhibit in vitro and
in vivo growth of various cancer cell lines by inducing
apoptosis without significant toxic side effects, suggesting 13-MTD as
a potential candidate for chemotherapy of human cancers. | Introduction |
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Although these results are important and exciting, most chemotherapeutic agents studied thus far have undesired toxic side effects to the host animals and humans. Therefore, it is very critical that efforts should be made to discover new agents with which cancers could be treated safely without serious side effects. A soy fermentation product, Yang Zhen Hua 851, manufactured by Pentagenic Pharmaceuticals, Inc. (Diamond Bar, CA) through an innovative bacterial fermentation, has been used as a nutritional and therapeutic supplement by tens of thousands of cancer patients with different clinical stages since 1985. The results from these patients indicated that the product could effectively improve patients clinical condition as well as survival rate, and laboratory studies showed inhibition of tumor cell growth by this product.3 Several compounds with similar anticancer effects were purified from this product and named SBAs4 (United States patent pending). The structural and biochemical analysis had shown that SBAs represent a group of terminally branched-chain saturated fatty acids (C1521). One of them, 13-MTD (iso-C15), is the most abundant component in Yang Zhen Hua 851 and was chosen for this study. The branched-chain fatty acid occurs naturally only in trace amounts and is not synthesized de novo in human and other mammalians (7, 8, 9) . The presence of the isopropyl group gives 13-MTD a characteristic gas chromatographic behavior to serve as a structural marker for investigating adipose tissue turnover in human and other mammalians (8, 9, 10) .
Inthe present report, we studied 13-MTD as a potential anticancer agent to inhibit tumor cell growth. Our in vitro cell culture studies showed that 13-MTD could cause cell death through apoptosis in several human tumor cell lines tested. The cell death could be observed as early as 2 h after treatment of tumor cells with 13-MTD. The MetaMouse orthotopic model was used to evaluate the in vivo inhibition of tumor growth by 13-MTD. The results indicated that oral administration of 13-MTD could effectively inhibit the growth of tumors orthotopically implanted into nude mice. Altogether, our in vitro and in vivo data demonstrated that 13-MTD could effectively inhibit tumor cell growth by inducing apoptosis and is a potential agent for cancer chemotherapy.
| Materials and Methods |
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Cell Culture.
Human cancer cell lines DU 145 (prostate carcinoma), K-562 (leukemia),
HCT 116 (colon carcinoma), NCI-H1688 (lung small cell carcinoma),
SNU-423 (liver carcinoma), MCF7 (mammary adenocarcinoma), BxPC-3
(pancreatic adenocarcinoma), and NCI-SNU-1 (gastric carcinoma) were
obtained from ATCC (Manassas, VA). All cell lines were maintained in
RPMI 1640, DMEM, or McCoys medium supplemented with 10% fetal bovine
serum according to the culture conditions suggested by ATCC. K-562 and
NCI-SNU-1 are suspension cells, and the subcultures were established by
centrifugation of the suspension with subsequent resuspension in fresh
medium. The other tumor cell lines are adherent cells, and the
subcultures were achieved by dispersing the cells with 0.05%
trypsin/0.01% EDTA (Irvine Scientific, CA) and by subsequently
resuspending the cells in fresh medium.
Cell Cytotoxicity Assays.
ID50, ID75, and
ID90 were defined as the concentration of 13-MTD
killing 50, 75, and 90% of the cells, respectively.
ID50, ID75, and
ID90 were determined for all eight tumor cell
lines. Serial dilutions of 13-MTD were used at 0, 1.5, 3.0, 6.0, 15.0,
30.0, and 60.0 µg/ml. All tumor cell lines were seeded in 96-well
microplates with 5 x 104 cells/well and divided
into control and treatment groups. The control groups consisted of
controls treated with same volume of solvent and controls without any
treatment. After 48 h, cells were removed from each well, stained
with trypan blue, and counted under a microscope for viable and dead
cells. The results were then calculated by nonlinear regression
analysis with CalcuSyn software (Biosoft, Cambridge, United Kingdom).
MTT assays were performed in the K-562 cell line to measure the cytotoxicity of MTD to tumor cells. The rationale of MTT assay is based on the mitochondrial metabolism of the MTT salt into formazan. Because the conversion takes place only in living cells, the amount of formazan produced correlates with the number of viable cells present.
13-MTD Treatment of Cancer Cells.
Tumor cells were seeded in T75 flasks at 2 x 106 cells/flask in culture medium supplemented
with 10% fetal bovine serum and incubated overnight at 37°C with 5%
CO2. 13-MTD was dissolved in PBS with 0.8% Tween
80 and sterilized by filtration. After testing different concentrations
of 13-MTD in all cell lines, 35 µg/ml of 13-MTD was chosen for this
study because significant tumor cell death was observed at this
concentration. After incubating with either 35 µg/ml 13-MTD or
solvent for 1, 2, 4, 8, 24, and 48 h, cells were collected and
prepared for in situ cell death detection assay and DNA
fragmentation analysis.
DNA Fragmentation PCR and Electrophoresis.
Cells treated with either 13-MTD or solvent for 8 and 24 h were
collected for DNA extraction. Cells were lysed in lysis buffer
containing 0.2 M NaCl, 2% SDS, and 20 mM EDTA.
Cell lysates were treated with DNase-free RNase at 37°C for 1 h
and then extracted with phenol/chloroform. Fragmentation from cellular
endonuclease cleavage of genomic DNA during apoptosis in tumor cells
treated by either 13-MTD or solvent was examined by using the ApoAlert
LM-PCR Ladder Assay kit (Clontech, Palo Alto, CA), following the
procedure from the manufacturer. Briefly, 0.5 µg genomic of DNA from
each sample was ligated to adaptors by T4 ligase and then amplified by
LM-PCR with Advantage cDNA polymerase from the manufacturer. The PCR
product was electrophoresed on a 1.2% agarose/ethidium bromide gel at
100 V for about 1 h, and the ladder of fragmented DNA was
visualized under UV light.
In Situ Apoptotic Cell Death Detection.
The cell suspensions from 13-MTD or control treatments were counted and
adjusted to 0.5 x 106 cells/ml.
Fifty µl of each cell suspension were dropped onto a glass slide and
air dried. The apoptotic cell death was detected in the cell
preparations using the In Situ Cell Death Detection Kit,
peroxidase from Boehringer Mannheim. Briefly, the cells were
fixed with freshly prepared formaldehyde solution (4% in PBS, pH 7.4)
for 30 min at room temperature. After incubating with blocking solution
(0.3% H2O2 in methanol)
and subsequently in permeabilization solution (0.1% Triton X-100 in
0.1% sodium citrate), each slide was incubated with 50 µl of
terminal deoxynucleotidyl transferase-mediated nick end labeling
reaction mixture in a humidified chamber for 60 min at 37°C and then
incubated with 50 µl of Converter-POD for 30 min at 37°C. The
slides were then incubated with 3-amino-9-ethylcarbazole
substrate solution for the signal conversion, counterstained with
hematoxylin, and mounted with glass coverslips. The results were
analyzed under light microscope and documented on film.
In Vivo Determination of LD50.
To determine the acute toxicological effect of 13-MTD, the
LD50 test was performed in ICR mice. ICR mice of
both sexes at 6 weeks of age were randomly selected for each experiment
group with body weight of 20.522.5 g. The mice were treated with
13-MTD at 20, 40, 80, 160, and 800 mg/kg and 2.5 g/kg body weight by
intragastric administration twice daily for 14 days. The control mice
were administered with same volume of solvent for the same period of
time.
Inhibition of Tumor Growth in MetaMouse Orthotopic Model.
The ability of 13-MTD to inhibit tumor growth in vivo was
tested by the MetaMouse orthotopic model performed by AntiCancer, Inc.
(San Diego, CA) for human hepatocellular carcinoma LCI-D35 and human
prostate cancer DU 145 cell lines. Human hepatocellular carcinoma cell
line LCI-D35 was established by AntiCancer, Inc. from a primary liver
tumor. The tumor cells were first implanted and maintained s.c. in
athymic nude mice. The tumors were then harvested, and any grossly
necrotic or suspected necrotic tumor tissues were removed prior to
orthotopic implantation. The tumor tissues were then cut into small
pieces about 1 mm3 each. Three DU 145 fragments
were implanted into each mouse prostate, and animals were randomly
divided into four groups with eight mice for each group. The mice were
administered with solvent, 35, 70, or 105 mg/kg of 13-MTD for 43 days.
Two LCI-D35 fragments were orthotopically implanted into the left lobe
of liver of each BALB/c mouse, and animals were then randomly divided
into two groups with eight mice each. One group of mice was given 70
mg/kg/day of 13-MTD p.o. for 40 days, and the other group was given the
same volume of the solvent solution. The administration of 13-MTD and
solvent was carried out through gavage once a day. At the end of the
study, mice were sacrificed. Tumors grown in mouse liver or prostate
were inspected and weighed. Tissue sections were prepared for H&E
staining and routine pathological analysis. The primary tumor weight
data were analyzed by Student t test with
equal to 0.05
(one-tailed).
| Results |
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13-MTD Causes Tumor Cell Death through Induction of Apoptosis.
DNA fragmentation electrophoresis was performed to illustrate the
apoptotic changes in 13-MTD-treated tumor cells in this study. Our
results show that apoptotic DNA fragmentation could be detected in all
cancer cell lines studied after 8 h of 13-MTD treatment. The
representative results from cell lines MCF7 and DU 145 were shown in
Fig. 1
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| Discussion |
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Fatty acids and unsaturated fatty acids have been reported to induce apoptosis in several cell types including cancer cells (11, 12, 13, 14, 15, 16) . The role of ceramide and other metabolites of sphingomyelin pathway in apoptosis has been well established (17, 18, 19, 20, 21) . Ceramide-mediated apoptosis has been primarily described as a result of hydrolysis of a plasma membrane-derived pool of sphingomyelin (22) . In comparison with other fatty acids related to apoptosis, 13-MTD has unique and distinguished characteristics and could be a better agent for cancer chemotherapy. 13-MTD occurs naturally only in trace amounts and is not synthesized de novo in the body of mammalians (7, 8, 9) , whereas cellular ceramide is normally produced either by the cleavage of sphingomyelin by sphingomelinase or by de novo synthesis from palmitate and stearate (11) . Because ceramide is a normal element of the sphingomyelin pathway, its apoptosis induction often depends on cell type and stress-related, environmental factors. Ceramide can also give rise to proliferation and differentiation (22) . On the other hand, 13-MTD is foreign to the body and therefore may be more effective and less affected by cell type and stress-related environment factors in triggering apoptosis in tumor cells. 13-MTD induced apoptosis in eight different cancer cell lines in our study, despite of the differences of the genetic alterations among them, and the induction was not affected by the fetal bovine serum in the culture medium, whereas ceramide and other fatty acids worked in serum free medium or with only 2% of fetal bovine serum (12 , 18 , 23) . Furthermore, the terminally branched methyl group may give 13-MTD advantages over straight carbon chain fatty acids to perform the function of apoptotic induction.
As a 15-carbon fatty acid, 13-MTD is absorbed by the intestine when given p.o. and transported primarily as chylomicrons in the lymph into the circulation through the thoracic duct (8, 9, 10) . The process avoids the transportation of this fatty acid by the portal circulation directly into the liver to be oxidized and therefore delivers a higher concentration of 13-MTD in the circulation to reach organs and tissues. This property might be important for 13-MTD to reach proper concentration in local tumor tissues to induce apoptosis. The results of MetaMouse orthotopic models showed that oral administration of 13-MTD at a dosage as low as 35 mg/kg of mouse body weight daily could significantly inhibit the growth of orthotopically implanted tumors, suggesting the significance of the absorption and transportation through lymph to bypass the liver metabolism of the branched-chain fatty acid. In addition, the present of the isopropyl group gives 13-MTD a characteristic gas chromatographic behavior to serve as a structural marker for investigating its tissue distributions and turnover rate to monitor the in vivo effectiveness of tumor treatment.
The other advantage of 13-MTD in cancer treatment is its low toxicity. LD50 for intragastric administration of 13-MTD is more than 5 g/kg/day, whereas the therapeutic dosage in our orthotopic tumor implant mouse model was <75 mg/kg/day. This offers a wide safety zone between the lethal dosage and therapeutic dosage and suggests that 13-MTD may be a potent and safe agent for cancer chemotherapy. This notion was supported by the normal gross and microscopic morphology in the different mouse organs and tissues from MetaMouse orthotopic experiments for both DU 145 and LCI-D35 cancer cell lines after fed mice with 13-MTD for 40 days. It was also supported by the results from published studies in which 13-MTD was safely used as an indicator of adipose tissue turnover in experimental animals and human volunteers at high doses for as long as 42 days (8, 9, 10) .
In summary, 13-MTD is a saturated branched-chain fatty acid purified from the soy fermentation product Yang Zhen Hua 851. Our results suggest that 13-MTD could effectively inhibit in vitro and in vivo tumor growth by inducing apoptosis of cancer cells. Although the mechanism for inducing apoptosis in tumor cells is not known and needs further investigation, 13-MTD presents a potential chemotherapy agent without significant undesired side effects.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 Supported by a grant from Pentagenic
Pharmaceuticals, Inc. ![]()
2 To whom requests for reprints should be
addressed, at Pentagemic Pharmaceuticals, Inc., 21660 Copley Drive,
Suite 180, Diamond Bar, CA 91765. ![]()
3 Zhenhua Yang, unpublished data. ![]()
4 The abbreviations used are: SBA, small
biosynthetic anticancer agent; 13-MTD, 13-methyltetradecanoic acid;
ATCC, American Type Culture Collection; MTT,
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. ![]()
Received 11/ 5/99. Accepted 12/ 8/99.
| REFERENCES |
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