DMBA-induced Carcinogenesis Research Articles

Role of ER in the differential response of Stat5a loss in susceptibility to mammary preneoplasia and DMBA-induced carcinogenesis

Deregulated estrogen signaling is evidently linked to breast cancer pathophysiology, although the role of signal transducer and activator of transcription (Stat)5a, integral to normal mammary gland development, is less clear. A mouse model of mammary epithelial cell-targeted deregulated estrogen receptor alpha (ERalpha) expression [conditional ERalpha in mammary epithelium (CERM)] was crossed with mice carrying a germ line deletion of Stat5a [Stat5a-/-] to investigate interactions between ERalpha and Stat5a in mammary tissue. CERM, CERM/Stat5a+/-, CERM/Stat5a-/-, Stat5a+/-, Stat5a-/- and wild-type (WT) mice were generated to test the roles of ERalpha and Stat5a on pubertal differentiation and cancer progression with and without exposure to the chemical carcinogen 7,12-dimethylbenz[a]anthracene (DMBA). Only CERM/Stat5a-/- mice demonstrated delayed pubertal terminal end bud differentiation. Without DMBA exposure, Stat5a loss abrogated ERalpha-initiated hyperplastic alveolar nodule (HAN) development and, similarly, Stat5a-/- mice did not develop HANs. However, although Stat5a loss still reduced ERalpha-initiated HAN prevalence following DMBA exposure, Stat5a loss without deregulated ERalpha was associated with an increased HAN prevalence compared with WT. Progression to ERalpha(+) and ERalpha(-) adenocarcinoma was found in all CERM-containing genotypes (CERM, CERM/Stat5a+/-, CERM/Stat5a-/-) and ERalpha(+) adenocarcinoma in the Stat5a-/- genotype. The mammary epithelial cell proliferative index was increased only in CERM mice independent of Stat5a loss. No differences in apoptotic indices were found. In summary, Stat5a cooperated with deregulated ERalpha in retarding pubertal mammary differentiation and contributed to ERalpha-initiated preneoplasia, but its loss did not prevent development of invasive cancer. Moreover, in the absence of deregulated ERalpha, Stat5a loss was associated with development of both HANs and invasive cancer following DMBA exposure.

Abstract A64: Chemopreventive potential of Bauhinia variegata against DMBA-induced skin papillomagenesis in Swiss albino mice

Abstract The present study is an attempt to evaluate the cancer chemopreventive potential of Bauhinia variegata bark against DMBA-induced skin papillomagenesis in mice. We investigated chemopreventive effect of three different doses (2%, 4% and 6% w/w) of test diets of bark of B. variegata during DMBA-induced skin papillomagenesis in mice and tumor cell proliferation and apoptosis. Its effect was also studied in a short-term animal protocol on carcinogen metabolizing enzymes in liver. DMBA and croton oil was used to induce and promote skin papillomagenesis, respectively. Skin papillomagenesis study was done by using three different doses of B. variegata before, during and after the DMBA treatment to mice till termination of the experiment (120 days). In addition, the expression of proliferation [proliferating cell nuclear antigen (PCNA), glutathione-S-transferse (GST-π) and apoptosis were analyzed in the skin tumors by immunohistochemistry. For biochemical studies, mice were given with the same doses of B. variegata in the test diet for two weeks. The specific activities/levels of phase-I and phase-II enzymes, antioxidant enzymes, lactate dehydrogenase, glutathione content, and peroxidative damage were determined in the liver of the mice. Results showed a significant reduction in the skin tumors in B. variegata treated animals, as compared to the control group of animals. The tumor incidence in case of control group of animals was 100% whereas it was 90%, 70% and 99% in groups treated with 2%, 4% and 6% test diets, respectively. Tumor multiplicity in control group was 12±3.9 whereas it was reduced to 8±3.7, 3±2.9 and 4±2.4 by the lower, intermediate and higher dose of B. variegata treatment. The dietary administration of three different doses of B. variegata significantly decreased the expression of PCNA, GST-π, Bcl-2 and VEGF and on the other hand significantly increased the expression of Bax and total Caspase 3 as compared to DMBA and croton oil treated group of animals. The effect of 2 weeks of dietary feeding of B. variegata inhibited phase I, activated phase II and antioxidant enzymes in the mouse liver. The content of reduced glutathione was significantly elevated whereas the peroxidative damage and specific activity of lactate dehydrogenase exhibited a significant reduction with all the doses of test diets, respectively. All these findings were indicative of that Bauhinia variegata has chemopreventive potential against DMBA-induced skin carcinogenesis. It would be of interest to investigate for active cancer chemopreventive agents in Bauhinia variegata for its future implication in cancer prevention and control. Citation Information: Cancer Prev Res 2010;3(1 Suppl):A64.

A role for prostaglandins in the suppression of cutaneous cellular immunity and tumour development in benzo(a)pyrene- but not dimethylbenz(a)anthracene-treated mice

Prostaglandins have been implicated in the immune suppression associated with the development of some tumours. Application of the prostaglandin synthetase inhibitor indomethacin, to murine skin prior to treatment with the chemical carcinogens benzo(a)pyrene (BP) or 7,12 dimethylbenz(a)anthracene (DMBA), restored contact sensitivity responses to 2,4-dinitrofluorobenzene in BP- but not DMBA-treated mice. However, indomethacin failed to restore antibody responses in either group of mice. Prolonged treatment with BP or DMBA led to cutaneous tumour formation. Indomethacin was found to delay the onset and reduce the size of tumours in BP- but not DMBA-treated mice. It is proposed that prostaglandin-induced suppression of cellular cutaneous immunity may play a role in BP- but not DMBA-induced cutaneous carcinogenesis.

Temperature effect on chemical-induced carcinogenesis in hamster cheek pouch

7,12-Dimethylbenz[ a]anthracene (DMBA), a potent chemical carcinogen, was used to induce oral cancer on hamster buccal pouch, under two temperature regimes (22 ± 2 and 28 ± 2 °C) for 25 weeks of observation. The animal group under high temperature showed rapid tumour incidence and weight loss. It also exhibited biochemical changes such as reduced lipid peroxidation in the oral tumour tissue, accompanied by significant increase in the levels of reduced glutathione, glutathione peroxidase and glutathione- s-transferase. Therefore, we propose that elevated temperature is a cofactor, accelerating the process of DMBA-induced carcinogenesis in hamster cheek pouch.

Decreased 7,12-dimethylbenz[a]anthracene-induced carcinogenesis coincides with the induction of antitumor immunities in adult female B6C3F1 mice pretreated with genistein

The objective of this study was to determine if genistein (GEN) modulation of the immune responses might contribute to the increased host resistances to tumors. A time-course study was performed in adult female B6C3F1 mice that had been exposed to GEN for 1-4 weeks at the dose level of 20 mg/kg by gavage. A significant increase in ex vivo cytotoxic T lymphocyte (CTL) activity was observed in the periods of 2 weeks and 4 weeks. Moreover, increased activities of CTLs were associated with a decrease in the percentage of CD4(+)CD25(+) T cells and an increase in the production of interferon-gamma and activation of STAT1 (signal transducer and activator of transcription 1) and STAT4. Additionally, exposure of mice to GEN increased the activities of in vivo CTLs. An increased activity of natural killer (NK) cells was also observed. Further study in the B16F10 tumor model suggested that GEN-mediated enhancement in host resistance to B16F10 tumor was partially related to its potentiating effect on NK cells. Finally, 7,12-dimethylbenz[a]anthracene (DMBA)-induced tumor model was employed to determine the chemopreventive effect of oral GEN treatment. Mice pretreated with GEN for 2 weeks by gavage, the time when an enhanced CTL activity had been produced, had a decreased susceptibility toward DMBA-mediated carcinogenesis, while treatment with GEN after tumor induction conferred no protection. In conclusion, pretreatment with GEN by gavage could enhance host resistances to the B16F10 tumor and DMBA-induced carcinogenesis, suggesting that GEN modulation of immune response was, at least partially, responsible for the antitumor effect of this compound.

Therapeutic effect of boron neutron capture therapy (BNCT) on field cancerized tissue: Inhibition of DNA synthesis and lag in the development of second primary tumors in precancerous tissue around treated tumors in DMBA-induced carcinogenesis in the hamster cheek pouch oral cancer model

Objective We previously reported the therapeutic success of different BNCT protocols in the treatment of oral cancer, employing the hamster cheek pouch model. The aim of the present study was to evaluate the effect of these BNCT protocols on DNA synthesis in precancerous and normal tissue in this model and assess the potential lag in the development of second primary tumors in precancerous tissue. The data are relevant to potential control of field cancerized tissue and tolerance of normal tissue. Materials and methods We evaluated DNA synthesis in precancerous and normal pouch tissue 1–30 days post-BNCT mediated by boronophenylalanine (BPA), GB-10 (Na 2 10B 10H 10) or (BPA + GB-10) employing incorporation of 5-bromo-2′-deoxyuridine as an end-point. The BNCT-induced potential lag in the development of second primary tumors from precancerous tissue was monitored. Results A drastic, statistically significant reduction in DNA synthesis occurred in precancerous tissue as early as 1 day post-BNCT and was sustained at virtually all time-points until 30 days post-BNCT for all the protocols. The histological categories evaluated individually within precancerous tissue (dysplasia, hyperplasia and NUMF [no unusual microscopic features]) responded similarly. DNA synthesis in normal tissue treated with BNCT oscillated around the very low pre-treatment values. A BNCT-induced lag in the development of second primary tumors was observed. Conclusions BNCT induced a drastic fall in DNA synthesis in precancerous tissue that would be associated to the observed lag in the development of second primary tumors. The minimum variations in DNA synthesis in BNCT-treated normal tissue would correlate with the absence of normal tissue radiotoxicity. The present data would support the control of field-cancerized areas by BNCT.

Vitamin D receptor (VDR) ablation alters carcinogen-induced tumorigenesis in mammary gland, epidermis and lymphoid tissues

The Vitamin D receptor (VDR) and its ligand, 1,25(OH) 2D 3, regulate cell proliferation, differentiation and apoptosis in vitro, yet the physiological significance of this regulation is unclear. In these studies, we used VDR knockout (VDRKO) mice to examine the impact of VDR on chemical carcinogen-induced tumorigenesis in vivo. Wild type (WT) and VDRKO littermates were fed a high calcium diet to prevent disturbances in calcium homeostasis and were gavaged with dimethylbenzanthracence (DMBA) using a protocol designed to induce mammary tumors. Compared to WT littermates, VDRKO mice exhibited an increased incidence of mammary gland hyperplasia and a higher percentage of hormone independent tumors with squamous differentiation. VDR ablation also significantly enhanced tumor development in epidermis and lymphoid tissues, but did not affect tumor development in ovary, uterus, lung or liver. These data indicate that VDR ablation alters susceptibility to DMBA-induced carcinogenesis in a tissue specific fashion, and provide support that optimal VDR signaling may act to suppress tumorigenesis.

Effect of radiofrequency radiation exposure on mouse skin tumorigenesis initiated by 7,12-dimethybenz[α]anthracene

Purpose: Although radiofrequency (RF) radiation is not considered mutagenic, it has been suggested as a promoter of tumorigenesis. To study if RF radiation has a tumor promoting effect, we exposed mice with skin tumorigenesis initiated by 7,12-dimethybenz[α]anthracene (DMBA) to RF radiation.Materials and methods: Eighty male ICR mice were subjected to a single DMBA application (100 μg/100 μl acetone/mouse) on shaved dorsal skin at the age of 7 weeks. After one week, the mice were randomized into four equal groups of 20 mice each: i.e., sham-, 849 MHz-, 1,763 MHz-exposed, and 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated groups. The RF exposure was conducted at a whole body average specific absorption rate (SAR) of 0.4 W/Kg, for 2 cycles of 45 min exposure with a 15 min interval each day, 5 days a week for 19 weeks. The TPA-treated group served as a positive control for skin tumorigenesis and were administered TPA (4 μg/100 μl acetone/mouse) twice weekly without RF exposure.Results: All mice were examined weekly at a macroscopic level. No skin tumors were observed in any groups except in the TPA-treated positive control group. TPA is known tumor promoter in DMBA-induced skin carcinogenesis and tumor incidence in the TPA treated group was 95%. At week 20 after DMBA initiation, skin tissues were analyzed immunohistochemically using anti-proliferating cell nuclear antigen (PCNA) antibody. No differences were observed by pathological examination or by PCNA staining between the sham- and the RF-exposed groups. The expression of cyclin D1 and c-fos were detected only in the tumorous skin tissues of the TPA-treated group.Conclusion: No evidence was found that RF radiation serves as a tumor promoter for skin tumors. Our data suggests that 849 MHz and 1,763 MHz RF radiations, similar to those emitted from mobile phones, do not have any promoting effect on skin tumor development in DMBA-initiated mice.

Possible enhancing effects of atrazine and nonylphenol on 7,12‐dimethylbenz[a]anthracene‐induced mammary tumor development in human c‐Ha‐ras proto‐oncogene transgenic rats

Our transgenic (Tg) strain carrying copies of the human c-Ha-ras proto-oncogene is highly susceptible to 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis, possibly due to activation of the transgene, and can be used in medium-term bioassay models to test for modifying effects of estrogenic environmental compounds on tumor development. The present study was conducted to assess the influence of dietary feeding of the endocrine disruptors atrazine and nonylphenol on DMBA-induced carcinogenesis in c-Ha-ras Tg rats. Animals of both sexes were given a single oral dose of DMBA (25 mg/kg body weight) at 50 days of age and thereafter received soybean-free diet containing 5, 50 or 500 ppm atrazine, or 10, 25, 100 or 250 ppm nonylphenol. In female Tg rats, atrazine at a dose of 5 ppm increased the incidences of mammary adenomas and adenocarcinomas (P < 0.01 and P < 0.05), while 50 ppm increased the adenocarcinoma incidence (P < 0.05). In males, skin tumor development, in contrast, was significantly decreased at the highest dose. Nonylphenol at 10 ppm increased adenocarcinoma and total mammary tumor multiplicity in female Tg rats (P < 0.05), but there was no dose dependence, a significant quadratic dose-response trend rather being observed (P < 0.05). In vitro, atrazine did not cause proliferation of MCF-7 cells at any of a range of doses tested. These results suggest that endocrine disruptors may enhance mammary carcinogenesis, but only in a certain limited dose range under the present experimental conditions. The doses applied, moreover, were all extremely high compared to the possible environmental human exposure levels.

Glutamine supplementation reduces glutathione levels and stimulates apoptosis in DMBA-induced mammary tumors

Our previous studies have established that glutamine supplementation reduced significantly tumor development in DMBA-breast cancer model and restored the depressed serum- and normal tissue levels of the natural anti-oxidant glutathione (GSH). Since it is now well known that there is a relationship between GSH levels and apoptosis, we hypothesized that GLN reduces GSH levels of cancer cells, which results in stimulation of apoptosis and inhibition the tumor development. In order to prove our hypothesis, we examined the levels of GSH in the tumorous tissues of DMBA-treated female Sprague-Dawley rats by a standard enzymatic recycling method. The activity of caspase-3 enzyme, which is one of the main executive enzymes in apoptosis, was assayed by a commercial colorimetric enzyme assay. In addition, we compared the Bcl-2 and Bax mRNAs levels in tumors from GLN- and non-GLN fed animals by relative RT-PCR. The results have shown that oral GLN supplementation significantly reduced GSH levels by 30% in the cancer cells, which was accompanied by 40% increase in the enzyme activity of caspase-3. GLN supplementation resulted also in a significant up-regulation of Bax and down-regulation of Bcl-2 gene expression. In conclusion, our results suggest that GLN supplementation is a critical regulator of GSH synthesis in malignant diseases and inhibits DMBA-induced carcinogenesis in mammary glands through stimulation of apoptosis.

Growth hormone-deficient dwarf animals are resistant to dimethylbenzanthracine (DMBA)-induced mammary carcinogenesis.

Increased plasma IGF-1 has consistently been associated with a variety of human cancers, whereas reduced levels of IGF-1 are associated with increased lifespan in other species. However, the aforementioned relationships are correlational or are derived from animal models that are not specific for growth hormone/IGF-1 excess or deficiency. This study was designed to assess the effects of physiological changes in growth hormone and IGF-1 expression on dimethylbenzanthracine (DMBA)-induced mammary carcinogenesis. At 50 days of age, female heterozygous (dw/+) and growth hormone deficient dwarf (dw/dw) rats of the Lewis strain received a single dose of DMBA (80 micro g/g of body weight) via oral gavage. Animals were assigned to one of four experimental groups: a) heterozygous animals (normal size), b) dwarf animals administered vehicle, c) dwarf animals administered low levels of porcine growth hormone (50 micro g twice daily), and d) dwarf animals administered high levels of porcine growth hormone (200 micro g twice daily). At study termination, heterozygous animals exhibited a 70% incidence of mammary tumors, whereas no tumors were observed in saline-treated dwarf animals. Administration of either 100 micro g or 400 micro g growth hormone/day resulted in a dose dependent increase in incidence of mammary tumors (83 and 100%, respectively). Furthermore, heterozygous animals exhibited 1.5 +/- 0.25 tumors per tumor-bearing animal, whereas dwarf animals administered 100 micro g and 400 micro g growth hormone per day had 1.9 +/- 0.63 and 3.4 +/- 0.83 tumors per animal, respectively. The present study demonstrates that DMBA-induced carcinogenesis is dependent on critical plasma levels of growth hormone and IGF-1, and that growth hormone/IGF-1 deficient animals are resistant to DMBA-induced carcinogenesis.

Targeted Disruption of the Microsomal Epoxide Hydrolase Gene: MICROSOMAL EPOXIDE HYDROLASE IS REQUIRED FOR THE CARCINOGENIC ACTIVITY OF 7,12-DIMETHYLBENZ[a]ANTHRACENE

Microsomal epoxide hydrolase (mEH) is a conserved enzyme that is known to hydrolyze many drugs and carcinogens, and a few endogenous steroids and bile acids. mEH-null mice were produced and found to be fertile and have no phenotypic abnormalities thus indicating that mEH is not critical for reproduction and physiological homeostasis. mEH has also been implicated in participating in the metabolic activation of polycyclic aromatic hydrocarbon carcinogens. Embryonic fibroblast derived from the mEH-null mice were unable to produce the proximate carcinogenic metabolite of 7,12-dimethylbenz[a]anthracene (DMBA), a widely studied experimental prototype for the polycylic aromatic hydrocarbon class of chemical carcinogens. They were also resistant to DMBA-mediated toxicity. Using the two-stage initiation-promotion skin cancer bioassay, the mEH-null mice were found to be highly resistant to DMBA-induced carcinogenesis. In a complete carcinogenesis bioassay, the mEH mice were totally resistant to tumorigenesis. These data establish in an intact animal model that mEH is a key genetic determinant in DMBA carcinogenesis through its role in production of the ultimate carcinogenic metabolite of DMBA, the 3,4-diol-1,2-epoxide.

In vivo regulation of the insulin-like growth factor system of mitogens by human chorionic gonadotropin.

Human chorionic gonadotropin (hCG) is a differentiating agent and chemopreventive in rat DMBA-induced breast carcinogenesis. Insulin-like growth factors (IGFs) are potent mitogens for breast cancer cells. We report that the administration of hCG to female rats resulted in a significant increase in serum IGFBP-3 levels at doses greater than 10 UI and a significant decrease in serum IGF-I levels. Northern blot analysis revealed that hCG inhibited hepatic and mammary IGF-I gene expression at doses greater than 10 UI. Mammary IGFBP-5 and IGFBP-2 gene expression significantly increased at high doses of hCG while IGFBP-4 slightly decreased. Treatments greater than 10 UI of hCG resulted in a significant suppression of mammary IGFBP-3 and IGF-I receptor expression. Since IGFs are potent mitogens and antiapoptotic agents for breast cancer, this newly described activity of hCG may contribute to its antiproliferative properties, particularly with regard to the differentiation and inhibition of mammary tumours seen in animal models.

Effect of Sobatum on tumour development and chemically induced carcinogenesis.

The partially purified component of Solanum trilobatum named Sobatum was obtained from the petroleum ether/ethyl acetate (75:25) extractable portion. It was found to be cytotoxic in Dalton's Lymphoma ascites (DLA), Ehrlich ascites (EA) cell lines and tissue culture cells (L929 and Vero). Sobatum significantly inhibited peritoneal tumours induced by DLA and EA tumour cells. Sobatum was also found to reduce solid tumour growth in mice, when given either simultaneously or prophylactically, and is more active in simultaneous administration (EA). It was found that Sobatum was more active against EA cells-induced solid tumour than DLA-induced solid tumours. On exposure to 7,12-dimethylbenz(a)anthracene (DMBA), about 85.67% animals had induced skin carcinogenesis, which was significantly inhibited to 44.4% by the application of Sobatum. It can be concluded that the Sobatum has the ability to retard the development of solid tumours and DMBA-induced carcinogenesis.

Research and development of cancer chemopreventive agents in China

Since the late 1970s, a comprehensive search for cancer chemopreventive agents has been established in our Institute. A series of new retinoids have been synthesized and screened on the basis of established methodologies of experimental chemoprevention in vitro as well as in vivo. Pharmacological studies demonstrated that N-4-(carboxyphenyl)retinamide (RII) induces cell differentiation of HL-60 cells and inhibits dimethylnitrosamine-induced carcinogenesis of the forestomach in mice, 7,12-dimethylbenz[a]anthracene (DMBA)-induced papilloma in mouse skin, and DMBA-induced carcinogenesis of the buccal pouch in Syrian golden hamsters. It significantly promoted lymphoblastic transformation and activated macrophages. In further studies, RII significantly inhibited ornithine decarboxylase activity. After 6 months of chronic toxicological studies in rats and dogs, RII was recommended for clinical trial. Phase II studies found that RII is effective in treating oral and vulvar leukoplakia. It is also effective in treating myelodysplastic syndrome and dysplasia of uterine cervix. The chalcone retinoidal compounds were discovered when the search for new retinoids with less toxicity and higher potency led to third-generation retinoids, which were synthesized and screened. Structure-activity relationship studies found that 3,5-di-tert-butyl-4-methoxy-4-carboxyl chalcone (R9158) is the most active inhibitor of a variety of cancer cells. It has no effect on the Colony Forming Unit-Granulocyte/Macrophage (CFU-GM) of bone marrow in mice. In in vivo studies, R9158 showed a remarkable inhibition of chondrosarcoma in rats. It had no cross-resistance to vincristine, but was cross-resistant to all-trans retinoic acid. Red ginseng, a processed Panax ginseng, is considered a typical tonic in traditional Chinese medicine. Our studies demonstrated that red ginseng extract inhibited DMBA-induced skin papilloma significantly. Experiments showed that glycyrrhetinic acid inhibited croton oil-induced ear edema in mice. It also inhibited epidermal ornithine decarboxylase as well as the rapid DNA damage induced by the carcinogen benzo[a]pyrene (B[a]P). Our pharmacological studies demonstrated that Chinese gallotannin inhibited the malignant transformation of B[a]P-induced V79 cells in vitro and B[a]P-induced pulmonary adenoma in A/J mice in vivo significantly.

Sequential expression of myc-, ras-, oncogene products and EGF receptor during DMBA-induced tongue carcinogenesis

The mechanism leading to development of oral cancer has not been completely understood. It is currently believed that alternation of a number of genes can result in the development of epidermoid carcinomas. In this investigation, we used a 9,10-dimethyl 1,2-benzanthracene (DMBA)-induced carcinogenesis in a hamster tongue model to investigate the expression of c-myc, c-Ha-ms proteins and epidermal growth factor receptor (EGFr). During the DMBA-carcinogenesis of the tongue, the number of c-myc protein positive cells were increased in epithelial dysplasia and elevated throughout the process of tumorigenesis. The expression of c-Ha-ras protein was detected in normal epithelium. The level of c-Ha-ras protein expression was decreased in the dysplastic stage, and it was almost negative in squamous cell carcinomas. Detection of EGFr overexpression occurred only after 1-4 weeks of DMBA treatment, at a very early stage of tumor development, and increased through carcinogenesis varying individually within the malignant tissues. These results suggest that c-myc protein and c-Ha-ras protein expression may have an important role in malignant transformation, and the overexpression of EGFr can be correlated to very early stages of tumor development in the DMBA-induced in vivo tongue carcinogenesis.

Inhibitory effect of dietary flavonol quercetin on 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis.

The inhibitory effect of dietary supplementation with flavonol quercetin on 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal pouch carcinogenesis was investigated. Dietary quercetin inhibited the incidence of both papillomas and tumors induced by DMBA. The fluorescence spectra of papillomas and tumors showed different prominent maxima and a characteristic peak around 620-630 nm, which could be attributed to the accumulation of porphyrin compounds. Further, the fluorescence intensities at 630 nm (FI630nm) were elevated, whereas the ratio FI530nm/FI630nm was decreased in DMBA-induced lesions. Quercetin treatment significantly decreased FI630nm and increased the ratio FI520nm/FI630nm when compared with DMBA-induced lesions. It is therefore evident that quercetin has an inhibitory effect on DMBA-induced carcinogenesis and further studies will throw more light on its use as a chemopreventive agent against oral cancer.

The inhibition of DMBA-induced carcinogenesis by neoxanthin in hamster buccal pouch.

Neoxanthin, a major carotenoid pigment of spinach, is found in the Chloroplast membrane and has an unknown function in plants. Neoxanthin inhibited the production of superoxide anions in an artificial xanthine and xanthine oxidase system and depressed DNA synthesis in methylcholanthrene (MCA)-initiated C3H10T1/2 fibroblasts. in two-stage carcinogenesis experiments, neoxanthin at 0.2 micrograms/0.2 ml inhibited the formation of tumors that were induced sequentially by 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA) in the buccal pouch of Syrian Golden hamsters. To assess the ongoing process of carcinogenesis, the activity of ornithine decarboxylase (ODC), required for cell proliferation, was analyzed. Neoxanthin inhibited the activity of ODC when animals were treated with neoxanthin one hour before the application of TPA in two-stage carcinogenesis. However, neoxanthin did not inhibit ODC activity when animals were treated with neoxanthin one hour before the application of DMBA in two-stage carcinogenesis, and there was no subsequent tumor formation. In a short-term anti-initiation experiment, neoxanthin inhibited the covalent binding of isotope-labeled DMBA to DNA by 53%. These results indicate that neoxanthin inhibits the initiation stage and the promotion stage in two-stage carcinogenesis. This suggests that neoxanthin may act as a potential chemopreventive agent.

Creatine kinase isoenzymes activity in serum and buccal pouch tissue of hamsters during DMBA‐induced squamous cell carcinogenesis

The sequential changes of creatine kinase (CK) isoenzyme activity in serum and hamster buccal pouch tissue (HBPT) of normal, premalignant, and malignant stages during 13 wk of DMBA induced hamster buccal pouch squamous cell carcinogenesis, were studied. We found that the total CK activity in both serum and HBPT of the DMBA painted groups increased during the premalignant period (3-7 wk), with the peak being at 7 wk, while declining in the malignant period (9-13 wk). No significant difference in the serum and HBPT CK-MM, CK-MB and CK-BB activity, in DMBA-induced carcinogenesis, could be established. However, the macro CK type 2 (MCK-2), a cathodically migrating atypical creatine kinase isoenzyme, initially appeared in the sera and tissues of the 3rd wk DMBA-treated group. Its activity gradually increased during the premalignant and malignant stages, paralleling the increasing number of DMBA applications. There was a correlation between the degree of differentiation, and the size and number of the induced tumors with MCK-2. No MCK-2 could be detected in any of the sera or tissues of the control, nor in the 1st wk DMBA-treated group. We propose that MCK-2 is a potential tumor marker in oral malignancy and its presence may provide valuable information for early diagnosis of a possibly premalignant transforming oral lesion.

Antineoplastic properties of Maharishi-4 against DMBA-induced mammary tumors in rats

Maharishi-4 (M-4), an ayurvedic food supplement, was tested for anticarcinogenic and anticancer properties against 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors in rats. The 6% M-4-supplemented diet protected DMBA-induced carcinogenesis by reducing both tumor incidence and multiplicity during initiation and promotion phases. The control animals who developed tumors when supplemented with M-4 diet for four weeks showed tumor regression in 60% of cases. There was no significant difference in the food intake or weight gain in rats who were on M-4-supplemented diet compared to control group. Possible mechanisms of action of M-4 are discussed.