Oral chemoprevention of skin cancer in mice by benzophenone sunscreens dioxybenzone and octabenzone in drinking water

BACKGROUND

Sunscreen compounds with added benefit of skin cancer prevention have both public and commercial interests. Our earlier study using the Epstein-Barr virus early antigen in vitro assay reported on skin cancer chemoprevention potential of benzophenone sunscreens. We now report the in vivo antitumor activity of two of the benzophenone sunscreens which tested positively in the in vitro assay, octabenzone (UV-1) and dioxybenzone (UV-2), in the two-stage mouse skin carcinogenesis model using (±)-(E)-4-methyl-2-[-(E)-hydroxyamino]-5-nitro-6-methoxy-3-hexanamide (NOR-1) as inducer and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) as promoter.

MATERIALS AND METHODS

Pathogen-free, female hairless mice of HOS:HR-1 strain, 15 animals per control and test groups, were used. Skin tumors were induced by a single dose of NOR-1 (390 nmol in 100 μl of acetone). One week later, TPA (1.7 nmol in 100 μl of acetone) was applied to skin twice weekly for 20 weeks as tumor a promoter. The test compounds UV-I or UV-2 were administered at 0.0025% to mice through drinking water ad libitum, starting one week prior to and stopping one week after tumor initiation. All animals were examined weekly for the development of skin papillomas.

RESULTS

In both UV-1- and UV-2-treated mice, a two-week delay in tumor appearance, and significant inhibition (p<0.001) of tumor incidence (50% and 60%, respectively) and tumor burden (papilloma inhibition/mouse, 50% and 70%, respectively) were observed when compared to the positive control group. UV-2 (dihydroxy derivative) was a more potent inhibitor of skin tumor than UV-1 (monohydroxy derivative), which followed their antioxidant activity ranking.

CONCLUSION

The results affirm the skin cancer chemoprevention potential of orally-ingested benzophenone sunscreens in mice and warrant studies in humans to validate synergistic protection achievable by complementation of oral and topical sunscreen usage.

Abstract 3699: Chemoprevention of skin cancer by benzophenone sunscreen agents in mice

Our recent study demonstrated the skin cancer chemoprevention potential of commonly used benzophenone sunscreen agents using the Epstein-Barr virus early antigen in vitro assay (Int. J. Cosmet. Sci. 2012: doi:10.1111/ics.12015). We now report the in vivo anti-tumor activity of two of the benzophenone sunscreens tested positive in the above in vitro assay, octabenzone (UV-1) and dioxybenzone (UV-2), in the two-stage mouse skin carcinogenesis test model utilizing (±)-(E)-4-methyl-2-[-(E)-hydroxyamino]-5-nitro-6-methoxy-3-hexanamide (NOR-1) as inducer and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) as promoter. Studies were conducted in pathogen-free, female hairless mice of HOS-HR-1 strain, 15 animals per control and test groups. Tumor was induced by a single dose of NOR-1 (390 nmol in 100 μl of acetone). One week later, TPA (1.7 nmol in 100 μl of acetone) was applied to skin twice weekly for 20 weeks as a tumor promoter. The test compounds, 0.0025% of UV-1 or UV-2 were administered to the animals through drinking water ad libitum, starting 1 week prior to tumor initiation and stopping 1 week after tumor initiation. All animals were examined weekly for the development of skin papillomas and the following were recorded: the week papillomas appeared, number of mice bearing papillomas and number of papillomas per mouse. In both UV-1 and UV-2 treated mice, 2-week delay in tumor appearance and significant inhibition of tumor incidence (50% and 60%, respectively) and burden (papilloma inhibition/mouse, 50% and 70%, respectively) were observed when compared to the positive control group. Also, treatment with both benzophenone sunscreens produced marked reduction in the average number of tumors formed per mouse (5 and 3 papillomas/mouse for UV-1 and UV-2, respectively compared to 10 papillomas in positive control group) at the end of the 20-week experimental period. These in vivo results in mice further affirm the skin cancer chemoprevention potential of benzophenone sunscreen use in humans.

Citation Format: Govind J. Kapadia, G Subba Rao, Midori Takasaki, Akira Iida, Nobutaka Suzuki, Takao Konoshima, Harukuni Tokuda. Chemoprevention of skin cancer by benzophenone sunscreen agents in mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3699. doi:10.1158/1538-7445.AM2013-3699

Cancer chemopreventive activity of diversin from Ferula diversivittata in vitro and in vivo

A prenylated coumarin (diversin, 1) together with four new sesquiterpene lactones (diversolides A, D, F and G, 2-5) isolated from the roots of Ferula diversivittata were studied for their possible inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). All of the tested compounds were active against EBV-EA activation. Among these compounds diversin (IC(50): 7.7) exhibited the strongest inhibitory effect and was selected to examine its effects on in vivo two-stage mouse skin carcinogenesis induced by 7,12-dimethylbenz[a]anthracene (DMBA) as initiator and TPA as promoter. Treatment with compound 1 (85nmol) along with DMBA/TPA inhibited papilloma formation up to week 7 and the percentage of papilloma bearers was approximately 93.3% at week 20. The average number of papillomas formed per mouse was only 5.5 even at week 20. The results of the present investigation indicated that diversin might be valuable as a potent cancer chemopreventive agent and its potency was comparable with those of curcumin and quercetin, two well-known cancer chemopreventive agents.

Abstract B72: Cancer chemopreventive potential of henna

B72

“Henna” is a powder of the leaves of Lawsonia inermis L. This powder is used mainly as a pigment for coloring skin, hair, fingernails, leather, silk and wool. The anticancer potential of henna powder was evaluated using in vitro and in vivo assays. Henna inhibited tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) - induced activation of Epstein-Barr virus early antigen in lymphoblastoid Raji cells. This indicated the anticancer potential of henna powder. The activity of henna powder was also studied in the ultraviolet B light (280-320 nm wavelength, 34.3 kJ/m2) - initiated and TPA- promoted two stage mouse skin carcinogenesis model. Topical application of a suspension of henna (0.5 mg/ml acetone) decreased tumor incidence in this model system by 70% and tumor multiplicity by 40% at ten weeks of treatment. Lawsone and its precursors 1, 2, 4-trihydroxynaphthalene-1,4-di-beta-glucopyranoside and 1, 2-dihydroxy-4-O-glucosyloxynaphthalene may be the pharmacologically active compounds in henna. In the present study lawsone inhibited TPA-induced activation of Epstein-Barr virus early antigen by 94%. The cancer inhibitory effect of topically applied henna powder was further demonstrated in the peroxynitrite (PN) -initiated and TPA - promoted two stage mouse skin carcinogenesis model system. In this model system, henna decreased tumor incidence by 55% and tumor multiplicity by 57% at 11 weeks of treatment. These data suggest that henna powder as well as its major coloring pigment, lawsone and/or its precursors may be useful as cancer preventive agents. The ability of lawsone and its precursors to perturb electron transfer reactions and free radical processes may partially account for their cancer preventive effects.

Citation Information: Cancer Prev Res 2008;1(7 Suppl):B72.

Cowaniin, a C-Glucosidic Ellagitannin Dimer Linked through Catechin from Cowania mexicana

A new complex tannin, cowaniin (1) was isolated from the leaves and stems of Cowania mexicana (Rosaceae), and its structure was characterized as novel C-glucosidic tannin dimer linked through (+)-catechin on the basis of spectral and chemical evidence. The inhibitory effect on activation of the Epstein-Barr virus early antigen was assessed for cowaniin. Six known polyphenols and related compounds, including a nitrile glucoside, purshianin, were also characterized.

Arctigenin from Fructus Arctii is a novel suppressor of heat shock response in mammalian cells

Because heat shock proteins (Hsps) are involved in protecting cells and in the pathophysiology of diseases such as inflammation, cancer, and neurodegenerative disorders, the use of regulators of the expression of Hsps in mammalian cells seems to be useful as a potential therapeutic modality. To identify compounds that modulate the response to heat shock, we analyzed several natural products using a mammalian cell line containing an hsp promoterregulated reporter gene. In this study, we found that an extract from Fructus Arctii markedly suppressed the expression of Hsp induced by heat shock. A component of the extract arctigenin, but not the component arctiin, suppressed the response at the level of the activation of heat shock transcription factor, the induction of mRNA, and the synthesis and accumulation of Hsp. Furthermore, arctigenin inhibited the acquisition of thermotolerance in mammalian cells, including cancer cells. Thus, arctigenin seemed to be a new suppressive regulator of heat shock response in mammalian cells, and may be useful for hyperthermia cancer therapy.

Potent Skin Cancer Chemopreventing Activity of Some Novel Semi-synthetic Cembranoids from Marine Sources

In the course of our continuing research in development and evaluation of novel skin cancer chemopreventive agents from marine sources, five semi-synthetic cembranoids derived from the marine natural product sarcophine, isolated from the soft coral Sarcophyton glaucum, were synthesized and shown to exhibit a remarkable chemopreventive activity in the in-vitro Epstein Barr Virus Early Antigen (EBV-EA) activation assay. These compounds were assayed in vivo using the two-stage carcinogenesis test of mouse skin tumors induced by 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator, and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoter by topical administration. They showed potent inhibition of both percentage incidence of skin tumor as well as the multiplicity of skin tumors per mouse compared to untreated controls.

Neolignans from Piper futokadsura and Their Inhibition of Nitric Oxide Production

From a MeOH extract of the aerial part of Piper futokadsura, the tetrahydrofuran lignans, futokadsurin A [(7S,8S,7'S,8'R)-3,4,3'-trimethoxy-4'-hydroxy-7,7'-epoxylignan], futokadsurin B [(7R,8R,7'R,8'S)-3,4-dimethoxy-3',4'-methylenedioxy-7,7'-epoxylignan], and futokadsurin C [(7R,8R,7'S,8'S)-3,4-methylenedioxy-3',4'-dimethoxy-7,7'-epoxylignan] were isolated, together with nine known neolignans. In addition, L-tryptophan, pellitorine, phytol, elemicin, and 1,2,4-trimethoxyphenyl-5-aldehyde were isolated. The structures of the new compounds were elucidated using spectroscopic methods. These lignans inhibited nitric oxide production by a murine macrophage-like cell line (RAW 264.7), which was activated by lipopolysaccharide and interferon-gamma.

Cancer chemopreventive effect of phenothiazines and related tri-heterocyclic analogues in the 12-O-tetradecanoylphorbol-13-acetate promoted Epstein-Barr virus early antigen activation and the mouse skin two-stage carcinogenesis models

In continuation of our search for novel agents, we have investigated 29 phenothiazines and related tri-heterocyclic compounds as potential cancer chemopreventive agents in a short-term in vitro assay of Epstein-Barr virus early antigen (EBV-EA) activation induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Among the evaluated compounds, chlorpromazine, phenoxazine, ethylpropazine, 9-oxo-9H-thioxanthene-3-carbonitrile-10,10-dioxide, thiothixene and phenothiazine showed profound inhibition of EBV-EA in the in vitro assay. This activity was influenced by a modification of the phenothiazine ring. Replacement of nitrogen in the phenothiazine ring with sulfur atoms decreased the anti-tumor activity. Overall analysis showed that the simple tri-cyclic compound phenoxazine was the most active anti-tumor promoting compound in the test system. Therefore, we assessed the anti-tumor promoting effect of phenoxazine in vivo in two different chemical carcinogen-induced-promotion experimental models in mice namely the 7,12-dimethylbenz(a)anthracene (DMBA) initiated and TPA-promoted ICR mouse skin two-stage carcinogenesis protocol and the peroxynitrite (PN)-induced and TPA-promoted skin carcinogenesis in HOS:HR-1 mouse. Following tumor initiation with DMBA, topical application of 0.0025% phenoxazine to the dorsal initiated mouse skin resulted in a highly significant inhibition of TPA tumor promotion. The compound exhibited remarkable inhibitory effects on the mouse skin tumor promotion in terms of a reduction in tumor multiplicity (>50%) and incidence, accompanied by an extension of the tumor latency. In the PN-induced and TPA-promoted two-stage mouse skin carcinogenesis, oral administration of phenoxazine (0.0025%) for 2 weeks showed profound decrease in both the tumor incidence and burden by more than 20 and 80%, respectively, at 10 weeks of treatment. This was also accompanied by a 20% delay in the tumor latency period. In all the treatment groups, there was no toxicity due to phenoxazine in the treatment groups as compared to the control animals. These significant anti-tumor potentials of phenoxazine either via topical or oral administration might be due to the inherent cytotoxicity of these classes of compounds, which can be utilized in the prevention of development of overt tumors, immunopotentiation, induction of differentiation and apoptosis. In addition, since phenoxazine derivatives and other related phenothiazine compounds in use, as anti-psychotic agents without any reported adverse effect are known to pass the blood-brain barrier, they represent a new class of cancer chemopreventive agents with greater implication in the prevention of brain cancers.

An Improved Synthesis of 7, 8-Epoxy-1,3,11-cembratriene- 15R(α), 16-diol, a Cembranoid of Marine Origin with a Potent Cancer Chemopreventive Activity

An effective method for the synthesis of 7,8-epoxy-1,3,11-cembratriene- 15R(α),16-diol and its in vitro Epstein-Barr Virus Early Antigen (EBV-EA) Activation Chemopreventive Assay are reported. This semisynthetic product is a new cembranoid with a potent tumor inhibitory activity that is expected to be a lead compound for a new class of chemopreventive agents of marine origin.

Seco-labdane type diterpenes from Excoecaria agallocha

Labdane-type diterpenes, called excoecarins S, T1, and T2 were isolated from the resinous wood of Excoecaria agallocha, along with three known compounds, ent-12-oxo-2,3-secobeyer-15-ene-2,3-dioic acid, agallochin H, and ent-15-epoxy-beyerane-3alpha-ol. Their structures were elucidated on the basis of spectroscopic data, chemical evidence, and X-ray analysis.

Absolute configuration of sesquiterpenes from Crossopetalum tonduzii and their inhibitory effects on Epstein-Barr virus early antigen activation in Raji cells

Two new sesquiterpenoids (1 and 2) with a dihydro-beta-agarofuran skeleton were isolated from Crossopetalum tonduzii. Their structures were elucidated on the basis of spectral analysis, including homonuclear and heteronuclear correlation NMR experiments (COSY, ROESY, HSQC, and HMBC). Their absolute configurations were determined by CD studies on 3, the benzoylated derivative of 1. Chemical correlations have allowed the absolute configurations of 4 and 5, two previously known dihydro-beta-agarofuran analogues, to be reported for the first time. Compounds 1, 2, and 5 showed strong antitumor-promoting effects on Epstein-Barr virus early antigen (EBV-EA) activation.

Anticarcinogenic activity of natural sweeteners, cucurbitane glycosides, from Momordica grosvenori

To search for cancer chemopreventive agents from natural resources, many phytochemicals and food additives have been screened. Consequently, two natural sweeteners, mogroside V and 11-oxo-mogroside V isolated from the fruits of Momordica grosvenori, exhibited strong inhibitory effect on the primary screening test indicated by the induction of Epstein-Barr virus early antigen (EBV-EA) by a tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA). These sweet glycosides, having cucurbitane triterpenoid aglycon, exhibited the significant inhibitory effects on the two-stage carcinogenesis test of mouse skin tumors induced by peroxynitrite (ONOO-) as an initiator and TPA as a promoter. Further, 11-oxo-mogroside V also exhibited the remarkable inhibitory effect on two-stage carcinogenesis test of mouse skin tumor induced by 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and TPA as a promoter.

Chemoprevention of DMBA-induced UV-B promoted, NOR-1-induced TPA promoted skin carcinogenesis, and DEN-induced phenobarbital promoted liver tumors in mice by extract of beetroot

Our previous studies identified the extract of Beta vulgaris (beetroot), commercially also known as betanin, as a potent cancer chemopreventive agent in both in vitro Epstein-Barr early antigen activation assay and in an in vivo two-stage mouse lung and skin carcinogenesis. To explore this issue further, we have now investigated its cancer chemopreventive potentials in three different chemical carcinogen initiation-promotion experimental tumor models in mice. Following tumor initiation with 390 nmol of 7,12-dimethylbenz(a)anthracene (DMBA) in 100 microl of acetone, the mouse skin tumor promotion with 3430 J/m(2) of ultraviolet light-B (UV-B) as well as splenomegaly was significantly inhibited by oral administration of 0.0025% betanin. At the same dose, betanin also afforded significant protection in the mouse skin cancer model following the topical application of 390 nmol of (+/-)-(E)-4-methyl-2-[(E)-hydroxyamino]-5-nitro-6-methoxy-3-hexanamide (NOR-1) in 100 microl of acetone and promoted by topical administration of 1.7 nmol of 12-O-tetradecanoylphorbol-13-acetate (TPA). In the two-stage model of hepatocarcinogenesis in mice with N-nitrosodiethylamine (DEN, 30 mg/kg) as the initiator and phenobarbital as the promoter, oral administration of 0.0025% betanin also showed a very significant inhibition of both the incidence and multiplicity of the liver tumors. These findings along with our initial reports suggest that betanin which is a regularly consumed natural product colorant is an effective cancer chemopreventive agent in mice. The most interesting observation is that the cancer chemopreventive effect was exhibited at a very low dose used in the study and thus indicating that beetroot warrants more attention for possible human applications in the control of malignancy.

New bis-secolabdane diterpenoids from Excoecaria agallocha

Two new bis-secolabdane diterpenoids, excoecarins R1 (1) and R2 (2), were isolated from the resinous wood of Excoecaria agallocha. The structures of 1 and 2 were established on the basis of spectroscopic data interpretation and chemical evidence.

Three Diterpenoids (Excoecarins V1-V3) and a Flavanone Glycoside from the Fresh Stem of Excoecaria agallocha

Three new diterpenoids, excoecarins V1-V3 (1-3) and a new flavanone glycoside (7) were isolated from the fresh stem of Excoecaria agallocha L. Their structures were elucidated as: 2alpha,3alpha,18-trihydroxy-3beta,20-epoxybeyer-15-ene (1), ent-2,3-secokaur-16-en-2,3-dioic acid (2), ent-3,4-seco-16alpha-hydroxyatis-4(19)-en-3-oic acid (3), and 3,5,7,3',5'-pentahydroxy-2R,3R-flavanonol 3-O-alpha-L-rhamnopyranoside (7) on the basis of spectroscopic data, chemical evidence, and/or X-ray analysis.

Semisynthesis of new sarcophine derivatives with chemopreventive activity

The natural cembranolide sarcophine (3) and its lactone ring-opened analogue (10) were oxidized using selenium dioxide under different reaction temperatures to prepare hydroxylated derivatives. Nine new compounds were obtained, six of them targeted hydroxylated derivatives. The determination of regio- and stereochemistry as well as the mechanistic considerations on the selectivity observed in these reactions are discussed on the basis of 2D NMR and molecular modeling. In preliminary in vitro tests on inhibition of EBV-EA activation, compounds 10 and 12-15 have shown higher activity than the known chemopreventive agent sarcophytol A.

Antiproliferative sesquiterpene lactones from the roots of Inula helenium

The MeOH extract of the roots of Inula helenium showed a high inhibitory activity for cell growth against MK-1, HeLa and B16F10 cell lines. Significant activity was found in the hexane-soluble fraction. From the hexane-soluble fraction, seven sesquiterpenes, namely, one germacrane (4beta,5alpha-epoxy-1(10),11(13)-germacradiene-8,12-olide), one elemane (igalane), and five eudesmanes (alantolactone, isoalantolactone, 11alpha,13-dihydroalantolactone, 11alpha,13-dihydro-isoalantolactone, 5-epoxyalantolactone) were isolated. In vitro antiproliferative activities of the isolates against MK-1, HeLa and B16F10 cells are reported.

Chemopreventive effect of resveratrol, sesamol, sesame oil and sunflower oil in the Epstein-Barr virus early antigen activation assay and the mouse skin two-stage carcinogenesis

Resveratrol, sesamol, sesame oil and sunflower oil are known natural dietary components with intrinsic cancer chemopreventive potentials. As a part of our study of dietary constituents as potential cancer chemopreventive agents, we have assessed the anti-cancer potentials of these products in the promotion stage of cancer development employing the in vitro Epstein-Barr virus early antigen activation assay induced by the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA). Further, we studied the activities of these compounds in the brine shrimp cytotoxicity assay as well as on the stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging bioassay with a view to comparing some of the mechanisms of their anti-cancer activity. Finally, we compared the observed chemoprotective capabilities of the four products in the in vivo 7,12 dimethylbenz(a)anthracene initiated and TPA-promoted mouse skin two-stage carcinogenesis protocols. All the products tested showed a profound inhibitory effect on the Epstein-Barr virus early antigen induction using Raji cells. Comparatively, sesame oil was the most potent followed by sesamol and then resveratrol. Only sesamol and resveratrol showed a remarkable cytotoxic activity in the brine shrimp lethality assays as well as profound free radical scavenging activity in the DPPH bioassay. In both test systems, sesamol exhibited a more remarkable activity than resveratrol while sesame oil and sunflower oil did not exhibit any appreciable activity even at the highest concentrations tested (4000 microg ml(-1) ). In our in vivo assay at a 50-fold molar ratio to TPA, sesamol offered 50% reduction in mouse skin papillomas at 20 weeks after promotion with TPA. Under an identical molar ratio to TPA, resveratrol offered a 60% reduction in the papillomas in mouse at 20 weeks. Thus sesamol seems to be an almost equally potent chemopreventive agent. Sesame oil and sunflower oil offered 20 and 40% protection, respectively, in the mouse skin tumor model. The anti-oxidant capabilities of these compounds could not solely explain the observed anti-cancer characteristics. Resveratrol is present in grapes. Sesamol, a constituent of sesame oil and sunflower oil are regularly consumed dietary natural products. The observed chemopreventive effect of these products particularly warrants more attention since they already exist in the population with no known adverse effects.

Cancer chemopreventive activity of Achyranthes aspera leaves on Epstein-Barr virus activation and two-stage mouse skin carcinogenesis

Achyranthes aspera leaves have been assessed for chemopreventive activity. The MeOH extract, alkaloid, non-alkaloid and saponin fractions exhibited significant inhibitory effects (concentration 100 microg) on the Epstein-Barr virus early antigen activation induced by the tumor promotor 12-O-tetradecanoylphorbol-13-acetate in Raji cells. In this in vitro assay the non-alkaloid fraction containing mainly non-polar compounds showed the most significant inhibitory activity (96.9%; 60% viability). In the in vivo two-stage mouse skin carcinogenesis test the total methanolic extract possessed a pronounced anticarcinogenic effect (76%). The present study suggests that A. aspera leaf extract and the non-alkaloid fraction are valuable antitumor promotors in carcinogenesis.

Six new 2-(2-phenylethyl)chromones from Agarwood

Six new chromones, 6-methoxy-2-[2-(3-methoxy-4-hydroxyphenyl)ethyllchromone (2), 6,8-dihydroxy-2-(2-phenylethyl)chromone (3), 6-hydroxy-2-[2-(4-hydroxyphenyl)ethyl]chromone (4), 6-hydroxy-2-[2-(2-hydroxyphenyl)ethyl]chromone (5), 7-hydroxy-2-(2-phenylethyl)chromone (6), and 6-hydroxy-7-methoxy-2-(2-phenylethyl)chromone (7) were isolated from the ether extract of agarwood in addition to a known compound, 2-(2-phenylethyl)chromone or flidersiachromone (1). Their structures were determined by spectroscopic methods including UV, IR, and NMR spectral data and comparisons with the calculated values using the hydroxyl and methoxyl substituent increments of the chromone ring.

Anti-tumor-promoting activity of the diterpene from Excoecaria agallocha. II

Eight new diterpenoids (1-8) have been isolated from the wood of Excoecaria agallocha (Euphorbiaceae) and their inhibitory effects on the induction of Epstein-Barr virus early antigen (EBV-EA) in Raji cells were examined to search for potent anti-tumor-promoters from natural resources. Of these compounds, the secolabdane-type diterpenoid, compound 7 exhibited a remarkable inhibitory effect on EBV-EA induction, and a significant anti-tumor-promoting effect in the mouse two-stage carcinogenesis test using 7,12-dimethylbenz[a]anthracene and 12-O-tetradecanovl-phorbol-13-acetate.

Cancer chemoprevention by ginseng in mouse liver and other organs

Oral administration of red ginseng extracts (1% in diet for 40 weeks) resulted in the significant suppression of spontaneous liver tumor formation in C3H/He male mice. Average number of tumors per mouse in control group was 1.06, while that in red ginseng extracts-treated group was 0.33 (p<0.05). Incidence of liver tumor development was also lower in red ginseng extracts-treated group, although the difference from control group was not statistically significant. Anti-carcinogenic activity of white ginseng extracts, besides red ginseng extracts, was also investigated. In the present study, the administration of white ginseng extracts was proven to suppress tumor promoter-induced phenomena in vitro and in vivo. It is of interest that oral administration of the extracts of Ren-Shen-Yang- Rong-Tang, a white ginseng-containing Chinese medicinal prescription, resulted in the suppression of skin tumor promotion by 12-o-tetradecanoylphorbol-13-acetate in 7,12-dimethylbenz[a]anthracene-initiated CD-1 mice. These results suggest the usefulness of ginseng in the field of cancer prevention.

Cancer chemopreventive activity of phenylpropanoid esters of sucrose, vanicoside B and lapathoside A, from Polygonum lapathifolium

To search for cancer chemopreventive agents from natural resources, many phytochemicals have been screened using the in vitro synergistic assay indicated by the inhibitory effects on the induction of Epstein-Barr virus early antigen (EBV-EA) by 12-O-tetradecanoylphorbol-13-acetate (TPA). Two phenylpropanoid esters of sucrose, vanicoside B and lapathoside A, were isolated from the aerial part of Polygonum lapathifolium as inhibitors on the EBV-EA induction. These compounds also exhibited significant anti-tumor-promoting effects on mouse two-stage skin carcinogenesis induced by 7,12-dimethylbenz[a]anthracene (DMBA, as an initiator) and TPA as a promoter. Further, vanicoside B exhibited the remarkable inhibitory effect on two-stage carcinogenesis test of mouse skin tumors initiated with an NO donor, NOR-1.

New phenylpropanoid esters of sucrose from Polygonum lapathifolium

Four new phenylpropanoid esters of sucrose, lapathosides A (1), B (2), C (3), and D (4), were isolated from the aerial parts of Polygonum lapathifolium together with known esters, vanicoside B (5) and hydropiperoside (6). The structures of 1-4 were determined by spectral (1D and 2D NMR and MS) analysis. Lapathoside A (1) and vanicoside B (2) showed significant inhibitory effects on the Epstein-Barr virus early antigen activation by tumor-promoters.

Steroidal saponins from Hemerocallis fulva var. kwanso

Two steroidal saponins, hemeroside A and B, were isolated from the aerial part of Hemerocallis fulva var. kwanso for the first time. The structures of these compounds were established as 24S-hydroxy-neotokorogenin 1-O-alpha-L-arabinopyranosyl 24-O-beta-D-glucopyranoside (1) and isorhodeasapogenin 3-O-beta-D-glucopyranosyl-(1-->3)-[beta-D-xylopyranosyl-(1-->2)]-beta-D-glucopyranosyl-(1-->4)-beta-D-galactopyranoside (2) through NMR experiments.

Inhibition of epstein-barr virus early antigen activation promoted by 12-O-tetradecanoylphorbol-13-acetate by the non-steroidal anti-inflammatory drugs

As part of our screening program for cancer inhibitory agents effective specifically in the promotion stage of cancer development, we have evaluated the possible inhibitory effects of 36 non-steroidal anti-inflammatory drugs (NSAIDs) on the Epstein-Barr virus early antigen (EBV-EA) activation which was induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. All the drugs were observed to inhibit the EBV-EA activation at low doses with low toxicity. The two most active anti-tumor promoting agents were the arylacetic acid derivatives, etodolac and sulindac. We also report for the first time the activities of 14 new NSAIDs belonging to different classes as potential cancer chemopreventive agents. A structure-activity relationship study showed that among the salicylic acid derivative tested, the oxidation of the thiol group to dithiol derivatives results in the reduction of the activity. Introduction of amino group on the salicylic acid molecules also results in the reduction of activity in the EBV-EA assay. The results are of great interest in the development of NSAIDs as cancer chemopreventive agents, which halt cancer progression in multistage carcinogenesis, where successive activities are required to evolve into fully-fledged and metastatic cancer.

Antitumor-promoting effects of cyclic diarylheptanoids on Epstein-Barr virus activation and two-stage mouse skin carcinogenesis

Eleven cyclic diarylheptanoids were screened as potential antitumor promoters by examining the ability of the compounds to inhibit Epstein-Barr virus early antigen activation (induced by 12-O-tetradecanoylphorbol-13-acetate) in Raji cells. 13-Oxomyricanol and myricanone showed the highest activity and also exhibited remarkable inhibitory effects on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test. These data suggest that certain diarylheptanoids might be valuable antitumor promoters and/or chemopreventors.

Anti-tumor-promoting activity of lignans from the aerial part of Saussurea medusa

In the course of our continuing search for novel cancer chemopreventive agents from natural sources, several kinds of Compositae plants were screened. Consequently, the lignans, arctiin (ARC) and arctigenin (ARC-G), were obtained from the aerial part of Saussurea medusaas active constituents. These compounds exhibited the remarkable anti-tumor-promoting effect on two-stage carcinogenesis test of mouse skin tumors induced by 7, 12-dimethylbenz[a]anthracene as an initiator and 12-O-tetradecanoyl phorbol-13-acetate as a promoter by both topical application and oral administration. Furthermore, ARC-G exhibited potent anti-tumor-promoting activity on two-stage carcinogenesis test of mouse pulmonary tumors induced by 4-nitroquinoline-N-oxide as an initiator and glycerol as a promoter.

Cancer chemopreventive activity of an iridoid glycoside, 8-acetylharpagide, from Ajuga decumbens

In the course of our continuing search for novel cancer chemopreventive agents from natural sources, several kinds of Labiatae plants were screened. Consequently, the iridoid glycoside derivative, 8-acetylharpagide (8-AcHarp), was obtained from the flowering whole plant of Ajuga decumbens as an active constituent. This glycoside exhibited the remarkable inhibitory effect on two-stage carcinogenesis test of mouse skin tumors induced by nitric oxide (NO) donor, (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexen eamide (NOR 1) as an initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoter. Further, 8-AcHarp exhibited potent anti-tumor-promoting activity on two-stage carcinogenesis test of mouse hepatic tumor using N-nitrosodiethylamine (DEN) as an initiator and phenobarbital (PB) as a promoter.

Flavonoid and benzophenone glycosides from Coleogyne ramosissima

A benzophenone glucoside and two flavonol glycosides were isolated together with 27 known polyphenols from the aerial parts of Coleogyne ramosissima, and their structures were elucidated by spectroscopic and chemical methods as iriflophenone 2-O-beta-glucopyranoside, isorhamnetin 3-O-2G-rhamnopyranosylrutinoside-7-O-alpha-rhamnopyranoside and limocitrin 3-O-rutinoside-7-O-beta-glucopyranoside, respectively.

Cancer chemopreventive activity of euglobal-G1 from leaves of Eucalyptus grandis

In the course of our continuing search for novel cancer chemopreventive agents from natural sources, several kinds of Eucalyptus plants were screened. Consequently, the phlorogrucinol-monoterpene derivative, euglobal-G1 (EG-1), was obtained from the leaves of Eucalyptus grandis as an active constituent. EG-1 exhibited the remarkable inhibitory effect on two-stage carcinogenesis test of mouse skin tumors induced by 7, 12-dimethylbenz[a]anthracene (DMBA) as an initiator and fumonisin-B1, which has been known as one of mycotoxins produced by Fusarium monifliforme, as a promoter. Further, EG-1 exhibited potent anti-tumor-promoting activity on two-stage carcinogenesis test of mouse pulmonary tumor using 4-nitroquinoline-N-oxide (4-NQO) as an initiator and glycerol as a promoter.

Anti-tumor promoting effects of sesquiterpenes from Maytenus cuzcoina (Celastraceae)

Ten sesquiterpenoids (1-10), with a dihydro-beta-agarofuran skeleton, were isolated from Maytenus cuzcoina (Celastraceae). Their structures were elucidated on the basis of spectral analysis, including homo- and heteronuclear correlations NMR experiments (COSY, ROESY, HMQC and HMBC), and chemical correlations. The compounds have been tested for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), as a test for potential cancer chemopreventive agents. Compounds 1-3, 6 and 7 showed strong inhibitory effects on EBV-EA induction (100% inhibition at 1000 mol ratio/TPA). Their structure-activity relationship is discussed.

Excoecarins D, E, and K, from excoecaria agallocha

Three novel diterpenoids, excoecarins D, E, and K (1-3), were isolated from Excoecaria agallocha. The structures of 1-3 were established as 3alpha,18-dihydroxy-3beta,20-epoxybeyer-15-ene, (15R, 16S)-ent-15,16-epoxybeyeran-3-one, and ent-3beta-hydroxykaur-16-en-2-one, respectively, on the basis of extensive NMR experiments and, in the case of 1, by X-ray analysis.

Cancer chemopreventive activity of majonoside-R2 from Vietnamese ginseng, Panax vietnamensis

In the course of our continuing search for novel cancer chemopreventive agents from natural sources, several kinds of Panax plants were screened. Consequently, the ocotillol-type saponin, majonoside-R2 (MR2), was obtained from the rhizome and root of Panax vietnamensis (Vietnamese ginseng) as an active constituent. MR2 exhibited potent anti-tumor-promoting activity on two-stage carcinogenesis test of mouse hepatic tumor using N-nitrosodiethylamine (DEN) as an initiator and phenobarbital (PB) as a promoter. Further, MR2 exhibited the remarkable inhibitory effect on two-stage carcinogenesis test of mouse skin induced by nitric oxide (NO) donor/12-O-tetradecanoylphorbol-13-acetate (TPA) or peroxynitrite/TPA.

Anti-carcinogenic activity of the roots of Panax notoginseng. II

The extract of the roots of Panax notoginseng (Araliaceae) exhibited a significant anti-tumor-promoting activity on two-stage carcinogenesis of mouse skin tumors induced by 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and a mycotoxin, fumonisin B1, as a non-12-O-tetradecanoylphorbol-13-acetate (non-TPA) type promoter. Further, the extract exhibited the anti-tumor-initiating activity on two-stage carcinogenesis of mouse skin tumors induced by a nitric oxide donor, (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexen amide (NOR-1) as an initiator and TPA as a promoter.

Inhibitory effects of monoacylated 2-O-beta-galactosylglycerols on Epstein-Barr virus activation: the significant role of the hexanoyl chain

Three series of monoacyl-2-O-beta-D-galactosylglycerols bearing an acyl chain of varying length, from C4 to C10, were studied due to their antitumor promoting effects on the activation of the Epstein-Barr virus early antigen (EBV-EA), such activation being induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). This study indicates that it is more the length of the acyl chain that is important for the activity, six carbon atoms resulting in maximum effect, rather than the position of the ester function and the nature of the sugar (galactose or glucose).

Anti-tumor promoting activity of polyphenols from Cowania mexicana and Coleogyne ramosissima

Chemical investigation on polyphenol-rich fractions of Cowania mexicana and Coleogyne ramosissima (Rosaceae) which showed significant inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), has led to the characterization of 10 compounds including C-glucosidic ellagitannin monomers and dimers from the former plant, and 17 polyphenols including flavonoid glycosides from the latter. The effects of individual components and their analogues with related structures on the TPA-induced EBV-EA activation were then evaluated. Among the compounds isolated from C. mexicana, two C-glucosidic ellagitannins, alienanin B and stenophyllanin A and a nitrile glucoside (lithospermoside), and among the constituents from C. ramosissima, two flavonoid glycosides, isorhamnetin 3-0-beta-D-glucoside and narcissin were revealed to possess strong inhibitory effects on EVB-EA activation, the potencies of which were either comparable to or stronger than that of a green tea polyphenol, (-)-epigallocatechin gallate. These polyphenols except for nitrile glucoside, which was not tested owing to an insufficient amount, were also found to exhibit anti-tumor promoting activity in two-stage mouse skin carcinogenesis using 7,12-dimethylbenz[a]anthracene (DMBA) and TPA.

Cancer chemopreventive agents (antitumor-promoters) from Ajuga decumbens

Sixteen compounds (1-16) isolated from the flowering whole plant of Ajuga decumbens have been tested for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) induction by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), as a primary screening test for antitumor-promoters (potential cancer chemopreventive agents). Five compounds (6, 9, and 12-14) showed strong inhibitory effects on EBV-EA induction. Of these active compounds, two major constituents of this plant, cyasterone (6) and 8-acetylharpagide (13), showed potent antitumor-promoting activities on a mouse-skin in vivo two-stage carcinogenesis procedure, using 7, 12-dimethylbenz[a]anthracene as initiator and TPA as promoter. Further, compound 13 also exhibited potent chemopreventive activity in a mouse pulmonary tumor model.

Anti-carcinogenic activity of Taraxacum plant. II

Eleven triterpenoids (1-11) from the roots of Taraxacum japonicum (Compositae) were examined for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) induced by the tumor promoter, 12-O-tetrade-canoylphorbol-13-acetate (TPA), in Raji cells as a primary screening test for anti-tumor-promoters (cancer chemopreventive agents). Of these triterpenoids, taraxasterol (1) and taraxerol (7) exhibited significant inhibitory effects on EBV-EA induction, but the inhibitory effects of their acetates 2 and 8 were weaker than those of 1 and 7. Furthermore, 1 and 7 exhibited potent anti-tumor-promoting activity in the two-stage carcinogenesis tests of mouse skin using 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and TPA as a promoter, and 1 showed a remarkable inhibitory effect on mouse spontaneous mammary tumors using C3H/OuJ mouse. These results strongly suggested that taraxasterol (1) could be a valuable chemopreventive agent.

Anti-carcinogenic activity of Taraxacum plant. I

An extract of the roots of Taraxacum japonicum (Compositae) exhibited strong anti-tumor-promoting activities on the two-stage carcinogenesis of mouse skin tumor induced by dimethylbenz[a] anthracene (DMBA) as an initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoter, as well as on that induced by DMBA and fumonisin B1. Further, the extract exhibited anti-tumor-initiating activity on the two-stage carcinogenesis of mouse skin tumor induced by (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexen amide (NOR-1) as an initiator and TPA as a promoter. These results suggested that an extract of the roots of the Taraxacum plant could be a valuable chemopreventive agent against chemical carcinogenesis.

Inhibitory effects of dehydrozingerone and related compounds on 12-O-tetradecanoylphorbol-13-acetate induced Epstein-Barr virus early antigen activation

Dehydrozingerone, 4-(4-hydroxy-3-methoxyphenyl)-3-buten-2-one, is half an analog of curcumin which is known to have anti-tumor activity. The anti-tumor promoting activity of dehydrozingerone was evaluated by determining the inhibitory effect on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). The concentration needed for 50% inhibition of the tumor promotion (IC50) of dehydrozingerone was similar to that of curcumin. To elucidate the structure-activity relationship on the anti-tumor promoting activity, dehydrozingerone, curcumin, isoeugenol, which has no carbonyl group in the side chain, benzalacetone, which is the basic structure of dehydrozingerone, o-dehydrozingerone, which is the ortho-hydroxyl substituted compound of dehydrozingerone, and their related compounds were investigated using the in vitro short-term assay on TPA-induced EBV-EA activation. o-Dehydrozingerone showed the most potent inhibitory effect in a series of tested dehydrozingerone derivatives and their related monosubstituted benzalacetones. This suggests that the occupation at both ortho positions of the hydroxyl group enhances the anti-tumor promoting activity. Isoeugenol inhibited the tumor promoting activity at a concentration of about one-third of the IC50 of dehydrozingerone. This indicates that the carbonyl group in the side chain has a negative impact on the anti-tumor promoting activity. The inhibitory effects of the carbon-carbon bond in the side chain were studied using benzylacetone with a single bond, benzalacetone with a double bond and 4-phenyl-3-butyn-2-one with a triple bond. 4-Phenyl-3-butyn-2-one inhibited the most potent activity followed by benzalacetone and benzylacetone.

Five phloroglucinol-monoterpene adducts from Eucalyptus grandis

Five new euglobals possessing the phloroglucinol-monoterpene structure, euglobals G8-G12, together with a known euglobal-IIc were isolated from the hexane fraction of the methanol extract of the leaves of Eucalyptus grandis. Euglobal-G8 is an adduct of formyl-isovaleroyl-phloroglucinol and gamma-terpinene whereas -G9, -G10 and -G11 have the same phloroglucinol moiety fused with alpha-terpinene, while Euglobal-G12 has terpinolene fused with the same phloroglucinol moiety. The structures of these compounds were elucidated on the basis of spectral evidences. Biomimetic synthesis of euglobals suggests that these compounds are derived biogenetically by the Diels-Alder type cycloaddition of the corresponding terpenes with an ortho-quinone methide generated from grandinol.