Evaluation of skin cancer chemoprevention potential of sunscreen agents using the Epstein-Barr virus early antigen activation in vitro assay.

In our continuing search for novel cancer chemopreventive compounds of natural and synthetic origin, we have evaluated 14 commonly used ultraviolet (UV) sunscreen agents (designated UV-1 to UV-14) for their skin cancer chemoprevention potential. They belong to 8 different chemical categories: aminobenzoate (UV-5, UV-7, UV-8 and UV-14), benzophenone (UV-1, UV-2, UV-3 and UV-13), benzotriazole (UV-10), benzyloxyphenol (UV-9), cinnamate (UV-6), quinolone (UV-4), salicylate (UV-11) and xanthone (UV-12). In the in vitro assay employed, the sunscreens were assessed by their inhibition of the Epstein-Barr virus early antigen (EBV-EA) activation induced by the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in human lymphoblastoid Raji cells. All sunscreens tested were found to exhibit anti-tumour promoting activity: listed in decreasing order, moderate (UV-11, UV-2, UV-7, UV-12, UV-3, UV-9 and UV-14) to weak (UV-1, UV-6, UV-8, UV-16, UV-5, UV-4 and UV-10) with octyl salicylate (UV-11) as the most potent and drometrizole (UV-10) as the least potent among the compounds evaluated. A plausible relationship between the antioxidant property of sunscreens and their ability to promote anti-tumour activity was noted. The results call for a comprehensive analysis of skin cancer chemoprevention potential of currently used UV sunscreen agents around the globe to identify those with the best clinical profile.

Inhibitory effects of alpha-carotene on proliferation of the human neuroblastoma cell line GOTO.

alpha-Carotene inhibited the proliferation of the human neuroblastoma cell line GOTO in a dose- and time-dependent manner. In addition, it was about 10 times more inhibitory than beta-carotene. Northern blot analysis indicated that alpha-carotene caused maximum suppression of the level of the N-myc messenger RNA of GOTO cells. This suppression occurred within 18 hours of alpha-carotene treatment, after which the level of the N-myc messenger RNA gradually recovered to the basal level. Analysis by flow cytometry indicated that when GOTO cells were exposed to alpha-carotene, they were arrested in the G0-G1 phase of their cell cycle. However, as the level of the N-myc messenger RNA was recovering, these cells resumed normal cycling. These results indicate that the reduction in the level of the N-myc messenger RNA caused by alpha-carotene is closely linked with G0-G1 arrest.

Inhibition of the tumor-promoting action of 12-O-tetradecanoylphorbol-13-acetate by some oleanane-type triterpenoid compounds.

Since glycyrrhetinic acid was proved to suppress tumor promoter effects, several oleanane-type triterpenes which were chemically derived from oleanolic acid and hederagenin were tested in vitro and in vivo against the action of tumor promoter, 12-O-tetradecanoylphorbol 13-acetate. By in vitro experiment monitoring with 12-O-tetradecanoylphorbol-13-acetate-induced stimulation of 32Pi incorporation into phospholipids and an in vivo test on skin tumor formation in mice initiated with 7,12-dimethylbenz[a]anthracene and promoted with 12-O-tetradecanoylphorbol-13-acetate, 18 beta-olean-12-ene-3 beta,28-diol (= erythrodiol), 18 beta-olean-12-ene-3 beta,23,28-triol, 18 alpha-olean-12-ene-3 beta,28-diol, and 18 alpha-olean-12-ene-3 beta,23,28-triol showed remarkable suppressive effects. Especially 18 alpha-oleanane derivatives having a CH2OH grouping converted from the COOH group initially allocated at C-17 were 100 times more effective than glycyrrhetinic acid both in vitro and in vivo.

Potent preventive action of alpha-carotene against carcinogenesis: spontaneous liver carcinogenesis and promoting stage of lung and skin carcinogenesis in mice are suppressed more effectively by alpha-carotene than by beta-carotene.

Although beta-carotene has been considered to be a key cancer preventive agent in green and yellow vegetables, other types of carotenoids, such as alpha-carotene, may also contribute to anticarcinogenic action, since these carotenoids usually coexist with beta-carotene and are detectable in human blood and tissues. In this study, we compared the inhibitory effect of natural alpha-carotene, obtained from palm oil, with that of beta-carotene on spontaneous liver carcinogenesis in C3H/He male mice. The mean number of hepatomas per mouse was significantly decreased by alpha-carotene supplementation (per os administration in drinking water at a concentration of 0.05%, ad libitum) as compared with that in the control group (P < 0.001, Student's t test). On the other hand, beta-carotene, at the same dose as alpha-carotene, did not show any such significant difference from the control group. Furthermore, we also compared the antitumor-promoting activity of alpha-carotene with that of beta-carotene against two-stage mouse lung carcinogenesis (initiator, 4-nitroquinoline 1-oxide; promoter, glycerol). alpha-Carotene, but not beta-carotene, reduced the number of lung tumors per mouse to about 30% of that in the control group (P < 0.001, Student's t test). The higher potency of the antitumor-promoting action of alpha-carotene compared to beta-carotene was confirmed in other experimental systems; e.g., alpha-carotene was also found to have a stronger effect than beta-carotene in suppressing the promoting activity of 12-O-tetradecanoylphorbol-13-acetate on skin carcinogenesis in 7,12-dimethylbenz[a]anthracene-initiated mice. These results suggest that not only beta-carotene, but also other types of carotenoids, such as alpha-carotene, may play an important role in cancer prevention.

Anti-tumor promoting activity of Dryopteris phlorophenone derivatives.

As a part of screening studies for cancer chemopreventive agents (anti-tumor promoters) 33 Dryopteris phlorophenone derivatives have been evaluated. The compounds tested comprised of monomeric acylphloroglucinols (e.g. desaspidinol, aspidinol) as well as dimeric (e.g. aspidin, desaspidin), trimeric (e.g. filixic acids), and tetrameric (e.g. dryocrassin) phlorophenone, wherein hexacyclic rings are bound together by a methylene bridge. These compounds were examined for their in vitro anti-tumor promoting effect on Epstein-Barr virus antigen activation induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). The two dimeric compounds aspidin and desaspidin, which were found to be the most active among the tested phlorophenones, were also examined in vivo on two stage mouse skin carcinogenesis, and found to show significant inhibitory effect on 7,12-dimethylbenz[alpha]anthracene (DMBA)-TPA tumor promotion.

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.

Anti-tumor-promoting activity of derivatives of abieslactone, a natural triterpenoid isolated from several Abies genus.

Abiesenonic acid methyl ester (AVB-I acid methyl ester), a triterpenoid compound prepared from abieslactone, suppressed tumor promoter-induced phenomena in vitro and in vivo; i.e., AVB-I acid methyl ester inhibited 12-o-tetradecanoylphorbol-13-acetate (TPA)-stimulated 32Pi-incorporation into phospholipids of cultured cells and the promoting action of TPA on skin tumor formation in mice initiated with 7,12-dimethylbenz[a]anthracene.

Xanthones as inhibitors of Epstein-Barr virus activation.

To search for possible antitumor promoters, we carried out a primary screening of 20 xanthones isolated from plants of the Guttiferae family, using their possible inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. Some of these xanthones, namely 1,3,7-trihydroxy-2-(3-methyl-2-butenyl)xanthone (8), dulxanthone-B (10) and latisxanthone-C (15), were observed to significantly inhibit the EBV-EA activation. The investigation indicated that 8, 10 and 15 might be valuable antitumor promoters.

Inhibitory effect of flavonoids from citrus plants on Epstein-Barr virus activation and two-stage carcinogenesis of skin tumors.

To search for possible anti-tumor promoters, thirteen flavones (1-13) obtained from the peel of Citrus plants were examined for their inhibitory effects on the Epstein-Barr virus early antigen (EBV-EA) activation by a short-term in vitro assay. Of these flavones, 3,5,6,7,8,3',4'-heptamethoxyflavone (HPT) (13) exhibited significant inhibitory effects on the EBV-EA activation induced by the tumor promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA). Further, compound 13 exhibited remarkable inhibitory effects on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test.

Cancer chemopreventive activity of synthetic colorants used in foods, pharmaceuticals and cosmetic preparations.

In continuation with our studies to uncover cancer chemopreventive effects of non-toxic natural colorants and other products of biologic and synthetic origin, we tested several Food and Drug Administration-approved synthetic colorants for antitumor promoting potential by the in vitro Epstein-Barr virus early antigen activation in Raji cells in response to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Among 29 such colorants used in foods, pharmaceuticals and cosmetics and evaluated in vitro, six of the 10 most effective had an azo group. Three structurally unrelated colorants tested in this assay were also studied in vivo for chemoprevention of 7,12-dimethylbenz[a]anthracene (DMBA)-induced TPA-promoted mouse skin carcinogenesis. The results indicate that tartrazine, indigo carmine and erythrosine are potent inhibitors of skin tumor promotion in mice treated with DMBA and TPA.

Inhibitory effect of Epstein-Barr virus activation by Citrus fruits, a cancer chemopreventor.

To search useful compounds in Citrus fruit for cancer chemoprevention, we carried out a primary screening of extracts of fruit peels and seeds from 78 species of the genus Citrus and those from two Fortunella and one Poncirus species, which were closely related to the genus Citrus. These Citrus extracts inhibited the Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol 13-acetate (TPA) as a useful screening method for anti-tumor promoters. Our results indicated that Citrus containing substances may be inhibit susceptibility factors involved in the events leading to the development of cancer.

Cancer prevention by natural carotenoids.

Various natural carotenoids were proven to have anticarcinogenic activity. Epidemiological investigations have shown that cancer risk is inversely related to the consumption of green and yellow vegetables and fruits. Since beta-carotene is present in abundance in these vegetables and fruits, it has been investigated extensively as possible cancer preventive agent. However, various carotenoids which co-exist with beta-carotene in vegetables and fruits also have anti-carcinogenic activity. And some of them, such as alpha-carotene, showed higher potency than beta-carotene to suppress experimental carcinogenesis. Thus, we have carried out more extensive studies on cancer preventive activities of natural carotenoids in foods; i.e., lutein, lycopene, zeaxanthin and beta-cryptoxanthin. Analysis of the action mechanism of these natural carotenoids is now in progress, and some interesting results have already obtained; for example, beta-cryptoxanthin was suggested to stimulate the expression of RB gene, an anti-oncogene, and p73 gene, which is known as one of the p53-related genes. Based on these results, multi-carotenoids (mixture of natural carotenoids) seems to be of interest to evaluate its usefulness for practice in human cancer prevention.

Antitumor-promoting activity of eperisone.

Eperisone, a Ca2+ entry blocker, suppressed the action of tumor promoter in vitro and in vivo, inhibited tumor-promoter-stimulated 32Pi incorporation into phospholipids of cultured cells, and also proved to have antitumor-promoting activity in mouse skin carcinogenesis induced by 7,12-dimethylbenz[a]anthracene plus tumor promoter, 12-O-tetradecanoylphorbol-13-acetate.

[Anticarcinogenesis activity of natural carotenes]. / Activité anticarcinogénétique des carotènes naturels.

Natural carotene sample obtained from palm oil was proved to suppress the promoting stage of two-stage carcinogenesis of mouse skin, and also inhibit the proliferation of human malignant tumor cells, such as neuroblastoma GOTO cells, stomach cancer HGC-27 cells, and pancreatic cancer PANC-I cells. Among the major constituents of palm carotene, alpha-carotene showed stronger anti-proliferative effect than beta-carotene. The present results indicate that further investigation for not only beta-carotene but also other kinds of natural carotenes, such as alpha-carotene, should be carried out.

Studies on the antitumor-promoting activity of naturally occurring substances. II. Inhibition of tumor-promoter-enhanced phospholipid metabolism by umbelliferous materials.

Ninety-five extracts prepared from 14 kinds of Umbelliferous materials were studied to determine their effects on tumor-promoter-induced phenomena in vitro. Of the materials, 5 Chinese crude drugs, two Bai-Hua Qian-Hu classified as Q-I and Q-II types, the root of Peucedanum praeruptorum Dunn., Zi-Hua Qian-Hu, the root of P. decursivum Maxim., Tang-Bai-Zhi, the root of Angelica dahurica Benth, et Hook. var. pai-chi Kimura, Hata et Yen., Dang-Gui, the root of A. acutiloba Kitagawa and 2 Umbelliferous plants, ashita-ba. A. keiskei Koidz., and ama-nyuu, A. edulis Miyabe, showed potent inhibitory effects on 12-O-tetradecanoylphorbol-13-acetate (TPA)-stimulated 32Pi incorporation into phospholipids of cultured cells. From the active fraction of the crude drug "Tang-Bai-Zhi," imperation (1), isoimperatoin (2), oxypeucedanin (3), pabulenol (4), neobyakangelicol (5) and byakangelicin (6) were identified as active or inactive principles. Compound 4 had not previously been isolated from Tang-Bai-Zhi, A. dahurica var. pai-chi. We also discuss the structure-activity relationship among the above 6 kinds of linear-type furanocoumarins, together with 3 kinds of antitumor-promoter coumarins having the same skeleton, psoralen (7), bergapten (8) and xanthotoxin (9), obtained from "ashita-ba" (eaten as a vegetable in Japan). Among the compounds in the present experiment, compounds 1 and 2 showed potent inhibitory activity at the concentration of 50 micrograms/ml and 3-9 were found to have less or no activity.

Anti-tumor-promotion by principles obtained from Angelica keiskei.

Potent anti-tumor promoter activity has been found in the nonpolar extracts of the root of "Ashita-Ba", Angelica keiskei Koidz. (Umbelliferae), which is eaten as a vegetable in Japan. From this active fraction, two angular furanocoumarins, archangelicin (1) and 8(S),9(R)-9-angeloyloxy-8,9-dihydrooroselol (2), three linear furanocoumarins, psoralen (3), bergapten (4) and xanthotoxin (5), and three chalcones, 4-hydroxyderricin (6), xanthoangelol (7) and a novel chalcone named ashitaba-chalcone (8), were isolated. Among these compounds, two angular type furanocoumarins, 1 and 2, and three chalcones, 6-8, suppressed 12-O-tetradecanoylphorbol-13-acetate (TPA)-stimulated 32Pi-incorporation into phospholipids of cultured cells, whereas coumarins 3-5 were less effective. In addition, chalcones 6 and 7 were proved to have anti-tumor-promoting activity in mouse skin carcinogenesis induced by 7,12-dimethylbenz[a]anthracene (DMBA) plus TPA. Since chalcones 6 and 7 showed calmodulin-interacting property, both chalcones may reveal anti-tumor-promoting activity via the modulation of calmodulin involved systems. These chalcones may be useful to develop the effective method for cancer prevention.

Structures of new coumarins and antitumor-promoting activity of coumarins from Angelica edulis.

From the fruits of Angelica edulis Miyabe (Umbelliferae), three new angular furanocoumarins, edulisin III (1), edulisin IV (2), and edulisin V (3), were isolated along with three known coumarins, 2'(S), 3'(R)-3'-isobutyryloxy-4'-acetoxy-2',3'-dihydrooroselol (4), edultin (5), and 2'(S),3'(R)-3'-senecioyloxy-4'-acetoxy-2',3'-dihydrooroselol (6), respectively. The structures of 1 and 2 were established to be 2'(S),3'(R)-3'-(2-methylbutyryloxy)-4'-acetoxy-2',3'-dihydrooro selol and 2'-(S),3'(R)-3'-propyryloxy-4'-acetoxy-2',3'-dihydrooroselol by chemical studies and spectral analyses. Coumarin 3 was proved to be 3'-(2-methylbutyryl-oxy)-4'-angeloyloxy-2',3'-dihydrooroselol++ + by chemical and spectral analyses and H-C COLOC. Coumarins 1-6 were examined for the effects on tumor-promotor induced phenomena in vitro. Among these coumarins, 3 showed the most potent inhibitory activity on 12-O-tetradecanoylphorbol 13-acetate (TPA)-stimulated 32Pi incorporation into phospholipids of cultured cells.

Cancer chemopreventive activity of odorine and odorinol from Aglaia odorata.

In the course of our continuing search for novel cancer chemo-preventive agents from natural sources, we have carried out a primary screening in vitro assay of the compounds isolated from Aglaia odorata. Consequently, aminopyrrolidine-diamides, odorine and odorinol, were obtained as active constituents. These compounds exhibited potent anti-carcinogenic effects in a two-stage carcinogenesis test of mouse skin induced by 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoter. Further, both compounds showed remarkable inhibitory effects in two-stage mouse skin carcinogenesis models induced by nitric oxide (NO) donors such as (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexenamide (NOR-1) or peroxynitrite as an initiator and TPA as a promoter. From these results, it was concluded that odorine and odorinol inhibited both the initiation and promotion stages of two-stage skin carcinogenesis.