Aminonaphthoquinones--a novel class of compounds with potent antimalarial activity against Plasmodium falciparum.

Malaria is a major tropical disease, which kills two million people annually. The population at risk from this disease has increased because of the difficulties in eradicating the mosquito vector in the endemic regions and the emergence and spread of parasite resistance to all the commonly used antimalarials. Since antimalarials are the major arsenal for treatment of the disease, there is an urgent need for newer drugs with novel mechanisms of action, which will be effective against all strains of the parasite. As a part of our anti-infective drug discovery program, we have investigated 18 compounds including several synthetic and natural naphthoquinones as potential antimalarial agents. We have identified aminonaphthoquinones, as a class of antimalarial compounds with antimalarial activity against Plasmodium falciparum. Among these compounds, 2-amino-3-chloro-1,4-naphthoquinone is the most potent. It had an IC(50)of 0.18 micro M (37.3 ng ml(-1)) against the W2 clone, and is more potent than chloroquine, which had an IC(50)of 0.23 micro M (72 ng ml(-1)). It was also active against the D6 clone. In general, 2-amino-1,4-naphthoquinone analogs and the 4-amino-1,2-napthoquinone analog showed promising antimalarial activity in the bioassay. In contrast, a number of 2-hydroxy-1,4-naphthoquinones and dimeric quinones were less active.

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.

Adjuvant chemoprevention of experimental cancer: catechin and dietary turmeric in forestomach and oral cancer models.

Catechin and dietary turmeric (Curcuma longa) were used as chemopreventive agents in benzo[a]pyrene induced forestomach tumors in Swiss mice and methyl-(acetoxymethyl)-nitrosamine induced oral mucosal tumors in Syrian golden hamsters. Catechin in drinking water and dietary turmeric significantly inhibited the tumor burden and tumor incidence in both tumor models. The induction of oral tumors in golden hamsters was delayed by catechin and dietary turmeric. Adjuvant chemoprevention utilising both catechin and dietary turmeric inhibited both the gross tumor yield and burden more effectively than when compared to individual components in both tumor models. A single i.p. injection of catechin to male Swiss mice induced increased forestomach and hepatic glutathione S-transferase (GST) activity when compared to controls. These findings suggest that catechin and turmeric which are regularly consumed natural products, are effective in mice or golden hamsters as chemopreventive agents.

Chemoprevention of mammary tumor virus-induced and chemical carcinogen-induced rodent mammary tumors by natural plant products.

The natural plant products turmeric, beta-carotene, catechin, and betel leaf extract were evaluated for their antitumor effects on mammary tumorigenesis in murine mammary tumor expressing C3H (Jax) mice and in Wistar rats treated with the chemical carcinogen 7-12-dimethylbenz(a)anthracene (DMBA). Administration of turmeric through the diet and of beta-carotene, catechin, and betel leaf extract through the drinking water to virgin female C3H mice resulted in decreased tumor incidence and tumor burden. Administering 5% turmeric in the diet from 2 months of age showed suppression of mammary tumor virus-related reverse transcriptase activity and of preneoplastic changes in the mammary glands. Furthermore, feeding turmeric from 6 months of age resulted in a 100% inhibition of mammary tumors. In the DMBA model of rat mammary tumorigenesis, administration of turmeric, catechin, and betel leaf extract resulted in decreased tumor burden and tumor incidence, and a delay in the onset of mammary tumors.

Protective single/combined treatment with betel leaf and turmeric against methyl (acetoxymethyl) nitrosamine-induced hamster oral carcinogenesis.

The inhibitory effect of oral administration of betel-leaf extract (BLE) and 2 of its constituents, beta-carotene and alpha-tocopherol, as single agents or in combination with dietary turmeric on methyl(acetoxymethyl)nitrosamine (DMN-OAC)-induced oral carcinogenesis in Syrian hamsters was studied. DMN-OAC was administered twice monthly for 6 months. The chemopreventive effect of BLE or its constituents with turmeric was determined by comparing tumor incidence observed in treated groups with that seen in control animals. The apparent site-specific chemopreventive effect of BLE or its constituents was demonstrated by inhibition of tumor incidence, reduction of tumor burden, extension of the tumor latency period and regression of established, frank tumors. The inhibitory effect of BLE or its constituents combined with turmeric was higher than that of the individual constituents. The study suggests that BLE could be developed as a potential chemopreventive agent for human oral cancer.

Antimutagenic and anticarcinogenic effects of carotenoids and dietary palm oil.

Four carotenoids, canthaxanthin, beta-carotene, 8H-apo-beta-carotenal, and 8'-apo-beta-carotene methylester were tested for their ability to suppress the mutagenicity of 1-methyl-3-nitro-1-nitrosoguanidine and benzo[a]pyrene (BP) in Salmonella typhimurium tester strain TA 100. The anticarcinogenic efficacy of the four carotenoids was further assessed in the BP-induced forestomach tumor model in female Swiss mice. The effect of dietary palm oil was also examined in BP-induced neoplasia in the female Haffkine Swiss mouse strain. Canthaxanthin, beta-carotene, 8'-apo-beta-carotenal, and 8'-apo-beta-carotene methylester showed a dose-dependent decrease in the mutagenicity compared with 1-methyl-3-nitro-1-nitrosoguanidine and BP in strain TA 100. In the BP-induced forestomach tumor model, all four carotenoids showed a similar significant anticarcinogenic effect. Dietary administration of palm oil showed a dose-dependent antitumor activity in the animals. Our results show that the intrinsic antimutagenic and anticarcinogenic properties of the carotenoids are not significantly influenced by their conversion to vitamin A.

Protective role of aqueous turmeric extract against mutagenicity of direct-acting carcinogens as well as benzo [alpha] pyrene-induced genotoxicity and carcinogenicity.

Turmeric (Curcuma longa Linn.) has been shown to inhibit chemical carcinogenesis. In this study, we compared the chemopreventive efficacy of an aqueous turmeric extract (AqTE) and its constituents, curcumin-free aqueous turmeric extract (CFAqTE) and curcumin, using the Salmonella typhimurium mutagenicity assay and the bone marrow micronucleus test in female Swiss mice. AqTE exhibited antimutagenic activity against direct-acting mutagens, 4-nitro-O-phenylenediamine and 1-methyl-3-nitro-1-nitrosoguanidine, in strains TA 98 and TA 100 respectively. Both AqTE and CFAqTE inhibited the mutagenicity of benzo [alpha]pyrene in the two strains in the presence of Aroclor-1254-induced rat liver homogenate. The inhibition in both studies was dose-dependent. Administration of AqTE, CFAqTE and curcumin at a dose of 3 mg/animal 18 h prior to i.p. benzo [alpha]pyrene injection (250 mg/kg) significantly inhibited bone marrow micronuclei formation in female Swiss mice by 43%, 76%, and 65% respectively. Furthermore, the incidence and multiplicity of forestomach tumours induced by benzo [alpha]pyrene (1 mg/animal, twice weekly, p.o. for 4 weeks) in female Swiss mice were significantly inhibited by AqTE, CFAqTE and curcumin given 2 weeks before, during and after the carcinogen treatment. These data indicate that the protection against genomic damage by turmeric extract and its components tested could be necessary for some aspects of its cancer chemoprevention.

Chemopreventive effect of turmeric against stomach and skin tumors induced by chemical carcinogens in Swiss mice.

The anticarcinogenic effect of dietary turmeric on benzo[a]pyrene-(BP) induced forestomach neoplasia and 7,12-dimethylbenz[a]anthracene (DMBA)-induced skin tumorigenesis in female Swiss mice was evaluated. To further elucidate the mechanism of antineoplastic action of turmeric, its effect on the hepatic cytochrome b5, cytochrome P-450, glutathione, and glutathione S-transferase activities was studied in female Swiss mice. Turmeric (2% or 5%) in the diet significantly inhibited the BP-induced forestomach tumors, and this response was dose and time dependent. The 2% turmeric diet significantly suppressed DMBA-induced skin tumors in mice. The 5% turmeric diet for seven consecutive days resulted in a 38% decrease in the hepatic cytochrome b5 and cytochrome P-450 levels. Glutathione content was increased by 12%, and the glutathione S-transferase activity was enhanced by 32% in the liver. Our results document a protective effect of turmeric on BP-induced forestomach and DMBA-induced skin tumors in mice.

Chemopreventive efficacy of a betel leaf extract against benzo[a]pyrene-induced forestomach tumors in mice.

The effect of betel leaf extract and some of its constituents, eugenol, hydroxychavicol, beta-carotene and alpha-tocopherol, on benzo[a]pyrene-induced forestomach neoplasia in male Swiss mice was examined. Betel leaf and its constituents decreased the number of papillomas per animal with the maximum protection, considering molar dosage, exhibited by beta-carotene and alpha-tocopherol. Except for beta-carotene, eugenol, hydroxychavicol and alpha-tocopherol increased the levels of reduced glutathione in the liver while glutathione S-transferase activity was enhanced by all except eugenol. Of seven sources, Banarasi betel leaves showed the maximum amounts of beta-carotene and alpha-tocopherol.

Chemopreventive efficacy of betel leaf extract and its constituents on 7,12-dimethylbenz(a)anthracene induced carcinogenesis and their effect on drug detoxification system in mouse skin.

Effects of topically applied betel leaf extract (BLE) and its constituents. beta-carotene, alpha-tocopherol, eugenol and hydroxychavicol on 7,12-dimethylbenz(a)anthracene (DMBA) induced skin tumors were evaluated in two strains of mice. BLE, beta-carotene and alpha-tocopherol, significantly inhibited the tumor formation by 83, 86, 86% in Swiss mice and 92, 94 and 89% in male Swiss bare mice respectively. Hydroxychavicol showed 90% inhibition in Swiss bare mice at 24 weeks of treatment. Eugenol showed minimal protection in both strains of mice. The mean latency period and survivors in BLE, beta-carotene, alpha-tocopherol and hydroxychavicol treated groups were remarkably high as compared to DMBA alone treated group. Intraperitoneal injection of betal leaf constituents showed a significant effect on both glutathione and glutathione S-transferase levels in the Swiss mouse skin.