Chemical and Biological Study of Novel Aplysiatoxin Derivatives from the Marine Cyanobacterium Lyngbya sp

Since 1970s, aplysiatoxins (ATXs), a class of biologically active dermatoxins, were identified from the marine mollusk Stylocheilus longicauda, whilst further research indicated that ATXs were originally metabolized by cyanobacteria. So far, there have been 45 aplysiatoxin derivatives discovered from marine cyanobacteria with various geographies. Recently, we isolated two neo-debromoaplysiatoxins, neo-debromoaplysiatoxin G (1) and neo-debromoaplysiatoxin H (2) from the cyanobacterium Lyngbya sp. collected from the South China Sea. The freeze-dried cyanobacterium was extracted with liquid-liquid extraction of organic solvents, and then was subjected to multiple chromatographies to yield neo-debromoaplysiatoxin G (1) (3.6 mg) and neo-debromoaplysiatoxin H (2) (4.3 mg). They were elucidated with spectroscopic methods. Moreover, the brine shrimp toxicity of the aplysiatoxin derivatives representing differential structural classifications indicated that the debromoaplysiatoxin was the most toxic compound (half inhibitory concentration (IC50) value = 0.34 ± 0.036 µM). While neo-aplysiatoxins (neo-ATXs) did not exhibit apparent brine shrimp toxicity, but showed potent blocking action against potassium channel Kv1.5, likewise, compounds 1 and 2 with IC50 values of 1.79 ± 0.22 µM and 1.46 ± 0.14 µM, respectively. Therefore, much of the current knowledge suggests the ATXs with different structure modifications may modulate multiple cellular signaling processes in animal systems leading to the harmful effects on public health.

Oscillatoxin I: A New Aplysiatoxin Derivative, from a Marine Cyanobacterium

Cyanobacteria have been shown to produce a number of bioactive compounds, including toxins. Some bioactive compounds obtained from a marine cyanobacterium Moorea producens (formerly Lyngbya majuscula) have been recognized as drug leads; one of these compounds is aplysiatoxin. We have isolated various aplysiatoxin derivatives from a M. producens sample obtained from the Okinawan coastal area. The frozen sample was extracted with organic solvents. The ethyl acetate layer was obtained from the crude extracts via liquid-liquid partitioning, then separated by HPLC using a reversed-phase column. Finally, 1.1 mg of the compound was isolated. The chemical structure of the isolated compound was elucidated with spectroscopic methods, using HR-MS and 1D and 2D NMR techniques, and was revealed to be oscillatoxin I, a new member of the aplysiatoxin family. Oscillatoxin I showed cytotoxicity against the L1210 mouse lymphoma cell line and diatom growth-inhibition activity against the marine diatom Nitzschia amabilis.

A new lyngbyatoxin from the Hawaiian cyanobacterium Moorea producens

Lyngbyatoxin A from the marine cyanobacterium Moorea producens (formerly Lyngbya majuscula) is known as the causative agent of “swimmer’s itch” with its highly inflammatory effect. A new toxic compound was isolated along with lyngbyatoxin A from an ethyl acetate extract of M. producens collected from Hawaii. Analyses of HR-ESI-MS and NMR spectroscopies revealed the isolated compound had the same planar structure with that of lyngbyatoxin A. The results of optical rotation and CD spectra indicated that the compound was a new lyngbyatoxin A derivative, 12-epi-lyngbyatoxin A (1). While 12-epi-lyngbyatoxin A showed comparable toxicities with lyngbyatoxin A in cytotoxicity and crustacean lethality tests, it showed more than 100 times lower affinity for protein kinase Cδ (PKCδ) using the PKCδ-C1B peptide when compared to lyngbyatoxin A.

Climate change: links to global expansion of harmful cyanobacteria

Cyanobacteria are the Earth's oldest (∼3.5 bya) oxygen evolving organisms, and they have had major impacts on shaping our modern-day biosphere. Conversely, biospheric environmental perturbations, including nutrient enrichment and climatic changes (e.g. global warming, hydrologic changes, increased frequencies and intensities of tropical cyclones, more intense and persistent droughts), strongly affect cyanobacterial growth and bloom potentials in freshwater and marine ecosystems. We examined human and climatic controls on harmful (toxic, hypoxia-generating, food web disrupting) bloom-forming cyanobacteria (CyanoHABs) along the freshwater to marine continuum. These changes may act synergistically to promote cyanobacterial dominance and persistence. This synergy is a formidable challenge to water quality, water supply and fisheries managers, because bloom potentials and controls may be altered in response to contemporaneous changes in thermal and hydrologic regimes. In inland waters, hydrologic modifications, including enhanced vertical mixing and, if water supplies permit, increased flushing (reducing residence time) will likely be needed in systems where nutrient input reductions are neither feasible nor possible. Successful control of CyanoHABs by grazers is unlikely except in specific cases. Overall, stricter nutrient management will likely be the most feasible and practical approach to long-term CyanoHAB control in a warmer, stormier and more extreme world.

Toxins of cyanobacteria

Blue-green algae are found in lakes, ponds, rivers and brackish waters throughout the world. In case of excessive growth such as bloom formation, these bacteria can produce inherent toxins in quantities causing toxicity in mammals, including humans. These cyanotoxins include cyclic peptides and alkaloids. Among the cyclic peptides are the microcystins and the nodularins. The alkaloids include anatoxin-a, anatoxin-a(S), cylindrospermopsin, saxitoxins (STXs), aplysiatoxins and lyngbyatoxin. Both biological and chemical methods are used to determine cyanotoxins. Bioassays and biochemical assays are nonspecific, so they can only be used as screening methods. HPLC has some good prospects. For the subsequent detection of these toxins different detectors may be used, ranging from simple UV-spectrometry via fluorescence detection to various types of MS. The main problem in the determination of cyanobacterial toxins is the lack of reference materials of all relevant toxins. In general, toxicity data on cyanotoxins are rather scarce. A majority of toxicity data are known to be of microcystin-LR. For nodularins, data from a few animal studies are available. For the alkaloids, limited toxicity data exist for anatoxin-a, cylindrospermopsin and STX. Risk assessment for acute exposure could be relevant for some types of exposure. Nevertheless, no acute reference doses have formally been derived thus far. For STX(s), many countries have established tolerance levels in bivalves, but these limits were set in view of STX(s) as biotoxins, accumulating in marine shellfish. Official regulations for other cyanotoxins have not been established, although some (provisional) guideline values have been derived for microcystins in drinking water by WHO and several countries.

Health effects of recreational exposure to Moreton Bay, Australia waters during a Lyngbya majuscula bloom

A survey of residents in an area subject to annual toxic cyanobacterial blooms was undertaken to examine potential health effects of cyanobacteria toxins. The survey assessed the health of marine recreational water users in Deception Bay/Bribie Island area in northern Moreton Bay, Queensland, which is exposed to blooms of the nuisance and potentially harmful cyanobacterium Lyngbya majuscula. A postal survey was mailed to 5000 residents with a response rate of 27%. High numbers of people (78%) responding to the survey reported recreational water activity in Moreton Bay. Of those having marine recreational water activity, 34% reported at least one symptom after exposure to marine waters, with skin itching the most reported (23%). Younger participants had greater water exposure and symptoms than older participants. Participants with greater exposures were more likely to have skin and eye symptoms than less exposed groups, suggesting agents in the marine environment may have contributed to these symptoms. Of those entering Moreton Bay waters 29 (2.7%) reported severe skin symptoms, 12 of whom attended a health professional. Six (0.6%) reported the classic symptoms of recreational water exposure to L. majuscula, severe skin symptoms in the inguinal region. Participants with knowledge of L. majuscula were less likely to report less skin, gastrointestinal and fever and headache symptoms. In conclusion, high numbers of participants reported symptoms after exposure to waters subject to L. majuscula blooms but only a small number appeared to be serious in nature suggesting limited exposure to toxins.

Pharmacology and toxicology of pahayokolide A, a bioactive metabolite from a freshwater species of Lyngbya isolated from the Florida Everglades

The genus of filamentous cyanobacteria, Lyngbya, has been found to be a rich source of bioactive metabolites. However, identification of such compounds from Lyngbya has largely focused on a few marine representatives. Here, we report on the pharmacology and toxicology of pahayokolide A from a freshwater isolate, Lyngbya sp. strain 15-2, from the Florida Everglades. Specifically, we investigated inhibition of microbial representatives and mammalian cell lines, as well as toxicity of the compound to both invertebrate and vertebrate models. Pahayokolide A inhibited representatives of Bacillus, as well as the yeast, Saccharomyces cerevisiae. Interestingly, the compound also inhibited several representatives of green algae that were also isolated from the Everglades. Pahayokolide A was shown to inhibit a number of cancer cell lines over a range of concentrations (IC50 varied from 2.13 to 44.57 microM) depending on the cell-type. When tested against brine shrimp, pahayokolide was only marginally toxic at the highest concentrations tested (1 mg/mL). The compound was, however, acutely toxic to zebrafish embryos (LC50=2.15 microM). Possible biomedical and environmental health aspects of the pahayokolides remain to be investigated; however, the identification of bioactive metabolites such as these demonstrates the potential of the Florida Everglades as source of new toxins and drugs.

Pathological effects of lyngbyatoxin A upon mice

Histopathological changes induced in mice by lyngbyatoxin A were studied in connection with the occurrence of the toxin in marine turtles implicated in human intoxication. Lyngbyatoxin A showed an i.p. lethal dose 250 microg/kg in immature mice (3-week old) and most severely damaged capillaries of villi in the small intestine. Immature mice were more sensitive than matured ones and died of bleeding from the small intestines. With sublethal doses were observed erosion in the stomach, small intestine, cecum, and large intestine, as well as inflammation in the lung. Time course changes observed after p.o. administration of sublethal doses indicated severe mucus secretion and injuries to occur within 60 min in the intestine and within 24h in the stomach. Increased inflammatory cells followed these injuries. The injuries in the lung, stomach, and small intestine took a few weeks for recovery. The cause of death and the effective dose levels resembled those of aplysiatoxin poisoning.

Lyngbyabellin B, a toxic and antifungal secondary metabolite from the marine cyanobacterium Lyngbya majuscula

Lyngbyabellin B (1) was isolated from a marine cyanobacterium, Lyngbya majuscula, collected near the Dry Tortugas National Park, Florida. This new cyclic depsipeptide displayed potent toxicity toward brine shrimp and the fungus Candida albicans. The planar structure was deduced using 1D and 2D NMR spectroscopic methods, and the stereochemistry is proposed through a combination of NMR and chiral GC/MS analysis.

Bleeding from the small intestine caused by aplysiatoxin, the causative agent of the red alga Gracilaria coronopifolia poisoning

The cause of death by aplysiatoxin poisoning was bleeding from the small intestine in mice. The pathological changes related to the cause and progression of bleeding were studied morphologically. Bleeding from the capillaries was observed 60 min after i.p. treatment at 250 microg/kg, and this was preceded by dilatation of the lymphatic vessel and congestion of capillaries in the lamina propria from 10 min after the injection. At 100 microg/kg i.v., the target vessels were in the lung, where fibrin deposition was observed in the dilated pulmonary artery, and blood flowed out through a gap in the artery. Then, in the small intestine, similar changes appeared to have occurred, and bleeding was induced in two characteristic ways, one through deposition of fibrin in the lumen and the other via distension of the capillary wall.

Morphological observations of diarrhea in mice caused by aplysiatoxin, the causative agent of the red alga Gracilaria coronopifolia poisoning in Hawaii

Diarrhea caused by the red alga Gracilaria coronopifolia poisoning was investigated in mice. The target site of a lethal dose was the whole small intestine where the toxin caused bleeding, resulting in hemorrhagic shock. With a sublethal dose, diarrhea appeared about 4.5 h after i.p. injection and continued for about 4 h intermittently. The site of diarrhea was the large intestine, where the submucosa first accumulated fluid from edema. Then the fluid moved into the lamina propria, the surface epithelial cells were broken and the fluid flowed into the lumen. Finally, diarrheic components apparently originating from capillaries were secreted directly into the lumen. The cecum was the main target of the diarrhea. After the diarrhea ended, the number of goblet cells was increased remarkably and many fine cracks were left on the surface of the epithelium.

New saxitoxin analogues from the freshwater filamentous cyanobacterium Lyngbya wollei

Along with decarbamoylsaxitoxin and decarbamoylgonyautoxin-2 and -3, six new saxitoxin analogues were isolated from the freshwater mat-forming filamentous cyanobacterium Lyngbya wollei collected from Guntersville Reservoir on the Tennessee River in Alabama. Their structures were determined by electrospray ionization mass spectrometry and several NMR techniques. Five of the toxins contain an acetyl moiety attached to the side chain, which is the first report of these saxitoxin analogues. In three of the toxins a hydrated ketone at C-12 was reduced to alpha-alcohol. The presence of acetate in the side chain resulted in a sevenfold to 17-fold times decrease in mouse toxicity compared to their carbamoyl counterparts, while the reduction at C-12 resulted in a complete loss of mouse toxicity.

Manauealides, some of the causative agents of a red alga Gracilaria coronopifolia poisoning in Hawaii

Manauealides A-C (1-3), compounds related to debromoaplysiatoxin (5), were isolated and characterized from a red alga Gracilaria coronopifolia. Compounds 1 and 2 are presumed to be the causative toxins of G. coronopifolia food poisoning in Hawaii. Manauealide A (1) and C (3) are new macrolides, whereas manauealide B (2) is a known semisynthetic product of 5.

Evidence for paralytic shellfish poisons in the freshwater cyanobacterium Lyngbya wollei (Farlow ex Gomont) comb. nov

Lyngbya wollei (Farlow ex Gomont) comb. nov., a perennial mat-forming filamentous cyanobacterium prevalent in lakes and reservoirs of the southeastern United States, was found to produce a potent, acutely lethal neurotoxin when tested in the mouse bioassay. Signs of poisoning were similar to those of paralytic shellfish poisoning. As part of the Tennessee Valley Authority master plan for Guntersville Reservoir, the mat-forming filamentous cyanobacterium L. wollei, a species that had recently invaded from other areas of the southern United States, was studied to determine if it could produce any of the known cyanotoxins. Of the 91 field samples collected at 10 locations at Guntersville Reservoir, Ala., on the Tennessee River, over a 3-year period, 72.5% were toxic. The minimum 100% lethal doses of the toxic samples ranged from 150 to 1,500 mg kg of lyophilized L. wollei cells-1, with the majority of samples being toxic at 500 mg kg-1. Samples bioassayed for paralytic shellfish toxins by the Association of Official Analytical Chemists method exhibited saxitoxin equivalents ranging from 0 to 58 micrograms g (dry weight)-1. Characteristics of the neurotoxic compound(s), such as the lack of adsorption by C18 solid-phase extraction columns, the short retention times on C18 high-performance liquid chromatography (HPLC) columns, the interaction of the neurotoxins with saxiphilin (a soluble saxitoxin-binding protein), and external blockage of voltage-sensitive sodium channels, led to our discovery that this neurotoxin(s) is related to the saxitoxins, the compounds responsible for paralytic shellfish poisonings. The major saxitoxin compounds thus far identified by comparison of HPLC fluorescence retention times are decarbamoyl gonyautoxins 2 and 3. There was no evidence of paralytic shellfish poison C toxins being produced by L. wollei. Fifty field samples were placed in unialgal culture and grown under defined culture conditions. Toxicity and signs of poisoning for these laboratory-grown strains of L. wollei were similar to those of the field collection samples.

Aplysiatoxin and debromoaplysiatoxin as the causative agents of a red alga Gracilaria coronopifolia poisoning in Hawaii

The causative toxins of a red alga Gracilaria coronopifolia poisonings in Hawaii, which broke out in succession in September of 1994, were studied. Two major toxins were isolated from both extracts of the two original algal samples which caused separate poisonings. By spectroscopic method, these toxins were shown to be completely identical with aplysiatoxin and debromoaplysiatoxin which have previously been obtained from the sea hare and also from blue green algae. The human symptoms and the amount of these toxins in the original algal samples indicate that aplysiatoxin and debromoaplysiatoxin were the causative agents of the human poisoning incidents. This is the first reported case of the implication of aplysiatoxin and debromoaplysiatoxin in food poisoning. The existence of these toxins in the residue of algae washed in saline was confirmed by HPLC analysis. Furthermore, we observed blue-green algal parasitism on the surface of the toxic G. coronopifolia. Therefore, epiphytic organisms such as blue-green algae might be the true origin of the toxins in G. coronopifolia.

Specific protein interacting with a tumor promoter, debromoaplysiatoxin, in bovine serum is alpha 1-acid glycoprotein

Aplysiatoxin and debromoaplysiatoxin, a debrominated form of aplysiatoxin, have both been shown to be potent tumor promoters in a two-stage carcinogenesis experiment on mouse skin. However, debromoaplysiatoxin did not behave like aplysiatoxin in most of the biological assay systems using cultured cells. The discrepancy was supposed to be due to a factor in the bovine serum used for culture, a similar factor not being present in sera of eight other animal species examined. The factor was purified to homogeneity from bovine serum by ammonium sulfate fractionation and chromatographies on DEAE-cellulose, Sephadex G-150, hydroxyapatite, and a reversed-phase HPLC column. The factor was a 40-kDa protein, and partial amino-acid sequencing of its tryptic peptides indicated that the factor is alpha 1-acid glycoprotein. Both the purified factor and the commercially available bovine alpha 1-acid glycoprotein abolished in vitro the activation of protein kinase C by debromoaplysiatoxin but not that by aplysiatoxin. Debromoaplysiatoxin induced differentiation of HL-60 cells into macrophages at a comparable concentration to aplysiatoxin, when serum-free medium was used. These results suggest that alpha 1-acid glycoprotein, which interacts specifically with debromoaplysiatoxin, contained in bovine serum must have masked the in vitro properties of the tumor promoter in the biological assay systems.

Comparison of 12-O-tetradecanoylphorbol-13-acetate and teleocidin for induction of epidermal hyperplasia, activation of epidermal PKC isozymes and skin tumor promotion in SENCAR and C57BL/6 mice

The present study compared the ability of 12-O-tetradecanoylphorbol-13-acetate (TPA) and teleocidin to induce sustained epidermal hyperplasia, activate partially purified epidermal protein kinase C (PKC) isozymes and promote skin tumors in SENCAR and C57BL/6 mice. Teleocidin was less effective than TPA on a molar basis for inducing sustained epidermal hyperplasia, promoting skin tumors and activating partially purified epidermal PKC isozymes in vitro when examined using SENCAR mice. In contrast, teleocidin was more effective than TPA on a molar basis for inducing sustained epidermal hyperplasia, approximately equi-effective for promoting skin tumors and significantly less effective for activating PKC isozymes in vitro when examined using C57BL/6 mice. Despite the differences in response of C57BL/6 mice to TPA and teleocidin, this mouse strain was still highly resistant to skin tumor promotion by both types of promoters when compared with SENCAR mice. The current results, when considered in light of our recent studies (Cancer Res., 51, 1398-1405, 1991), indicate that C57BL/6 are generally resistant to a variety of classes of skin tumor promoters, including the teleocidins. In addition, except for the phorbol esters, the induction of sustained epidermal hyperplasia does not appear to be as good a marker for overall promotion responsiveness between SENCAR and C57BL/6 mice with other classes of tumor promoters; although the induction of a significant sustained hyperplasia in the latter mouse strain did yield a weak tumor response. Taken together, the current data suggest that factors in addition to the induction of sustained epidermal hyperplasia, control responsiveness of C57BL/6 mice to skin tumor promotion by diverse promoting stimuli.

Absence of synergistic effects on tumor promotion in CD-1 mouse skin by simultaneous applications of two different types of tumor promoters, okadaic acid and teleocidin

Okadaic acid, a specific inhibitor of protein phosphatases 1 and 2A, and teleocidin, an activator of protein kinase C, are both potent tumor promoters on mouse skin. The effects of simultaneous treatment of the two different types of tumor promoters on tumor promotion as well as on their biochemical activities were studied. Three independent experiments with different doses of tumor promoters revealed that simultaneous repeated applications of okadaic acid and teleocidin did not induce any synergistic or additive effects on tumor promotion in mouse skin initiated with 7,12-dimethylbenz(a)anthracene (DMBA). In Experiment 1, the group treated with a single application of DMBA, followed by repeated applications of 1.0 micrograms (1.2 nmol) okadaic acid and 2.5 micrograms (5.7 nmol) teleocidin, resulted in 64.3% tumor-bearing mice at week 20. But the groups treated with DMBA plus okadaic acid or DMBA plus teleocidin gave 73.3% and 71.4%, respectively. The biochemical activities were studied by means of induction of ornithine decarboxylase in mouse skin and protein phosphorylation in the cells. Simultaneous application of okadaic acid at three different doses with teleocidin did not induce ornithine decarboxylase activity synergistically or additively. Phosphorylation of proteins, cytokeratins, or heat shock protein 27 was not synergistically increased in human keratinocytes treated with okadaic acid and teleocidin, although the cotreatment in a cell-free system synergistically increased protein phosphorylation. Thus, the absence of synergistic effects on tumor promotion in mouse skin was also confirmed in two systems, induction of ornithine decarboxylase in mouse skin and protein phosphorylation in human keratinocytes. The effect of cotreatment of okadaic acid and teleocidin is discussed at the molecular level.

Pendolmycin, a new tumor promoter of the teleocidin A class on skin of CD-1 mice

Pendolmycin, isolated from Nocardiopsis, is a compound structurally similar to teleocidin A, one of the 12-O-tetradecanoylphorbol-13-acetate (TPA)-type tumor promoters. Pendolmycin has a C5 dimethyl allyl group attached to C-7 of (-)-indolactam-V, whereas teleocidin A has a C10 linalyl group attached to the molecule. The structure-activity relationships of a hydrophobic moiety attached to (-)-indolactam-V were studied in four compounds, (-)-indolactam-V, pendolmycin, teleocidin A and newly synthesized 7-(nerolidyl)-(-)-indolactam-V in tests on inhibition of the specific [3H]TPA binding to a particulate fraction of mouse skin, activation of protein kinase C and induction of both adhesion of HL-60 cells and ornithine decarboxylase in mouse skin. The potencies of the compounds for these activities increased mainly depending on the length of the hydrophobic group. Pendolmycin had a tumor-promoting activity on mouse skin initiated with a single application of 7,12-dimethyl-benz[a]anthracene, and its potency was just between those of (-)-indolactam-V and teleocidin A. The role of the hydrophobic moiety is discussed with particular emphasis on the results obtained with 7-(nerolidyl)-(-)-indolactam-V.

New antitumor promoters: (-)-epigallocatechin gallate and sarcophytols A and B

EGCG, the main constituent of green tea, and sarcophytols A and B, isolated from a soft coral, inhibited tumor promotion by teleocidin in a two-stage carcinogenesis experiment on mouse skin. EGCG and sarcophytols showed inhibition of tumor development by chemical carcinogenesis. A possibility of developing these compounds as cancer chemopreventives for human beings is discussed.

Identification of tumor promoters by their inhibitory effect on intercellular transfer of lucifer yellow

The effect of the tumor promoters 12-O-tetradecanoylphorbol-13-acetate (TPA), mezerein, teleocidin, anthralin, the Ca2+-ionophore A23187, butylated hydroxytoluene (BHT), dichlorodiphenyltrichloroethane (DDT) and phenobarbital (PB) on lucifer yellow transfer in cultures of SV-40-transformed Djungarian hamster fibroblasts was studied. TPA, mezerein, teleocidin, A23187, DDT and BHT exerted a strong inhibitory effect on cell-to-cell dye transfer. Anthralin uncoupled cells in 3 experiments out of 6. PB appeared to enhance lucifer yellow transfer. Sodium nitrite, a substance with unknown promoting activity, effectively uncoupled cells. All the promoters investigated had a reversible effect on the dye transfer. The value of the dye transfer method for promoter screening is discussed.

Similar, potent tumor-promoting activity of all isomers of teleocidins A and B in a two-stage carcinogenesis experiment on the skin of CD-1 mice

Teleocidin, isolated from mycelia of Streptomyces mediocidicus is a mixture of two teleocidin A isomers with molecular weights of 437 (A-1 and A-2) and four teleocidin B isomers with molecular weights of 451 (B-1, B-2, B-3, and B-4). Previously we found that each purified isomer of teleocidins A and B had approximately the same activity as teleocidin in an irritant test on mouse ear, in inductions of ornithine decarboxylase in mouse skin and adhesion of human promyelocytic leukemia (HL-60) cells, and in inhibition of the specific binding of [3H]-12-O-tetradecanoylphorbol-13-acetate to a mouse skin particulate fraction. This paper reports the strong activation of protein kinase C in vitro by each isomer of teleocidins A and B at a concentration of 1 microgram/ml. Detailed studies on the potent tumor promoting activities of the two teleocidin A isomers and four teleocidin B isomers in a two-stage carcinogenesis experiment on mouse skin are also reported, including histological findings on the tumors. Treatment of mice with 100 micrograms of 7,12-dimethylbenz(a)anthracene and then 2.5 micrograms of any one of the six isomers of teleocidins A and B twice a week induced tumors in 80.0 to 91.7% of the mice with 2.8 to 5.2 tumors/mouse in week 30. Scarcely any tumors developed in groups treated with 7,12-dimethylbenz(a)anthracene or any one of the isomers of teleocidins A or B alone. The percentages of incidences of mice bearing papillomas and carcinomas in the six groups treated with 7,12-dimethylbenz(a)anthracene plus one isomer of teleocidins A or B were 90.9 to 98.3% and 1.7 to 9.1%, respectively. These results indicate that all of the isomers of teleocidins A and B have potent tumor promoting activity on mouse skin, irrespective of the structural differences between teleocidins A-1 and A-2, and among the four isomers of teleocidin B. The structure-activity relationship of teleocidins A and B is discussed on the basis of our recent results. Based on the structures of related compounds, we propose a revised numbering system for compounds of the teleocidin class.

Structure-activity studies of the indole alkaloid tumor promoter teleocidins

New teleocidin derivatives with various substituents at positions 2, 5 and 7 of the indole ring were prepared from (-)-indolactam V, which is the fundamental structure of teleocidins and has a tumor-promoting activity, to examine the contribution of the alkyl substituents of teleocidins to the activity. Their possible tumor-promoting activities in vivo were evaluated by Epstein-Barr virus early antigen-inducing activity and inhibition of specific binding of [3H]TPA to a mouse epidermal particulate fraction. These two biological activities correlated well for each derivative. Large substituents at positions 2 and 5 remarkably lowered the activities, indicating that the structural requirements for the activities of these domains are especially strict. To investigate in detail the contribution of position 2 of (-)-indolactam V to the activities, new microbial metabolites, (-)-2-oxy-indolactam V, and blastmycetin B and C, were also tested. These compounds proved to be inactive, suggesting that the double bond at position 2 plays an important role for the activities. Substituents at position 7 generally enhanced the activities and even blastmycetin A, which is a dimer of (-)-indolactam V, showed high activities. The effects of the substituents on binding ability to the 12-O-tetradecanoylphorbol-13-acetate receptor were analyzed quantitatively using physicochemical substituent parameters and regression analysis. The results exhibited the fact that hydrophobicity of the substituents plays a critical role for receptor binding, and supported the hypothesis that the monoterpenoid moiety of teleocidins is involved in the non-specific hydrophobic interaction with phospholipids in cell membrane.

Studies on environmental chemical carcinogenesis in Japan

The historical background of studies in Japan on chemical carcinogenesis from environmental sources is described from personal experience.

Palytoxin is a non-12-O-tetradecanoylphorbol-13-acetate type tumor promoter in two-stage mouse skin carcinogenesis

Palytoxon, which is a toxin with a molecular weight of 2681 daltons isolated from a marine coelenterate, is a potent skin irritant. However, it did not induce ornithine decarboxylase in mouse skin, or adhesion of human promyelocytic leukemia cells (HL-60). Moreover, it did not inhibit the specific binding of [3H]12-O-tetradecanoylphorbol-13-acetate (TPA) to a mouse skin particulate fraction or activate protein kinase C isolated from mouse brain in vitro. Since palytoxin showed strong irritation on mouse ear in one short-term screening test for a promoter, it was examined in a two-stage carcinogenesis experiment. The incidence of tumors in a group of mice treated with 7,12-dimethylbenz[a]anthracene plus palytoxin was 62.5% in week 25. These tumors were identified histologically as seven papillomas and one carcinoma. This paper reports the potent tumor-promoting activity of palytoxin, which is classified as a non-TPA-type tumor promoter.

Des-O-methylolivoretin C is a new member of the teleocidin class of tumor promoters

Des-O-methylolivoretin C, a demethylated form of olivoretin C, is a naturally occurring compound in Streptomyces mediocidicus and Streptoverticillium olivoreticuli. Des-O-methylolivoretin C is a regioisomer of teleocidin B, which has the same activity as teleocidin. The tumor-promoting activity of des-O-methylolivoretin C was studied in a two-stage carcinogenesis experiment on mouse skin in comparison with that of teleocidin. Treatments with 7,12-dimethylbenz[a]anthracene (DMBA) plus des-O-methylolivoretin C and DMBA plus teleocidin induced tumors in 63.3% and 84.6% of the mice, respectively, in week 30. The difference in the tumor-promoting activities of des-O-methylolivoretin C and teleocidin is presumably related to the regioisomeric difference in the cyclohexene ring.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced epidermal ornithine decarboxylase activity and tumor promotion by N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) in mouse skin

N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) inhibited epidermal ornithine decarboxylase (ODC) induction caused either by 12-O-tetradecanoylphorbol-13-acetate (TPA) or teleocidin in CD-1 mice. Inhibitory effect of W-7 on TPA-caused ODC induction was also observed in 7,12-dimethylbenz[a]anthracene (DMBA)-initiated skin and even after repetitive TPA treatment. TPA-induced skin tumor promotion was also suppressed by W-7. Meanwhile, W-7 showed only slight inhibitory effects on calcium-activated, phospholipid-dependent protein kinase (protein kinase C) activity of mouse epidermis stimulated either by Ca2+ or TPA in the presence of phosphatidylserine. Thus, it is unlikely that the anti-ODC-inducing and anti-tumor-promoting actions of W-7 are due to its inhibitory effect on protein kinase C. It may be possible that a calmodulin-mediating process is involved in the mechanism of epidermal ODC induction and tumor promotion caused by tumor promoters such as TPA and teleocidin.

Glycyrrhetic acid inhibits tumor-promoting activity of teleocidin and 12-O-tetradecanoylphorbol-13-acetate in two-stage mouse skin carcinogenesis

Glycyrrhetic acid suppressed tumor promoter-induced effects in vitro, such as stimulation of 32Pi-incorporation into phospholipids of cultured cells and down-regulation of the epidermal growth factor receptor. Glycyrrhetic acid inhibited the promoting activity of both 12-O-tetradecanoylphorbol-13-acetate (TPA) and teleocidin on skin tumor formation in mice initiated with 7,12-dimethylbenz[a]anthracene (DMBA). The percentage of tumor-bearing mice in the group treated with DMBA plus teleocidin was 88% at week 18, whereas that in the group treated with DMBA plus teleocidin and glycyrrhetic acid (10 mumol/painting) was 6%. Similarly, the percentage of tumor-bearing mice of the group treated with DMBA plus TPA was 97% at week 20, whereas that of the group treated with DMBA plus TPA and glycyrrhetic acid was 40%. Therefore, glycyrrhetic acid was proved to inhibit the activity of two different tumor promoters, teleocidin and TPA, in mouse skin.

Activation of protein kinase C by tumor promoting phorbol esters, teleocidin and aplysiatoxin in the absence of added calcium

We have found that maximum stimulation (greater than 10-fold) of kinase activity of a bovine brain preparation of calcium- and phospholipid-dependent protein kinase (PKC) by 12-O-tetradecanoylphorbol-13-acetate (TPA) occurs in the presence of phospholipid, but in the absence of added Ca2+. In effect, nM concentrations of TPA substitute for mM concentrations of added Ca2+, and the two agents are not synergistic. Biologically active analogs of TPA such as phorbol-12,13-dibutyrate (PDBu), 12-O-hexadecanoyl-16-hydroxyphorbol-13-acetate (HHPA) or mezerein were also effective activators of PKC, as were the chemically unrelated tumor promoters teleocidin and aplysiatoxin, when tested at nM concentrations in the absence of added Ca2+. On the other hand, the biologically inactive compounds phorbol, 4-alpha-phorbol-12,13-didecanoate (4-alpha-PDD), HHPA-13,20-diacetate and 1,2-dihydro-20-deoxy-HHPA did not affect PKC activity in the absence or presence of Ca2+. Our results are consistent with a stereochemical model in which the hydrophilic domains of certain diterpenes, teleocidin and aplysiatoxin interact specifically with PKC apoenzyme, while their hydrophobic domains interact with phospholipid, thus forming an enzymatically active ternary complex.

Macrophage oxidative burst and related cytotoxicity. I. Differential activation by tumor-promoting and non-tumor-promoting phorbol esters

Mouse peritoneal macrophages elicit an oxidative burst (OB) response upon stimulation with the tumor promoter 12-O-tetradecanoyl-phorbol 13-acetate (TPA). In this study we compare the OB-stimulating capacity of phorbol ester derivatives, structurally related to TPA, which differ in their tumor-promoting activity. Non-tumor-promoting derivatives such as phorbol 13-acetate, phorbol 12-myristate, TPA-20-aldehyde and 4-O-methyl TPA were tested. These reagents stimulate macrophages to generate OB products such as O-2 and H2O2, yet the amounts required for stimulation are 1,000 times higher than the amounts of TPA required to elicit a comparable response. It has also been observed that, in the same order of magnitude, the above-mentioned derivatives are less efficient than TPA in rendering macrophages cytolytic toward erythrocytes. Another strong tumor promoter tested, teleocidin, has been found to be as potent as TPA in the activation of macrophage OB and in related activities.

The proliferative response of low-density human cell cultures to tumor promoters and its relevance to carcinogenic mechanisms in vitro

The effects of the tumor promoter -12-O-tetradecanoyl phorbol-13-acetate, its analogues, and other tumor promoters, on the proliferation of human skin fibroblasts (SF) have been investigated. We have previously shown (Kopelovich and Bias, 1979), that TPA caused a biphasic (upward concave) dose effect in the cloning efficiency assay of normal and mutant human fibroblastic cell strains. Here we report that the biphasic dose response pattern, consisting of an inhibitory phase and a stimulatory phase, was shared by the active analogues of TPA, e.g., phorbol-12,13-dibutyrate and phorbol-12,13-dibenzoate. This biphasic dose effect relationship, however, was not seen with phorbol-12,13-diacetate or the inactive analogues of TPA such as phorbol and 4-O-methyl-12-O-tetradecanoyl phorbol-13-acetate, nor was it seen with mezerein, teleocidin, or bile-acid derivatives of humans. An analysis of the cloning efficiency data by the median-effect equation (Chou and Talalay, 1981) showed that in low-density cultures both the inhibitory phase and the stimulatory phase of the dose-effect relationships of TPA, its analogues, mezerein, and teleocidin exhibited a linear median-effect plot and thus closely followed the basic mass-action principle. The median-effect plot of these data allowed quantitative determination of growth curve characteristic such as regression coefficient, slope (a measure of sigmoidicity), median-effect concentrations such as I50 for the inhibitory effect, and A50 for the stimulatory effect (i.e., the relative potency of the analogues) and the transition point of the biphasic phenomenon in the case of the phorbol esters. In addition, we have demonstrated a relationship between the dose response effect of TPA on the proliferation of various human cells and tumor progression in vitro.

The effect of 12-O-tetradecanoylphorbol-13-acetate and other tumor promoters on the colony formation of rat tracheal epithelial cells in culture

Normal primary rat tracheal epithelial (RTE) cells were isolated and exposed in culture to tumor promoters and irritants of diverse chemical classes. The phorbol derivative class of tumor promoters greatly stimulated colony forming efficiency (CFE) in culture. The efficacies of the agents tested were ranked in the order: mezerein greater than 12-O-tetradecanoyl-phorbol-13-acetate (TPA) greater than phorbol didecanoate greater than phorbol dibutyrate greater than phorbol dibenzoate greater than 4-O-methyl TPA greater than phorbol diacetate. The parent alcohol phorbol did not stimulate CFE under the conditions tested. The indole alkaloid tumor promoter teleocidin stimulated CFE at concentrations at least 10-fold lower than those required for TPA. Other irritants and non-phorbol ester tumor promoters such as anthralin, benzoyl peroxide, calcium ionophore A23187, and ethylphenyl propiolate were either inactive or reduced CFE. Phenobarbital marginally stimulated CFE at one concentration but reduced CFE at higher concentrations. Increases in CFE elicited by TPA and analogs were dependent upon the time of addition of TPA to the cultures. Maximum increases in CFE were observed when the cells were plated into medium containing TPA. If TPA was added 40 h after plating, stimulation of CFE did not occur. This 40 h time interval may represent a crucial period for the commitment of RTE stem cells to proliferation or differentiation. Whether the stimulation of colony formation seen in normal RTE cells exposed to phorbol derivatives also occurs in carcinogen-altered cells, thereby causing their proliferative expansion, remains to be determined.

Antitumor-promoting activity of glycyrrhetic acid in mouse skin tumor formation induced by 7,12-dimethylbenz[a]anthracene plus teleocidin

Glycyrrhetic acid inhibited the action of tumor promoter in vitro and in vivo. Glycyrrhetic acid inhibited the increased phospholipid metabolism of cultured cells induced by tumor promoters, 12-O-tetradecanoylphorbol-13-acetate or teleocidin, and it markedly suppressed the promoting effect of teleocidin on skin tumor formation in mice initiated with 7,12-dimethylbenz[a]anthracene.

Studies on olivoretins indicate a requirement for a free hydroxyl group for teleocidin B activity

Three olivoretins, A, B and C (isolated from Streptoverticillium olivoreticuli), which are O-methylated teleocidin B isomers, were found to be biologically inactive. A fourth olivoretin, D, which has a free hydroxyl group and is identical to one of the four teleocidin B isomers, teleocidin B-4 (teleocidin B of Hirata) was biologically active. These findings indicate that the free primary hydroxyl group of teleocidin B isomers is necessary for activity. The effect on biological activity of the structural difference between des-O-methylolivoretin B (teleocidin B-1) and des-O-methylolivoretin C was also studied.

Distinct responses of 3T3-L1 cells to dihydroteleocidin B and the phorbol ester tumor promoters: relation to adipocyte differentiation, DNA synthesis and cell division

We have recently shown that an indole alkaloid tumor promoter, dihydroteleocidin B (DHTB) is significantly different from the phorbol ester tumor promoters such as 12-O-tetradecanoylphorbol-13-acetate (TPA) in its potency and mode of inhibiting the adipocyte differentiation of 3T3-L1 cells (1). DHTB almost completely inhibited the differentiation induced by dexamethasone (DEX) and 1-methyl-3-isobutylxanthine (MIX) regardless of when the tumor promoter was added: before, during, or after the addition of inducers. Similar inhibition was observed by TPA with over 90% less efficiency and only when it was added during the inducer treatment. Both DHTB and TPA stimulated DNA synthesis to the same level during the initial 22 hr. The DNA synthesis of resting 3T3-L1 cells triggered by DHTB resulted in cell division, whereas TPA-stimulated DNA synthesis did not facilitate cell division. This observation is in sharp contrast to the previous findings that both DHTB and TPA stimulate a number of growth-arrested fibroblasts (2), including Swiss/3T3 from which 3T3-L1 cells were derived, to initiate DNA synthesis and undergo cell division (3). In order to further clarify this point we attempted to isolate cell variants which were no longer responsive to the mitogenic action of DHTB. Among 14 variant lines isolated, we found two stable variant lines, 1-2 and 2-3, whose DNA synthesis was not initiated by DHTB. DNA synthesis of another variant line, 3-4, was stimulated by DHTB but not followed by cell division. From these findings it is proposed that the modes of action of DHTB and TPA are similar in triggering DNA synthesis of G1-arrested 3T3-L1 cells, but DHTB can further act on 3T3-L1 cells at a point during or after S phase to stimulate events of mitosis.