A diacetylenic spiroketal enol ether epoxide, AL-1, from Artemisia lactiflora inhibits 12-O-tetradecanoylphorbol-13-acetate-induced tumor promotion possibly by suppression of oxidative stress

The inhibitory effects of the diacetylenic spiroketal enol ether epoxide AL-1 from Artemisia lactiflora on a variety of tumor promoter-induced biological responses such as oxidative stress as well as tumor promotion in ICR mouse skin were investigated. AL-1 inhibited TPA-induced intracellular peroxide formation in differentiated HL-60 cells, suggesting that this suppression might be attributable to the inhibition of O₂⁻ generation. In a double TPA application system in mouse skin, double pretreatments of AL-1 (810 nmol) significantly suppressed double TPA application-induced H₂O₂ generation. Pretreatment of AL-1 only before the second TPA treatment was sufficient to inhibit, while only with first treatment was not. From these results we concluded that AL-1 is a specific inhibitor of the activation phase in H₂O₂ production induced by double TPA treatments. In addition, AL-1 strongly inhibited tumor promoter-induced Epstein–Barr virus (EBV) activation in Raji cells (IC₅₀=0.5 μM), which was comparable to or even stronger than that of curcumin, a well-known antioxidative chemopreventer from turmeric. In a two-stage carcinogenesis experiment with TPA (topical application at 1.6 nmol) and 7,12-dimethylbenz[a]anthracene (DMBA, at 0.19 μmol) in ICR mouse skin, topical application of AL-1 (at 160 nmol) significantly reduced tumor incidence, the numbers of tumors per mouse, and edema formation by 58% (P<0.01 in t-test), 20% (P<0.005 in χ²-test) and 42% (P<0.01), respectively. These results together indicate that an inhibitor of O₂⁻ generation is an effective chemopreventer of mouse skin carcinogenesis by their antioxidative property.     

Gomisin A inhibits tumor promotion by 12-O-tetradecanoylphorbol-13-acetate in two-stage carcinogenesis in mouse skin.

Gomisin A, isolated from the fruits of Schisandra chinensis, is one of the dibenzocyclooctadiene lignans. Application of 12-O-tetradecanoylphorbol-13-acetate (TPA, 1 microgram/ear), a tumor-promoting agent, to the ears of mice induces inflammation. Among seven dibenzocyclooctadiene lignans assayed, gomisin A, gomisin J, and wuweizisu C inhibited the inflammatory activity induced by TPA in mice. The ED50 of these compounds for TPA-induced inflammation was 1.4-4.4 mumol. Gomisin A, with an ED50 of 1.4 mumol, showed the strongest inhibitory effect. Furthermore, at 5 mumol/mouse, it markedly suppressed the promotion effect of TPA (2.5 micrograms/mouse) on skin tumor formation in mice following initiation with 7,12-dimethylbenz[a]anthracene (50 micrograms/mouse). It is assumed that the inhibition of tumor promotion by gomisin A is due to its anti-inflammatory activity.     

Studies on the anti-tumor-promoting activity of naturally occurring substances. IV. Pd-II [(+)anomalin, (+)praeruptorin B], a seselin-type coumarin, inhibits the promotion of skin tumor formation by 12-O-tetradecanoylphorbol-13-acetate in 7,12-dimethylbenz[a]anthracene-initiated mice

Since Pd-II [(+)anomalin, (+)praeruptorin B], a seselin-type coumarin, was found to inhibit tumor promoter induced phenomenon in vitro, the effect of Pd-II on the in vivo tumor-promoting action of 12-O-tetradecanoylphorbol-13-acetate (TPA) in 7,12-dimethylbenz[a]anthracene-initiated mouse skin was investigated. Pd-II, applied 40 min before the TPA treatment, at a dose of 10 mumol/painting, completely suppressed tumor formation up to 20 weeks of tumor promotion, without any toxicity. Besides Pd-II, various anti-tumor-promoter coumarins were found in the traditional Chinese medicine Qian-Hu, from which Pd-II was obtained. These coumarins may be useful for the development of an effective method to prevent cancer.     

Induction of superoxide by 12-O-tetradecanoylphorbol-13-acetate and thapsigargin,a non-phorbol-ester—type tumor promoter,in peritoneal macrophages elicited from SENCAR and B6C3F1 mice: A permissive role for the arachidonic acid cascade in signal transduction

Local production of reactive oxygen intermediates, e.g., superoxide anion, by tumor promoter—stimulated inflammatory macrophages (MPs) may contribute significantly to tumor development in classical models of two-stage chemical-induced carcinogenesis in murine skin. In the studies reported herein, peritoneal MPs elicited from phorbol-ester—sensitive SENCAR mice demonstrated a time- and dose-dependent release of superoxide anion (4–6 nmol/10⁶ cells) when stimulated by 200 nM 12-O-tetradecanoylphorbol-13-acetate (TPA) in vitro; MP superoxide response was significantly inhibited (50–70%) by preincubation with 40 μM 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine (H-7), a protein-kinase inhibitor. Alternatively, TPA-stimulated MPs derived from relatively resistant B6C3F1 mice generated negligible superoxide under the same conditions. A similar strain-dependent induction of superoxide was observed when MPs were stimulated with thapsigargin (TG), a tumor promoter previously shown to act independently of protein kinase C (PKC). TG-stimulated SENCAR MPs released a significant amount of superoxide (2–3 nmol/10⁶ cells) that was not inhibited by H-7; MPs from B6C3F1 mice demonstrated negligible stimulation by TG. Preincubation of SENCAR MPs with 100 μM dibromoacetophenone, an inhibitor of phospholipase A₂, completely suppressed the superoxide induced by TPA and TG stimulation. Like TPA, 50 μM 1-oleoyl-2-acetylglycerol, a diacylglycerol analogue and PKC activator, also induced a significant amount of superoxide from SENCAR MPs only. In parallel with the superoxide findings, TPA and TG stimulated significantly greater [³H]arachidonic acid release from prelabeled SENCAR MPs (a 32% and 48% increase, respectively, over unstimulated controls) relative to MPs from B6C3F1 mice. Two-dimensional gel-electrophoretic analysis indicated that TPA-induced phosphorylation of a 47-kDa protein (a presumed substrate for PKC previously linked to NADPH oxidase activation in guinea pig and human polymorphonuclear leukocytes) occurred in MPs from both SENCAR and B6C3F1 mice. Therefore, arachidonic acid production may be a common biochemical pathway by which phorbol-ester— and non-phorbol-ester—type tumor promoters activate MPs in SENCAR mice; such a response may be “permissive” for additive (or synergistic) interactions with PKC-driven signal pathways.