Topical Application Of 12-O-tetradecanoylphorbol-13-acetate Research Articles

Immature myeloid cells directly contribute to skin tumor development by recruiting IL-17-producing CD4+ T cells.

Evidence links chronic inflammation with cancer, but cellular mechanisms involved in this process remain unclear. We have demonstrated that in humans, inflammatory conditions that predispose to development of skin and colon tumors are associated with accumulation in tissues of CD33+S100A9+ cells, the phenotype typical for myeloid-derived suppressor cells in cancer or immature myeloid cells (IMCs) in tumor-free hosts. To identify the direct role of these cells in tumor development, we used S100A9 transgenic mice to create the conditions for topical accumulation of these cells in the skin in the absence of infection or tissue damage. These mice demonstrated accumulation of granulocytic IMCs in the skin upon topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA), resulting in a dramatic increase in the formation of papillomas during epidermal carcinogenesis. The effect of IMCs on tumorigenesis was not associated with immune suppression, but with CCL4 (chemokine [C-C motif] ligand 4)-mediated recruitment of IL-17-producing CD4+ T cells. This chemokine was released by activated IMCs. Elimination of CD4+ T cells or blockade of CCL4 or IL-17 abrogated the increase in tumor formation caused by myeloid cells. Thus, this study implicates accumulation of IMCs as an initial step in facilitation of tumor formation, followed by the recruitment of CD4+ T cells.

Characterization of 99mTc-labeled cytokine ligands for inflammation imaging via TNF and IL-1 pathways

TNFR2-Fc and IL-1ra-Fc are recombinant cytokine ligands that target TNF and IL-1. TNFR2-Fc-IL-1ra, a dual-domain agent that incorporates both ligands, allows bifunctional binding of IL-1 receptors and TNF. This study was designed to characterize (99m)Tc-labeled forms of these ligands, (99m)Tc-IL-1ra-Fc (IF), (99m)Tc-TNFR2-Fc (TF), and (99m)Tc-TNFR2-Fc-IL-1ra (TFI), for inflammation imaging. The cytokine ligands were labeled with (99m)Tc by a direct approach via 2-iminothiolane (2-IT) reduction at various 2-IT/protein molar ratios. In vivo inflammation targeting studies were carried out in a mouse ear edema model created by topical application of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on the right ear of ICR mice. Radiolabeling yields increased with increasing amounts of 2-IT. When the 2-IT/protein ratio reached 1000, the radiolabeling yield was greater than 90% without significant colloid production. TPA-treated ears showed high radioligand uptake, which was clearly detected by SPECT and autoradiographic imaging. The activities (%ID/g) in the inflamed and control ears at 3h after injection were 2.76 ± 0.20 vs. 0.69 ± 0.12 for IF, 5.86 ± 0.40 vs. 2.86 ± 0.61 for TF, and 7.61 ± 0.86 vs. 1.99 ± 0.31 for TFI (P<0.05 vs. controls). TFI showed significantly higher uptake in the inflamed ears compared to TF and IF (P<0.05). Blocking study results indicated specificity of radioligand binding with decreased radioactive uptake in the inflamed ears. Western blotting and ELISA analysis further confirmed a high expression of IL-1β and TNF-α in the inflamed ears. (99m)Tc-labeled cytokine ligands are a promising approach for detecting and understanding the inflammatory process. TFI may be more useful than the single-domain ligands for noninvasive detection of inflammatory sites.

Topical anti-inflammatory activity of Calea prunifolia HBK (Asteraceae) in the TPA model of mouse ear inflammation

Phytochemical study of Calea prunifolia HBK identified two compounds derived from p-hydroxyacetophenone, the 1-(2-hydroxy-5-(1-methoxyethyl)phenyl)-3-methylbut-2 -en-1-one showed a satisfactory anti-inflammatory activity (58.33%), when considering that this is a natural product. Although the two derived compounds are structurally similar, the anti-inflammatory activity of 1-(2-hydroxy-5-methoxyphenyl)-3-methylbut-2-en-1-one was not significant (2.08%). The test was conducted in a model of inflammation induced by topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) in the ear of mice. The positive control was tested with indomethacin and the negative control was done only with vehicle. These results allow the identification of a pharmacophore group that through molecular modeling studies and organic synthesis can result in compounds with improved anti-inflammatory activity.

Topical Anti-Inflammatory Activities ofVitis rotundifolia(Muscadine Grape) Extracts in the Tetradecanoylphorbol Acetate Model of Ear Inflammation

The ability of muscadine grape skin, seed, or combined skin and seed extracts to inhibit mouse ear inflammation, edema, and polymorphonuclear leukocyte infiltration was tested following topical application of 12-O-tetradecanoylphorbol 13-acetate (TPA). Ethanolic extracts of skins, seeds, or a combination of these from purple (Ison) cultivars were applied to both ears of female Swiss mice 30 minutes after TPA (2 microg per ear) administration. Control mice were treated with indomethacin or 50% ethanol vehicle 30 minutes after TPA. Ear thickness was measured before TPA and at 4 and 24 hours post-TPA administration to assess ear edema. Ear punch biopsies were collected at 24 hours and weighed as a second marker of edema. Myeloperoxidase (MPO) (EC 1.11.1.7) activity was measured in each ear punch biopsy as an index of neutrophil infiltration. Extracts of muscadine skin, seed, and combination treatments significantly reduced ear edema, ear biopsy weight, and MPO activity compared to TPA vehicle control. There was no significant difference in anti-inflammatory activity of the skin and seed extracts. However, an additive effect was observed with the combination treatment that was statistically similar to the anti-inflammatory activity of indomethacin treatment. It can be concluded that muscadine skin, seed, and combination skin/seed extracts exhibit significant topical anti-inflammatory properties.

Oral Administration of (11E)‐13‐Oxo‐15,16‐dinorlabda‐8(20),11‐dien‐19‐oic Acid Strongly Reduces Photocarcinogenesis in Mouse Skin Exposed to UV‐B Irradiation

(11E)-13-Oxo-15,16-dinorlabda-8(20),11-dien-19-oic Acid (1), obtained either from the stem bark of Thuja standishii or readily prepared in larger quantities from the related constituent 2, was found to significantly reduce the formation of papilloma in an in vivo two-stage mouse-skin-carcinogenesis model. Carcinogenesis was initiated by skin exposure to UV-B irradiation and promoted by topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA). Oral administration of 1, starting one week before and ending one week after irradiation, exhibited remarkable effects. First, papilloma formation started two weeks later than in the control group (lacking 1). Second, the average number of skin papilloma after 20 weeks was reduced by ca. 50% in the test group relative to the control.

Phytosphingosine Stimulates the Differentiation of Human Keratinocytes and Inhibits TPA-Induced Inflammatory Epidermal Hyperplasia in Hairless Mouse Skin

The binding of sphingoid bases to peroxisome proliferator-activated receptor (PPAR) has been detected in a solid-phase binding assay. However, sphingoid base-induced changes in PPAR transactivation activity have not been examined. In this report, we show by reporter gene analyses that phytosphingosine (PS), a natural sphingoid base, activates the transcriptional activity of PPARs in the immortalized human keratinocyte, HaCaT. Real-time PCR analyses showed that the mRNA level of PPARgamma was increased after PS treatment in HaCaT cells in a dose- and time-dependent manner. Because PPARs play important roles in skin barrier homeostasis by regulating epidermal cell growth, terminal differentiation, and inflammatory response, we examined the effect of PS on normal human epidermal keratinocytes (NHEKs) and mouse skin. PS increased the production of cornified envelope in NHEKs by approximately 1.8-fold compared with controls. Epidermal differentiation marker proteins such as involucrin, loricrin, and keratin1 were also increased in PS-treated NHEKs, by ELISA or Western blotting analysis. A [(3)H]thymidine incorporation assay showed that PS inhibited DNA synthesis in NHEKs to 20% compared with controls. The antiproliferative and anti-inflammatory effects of PS were examined in a mouse model of irritant contact dermatitis produced by topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA). PS blocked epidermal thickening and edema and the infiltration of inflammatory cells into the dermis in the skin of TPA-treated hairless mice. The anti-inflammatory effects of PS were confirmed by the observation that PS blocked the TPA-induced generation of prostaglandin E(2) in peripheral mononuclear leukocytes. Taken together, our results provide an insight into the multiple regulatory roles of PS in epidermal homeostasis, and furthermore point to the potential use of PS as a therapeutic agent in the treatment of inflammatory and proliferative cutaneous diseases.

Induction of thymidine kinase in mouse skin exposed to 12-O-tetradecanoylphorbol-13-acetate

Topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) exhibited an increase in the epidermal thymidine kinase (TK) activity in a dose dependent manner. Maximum induction of TK was observed at a TPA concentration of 2.5 μg per animal. The induction of TK by TPA appeared to be a function of time with the maximum TK induction between 4 and 16 h after TPA application. Repeated applications of TPA every 24 h did not show any cumulative effect rather TK activity appeared to be normal after two applications. However, repeated applications of TPA at an interval of 48 h exhibited increased TK activity even after 16 applications. Cycloheximide and actinomycin D, the inhibitors of protein and RNA synthesis, inhibited the TPA induced activation of TK. Our results demonstrated that TPA induced the TK activity may be, by increasing de novo synthesis of enzyme protein and this induction might lead to increased de novo DNA synthesis after TPA application. DMBA was used as a reference compound. As far as the authors are aware, this is the first report on TK induction by topical application of TPA.

In Vivo Detection of Human Vascular Endothelial Growth Factor Promoter Activity in Transgenic Mouse Skin

We have generated transgenic mice expressing green fluorescent protein (GFP) driven by 2.453-kb (-2,362 to +91) of the 5'-upstream region of the human vascular endothelial growth factor (VEGF) promoter to monitor changes of VEGF gene transcription in situ. Neonatal transgenic mice exhibited GFP-derived fluorescence in tissues that have been previously reported to express VEGF mRNA expression, including lung, cartilage, and brain. In normal skin during postnatal development, moderate fluorescence was observed in the upper epidermis and, more prominently, in the outer root sheath keratinocytes of hair follicles. Strong up-regulation of GFP fluorescence was observed in the hyperplastic epidermis of the wound edge at 48 hours after wounding, whereas little GFP fluorescence was detected in the dermis. In situ hybridization confirmed an identical expression pattern of VEGF mRNA in these wounds. Topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) induced strong VEGF-GFP expression in suprabasal epidermis. Little or no fibroblast-derived fluorescence was seen both in the wound model and after TPA application. By confocal laser microscopy, increased GFP fluorescence was detectable in the epidermis of intact mouse ear skin as early as 6 hours after topical TPA treatment. Importantly, GFP fluorescence was also measurable in the skin of living transgenic mice. These results resolve the present controversy regarding the ability of VEGF-GFP transgenic mouse models to correctly reflect established patterns of VEGF expression, and show the model to be a powerful tool for the in vivo monitoring of VEGF gene expression.

Beta2 integrin/ICAM-1 adhesion molecule interactions in cutaneous inflammation and tumor promotion.

The beta2 integrin (CD 18/CD 11 a, b, c) family of proteins mediate adherence of leukocytes to vascular endothelium and the associated ligand, intercellular adhesion molecule-1 (ICAM-1; CD 54), interacts with beta2 integrin proteins to allow transendothelial migration of leukocytes into sites of inflammation. The present study examines the function of these proteins in a murine model of acute cutaneous inflammation induced following topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) to the dorsal epidermis of SENCAR mice and in a model of skin multistage carcinogenesis. At 24 h following topical application of TPA to the dorsal epidermis of mice, dermal leukocytes expressed higher levels of beta2 integrin protein compared with the lower levels of beta2 integrin protein expression by peripheral blood leukocytes. ICAM-1 protein was localized to epidermal keratinocytes and vascular endothelium in TPA-treated skin and to proliferating papilloma cells. Intravenous (i.v.) injection of either 50 microg anti-beta2 integrin antibody alone or in combination with anti-ICAM-1 antibody significantly inhibited both TPA-stimulated neutrophil infiltration into the dermis (P < 0.001) and myeloperoxidase (MPO) activity (P < 0.03 anti-beta2 integrin antibody; P < 0.01 anti-beta2 integrin + ICAM-1 adhesion molecule antibodies), but had no effect on TPA-induced epidermal hyperplasia. In addition, injection of either anti-ICAM-1 adhesion molecule antibody alone (P < 0.004) or in combination with anti-beta2 integrin antibody (P < 0.001) significantly inhibited TPA-induced production of 7,8-dihydroxy-2'-deoxyguanosine (8-OHdG) immunoreactive proteins by epidermal keratinocytes. Beta2 integrin/ICAM-1 adhesion molecules work in concert to regulate migration, retention and functional activation of leukocytes within the dermis during TPA-induced skin inflammation and within stromal tissue of papillomas that form during multi-stage carcinogenesis. Agents that inhibit these receptor/ligand interactions may be useful in defining the roles of specific cell populations in cutaneous inflammation and multistage carcinogenesis and may also have potential as anti-promoting and anti-progression agents.

Inhibition of pro-inflammatory cytokine gene expression and papilloma growth during murine multistage carcinogenesis by pentoxifylline.

Topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) to the dorsal epidermis of Sencar mice induces synthesis of pro-inflammatory cytokines, including interleukin-1 alpha (IL-1 alpha) and tumor necrosis factor-alpha (TNF-alpha). These proteins differentially regulate proliferation of epidermal keratinocytes, as well as stimulate chemotaxis, migration and production of reactive oxygen and nitrogen intermediates by leukocytes. Studies over the past several years have demonstrated that pentoxifylline ([1-(5-oxohexyl)-3,7-dimethyl-xanthine], oxpentifylline), which is a methylxanthine derivative used clinically for treatment of vascular insufficiency, has the unique ability to inhibit synthesis of pro-inflammatory cytokines. The present studies were performed to examine the effects of acute and chronic administration of pentoxifylline on TPA-induced cutaneous inflammation in female Sencar mice treated once with 10 micrograms TPA and also to determine the ability of pentoxifylline to inhibit the tumor promotion process in mice treated with a single application of 25 nmol 7,12-dimethylbenz[a]anthracene (DMBA) followed for 8 weeks by twice weekly topical application of TPA. Intraperitoneal injection of 50 micrograms/g pentoxifylline at 30 min prior to topical application of 10 micrograms TPA to the dorsal epidermis of Sencar mice inhibited TPA-induced IL-1 alpha and TNF-alpha gene expression 24 h after TPA treatment. Administration of pentoxifylline also significantly inhibited all parameters of acute TPA-induced inflammatory response examined 24 h later, including skin thickening (P < 0.005), infiltration of neutrophils into the dermis (P < 0.001), the corresponding dermal myeloperoxidase activity (P < 0.01) and epidermal hyperplasia (P < 0.001). Injection of 50 micrograms/g pentoxifylline over an 8 week time period significantly inhibited DMBA/TPA-induced papilloma growth (P < 0.05). These results indicate that administration of pentoxifylline is an effective means of inhibiting acute TPA-induced cutaneous inflammation and pro-inflammatory cytokine gene expression, as well as is effective as an antipromoter that inhibits papilloma growth.

Staurosporine, a potent protein kinase C inhibitor, augments phorbol ester-caused ornithine decarboxylase induction in mouse epidermis.

A single topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) to mouse skin caused an induction of epidermal ornithine decarboxylase (ODC) activity. When mice were topically pretreated with staurosporine, a most potent protein kinase C inhibitor, 6-84 h prior to TPA treatment, TPA-caused ODC induction was markedly enhanced. The enhancement of TPA-caused ODC induction by staurosporine was most pronounced when the time interval between staurosporine and TPA treatment was 36 h. Staurosporine elicited this enhancing effect in a dose-related manner. Staurosporine by itself also induced epidermal ODC activity. But the activity induced was very slight and would not directly contribute to the enhancing effect of this compound. Although staurosporine markedly augmented TPA-caused ODC induction, staurosporine-caused ODC induction was not augmented by this compound. Other protein kinase C inhibitors, such as 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, sphingosine and palmitoylcarnitine did not mimic the enhancing effect of staurosporine. These results indicate that the enhancement of ODC induction by staurosporine is specific for the induction caused by TPA and that this enhancing effect is not related to the protein kinase C inhibitory action of staurosporine. TPA-caused epidermal ODC induction was inhibited by indomethacin, and this inhibition was reversed by prostaglandin E2 (PGE2). Staurosporine-caused ODC induction was also inhibited by indomethacin but the inhibition was not reversed by PGE2, indicating that the mechanism of staurosporine-caused ODC induction is different from that of TPA.

Immunological demonstration of a calcium-unresponsive protein kinase C of the delta-type in different species and murine tissues. Predominance in epidermis

An antiserum raised against a delta-protein kinase C (delta-PKC)-specific peptide recognized the purified calcium-unresponsive 76-kDa protein kinase of porcine spleen in the native and the denatured form. This antiserum was used to demonstrate the delta-PKC-like enzyme in spleen of different species, in various cell types and in murine tissues by immunoblotting of the respective extracts. Due to species differences, delta-PKC-like kinases with slightly different molecular weights were observed. The enzyme was found to be present in primary murine keratinocytes, primary bovine endothelial cells, and many cell lines originating from human, rat, and murine tissues. It was present also in all murine tissues tested, predominantly in epidermis, uterus, placenta, lung, brain, spleen, and kidney. In contrast to the conventional alpha, beta, gamma-PKC, it was located almost exclusively in the particulate fraction. The delta-like PKC could be demonstrated in the epidermis and brain of newborn mice, and in both tissues its concentration increased dramatically between day 7 and 14 after birth. The delta-PKC-like kinase of mouse epidermis (p82-kinase) was down-regulated after topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) to mouse skin. The amount of the enzyme decreased to less than 20% of the controls within 16 h and recovered almost completely within 72 h after TPA. The existence of the delta-PKC-like kinase in mouse skin, papillomas, and carcinomas could also be demonstrated by immunocytochemical staining of the respective sections. The enzyme was observed predominantly in epithelial layers. A remarkable immunostaining of nuclei in skin sections disappeared after TPA treatment of the animals.

Assessment of the antioxidant/prooxidant status of murine skin following topical treatment with 12-O-tetradecanoylphorbol-13-acetate and throughout the ontogeny of skin cancer. Part II: quantitation of glutathione and glutathione disulfide

Tissue glutathione (GSH) and glutathione disulfide (GSSG) contents were quantitated in the skins of female SENCAR mice following the topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA), and in the skin tumors generated by an initiation-promotion protocol. Total epidermal GSHt (GSH + GSSG) and GSSG contents were not reproducibly and significantly altered 0.5, 4 or 24 h after one or four topical applications of 1 microgram TPA, relative to the values obtained in age-matched, solvent-treated mice. Similar findings held for dermal GSHt at all times of analyses, and for dermal GSSG contents 0.5 and 4 h after TPA application. However, dermal GSSG contents were slightly elevated 24 h after TPA application. The GSHt and GSSG contents of skins initiated with 10 nmol 7,12-dimethylbenz[a]anthracene (DMBA) and harvested 17, 29 and 37 days after the cessation of chronic treatment with acetone (14 weeks, twice a week) were comparable to the values measured in age-matched, non-treated skins. In contrast, GSHt contents of papillomas harvested 17, 29 and 37 days after the cessation of chronic treatment with 1 microgram TPA (14 weeks, twice a week) were 2- to 4-fold greater than the values measured in non-treated mice, and DMBA-initiated, acetone-promoted mice, and the non-tumorous tissue adjacent to the papillomas. Comparable changes did not occur in papilloma GSSG contents. GSHt contents in squamous cell carcinomas (SCC) were twice the values measured in papillomas and 5- to 8-fold greater than the values measured in non-treated skins, and the non-tumorous tissue adjacent to SCC. Similarly, GSSG contents in SCC were elevated multifold relative to papillomas, non-treated skin and the non-tumorous tissue adjacent to SCC. Epidermal cell suspensions prepared by the trypsin-flotation procedure retained less than 2% of their original GSHt content and had reduced GSHt/GSSG ratios. Collectively these studies suggest that (i) if promoting doses of TPA induce oxidative stress in murine epidermis, it cannot be detected by measurements of GSH/GSSG; (ii) the antioxidant capacity of epidermal cells prepared by the trypsin-flotation procedure is severely compromised; and (iii) GSHt contents progressively increase during skin tumor ontogeny.

Evidence for autocrine/paracrine growth stimulation by transforming growth factor‐α during the process of skin tumor promotion

A single topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) to mouse skin decreased 125I-labeled epidermal growth factor (EGF) binding in epidermal membrane preparations within 1 h while 1,8-dihydroxy-3-methyl-9-anthrone (chrysarobin) gradually reduced binding with maximum inhibition at 15 h. Subsequently, 125I-EGF binding increased to approximately 200% of control in epidermal membrane preparations from both TPA- and chrysarobin-treated mice. A single application of TPA but not chrysarobin resulted in a rapid translocation of protein kinase C (PKC) to the membrane; however, treatment with both promoters ultimately led to a time-dependent loss of PKC activity in both membrane and cytosol fractions. The initial inhibition of 125I-EGF binding was sustained for at least 24 h after single and multiple treatments with both promoting agents. Acid washing restored EGF binding to control levels in membrane preparations obtained 24 h after a single application, whereas acid washing of membrane preparations obtained 24 h after a second application of TPA or chrysarobin increased binding (2.5-fold and 1.5-fold that of the control, respectively). The presence of increased amounts of ligands for the EGF receptor in tumor promoter-treated epidermis was initially confirmed in 125I-EGF binding competition experiments using NRK-49F cells. A single topical application of TPA or chrysarobin induced elevated levels of transforming growth factor-alpha (TGF-alpha) mRNA at 6 h or 15-24 h, respectively. Elevated levels of a TGF-alpha precursor (21 kDa) were subsequently observed in cytosol and membrane preparations after single and multiple applications of TPA or chrysarobin. These results suggest that repeated topical application of tumor promoters may lead to sustained loss of a negative-feedback mechanism involving phosphorylation at Thr-654 of the EGF receptor by PKC. The concomitant elevation of ligands, such as TGF-alpha, may provide a mechanism for sustained cell proliferation essential for skin tumor promotion.

The potent anti-tumor-promoting agent isoliquiritigenin

A topical application of a chalcone derivative, 4,2',4'-trihydroxychalcone (isoliquiritigenin) inhibited epidermal ornithine decarboxylase (ODC) induction and ear edema formation, i.e. inflammation, caused by a topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) in CD-1 mice. In addition, isoliquiritigenin potently inhibited 7,12-dimethylbenz[alpha]anthracene (DMBA)-initiated and TPA-promoted skin papilloma formation. This inhibitory effect of isoliquiritigenin was not due to any damage inflicted on the initiated cells but due to its anti-tumor-promoting action. Isoliquiritigenin also inhibited epidermal ODC induction and skin tumor promotion caused by 7-bromomethylbenz[alpha]anthracene (BrMBA), a non-TPA type of tumor-promoting agent, in DMBA-initiated mice. Isoliquiritigenin inhibits neither 12-lipoxygenase nor cyclooxygenase in epidermal subcellular fractions. This compound, however, inhibited TPA-stimulated prostaglandin E2 (PGE2) production in intact epidermal cells. ODC induction caused by TPA was inhibited by a topical application of cyclooxygenase inhibitor, indomethacin. Inhibition of ODC induction by indomethacin was counteracted by a topical application of PGE2, while inhibition caused by isoliquiritigenin was not overcome by PGE2. The results suggest that a mechanism other than the inhibition of PGE2 production is involved in the anti-tumor-promoting action of isoliquiritigenin. Isoliquiritigenin failed to inhibit phospholipase A2 activity of platelet sonicates, but inhibited platelet 12-lipoxygenase and 5-lipoxygenase in polymorphonuclear leukocytes. Therefore, it might be possible that isoliquiritigenin exerts its anti-tumor-promoting action through the lipoxygenase inhibition by acting on cells other than the target epidermal cells. Our present results, in combination with our previous data, demonstrate that some chalcone derivatives and flavonoids which show a potent lipoxygenase inhibitory action act on a common step in the skin tumor promotion caused by two different types of tumor-promoting agents, i.e. TPA and BrMBA, and suggest that these compounds show promise as drugs to prevent tumor promotion.

Induction of metallothionein mRNA by tumor promoters in mouse skin and its constitutive expression in papillomas

A single topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) was found to induce mRNA of a metallothionein (MT) gene or genes in the skin of Sencar mice, and papillomas produced by repeated applications of TPA were shown to have elevated levels of MT mRNA. Induction of MT mRNA was maximal 4-8 h after application of TPA and returned to the control level 24 h later. A dose-dependent increase of MT mRNA was observed with doses of TPA of 1-5 micrograms. Of the other promoters tested, phorbol-12, 13-didecanoate, mezerein, and the ionophore A23187 also induced MT mRNA, but 4-O-methyl-TPA and benzoyl peroxide did not. Phorbol and 4 alpha-phorbol-12,13-didecanoate, which are not promoters, also did not induce MT mRNA. Retinoic acid and 1 alpha, 25-dihydroxyvitamin D3, inhibitors of tumor promotion, did not induce MT mRNA themselves or inhibit the induction of MT mRNA by TPA. In C57BL/6 promotion-resistant mice, TPA caused only slight induction of MT mRNA. These data suggest a correlation between induction of MT mRNA and epidermal hyperplasia. The constitutive elevation of MT mRNA levels in papillomas may be due to the loss, during the process of tumor promotion, of some mechanism regulating MT gene expression.

Palmitoylcarnitine reverses 12-O-tetradecanoylphorbol-13-acetate-induced refractory state for the TPA-caused ornithine decarboxylase induction in mouse epidermis

When a single topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) was performed 12 h before the second application, ornithine decarboxylase (ODC) induction by the second application of TPA was markedly suppressed (refractory state). However, at intervals of 96 h between the first and the second application, the ODC activity induced by the second application of TPA was higher (enhanced state) than the activity induced by the single application. When various anti-tumor promoting agents, i.e. p-bromophenacyl bromide, nordihydroguaiaretic acid, quercetin, 1-tosylamide-2-phenylethyl chloromethyl ketone, retinoic acid and palmitoylcarnitine, were applied concurrently with the first TPA application, the ODC induction in the refractory state was restored only by palmitoylcarnitine, but not by other antitumor promoting agents. None of these anti-tumor promoting agents affected the ODC induction in the enhanced state. Stearoylcarnitine also had the restorative effect but was less effective than palmitoylcarnitine. Acetylcarnitine and palmitic acid were not effective. Pretreatment of mice with TPA 12 h or 96 h before the second TPA application resulted in the reduction or the increase in the Vmax values of ODC both for ornithine and pyridoxal-5'-phosphate, respectively. Palmitoylcarnitine restored these reduced Vmax values to the control values. Twelve hours after TPA treatment, the epidermal protein kinase C activity of both cytosol and particulate fractions decreased moderately. At 96 h after TPA application, protein kinase C activities of both cytosol and particulate fractions were fully or at least partially restored to the control levels. Protein kinase C activities both in the cytosol and the particulate fractions tended to be restored by palmitoylcarnitine, but the effect was not always reproducible. The TPA-induced refractory state and the enhanced state for ODC induction appear to result from the changes in the protein kinase C activities caused by TPA. However, it is not known whether such changes in the protein kinase C activities are the major causes for the TPA-induced refractory and/or enhanced state for ODC induction and whether or not the restorative effect of palmitoylcarnitine is due to its modulating action on protein kinase C activity.

Modulation of natural killer activity by 12-O-tetradecanoylphorbol-13-acetate and benzoyl peroxide in phorbol ester-sensitive (SENCAR) and resistant (B6C3F1) mice.

Following two weeks of topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) at 2, 4 and 8 micrograms/mouse on alternate days (7X total) or benzoyl peroxide (BZP) at 10, 20 and 40 mg/mouse, natural killer (NK) activity was determined in local (lymph nodes draining the lower dorsal region) and systemic (spleen) lymphoid tissue in phorbol ester-sensitive (SENCAR) and resistant (B6C3F1) mice. SENCAR mice, sensitive to tumor induction by TPA in two-stage chemical-induced carcinogenesis protocols, demonstrated suppression of NK activity in the spleen (no significant change in lymph nodes) and substantial dose-dependent increases in cell numbers in these organs after topical exposure to TPA. B6C3F1 (C57BL/6 X C3H F1) mice, reported to be resistant to TPA-induced promotion, demonstrated significant increases in NK activity in lymph nodes/spleen with an increase in cell numbers in the draining nodes only. Unlike the C57BL/6 parental strain, B6C3F1 mice are also reported to be resistant to promotion with BZP. Significantly, studies in this laboratory indicated that B6C3F1 mice dosed with BZP demonstrated increased NK activity in the spleen as was observed after dosing with TPA. These data suggest that alterations in NK activity as a result of exposure to tumor promoters may, in part, account for the resistance of particular strains of mice to tumor development. In both SENCAR and B6C3F1 mice, the blastogenic response of spleen cell suspensions isolated from TPA-dosed animals to phytohemagglutinin (PHA), a T cell lectin, was suppressed in a dose-dependent manner; BZP had no effect on spleen cell responses in either strain. Blastogenic responses of lymph node cells to PHA were enhanced in both strains of mice after topical application of TPA and BZP. Therefore, alterations in lymphoid cell responsiveness to PHA appeared unrelated to the reported sensitivities of SENCAR and B6C3F1 mice to tumor promotion.

Effects of antiinflammatory agents on edema and DNA synthesis induced by 12-O-tetradecanoylphorbol-13-acetate in the guinea pig.

Inflammation and hyperplasia are frequently associated in skin diseases. In order to verify this relationship, we studied the antagonistic effect of different classes of antiinflammatory agents on the inflammatory and hyperplasiogenic responses elicited by one topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) to the ear of the guinea-pig. Edema and DNA synthesis were chosen as relevant parameters. All antiinflammatory agents tested significantly inhibited DNA synthesis induced by TPA. Moreover, all compounds except quinacrine and phenylbutazone also inhibited edema formation. In conclusion, our results demonstrate that while edema and hyperplasia are frequently associated, this is not always the case.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced epidermal ornithine decarboxylase activity by lipoxygenase inhibitors: possible role of product(s) of lipoxygenase pathway.

Induction of epidermal ornithine decarboxylase (ODC) by a topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA), a tumor promoter, was inhibited by treatment of mouse skin with phenidone (3-90 mumol/mouse), nordihydroguaiaretic acid (30 mumol/mouse) or 3-amino-1-[m-(trifluoromethyl)-phenyl]-2-pyrazoline (BW 755C, 30 mumol/mouse), which are well-known lipoxygenase inhibitors. Phenidone and BW 755C are also to be cyclooxygenase inhibitors. Inhibition of TPA-induced ODC by indomethacin (1.12 mumol/mouse), a selective cyclooxygenase inhibitor, was counteracted by prostaglandin E2 (PGE2) (140 nmol/mouse). This counteracting effect of PGE2 was reversed by the treatment of mice with nordihydroguaiaretic acid (30 mumol/mouse) or phenidone (30 mumol/mouse). ODC activity which was suppressed by nordihydroguaiaretic acid or phenidone at a dose of 180 mumol/mouse was not further inhibited by indomethacin (1.12 mumol/mouse). In addition, the counteracting action of PGE2 (140 nmol/mouse) was not observed in mice treated with nordihydroguaiaretic acid or phenidone at a dose of 180 mumol/mouse. Thus, the suppressive effect of nordihydroguaiaretic acid or phenidone on the ODC induction by TPA would be due to the inhibition of lipoxygenase. The above findings strongly suggest that not only cyclooxygenase product (i.e., PGE2) but also lipoxygenase product(s) are involved in the mechanism of ODC induction in mouse epidermis, and a lack of either cyclooxygenase product or lipoxygenase product(s) causes a failure of ODC induction by TPA.