促癌物TPA诱导小鼠表皮鸟氨酸脱羧酶mRNA表达和维甲类化合物对该表达的影响

強皮肤促癌物十四烷酰佛波醋酸酯(TPA)局部应用时可触发一系列的生物化学改变,其中最明显的事件之一就是对ODC活性的短暂而急到的诱导,而这种诱导作用与其促癌作用密切相关。利用Northern印迹分析和条带(Slot)印迹分析证明,10nmol/L TPA一次局部处理小鼠背部皮肤可刺激ODC mRNA(2.0kb大小)表达,在4h左右最为明显,随后逐渐降低。10nmol/L TPA多次处理小鼠皮肤(每2天一次,共4次)也有类似的促进作用,但却在6h左右最为明显。在二甲基苯蒽和巴豆油诱发的二阶段小鼠皮肤乳头瘤和癌组织中也观察到了相同大小的ODC mRNA的高水平表达,尤以癌组织最高。新维甲类化合物R8605虽能明显抑制巴豆油诱导的ODC活性,但却未见对TPA诱导的ODC mRNA增加有明显抑制作用。     

Only a subset of 12-O-tetradecanoylphorbol-13-acetate-promoted mouse skin papillomas are promotable by benzoyl peroxide

The two-stage skin carcinogenesis model of initiation and promotion in Carcinogenesis-susceptible (Car-S) mice has been used to investigate the pathways of promotional activity of 12-O-tetradecanoylphorbol-13-acetate (TPA), a phorbol ester tumor promoter, and benzoyl peroxide (BzPo), a free radical-generating compound. To test whether distinct populations of 9,10-dimethyl-1,2-benzanthracene (DMBA)-initiated epidermal keratinocytes are responsive to the two promoters, tandem experiments were performed. DMBA-initiated Car-S mice were promoted twice weekly with maximal promoting doses of TPA or BzPo. When the number of papillomas/mouse reached a plateau, promotion in the TPA and BzPo groups was switched to BzPo or TPA, respectively, until achievement of a new plateau. Mice promoted with BzPo developed 11.0 +/- 1.3 papillomas/mouse and subsequent TPA promotion induced 13.8 additional papillomas, for a total of 24.8 +/- 2.1 papillomas/mouse. TPA-promoted mice developed 23.3 +/- 1.1 papillomas/mouse, and subsequent BzPo promotion for 91 days did not promote additional papillomas. Our results show a less than additive tumor response after sequential promotion with BzPo and TPA, or vice versa, indicating that the pathways of promotional activity of TPA and BzPo are interacting. While the final papilloma yield was similar at the end of the two tandem promotion experiments independently of promoter sequence, the percentage of mice developing carcinomas was significantly higher in mice that were promoted with BzPo in the first stage. No significant differences in the frequency and type of c-Ha-ras mutations were observed in TPA- and BzPo-promoted tumors, suggesting that promotion of DMBA-initiated cells by BzPo requires introduction of additional molecular alterations compared to TPA.     

12-O-tetradecanoylphorbol-13-acetate and UV radiation-induced nucleoside diphosphate protein kinase B mediates neoplastic transformation of epidermal cells

The molecular changes associated with early skin carcinogenesis are largely unknown. We have previously identified 11 genes whose expression was up- or down-regulated by 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse skin keratinocyte progenitor cells (Wei, S.-J., Trempus, C. S., Cannon, R. E., Bortner, C. D., and Tennant, R. W. (2003) J. Biol. Chem. 278, 1758-1768). Here, we show an induction of a nucleoside diphosphate protein kinase B (NDPK-B) gene in response to TPA or UV radiation (UVR). TPA or UVR significantly induced the expression of NDPK-B both in vivo hyperplastic mouse skin and in vitro mouse JB6 Cl 41-5a epidermal cells. Indeed, this gene was also up-regulated in TPA or UVR-mediated skin tumors including papillomas, spindle cell tumors, and squamous cell carcinomas, relative to adjacent normal skins. Functional studies by constitutive expression of nm23-M2/NDPK-B in TPA susceptible JB6 Cl 41-5a and TPA-resistant JB6 Cl 30-7b preneoplastic epidermal cell lines showed a remarkable gene dosage-dependent increase in foci-forming activity, as well as an enhancement in the efficiency of neoplastic transformation of these cells in soft agar but no effect on proliferation in monolayer cultures. Interestingly, stable transfection of the nm23-M2/NDPK-B del-RGD or G106A mutant gene in JB6 Cl 41-5a cells selectively abrogated NDPK-B-induced cellular transformation, implicating a possible Arg105-Gly106-Asp107 regulatory role in early skin carcinogenesis.     

Biological and molecular aspects of radiation carcinogenesis in mouse skin

The process of mouse skin carcinogenesis can be operationally subdivided into at least three stages which have been termed initiation, promotion, and progression. Ionizing radiation has been found to be a weak initiator of malignant squamous cell carcinomas (SCCs) when radiation was followed by repeated treatments of the skin with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Besides SCCs, ionizing radiation was found to induce, independent of tumor promoters, basal cell carcinomas (BCCs), a tumor histology not normally seen with chemical carcinogens and mouse skin. Fractionated doses of 1 MeV electrons were found to enhance the conversion of chemically induced benign papillomas to malignant SCCs. In addition to the biological studies, questions related to dominant transforming genes and differential gene expression in the radiation-initiated mouse skin tumors have been explored. Distinct non-ras dominant transforming gene(s) have been detected in radiation-initiated, TPA-promoted SCCs. Differences in the expression pattern of tumor-associated genes were seen in comparing chemically to radiation-induced benign and malignant skin tumors. Therefore, ionizing radiation has been shown to be active in the initiation of malignant skin tumors and progression of benign to malignant tumors in the mouse skin. The ability to divide the process of carcinogenesis into multiple stages in the mouse skin model has facilitated mechanistic studies that may elucidate the molecular pathways involved in radiation-versus chemically induced tumor development.     

Transfection of the EJ rasHa gene into keratinocytes derived from carcinogen-induced mouse papillomas causes malignant progression.

The development of malignant tumors in carcinogen-treated mouse skin appears to involve several genetic changes. Genetic changes which initiate the process are believed to induce alterations in the normal pattern of epidermal differentiation, resulting in the formation of benign tumors, i.e., epidermal papillomas. Subsequent changes appear to be required for the malignant conversion of papillomas to epidermal, squamous-cell carcinomas. Activation of the rasHa gene occurs frequently in chemically induced benign skin papillomas as well as squamous cell carcinomas and thus may represent one mechanism to achieve the initiation step. In the present study, we analyzed several cell lines derived from chemically induced mouse skin papillomas for the presence of transforming oncogenes by transfection of their DNA into NIH 3T3 cells. These papilloma cell lines exhibit an altered differentiation program, i.e., the ability to proliferate under culture conditions favoring terminal differentiation. When DNA from six separate cell lines was tested in the NIH 3T3 transfection assay, active transforming activity was not detected. However, when the EJ rasHa gene was introduced into three of the papilloma cell lines by DNA transfection, transfectants showed an enhanced capacity to proliferate under differentiating culture conditions and formed rapidly growing, anaplastic carcinomas in nude mice. Our findings suggest that in some papilloma cells, a genetic change distinct from rasHa activation may produce an altered differentiation program associated with the initiation step, and this genetic alteration may act in a cooperating fashion with an activated ras gene to result in malignant progression.     

Ionizing radiation as an initiator in the mouse two-stage model of skin tumor formation

The initiating potential of a range (7.5 to 22.5 Gy) of 4 MeV X rays was studied using the mouse skin two-stage model of carcinogenesis. A single dose of radiation was followed by 60 weeks of promotion with 12-O-tetradecanoyl phorbol-13-acetate (TPA) (8 nmol, two times per week). Since the proliferative state of a target cell population is known to influence carcinogen-induced tumorigenesis, we also investigated the effect of TPA on tumor incidence when applied as a single dose (17 nmol) 24 h prior to irradiation. Evidence presented here indicates that ionizing radiation can act as an initiator in this model system. All groups of animals that were promoted with TPA developed papillomas regardless of radiation treatment; however, only those groups of animals that received irradiation followed by TPA promotion developed squamous cell carcinomas. The incidence of nonepidermal tumors was similar between all radiation dose groups and was independent of TPA promotion. Our results also indicate that TPA pretreatment prior to irradiation results in an overall increase in the total tumor incidence, including both epidermal and nonepidermal tumors.     

转化生长因子β mRNA在佛波酯刺激的小鼠表皮和化学性诱发的小鼠皮肤肿瘤中的高水平表达

转化生长因子β是一种细胞多功能调节肽,目前研究认为其和促癌过程有密切关系。本文利用Northern印迹分析技术研究了TGF-β mRNA在促癌物佛波酯刺激的小鼠表皮和化学性诱发的小鼠二阶段皮肤肿瘤中的表达情况。结果证明,巴豆油2—20 μL和TPA 5—40nmol一次局部涂用于小鼠皮肤,均可明显增加小鼠表皮TGF-β mRNA,呈较好的浓度依赖性。TGF-β mRNA表达在二甲基苯蒽(DMBA)和巴豆油诱发的二阶段小鼠皮肤乳头瘤和癌中均高于正常和瘤旁表皮。所检测到的TGF-βmRNA为2.5kb和1.9kb二种条带,但以2.5kb为主。     

The genetic control of chemically and radiation-induced skin tumorigenesis: a study with carcinogenesis-susceptible and carcinogenesis-resistant mice

Outbred carcinogenesis-resistant (Car-R) and carcinogenesis-susceptible (Car-S) mouse lines were generated by phenotypic selection for resistance or susceptibility to two-stage skin carcinogenesis. These two Car mouse lines differ by >100-fold in susceptibility. In the present study, we tested the hypothesis that a subset of genetic loci responsible for susceptibility or resistance to chemical skin tumorigenesis may also be involved in radiation-induced skin tumorigenesis. Skin tumorigenesis was tested in groups of Car-S/R mice after X-ray initiation and 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion. We found that ionizing radiation can initiate skin tumors in Car-S mice but not in Car-R mice. In Car-S mice, the most effective radiation doses (6 and 10 Gy given in four fractions) gave a threefold increase in tumor multiplicity and a twofold increase in tumor incidence compared to a TPA-only control group. We performed a molecular analysis of Hras gene mutations in skin tumors of Car-S mice induced by X-ray initiation/TPA promotion or by TPA promotion alone. The most notable difference emerging from the comparison of these mutation patterns is the high incidence ( approximately 50%) of papillomas lacking Hras gene mutations in X-ray-initiated/TPA-promoted papillomas compared to 13% in papillomas induced by TPA alone, suggesting that lack of Hras gene mutations is a consistent feature of radiation-induced papillomas.     

Cancer preventive agents. Part 1: chemopreventive potential of cimigenol, cimigenol-3,15-dione, and related compounds

In continuation of our previous report, cimigenol (1) and 15 related compounds were screened as potential antitumor promoters by using the in vitro short-term 12-O-tetradecanoylphorbol-13-acetate (TPA)--induced Epstein-Barr virus early antigen (EBV-EA) activation assay. Cimigenol-3,15-dione (2) displayed the greatest potency (100% inhibition at 1000 mol ratio/TPA) and consequently was further examined for antitumor-promoting activity in a two-stage carcinogenesis assay of mouse skin tumors (DMBA/TPA). In this assay, compound 2 showed significant activity, reducing the number of papillomas per mouse to 48% of the control group at 20 weeks. In addition, compounds 1 and 2 were examined for antitumor-initiating activity in a two-stage carcinogenesis assay of mouse skin tumors induced by peroxynitrite as an initiator and TPA as a promoter. Results showed that these two triterpenoids were almost equipotent with epigallocatechin gallate (EGCG) and slightly more potent than tocinol (group V), the positive controls. Thus, compounds 1 and 2 exhibited not only strong antitumor-promoting activity but also significant antitumor-initiating effect on mouse skin. These data suggest that both compounds might be valuable chemopreventors.     

Genetic changes in skin tumor progression: correlation between presence of a mutant ras gene and loss of heterozygosity on mouse chromosome 7

Initiation of tumorigenesis in mouse skin can be accomplished by mutagenesis of the H-ras gene by treatment with chemical carcinogens. A mouse model system has been developed to study the additional genetic events that take place during tumor progression. Skin carcinomas were induced in F1 hybrid mice exhibiting restriction fragment length polymorphisms at multiple chromosomal loci. Analysis of loss of heterozygosity in such tumors showed that imbalance of alleles on mouse chromosome 7, on which the H-ras gene is located, occurs very frequently in skin carcinomas. The chromosomal alterations detected, which included both nondisjunction and mitotic recombination events, were only seen in tumors that have activated ras genes. We conclude that gross chromosomal alterations that elevate the copy number of mutant H-ras and/or lead to loss of normal H-ras are a consistent feature of mouse skin tumor development.     

Retroviral transduction of the human c-Ha-ras-1 oncogene into midgestation mouse embryos promotes rapid epithelial hyperplasia.

Infection of mouse embryos at 8 days of gestation with a replication-defective retrovirus carrying the human c-Ha-ras-1 oncogene led to efficient and rapid induction of hyperplastic lesions. Twenty-four percent of viable off-spring developed abnormal growths after infection with purified virus. The lesions contained a single integrated provirus and produced viral RNA and the Ha-ras oncogene product (p21). The latency period between the time of infection and appearance of the lesions suggested that secondary alterations in addition to activated ras were necessary for neoplasms to develop. The earliest and most abundant growths were cutaneous and appeared from 4 to 36 weeks of age, with a median of 4 weeks of age. A number of subcutaneous lesions also developed over the same time span but at a median of 18 weeks of age. The rapid development of cutaneous lesions in response to transduction of the ras oncogene contrasts with other studies in which adult skin required secondary treatment with promoters prior to ras induction of epithelial hyperplasia. These results demonstrate that infection of midgestation mouse embryos allows rapid analysis of oncogene potency in skin.     

Presence of specific mutation of Ha-ras oncogene in skin tumors of mice induced under different experimental conditions

The mutation was revealed with substitution of A for T in the second position of the 61 Ha-ras oncogene codon in the DNA of 31 skin tumours (26 papillomas and 5 carcinomas) and in 23 mice treated with 12-O-tetradecanoyl phorbol-13-acetate (TPA). Part of these mice were F progeny (n-6) and F progeny (n-4) following DMBA administration during pregnancy, another part F progeny (n-5) following ENU action on males prior to mating, the rest mice (n-3) did not undergo additional actions. The mutation under study was revealed only in 3 out of 5 papillomas and in all 5 carcinomas of mice subjected to DMBA administration during pregnancy.     

The presence of bovine papillomavirus type 4 DNA is not required for the progression to, or the maintenance of, the malignant state in cancers of the alimentary canal in cattle.

In the Western Highlands of Scotland there is a very high incidence of alimentary cancers in cattle. The carcinomas of the upper alimentary canal are found in association with virus-induced benign papillomas, and transformation of papillomas to carcinomas has been observed. Strong circumstantial evidence suggests that the progression to malignancy is due to the interplay between the virus, bovine papillomavirus type 4 (BPV-4), and carcinogen(s) present in bracken fern, which infests the marginal upland grazing grounds. The carcinomas are often accompanied by adenomas and adenocarcinomas of the lower bowels. To elucidate the role of the virus in the transformation process, we have analysed several malignancies of the alimentary canal, and have detected the viral genome in only one case of transforming papilloma of the oesophagus and one case of carcinoma of the tongue. We conclude that, although required for the induction of papillomas, the presence of the BPV-4 DNA is not necessary for the progression to, or the maintenance of, the transformed state.     

Polyamine biosynthesis and skin tumor promotion: inhibition of 12-O-tetradecanoylphorbol-13-acetate-promoted mouse skin tumor formation by the irreversible inhibitor of ornithine decarboxylase alpha-difluoromethylornithine

Application of 12-0-tetradecanoylphorbol-13-acetate (TPA) to mouse skin leads to the induction of ornithine decarboxylase (EC 4.1.1.17) and the accumulation of putrescine. The relevance of these TPA-induced changes to the mechanism of tumor promotion was determined using α-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase. α-Difluoromethylornithine applied to the skin of mice or administered in drinking water in conjunction with applications of TPA to 7,12-dimethylbenz[a]anthracene-initiated mouse skin inhibited the formation of mouse skin papillomas by 50 and 90% respectively; TPA-induced ornithine decarboxylase activity and the accumulation of putrescine were almost completely inhibited.     

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.     

IL-1 alpha,innate immunity,and skin carcinogenesis: the effect of constitutive expression of IL-1 alpha in epidermis on chemical carcinogenesis

Tumor promoters such as the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) are proinflammatory agents, and their mechanism of action in epithelial carcinogenesis has been linked to the release of IL-1 alpha and the induction of chronic inflammation in skin. To test the role of IL-1 alpha and inflammation in models of cutaneous carcinogenesis, we used our previously described FVB/N transgenic mice overexpressing 17-kDa IL-1 alpha in the epidermis under the keratin 14 (K14) promoter. Strikingly, the K14/IL-1 alpha mice were completely resistant to papilloma and carcinoma formation induced by a two-stage DMBA/TPA protocol, while littermate controls developed both tumor types. K14/IL-1 alpha mice crossed with the highly sensitive TG.AC mice, constitutively expressing mutant Ha-Ras, also failed to develop papillomas or carcinomas. When the K14/IL-1 alpha transgene was bred onto a recombinase-activating gene-2-deficient background, the resistance persisted, indicating that innate, but not acquired, mechanisms may be involved in the resistance to the initiation/promotion model. As an alternative approach, a complete carcinogenesis protocol using repetitive application of DMBA alone was applied. Surprisingly, although the IL-1 alpha mice still did not develop papillomas, they did develop carcinomas de novo at an accelerated rate compared with controls. We conclude that constitutive IL-1 alpha expression rendered FVB mice completely resistant to carcinomas that required evolution from prior papillomas, but facilitated carcinomas that did not evolve from papillomas, as in the complete carcinogenesis protocol. Thus, the role of IL-1 alpha and, by extension that of other proinflammatory factors, in epithelial carcinogenesis are more complex than previously appreciated. These mice may provide a mechanism to investigate the validity of these models of human skin tumorigenesis.     

Epstein-Barr virus-encoded latent membrane protein 1 (LMP1) and LMP2A function cooperatively to promote carcinoma development in a mouse carcinogenesis model

The Epstein-Barr virus (EBV) proteins latent membrane proteins 1 and 2 (LMP1 and LMP2) are frequently expressed in EBV-associated lymphoid and epithelial cancers and have complex effects on cell signaling and growth. The effects of these proteins on epithelial cell growth were assessed in vivo using transgenic mice driven by the keratin 14 promoter (K14). The development of papillomas and carcinomas was determined in the tumor initiator and promoter model using dimethyl benzanthracene (DMBA), followed by repeated treatments of 12-O-tetradecanoyl phorbol 13-acetate (TPA). In these assays, LMP1 functioned as a weak tumor promoter and increased papilloma formation. In contrast, mice expressing LMP2A did not induce or promote papilloma formation. Transgenic LMP1 mice had slightly increased development of squamous cell carcinoma; however, the development of carcinoma was significantly increased in the doubly transgenic mice expressing both LMP1 and LMP2A. DMBA treatment induces an activating mutation in the Harvey-ras (H-ras(61)) oncogene, and this mutation was identified in most papillomas and carcinomas although several papillomas and carcinomas in K14-LMP1 and K14-LMP1/LMP2A mice lacked the mutation. Analysis of signaling pathways that are known to be activated by LMP1 and/or LMP2 indicated that all genotypes had high levels of activated extracellular signal-regulated kinase (ERK) and Stat3 in carcinomas with significantly higher activation in the doubly transgenic carcinomas. These findings suggest that, in combination, LMP1 and LMP2 contribute to carcinoma progression and that this may reflect the combined effects of the proteins on activation of multiple signaling pathways. This study is the first to characterize the effects of LMP2 on tumor initiation and promotion and to identify an effect of the combined expression of LMP1 and LMP2 on the increase of carcinoma development.     

Increased incidence of squamous cell carcinomas in Mastomys natalensis papillomavirus E6 transgenic mice during two-stage skin carcinogenesis

Papillomaviruses cause certain forms of human cancers, most notably carcinomas of the uterine cervix. In contrast to the well-established involvement of papillomavirus infection in the etiology of cervical carcinomas and in carcinomas of a rare hereditary condition, epidermodysplasia verruciformis, a causative role for cutaneous human papillomavirus types in the development of nonmelanoma skin cancer has not been proven. In order to better understand the functions of individual genes of cutaneous papillomavirus types, we generated transgenic mice carrying oncogene E6 of the Mastomys natalensis papillomavirus (MnPV), which causes keratoacanthomas of the skin in its natural host. In the present study, we demonstrate that under conditions of experimental two-stage skin carcinogenesis, fast-paced squamous cell carcinomas develop in nearly 100% of MnPV E6 transgenic mice in comparison to 10% in their nontransgenic littermates (log rank test; P < 0.0001). Therefore, we conclude that the MnPV E6 transgene favors the malignant progression of chemically induced tumors. Whereas an activating H-ras mutation is a consistent feature in benign and malignant tumors in wild-type mice, the majority of papillomas and keratoacanthomas and all squamous cell carcinomas obtained in MnPV E6 transgenic mice contain nonmutated ras alleles. These results indicate that the development of squamous cell carcinomas in MnPV E6 transgenic mice does not depend on an activated H-ras oncogene.     

Identification of Dss1 as a 12-O-tetradecanoylphorbol-13-acetate-responsive gene expressed in keratinocyte progenitor cells,with possible involvement in early skin tumorigenesis

This study identifies genes expressed early in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced skin carcinogenesis in genetically initiated Tg.AC v-Ha-ras transgenic mice. Keratinocyte progenitor cells from TPA-treated Tg.AC mice were isolated with fluorescence-activated cell sorting and expression was analyzed using cDNA microarray technology. Eleven genes were identified whose expression changed significantly in response to carcinogen treatment. Deleted in split hand/split foot 1 (Dss1) is a gene associated with a heterogeneous limb developmental disorder called split hand/split foot malformation. cDNA microarray expression analysis showed that the mouse homologue of Dss1 is induced by TPA. Dss1 overexpression was detected by Northern blot analysis in early TPA-treated hyperplastic skins and in JB6 Cl 41-5a epidermal cells. Interestingly, Dss1 expression was also shown to be elevated in skin papillomas relative to normal skins, and further increased in squamous cell malignancies. Functional studies by ectopically constitutive expression of Dss1 in JB6 Cl 41-5a preneoplastic cells strongly increased focus formation and proliferation of these cells and enhanced efficiency of neoplastic transformation of the cells in soft agar. These results strongly suggest that Dss1 is a TPA-inducible gene that may play an important role in the early stages of skin carcinogenesis.     

The carcinogenic effect of TPA (12-0-tetradecanoylphorbol-13-acetate) when applied to the skin of hairless mice

Groups of hairless mice received one, two, five and fifty applications of 20 nmoles TPA (12-0-tetradecanoylphorbol-13-acetate) on the skin of the back, and were observed for 20 months. The animals developed some papillomas, some squamous cell carcinomas, some fibrosarcomas of the dermis, and some malignant and benign tumours in internal organs. There was a small, not significantly different, incidence of benign and malignant tumours after 1, 2 and 5 paintings, and a significantly higher tumour incidence after 50 applications. Apart from reticuloses, which are commonly seen in these animals, the occurrence of other tumours is believed to be related to the TPA treatment. The results are interpreted as showing that TPA, like croton oil, should be regarded as a complete carcinogen.