Involvement of PTEN/Akt signaling in capsular invasive carcinomas developed in a rat two-stage thyroid carcinogenesis model after promotion with sulfadimethoxine

Purpose  

Rat thyroid follicular cell carcinomas invading into the thyroid capsule are highly produced by promotion with sulfadimethoxine (SDM) in a rat two-stage thyroid carcinogenesis model. In this study, we investigated the participation of phosphoinositide 3-kinase (PI3K) signaling pathway that is associated with malignant phenotypes of many cancers on the development of SDM-induced capsular invasive carcinomas.     

Sarcophytols A and B inhibit tumor promotion by teleocidin in two-stage carcinogenesis in mouse skin

Summary Sarcophytols A and B, isolated from a soft coral, Sarcophyton glaucum, are cembrane-type diterpenes with different numbers of hydroxyl groups. Sarcophytols A and B inhibited tumor promotion by teleocidin in two-stage carcinogenesis experiments on mouse skin. The inhibitory effect of sarcophytol A was demonstrated with two different initiating doses of 7,12-dimethylbenz[a]anthracene (DMBA): 50 g (experiment 1) and 100 g (experiment 2). In experiment 1, three groups of mice were treated with DMBA, and then twice a week with doses (1.6 g, 16 g, and 82 g) of sarcophytol A followed by 2.5 g teleocidin. In week 25, the incidences of tumors in these groups were only 7.1%, 20.0%, and 13.3%, respectively, whereas that in the control group treated with DMBA plus teleocidin was 53.3%. Moreover, at this time, the average numbers of tumors per mouse in these groups were 0.1, 0.3, and 0.3, respectively, while that in the control group was 2.1. In experiment 2 an amount of sarcophytol A (1.6 g) or B (1.7 g) equimolar to 2.5 g teleocidin was applied twice a week, as in experiment 1, and results showed that sarcophytol B also inhibited tumor promotion by teleocidin. Both sarcophytols A and B caused delay in onset of tumor formation, and reduced the percentage of tumor-bearing mice and the average number of tumors per mouse. The effective concentrations of sarcophytols A and B were in the microgram range with an equimolar amount of teleocidin.Abbreviations DMBA 7,12-dimethylbenz[a]anthracene - TPA 12-O-tetradecanoylphorbol-13-acetate     

A tumor suppressor role for thyroid hormone beta receptor in a mouse model of thyroid carcinogenesis

We have created a knockin mutant mouse by targeting a mutation (PV) into the thyroid hormone receptor beta gene (TRbetaPV mouse). TRbetaPV/PV mice, but not TRbetaPV/+ mice, spontaneously develop follicular thyroid carcinoma. To identify other genetic changes in the TRbeta gene that could also induce thyroid carcinoma, we crossed TRbetaPV mice with TRbeta-/- mice. As TRbetaPV/- mice (mutation of one TRbeta allele in the absence of the other wild-type allele) aged, they also spontaneously developed follicular thyroid carcinoma through the pathological progression of hyperplasia, capsular and vascular invasion, anaplasia, and eventually metastasis to the lung, but not to the lymph nodes. The pathological progression of thyroid carcinoma in TRbetaPV/- mice was indistinguishable from that in TRbetaPV/PV mice. Analyses of the expression patterns of critical genes indicated activation of the signaling pathways mediated by TSH, peptide growth factors (epidermal growth factor and fibroblast growth factor), TGF-beta, TNF-alpha, and nuclear factor-kappaB, and also suggested progressive repression of the pathways mediated by the peroxisome proliferator-activated receptor gamma. The patterns in the alteration of these signaling pathways are similar to those observed in TRbeta(PV/PV) mice during thyroid carcinogenesis. These results indicate that in the absence of a wild-type allele, the mutation of one TRbeta allele is sufficient for the mutant mice to spontaneously develop follicular thyroid carcinoma. These results provide, for the first time, in vivo evidence to suggest that the TRbeta gene could function as a tumor suppressor gene. Importantly, these findings present the possibility that TRbeta could serve as a novel therapeutic target in thyroid cancer.     

Effective genetic therapy of established medullary thyroid carcinomas with murine interleukin-2: dissemination and cytotoxicity studies in a rat tumor model

Replication-defective adenovirus (AdCMVmIL2) expressing murine interleukin-2 was directly injected into rat medullary thyroid carcinomas to examine antitumor activity. AdCMVmIL2 cured 42.9% of all treated tumor bearing animals. Most cured rats were protected against tumor growth after subsequent rechallenge with wild-type tumor cells, reflecting the immunity obtained from the original treatment. Studies of viral dissemination showed that the intratumoral inoculated viruses can enter the circulation, infect peripheral tissues, and express genes driven by the CMV promoter. Liver is the main target organ. In a toxicity study, AdCMVmIL2 was administered i.v. at a dose five times higher than that given directly into tumor. No detectable side effect was found. Histological studies showed variable degrees of lymphocyte infiltration in the livers of studied animals, and no functional change indicated by the normal serum level of glutamic oxalacetic transaminase and glutamic pyruvic transaminase was found in all animals studied. These data demonstrate that AdCMVmIL2 is an effective antitumor agent in this animal model, and that virus treatment can be given without significant toxicity to other organs.     

Gelsolin: a novel thyroid hormone receptor-beta interacting protein that modulates tumor progression in a mouse model of follicular thyroid cancer

Follicular thyroid cancer (FTC) is known to metastasize to distant sites via hematogenous spread; however, the underlying pathways that contribute to metastasis remain unknown. Recent creation of a knockin mutant mouse that expresses a mutant thyroid hormone receptor-beta (TRbeta(PV/PV) mouse) that spontaneously develops thyroid cancer with metastasis similar to humans has provided new opportunities to study contributors to FTC metastasis. This study evaluates the role of gelsolin, an actin-regulatory protein, in modulating the metastatic potential of FTC. Gelsolin was previously found by cDNA microarray analysis to be down-regulated in TRbeta(PV/PV) mice as compared with wild-type mice. This study found an age-dependent reduction of gelsolin protein abundance in TRbeta(PV/PV) mice as tumorigenesis progressed. Knockdown of gelsolin by small interfering RNA resulted in increased tumor cell motility and increased gelsolin expression by histone deacetylase inhibitor (trichostatin A) led to decreased cell motility. Additional biochemical analyses demonstrated that gelsolin physically interacted with TRbeta1 or PV in vivo and in vitro. The interaction regions were mapped to the C terminus of gelsolin and the DNA binding domain of TR. The physical interaction of gelsolin with PV reduced its binding to actin, leading to disarrayed cytoskeletal architectures. These results suggest that PV-induced alteration of the actin/gelsolin cytoskeleton contributes to increased cell motility. Thus, the present study uncovered a novel PV-mediated oncogenic pathway that could contribute to the local tumor progression and metastatic potential of thyroid carcinogenesis.     

去势对化学诱导大鼠肝细胞癌发生发展的影响

目的 探讨去势对化学诱导大鼠肝细胞癌(HCC)发生发展的影响.方法 将100只5～6周龄SPF级SD大鼠(雌雄各半)均分为雌性去势组、雌性对照组、雄性去势组、雄性对照组.建立二乙基亚硝胺联合N-亚硝基吗啉诱导的SD大鼠HCC模型,分别观察去势对大鼠HCC发生和转移的影响.结果 雌鼠去势后HCC发生率显著升高(11/11比5/14),雄鼠去势后HCC发生率显著降低(3/10比12/12),差异均有统计学意义(P值均=0.001).去势可显著促进雌鼠HCC的生长(P=0.013)及侵袭转移(P=0.036),雄鼠去势则无此效应.雄性对照组、雄性去势组、雌性对照组、雌性去势组大鼠首发肝硬化的时间分别为8、12、16、12周,首发HCC的时间分别为16、20、20、16周,去势可促进雌鼠的癌变进程、减缓雄鼠的癌变进程.结论 性激素影响大鼠HCC的发生、发展和转移,其中雌激素的影响更大.     

去势对化学诱导大鼠肝细胞癌发生发展的影响

目的 探讨去势对化学诱导大鼠肝细胞癌(HCC)发生发展的影响.方法 将100只5～6周龄SPF级SD大鼠(雌雄各半)均分为雌性去势组、雌性对照组、雄性去势组、雄性对照组.建立二乙基亚硝胺联合N-亚硝基吗啉诱导的SD大鼠HCC模型,分别观察去势对大鼠HCC发生和转移的影响.结果 雌鼠去势后HCC发生率显著升高(11/11比5/14),雄鼠去势后HCC发生率显著降低(3/10比12/12),差异均有统计学意义(P值均=0.001).去势可显著促进雌鼠HCC的生长(P=0.013)及侵袭转移(P=0.036),雄鼠去势则无此效应.雄性对照组、雄性去势组、雌性对照组、雌性去势组大鼠首发肝硬化的时间分别为8、12、16、12周,首发HCC的时间分别为16、20、20、16周,去势可促进雌鼠的癌变进程、减缓雄鼠的癌变进程.结论 性激素影响大鼠HCC的发生、发展和转移,其中雌激素的影响更大.

Abstract：

Objective To assess the effects of gonadectomy on carcinogenesis and development of hepatocellular carcinoma (HCC) induced by chemical substances in rat model. Methods Fifty male and 50 female Sprague-Dawley rats (age of 5-6 weeks) were equally divided into four groups: male experimental (surgical castration) and control groups and female experimental (surgical castration)and control groups. The HCC model was induced by diethylnitrosamine (DEN) and Nnitrosomorpholine (NMOR) in SD rats. The effects of gonadectomy on occurring and development of HCC were observed. Results The incidence of HCC in female experimental group was higher than that in female control group (11/11 vs 5/14, P=0. 001), while it was lower in male experimental group than that in male control group (3/10 vs 12/12, P=0. 001). It was demonstrated that gonadectomy could increase the growth of HCC (P=0. 013) and tumor metastasis (P=0. 036) in female rats, but not in male rats. The formation of liver cirrhosis and HCC was found at 8 and 16 weeks in male experimental group, at 12 and 20 weeks in male control group, at 16 and 20 weeks in female experimental group and at 12 and 16 weeks in female control group. These findings showed that gonadectomy could improve the development of carcinogenesis in female rats and delay the carcinogenesis in male rats. Conclusion Sex hormones, especially estrogens, may be involved in development and metastasis of rats HCC.     

去势对化学诱导大鼠肝细胞癌发生发展的影响

目的 探讨去势对化学诱导大鼠肝细胞癌(HCC)发生发展的影响.方法 将100只5～6周龄SPF级SD大鼠(雌雄各半)均分为雌性去势组、雌性对照组、雄性去势组、雄性对照组.建立二乙基亚硝胺联合N-亚硝基吗啉诱导的SD大鼠HCC模型,分别观察去势对大鼠HCC发生和转移的影响.结果 雌鼠去势后HCC发生率显著升高(11/11比5/14),雄鼠去势后HCC发生率显著降低(3/10比12/12),差异均有统计学意义(P值均=0.001).去势可显著促进雌鼠HCC的生长(P=0.013)及侵袭转移(P=0.036),雄鼠去势则无此效应.雄性对照组、雄性去势组、雌性对照组、雌性去势组大鼠首发肝硬化的时间分别为8、12、16、12周,首发HCC的时间分别为16、20、20、16周,去势可促进雌鼠的癌变进程、减缓雄鼠的癌变进程.结论 性激素影响大鼠HCC的发生、发展和转移,其中雌激素的影响更大.     

Hyperlipoproteinemia induced by a transplantable pituitary tumor in the rat.

The MtT-F4 tumor, a transplantable pituitary tumor of rats, induces significant hyperlipidemia in male Fisher 344 rats. The increasive hypercholesterolemia was accompanied by hypertriglyceridemia only in the first month of tumor implantation. Clofibrate feeding inhibited the development of hypercholesterolemia and maintained normal serum triglyceride levels. In contrast to the changes in lipoprotein cholesterol distribution and profile found in experimental hyperlipidemia induced by high fat and cholesterol feeding, the hypercholesterolemic tumor-bearing rats showed no accumulation of cholesterol in the very low density and intermediate density lipoproteins, and no appearance of a new class of lipoprotein, B-VLDL. An HDLc-like lipoprotein appeared as hypercholesterolemia developed. Increased amounts of cholesterol were deposited in the aorta. The effects are attributed to the lipolytic hormones secreted by the tumor and antagonism to their action by clofibrate.     

Pineal melatonin inhibition of tumor promotion in theN-nitroso-N-methylurea model of mammary carcinogenesis: potential involvement of antiestrogenic mechanisms in vivo

Summary TheN-methyl-N-nitrosurea (NMU) model of hormone-responsive rat mammary carcinogenesis was used to address the hypothesis that melatonin (Mel), the principle hormone of the pineal gland, inhibits tumorigenesis by acting as an anti-promoting rather than an anti-initiating agent. Daily late-afternoon injections of Mel (500 g/day), restricted to the initiation phase of NMU mammary tumorigenesis, were ineffective in altering tumor growth over a 20-week period. When Mel treatment was delayed for 4 weeks after NMU and then continued through the remainder of the promotion phase, only tumor number was significantly lower than in controls. However, when Mel injections encompassed the entire promotion phase, both tumor incidence and number were significantly lower than in the controls. Although elimination of the endogenous Mel signal via pinealectomy promoted tumor growth, the effect was not statistically significant. Serum levels of estradiol and tumor estrogen receptor content were unaltered by either Mel or pinealectomy. While Mel treatment failed to affect circulating prolactin levels, pinealectomy caused a two-fold increase in serum prolactin. The estradiol-stimulated recrudescence of tumors following ovariectomy was completely blocked by either 20, 100 or 500 g Mel/day or tamoxifen (20 g/day). Thus, Mel appears to be an antipromoting hormone that may antagonize the tumor-promoting actions of estradiol in this model of mammary tumorigenesis.Abbreviations Mel melatonin - NMU N-nitroso-N-methylurea - E₂ estradiol - PRL prolactin - ER estrogen receptor - Tam tamoxifen - DMBA 7,12-dimethylbenzanthracene Supported by PHS grant CA-42424 from the NCI     

Aging of FRTL-5 rat thyroid cells causes sensitivity to cytotoxicity induced by tumor necrosis factor-alpha.

While investigating the modulation of the growth and function of the FRTL-5 rat thyroid cell line by recombinant human tumor necrosis factor-alpha (TNF alpha), we noticed that pronounced changes in several response parameters occurred with increasing passage number. For young cells (passage less than 20), TNF alpha by itself slightly increased [3H]thymidine incorporation and DNA content, and had a minimal effect on basal 125I uptake. When combined with TSH, TNF alpha had no influence on TSH-stimulated [3H]thymidine incorporation, but significantly inhibited TSH-stimulated 125I uptake. Compared with young cells, aged cells (passage greater than 40), in contrast, developed a high sensitivity to TNF alpha. TNF alpha markedly stimulated [3H]thymidine incorporation into DNA, inhibited TSH-stimulated 125I uptake per micrograms DNA, but dramatically decreased the total DNA content and cell number. TSH augmented the TNF alpha effect in aged cells, resulting in a further reduction of DNA content. Aphidicolin, a specific inhibitor of DNA polymerase-alpha which is associated with DNA replication, dramatically inhibited TNF alpha-induced [3H]thymidine incorporation in both young and aged cells; this suggested that the effect of TNF alpha on FRTL-5 cell growth is related to DNA replication, rather than DNA repair. 51Cr release from FRTL-5 cells, a measure of cytotoxicity, increased 2-fold over baseline in aged cells at a dose of 400 ng/ml TNF alpha and decreased to 70% of baseline in young cells at this same dose. The protein kinase-A (PKA) and protein kinase-C (PKC) signal transduction mechanisms of TNF alpha in aged cells (passage greater than 40) were also studied. TNF alpha increased cAMP and also increased relative PKA and PKC activity in 1-40 min. Phorbol myristate acetate (PMA), an activator of PKC, increased [3H]thymidine incorporation and DNA content. PMA did not affect the TNF alpha-induced increase in [3H]thymidine incorporation or its reduction of DNA content. When the cells were pretreated with a high concentration of PMA (1 microM/24 h) to down-regulate PKC, the TNF alpha dose-dependent increase in [3H]thymidine incorporation and decrease in DNA content were only slightly inhibited, suggesting that the main effects of TNF alpha are independent of PKC. We conclude that the sensitivity of FRTL-5 cells to the cytotoxic effect of TNF alpha increases with aging.     

Alteration in the transmission of TSH-message to thyroid target in a transplantable rat thyroid tumor

Plasma membranes derived from a transplantable rat thyroid tumor (line 1-5G in Wollman's classification), which is unresponsive to thyrotropin (TSH) but is responsive to dibutyryl 3', 5' cAMP, have been evaluated to localize the defect. TSH binding in tumor plasma membrane is slightly lower than in normal rat thyroid membranes. No change in affinity, but simply a lower capacity was observed. The glycoprotein component of the TSH receptor exhibits similar binding and solubilization properties to the glycoprotein component derived from normal rat thyroid. Analogously to normal rat thyroid membranes, gangliosides more complex than N-acetylneuraminylgalactosylglucosyl-ceramide (GM3) are also present in tumor line 1-5G membranes. Phospholipid content of tumor line 1-5G is 50% lower than that of normal rat thyroid. At variance also with normal rat thyroid, 32P incorporation in tumor line 1-5G phospholipids such as phosphatidylserine and phosphatidylethanolamine is not modified after in vitro incubation with TSH. An even more pronounced effect by TSH on 32P incorporation into phosphatidylinositol is evident in tumor line 1-5G by comparison to normal. The 1-5G thyroid tumor membranes has a 12-fold higher basal adenylate cyclase activity than that of rat thyroid membranes. The high basal adenylate cyclase activity is associated with high ADP ribosylation activity. Both enzymes of tumor are only slightly responsive to TSH. These results suggest that the block in the transmission of TSH message to the cell machinery is localized to the regulatory domains between TSH receptor and adenylate cyclase catalytic subunit.     

Mice with a mutation in the thyroid hormone receptor beta gene spontaneously develop thyroid carcinoma: a mouse model of thyroid carcinogenesis.

The molecular genetic basis of thyroid carcinogenesis is not well understood. Most of the existing models of thyroid cancer only rarely show metastases, and this has limited progress in the understanding of the molecular events in thyroid cancer invasion and metastasis. We have recently generated a mutant mouse by introducing a dominant negative mutant thyroid hormone nuclear receptor gene, TRbetaPV, into the TRbeta gene locus. In this TRbetaPV mouse, the regulation of the thyroid-pituitary axis is disrupted, leading to a mouse with high levels of circulating thyroid-stimulating hormone and extensive hyperplasia of follicular epithelium within the thyroid. As TRbeta(PV/PV) mice, but not TRbeta(PV/+) mice, aged, metastatic thyroid carcinoma developed. Histologic evaluation of thyroids of 5-14-month-old mice showed capsular invasion (91%), vascular invasion (74%), anaplasia (35%), and metastasis to the lung and heart (30%). Previous models of thyroid cancer have focused on genes that control initial carcinogenesis, but this model provides an unusual opportunity to study the alterations in gene regulation that occur with clinically relevant changes during progression and metastasis in a predictable fashion.     

黄曲霉毒素B1诱发大鼠肝癌过程中β连环蛋白的变化

许多研究表明,黄曲霉毒素B1（aflatoxin B1,AFB1）与HCC密切相关,而β连环蛋白是近年肿瘤研究的一个热点,其基因突变和表达异常与HCC等肿瘤密切相关。研究人HCC往往只能对癌及癌旁组织（或加上正常组织）进行比较,无法知道基因在哪个阶段开始出现异常,而且患者往往在发病前接触过很多致癌因素,很难明确是哪些引起β连环蛋白表达量增高。本研究仅用AFB1处理大鼠诱发HCC,于不同时段进行肝活组织检查,[第一段]     

Cepharanthine inhibits two-stage tumor promotion by 12-O-tetradecanoylphorbol 13-acetate and mezerein on skin tumor formation in mice initiated with 7,12-dimethylbenz[a]anthracene

Summary Cepharanthine, isolated fromStephania cepharantha, is one of the bisbenzylisoquinoline-type alka-loids. We have found that it inhibits tumor promotion after topical application in two-stage carcinogenesis in mouse skin. Epidermal ornithine decarboxylase activities inhibited by topical application of cepharanthine, with an 5 g/mouse) and mezerein (5 g/mouse) were found to be inhibited by topical application of cepharanthine, with a ED₅₀ of 1.2 mol and 1.4 mol respectively. These inhibitory effects of cepharanthine are considered to be related to its antitumor activity in two-stage carcinogenesis in mouse skin. Cell-mediated immunosuppression by TPA was unaffected by topical application of cepharanthine. A diet containing 0.005% cepharanthine (about 0.5 mg mouse^– day^–) slightly suppressed the two-stage promotion of skin tumors by twice-weekly applications of 2.5 g TPA for 2 weeks (first stage) followed by twice-weekly applications of 2.5 g mezerein for 23 weeks (second stage) in ICR mice following initiation by 50 g 7,12-dimethylbenz[a]anthracene. Oral administration of cepharanthine inhibits the tumor promotion in two-stage carcinogenesis in mouse skin.Abbreviations DMBA 7,12-dimethylbenz[a]anthracene - DTH delayed-type hypersensitivity - ODC ornithine decarboxylase - TPA 12-O-tetradecanoylphorbol 13-acetate     

Radiation-induced thyroid carcinogenesis as a function of time and dietary iodine supply: an in vivo model of tumorigenesis in the rat

It is believed that a combination of environmental factors with mutagens induces carcinomas derived from thyroid follicular cells. In this study we tried to ascertain whether a single short-term exposure to external radiation is sufficient to induce thyroid carcinomas in rats under long-term high or low dietary iodine intake. Rats were tested over a period of 110 wk under high (approximately 10-fold of normal), normal, and low (approximately 0.1-fold of normal) daily iodine intake. Forty-day-old animals were subjected to single external radiation of 4 Gy or sham radiation. Thyroid function was tested weekly, and thyroid morphology was determined after 15, 35, 55, and 110 wk. Iodine deficiency, but not high iodine intake, led to a decrease in T(3) and T(4) plasma levels, but to an increase in TSH, which became significant after 9 and 11 wk of treatment, respectively. Both high and low iodine treatment significantly increased the proliferation rate and induced thyroid adenomas, but no malignancies after 55 and 110 wk. Radiation with 4 Gy resulted in a significant destruction of the follicular structure. Under high and low iodine intakes (50-80% of animals), but not under normal iodine supply, thyroid carcinomas were observed in irradiated rats. Thus, the increased proliferation rate induced under the experimental conditions described in this study is apparently not sufficient to cause thyroid carcinomas, but the presence of a mutagen-like radiation is required. This model may help to define genetic alterations long before histological changes are detectable.     

p53 constrains progression to anaplastic thyroid carcinoma in a Braf-mutant mouse model of papillary thyroid cancer

Anaplastic thyroid carcinoma (ATC) has among the worst prognoses of any solid malignancy. The low incidence of the disease has in part precluded systematic clinical trials and tissue collection, and there has been little progress in developing effective therapies. v-raf murine sarcoma viral oncogene homolog B (BRAF) and tumor protein p53 (TP53) mutations cooccur in a high proportion of ATCs, particularly those associated with a precursor papillary thyroid carcinoma (PTC). To develop an adult-onset model of BRAF-mutant ATC, we generated a thyroid-specific CreER transgenic mouse. We used a Cre-regulated Braf^V600E mouse and a conditional Trp53 allelic series to demonstrate that p53 constrains progression from PTC to ATC. Gene expression and immunohistochemical analyses of murine tumors identified the cardinal features of human ATC including loss of differentiation, local invasion, distant metastasis, and rapid lethality. We used small-animal ultrasound imaging to monitor autochthonous tumors and showed that treatment with the selective BRAF inhibitor PLX4720 improved survival but did not lead to tumor regression or suppress signaling through the MAPK pathway. The combination of PLX4720 and the mapk/Erk kinase (MEK) inhibitor PD0325901 more completely suppressed MAPK pathway activation in mouse and human ATC cell lines and improved the structural response and survival of ATC-bearing animals. This model expands the limited repertoire of autochthonous models of clinically aggressive thyroid cancer, and these data suggest that small-molecule MAPK pathway inhibitors hold clinical promise in the treatment of advanced thyroid carcinoma.Mutations in the v-raf murine sarcoma viral oncogene homolog B (BRAF) kinase occur in ∼60% of papillary thyroid carcinomas (PTCs) (www.cbioportal.org/public-portal/data_sets.jsp). PTC generally exhibits an excellent prognosis with conventional therapy, including surgery and selective use of radioiodine (1). PTC may progress to clinically aggressive forms of thyroid cancer, including poorly differentiated thyroid carcinoma (PDTC), which exhibits more rapid growth and poorer clinical outcome. Less commonly, PTC progresses to undifferentiated (anaplastic) thyroid carcinoma (ATC) that is associated with a grim prognosis with a median survival of 5 mo and a 1-y survival of only 20% (2).Focused sequencing of clinically aggressive subsets of thyroid cancers including PDTC and ATC suggests acquired cooperating mutations drive thyroid cancer progression (3, 4). Mutations in tumor protein p53 (TP53) occur with increasing frequency in more aggressive forms of thyroid cancer, culminating in ATC, which harbors the highest frequency of TP53 mutations (5–7). ATC may progress from well-differentiated thyroid carcinomas and is also believed to arise spontaneously, possibly from clinically undetectable microscopic well-differentiated thyroid tumors. In the former scenario, ATCs frequently harbor mutations in BRAF, and these mutations are concordant between the anaplastic and papillary components. This implicates BRAF mutation as an initiating somatic genetic event and supports the hypothesis that loss of p53 function is important for progression to ATC (3, 8).Mouse models of thyroid cancer have supported the model of acquired mutations driving tumor progression. Although each study has technical limitations, including embryonic oncogene expression and/or elevated circulating thyroid-stimulating hormone (TSH) levels, this work generally supports the notion that BRAF^T1799A is sufficient to initiate PTC (9–12). In addition, deletion of p53 enabled tumor progression to high-grade thyroid carcinomas in a transgenic mouse model of translocations targeting the ret proto-oncogene (RET/PTC) driven PTC, and a model of follicular thyroid carcinoma initiated by tissue-specific phosphatase and tensin homolog (Pten) deletion (13, 14). These studies provide functional evidence of an important tumor suppressive role for p53 during thyroid carcinoma progression, although to date this has not been tested in models of BRAF-mutant PTC.Given the high frequency of BRAF and RAS mutations in thyroid carcinomas and the success of targeted therapy trials for advanced thyroid cancers, the potential utility of small-molecule inhibitors of the MAPK pathway has garnered much recent attention (15). These drugs have also been studied in models of BRAF-mutant thyroid carcinoma. Initial observations using a thyroid-specific doxycycline-inducible BRAF^T1799A allele suggested that BRAF or mapk/Erk kinase (MEK) inhibition induced thyroid carcinoma regression and differentiation (9). However, a recent study from the same laboratory showed a mitigated response to BRAF (PLX4032, vemurafenib) inhibition in human papillary and ATC cell lines and in an endogenous Braf^V600E-driven PTC mouse model. In response to PLX4032/vemurafenib, feedback inhibition of the human epidermal growth factor receptor 3 (HER3) receptor tyrosine kinase was abrogated, leading to reactivation of MAPK signaling (16). In addition, responses in patients treated with the BRAF inhibitor vemurafenib have exhibited modest activity (17).To develop an adult-onset autochthonous model of clinically aggressive thyroid carcinoma, we generate a thyroid-specific CreER transgenic mouse and use conditional Braf^T1799A and Trp53 alleles. We demonstrate that expression of BRAF^V600E is sufficient to initiate tumorigenesis in adult animals, and p53 loss enables progression to bona fide ATC recapitulating the cardinal features of the human disease including intrinsic resistance to BRAF inhibitors.     

Polymorphic genetic control of tumor invasion in a mouse model of pancreatic neuroendocrine carcinogenesis

Cancer is a disease subject to both genetic and environmental influences. In this study, we used the RIP1-Tag2 (RT2) mouse model of islet cell carcinogenesis to identify a genetic locus that influences tumor progression to an invasive growth state. RT2 mice inbred into the C57BL/6 (B6) background develop both noninvasive pancreatic neuroendocrine tumors (PNET) and invasive carcinomas with varying degrees of aggressiveness. In contrast, RT2 mice inbred into the C3HeB/Fe (C3H) background are comparatively resistant to the development of invasive tumors, as are RT2 C3HB6(F1) hybrid mice. Using linkage analysis, we identified a 13-Mb locus on mouse chromosome 17 with significant linkage to the development of highly invasive PNETs. A gene residing in this locus, the anaplastic lymphoma kinase (Alk), was expressed at significantly lower levels in PNETs from invasion-resistant C3H mice compared with invasion-susceptible B6 mice, and pharmacological inhibition of Alk led to reduced tumor invasiveness in RT2 B6 mice. Collectively, our results demonstrate that tumor invasion is subject to polymorphic genetic control and identify Alk as a genetic modifier of invasive tumor growth.