Epidermal growth factor (EGF) regulates pituitary development, hormone synthesis, and cell proliferation. Although ErbB receptor family members are expressed in pituitary tumors, the effects of EGF signaling on pituitary tumors are not known. Immunoprecipitation and Western blot confirmed EGF receptor (EGFR) and p185 c-neu protein expression in GH3 lacto-somatotroph but not in adrenocorticotropic hormonesecreting AtT20 pituitary tumor cells. EGF (5 nmol/L) selectively enhanced baseline (f4-fold) and serum-induced (>6-fold) prolactin (PRL) mRNA levels, whereas gefitinib, an EGFR antagonist, suppressed serum-induced cell proliferation and Pttg1 expression, blocked PRL gene expression, and reversed EGF-mediated somatotroph-lactotroph phenotype switching. Downstream EGFR signaling by ERK, but not phosphoinositide-3-kinase or protein kinase C, mediated the gefitinib response. Tumors in athymic mice implanted s.c. with GH3 cells resulted in weight gain accompanied by increased serum PRL, growth hormone, and insulin growth factor 1. Gefitinib decreased tumor volumes and peripheral hormone levels by f30% and restored normal mouse body weight patterns. Mice treated with gefitinib exhibited decreased tumor tissue ERK1/2 phosphorylation and downregulated tumor PRL and Pttg1 mRNA abundance. These results show that EGFR inhibition controls tumor growth and PRL secretion in experimental lacto-somatotroph tumors. EGFR inhibitors could therefore be useful for the control of PRL secretion and tumor load in prolactinomas resistant to dopaminergic treatment, or for those prolactinomas undergoing rare malignant transformation. [Cancer Res 2008;68(15):6377-86]
Intrinsic and extrinsic stimuli result in profound pituitary growth changes ranging from hypoplasia to hyperplasia. Pituitary tumor transforming gene (PTTG) abundance correlates with pituitary trophic status. Mice with Pttg inactivation exhibit pituitary hypoplasia, whereas targeted pituitary PTTG overexpression driven by alpha-subunit glycoprotein (alphaGSU) promoter results in focal pituitary hyperplasia. To test the impact of pituitary hyperplasia on tumor development, we crossbred alphaGSU.PTTG with Rb+/- mice, which develop pituitary tumors with high penetrance. Pituitary glands of resulting bitransgenic alphaGSU.PTTGxRb+/- mice were compared with monotransgenic alphaGSU.PTTG, Rb+/-, and wild-type mice. Confocal microscopy showed that PTTG-overexpressing cells have enlarged nuclei and marked redistribution of chromatin, and electron microscopy of alphaGSU.PTTG pituitaries showed enlarged gonadotrophs with prominent Golgi complexes and numerous secretory granules. These morphological findings were even more remarkable in alphaGSU.PTTGxRb+/- pituitaries. Mice from all four genotypes were sequentially imaged by magnetic resonance imaging to evaluate pituitary volume, and glands from alphaGSU.PTTGxRb+/- mice were the largest as early as 2 months of age (P = 0.0003). Cumulative incidence of pituitary tumors visualized by magnetic resonance imaging did not differ between Rb+/- and alphaGSU.PTTGxRb+/- mice. However, anterior lobe tumors determined after necropsy were 3.5 times more frequent in alphaGSU.PTTGxRb+/- than in Rb+/- mice (P = 0.0036), whereas the frequency of intermediate lobe tumors was similar. In summary, alphaGSU.PTTGxRb+/- pituitary glands exhibit enhanced cellular activity, increased volume, and higher prevalence of anterior pituitary tumors, indicating that changes in pituitary PTTG content directly relate to both pituitary trophic status and tumorigenic potential.
The role of tumor stem cells in benign tumors such as pituitary adenomas remains unclear. We investigated whether cells within pituitary adenomas that spontaneously develop in Rb+/− mice are hierarchically distributed with a subset being responsible for tumor growth. Cells derived directly from such tumors grew as spheres in serum-free culture medium supplemented with EGF and bFGF. Some cells within growing pituitary tumor spheres (PTS) expressed common stem cell markers (Sca1, Sox2, Nestin, CD133), but were devoid of hormone-positive differentiated cells. Under subsequent differentiating conditions (matrigel-coated growth surface), PTS expressed all six pituitary hormones. We next searched for specific markers of the stem cell population and isolated a Sca1+ cell population that showed increased sphere formation potential, lower hormone mRNA expression, higher expression of stem cell markers (Notch1, Sox2, Nestin), and increased proliferation rates. When transplanted into NOD scid gamma mice brains, Sca1+ pituitary tumor cells exhibited higher rates of tumor formation (brain tumors observed in 11/11 [100%] vs. 7/12 [54%] of mice transplanted with Sca1+ and Sca1− cells, respectively). Magnetic resonance imaging and histological analysis of brain tumors showed that those derived from Sca1+ pituitary tumor cells were also larger and plurihormonal. Our findings show that Sca1+ cells derived from benign pituitary tumors exhibit an undifferentiated expression profile and tumor proliferative advantages, and we propose that they could represent putative pituitary tumor stem/progenitor cells.
RESUMOAcromegalia é uma doença debilitante e desfigurante que, se não controlada adequadamente, reduz a expectativa de vida do paciente.Complicações cardiovasculares e respiratórias representam as principais causas de morte nos acromegálicos. Atualmente, o diagnóstico é realizado de acordo com as diretrizes do consenso de 2000: ausência de supressão do GH para um valor <1ng/mL e IGF-1 elevado. Avanços em todas as modalidades terapêuticas têm ocorrido, propiciando o controle bioquímico da doença em um número cada vez maior de pacientes. Estudos prévios mostraram que a obtenção de níveis seguros de GH (GH médio <2,5ng/mL) e de IGF-1 normal reduz a taxa de mortalidade para o normal. Em 2002, foram publicadas diretrizes para o manejo da acromegalia, o qual envolve, muitas vezes, uma abordagem multidisciplinar. Neste artigo, fazemos uma avaliação crítica do que dispomos no Brasil para seguirmos as diretrizes estabelecidas nos consensos sobre diagnóstico e tratamento da acromegalia. ABSTRACT Diagnosis and Treatment of Acromegaly in Brazil.Acromegaly is a disabling and disfiguring illness, which, if not adequately controlled, decreases life expectancy. Cardiovascular and respiratory complications represent the main causes of death in acromegalic patients. Nowadays, the diagnosis is made following the guidelines reported in the 2000 consensus: Failure of GH to suppress to less than 1ng/mL and an increased IGF-1. Progress in all therapeutic modalities has been made, allowing biochemical disease control in more patients. Previous studies demonstrated that achieving safe GH levels (mean GH <2.5ng/mL) and normal IGF-1 decreases mortality rate to normal. In 2002, the guidelines for management of acromegaly were published which encompass, many times, a multidisciplinary approach. In this article, we critically evaluate what is available in Brazil that allows us to follow the guidelines established in the diagnosis and treatment consensus.
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