16 research outputs found
A análise do trabalho docente na educação a distância: estudo comparativo entre UFSC e IFSC
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Sócio-Econômico, Programa de Pós-Graduação em Administração, Florianópolis, 2015.Muitas são as atribuições do profissional docente nos Cursos ofertados a distância, e não raro estes acumulam paralelamente outras funções, contribuindo de diversas maneiras para os resultados obtidos nos Cursos EAD. Este estudo objetiva analisar o trabalho docente no Curso de Especialização em Gestão Pública do IFSC e da UFSC. Para tanto, se desenvolveu uma pesquisa que considerou como categorias de análise as seguintes dimensões do trabalho docente na EAD: didática, pedagógica, tecnológica e a administrativa. A pesquisa teve uma abordagem qualitativa, sendo enquadrada como descritiva tendo como estratégia o estudo de caso. Foram realizadas pesquisas documentais, bibliográficas e entrevistas semiestruturadas. Na sequência foi realizada uma análise qualitativa dos dados coletados por meio de análise do discurso. Obteve-se como resultado, uma análise do trabalho docente em cada instituição, considerando as seguintes dimensões: pedagógicas, didáticas, tecnológicas e administrativas. Apresenta também as dificuldades encontradas pelos docentes, seja no gerenciamento de um Curso á distância ou nas atividades de ensino aprendizagem. A pesquisa também apresenta uma descrição dos Cursos de Especialização em Gestão Pública em ambas as instituições e dessa forma pode-se perceber as aproximações e distanciamentos os Cursos selecionados, que apesar de possuírem práticas distintas na condução das suas ações, existem pontos convergentes. Compararam-se os resultados encontrados em cada Curso e destacaram-se os aspectos positivos e aqueles que necessitam de melhorias nas práticas docentes de ambas os Cursos, por fim identificaram-se os fatores que influenciaram na efetividade do trabalho docente na educação à distância.Abstract : Many are the duties of the teaching profession in the distance courses offered, and often these accumulate alongside other functions, contributing in various ways to the results obtained in the distance education courses. This study aims to analyze the teaching work in the Specialization Course in Public Management from the IFSC and UFSC. To this end developed a survey that considered as categories of analysis the following dimensions of the teaching work in distance education: teaching, educational, technological and administrative. The research had a qualitative approach, being framed as descriptive, having a strategy case study. Documentary, bibliographic and research semistructured interviews were conducted. Subsequently it carried out a qualitative analysis of the data collected through discourse analysis. Was obtained as a result, an analysis of the teaching work in each institution, considering the following dimensions: pedagogical, didactic, technological and administrative. It also presents the difficulties encountered by teachers, either in managing a course at a distance or in teaching and learning activities. The survey also provides a description of the specialization courses in Public Management in both institutions and thus can realize the similarities and differences selected courses, which even though they possess different practices in the conduct of their actions, there is converging points. They compared the results found in each course and stood out the positive aspects and those that need improvement in teaching practices of both the courses; finally identified the factors that influence the effectiveness of teaching work in distance education
Sistemática de apoio à priorização na gestão do Conselho Comunitário de Segurança : CONSEG Carianos
No full textIn this thesis, we present the development of a system of support
for prioritization in the management of the Community Security
Council - Conseg Carianos, located in Florianopolis - Santa
Catarina. Considering the potential of CONSEG contribution to
public safety and challenges facing management to multiple
demands, interactions and possibilities of action, defined as
research question for the construction of a systematic decision
support: what to prioritize in managing Conseg Carianos ? This
is a qualitative research with descriptive exploratory approach,
which followed the steps Multicriteria Methodology Decision
Support - Constructivist (MCDA-C). The survey was conducted
from August 2014 to November 2015, through semi-structured
interviews, debates and attendance at meetings and Conseg
workshops involving various players in the public security
system in Santa Catarina. From the data analysis, we identified
elements Primary Assessment (EPA), ie, the first concerns raised
by decision makers when faced with a given situation, as well as
the Fundamental Viewpoints (PVFS), which served as the basis
for development of cognitive maps and tree views or values of
hierarchical structure, divided into six themes: empowerment,
participation, information, planning, promotion, and
coordination with other organizations. Each of these themes is
composed of EPA and PVFS, which reflect the themes and
actions considered relevant in the management of Conseg
Carianos, articulated in cognitive maps and tree views. The work
is based on a context of the issue of public safety and violence,
today, with the concept of community policing and the
philosophy of community policing, based on continuous
interaction between law enforcement agencies, community
organizations and citizens in promoting public safety in priority
preventive. It is believed that advances in CONSEG
management, as it sought to contribute through this study, tend
to increase the realization of its potential in the co-production of public safety. Cognitive maps and the trees of views, as a product
of this construction based on MCDA-C, are a tool to help define
the problems and priorities of decision-makers of this Council,
considering its context and its values.Nesta dissertação, apresentamos o desenvolvimento de uma
sistemática de apoio à priorização na gestão do Conselho
Comunitário de Segurança - Conseg Carianos, localizado em
Florianópolis - Santa Catarina. Considerando o potencial de
contribuição dos Consegs para a segurança pública e seus
desafios de gestão frente às múltiplas demandas, interações e
possibilidades de ação, definimos como pergunta de pesquisa
para a construção da sistemática de apoio à decisão: o que
priorizar na gestão do Conseg Carianos? Trata-se de uma
pesquisa qualitativa, com abordagem exploratório-descritivo,
que seguiu etapas da Metodologia Multicritério de Apoio à
Decisão - Construtivista (MCDA-C). A pesquisa foi realizada no
período de agosto de 2014 a novembro de 2015, por meio de
entrevistas semiestruturadas, debates e presença em reuniões e
oficinas do Conseg, envolvendo diversos atores que integram o
sistema de segurança pública em Santa Catarina. A partir da
análise dos dados, foram identificados Elementos Primários de
Avaliação (EPAs), ou seja, as primeiras preocupações
manifestadas pelos decisores quando se deparam com dada
situação, bem como os Pontos de Vista Fundamentais (PVFs),
que serviram de base para a elaboração de mapas cognitivos e
árvores de pontos de vista, ou estrutura hierárquica de valores,
divididas em seis temas: capacitação, participação, informação,
planejamento, divulgação, e articulação com outras
organizações. Cada um desses temas compõe-se de EPAs e
PVFs, que refletem os temas e ações consideradas relevantes na
gestão do Conseg Carianos, articuladas em mapas cognitivos e
árvores de pontos de vista. O trabalho fundamenta-se em uma
contextualização da temática da segurança pública e da
violência, na atualidade, apresentando o conceito de polícia
comunitária e a filosofia do policiamento comunitário, baseada
na interação contínua entre órgãos de segurança pública,
organizações comunitárias e cidadãos na promoção de segurança pública, em caráter prioritariamente preventivo.
Acredita-se que os avanços na gestão de Consegs, como o que
se buscou contribuir por meio deste estudo, tendem a ampliar a
realização de seu potencial na coprodução da segurança pública.
Os mapas cognitivos e as árvores de pontos de vista, como
produto desta construção com base na MCDA-C, são uma
ferramenta para auxiliar na definição dos problemas e
prioridades dos tomadores de decisão desse Conselho,
considerando seu contexto e seus valores.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio
Triagem anti-herpética de amostras da biodiversidade marinha e terrestre: fracionamento biomonitorado da esponja Petromica citrina
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Biológicas, Programa de Pós-Graduação em Biotecnologia e Biociências, Florianópolis, 2013A pesquisa por novos compostos biologicamente ativos obtidos a partir de produtos naturais, nos últimos anos, tem sido incentivada em todo o mundo, pois são considerados muito importantes na descoberta de novos fármacos para varias doenças. Diversas estratégias, baseadas em diferentes tipos de observações, juntamente com triagens randomizadas, têm sido usadas na investigação da biodiversidade com o intuito de contribuir para o aumento do arsenal terapêutico anti-herpético. As infecções causadas pelos vírus herpéticos são um grave problema de saúde pública, devido à capacidade dos mesmos de causarem infecções agudas e recorrentes, além do aparecimento de cepas resistentes ao aciclovir, fármaco de primeira escolha disponível. Diante deste quadro, o Laboratório de Virologia Aplicada da UFSC avalia, há vários anos, a atividade antiviral de produtos naturais e sintéticos, tendo encontrado resultados promissores para muitas das amostras testadas. Inicialmente, a citotoxicidade (CC50) e a atividade anti-HSV (CI50) foram avaliadas através do ensaio colorimétrico do MTT e do ensaio de redução do número de placas de lise, respectivamente. De acordo com os resultados obtidos através da triagem dos representantes oriundos da biodiversidade terrestre e marinha, três amostras (a fração rica em trissulfato de halistanol: TSH e os compostos TSH-A e TSH-C) foram selecionadas devido aos seus promissores índices de seletividade (IS= CC50/CI50) de 15,33; 2,46 e 1,95 frente ao HSV-1 (cepa KOS). O mecanismo de ação foi avaliado através de uma sequência de ensaios, que visou avaliar a possível interferência destas amostras nas diversas etapas do ciclo de replicação viral. Na avaliação do tempo de adição, estas amostras inibiram significativamente a replicação viral, quando foram adicionadas simultaneamente ou até 3h pós-infecção. As amostras avaliadas apresentaram atividade virucida e inibiram a entrada dos vírus nas células Vero (adsorção e penetração). A análise da expressão proteica viral por Western blotting mostrou que as amostras TSH-A e TSH-C inibiram a expressão das proteínas ? (ICP27) e ? (gB), em diferentes intensidades e a TSH foi a única amostra que inibiu a expressão de todas as proteínas virais. Ao serem combinadas com o aciclovir, elas também demostraram efeito sinérgico, em concentrações equivalentes a 2x seus valores de CI50. O conjunto destes resultados indica a potencialidade destas amostras como compostos antivirais, mas ainda são necessários estudos mais aprofundados.Asbtract : The search for new biological active compounds derived from natural products in recent years has been stimulated throughout the world, because they are still considered a very important source to find new medicines against some diseases. Several strategies based in different types of observations and randomized screenings have been used to evaluate the biodiversity in order to increase the number of available anti-herpes drugs. The infections caused by herpesvirus are a serious worldwide public health problem, because these viruses are able to cause acute and persistent infections, besides the emergence of strains resistant to acyclovir, the available drug of choice. In this context, the Laboratory of Applied Virology from UFSC has been evaluating, for several years, the antiviral activity of natural and synthetic products, and found promising results for many of the samples tested. Initially, the cytotoxicity (CC50) and anti-HSV activity (IC50) were assessed by MTT and viral plaque number reduction assays, respectively. According to the results obtained through the anti-HSV screening of different taxons from the terrestrial and marine biodiversity, three samples (fraction rich in halistanol trisulphate: TSH and the compounds TSH-A and TSH-C) were selected due to their promising selectivity indices (SI=CC50/IC50) of 15.33, 2.46 and 1.95 against HSV-1 replication (KOS strain). The mechanism of action was evaluated through different methodological strategies, which aimed to detect the possible interference of these samples at various stages of the viral replication cycle. The evaluation of these samples in the addition time assay showed a significant viral replication inhibition when they were added simultaneously or up to 3h post-infection. These samples were virucidal and also inhibited viral entry into Vero cells (adsorption and penetration). In addition, the analysis of viral protein expression by Western blotting showed that the samples TSH-A and TSH-C inhibited the expression of á (ICP27) and ã (gB) proteins, at different levels of intensity and a TSH was the unique sample who inhibited all virus protein expression. When combined with acyclovir, they also demonstrated synergistic effects at concentrations equivalent to 2x their IC50 values. Taken together, these results indicate the potential of these samples as antiviral compounds, but further studies are needed
BRS Capiaçu e BRS Kurumi: cultivo e uso.
No full textA BRS Capiaçu foi desenvolvida para atender a demanda por cultivares para corte (picado verde) e silagem, apresentando elevado potencial de produção, bom valor nutritivo e facilidade de mecanização. A BRS Kurumi apresenta porte baixo e atende a demanda por cultivares para pastejo, apresentando elevado valor nutritivo e facilidade de manejo em relação às outras variedades de capim-elefante. O plantio dessas cultivares expandiu rapidamente por todo o Brasil. Por terem sido lançadas recentemente, ainda persistem entre os produtores inúmeras dúvidas sobre a melhor forma de explorar essas cultivares. Assim, grande número de perguntas a respeito das recomendações para cultivo e manejo da capineira e da pastagem têm sido encaminhados ao Serviço de Atendimento ao Cidadão (SAC) da Embrapa. Desta forma, o objetivo do livro é descrever as principais características das BRS Capiaçu e BRS Kurumi e esclarecer as questões a respeito do cultivo e uso dessas cultivares, por meio de perguntas e respostas elaboradas por uma equipe multidisciplinar de pesquisadores da Embrapa Gado de Leite e da Embrapa Clima Temperado.Também publicado no formato e-book
Participação da substância cinzenta periaquedutal dorso-lateral na modulação do efeito ansiogênico do pentilenotetrazol em ratos submetidos ao labirinto em cruz elavado
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências da Saúde. Programa de Pós-Graduação em Farmacologia.Estudos prévios demonstraram que a administração sistêmica de [pentilenotetrazol] (PTZ) causa uma redução da exploração dos braços abertos em ratos submetidos ao [labirinto em cruz elevado] (LCE), interpretada como um [efeito tipo-ansiogênico]. Um perfil semelhante de comportamento é observado em ratos submetidos ao LCE após a estimulação química com glutamato na [substância cinzenta periaquedutal dorso-lateral] (SCPdl). No presente trabalho procuramos investigar o papel da SCPdl na modulação do efeito tipo-ansiogêncio do PTZ em ratos submetidos ao teste/re-teste no LCE. Nossos resultados confirmaram o efeito tipo-ansiogênico do PTZ sistêmico em ratos que receberam líquor na SCPdl. O efeito do PTZ foi bloqueado após administração de lidocaína na SCPdl, mas não no colículo superior, de ratos submetidos ao teste no LCE, sugerindo que a SCPdl seria uma estrutura chave na expressão do efeito tipo-ansiogênico induzido pelo PTZ. Além disso, nossos resultados sugerem também que os neurotransmissores GABA e GLU presentes na SCPdl parecem mediar a expressão do efeito tipo-ansiogênico do PTZ, uma vez que o aumento da atividade GABAérgica ou a redução da atividade glutamatérgica bloquearam o efeito do PTZ sistêmico. Os resultados obtidos a partir do protocolo teste/re-teste sugerem que a SCPdl estaria envolvida na mediação da expressão do efeito ansiogênico do PTZ, porém não estaria relacionada à aquisição de aprendizado. Em resumo, nossos resultados sugerem um papel importante da SCPdl na organização da resposta animal para um medo aumentado, como o produzido pelo PTZ
Of good use or serious pleasure : Vitruvius Britannicus and early eighteenth century architectural discourse
No full textThe central thesis of this work is that Colen Campbell's
three volume Vitruvius Britannicus (1715-25) is not, as it has been frequently seen, a Palladian manifesto designed to change architectural practice in England (and in the process Campbell's own fortunes as an architect), but rather a publication celebrating architectural achievements, consumed by polite society.
The twentieth century view of Vitruvius Britannicus, stems from John Surnmerson's seminal work, Architecture in Britain 1530-1830. It posits Vitruvius Britannicus as a stylistic manifesto that served the particular interests of Colen Campbell and his associates as advocates of and builders in the Palladian style, and foregrounds the idea of the author. This view has been incorporated almost unquestioningly into subsequent interpretations not least
because it conforms to a powerful 'Whig' interpretation of history emphasising periodisation, style, revolution, development, and the search for origins. In contrast I argue that Vitruvius Britannicus met the demands of a market interested in architecture as a topic of polite
conversation. The subscription lists for Vitruvius Britannicus show that it was neither priced to be, nor received as, a builder's manual, nor was it a stylistic manifesto. Rather, it was a celebration of contemporary British architecture that gave pleasure and some instruction to polite society. Drawing on disciplines outside of art and architectural history, I consider
Vitruvius Britannicus as an object of consumption offering an alternative reading of the publication that highlights a number of important avenues for further research.
Chapter 1 positions the thesis within critiques of stylistic history. Chapter 2 briefly introduces
some historiographic issues, and then considers the contents and style of the publication, and
the nature of its subscribers. This highlights issues neglected in histories of Vilruvius Britannicus and challenges many of the commonly held conceptions of the publication. These conceptions are then examined in Chapter 3 in the light of evidence and issues raised in the
previous chapter. Chapter 4 considers other architectural and illustrated books and positions Campbell's work within wider publishing paradigms such as cartography and a literature of tourism. Chapter 5 outlines some of the intellectual ideas that influenced the way in which
publications such as Vitruvius Britannicus were understood. This is developed in Chapter 6 which considers the way in which Vitruvius Britannicus functioned within a contemporary
architectural discourse that codified the group identity of a polite elite
Seismicity and regional tectonics of the Estremadura, Southwestern Portugal
No full textThe RESTE Project was an integrated geophysical-geological study of the Estremadura, southwestern Portugal. The core of the programme consisted of the acquisition and analysis of microearthquake data. This was complemented by an investigation of the structural evolution of the sedimentary basins of the Estremadura. The geological evolution of the Lusitanian Basin was strongly marked by the reactivation of Palaeozoic basement faults, in response to a sequence of tectonic events: opening of the Central Atlantic, opening of the North Atlantic and Alpine convergence between Africa and Eurasia. The current tectonics are regarded as a subdued continuation of the Miocene deformation (Betic Orogeny), and the "tectonic memory" revealed by the Lusitanian and Lower Tagus Basins is explored to characterize the current tectonic processes. Strike-slip tectonics are identified as a dominant feature of several stages of the evolution of the basins, with particular relevance during the Miocene. The technique of "backstripping" is applied to well data, to constrain the history of vertical movement in the basins. This analysis highlighted the pre mature truncation, in the Late Jurassic, of a normal passive-margin evolution. Tectonic unstability caused the structural inversion of areas within the basins, and seems to have inhibited the predictable thermal subsidence. The rifting process, initially taking place at the Lusitanian Basin, jumped westwards in the Late Jurassic. Crustal underplating and the activity of transfer faults are in-voked as possible explanations for the subsequent deformation of the aborted rift. An upper-plate margin configuration is in good agreement with several observations. The tendency for structural inversion continued throughout theCretaceous, and with the onset of the Alpine convergence in the Turonian the control of the tectonic activity seems to have switched from the Atlantic to the Mediterranean. This reinforced the tectonic unstability, marked by magmatic activity and by a regional upwarp that was to last until the Eocene. Of particular interest was the behaviour, during the Late Cretaceous, of the Setúbal Peninsula sub-basin, which seems to have tilted towards the NW as a block, with a hinge line along the present Lower Tagus Valley. When sedimentation was resumed in the Eocene, a pattern of differential vertical movement was established, with some areas continuing to undergo inversion while nearby areas subsided. This pattern characterized the Cainozoic evolution of the basins, and probably still applies to the neotectonic deformation. The activity of strike-slip basement faults, reactivated under the compressive regime caused by the Afro-Eurasian conver-gence, is proposed as the best explanation for the Miocene deformation, with particular relevance for the Lower Tagus Valley. The RESTE Microearthquake Survey is described, and the data acquired with the RESTE network are analysed. The local earthquakes are accurately located, and focal mechanism solutions are obtained for some of them. This information is used to discuss a neotectonic model for the Lower Tagus Valley. In view of their small magnitudes (l.1< M(_L) < 3.8), the focal mechanisms of these events cannot be interpreted directly in terms of the current tectonics. Such small events are usually local readjustments to previous episodes of deformation. However, such features as the along-strike reversal of the polarity of vertical motion or the coexistence at the same region of different types of source mechanism are diagnostic of strike-slip deformation. This model was supported by the occurrence of a macroearthquake (M(_D)=3.8) with an interpreted source mechanism of sinistral strike-slip. The alignment of four hypocentres along the direction of the Lower Tagus Valley, with a compatible orientation of the interpreted nodal planes, supports the existence of a crustal fracture associated with the Valley. The hypocentral depths of the recorded events reach 20 km, showing that the basement faults responsible for the seismicity affect at least the entire upper crust. Since the limited existing data suggest a high level of heat flow in the Lusitanian Basin, the depths reached by the microearthquakes may indicate an abnormally thick seismogenic layer. An investigation of the broad velocity structure of the lithosphere underneath the RESTE Network using the technique of teleseismic tomographic inversion suggested a correlation between Moho undulations and the inversion of areas of the Lusitanian Basin, and this may indicate that the controlling faults cut the entire crust. In order to provide a rationale for the intraplate seismicity of western Portugal, the neotectonics of Iberia are discussed, and a new kinematic model, centred on the idea of continental extrusion, is proposed. According to the model, a continental block formed by Iberia and northern Morocco is being pushed west wards by the convergence between Africa and Eurasia. The resistance offered by the oceanic parts of the plates varies across the East Azores Transform, leading to dextral shear in the Betic Range. The regional stress field induced by the continental convergence can explain the reactivation, in a simple-shear regime, of basement faults of Hercynian orientation, in particular that proposed for the Lower Tagus Valley
Measurement of the muon charge asymmetry in inclusive pp →W + X production at s=7 TeV and an improved determination of light parton distribution functions
No full textPublished by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published articles title, journal citation, and DOI.Measurements of the muon charge asymmetry in inclusive pp → W + X production at root s= 7 TeV are
presented. The data sample corresponds to an integrated luminosity of 4.7 fb−1 recorded with the CMS
detector at the LHC. With a sample of more than 20 million W → μν events, the statistical precision is
greatly improved in comparison to previous measurements. These new results provide additional
constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable
x from 10−3 to 10−1. These measurements and the recent CMS measurement of associated W þ charm
production are used together with the cross sections for inclusive deep inelastic e p scattering at HERA in
a next-to-leading-order QCD analysis. The determination of the valence quark distributions is improved,
and the strange-quark distribution is probed directly through the leading-order process g þ s → W þ c in
proton-proton collisions at the LHC.the Austrian Federal Ministry of Science and Research and the Austrian Science Fund; the Belgian Fonds de la Recherche Scientifique, and Fonds voor Wetenschappelijk Onderzoek; the Brazilian Funding Agencies (CNPq, CAPES, FAPERJ, and FAPESP); the Bulgarian Ministry of Education and Science; CERN; the Chinese Academy of Sciences, Ministry of Science and Technology, and National Natural Science Foundation of China; the Colombian Funding Agency (COLCIENCIAS); the Croatian Ministry of Science, Education and Sport, and the Croatian Science Foundation; the Research Promotion Foundation, Cyprus; the Ministry of Education and Research, Recurrent financing contract SF0690030s09 and European Regional Development Fund, Estonia; the Academy of Finland, Finnish Ministry of Education and Culture, and Helsinki Institute of Physics; the Institut National de Physique Nucléaire et de Physique des Particules/CNRS, and Commissariat à l’Énergie Atomique et aux Énergies Alternatives/CEA, France; the Bundesministerium für Bildung und Forschung, Deutsche Forschungsgemeinschaft, and Helmholtz-Gemeinschaft Deutscher Forschungszentren, Germany; the General Secretariat for Research and Technology, Greece; the National Scientific Research Foundation, and National Innovation Office, Hungary; the Department of Atomic Energy and the Department of Science and Technology, India; the Institute for Studies in Theoretical Physics and Mathematics, Iran; the Science Foundation, Ireland; the Istituto Nazionale di Fisica Nucleare, Italy; the Korean Ministry of Education, Science and Technology and the World Class University program of NRF, Republic of Korea; the Lithuanian Academy of Sciences; the Mexican Funding Agencies (CINVESTAV, CONACYT, SEP, and UASLP-FAI); the Ministry of Business, Innovation and Employment, New Zealand; the Pakistan Atomic Energy Commission; the Ministry of Science and Higher Education and the National Science Centre, Poland; the Fundação para a Ciência e a Tecnologia, Portugal; JINR, Dubna; the Ministry of Education and Science of the Russian Federation, the Federal Agency of Atomic Energy of the Russian Federation, Russian Academy of Sciences, and the Russian Foundation for Basic Research; the Ministry of Education, Science and Technological Development of Serbia; the Secretaría de Estado de Investigación, Desarrollo e Innovación and Programa Consolider-Ingenio 2010, Spain; the Swiss Funding Agencies (ETH Board, ETH Zurich, PSI, SNF, UniZH, Canton Zurich, and SER); the National Science Council, Taipei; the Thailand Center of Excellence in Physics, the Institute for the Promotion of Teaching Science and Technology of Thailand, Special Task Force for Activating Research and the National Science and Technology Development Agency of Thailand; the Scientific and Technical Research Council of Turkey, and Turkish Atomic Energy Authority; the Science and Technology Facilities Council, UK; the U.S. Department of Energy, and the U.S. National Science Foundation. Individuals have received support from the Marie-Curie programme and the European Research Council and EPLANET (European Union); the Leventis Foundation; the A. P. Sloan Foundation; the Alexander von Humboldt Foundation; the Belgian Federal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); the Ministry of Education, Youth and Sports (MEYS) of Czech Republic; the Council of Science and Industrial Research, India; the Compagnia di San Paolo (Torino); the HOMING PLUS programme of Foundation for Polish Science, cofinanced by EU, Regional Development Fund; and the Thalis and Aristeia programmes cofinanced by EU-ESF and the Greek NSRF
Towards the optimization of tumor targeting radiolabeled peptides for molecular imaging and therapy
No full textRadiopharmaceuticals based on regulatory peptides have become an indispensable tool in nuclear medicine for the diagnosis (molecular imaging) and radionuclide therapy of cancer. The specificity of these radiopeptides towards G-protein-coupled receptors (GPCR), which are overexpressed by various cancer cells and their favorable pharmacological properties make them ideal vectors for the targeted delivery of radioactivity to tumors and metastases. However, there are still challenges to be met in order to develop peptide-based radiopharmaceuticals with ideal properties in terms of imaging quality and therapeutic efficacy where therapeutic radionuclides are employed.
A potential drawback of several radiolabeled peptides under investigation is represented by a rapid washout of radioactivity after receptor-mediated internalization into tumor cells. In certain cases, the washout of radioactivity from cells occurs at a rate comparable to that required for accumulation in cancerous tissues. This not only renders the initial efforts of targeted delivery in part futile but also results in an imaging quality and therapeutic efficiency lower than achievable. To address this issue, novel strategies are needed to improve the cellular retention of the radioactivity. A possible approach may include the employment of multi-targeting radioconjugates made of different moieties specific for extra- and intracellular targets. Towards this goal, we investigated the combination of tumor targeting peptides with an additional moiety specific for an intracellular target and radiolabeled the conjugate with the 99mTc-tricarbonyl core as a reporter probe for single-photon emission computed tomography (SPECT). We envisioned that enabling interactions of radioconjugates with intracellular targets after receptor-mediated uptake by endocytosis would result in the trapping of radioactivity in tumors.
Specifically, we combined a modified binding sequence of the peptide bombesin, [Nle14]BBS(7-14), for extracellular targeting of the tumor-associated gastrin releasing peptide receptor (GRP-r) with a triphenylphosphonium group for intracellular targeting of the organelle mitochondria or with the peptide shepherdin, an inhibitor of the cytosolic chaperon heat-shock protein 90 (Hsp90). The conjugates were assembled by the "Click-to-Chelate" approach, an efficient synthetic strategy for the preparation of bifunctional 99mTc-labeled radiopharmaceuticals. The radioconjugates were evaluated in vitro using GRP-r-overexpressing PC-3 cells. Our investigations revealed that the additional moiety for intracellular targeting did not impact the tumor-targeting capability of the bombesin-derived conjugates but neither did it result in an improved cellular retention of the radioactivity. Drawing from our experience and considering recent literature data, we conclude that endosomal entrapment or lysosomal degradation of the bifunctional radiopeptide conjugates is likely to impede with intracellular interactions and thus, responsible for the observed unaltered cellular efflux of radioactivity. Future studies will be directed towards the combination of bifunctional radiopeptide conjugates with drug delivery systems designed to facilitate endosomal escape.
A different approach for the optimization of peptidic radiotracers includes the improvement of their metabolic stability since most of them exhibit a very short biological half-life due to rapid degradation by endogenous peptidases. Enhancement of the stability of radiopeptides results in a prolonged circulation time in the blood and, as a consequence, an improved tumor uptake in vivo. A number of different strategies have been reported for the stabilization of regulatory peptides, however, with varying degree of success in providing peptidomimetics with retained affinity to the corresponding GPCR. In an effort to probe a novel peptide backbone modification methodology, the use of 1,4-disubstituted 1,2,3-triazoles as metabolically stable trans amide bond isosters was investigated. The systematic replacement of amide bonds within the binding sequence of the tumor-affine peptide bombesin, [Nle14]BBS(7-14), by triazoles provided a series of 177Lu-labeled peptidomimetics with both retained affinity towards GRP-r and an increased stability in blood serum. In vivo evaluation of a lead compound in xenografted mice showed that the enhanced stability of the radiopeptidomimetic resulted in a doubling of the uptake of radioactivity in tumors. The described amide-to-triazole substitution methodology is currently being applied to other tumor targeting peptides of medicinal interest.
The specificity and affinity of radiopeptides towards different receptor subtypes is another aspect to consider for optimizations. Inhomogeneous expression of receptor subtypes by tumors may influence the efficiency of a radiotracer. For example, intratumoral administration of radiolabeled substance P (SP) led to significant differences in the clinical response of patients suffering from gliomas despite proven expression of its target, the neurokinin-1 receptor (NK1R). In an effort to identify factors that may be responsible for the varying therapeutic outcome observed, several SP conjugates were evaluated in vitro using four established glioma cell lines differing in their level of RNA expression of the full length and truncated receptor isoforms. Cell binding and internalization of SP-conjugates were only observed with cell lines exhibiting high expression of RNA of the full-length NK1R. Pre-therapeutic screening for NK1R isoforms may therefore be advisable for the selection of glioma patients for NK1R-targeted radionuclide therapy
