Tese (doutorado)—Universidade de Brasília, Instituto de Química, Programa de Pós-Graduação em Química, 2013. / Submitted by Alaíde Gonçalves dos Santos (alaide@unb.br) on 2014-01-10T10:55:15Z No. of bitstreams: 1 2013_DanielAugustoBarradeOliveira.pdf: 2428120 bytes, checksum: c456b5418b233575e486a336a32f5cb7 (MD5) / Approved for entry into archive by Guimaraes Jacqueline(jacqueline.guimaraes@bce.unb.br) on 2014-02-17T13:52:04Z (GMT) No. of bitstreams: 1 2013_DanielAugustoBarradeOliveira.pdf: 2428120 bytes, checksum: c456b5418b233575e486a336a32f5cb7 (MD5) / Made available in DSpace on 2014-02-17T13:52:04Z (GMT). No. of bitstreams: 1 2013_DanielAugustoBarradeOliveira.pdf: 2428120 bytes, checksum: c456b5418b233575e486a336a32f5cb7 (MD5) / As proteínas quinases são importantes por atuar em processos biológicos conhecidos, como a transdução de sinais. Esses processos estão intimamente relacionados com o desenvolvimento de neoplasias malignas. Desse modo, o conhecimento da atuação de drogas, relacionadas com essas proteínas, é relavante para o tratamento de alguns tipos de câncer. Neste trabalho, procurou-se estudar inibidores da proteína quinase de adesão focal (FAK), a fim de correlacionar propriedades teóricas, obtidas pela química computacional, com atividades biológicas calculadas a partir do IC50, para auxiliar no entendimento entre essas drogas e a FAK. Para realizar os cálculos foram usadas diversas aproximações de modelagem molecular, dentre as quais, mecânica molecular, métodos ab initio, e métodos híbridos. Para a aproximação de mecânica quântica foram usados os métodos Hartree-Fock, teoria do funcional de densidade, e semi-empíricos PM3, PM6 e MNDO, para descrever a interação entre o sítio catalítico da FAK e os inibidores. O programa O programa auto-docking Vina foi usado para o ancoramento rígido. As atividades de inibidores da classe 7-h-pirrolo-pirimidina foram comparadas com dados provenientes da mecânica quântica, cujo resultado mostrou a importância dos orbitais de fronteira próximos ao aminoácido Cys502. Quanto mais estendidos esses orbitais, maior poderá ser atividade de inibição da FAK. São ainda observadas interações moleculares com os aminoácidos Arg424 e Lys454. Os inibidores dasatinib, sulfonamida e tiazole também foram estudados com métodos de química quântica. Esses inibidores mostram tendências químicas semelhantes com aqueles da classe pirrolo pirimidina, no que se refere às interações com os aminoácidos da tríade catalítica, enfatizando a necessidade dessas interações na construção de novos inibidores. Além disso, a partir da análise de componentes principais, foi mostrada uma correlação entre atividades e propriedades eletrônicas. A soma de todos esses estudos leva a novas fronteiras para o entendimento da interação de fármacos inibidores da proteína quinase e, consequentemente, a compreensão da inibição da metástase, que são uma das maiores causas de morte no mundo moderno. _______________________________________________________________________________________ ABSTRACT / The kinases proteins play important role acting in known biological process, as the signal transduction. These processes are strongly related to the development of malignant neoplasms. Therefore, the knowledge of the drug action related to the kinase protein is relevant for the cancer treatment. In this work, it was studied inhibitors of focal adhesion kinase (FAK) protein in order to correlate theoretical properties with biological activity via IC50, to understand the interaction between these drugs with FAK. In order to perform the calculations it was employed several approaches of molecular modeling, as molecular mechanics, ab initio and hybrid methods. For the quantum mechanical approach we have used Hartree-Fock, density functional theory and semi-empirical PM3, PM6, MNDO methods to describe the interaction between the catalytic site of FAK binding and the selected inhibitors. Auto Docking Vina program was employed to perform the rigid docking. The inhibitor activities of 7-h-pirrole-pirimidines were compared to the results of quantum mechanical approaches, and these results shows the important relation to the frontier orbitals close to the Cys502 aminoacid. The largest contribution of these orbitals is closely related to the FAK inhibition. The molecular interaction with Arg454 and Lys454 aminoacids were also showed. Dasatinib, sulfonamide and thiazole inhibitors also presents these main interactions, emphasizing the relevance of catalytic site interaction of FAK with new inhibitors. Furthermore, from the principal component analysis, it was shown a correlation between activity and electronic properties. The present study leads to new frontiers for the understanding the interaction between focal adhesion kinase and the inhibitors, which is related to the metastase, one o the main reason of death in the world.

Abstract FAP52 (focal adhesion protein, 52 kDa) is a focal adhesion-associated protein composed of a highly α-helical NH2-terminus containing a poorly characterized FCH (Fes/CIP4 homology) domain, unstructured linker region and the COOH-terminal SH3 domain. FAP52 is also known as PACSIN 2 or syndapin II. Together with other PACSINs and syndapins FAP52 shares a common domain architecture. The aim of this study was to characterize FAP52 in structural and functional terms. The function was pursued by identifying binding partners for FAP52, and by overexpressing the recombinant FAP52 in cultured cells. For the structural studies, various physico-chemical methods, such as chemical cross-linking, gel filtration chromatography, circular dichroism and X-ray crystallography were applied. In addition, the histological distribution of FAP52 in chicken tissues was explored. FAP52 binds filamin, a protein that regulates the dynamics of the cytoskeleton by crosslinking actin filaments. The binding site in FAP52 was mapped to the NH2-terminal 184 amino acids, of which the residues 146–184 form the core of the binding. In filamin, the binding site resides in the repeats 15–16 in the rod-like molecule encompassing 24 such repetitive domains. Overexpression of FAP52 or its filamin-binding domain in chicken embryo heart fibroblasts induced the formation of filopodial extensions on the cell surface and reduced the number of focal adhesions, suggesting a role in the organization of the cellular cytoskeleton and in cell adhesion machinery. Experiments utilizing surface plasmon resonance analysis, size exclusion chromatography and chemical cross-linking showed that FAP52 self-associates in vitro and in vivo. The region responsible for the self-association was mapped to the amino acids 146–280, which is predicted to fold into a coiled-coil arrangement. FAP52 was crystallized by using the hanging-drop vapor-diffusion method and ammonium sulfate grid screen. Native dataset was collected from two crystals, which diffracted to 2.8 Å and 2.1 Å resolution. For one form of crystals, phasing was performed using the native dataset and the datasets from two xenon-derivatized crystals. X-ray crystallography studies revealed a dimer in asymmetric unit. Histological and in vitro studies showed that, in liver, FAP52 is preferentially expressed in bile canaliculi. In other tissues, FAP52 showed a specific staining pattern in gut, kidney, brain and gizzard. Together, these data show that FAP52 self-associates in vivo and, probably via its interaction with its binding partner filamin, participates in the organization of the cytoskeletal architecture, especially of the cell surface protrusions, such as filopodia and microvilli of bile canaliculi.

Adhesion complexes (ACs) are large macromolecular complexes of integrins and associated proteins that connect the actin cytoskeleton to the extracellular matrix. In migrating cells, ACs are highly dynamic -- forming and maturing at the cell front and disassembling at the cell rear. The turnover of ACs enables and localises the necessary traction forces required for cell migration. There is evidence for the spatiotemporal recruitment of specific proteins during AC maturation or disassembly; however, a holistic understanding of the compositional changes to ACs during these states is lacking. To this end, we sought to characterise the dynamic changes that occur at ACs during turnover using a mass spectrometry (MS)-based proteomics approach. A major challenge in studying AC turnover is the desynchronised nature of AC formation, maturation and disassembly within a population of cells. Therefore a nocodazole-washout assay was used to synchronise microtubule-induced AC maturation and disassembly. To study the dynamics of AC turnover by MS, an AC isolation method was optimised for use with the nocodazole-washout assay. Subsequently, the maturation of ACs by the loss of microtubules was studied by MS-based proteomics, and it was found that this resulted in the overall accumulation of adhesion proteins, and also the conversion of fibrillar adhesions to focal adhesions. Studying the dynamic process of AC disassembly requires a sensitive MS quantification method; as such, label-free quantitative methods were compared, and it was found that LC-MS peak ion intensity quantification performed better than spectral counting. Using optimised methodologies for isolation of ACs and MS quantification, the dynamics of AC disassembly was analysed over the course of the nocodazole-washout assay. It was found that in general, microtubules were enriched around ACs, whereas many structural AC proteins decreased over time. In summary, we have optimised methods for the study of ACs by MS-based proteomics, and applied these methods to the study of AC turnover.

The protein p130Cas (human ortholog BCAR1) is a major substrate for phosphorylation by the Src family kinase and plays a central role in oncogenic transformation. Increased level of BCAR1 correlates with primary tumour growth and cancer progression. Localized to focal adhesion, p130Cas serves as a mechanosensor and mediates key interactions with the extracellular environment. The structure of p130Cas is crucial for its function, mainly the anchoring domains SH3 and CCH, together with the substrate domain which is extended when under tension. This Master's thesis presents a newly developer FRET mechanosensor based on the structure of p130Cas. The sensor utilizes the anchoring domains of p130Cas for proper localization to focal adhesions, where it can detect tension in living cells. Key words: p130CAS, FRET, focal adhesions, mechanosensing

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第20587号 / 農博第2239号 / 新制||農||1052(附属図書館) / 学位論文||H29||N5076(農学部図書室) / 京都大学大学院農学研究科応用生命科学専攻 / (主査)教授 植田 和光, 教授 矢﨑 一史, 教授 宮川 恒 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

The protein p130Cas (human ortholog BCAR1) is a major substrate for phosphorylation by the Src family kinase and plays a central role in oncogenic transformation. Increased level of BCAR1 correlates with primary tumour growth and cancer progression. Localized to focal adhesion, p130Cas serves as a mechanosensor and mediates key interactions with the extracellular environment. The structure of p130Cas is crucial for its function, mainly the anchoring domains SH3 and CCH, together with the substrate domain which is extended when under tension. This Master's thesis presents a newly developer FRET mechanosensor based on the structure of p130Cas. The sensor utilizes the anchoring domains of p130Cas for proper localization to focal adhesions, where it can detect tension in living cells. Key words: p130CAS, FRET, focal adhesions, mechanosensing

Introdução: A isquemia cerebral é uma desordem da função cerebral ocasionado pela supressão sanguínea no tecido cerebral sem nenhuma outra causa aparente do que a vascular. Estudos revelam os danos causados pela isquemia cerebral focal repercutem não apenas na região da lesão isquêmica, mas também em outras regiões do encéfalo, dentre elas o cerebelo. O etanol atua diminuindo o tempo de reação do corpo e a resposta reflexa, produzindo até mesmo perda de coordenação motora. Por tempos, estudos tem verificado a ação do etanol no cerebelo. Objetivos: Este trabalho tem por objetivo analisar o córtex cerebelar de ratos submetidos a um modelo experimental de isquemia cerebral focal transitória por oclusão da ACM durante 90 minutos, seguida por reperfusão de 48 horas, associado ou não a modelo de alcoolismo. Material e métodos: Foram utilizados 50 ratos Wistar adultos, subdivididos em 5 grupos experimentais: grupo controle (C): animais submetidos apenas à anestesia; grupo sham (S): animais submetidos à simulação completa do procedimento cirúrgico; grupo isquêmico (I): animais submetidos à isquemia cerebral focal por 90 minutos seguido por reperfusão de 48 horas; grupo alcoolizado (A): animais que receberam diariamente álcool etílico absoluto diluído a 20% em água durante quatro semanas; e, grupo isquêmico e alcoolizado (IA): animais submetidos ao mesmo tratamento do grupo A e que, após quatro semanas foram submetidos à isquemia cerebral focal durante 90 minutos, seguido por reperfusão de 48 horas. As amostras do cerebelo coletadas e realizado a análise de imunohistoquímica da proteína CASPASE-9 e a análise sérica por meio de PCR - RT dos miRNAS miR-21, miR-126 e o miR155. Resultados: A expressão de CASPASE 9 teve maior expressão no grupos I, A e I+A. A análise dos miRNAS, o miR-126 foi maior nos grupos A e I+A, o miR-155 foi maior nos grupos I e I+A. Conclusões: Podemos concluir que a ocorrência de apoptose no córtex cerebelar, mesmo distante do foco isquêmico e ques miRNAs 126 e 155 apresentam correlação com a apoptose celular em ratos isquêmicos e submetidos ao modelo de alcoolismo crônico / INTRODUCTION: Cerebral ischemia is a disorder of brain function caused by blood suppression in brain tissue with no apparent cause other than vascular. Studies reveal the damage caused by focal cerebral ischemia to affect not only the region of the ischemic lesion but also other regions of the brain, including the cerebellum. Ethanol acts by decreasing the reaction time of the body and the reflex response, producing even loss of motor coordination. For some time, studies have verified the action of ethanol in the cerebellum. AIMS: This study aims to analyze the cerebellar cortex of rats submitted to an experimental model of transient focal cerebral ischemia by ACM occlusion for 90 minutes, followed by reperfusion of 48 hours, associated or not with the model of alcoholism. METHODS: Fifty adult Wistar rats were used, subdivided into 5 experimental groups: control group (C): animals submitted to anesthesia only; sham group (S): animals submitted to complete simulation of the surgical procedure; ischemic group (I): animals submitted to focal cerebral ischemia for 90 minutes followed by reperfusion of 48 hours; alcoholic group (A): animals that received daily absolute ethanol diluted 20% in water for four weeks; and ischemic and alcoholized group (AI): animals submitted to the same treatment as group A and after four weeks were submitted to focal cerebral ischemia for 90 minutes, followed by reperfusion of 48 hours. The cerebellum samples were collected and the immunohistochemical analysis of the CASPASE-9 protein and the serum analysis by means of RT-PCR of miRNAS miR-21, miR-126 and miR155 were performed. RESULTS: The expression of CASPASE 9 had higher expression in groups I, A and I + A. The miRNAS analysis, miR-126 was higher in groups A and I + A, miR-155 was higher in groups I and I + A. CONCLUSIONS: We can conclude that apoptosis occurs in the cerebellar cortex, even if it is distant from the ischemic focus, and that miRNAs 126 and 155 present a correlation with cellular apoptosis in ischemic rats and submitted to the chronic alcohol model

A montagem e desmontagem das adesões focais (AF) desempenham um papel fundamental em diversos processos celulares, incluindo migração celular e sobrevivência. Resultados prévios do nosso laboratório mostram que fibroblastos nulos ou silenciados para miosina-Va sofrem um atraso na desmontagem das adesões, sugerindo um papel para a miosinaVa neste processo. Neste trabalho, visamos analisar a dinâmica de montagem das AF em fibroblastos murinos imortalizados NIH3T3, utilizando sondas fluorescentes para visualização de componentes de adesão focal. A formação das AF foi analisada após estímulo por soro de células quiescentes, o que leva a intensa polimerização de actina, reorganização do citoesqueleto e montagem das AF. A cinética de montagem das AF foi observada em ensaios ao longo do tempo, de células fixadas em 0, 5, 15, 30, 120 minutos após estímulo, e marcadas para miosina-Va fosforilada (p-miosina-Va, S1650), FAK fosforilada (p-FAK, Y397), vinculina, dinamina-2, integrina-?1, faloidina, Ki67 e DAPI. Os nossos resultados mostraram um aumento de fluorescência de p-miosina-Va por todo o citoplasma após a estímulo com soro, e revelaram que a p-miosina-Va co-localiza com pFAK nas AF logo após o estímulo, essa localização da p-miosina-Va nas AF diminui ao passar do tempo e retorna após 120 minutos. Isto é consistente com os resultados anteriores de um papel da miosina-Va na dinâmica das AF. Também é possível perceber uma maior concentração de p-miosina-Va e dinamina-2 na região perinuclear, 5 minutos após estímulo, e o espalhamento de ambas as proteínas pelo citoplasma com o passar do tempo. Demonstramos, por Western blotting, que o estímulo por soro não causa alteração na quantidade total de miosina-Va em nenhum dos tempos analisados em relação à condição de quiescência, mas induz, após 5 e 15 minutos, um aumento apreciável de p-miosina-Va, que sofre queda e variações nos tempos posteriores. Para nosso conhecimento, esta é a primeira demonstração de que a fosforilação da miosina-Va aumenta em resposta ao soro e estamos investigando se este evento está ligado à dinâmica das adesões focais em fibroblastos / The assembly and disassembly of focal adhesions (FA) play a critical role in several cellular process, including cell migration and survival. Previous work from our laboratory showed that fibroblasts without myosin-Va show a delay in focal adhesion disassembly, suggesting a role for myosin-Va in this process. In this work, we aim at imaging the dynamics of focal adhesion disassembly and reassembly in cells, with fluorescent probes for visualization of focal adhesion components. Here, we used murine NIH3T3 fibroblasts to analyze FA formation after serum stimulation of quiescent cells, which leads to intense polymerization of actin and reorganization of the cytoskeleton and FA assembly. The kinetics of FA assembly was observed in a time-course assay of cells fixed at 0, 5, 15, 30 and 120 min after serum stimulation, and stained for phosphorylated myosin-Va (p-myosin-Va, S1650), phosphorylated FAK (p-FAK, Y397), vinculin, phalloidin and DAPI. Our results showed an increase of pmyosin-Va staining throughout the cytoplasm upon serum stimulation, and revealed that pmyosin-Va does not colocalize with FAK in FA at early time points. However, colocalization is observed after 30 to 120 min. This is consistent with previous results of a role for myosin-Va in FA disassembly. It is also possible to observe a higher concentration of p-myosin-Va and dynamin-2 in the perinuclear region 5 minutes after stimulation, and the spreading of both proteins in the cytoplasm over time. We demonstrate by Western blotting that serum stimulation does not cause change in total amount of myosin-Va, in any of the times analyzed in relation to the quiescent condition, but induces, after 5 and 15 minutes, an appreciable increase of pmyosin-Va suffering drop and variations in the later times. To our knowledge, this is the first demonstration that phosphorylation of myosin-Va increases in response to serum and we are investigating whether this event is connected to the dynamics of focal adhesions in fibroblasts

INTRODUÇÃO: A Glomerulosclerose Segmentar e Focal (GESF) é a glomerulopatia primária mais prevalente no Brasil e sua incidência vem aumentando no mundo inteiro. Na sua forma primária, caracteriza-se clinicamente por acometer pessoas jovens e causar proteinúria acentuada, geralmente acompanhada de síndrome nefrótica. O mecanismo patogênico tem como evento principal a lesão ao podócito, desencadeado por fatores de natureza variada: vírus, drogas/medicamentos, imunológicos, etc. Em 2004, foi publicada a classificação de Columbia, propondo 5 variantes morfológicas distintas na GESF: colapsante (COL), usual (NOS), apical ou tip lesion (TIP), perihilar (PHI) e variante celular (CEL). Diversos estudos comprovam alterações moleculares em podócitos na GESF. Essas alterações são observadas em diversos sítios podocitários: em moléculas envolvidas na fenda de filtração (slit diaphragm), por exemplo, nefrina, podocina e CD2AP; em moléculas do citoesqueleto podocitário, como a -actinina-4 e sinaptopodina; em moléculas marcadoras de diferenciação dos podócitos, como CD10 e WT-1; e ainda em marcadores de divisão celular como Ki-67 e PCNA. Os objetivos desse estudo foram: 1-) classificar as lesões morfológicas de GESF em biópsia renais nas 5 variantes da GESF propostas na Classificação de Columbia; e 2-) analisar a ocorrência de alterações moleculares podocitárias nestes casos. MÉTODOS: Foram selecionados 131 casos de biópsias renais com diagnóstico de GESF primária no período de 1996 a 2006. Os casos foram classificados de acordo com os critérios de Columbia e posteriormente submetidos a reações imuno-histoquímicas para os marcadores CD10, WT-1, vimentina, sinaptopodina, -actinina-4, GLEPP-1, citoqueratina 8/18, citoqueratina 19 e Ki-67. Os resultados foram submetidos à análise estatística através do teste qui-quadrado. RESULTADOS: A classificação das variantes da GESF se distribuiu da seguinte forma: 38,2% de variante NOS, 36,6% de variante COL, 14,5% de variante TIP, 6,9% de variante PHI e 3,8% de variante CEL. Os casos da variante COL se destacaram das demais variantes pela perda de expressão de marcadores de diferenciação celular, como o CD10 e o WT-1 (p<0,01), perda da molécula do citoesqueleto -actinina-4 (p<0,01) e neo-expressão de citoqueratinas 8-18 (p<0,05) e 19 (p<0,01). Adicionalmente, os casos das variantes COL e CEL se destacam das outras variantes pela expressão do marcador de divisão celular Ki-67 (p<0,05). CONCLUSÃO: a variante COL destacou-se das demais em relação às alterações moleculares observadas na análise imuno-histoquímica. O diagnóstico diferencial desta forma de GESF tem importância clínica por ela estar associada a pior evolução e prognóstico em relação às demais variantes. A integração destes marcadores na rotina diagnóstica pode auxiliar no diagnóstico diferencial da GESF COL / INTRODUCTION: Focal segmental glomerulosclerosis (FSGS) is the most prevalent primary glomerulopathy in Brazil and its incidence is increasing worldwide. Primary FSGS is characterized clinically by affecting young people and causing severe proteinuria, often accompanied by nephrotic syndrome. The pathogenesis is related to podocyte injury, which may be due to several factors: viruses, drugs, immunological, etc. In 2004, the Columbia classification of FSGS identified five histological variants of the disease: collapsing (COL), usual (NOS), tip lesion (TIP), perihilar (PHI) and cellular variant (CEL). Several studies have demonstrated molecular changes in podocytes of FSGS patients, which were observed in molecules involved in the filtering function of these cells (nephrin, podocina and CD2AP), in podocyte cytoskeleton molecules (-actinin-4, and synaptopodin), as well as in molecular markers of podocyte differentiation (CD10 and WT-1) and of cell division (Ki-67 and PCNA). The aim of this study was to classify the FSGS biopsies according to the Columbia classification and to analyze the occurrence of molecular changes in the five morphological variants. METHODS: 131 cases of renal biopsies with a diagnosis of primary FSGS in the period 1996 to 2006 were classified according to the criteria of Columbia and then submitted to immunohistochemical reactions with the following antibodies: CD10, WT-1, Vimentin, Synaptopodin, -actinin-4, GLEPP-1, cytokeratin 8-18, cytokeratin 19, and Ki-67. RESULTS: FSGS cases were classified into five variants as follows: 38.2% of NOS variant, 36.6% COL, 14.5% TIP, 6.9% PHI and 3.8% CEL. The COL variant cases distinguished themselves among the other for having lost the expression of CD10 and WT-1 (p <0.01), and also of -actinin-4 (p <0, 01). Furthermore, they gained expression of the cytokeratin 8-18 (p <0.05) and 19 (p <0.01). The group of CEL and COL variants together differed from the other variants regarding the expression of cell division marker Ki-67 (p <0.05). CONCLUSION: COL variant of FSGS presents molecular changes that differs from others and can be demonstrated by immunohistochemistry. The differential diagnosis of this variant is important because of the worse clinical outcome and prognosis it presents in comparison with other variants. The identification of these markers by immunohistochemical on the routine practice may be useful in the diagnosis of COL FSGS

Introdução: O medicamento, imprescindível no tratamento e recuperação da saúde, cresce em importância, tanto para os profissionais de saúde como para a população. Objetivo: Incluir a experiência da população de baixa renda, na pesquisa em saúde pública, sobre necessidade de tomar medicamentos; apresentar dificuldades vivenciadas, em busca destes; relatar as estratégias adotadas, diante da impossibilidade de consegui-los gratuitamente; estudar a compreensão do valor monetário deste produto; identificar a possibilidade de aquisição de medicamentos de médio e alto custo. Método: Metodologia qualitativa, usando a técnica de grupo focal, com a construção de 3 grupos, com a participação de 31 sujeitos, no período de dezembro de 2008 a março de 2009. Os sujeitos são moradores da região do Butantã, SP/SP, com 40 anos ou mais, com renda mensal até 3 salários mínimos e usuários do SUS, fazendo uso de pelo menos um medicamento. Os três grupos foram formados por usuários de medicamentos de uso contínuo; usuários de medicamentos de médio e alto custo e por moradores de uma favela. As discussões foram conduzidas por 2 profissionais e, foram baseadas em 5 perguntas referentes aos objetivos. Para a análise das discussões, optou-se pelo método do DSC (Discurso do Sujeito Coletivo), com utilização do software Qualiquantisoft®. Resultados: As discussões geraram 23 respostas categorizadas, destacando: a necessidade do medicamento, a dificuldade para consegui-lo gratuitamente; a má divulgação e a falta de informação sobre os programas de distribuição gratuita; a dependência de terceiros para aquisição; a necessidade de procura do medicamento em vários postos de saúde; a necessidade de compra. Medicamentos com preço até 50 reais foram considerados caros para a maioria. Os de alto custo são adquiridos, com algumas dificuldades, destacando-se tempo de espera, e falhas na dispensação. Conclusão: O acesso aos medicamentos mostrou-se parcial, apesar do avanço das políticas públicas na área, fazendo-se necessário um amplo conjunto de medidas, que priorize a manutenção de estoques regulares, a humanização do atendimento, a disponibilidade de profissionais competentes e que tenham compromisso social, para que a população de baixa renda alcance gratuitamente o sucesso terapêutico desejado, de forma regular e sistemática. / Introduction: Prescription drugs are indispensable to medical treatment for both health professionals and the general population. Objective: the goals of this study were to include in public health research the experience of the poor population who needs prescription drugs; to describe practical difficulties of the poor population to obtain prescription drugs from public health units; to report the main actions taken by this population when it is not possible to obtain free drugs in public health units; to evaluate the comprehension of the financial value of these drugs within this demographic segment of the population; to identify the strategies to obtain prescription drugs of medium and high cost. Method: The focal group qualitative method was selected for this research, with three groups comprising 31 subjects, studied in the period from December 2008 to March 2009. Subjects had to be residents of Butantã District, São Paulo-SP; besides being over 40 years old, in use of at least one prescription drug; to have a monthly income of up to three minimum salaries; to be a regular user of the public health system and units. All subjects lived in slums and were under treatment with medium-high cost drugs of continuous use. Two professionals conducted discussions on the five questions concerning the objectives. The collective subject method (CSM) was used for the analysis, which was performed with the Qualiquantisoft® computer program. Results: the five questions generated 23 answers, which were characterized as follows: necessity of the drug; difficulty to obtain the drug from public health units; deficiency in the advertisement programs and lack of information on free distribution programs; reliance on other people to obtain the drugs; necessity to reach many public health units to obtain the drugs; necessity to buy the drug. Drugs with prices up to R$ 50,00 were considered expensive. High cost drugs are purchased with some difficulty, such as slot time and dismissing flaws. Conclusion: Despite the advances in public health policies, the access to prescription drugs was biased, revealing a demand for a set of actions to prioritize storage and regular maintenance of these drugs, well prepared professionals to speed up and humanize the advising and assistance strategies in public health units, in order to promote a better distribution of these drugs and the effective achievement of therapeutic success for this population in a regular and systematic way.