A role for adeno-associated viral vectors in gene therapy: [review]

Gene therapy constitutes a therapeutic intervention based on modification of the genetic material of living cells, by correcting genetic defects or overexpressing therapeutic proteins. The success of gene therapy protocols depends on the availability of therapeutically suitable genes, appropriate gene delivery systems and proof of safety and efficacy. Recent advances on the development of gene delivery systems, particularly on viral vectors engineering and improved gene regulatory systems, have led to marked progress in this field. Although the available vector systems can successfully transfer genes into cells, the ideal delivery vehicle has not been found. In this context, adeno-associated virus vectors (AAV) are arising as a promising tool for a wide range of applications, due to a combination of characteristics such as lack of pathogenicity and immunogenicity, wide range of cell tropism and long-term gene expression. Since its isolation, the biological properties of the adeno-associated virus have been increasingly understood, improving our ability to manipulate and use it as a safe and efficient gene therapy vector of wide spectrum. In this work, we review the bases of gene therapy, main types of gene transfer systems and basic properties and use of AAV vectors.

Polymorphic variation of mononucleotide microsatellites in healthy humans and its implication for microsatellite instability screening

BACKGROUND: Colorectal cancer is the sixth most common tumor and the fifth in mortality in Brazil. Molecular markers have been associated with disease prognosis, especially in relation to therapeutic response and overall survival rates. Among these, microsatellite instability has been extensively studied. Microsatellite stability status is usually determined by comparison of normal and tumoral tissues from the same patient and instability is characterized by the difference in the PCR-amplification profile of these tissues at a given locus. Usually, a panel of five markers is used for this purpose. Two of them (BAT-25 and BAT-26) are considered monomorphic in populations of European origin. AIM: To analyse the frequency of constitutive polymorphic variation at BAT-25 and BAT-26 loci in a sample of individuals from Southern Brazil. METHODS: Two-hundred and sixteen healthy and unrelated individuals were analised to assess the frequency of allelic variation at the BAT-25 and BAT-26 loci in DNA extracted from peripheral blood. Analysis was done by polymerase chain reaction - single strand conformation polymorphism (PCR-SSCP). RESULTS: From the sample of patients studied, 7 percent and 6 percent of the patients had possible constitutive allelic variation at the BAT-25 and BAT-26 loci, respectively. CONCLUSIONS: These results indicate that significant constitutive allelic variation of these loci does occur in heterogeneous populations such as ours, and reinforce the importance of comparative studies between tumoral and corresponding normal tissue to determine microsatellite stability status and correctly identify microsatellite instability in selected populations.

RACIONAL: No Brasil, o câncer colorretal é o sexto tumor em freqüência e o quinto em mortalidade. Marcadores moleculares têm sido associados com o prognóstico da doença, especialmente em relação à resposta terapêutica e taxa de sobrevida. Dentre eles, a instabilidade de microssatélites tem sido amplamente estudada. O estado de instabilidade de microssatélites é usualmente determinado pela comparação entre tecido tumoral e tecido normal correspondente de um mesmo paciente e a instabilidade se caracteriza pela diferença no perfil do produto de amplificação por PCR destes tecidos em um determinado locus. Usualmente, é utilizado um painel de cinco marcadores para este propósito. Dois deles (BAT-25 e BAT-26) são considerados monomórficos em populações de origem européia. OBJETIVO: Analisar a freqüência de variação constitutiva nos loci BAT-25 e BAT-26 em amostra de indivíduos do sul do Brasil. MÉTODOS: Duzentos e dezesseis indivíduos saudáveis e não relacionados foram analisados para determinar a freqüência de variação alélica nestes loci. O rastreamento de variantes alélicas foi feito por "polymerase chain reaction - single strand conformation polymorphism" (PCR-SSCP). RESULTADOS: Observou-se possível variação alélica constitutiva em 7 por cento e 6 por cento dos pacientes nos loci BAT-25 e BAT-26, respectivamente. CONCLUSÃO: Estes resultados indicam que há significativa variação alélica constitucional nos loci BAT-25 e BAT-26 em grupos selecionados, como nesta amostra de indivíduos brasileiros, e reforça a importância de estudos comparativos entre tecido tumoral e o tecido normal correspondente para identificar instabilidade de microssatélites em populações determinadas.

CYP1A1 and CYP2E1 polymorphism frequencies in a large Brazilian population

The enzymes encoded by the polymorphic genes CYP1A1 and CYP2E1 play an important role in the activation and inactivation of xenobiotics. These enzymes have been associated with xenobiotic-induced diseases, such as cancer, therapeutic failure and adverse effects of drugs. The aim of the present study was to determine the allelic and genotypic frequencies of these polymorphisms in a large, ethnically mixed Brazilian population sample from Rio de Janeiro. Polymorphisms CYP1A1 and CYP2E1 were determined in 870 unrelated individuals by PCR-RFLP analysis in peripheral blood DNA. The observed allelic frequencies were 0.90 for CYP1A1*1A and 0.95 for CYP2E1*1A, in the total sample. The allelic frequency of CYP1A1*2C in "pardos" (0.13) and Brazilian whites (0.11) was higher than in Caucasians (0.05), which may be a result of the Amerindian genetic component, that presents the highest frequency of this allele observed up to now. The genotype distributions for both polymorphisms were in Hardy-Weinberg equilibrium and were statistically different between males and females, and among ethnic groups.

Hereditary non-polipomatous colorectal cancer: hereditary predisposition, diagnosis and prevention

RACIONAL: O câncer colorretal é o terceiro tumor em freqüência e o segundo em mortalidade nos países desenvolvidos. No Brasil, está entre as seis neoplasias malignas mais encontradas e é a terceira em mortalidade. Cerca de 20% dos tumores colorretais têm etiologia hereditária. OBJETIVO: Revisão sobre aspectos genéticos e clínicos, bem como diagnóstico, tratamento e prevenção na síndrome do câncer colorretal hereditário não-polipomatoso, que apresenta a forma mais freqüente de câncer colorretal hereditário. A importância dessas abordagens se deve, principalmente, à possibilidade de manejo, prevenção e rastreamento específico para indivíduos em risco para câncer colorretal hereditário não-polipomatoso que conferem um aumento considerável na sobrevida desses pacientes e seus familiares em risco.