Synthesis of dialkylaminoaryl phosphonate bioisosteres of tyrosine and tyramine: a novel application of allene phosphonate chemistry for the synthesis of false substrates of tyrosinase.

Tyrosinase is the rate-limiting oxidase in the synthesis of melanin, making it an obvious target for the treatment of melanotic melanomas. Tyrosine and tyramine are its natural substrates, but many of their derivatives are inhibitors or false substrates, and are therefore prime candidates for melanoma chemotherapy. A series of dialkylphosphonate derivatives of tyramine have now been synthesized in order to extend the chemical diversity of tyrosinase substrates. The known reactivity between alkenephosphonates and nucleophiles was exploited by the addition of 4-(2-aminoethyl)phenol (tyramine) across the 2,3-double bond of 1,2-alkadiene phosphonates, to obtain the desired bisphosphonate derivatives. These reactions were highly chemoselective and regioselective but not stereoselective. Five of the reported novel dialkylphosphonate aminophenols were substrates for mushroom tyrosinase in vitro: dimethyl 2-[2(4-hydroxyphenyl)ethylamino]-3-methyl-1-butenephosphonate (3);diethyl 2-[2(4-hydroxyphenyl)ethylamino]-3-methyl-1-butenephosphonate (4);dimethyl 2-[2-(4- hydroxyphenyl)ethylamino]-2-cyclohexyl-1-ethenephosphonate (5);diethyl 2-[2-(4-hydroxyphenyl)ethylamino]- 2-cyclohexyl-1-ethenephosphonate (6);diethyl 2-[2-(4-hydroxyphenyl)ethylamino]ethanephosphonate (7). Compound 3 blocked the pigmentation of anagen hair in vivo in a murine animal model, a further demonstration that these compounds are able to enter and disrupt the melanogenic pathway.

Applications of nucleoside-based molecular probes for the in vivo assessment of tumour biochemistry using positron emission tomography (PET)

Positron emission tomography (PET) is a non-invasive nuclear imaging technique. In PET, radiolabelled molecules decay by positron emission. The gamma rays resulting from positron annihilation are detected in coincidence and mapped to produce three dimensional images of radiotracer distribution in the body. Molecular imaging with PET refers to the use of positron-emitting biomolecules that are highly specific substrates for target enzymes, transport proteins or receptor proteins. Molecular imaging with PET produces spatial and temporal maps of the target-related processes. Molecular imaging is an important analytical tool in diagnostic medical imaging, therapy monitoring and the development of new drugs. Molecular imaging has its roots in molecular biology. Originally, molecular biology meant the biology of gene expression, but now molecular biology broadly encompasses the macromolecular biology and biochemistry of proteins, complex carbohydrates and nucleic acids. To date, molecular imaging has focused primarily on proteins, with emphasis on monoclonal antibodies and their derivative forms, small-molecule enzyme substrates and components of cell membranes, including transporters and transmembrane signalling elements. This overview provides an introduction to nucleosides, nucleotides and nucleic acids in the context of molecular imaging.

A tomografia por emissão de pósitrons (TEP) é uma técnica de imagem não invasiva da medicina nuclear. A TEP utiliza moléculas marcadas com emissores de radiação beta positiva (pósitrons). As radiações gama medidas que resultam do aniquilamento dos pósitrons são detectadas por um sistema de coincidência e mapeadas para produzir uma imagem tridimensional da distribuição do radiotraçador no corpo. A imagem molecular com TEP refere-se ao uso de biomoléculas marcadas com emissor de pósitron que são substratos altamente específicos para alvos como enzimas, proteínas transportadoras ou receptores protéicos. A imagem molecular com TEP produz mapas espaciais e temporais de alvos que estejam sendo avaliados. A imagem molecular é uma importante ferramenta analítica no diagnóstico por imagem em medicina, no monitoramento de terapia e no desenvolvimento de novas drogas. A imagem molecular tem seus fundamentos na biologia molecular. Originalmente, a biologia molecular significava a biologia da expressão gênica, mas atualmente a biologia molecular envolve amplamente a biologia de macromoléculas, a bioquímica de proteínas, carboidratos complexos e ácidos nucléicos. A imagem molecular tem priorizado as proteínas, com ênfase nos anticorpos monoclonais e suas formas derivadas, substratos enzimáticos para pequenas moléculas e componentes de membranas celulares, incluindo os transportadores e elementos envolvidos com a sinalização trans-membrana.

Scintigraphic imaging of focal hypoxic tissue: development and clinical applications of 123I-IAZA

Affected tissues in a number of diseases, including cancer, stroke, cardiac infarction and diabetes, develop focal tissue hypoxia during their progression. The presence of hypoxic tissue may make the disease refractory to therapy, as in the case of solid tumor therapy using low LET ionizing radiation. In other pathologies, the detection of viable but hypoxic tissues may serve as a prodromal indicator of developing disease (e.g. diabetes),or as a prognostic indicator for management of the disease (e.g. stroke). Over the past two decades, a number of hypoxia radioimaging agents have been developed and tested clinically. Of these, 18F-Fmiso and 123I-IAZA are the most widely used radiotracers for PET and SPECT/planar imaging, respectively. IAZA and Fmiso are a 2-nitroimidazoles that chemically bind to subcellular components of viable hypoxic tissues. They sensitize hypoxic tumour to the killing effects of ionizing radiation via mechanisms that mimic the radiosensitizing effects of oxygen, and are therefore called oxygen mimetics. The oxygen mimetic effect is attributable in large part to the covalent binding of reductively-activated nitroimidazole intermediates to critical cellular macromolecules. Nitroimidazoles labelled with gamma-emitting radionuclides (e.g. 18F-Fmiso and 123I-IAZA) have been used as scintigraphic markers of tumour hypoxia, based on the need to identify radioresistant hypoxic tumour cells as part of the radiotherapy planning process. Broader interest in non-invasive, imaging-based identification of focal hypoxia in a number of diseases has extended hypoxia studies to include peripheral vascular disease associated with diabetes, rheumatoid arthritis, stroke, myocardial ischaemia, brain trauma and oxidative stress. In this review, the current status of hypoxia-selective studies with 123I-IAZA , an experimental diagnostic radiopharmaceutical, is reviewed with respect to its pre-clinical development and clinical applications