Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 24, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Professor Silvia S. Jurisson and Professor Charles J. Smith. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 64-81). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Degree granted in 1996 ; filmed in 1999. Typescript. Vita. Includes bibliographical references (leaves 64-81). Also available on the Internet.

Thesis (Ph. D.) University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on July 30, 2006). Includes bibliographical references.

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on March 25, 2010). Vita. Thesis advisor: Charles J. Smith. "December 2009" Includes bibliographical references.

Thesis (Ph.D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 12, 2009) Includes bibliographical references.

The present set of experiments were designed to examine the role of histamine, and its interaction with corticotropin releasing factor (CRF) and bombesin (BM) in food intake regulation of chickens. The hypothesis being tested was as follows: One component of the neuroregulation of food intake involves histaminergic activity in the hypothalamus, acting on either H1 or H2 receptors, how these receptors interact with CRF neurons and if BM elicits its effects on feeding through CRF release. Single Comb White Leghorn (SCWL) and broiler cockerels were utilized for these experiments. Birds were stereotaxically implanted with a 23-gauge thin-walled stainless steel guide cannula, and were provided a mash diet and water for ad libitum consumption. All compounds were infused into the right lateral ventricle. Effects were monitored at 15-minute intervals through three hours postinjection. Experiment 1 examined the effects of intracereboventricular (ICV) injections of histamine (HA) and two HA antagonists, the H1 receptor antagonist chloropheneramine maleate (CM) and H2 receptor antagonist cimetidine (CIM), on food and water consumption and body temperature. Histamine was infused using 0, 25, 50, and 100 µg per 10 µl of artificial cerebrospinal fluid (aCSF). Histamine significantly decreased food and water consumption (P< 0.05) over the three hour observation period in a dose-dependent manner. Histamine was then infused to observe if the decrease in water intake was dependent upon the decrease in food intake. Birds were not allowed access to feed during this experiment. Water intake was not affected by HA in either SCWL or broilers when food was not available. To observe the effects of HA on thermoregulation, HA was infused using the same dosages and body temperature recorded for three hours. Histamine produced hypothermia at a dose of 25 µg in SCWL cockerels, with a quadratic trend at 165 and 180 min. Broiler cockerels did not show hypothermia, but rather a constant hyperthermia compared to the control with a quadratic trend throughout the latter part of the experiment. The last phase of the first set of experiments, birds were pretreated with either CM or CIM (100 µg/10 µl aCSF) followed by HA. When the birds were pretreated with either CM or CIM, the hypophagic responses to HA were attenuated. The pair of experiments that utilized H1 and H2 receptors demonstrated that these receptors are involved in the neural regulation of food intake. These experiments also demonstrated that the aphagic effects of HA on food intake can be blocked with the pretreatment of antihistaminics affecting both H1 and H2 receptors. In Experiment 2, studies were conducted to determine if neuronal CRF elicited its effects on feeding through the release of HA. Birds were infused with 0 or 20 µg CRF and either 0 or 100 µg of CM or CIM. CRF decreased food and water intake in both SCWL and broiler cockerels. When birds were pretreated with CM, the hypophagic responses to CRF were attenuated. When birds were pretreated with CIM, the hypophagic responses of CRF were attenuated in broiler cockerels; this response was not seen in SCWL cockerels. Water intake followed a similar pattern. It was concluded that, contrary to studies showing that HA causes the release of CRF in other species, CRF may cause the release of HA in chickens. Experiment 3 was designed to investigate whether bombesin (BM) elicited its effects on feeding through the release of CRF. Birds were infused with either, 0 or 0.5 µg BM, 0 or 5 µg aCRF (9-41) (CRF antagonist), or a combination of both. These compounds were infused to test whether the effects of BM could be blocked with the pretreatment of anticorticotropics. Food and water consumption were significantly decreased (P< 0.05) with the infusion of BM in both SCWL and broiler cockerels. Food intake was not affected with the infusion of aCRF in SCWL or broilers cockerels. However, water consumption was increased when birds were given ICV injections of aCRF. When birds were pretreated with aCRF, the anorexigenic and adipsic effects of BM were attenuated. It was concluded that BM elicits its effects on feeding through the release of CRF. These results also demonstrate that the aphagic effects of BM could be blocked with the pretreatment of anticorticotropics. / Master of Science

Un diagnostic précoce suivi d'un traitement efficace et bien adapté au type de cancer sont les deux aspects les plus importants dans le traitement du cancer. L'imagerie par tomographie d'émission de positrons (TEP) est utilisée en oncologie pour le diagnostic ainsi que l'évaluation de la réponse a la thérapie. La TEP est l'outil le plus efficace dans la détection du cancer, des métastases ainsi que des récidives. Le radiotraceur le plus utilisé présentement en clinique est le 2-deoxy-2-[[exposant 18]F]-fluoro-D-glucose ([[exposant 18]F]-FDG). Ce radiotraceur est un analogue du glucose qui permet de détecter les tumeurs et d'évaluer le métabolisme de ces cellules. En effet, les cellules tumorales ont généralement un métabolisme beaucoup plus élevé que les cellules normales. L'imagerie est donc basé sur l'accumulation du radiotraceur plus rapidement dans les cellules tumorales. Malheureusement, certains types de cellules cancéreuses tels que les cellules de cancer de la prostate ont un métabolisme peu élevé et alors, le [[exposant 18]F]-FDG s'avère inefficace dans la détection de ces types de cancers. L'inverse est aussi vrai et pose également problème, c'est-à-dire que certains types de cellules saines ont un métabolisme élevé et, dans ces cas, le [[exposant 18]F]-FDG est, la aussi, inadéquat, tel que dans le cas du cancer du cerveau, par exemple, où les cellules du cerveau ont un métabolisme très élevé en tout temps rendant l'imagerie de ce cancer impossible. Même si le [[exposant 18]F]- FDG demeure un bon radiotraceur dans la majorité des cas, le développement de nouveaux radiotraceurs capables de cibler spécifiquement les cellules cancéreuses présente des avantages indéniables. Plusieurs traitements sont disponibles présentement en clinique pour traiter le cancer. Malheureusement, tous ces traitements comportent certaines lacunes dont la plus importante et la plus commune est la présence d'effets secondaires importants. Ces effets secondaires sont dus au manque de spécificité des molécules utilisées dans ces traitements. En effet, ces agents thérapeutiques ne ciblent pas spécifiquement les cellules cancéreuses, mais bien toutes les cellules en division, causant aussi des dommages aux cellules saines. La photothérapie est l'un de ces traitements éprouvés en clinique dont l'efficacité pour traiter certains types de cancers a déjà été demontrée. La présence d'un agent ciblant les cellules cancéreuses spécifiquement pourrait grandement améliorer l'efficacité et diminuer les effets secondaires. Le bombesin est un peptide de 14 acides aminés qui est exprimé chez plusieurs types cellulaires et qui possède plusieurs fonctions de régulation dans l'organisme. Ainsi, il participe à la thermorégulation, en plus de provoquer la sécrétion de plusieurs enzymes pancréatiques. Ce peptide doit son nom à la grenouille Bombina bombina chez laquelle il fut d'abord isolé et séquencé. Par la suite, son équivalent humain, le gastrin-releasing peptide (GRP), fut découvert et son étude démontra que ce peptide est hautement conservé chez les différentes espèces. Quatre sous-types ont été identifiés chez la grenouille et trois chez l'humain. Les récepteurs a bombesin sont exprimés en très bas niveau chez plusieurs types cellulaires normaux, mais ils sont particulièrement surexprimés chez certains types de cancers tels que le cancer du sein et de la prostate. De plus, la surexpression de certains sous-types tels que le gastrin-releasing peptide receptor (GRPR) est un indice de l'agressivité de la tumeur. Notre premier objectif était donc de créer un radiopeptide qui se lierait spécifiquement à des récepteurs surexprimés dans des cas de cancer du sein et de la prostate, les GRPR pour permettre l'imagerie TEP de ces types de tumeurs. En combinant un analogue du bombesin avec un radioisotope, le Cu-64, nous voulions obtenir un radiotraceur plus spécifique que celui utilisé présentement en clinique. Notre second objectif était d'évaluer le potentiel de ce même analogue du bombesin lié à un photosensibilisateur, l'AIPcS[indice inférieur 4]A[indice inférieur 1], en tant qu'agent photosensibilisant dans l'utilisation de la thérapie photodynamique (TPD) dans le traitement du cancer de la prostate.

Uma grande variedade de moléculas já foi identificada por apresentar alta afinidade por receptores superexpressos em células tumorais, e a radiomarcação dessas moléculas oferece a possibilidade de novos compostos com aplicações diagnósticas e terapêuticas em medicina nuclear. Dentre essas moléculas, a bombesina (BBN) é uma das que despertam maior interesse, uma vez que um de seus receptores BB2 são superexpressos em células de tumores de próstata, mama, cólon, pâncreas e pulmão, além de glioblastomas e neuroblastomas. Derivados da bombesina, agonistas e antagonistas dos receptores BB2 já foram propostos para essa finalidade e apresentaram resultados promissores em estudos pré-clínicos. Entretanto, a maioria deles apresenta o incoveniente da alta captação em tecidos sadios, como pâncreas e intestino, o que pode prejudicar a eficiência diagnóstica e causar efeitos adversos na terapia. Nesse contexto, o objetivo deste trabalho foi estudar a marcação de uma nova série de derivados da bombesina com índio-111 (111In) e gálio-68 (68Ga), de modo a avaliar seu potencial para diagnóstico de tumores que superexpressam BB2 por tomografia computadorizada por emissão de fóton único (SPECT) ou por emissão de pósitrons (PET). Os peptídeos estudados apresentam estrutura genérica YGn-BBN(6-14)-Q, em que Q é o grupamento quelante, n é o número de aminoácidos glicina do espaçador YGn e BBN(6-14) é a sequência original de aminoácidos da BBN do aminoácido 6 ao 14. Estudou-se também o derivado em que a metionina (Met) terminal da sequência da bombesina foi substituída pela norleucina (Nle). A avaliação experimental dos derivados da bombesina foi dividida em quatro etapas: estudos computacionais, marcadores moleculares para SPECT, marcadores moleculares para PET e estudos toxicológicos. Os estudos computacionais consistiram na determinação dos coeficientes de partição (log P) e distribuição (log D) teóricos dos derivados da bombesina conjugados ao quelante DTPA (ácido dietileno-triamino-pentacético e DOTA (1,4,7,10-tetraazaciclododecano-tetracético). No desenvolvimento de marcadores moleculares para SPECT os derivados da bombesina de diferentes espaçadores conjugados ao DTPA e radiomarcados com 111In foram avaliados para determinação do melhor espaçador para aplicação in vivo, considerando não apenas as propriedades in vivo, mas também a estabilidade. Uma vez definido o espaçador, o derivado escolhido conjugado ao quelante DTPA ou DOTA foi submetido a estudos comparativos in vitro e in vivo utilizando linhagens tumorais que expressam os receptores BB2 em níveis variados, de modo a determinar o agente quelante mais adequado para aplicação in vivo. Nessa fase experimental, alguns estudos foram realizados também com um derivado da BBN BZH3, amplamente descrito pela literatura. No desenvolvimento de marcadores moleculares para PET, o derivado composto pelo espaçador e quelante escolhido foi radiomarcado com 68Ga e submetido a estudos de biodistribuição in vivo. Por fim, estudos toxicológicos em ratos foram realizados por meio da administração de um excesso dos derivados da BBN, a fim de avaliar a segurança para futura aplicação em estudos clínicos. Todos os derivados conjugados ao DTPA foram radiomarcados com 111In com alta pureza radioquímica e alta atividade específica (174 GBq/&mu;mol). Os marcadores moleculares obtidos apresentaram alta estabilidade frente à reação de marcação e baixa estabilidade à temperatura ambiente, a qual foi aumentada com a adição de agentes estabilizantes. A análise em soro humano indicou degradação tempo-dependente dos marcadores moleculares pelas enzimas do soro e aumento da estabilidade com o acréscimo de aminoácidos glicina no espaçador, bem como pela substituição da Met terminal pela Nle. Os estudos em CLAE e de log P confirmaram os resultados de log P teórico e indicaram que os marcadores moleculares apresentam baixa lipofilicidade, a qual decresce com o aumento do espaçador e aumenta com a substituição do aminoácido terminal. Os estudos in vivo demonstraram que os marcadores moleculares de DTPA-111In apresentam rápido clareamento sanguíneo, excreção primariamente renal e baixo acúmulo abdominal. O marcador molecular que apresentou maior captação tumoral foi aquele com a Nle terminal (YG5N), e esse foi submetido à análise comparativa entre os quelantes bifuncionais DTPA e DOTA. O YG5N-DOTA foi radiomarcado com 111In com alta atividade específica (100 GBq/&mu;mol). Ensaios de saturação em células de tumor de próstata (PC-3 e LNCaP) e mama (T-47D) in vitro demonstraram afinidade semelhante para o peptídeo conjugado a ambos quelantes, mas o YG5N-DOTA-111In se ligou mais às células de tumor de próstata, mas não às células de tumor de mama. Esse marcador molecular também foi mais internalizado pelas células PC-3. Os estudos in vivo indicaram maior estabilidade do marcador molecular conjugado ao DOTA em soro de camundongo, mas captação dos dois peptídeos semelhante pelo tumor de células PC-3 e LNCaP, embora esse último tenha demonstrado uma concentração duas vezes menor do receptor BB2. A imagem SPECT/CT dos tumores foi possível com os dois peptídeos. Em comparação com o derivado BZH3-111In, os marcadores moleculares apresentaram captação tumoral semelhante, mas as imagens foram mais favoráveis devido à menor captação abdominal. O YG5N-DOTA foi então radiomarcado com 68Ga, obtendo-se alta pureza radioquímica, e seu perfil de distribuição foi semelhante ao do derivado radiomarcado com 111In, com significativa captação pelo tumor de células PC-3. Os ensaios de tolerância toxicológica demonstraram que os derivados da bombesina são seguros até a concentração administrada, não apresentando toxicidade hematológica, hepática ou renal. O derivado da BBN YG5N conjugado ao DTPA ou DOTA é uma ferramenta promissora e segura para o diagnóstico de tumores que superexpressam os receptores BB2 por SPECT e PET. / A high number of molecules have already been identified to have high affinity to some receptors overexpressed on tumour cells and the radiolabelling of those molecules offers the possibility of new compounds for tumour diagnosis and therapy by nuclear medicine. Among of those molecules, bombesin (BBN) has become focus of interest, as its BB2 receptors are known to be overexpressed in prostate, breast, colon, pancreatic and lung tumour, as long as glioblastomas and neuroblastomas. BBN agonists and antagonists have already been described for this purpose and promising results were obtained in preclinical studies. However, most of them exhibited high abdominal accumulation, especially in pancreas and intestines, which can compromise diagnosis accuracy and cause serious adverse effects in therapy. In this context, the goal of the present work to radiolabel new BBN derivatives with 111In and 68Ga and to evaluate their potential for BB2 positive tumors diagnosis by single photon emission tomography (SPECT) and positron emission tomography (PET). The structure of studied peptides was Q-YGn-BBN(6-14), where Q is the chelator, n is the number of glycine aminoacids in the spacer YGn and BBN(6-14) is the original bombesin sequence from the aminoacid 6 to 14. The derivative in which the last aminoacid (methionine, Met) was replaced by norleucine (Nle) was also evaluated. The experimental evaluation of the bombesin derivatives was divided into four steps: computational studies, molecular markers for SPECT, molecular markers for PET and toxicological studies. The teorical partition (log P) and distribution (log D) coefficients were calculated for all bombesin derivatives conjugated to DTPA (diethylenetriaminepentaacetic acid) and DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) chelators applying computational programmes. Bombesin derivatives for SPECT were developed by radiolabelling DTPA-conjugated bombesin derivatives with 111In to determine the best spacer for in vivo applications, regarding the stability and in vivo properties. The derivative with the most favorable properties and conjugated to DTPA or DOTA was evaluated in comparative in vitro and in vivo studies in different BB2 expressing tumour cells, in order to determine the best chelator to be used in vivo. Some comparative studies were also performed with the BBN analogue BZH3, which was described by the literature. The molecular marker for PET was developed by radiolabelling the derivative chosen with 68Ga and evaluating the biodistribution profile in healthy and tumour mice. Finally, toxicological studies were performed by injecting an excess of cold bombesin derivatives in rats to determine their safety for clinical querries. All derivatives conjugated to DTPA were radiolabelled with 111In at high radiochemical purity and high specific activity (174 GBq/&mu;mol). The molecular markers presented high stability during radiolabelling and low stability at room temperature and this stability was increased after the addition of stabilizer agents. Stability in human serum analysis suggested time-course degradation by human serum enzymes and the increase on glycine aminoacids in the spacer improved the molecular markers stability, as long as the replacement of terminal Met by Nle. HPLC and log P results confirmed the teorical log P data which showed that the BBN derivatives present low lipophilicity, which decreases with the increase on glycine aminoacids in the spacer and the replacement of terminal Met by Nle. In vivo studies demonstrated that 111In-DTPA-BBN analogues present fast blood clearance, excretion by renal pathway and low abdominal accumulation. Highest tumour uptake was observed with the Nle-terminal derivative (YG5N), which was used for the comparison between the DTPA and DOTA chelators. DOTA-YG5N was also radiolabeled with 111In at high specific activity (100 GBq/&mu;mol), but this was lower than for the DTPA derivatives. Saturation binding assays on prostate (PC-3 e LNCaP) and breast (T-47D) tumour cells showed similar affinity for the radiopeptide conjugated to DTPA and DOTA, higher binding of DOTA-peptide to PC-3 and LNCap cells was observed, but not for T-47D cells. This molecular marker was also more internalized by PC-3 cells. In vivo studies showed higher stability for 111In-DOTA-YG5N in mice serum, and the uptake of DTPA and DOTA peptide was similar by PC-3 and LNCaP tumour, although this last tumour has shown 2-fold less BB2 receptors than PC-3. SPECT/CT imaging of PC-3 and LNCaP was possible with both radiopeptides. When compared to 111In-BZH3, the molecular markers present similar tumour uptake, but with more favorable images, because of their lower abdominal uptake. DOTA-YG5N was radiolabeled with 68Ga with high radiochemical purity and the biodistribution profile was similar to the peptide labeled with 111In, with significative PC-3 tumour uptake. Toxicological studies showed the bombesin derivatives are safe up to concentration administered and did not present hematological, hepatic or renal toxicity. The BBN derivative YG5N conjugated to DTPA or DOTA is a promising and safe tool for BB2 expressing tumour diagnosis by SPECT and PET.

Uma grande variedade de moléculas já foi identificada por apresentar alta afinidade por receptores superexpressos em células tumorais, e a radiomarcação dessas moléculas oferece a possibilidade de novos compostos com aplicações diagnósticas e terapêuticas em medicina nuclear. Dentre essas moléculas, a bombesina (BBN) é uma das que despertam maior interesse, uma vez que um de seus receptores BB2 são superexpressos em células de tumores de próstata, mama, cólon, pâncreas e pulmão, além de glioblastomas e neuroblastomas. Derivados da bombesina, agonistas e antagonistas dos receptores BB2 já foram propostos para essa finalidade e apresentaram resultados promissores em estudos pré-clínicos. Entretanto, a maioria deles apresenta o incoveniente da alta captação em tecidos sadios, como pâncreas e intestino, o que pode prejudicar a eficiência diagnóstica e causar efeitos adversos na terapia. Nesse contexto, o objetivo deste trabalho foi estudar a marcação de uma nova série de derivados da bombesina com índio-111 (111In) e gálio-68 (68Ga), de modo a avaliar seu potencial para diagnóstico de tumores que superexpressam BB2 por tomografia computadorizada por emissão de fóton único (SPECT) ou por emissão de pósitrons (PET). Os peptídeos estudados apresentam estrutura genérica YGn-BBN(6-14)-Q, em que Q é o grupamento quelante, n é o número de aminoácidos glicina do espaçador YGn e BBN(6-14) é a sequência original de aminoácidos da BBN do aminoácido 6 ao 14. Estudou-se também o derivado em que a metionina (Met) terminal da sequência da bombesina foi substituída pela norleucina (Nle). A avaliação experimental dos derivados da bombesina foi dividida em quatro etapas: estudos computacionais, marcadores moleculares para SPECT, marcadores moleculares para PET e estudos toxicológicos. Os estudos computacionais consistiram na determinação dos coeficientes de partição (log P) e distribuição (log D) teóricos dos derivados da bombesina conjugados ao quelante DTPA (ácido dietileno-triamino-pentacético e DOTA (1,4,7,10-tetraazaciclododecano-tetracético). No desenvolvimento de marcadores moleculares para SPECT os derivados da bombesina de diferentes espaçadores conjugados ao DTPA e radiomarcados com 111In foram avaliados para determinação do melhor espaçador para aplicação in vivo, considerando não apenas as propriedades in vivo, mas também a estabilidade. Uma vez definido o espaçador, o derivado escolhido conjugado ao quelante DTPA ou DOTA foi submetido a estudos comparativos in vitro e in vivo utilizando linhagens tumorais que expressam os receptores BB2 em níveis variados, de modo a determinar o agente quelante mais adequado para aplicação in vivo. Nessa fase experimental, alguns estudos foram realizados também com um derivado da BBN BZH3, amplamente descrito pela literatura. No desenvolvimento de marcadores moleculares para PET, o derivado composto pelo espaçador e quelante escolhido foi radiomarcado com 68Ga e submetido a estudos de biodistribuição in vivo. Por fim, estudos toxicológicos em ratos foram realizados por meio da administração de um excesso dos derivados da BBN, a fim de avaliar a segurança para futura aplicação em estudos clínicos. Todos os derivados conjugados ao DTPA foram radiomarcados com 111In com alta pureza radioquímica e alta atividade específica (174 GBq/&mu;mol). Os marcadores moleculares obtidos apresentaram alta estabilidade frente à reação de marcação e baixa estabilidade à temperatura ambiente, a qual foi aumentada com a adição de agentes estabilizantes. A análise em soro humano indicou degradação tempo-dependente dos marcadores moleculares pelas enzimas do soro e aumento da estabilidade com o acréscimo de aminoácidos glicina no espaçador, bem como pela substituição da Met terminal pela Nle. Os estudos em CLAE e de log P confirmaram os resultados de log P teórico e indicaram que os marcadores moleculares apresentam baixa lipofilicidade, a qual decresce com o aumento do espaçador e aumenta com a substituição do aminoácido terminal. Os estudos in vivo demonstraram que os marcadores moleculares de DTPA-111In apresentam rápido clareamento sanguíneo, excreção primariamente renal e baixo acúmulo abdominal. O marcador molecular que apresentou maior captação tumoral foi aquele com a Nle terminal (YG5N), e esse foi submetido à análise comparativa entre os quelantes bifuncionais DTPA e DOTA. O YG5N-DOTA foi radiomarcado com 111In com alta atividade específica (100 GBq/&mu;mol). Ensaios de saturação em células de tumor de próstata (PC-3 e LNCaP) e mama (T-47D) in vitro demonstraram afinidade semelhante para o peptídeo conjugado a ambos quelantes, mas o YG5N-DOTA-111In se ligou mais às células de tumor de próstata, mas não às células de tumor de mama. Esse marcador molecular também foi mais internalizado pelas células PC-3. Os estudos in vivo indicaram maior estabilidade do marcador molecular conjugado ao DOTA em soro de camundongo, mas captação dos dois peptídeos semelhante pelo tumor de células PC-3 e LNCaP, embora esse último tenha demonstrado uma concentração duas vezes menor do receptor BB2. A imagem SPECT/CT dos tumores foi possível com os dois peptídeos. Em comparação com o derivado BZH3-111In, os marcadores moleculares apresentaram captação tumoral semelhante, mas as imagens foram mais favoráveis devido à menor captação abdominal. O YG5N-DOTA foi então radiomarcado com 68Ga, obtendo-se alta pureza radioquímica, e seu perfil de distribuição foi semelhante ao do derivado radiomarcado com 111In, com significativa captação pelo tumor de células PC-3. Os ensaios de tolerância toxicológica demonstraram que os derivados da bombesina são seguros até a concentração administrada, não apresentando toxicidade hematológica, hepática ou renal. O derivado da BBN YG5N conjugado ao DTPA ou DOTA é uma ferramenta promissora e segura para o diagnóstico de tumores que superexpressam os receptores BB2 por SPECT e PET. / A high number of molecules have already been identified to have high affinity to some receptors overexpressed on tumour cells and the radiolabelling of those molecules offers the possibility of new compounds for tumour diagnosis and therapy by nuclear medicine. Among of those molecules, bombesin (BBN) has become focus of interest, as its BB2 receptors are known to be overexpressed in prostate, breast, colon, pancreatic and lung tumour, as long as glioblastomas and neuroblastomas. BBN agonists and antagonists have already been described for this purpose and promising results were obtained in preclinical studies. However, most of them exhibited high abdominal accumulation, especially in pancreas and intestines, which can compromise diagnosis accuracy and cause serious adverse effects in therapy. In this context, the goal of the present work to radiolabel new BBN derivatives with 111In and 68Ga and to evaluate their potential for BB2 positive tumors diagnosis by single photon emission tomography (SPECT) and positron emission tomography (PET). The structure of studied peptides was Q-YGn-BBN(6-14), where Q is the chelator, n is the number of glycine aminoacids in the spacer YGn and BBN(6-14) is the original bombesin sequence from the aminoacid 6 to 14. The derivative in which the last aminoacid (methionine, Met) was replaced by norleucine (Nle) was also evaluated. The experimental evaluation of the bombesin derivatives was divided into four steps: computational studies, molecular markers for SPECT, molecular markers for PET and toxicological studies. The teorical partition (log P) and distribution (log D) coefficients were calculated for all bombesin derivatives conjugated to DTPA (diethylenetriaminepentaacetic acid) and DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) chelators applying computational programmes. Bombesin derivatives for SPECT were developed by radiolabelling DTPA-conjugated bombesin derivatives with 111In to determine the best spacer for in vivo applications, regarding the stability and in vivo properties. The derivative with the most favorable properties and conjugated to DTPA or DOTA was evaluated in comparative in vitro and in vivo studies in different BB2 expressing tumour cells, in order to determine the best chelator to be used in vivo. Some comparative studies were also performed with the BBN analogue BZH3, which was described by the literature. The molecular marker for PET was developed by radiolabelling the derivative chosen with 68Ga and evaluating the biodistribution profile in healthy and tumour mice. Finally, toxicological studies were performed by injecting an excess of cold bombesin derivatives in rats to determine their safety for clinical querries. All derivatives conjugated to DTPA were radiolabelled with 111In at high radiochemical purity and high specific activity (174 GBq/&mu;mol). The molecular markers presented high stability during radiolabelling and low stability at room temperature and this stability was increased after the addition of stabilizer agents. Stability in human serum analysis suggested time-course degradation by human serum enzymes and the increase on glycine aminoacids in the spacer improved the molecular markers stability, as long as the replacement of terminal Met by Nle. HPLC and log P results confirmed the teorical log P data which showed that the BBN derivatives present low lipophilicity, which decreases with the increase on glycine aminoacids in the spacer and the replacement of terminal Met by Nle. In vivo studies demonstrated that 111In-DTPA-BBN analogues present fast blood clearance, excretion by renal pathway and low abdominal accumulation. Highest tumour uptake was observed with the Nle-terminal derivative (YG5N), which was used for the comparison between the DTPA and DOTA chelators. DOTA-YG5N was also radiolabeled with 111In at high specific activity (100 GBq/&mu;mol), but this was lower than for the DTPA derivatives. Saturation binding assays on prostate (PC-3 e LNCaP) and breast (T-47D) tumour cells showed similar affinity for the radiopeptide conjugated to DTPA and DOTA, higher binding of DOTA-peptide to PC-3 and LNCap cells was observed, but not for T-47D cells. This molecular marker was also more internalized by PC-3 cells. In vivo studies showed higher stability for 111In-DOTA-YG5N in mice serum, and the uptake of DTPA and DOTA peptide was similar by PC-3 and LNCaP tumour, although this last tumour has shown 2-fold less BB2 receptors than PC-3. SPECT/CT imaging of PC-3 and LNCaP was possible with both radiopeptides. When compared to 111In-BZH3, the molecular markers present similar tumour uptake, but with more favorable images, because of their lower abdominal uptake. DOTA-YG5N was radiolabeled with 68Ga with high radiochemical purity and the biodistribution profile was similar to the peptide labeled with 111In, with significative PC-3 tumour uptake. Toxicological studies showed the bombesin derivatives are safe up to concentration administered and did not present hematological, hepatic or renal toxicity. The BBN derivative YG5N conjugated to DTPA or DOTA is a promising and safe tool for BB2 expressing tumour diagnosis by SPECT and PET.