Estimates of radiation-absorbed dose to kidneys in patients treated with 90Y-ibritumomab tiuxetan.

The aim of the present study was to retrospectively estimate the absorbed dose to kidneys in 17 patients treated in clinical practice with 90Y-ibritumomab tiuxetan for non-Hodgkin's lymphoma, using appropriate dosimetric approaches available. METHODS: The single-view effective point source method, including background subtraction, is used for planar quantification of renal activity. Since the high uptake in the liver affects the activity estimate in the right kidney, the dose to the left kidney serves as a surrogate for the dose to both kidneys. Calculation of absorbed dose is based on the Medical Internal Radiation Dose methodology with adjustment for patient kidney mass. RESULTS: The median dose to kidneys, based on the left kidney only, is 2.1 mGy/MBq (range, 0.92-4.4), whereas a value of 2.5 mGy/MBq (range, 1.5-4.7) is obtained, considering the activity in both kidneys. CONCLUSIONS: Irrespective of the method, doses to kidneys obtained in the present study were about 10 times higher than the median dose of 0.22 mGy/MBq (range, 0.00-0.95) were originally reported from the study leading to Food and Drug Administration approval. Our results are in good agreement with kidney-dose estimates recently reported from high-dose myeloablative therapy with 90Y-ibritumomab tiuxetan.

Catabolite repression in Pseudomonas aeruginosa PAO1 regulates the uptake of C4 -dicarboxylates depending on succinate concentration.

In Pseudomonas aeruginosa carbon catabolite repression (CCR) is exerted by the CbrA/B-CrcZ-Crc global regulatory system. Crc is a translational repressor that, in the presence of preferred carbon sources, such as C4 -dicarboxylates, impairs the utilization of less preferred substrates. When non-preferred substrates are present, the CrcZ sRNA levels increase leading to Crc capture, thereby allowing growth of the bacterium at the expense of the non-preferred substrates. The C4 -dicarboxylate transport (Dct) system in P. aeruginosa is composed of two main transporters: DctA, more efficient at mM succinate concentrations, and DctPQM, more important at μM. In this study, we demonstrate that the Dct transporters are differentially regulated by Crc, depending on the concentration of succinate. At high concentrations, Crc positively regulates the expression of the dctA transporter gene and negatively regulates dctPQM post-transcriptionally. The activation of dctA is explained by a Crc-mediated repression of dctR, encoding a transcriptional repressor of dctA. At low succinate concentrations, Crc regulation is impaired. In this condition, CrcZ levels are higher and therefore more Crc proteins are sequestered, decreasing the amount of Crc available to perform CCR on dctR and dctPQM. As a result, expression of dctA is reduced and that of dctPQM is increased.

Switching between apparently redundant iron-uptake mechanisms benefits bacteria in changeable environments.

Bacteria often possess multiple siderophore-based iron uptake systems for scavenging this vital resource from their environment. However, some siderophores seem redundant, because they have limited iron-binding efficiency and are seldom expressed under iron limitation. Here, we investigate the conundrum of why selection does not eliminate this apparent redundancy. We focus on Pseudomonas aeruginosa, a bacterium that can produce two siderophores-the highly efficient but metabolically expensive pyoverdine, and the inefficient but metabolically cheap pyochelin. We found that the bacteria possess molecular mechanisms to phenotypically switch from mainly producing pyoverdine under severe iron limitation to mainly producing pyochelin when iron is only moderately limited. We further show that strains exclusively producing pyochelin grew significantly better than strains exclusively producing pyoverdine under moderate iron limitation, whereas the inverse was seen under severe iron limitation. This suggests that pyochelin is not redundant, but that switching between siderophore strategies might be beneficial to trade off efficiencies versus costs of siderophores. Indeed, simulations parameterized from our data confirmed that strains retaining the capacity to switch between siderophores significantly outcompeted strains defective for one or the other siderophore under fluctuating iron availabilities. Finally, we discuss how siderophore switching can be viewed as a form of collective decision-making, whereby a coordinated shift in behaviour at the group level emerges as a result of positive and negative feedback loops operating among individuals at the local scale.

Normal kinetics of intestinal glucose absorption in the absence of GLUT2: evidence for a transport pathway requiring glucose phosphorylation and transfer into the endoplasmic reticulum.

Glucose is absorbed through the intestine by a transepithelial transport system initiated at the apical membrane by the cotransporter SGLT-1; intracellular glucose is then assumed to diffuse across the basolateral membrane through GLUT2. Here, we evaluated the impact of GLUT2 gene inactivation on this transepithelial transport process. We report that the kinetics of transepithelial glucose transport, as assessed in oral glucose tolerance tests, was identical in the presence or absence of GLUT2; that the transport was transcellular because it could be inhibited by the SGLT-1 inhibitor phlorizin, and that it could not be explained by overexpression of another known glucose transporter. By using an isolated intestine perfusion system, we demonstrated that the rate of transepithelial transport was similar in control and GLUT2(-/-) intestine and that it was increased to the same extent by cAMP in both situations. However, in the absence, but not in the presence, of GLUT2, the transport was inhibited dose-dependently by the glucose-6-phosphate translocase inhibitor S4048. Furthermore, whereas transport of [(14)C]glucose proceeded with the same kinetics in control and GLUT2(-/-) intestine, [(14)C]3-O-methylglucose was transported in intestine of control but not of mutant mice. Together our data demonstrate the existence of a transepithelial glucose transport system in GLUT2(-/-) intestine that requires glucose phosphorylation and transfer of glucose-6-phosphate into the endoplasmic reticulum. Glucose may then be released out of the cells by a membrane traffic-based pathway similar to the one we previously described in GLUT2-null hepatocytes.

H-2D ligand expression by Ly49A+ natural killer (NK) cells precludes ligand uptake from environmental cells: implications for NK cell function.

To study the adaptation of natural killer (NK) cells to their major histocompatibility complex (MHC) class I environment we have established a novel mouse model with mosaic expression of H-2D(d) using a Cre/loxP system. In these mice, we noticed that NK cells expressing the inhibitory receptor for D(d), Ly49A, were specifically underrepresented among cells with low D(d) levels. That was due to the acquisition of D(d) molecules by the Ly49A+ NK cells that have lost their D(d) transgene. The uptake of H-2D molecules via the Ly49A receptor was restricted to strong ligands of Ly49A. Surprisingly, when Ly49A+ NK cells were D(d+), uptake of the alternative ligand D(k) was not detectable. Similarly, one anti-Ly49A mAb (A1) bound inefficiently when Ly49A was expressed on D(d+) NK cells. Concomitantly, functional assays demonstrated a reduced capacity of Ly49A to inhibit H-2(b)D(d) as compared with H-2(b) NK cells, rendering Ly49A+ NK cells in D(d+) mice particularly reactive. Minor reductions of D(d) levels and/or increases of activating ligands on environmental cells may thus suffice to abrogate Ly49A-mediated NK cell inhibition. The mechanistic explanation for all these phenomena is likely the partial masking of Ly49A by D(d) on the same cell via a lateral binding site in the H-2D(d) molecule.

Development of a method to investigate the hydrolysis of xenobiotic esters by a Mycobacterium smegmatis homogenate.

One of the main problems in combating tuberculosis is caused by a poor penetration of drugs into the mycobacterial cells. A prodrug approach via activation inside mycobacterial cells is a possible strategy to overcome this hurdle and achieve efficient drug uptake. Esters are attractive candidates for such a strategy and we and others communicated previously the activity of esters of weak organic acids against mycobacteria. However very little is known about ester hydrolysis by mycobacteria and no biological model is available to study the activation of prodrugs by these microorganisms. To begin filling this gap, we have embarked in a project to develop an in vitro method to study prodrug activation by mycobacteria using Mycobacterium smegmatis homogenates. Model ester substrates were ethyl nicotinate and ethyl benzoate whose hydrolysis was monitored and characterized kinetically. Our studies showed that in M. smegmatis most esterase activity is associated with the soluble fraction (cytosol) and is preserved by storage at 5°C or at room temperature for one hour, or by storage at -80°C up to one year. In the range of homogenate concentrations studied (5-80% in buffer), k(obs) varied linearly with homogenate concentration for both substrates. We also found that the homogenates showed Michaelis-Menten kinetics behavior with both prodrugs. Since ethyl benzoate is a good substrate for the mycobacterial esterases, this compound can be used to standardize the esterasic activity of homogenates, allowing results of incubations of prodrugs with homogenates from different batches to be readily compared.

Cross-talk between glutamate and potassium regulation at the astrocyte membrane

Astrocytes play a central role in the brain by regulating glutamate and extracellular potassium concentrations ([K+]0), both released by neurons into the extracellular space during neuronal activity. Glutamate uptake is driven by the inwardly directed sodium gradient across the astrocyte membrane and involves the influx of three sodium ions and one proton and the efflux of one K+ ion per glutamate molecule. The glutamate transport induced rise in intracellular sodium stimulates the Na+/K+-ATPase which leads to significant energetic costs in astrocytes. To evaluate how these two fundamental functions of astrocytes, namely glutamate transport and K+ buffering, which are directly associated with neuronal activity, coexist and if they influence each other, in this thesis work we examined different cellular parameters of astrocytes. We therefore investigated the impact of altered [K+]0 on glutamate transporter activity. To assess this question we measured intracellular sodium fluctuations in mouse primary cultured astrocytes using dynamic fluorescence imaging. We found that glutamate uptake was tightly modulated both in amplitude and kinetics by [K+]0. Elevated [K+]0 strongly decreased glutamate transporter activity, with significant consequences on the cells energy metabolism. To ultimately evaluate potential effects of [K+]0 and glutamate on the astrocyte mitochondrial energy production we extended these studies by investigating their impact on the cytosolic and mitochondrial pH. We found that both [K+],, and glutamate strongly influenced cytosolic and mitochondrial pH, but in opposite directions. The effect of a simultaneous application of K+ and glutamate, however, did not fit with the arithmetical sum of each individual effects, suggesting that an additional non¬linear process is involved. We also investigated the impact of [K+]0 and glutamate transport, respectively, on intracellular potassium concentrations ([K+]0 in cultured astrocytes by characterizing and applying a newly developed Insensitive fluorescent dye. We observed that [K+]i followed [K+]0 changes in a nearly proportional way and that glutamate superfusion caused a reversible, glutamate-concentration dependent drop of [K+],, Our study shows the powerful influence of [K+]u on glutamate capture. These findings have strong implications for our understanding of the tightly regulated interplay between astrocytes and neurons in situations where [K+]0 undergoes large activity-dependent fluctuations. However, depending on the extent of K+ versus glutamate extracellular rise, energy metabolism in astrocytes will be differently regulated. Moreover, the novel insights obtained during this thesis work help understanding some of the underlying processes that prevail in certain pathologies of central nervous system, such as epilepsy and stroke. These results will possibly provide a basis for the development of novel therapeutic strategies. -- Les astrocytes jouent un rôle central dans le cerveau en régulant les concentrations de potassium (K+) et de glutamate, qui sont relâchés par les neurones dans l'espace extracellulaire lorsque ceux- ci sont actifs. La capture par les astrocytes du glutamate est un processus secondairement actif qui implique l'influx d'ions sodium (Na+) et d'un proton, ainsi que l'efflux d'ions K+, ce processus entraîne un coût métabolique important. Nous avons évalué comment ces fonctions fondamentales des astrocytes, la régulation du glutamate et du K+ extracellulaire, qui sont directement associés à l'activité neuronale, coexistent et si elles interagissent, en examinant différents paramètres cellulaires. Dans ce projet de thèse nous avons évalué l'impact des modifications de la concentration de potassium extracellulaire ([K+],,) sur le transport du glutamate. Nous avons mesuré le transport du glutamate par le biais des fluctuations internes de Na+ grâce à un colorant fluorescent en utilisant de l'imagerie à fluorescence dynamique sur des cultures primaires d'astrocytes. Nous avons trouvé que la capture du glutamate était étroitement régulée par [K+]0 aussi bien dans son amplitude que dans sa cinétique. Par la suite, nous avons porté notre attention sur l'impact de [K+]0 et du glutamate sur le pH cytosolique et mitochondrial de l'astrocyte dans le but, in fine, d'évaluer les effets potentiels sur la production d'énergie par la mitochondrie. Nous avons trouvé qu'autant le K+ que le glutamate, de manière individuelle, influençaient fortement le pH, cependant dans des directions opposées. Leurs effets individuels, ne peuvent toutefois pas être additionnés ce qui suggère qu'un processus additionnel non-linéaire est impliqué. En appliquant une nouvelle approche pour suivre et quantifier la concentration intracellulaire de potassium ([K+]0 par imagerie à fluorescence, nous avons observé que [K+]i suivait les changements de [K+]0 de manière quasiment proportionnelle et que la superfusion de glutamate induisait un décroissement rapide et réversible de [K+]i, qui dépend de la concentration de glutamate. Notre étude démontre l'influence de [K+]0 sur la capture du glutamate. Ces résultats permettent d'améliorer notre compréhension de l'interaction entre astrocytes et neurones dans des situations où [K+]0 fluctue en fonction de l'activité neuronale. Cependant, en fonction de l'importance de l'augmentation extracellulaire du K+ versus le glutamate, le métabolisme énergétique des astrocytes va être régulé de manière différente. De plus, les informations nouvelles que nous avons obtenues durant ce travail de thèse nous aident à comprendre quelques- uns des processus sous-jacents qui prévalent dans certaines pathologies du système nerveux central, comme par exemple l'épilepsie ou l'accident vasculaire cérébral. Ces informations pourront être importantes à intégrer dans la cadre du développement de nouvelles stratégies thérapeutiques.

Effects of gastric bypass and gastric banding on glucose kinetics and gut hormone release.

BACKGROUND: Bariatric surgery markedly improves glucose homeostasis in patients with type 2 diabetes even before any significant weight loss is achieved. Procedures that involve bypassing the proximal small bowel, such as Roux-en-Y gastric bypass (RYGBP), are more efficient than gastric restriction procedures such as gastric banding (GB). OBJECTIVE: To evaluate the effects of RYGBP and GB on postprandial glucose kinetics and gastro-intestinal hormone secretion after an oral glucose load. METHODS AND PROCEDURES: This study was a cross-sectional comparison among non-diabetic, weight-stable women who had undergone RYGBP (n = 8) between 9 and 48 months earlier or GB (n = 6) from 25 to 85 months earlier, and weight- and age-matched control subjects (n = 8). The women were studied over 4 h following ingestion of an oral glucose load. Total glucose and meal glucose kinetics were assessed using glucose tracers and plasma insulin, and gut hormone concentrations were simultaneously monitored. RESULTS: Patients who had undergone RYGBP showed a a more rapid appearance of exogenous glucose in the systemic circulation and a shorter duration of postprandial hyperglycemia than patients who had undergone GB and C. The response in RYGBP patients was characterized by early and accentuated insulin response, enhanced postprandial levels of glucagon-like peptide-1 (GLP-1) and polypeptide YY (PYY), and greater postprandial suppression of ghrelin. DISCUSSION: These findings indicate that RYGBP is associated with alterations in glucose kinetics and glucoregulatory hormone secretion. These alterations are probably secondary to the anatomic rearrangement of the foregut, given the fact that they are not observed after GB. Increased PYY and GLP-1 concentrations and enhanced ghrelin suppression are compatible with reduced food intake after RYGBP.

Drug uptake in a rodent sarcoma model after intravenous injection or isolated lung perfusion of free/liposomal doxorubicin.

The distribution of free and liposomal doxorubicin (Liporubicin) administered by intravenous injection (IV) or isolated lung perfusion (ILP) was compared in normal and tumor tissues of sarcoma bearing rodent lungs. A single sarcomatous tumor was generated in the left lung of 35 Fischer rats, followed 10 days later by left-sided ILP (n=20) or IV drug administration (n=12), using 100 microg and 400 microg free or liposomal doxorubicin, respectively. The tumor and lung tissue drug concentration was measured by HPLC. Free doxorubicin administered by ILP resulted in a three-fold (100 microg) and 10-fold (400 microg) increase of the drug concentration in the tumor and normal lung tissue compared to IV administration. In contrast, ILP with Liporubicin resulted in a similar drug uptake in the tumor and lung tissue compared to IV injection. For both drug formulations and dosages, ILP resulted in a higher tumor to lung tissue drug ratio but also in a higher spatial heterogeneity of drug distribution within the lung compared to IV administration. ILP resulted in a higher tumor to lung tissue drug ratio and in a more heterogeneous drug distribution within the lung compared to IV drug administration.

Proteomics fingerprinting of phagosome maturation and evidence for the role of a Galpha during uptake.

Phagocytosis, whether of food particles in protozoa or bacteria and cell remnants in the metazoan immune system, is a conserved process. The particles are taken up into phagosomes, which then undergo complex remodeling of their components, called maturation. By using two-dimensional gel electrophoresis and mass spectrometry combined with genomic data, we identified 179 phagosomal proteins in the amoeba Dictyostelium, including components of signal transduction, membrane traffic, and the cytoskeleton. By carrying out this proteomics analysis over the course of maturation, we obtained time profiles for 1,388 spots and thus generated a dynamic record of phagosomal protein composition. Clustering of the time profiles revealed five clusters and 24 functional groups that were mapped onto a flow chart of maturation. Two heterotrimeric G protein subunits, Galpha4 and Gbeta, appeared at the earliest times. We showed that mutations in the genes encoding these two proteins produce a phagocytic uptake defect in Dictyostelium. This analysis of phagosome protein dynamics provides a reference point for future genetic and functional investigations.

Defining secretion processes in astrocytes

During the last decade, evidence that release of chemical transmitters from astrocytes might modulate neuronal activity (the so-called "gliotransmission") occurs in situ has been extensively provided. Nevertheless, gliotransmission remains a highly debated topic because of the lack of direct morphological and functional evidence. Here we provided new information supporting gliotransmission, by i) deepen knowledge about specific properties of regulated secretion of glutamatergic SLMVs, and ii) investigating the involvement of astrocytes in the transmission of dopamine, a molecule whose interaction with astrocytes is likely to occur, but it's still not proven.¦VGLUT-expressing glutamatergic SLMVs have been previously identified both in situ and in vitro, but description of kinetics of release were still lacking. To elucidate this issue, we took advantage of fluorescent tools (styryl dyes and pHluorin) and adapted experimental paradigms and analysis methods previously developed to study exo-endocytosis and recycling of glutamatergic vesicles at synapses. Parallel use of EPIfluorescence and total internal reflection (TIRF) imaging allowed us to find that exo-endocytosis processes in astrocytes are extremely fast, with kinetics in the order of milliseconds, able to sustain and follow neuronal signalling at synapses. Also, exocytosis of SLMVs is under the control of fast, localized Ca2+ elevations in close proximity of SLMVs and endoplasmatic reticulum (ER) tubules, the intracellular calcium stores. Such complex organization supports the fast stimulus-secretion coupling we described; localized calcium elevations have been recently observed in astrocytes in situ, suggesting that these functional microdomains might be present in the intact tissue. In the second part of the work, we investigated whether astrocytes possess some of the benchmarks of brain dopaminergic cells. It's been known for years that astrocytes are able to metabolize monoamines by the enzymes MAO and COMT, but to date no clear information that glial cells are able to uptake and store monoamines have been provided. Here, we identified a whole apparatus for the storage, degradation and release of monoamines, at the ultrastructural level. Electron microscopy immunohistochemistry allowed us to visualize VMAT2- and dopamine-positive intracellular compartments within astrocytic processes, i.e. dense -core granules and cisterns. These organelles might be responsible for dopamine release and storage, respectively; interestingly, this intracellular distribution is reminiscent of VMAT2 expression in dendrites if neurons, where dopamine release is tonic and plays a role in the regulation of its a basal levels, suggesting that astrocytic VMAT2 is involved in the homeostasis of dopamine in healthy brains of adult mammals.¦Durant cette dernière décennie, de nombreux résultats sur le relâchement des transmetteurs par les astrocytes pouvant modulé l'activité synaptique (gliotransmission) ont été fournis. Néanmoins, la gliotransmission reste un processus encore très débattu, notamment à cause de l'absence de preuves directes, morphologique et fonctionnelle démontrant ce phénomène. Nous présentons dans nos travaux de nombreux résultats confortant l'hypothèse de la gliotransmission, dont i) une étude approfondie sur les propriétés spatiales et temporelles de la sécrétion régulée du glutamate dans les astrocytes, et ii) une étude sur la participation des astrocytes dans la transmission de la dopamine, une neuromodulateur dont l'interaction avec les astrocytes est fortement probable, mais qui n'a encore jamais été prouvée. L'expression des petites vésicules (SLMVs - Synaptic Like Micro Vesicles) glutamatergiques exprimant les transporteurs vésiculaires du glutamate (VGLUTs) dans les astrocytes a déjà été prouvé tant in situ qu'in vitro. Afin de mettre en évidence les propriétés précises de la sécrétion de ces organelles, nous avons adapté à nos études des méthodes expérimentales conçues pour observer les processus de exocytose et endocytose dans les neurones. Les résolutions spatiale et temporelle obtenues, grâce a l'utilisation en parallèle de l'épi fluorescence et de la fluorescence a onde évanescente (TIRF), nous ont permis de montrer que la sécrétion régulée dans les astrocytes est un processus extrêmement rapide (de l'ordre de la milliseconde) et qu'elle est capable de soutenir et de suivre la transmission de signaux entre neurones. Nous avons également découvert que cette sécrétion a lieu dans des compartiments subcellulaires particuliers où nous observons la présence du reticulum endoplasmique (ER) ainsi que des augmentations rapides de calcium. Cette organisation spatiale complexe pourrait être la base morphologique du couplage rapide entre le stimulus et la sécrétion. Par ailleurs, plusieurs études récentes in vivo semblent confirmer l'existence de ces compartiments. Depuis des années nous savons que les astrocytes sont capables de métaboliser les monoamines par les enzymes MAO et COMT. Nous avons donc fourni de nouvelles preuves concernant la présence d'un appareil de stockage dans les astrocytes participant à la dégradation et la libération de monoamines au niveau ultrastructurelle. Grâce à la microscopie électronique, nous avons découvert la présence de compartiments intracellulaires exprimant VMAT2 dans les processus astrocytaires, sous forme de granules et des citernes. Ces organelles pourraient donc être responsables à la fois du relâchement et du stockage de la dopamine. De manière surprenante, cette distribution intracellulaire est similaire aux dendrites des neurones exprimant VMAT2, où la dopamine est libérée de façon tonique permettant d'agir sur la régulation de ses niveaux de base. Ces résultats, suggèrent une certaine participation des VMAT2 présents dans les astrocytes dans le processus d'homéostase de la dopamine dans le cerveau.¦A de nombreuses reprises, dans des émissions scientifiques ou dans des films, il est avancé que les hommes n'utilisent que 10% du potentiel de leur cerveau. Cette légende provient probablement du fait que les premiers chercheurs ayant décrit les cellules du cerveau entre le XIXème et le XXeme siècle, ont montré que les neurones, les cellules les plus connues et étudiées de cet organe, ne représentent seulement que 10% de la totalité des cellules composant du cerveau. Parmi les 90% restantes, les astrocytes sont sans doute les plus nombreuses. Jusqu'au début des années 90, les astrocytes ont été plutôt considérés peu plus que du tissu conjonctif, ayant comme rôles principaux de maintenir certaines propriétés physiques du cerveau et de fournir un support métabolique (énergie, environnement propre) aux neurones. Grace à la découverte que les astrocytes ont la capacité de relâcher des substances neuro-actives, notamment le glutamate, le rôle des astrocytes dans le fonctionnement cérébral a été récemment reconsidérée.¦Le rôle du glutamate provenant des astrocytes et son impact sur la fonctionnalité des neurones n'a pas encore été totalement élucidé, malgré les nombreuses publications démontrant l'importance de ce phénomène en relation avec différentes fonctions cérébrales. Afin de mieux comprendre comment les astrocytes sont impliqués dans la transmission cérébrale, nous avons étudié les propriétés spatio-temporelles de cette libération grâce à l'utilisation des plusieurs marqueurs fluorescents combinée avec différentes techniques d'imagerie cellulaires. Nous avons découvert que la libération du glutamate par les astrocytes (un processus maintenant appelé "gliotransmission") était très rapide et contrôlée par des augmentations locales de calcium. Nous avons relié ces phénomènes à des domaines fonctionnels subcellulaires morphologiquement adaptés pour ce type de transmission. Plus récemment, nous avons concentré nos études sur un autre transmetteur très important dans le fonctionnement du cerveau : la dopamine. Nos résultats morphologiques semblent indiquer que les astrocytes ont la capacité d'interagir avec ce transmetteur, mais d'une manière différente comparée au glutamate, notamment en terme de rapidité de transmission. Ces résultats suggèrent que le astrocytes ont la capacité de modifier leurs caractéristiques et de s'adapter à leur environnement par rapport aux types de transmetteur avec lequel ils doivent interagir.

Photodynamic induced uptake of liposomal doxorubicin to rat lung tumors parallels tumor vascular density.

BACKGROUND: Visudyne®-mediated photodynamic therapy (PDT) at low drug/light conditions has shown to selectively enhance the uptake of liposomal doxorubicin in subpleural localized sarcoma tumors grown on rodent lungs without causing morphological alterations of the lung. The present experiments explore the impact of low-dose PDT on liposomal doxorubicin (Liporubicin™) uptake to different tumor types grown on rodent lungs. MATERIAL AND METHODS: Three groups of Fischer rats underwent subpleural generation of sarcoma, mesothelioma, or adenocarcinoma tumors on the left lung. At least five animals of each group (sarcoma, n = 5; mesothelioma, n = 7; adenocarcinoma, n = 5) underwent intraoperative low-dose (10 J/cm(2) at 35 mW/cm(2) ) PDT with 0.0625 mg/kg Visudyne® of the tumor and the lower lobe. This was followed by intravenous (IV) administration of 400 µg Liporubicin™. After a circulation time of 60 min, the tumor-bearing lung was processed for HPLC analyses. At least five animals per group underwent the same procedure but without PDT (sarcoma, n = 5; mesothelioma, n = 5; adenocarcinoma, n = 6). Five untreated animals per group underwent CD31 immunostaining of their tumors with histomorphometrical assessment of the tumor vascularization. RESULTS: Low-dose PDT significantly enhanced Liporubicin™ uptake to all tumor types (sarcoma, P = 0.0007; mesothelioma, P = 0.001; adenocarcinoma, P = 0.02) but not to normal lung tissue compared to IV drug administration alone. PDT led to a significantly increased ratio of tumor to lung tissue drug uptake for all three tumor types (P < 0.05). However, the tumor drug uptake varied between tumor types and paralleled tumor vascular density. The vascular density was significantly higher in sarcoma than in adenocarcinoma (P < 0.001) and mesothelioma (P < 0.001), whereas there was no significant difference between adenocarcinoma and mesothelioma. CONCLUSION: Low-dose Visudyne®-mediated PDT selectively enhances the uptake of systemically administered liposomal doxorubicin in tumors without affecting the drug uptake to normal lung. However, drug uptake varied significantly between tumor types and paralleled tumor vascular density.

Repeated injections of 131I-rituximab show patient-specific stable biodistribution and tissue kinetics.

PURPOSE: It is generally assumed that the biodistribution and pharmacokinetics of radiolabelled antibodies remain similar between dosimetric and therapeutic injections in radioimmunotherapy. However, circulation half-lives of unlabelled rituximab have been reported to increase progressively after the weekly injections of standard therapy doses. The aim of this study was to evaluate the evolution of the pharmacokinetics of repeated 131I-rituximab injections during treatment with unlabelled rituximab in patients with non-Hodgkin's lymphoma (NHL). METHODS: Patients received standard weekly therapy with rituximab (375 mg/m2) for 4 weeks and a fifth injection at 7 or 8 weeks. Each patient had three additional injections of 185 MBq 131I-rituximab in either treatment weeks 1, 3 and 7 (two patients) or weeks 2, 4 and 8 (two patients). The 12 radiolabelled antibody injections were followed by three whole-body (WB) scintigraphic studies during 1 week and blood sampling on the same occasions. Additional WB scans were performed after 2 and 4 weeks post 131I-rituximab injection prior to the second and third injections, respectively. RESULTS: A single exponential radioactivity decrease for WB, liver, spleen, kidneys and heart was observed. Biodistribution and half-lives were patient specific, and without significant change after the second or third injection compared with the first one. Blood T(1/2)beta, calculated from the sequential blood samples and fitted to a bi-exponential curve, was similar to the T(1/2) of heart and liver but shorter than that of WB and kidneys. Effective radiation dose calculated from attenuation-corrected WB scans and blood using Mirdose3.1 was 0.53+0.05 mSv/MBq (range 0.48-0.59 mSv/MBq). Radiation dose was highest for spleen and kidneys, followed by heart and liver. CONCLUSION: These results show that the biodistribution and tissue kinetics of 131I-rituximab, while specific to each patient, remained constant during unlabelled antibody therapy. RIT radiation doses can therefore be reliably extrapolated from a preceding dosimetry study.