Introduction Since its development by Al Wolf and colleagues in the 1970s1, [11C]cyanide has been a useful synthon for a wide variety of reactions, most notably those producing [1-11C]-labeled amino acids2. However, despite its position as rote gas-phase product, the catalytic synthesis is difficult to optimize and often only perfunctorily dis-cussed in the radiochemical literature. Recently, [11C]CN– has been used in the synthesis of indole-3-[1-11C]acetic acid ([11C]IAA), the principal phytohormone responsible for a wide variety of growth and development functions in plants3. The University of Wisconsin has expertise in cyclotron production and radiochemistry of 11C and previous experience in the PET imaging of plants4,5. In this abstract, we present work on optimizing [11C]CN– production for the synthesis of [11C]IAA and the PET imaging of auxin transport in living plants. Material and Methods [11C]CH4 was produced by irradiating 270 psi of 90% N2, 10% H2 with 30 µA of 16.1 MeV protons from a GE PETtrace cyclotron. After irradiation, the [11C]CH4 was converted to [11C]CN– by passing through a quartz tube containing 3.0 g of Pt wire and powder between quartz wool frits inside a 800–1000 ˚C Carbolite tube furnace. The constituents and flow rate of the [11C]CH4 carrier gas were varied in an effort to optimize the oven\'s catalytic production of [11C]CN– from CH4 and NH3. The following conditions were investigated: i. Directly flowing irradiated target gas versus trapping, purging and releasing [11C]CH4 from a −178 ˚C HayeSep D column in He through the Pt furnace. ii. Varying the amount of anhydrous NH3 (99.995%) mixed with the [11C]CH4 carrier gas prior to the Pt furnace. Amounts varied from zero to 35 % of gas flow. iii. Varying the purity of the added NH3 gas with the addition of a hydride gas purifier (Entegris model 35KF), reducing O2 and H2O impurities to < 12 ppb. iv. Varying the flow rate of He gas carrying trapped, purged and released [11C]CH4. After flowing through the Pt furnace, the gas stream was bubbled through 300 µL of DMSO containing IAA precursor gramine (1 mg), then passed through a 60×5 cm column containing ascarite to absorb [11C]CO2, followed by a −178˚C Porapak Q column to trap [11C]CH4 and [11C]CO. After bubbling, the DMSO/gramine vial was heated to 140 ˚C to react the gramine with [11C]CN–, forming the intermediate indole-3-[1-11C]acetonitrile ([11C]IAN), which was subsequently purified by solid phase extraction (SPE). The reaction mixture was diluted into 20 mL water and loaded onto a Waters Sep-Pak light C18 cartridge, followed by rinsing with 5 mL of 0.1% HCl : acetonitrile (99 : 1) and 10 mL of the same mixture in ratio 95 : 5, and finally eluted with 0.5 mL of diethyl ether. The ether was subsequently evaporated under argon flow, followed by the hydrolysis of [11C]IAN to [11C]IAA with the addition of 300 µL 1 M NaOH and heating to 140 ˚C for 5 minutes. After hydrolysis, the solution was neutralized with 300 µL 1 M HCl and purified using preparative high-performance liquid chromatography (HPLC) using a Phenomenex Luna C18 (10μ, 250×10mm) column with a mobile phase acetonitrile : 0.1% formic acid in H2O (35 : 65) at flow rate of 3 mL/min. The [11C]IAA peak, eluting at 12 minutes, was collected and rotary evaporated to dryness, then again after the addition of 5 mL acetonitrile, followed by its reconstitution in 50 µL of water. Analytical HPLC was performed on the [11C]IAA before and after this evaporation procedure using a Phenomenex Kinetex C18 (2.6μ, 75× 4.6 mm) column with a linear gradient elution over 20 minutes of 10 : 90–30 : 70 (acetonitrile : 0.1% formic acid) at a 1 mL/min flow rate, eluting at 7.6 minutes. The transport of [11C]IAA was monitored following administration through the severed petiole of rapid cycling Brassica oleracea (rcBo) using a Siemens microPET P4 scanner. Transport was compared following administration to the first true leaf versus the final fully formed leaf in plants with and without exposure to the polar auxin transport inhibitor naphthylphthalamic acid (NPA). Results and Conclusion Optimization of the [11C]CN– gas phase chemistry was performed using two key metrics for measuring conversion yield. First is the fraction of total produced radioactivity that trapped in the DMSO/gramine solution (denoted %DMSO), and second, the fraction of DMSO/gramine-trapped activity that was able to react with gramine to form [11C]IAN (denoted %CN–). Under certain conditions, the former of these metrics experienced significant losses due to unconverted [11C]CH4 or through combustion, forming [11C]CO2 or [11C]CO. The latter metric experienced losses due to production of incomplete oxidation products of the CH4-NH3 reaction, such as methylamine. Total [11C]CH4 to [11C]CN– con-version yields is reported by the product of the two metrics. It was initially hypothesized that the irradiation of a 90% N2, 10% H2 target gas would produce sufficient in-target-hot-atom-produced NH3 to convert [11C]CH4 to [11C]CN– in the Pt furnace. However, conversion yields were found to be low and highly variable, with 13 ± 8 % trapping in DMSO/gramine, 9 ± 9 % of which reacted as CN– (n = 15). While in disagreement with previous reports1, this is likely as a result the batch irradiation conditions resulting ammonia losses in the target chamber and along the tubing walls. Yields and reproducibility were improved when combining the target gas with a stream of anhydrous NH3 gas flow with conversion yields reported in TABLE 1. However, these yields remained undesirably low, potentially as a result of the 10% H2 carrier gas having an adverse effect on the oxidative conversion of [11C]CH4 to [11C]CN–. To remedy this, the irradiated target gas was trapped, purged, released in He and combined with NH3 gas before flowing through the Pt furnace. Initial experiments using 99.995% anhydrous NH3 gas resulted in very poor (< 0.1%) [11C]CN– yields as a result of nearly quantitative combustion forming [11C]CO2. Installation of a hydride gas purifier to reduce O2 and H2O impurities in NH3 improved yields for CH4 in He, but did not significantly affect those from [11C]CH4 in N2/H2 target gas. In disagreement with previous reports2, conversion yields were found to be highly sensitive to overall carrier gas flow rate, with lower flow rates giving the best yields, as shown in TABLE 1. Optimization experiments are continuing. The total decay-corrected yield for the 1 hour synthesis of [11C]IAA in 50 µL of water is 2.3 ± 0.7 %, based on the total produced [11C]CH4 with a specific activity ranging from 1–100 GBq/µmol. The principal radiochemical impurity was determined to be indole-3-carboxylic acid. The SPE procedure isolating the [11C]IAN intermediate product was optimized to minimize this impurity in the final sample. After a rapid distribution of the administered [11C]IAA through the cut petiole and throughout the rcBO plant, upward vascular transport of auxin and downward polar auxin transport was visualized through time-activity curves (TACs) of regions of interest along the shoot. Comparison of these TACS with and without exposure to NPA yields insight into the fundamental physiological process of polar auxin transport in plants. In conclusion, the Pt-catalyzed oxidative conversion of [11C]CH4 and NH3 to [11C]CN– is a challenging process to optimize and highly sensitive to carrier gas composition and flow rate. Optimization for our experimental conditions yielded several results which disagreed with previous reports. [11C]IAA produced using [11C]CN– is well suited for PET imaging of polar auxin transport in living plants.

The Angiotensin II Type 1 (AT1) receptor is the main receptor responsible for the effects of the renin-angiotensin system, and its expression pattern is altered in several diseases. [11C]Methyl-Losartan has been developed based on the clinically used AT1 receptor antagonist Losartan. The aim of this work is to characterize the pharmacokinetics, repeatability and reliability of measurements, binding specificity and selectivity of [11C]Methyl-Losartan in rats using in vivo small animal positron emission tomography (PET) imaging, ex vivo biodistribution and in vitro autoradiography methods. Also, we aim to measure the presence of metabolites in the kidney and plasma using high-performance liquid chromatography. We have demonstrated in vivo that [11C]Methyl-Losartan is taken up in the AT1 receptor-rich kidneys and that it is displaceable by selective AT1 receptor antagonists. Using ex vivo biodistribution, we have confirmed these results and demonstrated that [11C]Methyl-Losartan binds selectively to the AT1 receptor over the AT2, Mas and β-adrenergic receptors. In vitro autoradiography results confirmed these renal binding selectivity studies. [11C]Methyl-Losartan was also shown to have one and two C-11 labeled metabolites in the plasma and kidneys, respectively. In conclusion, [11C]Methyl-Losartan is a promising agent for studying the AT1 receptor in rat models with normal and altered AT1 receptor expression using small animal PET imaging.

Les maladies cardiovasculaires représentent la première cause de morbidité et mortalité dans le monde. L'athérosclérose, qui conduit à l'obstruction des artères, est à l'origine de 50% des décès dans les sociétés industrialisées. La rupture d'une plaque d'athérosclérose dite vulnérable entraîne de nombreuses complications qui, en fonction du territoire artériel considéré, vont de l'accident vasculaire cérébral à l'infarctus du myocarde. Pour pallier ce problème de santé publique majeur, l'enjeu clinique et en particulier diagnostic repose sur la prévention de ces complications cardiovasculaires dans une population à haut risque comme à l'île de la Réunion, qui se caractérise par une incidence élevée d'atteintes vasculaires et de mortalité associée. Or, il n'existe aucune technique d'imagerie permettant la détection précoce des plaques d'athérosclérose vulnérables. La médecine nucléaire possède une grande sensibilité et pourrait offrir des outils diagnostics performants permettant d'évaluer la formation de ces plaques. Parmi tous les biomarqueurs tissulaires et circulants produits lors de l'athérogenèse, nous avons choisi la Lp-PLA2 (phospholipase A2 associée aux lipoprotéines), enzyme associée aux processus inflammatoires (produite par les monocytes et macrophages) et transportée par les lipoprotéines, comme cible de l'athérosclérose en imagerie TEP (Tomographie par Émission de Positons). Nos travaux ont permis la synthèse puis le radiomarquage d'un puissant inhibiteur cette enzyme : le Darapladib, ainsi que d'analogues. Nous avons réussi à obtenir le 18F-Darapladib afin d'étudier son accumulation dans des modèles murin et ex vivo humain de plaques d’athérome. / Cardiovascular diseases are the leading cause of morbidity and mortality worldwide. Atherosclerosis, which leads to the obstruction of large arteries, represents 50% of deaths in industrialized societies. Rupture of a vulnerable atherosclerotic plaque can lead to several complications which, depending on the site, can cause stroke or myocardial infarction.To address this public health issue, there is a real need to develop new diagnostic tools to prevent these cardiovascular complications in a high risk population in Reunion island. However, no potent tool is available to doctors in order to predict the formation of vulnerable atherosclerotic plaques. Nuclear medicine with its high sensibility could offer new powerful diagnostic tools in order to assess vulnerable atheroma formation. Among all biomarkers available to the scientific community, we chose Lp-PLA2 (Lipoprotein-associated phospholipase A2) which is an enzyme associated to inflammatory processes (produced by monocytes and macrophages) as a target for PET (Positron Emission Tomography) imaging of atherosclerosis.Our work describes the radiolabelling of a potent inhibitor of this enzyme: Darapladib and associated analogs. We were able to perform its radiolabelling and to study its potential accumulation in atheroma murin models and in ex vivo human endarterectomy pieces.

Les maladies neurodégénératives sont un sujet de santé publique majeur. La maladie de Parkinson (MP), la démence à corps de Lewy (DCL) et l'atrophie multisystématisée (AMS) font partie d'une famille liées à l'accumulation pathologique d'une protéine : l'α-synucléine (α-syn), appelées les synucléinopathies. Il n'existe pas méthode de diagnostic formel pre-mortem de ces pathologies. À ce jour, la confirmation définitive de synucléinopathies n'est possible que sur des études post-mortem. Le mécanisme de survenue reste incompris. L'exploration des systèmes de neurotransmission et des voies métaboliques pourrait permettre d'élucider ces mécanismes. Les travaux effectués au cours de cette thèse se positionnent dans une optique de développement d'un outil de diagnostic précoce et de compréhension des mécanismes physiopathologiques grâce à l'imagerie TEP. Dans une première partie, nous avons caractérisé et validé un modèle murin de synucléinopathies. Nous avons conclu que le [18F]BF227 ne pouvait être employé comme radiotraceur des agrégats d'α-syn. La seconde partie a permis la mise au point d'une technique d'évaluation de l'affinité de molécules pour une cible donnée. Douze ligands froids ont pu être testés in vitro. Actuellement, aucun composé ne semble présenter les critères pour être un radiotraceur idéal. Enfin, la dernière partie a mis en évidence un hypométabolisme glucidique ainsi qu'une surexpression des récepteurs 5-HT1A à un stade précoce de la pathologie. Au final, cette étude a montré l'intérêt et les limites de l'imagerie TEP et des modèles animaux pour le développement d'un nouveau radiotraceur ainsi que pour l'exploration des mécanismes physiopathologiques / Neurodegenerative diseases are a major public health issue. Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA) are part of a family related to the pathological accumulation of a protein, α-synuclein (α- syn), and called synucleinopathies. To date, there is no pre-mortem formal diagnosis method for these diseases and the final confirmation only relies on postmortem studies. While the occurrence mechanisms remain unclear, exploration of neurotransmitter systems and metabolic pathways could bring more information on the underlying pathophysiological processes. The aims of this PhD work were (1) to develop the first radioligand targeting α-syn as an early diagnostic tool and (2) to investigate, with PET imaging, how neurotransmitter systems relates to pathophysiological mechanisms in an accelerated mouse model of synucleinopathy. In the first part of this study, we demonstrated the inability of in vivo PET imaging with [18F]BF227 to label α-syn aggregates in a model of synucleinopathy. The second part allowed the development of a competitive radioligand binding assay to determine α-syn binding parameters of non-radioactive candidate molecules. Twelve ligands were tested in vitro. Currently, no compound appears to present ideal α-syn binding properties. The last part of this study highlighted a serotoninergic hypometabolism and the overexpression of 5-HT1A receptors at an early stage of the disease in the synucleinopathy mouse model. Finally, this study demonstrated the advantages and limitations of PET imaging and animal models for the development of radiotracer and for the exploration of pathophysiological mechanisms

The Angiotensin II Type 1 (AT1) receptor is the main receptor responsible for the effects of the renin-angiotensin system, and its expression pattern is altered in several diseases. [11C]Methyl-Losartan has been developed based on the clinically used AT1 receptor antagonist Losartan. The aim of this work is to characterize the pharmacokinetics, repeatability and reliability of measurements, binding specificity and selectivity of [11C]Methyl-Losartan in rats using in vivo small animal positron emission tomography (PET) imaging, ex vivo biodistribution and in vitro autoradiography methods. Also, we aim to measure the presence of metabolites in the kidney and plasma using high-performance liquid chromatography. We have demonstrated in vivo that [11C]Methyl-Losartan is taken up in the AT1 receptor-rich kidneys and that it is displaceable by selective AT1 receptor antagonists. Using ex vivo biodistribution, we have confirmed these results and demonstrated that [11C]Methyl-Losartan binds selectively to the AT1 receptor over the AT2, Mas and β-adrenergic receptors. In vitro autoradiography results confirmed these renal binding selectivity studies. [11C]Methyl-Losartan was also shown to have one and two C-11 labeled metabolites in the plasma and kidneys, respectively. In conclusion, [11C]Methyl-Losartan is a promising agent for studying the AT1 receptor in rat models with normal and altered AT1 receptor expression using small animal PET imaging.

Parmi les différents isotopes du Scandium qui peuvent être utilisés en médecine nucléaire, on peut citer le ⁴⁷Sc et le ⁴⁴Sc. Le premier se désintègre en émettant un électron associé à un gamma de 159 keV et peut donc être utilisé soit pour faire de la radiothérapie, soit de l’imagerie TEMP. Le ⁴⁴Sc (3.97 h) se désintègre dans 94.27 % des cas en émettant un positron, accompagné d’un photon γ d’énergie égale à 1.157 MeV. Cet isotope est alors un candidat idéal pour des applications en imagerie TEP. Actuellement, le Cyclotron de haute énergie et haute intensité Arronax produit le ⁴⁴Sc et coproduit son état isomérique le ⁴⁴mSc (2.44 j). Le ⁴⁴mSc a des propriétés (Eᵧ=270 keV, 98.8 %) qui permet d’envisager son utilisation comme potentiel générateur in vivo. Les travaux précédents ont permis de montrer que le ligand DOTA est le plus adapté et le plus stable pour le Sc. Ce travail de thèse a pour but de mettre en évidence la faisabilité du générateur in vivo ⁴⁴m/⁴⁴Sc. Dans un premier temps une procédure a été optimisée et validée pour la production du ⁴⁴m/⁴⁴Sc avec une haute activité spécifique et pureté chimique. Le radiomarquage sur des peptides contenant du DOTA a été ensuite développé et optimisé. Des études théoriques et expérimentales ont été réalisées dans le but de démontrer la faisabilité du ⁴⁴m/⁴⁴Sc comme potentiel générateur in vivo. En fin des études de stabilité in vitro sur des complexes radiomarqués du ⁴⁴m/⁴⁴Sc suivi d’études de biodistribution et d’imagerie TEP ont été réalisées. / Among the different isotopes of Scandium that can be used in nuclear medicine may be mentioned the ⁴⁷Sc and ⁴⁴Sc. The first decays by emitting an electron associated with a 159 keV gamma can thus be used either for radiotherapy or TEMP imaging. The ⁴⁴Sc (3.97 h) decays in 94.27% in case by emitting a positron, with a γ photon energy equal to 1.157 MeV. This isotope is then an ideal candidate for applications in PET imaging. Currently, the Cyclotron of high energy and high intensity ARRONAX produce ⁴⁴Sc and co-produces the isomeric state the ⁴⁴mSc(2.44 d). The ⁴⁴mSc has properties (Eᵧ = 270 keV, 98.8%), which allows to consider its use as a potential in vivo generator. Previous work had demonstrated that the DOTA ligand is most suitable and stable for Sc. This thesis aims; make in evidence the feasibility of the in vivo ⁴⁴m/⁴⁴Sc generator. Initially a procedure was optimized and validated for the production of ⁴⁴m/⁴⁴Sc with a high specific activity and chemical purity. Radiolabeling of DOTA conjugated peptides was then developed and optimized. Theoretical and experimental studies have been performed in order to demonstrate the feasibility of ⁴⁴m/⁴⁴Sc as a potential in vivo generator. Finally, in vitro stability studies on radiolabeled ⁴⁴m / ⁴⁴Sc complexes were performed, followed by biodistribution studies and PET imaging.

Introduction 76Br is of interest for in vivo PET imaging applications. Its relatively long half-life (16.1 h) allows use not only on small molecules but also proteins which have slow excretion as carrier molecules. Irradiation using a low energy proton beam (~ 20 MeV) on an enriched Cu276Se target, followed by dry distillation with thermal chromatography, is one of the best methods to obtain sufficient amounts of 76Br for clinical applications1,2. However, the thermal chromatography is plagued by poor reproducibility and appears unsuitable for automation of its production, leading us to remove the thermal chroma-tography from the dry distillation. In this investigation we employed H2O solution to collect 76Br and optimized the distillation condition using a small amount of 77Br (57.0 h). We also produced large amount of 76Br under the optimized conditions to evaluate the dry distillation method. Material and Methods Target preparation and dry distillation were conducted based on the methods described in previous reports1,2. To produce 77Br, Cu2natSe target was irradiated with 20 MeV proton beams (5 µA) accelerated by AVF cyclotron in the Japan Atomic Energy Agency. The following two systems were used in the dry distillation optimization studies; (1) an initial system was composed of two furnaces, a main and an auxiliary furnace. Temperature of each furnace was set at 1050 °C (main) and 200 °C (auxiliary) respectively; (2) the second system was made of one large furnace composed of heating and cooling area. Temperature of the heating area was varied from 1050 to 1120 °C. In both systems PTFE tubing, leading to a H2O solution (15 mL), was inserted into the apparatus. The irradiated target was heated under streaming Ar gas (30 mL/min.). An enriched Cu276Se target (76Se enrichment: 99.67%) was used for 76Br production. Radioactivity was measured on a high-purity germanium (HPGe) detector coupled to a multichannel analyzer. TLC analyses were conducted on Al2O3 plates (Merck) using 7:1 acetone:H2O as the eluting solvent. Results and Conclusion Low efficiency (33 %) of 77Br recovery was ob-served in the initial system. Distribution of radioactivity inside the apparatus showed that 35 % was trapped in the PTFE tube and the quartz tube. The recovery yield was increased up to 54 % when the auxiliary furnace was turned off, indicating that the temperature gradient inside the quartz tube is suitable to carry 77Br effectively to the H2O trap. We initially used a quartz boat to place the irradiated target in the furnace, but found that using a reusable tungsten backing was better. However, we found that recovery yield was dramatically reduced to 18 %. The studies where the temperature was varied showed that releasing efficiency was increased up to 100 % at the temperature of 1120 °C. Good recovery yield (~ 77 %) was achieved after optimizing the temperature gradient (FIG. 1b). Using the optimized setup, 76Br production runs (n = 6) have been conducted, allowing us to recover up to 39.8 MBq/µAh (EOB) of 76Br. High specific activity (~4400 GBq/µmol) was obtained in the final solution. TLC analysis showed that chemical form obtained was bromide. We concluded that the dry distillation using H2O trap is capable of providing enough high purity 76Br for clinical applications.

Introduction The 80kD glycoprotein transferrin (TF) and its related receptor (TFR1) play a major role in the recruitment by cancer cells of factors for their multiplication, adhesion, invasion and metastatic potential. Though primarily designed to bind iron and then be internalised into cells with its receptor, TF can also bind most transition metals such as Co, Cr, Mn, Zr, Ni, Cu, V, In & Ga. Under certain conditions TF binds Ti (IV) even more tightly than it does Fe and that this occurs at the N-lobe (as distinct from C) of apoTF. Further, under physiological conditions the species Fe(C)Ti(N)-TF may provide the route for Ti entry into cells via TFR1 (1). Thus, the radiometal PET reporter isotope 45Ti with an ‘intermediate’ (~hrs) half-life suited to tracking cell-focused biological mechanisms is an attractive option for elucidating cellular mechanisms involving TF binding and internalisation, at least in (preclinical) animal models. 45Ti (T½ = 3.08 hr; + branching ratio = 85 %; mean β+ energy = 439keV, no significant dose-conferring non-511keV γ-emissions) was produced using the reaction 45Sc(p,n)45Ti by irradiating (monoisotopic) scandium discs with an energy-degraded proton beam produced by an 18MeV isochronous medical cyclotron. Separation and purification was achieved with an hydroxylamine hydrochloride functionalised resin. Comparative microPET imaging was performed in an immunodeficient mouse model, measuring biodistributions of the radiolabels 45Ti-oxalate and 45Ti-human-TF (45Ti-h-TF), out to 6hr post-injection. Materials and Methods High purity 15mm diameter scandium disc foils (99.5%, Goodfellow, UK) each thickness 0.100 ± 0.005 mm (55 mg) were loaded into an in-house constructed solid-targetry system mounted on a 300mm external beam line utilising helium-gas and chilled water to cool the target body (2). The proton beam was degraded to 11.7 MeV using a graphite disc integrated into the graphite collimator. This energy abolishes the competing ‘contaminant’ reactions 45Sc(p,n+p)44Sc and 45Sc(p,2n)44Ti. Beam current was measured using the well documented 65Cu(p,n)65Zn reaction. Calculations showed that the chosen energy is close to the optimal primary energy (~12 MeV) for maximising the (thin-target) yield from a 0.100 mm thick target. For separation of Ti from the Sc target two methods were examined; (i) ion exchange column separation using 2000 mg AG 50W-X8 resin conditioned with 10mL 9M HCl. Disc is dissolved in 1 mL of 9M HCl, which at completion of reaction is pipetted into column. Successive 1 mL volumes of 9M HCl are added, and subsequent elutions collected. (ii) Following Gagnon et al., (3) a method employing hydroxylamine hydro-chloride functionalised resin (’hydroxamate method’) was applied, similar to its use in our hands for purification and separation of 89Zr (2) following its original description for 89Zr by Holland et al., (4). Disc dissolved in 2mL 6M HCl, then diluted to 2M. Elute through column to waste fraction 1 (w1 – see FIG. 1). Then elute 6 mL of 2M HCl through column to w2, followed by 6 mL of traceSELECT H2O to w3. Finally, elute Ti into successive 1 mL product fractions (p1, 2 etc.) using 5 mL of 1M oxalic acid. This procedure takes approximate 1 hr. 45Ti in elution vials was measured using γ-spectroscopy. Sc in the same vials was determined later using ICP-MS. Results A typical production run using a beam current of 40 μA for 60min on a 0.100mm-thick disc produced an activity of 1.83 GBq. Radionuclidic analysis of an irradiated disc using calibrated cryo-HPGe γ-spectroscopy revealed T½ = 2.97–3.19 hr (95% CI) for 45Ti, and with contaminant 44Sc < 0.19 %, with no other isotopes detected. Despite systematic adjustments to column conditions satisfactory chemical separation was not achieved using the ion exchange column method (i), despite previous reports of its success (5). Typical results of separation using the successful hydroxamate method (ii) are shown on the FIGURE 1. It is seen that significant portion of 45Ti is lost in the initial washing steps leading to waste collection. N = 4 replicate experiments showed a variation (SD) of 10 % of the mean in each elu-tion fraction. Subsequent ICP-MS of the same elutions for (cold) Sc showed approximately 80 % by mass appeared in w1 and 20 % in w2, with negligible total mass (total fraction ~1/6000) of Sc in product (p1–4) vials. However, the FIG. 1 shows that a total of only 30% of the original activity of 45Ti (corrected to EOB) is available in the product vials, with the vial of highest specific activity (p1) containing 14 %. However, using a stack of 2×0.100mm thick Sc discs as a target yields isotope of adequate specific activity with-out need for concentration, for subsequent labelling and small-animal imaging purposes. In a ‘proof-of-principle’ experiment, two groups of healthy Balb/c-nu/nu female adult mice were administered with 45Ti radiotracers. The first group (N = 3) received approximately 20 MBq IP of 45Ti-oxalate buffered to pH = 7.0, and under-went microPET/CT imaging (Super Argus PET, Sedecal, Spain) out to 6hr post-injection, plus biodistribution analysis of radioactivity by dis-section at sacrifice (6hr). The second group (N = 3) received approximately 20 MBq IP of 45Ti-h-TF and were also studied to 6hr post-injection, followed by radioactive analysis after dissection at sacrifice. Organ and tissue biodistributions of the two groups at 6hr were similar but with 45Ti-oxalate showing slightly greater affinity for bone. Biodistribution by dissection results broadly confirmed the findings from PET images. However, TLC results suggested that similarity of radiolabel biodistributions of the two groups may be due to contamination of the TF radiolabel with non-conjugated Ti at time of injection. An alternative explanation is dechelation in vivo of 45Ti from 45Ti-h-TF. Conclusion Despite significant loss of 45Ti to the waste fractions of the separation process (total 53 %, corrected to EOB), 45Ti of acceptable specific activity and high radionuclidic purity has been produced from the reaction 45Sc(p,n)45Ti, with separation and purification of the product by hydroxamate column chemistry, confirming an earlier report. Though microPET in vivo imaging using 45Ti-based radiolabels was shown to be feasible, the similarity in the results for the label 45Ti-h-TF compared with ‘raw’ 45Ti-oxalate suggests further investigations. These may include a direct comparison of in vivo 45Ti-h-TF small-animal imaging plus post-dissection biodistribution with the same procedures using 89Zr labelled h-apotransferrin (6).

Ces dernières années, le ciblage des RCPG avec des ligands radiomarqués est devenu très important en imagerie nucléaire, notamment avec le remplacement progressif d’analogues peptidiques de la somatostatine marqués à l’111In pour la TEMP par d’autres marqués au 68Ga pour l'imagerie TEP qui présente une meilleure efficacité diagnostique. Les récepteurs de haute affinité de la bombésine (GRPR) ou de la neurotensine (NTR1) sont eux aussi des RCPG surexprimés par les cellules tumorales par rapport au tissu sain. Le GRPR est surexprimé dans 83% des carcinomes mammaires canalaires estrogènes dépendants. Dans la première partie de ce travail, nous avons démontré qu’un agoniste du GRPR, l’AMBA marqué au 68Ga, permettait la détection en TEP d’un modèle murin de cancer du sein humain estrogène-dépendant et qu’il permettait de prédire la réponse tumorale à une hormonothérapie de manière plus sensible que le 18F-FDG.L’équipe du Dr. Gruaz-Guyon a développé de nouveaux radioligands analogues de la neurotensine pour le ciblage des tumeurs exprimant le NTR1 et a étudié les propriétés de ces peptides marqués à l'111In dans un modèle de tumeurs d’adénocarcinome colique surexprimant le NTR1. L’obtention d’images TEMP de contraste élevé, permettant une détection des greffes tumorales dans des temps courts après injection, a conduit cette équipe à envisager ce traceur peptidique pour l’imagerie TEP. Dans la seconde partie de ce travail, nous avons réalisé le radiomarquage au 68Ga du meilleur de ces dérivés (DOTA NT20.3) et évalué son potentiel pour l'imagerie TEP et la détection de tumeurs d’adénocarcinome colique. La surexpression de NTR1 a été démontrée dans plusieurs autres cancers comme l’adénocarcinome pancréatique (PDAC) (75-88%). Nous avons donc voulu étudier l'expression du NTR1 dans une tumorothèque locale de PDAC. Nous avons ensuite démontré le potentiel du 68Ga-DOTA-NT20.3 pour l’imagerie TEP dans deux modèles murins de PDAC humains. Nous avons caractérisé sa biodistribution, évalué sa spécificité in vivo et l’avons comparé au 18F-FDG, notamment pour valider sa capacité à discriminer in vivo la pancréatite de l’adénocarcinome pancréatique. / In recent years, the targeting of G protein-coupled membrane receptors (GPCRs) with radiolabeled ligands has become very important in nuclear imaging, particularly with the progressive replacement of somatostatin analogues labelled with 111In for SPECT by others labelled with 68Ga for PET imaging, which improves diagnostic efficacy. High-affinity bombesin receptors (GRPR) or neurotensin receptors (NTR1) are also GPCRs overexpressed in many cancers as compared with normal tissue. GRPR is overexpressed in 83% of estrogen-dependent ductal carcinomas. In the first part of this work, we demonstrated that 68Ga-AMBA, an agonist ligand of GRPR, allowed the PET detection of a mouse model of estrogen-dependent breast cancer and could be more sensitive than 18F-FDG to predict and monitor tumour response to hormone therapy.Dr. Gruaz-Guyon's team has developed new neurotensin radioanalogues for targeting NTR1-positive tumours. They studied the properties of these 111In-labeled peptides in a model of colon adenocarcinoma overexpressing NTR1. Obtaining high-contrast images allowing the detection of cancer within a short time after injection, this team subsequently developed this peptide radiotracer for PET imaging. In the second part of this work, we carried out the 68Ga radiolabeling of the best-performing of these derivatives and evaluated its potential for PET imaging of colon adenocarcinoma in a tumor model. Overexpression of NTR1 has been demonstrated in several human cancers such as PDAC (75-88%). We characterized the expression of NTR1 using specimens of human pancreatic cancer and then demonstrated the potential of this PET radiotracer to image two mouse models of human PDAC. We characterized its biodistribution, assessed its specificity in vivo in comparison with 18F-FDG, in particular its ability to discriminate in vivo pancreatitis from pancreatic adenocarcinoma.

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