Rapid 64Cu radiolabeling and in vivo evaluation of DSPE-NODAGA liposomes in a murine mammary tumor model.

FDG-PET for response assessment: answers in search of questions

Remote-loading of liposomes with manganese-52 and in vivo evaluation of the stabilities of 52Mn-DOTA and 64Cu-DOTA using radiolabelled liposomes and PET imaging

Bystander Killing of Malignant Glioma by Bone Marrow–derived Tumor-Infiltrating Progenitor Cells Expressing a Suicide Gene

Fluorine-18 offers good radionuclide characteristics for incorporation into positron radiopharmaceuticals. Development of fluorine-18 radiopharmaceuticals for neuroreceptor imaging by positron emission tomography (PET) is a challenge that most of us in the PET community have encountered. The magnitude of the problem is due to the multidisciplinary nature of issues that a radiochemist faces, such as drug design, organic syntheses, in vitro pharmacology, radiolabeling methods, in vivo pharmacology, in vivo stability and radiotracer modeling methods in order to achieve the successful application of a radiopharmaceutical in meaningful human studies. The radiochemist is therefore forced to anticipate and take into account in the design process the potential hurdles that might be encountered upon arrival at each step. Fluorine is becoming a more common element that is incorporated into biologically interesting molecules within the pharmaceutical industry. When such fluorinated lead compounds from the pharmaceutical industry are available, development of a fluorine-18 radiopharmaceutical is somewhat simplified, and then largely depends upon radiolabeling methods, in vivo pharmacology, in vivo stability and radiotracer modeling methods. However, there remain a large number of potentially useful pharmaceuticals which are of interest to PET researchers that do not possess a fluorine atom. Therefore as a question of investment versus outcome should researchers, particularly radiochemists in the PET community, embark on new drug development rather than use only what is available from the pharmaceutical industry.

Metastasis of the osseous tissue is one of the frequent and severe aggravations as a result of several neoplastic conditions, such as metabolic disorders, infections, and cancer. The objective of this study was to evaluate the pertinence of [68Ga]-trans-1,2-cyclohexyldinitrilo tetramethylene phosphonic acid (CDTMP) as a potential bone imaging agent for positron emission tomography (PET) applications as well as to assess [188Re]-CDTMP for bone pain palliation in metastatic skeletal disorders. 68Ga complex of CDTMP was prepared at 80°C at pH 3.5, and 188Re complex of CDTMP was prepared at room temperature. [68Ga]-CDTMP complex was investigated as PET tracer while the therapeutic efficacy was assessed for [188Re]-CDTMP. Labeling efficiency, biodistribution, myelotoxicity, and imaging studies were carried out for the complexes synthesized. Both PET and MicroPET imaging studies were performed for [68Ga]-CDTMP whereas SPECT acquisitions were acquired for [188Re]-CDTMP. Data were analyzed semiquantitatively for all the scintigraphic scans obtained. The radiolabeling efficiency was observed to be >70% for [68Ga]-CDTMP. High bone uptake of [68Ga]-CDTMP as compared to contralateral tissue was found in PET imaging in Balb/C mice and New Zealand rabbit; the similar result for bone uptake was correlated in the biodistribution study of the compound in BALB/c mice at different time intervals. Biodistribution experiments carried out in mice showed maximum uptake of 6.12 ± 1.22%ID/g at 45 min postinjection. For [188Re]-CDTMP, total skeletal uptake was 8.12 ± 1.11%ID/g observed at 1 h postinjection from biodistribution data. High renal uptake confirms renal route of excretion. A good hydroxyapatite binding too was seen for both the complexes. No evidence of destruction or adverse functioning of vital organs was observed for the 188Re complex. [68Ga]-CDTMP complex can be used as a promising PET bone imaging agent and [188Re]-CDTMP as a surrogate moiety for therapeutic application. Owing to the short half-life of 68Ga (68 min), cyclotron-independent radiopharmacy, fast clearance, and rapid renal excretion as evidenced in preclinical animal models. Very low myelotoxicity and highly selective bone uptake prove the potential of [188Re]-CDTMP for therapeutic application.

Administered activity and metastatic cure probability during radioimmunotherapy of ovarian cancer in nude mice with 211At-MX35 F(ab′)2

Practice-Based Evidence of the Beneficial Impact of Positron Emission Tomography in Clinical Oncology

FXYD5 (related to ion channel, dysadherin) is a member of the FXYD family of single span type I membrane proteins. Five members of this group have been shown to interact with the Na,K-ATPase and to modulate its properties. However, FXYD5 is structurally different from other family members and has been suggested to play a role in regulating E-cadherin and promoting metastasis (Ino, Y., Gotoh, M., Sakamoto, M., Tsukagoshi, K., and Hirohashi, S. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 365-370). The goal of this study was to determine whether FXYD5 can modulate the Na,K-ATPase activity, establish its cellular and tissue distribution, and characterize its biochemical properties. Anti-FXYD5 antibodies detected a 24-kDa polypeptide that was preferentially expressed in kidney, intestine, spleen, and lung. In kidney, FXYD5 resides in the basolateral membrane of the connecting tubule, the collecting tubule, and the intercalated cells of the collecting duct. However, there is also labeling of the apical membrane in long thin limb of Henle's loop. FXYD5 was effectively immunoprecipitated by antibodies to the alpha subunit of Na,K-ATPase and the anti-FXYD5 antibody immunoprecipitates alpha. Co-expressing FXYD5 with the alpha1 and beta1 subunits of the Na,K-ATPase in Xenopus oocytes elicited a more than 2-fold increase in pump activity, measured either as ouabain-blockable outward current or as ouabain-sensitive (86)Rb(+) uptake. Thus, as found with other FXYD proteins, FXYD5 interacts with the Na,K-ATPase and modulates its properties.

Early detection and treatment of cancers can significantly increase patient prognosis and enhance the quality of life of affected patients. The emerging significance of the tumor microenvironment (TME) as a new frontier for cancer diagnosis and therapy may be exploited by radiolabeled tracers for diagnostic imaging techniques such as positron emission tomography (PET). Cancer-associated fibroblasts (CAFs) within the TME are identified by biomarkers such as fibroblast activation protein alpha (FAPα), which are expressed on their surfaces. Targeting FAPα using small-molecule 18F-labeled inhibitors (FAPIs) has recently garnered significant attention for non-invasive tumor visualization using PET. Herein, two potent aryl-fluorosulfate-based FAPIs, 12 and 13, were synthetically prepared, and their inhibition potency was determined using a fluorimetric FAP assay to be IC50 9.63 and 4.17 nM, respectively. Radiofluorination was performed via the sulfur [18F]fluoride exchange ([18F]SuFEx) reaction to furnish [18F]12 and [18F]13 in high activity yields (AY) of 39-56% and molar activities (Am) between 20-55 GBq/µmol. In vitro experiments focused on the stability of the radiolabeled FAPIs after incubation with human serum, liver microsomes and liver cytosol. Preliminary PET studies of the radioligands were performed in healthy mice to investigate the in vivo biodistribution and 18F defluorination rate. Fast pharmacokinetics for the FAP-targeting tracers were retained and considerable bone uptake, caused by either 18F defluorination or radioligand accumulation, was observed. In summary, our findings demonstrate the efficiency of [18F]SuFEx as a radiolabeling method as well as its advantages and limitations with respect to PET tracer development.

Blood Flow Imaging of the Brain: 50 Years Experience

Radiopharmacy at ETH has worked on the development of novel PET tracers for neuro-, cardiac- and tumor imaging for many years. In this paper, our efforts on targeting the glutamatergic system of the metabotropic glutamate receptor subtype 5 (mGluR5) and the ionotropic N-methyl-<small>D</small>-aspartate (NMDA) receptor are summarized. We briefly described the principles of positron emission tomography (PET) tracer development for the central nervous system (CNS) and the radiolabeling methods used in our laboratory. To assess the radioligands, results of in vitro autoradiography, biodistribution, and metabolite studies as well as PET imaging data are discussed. Furthermore, key PET parameters for kinetic modeling and quantification methods are provided. Two mGluR5 PET tracers, [11C]ABP688 and [18F]PSS232, were translated in our GMP labs and evaluated in human subjects. The newly developed GluN2B PET tracer [11C]Me-NB1 is currently being investigated in a first-in-human PET study and several F-18 labeled tracers are being evaluated in non-human primates in which the first-in-class will be translated for human studies.

18F-labeled FECNT: a selective radioligand for PET imaging of brain dopamine transporters

Biological tumor characterization based on functional and molecular imaging might be highly valuable for radiotherapy (RT). On the one hand, it could allow for an improved target volume definition and an individualized dose prescription within the tumor according to local biological characteristics. Such dose painting strategies can be readily applied with the technical availability of intensity modulated RT (IMRT). Moreover, functional imaging might be of high value for early response assessment and potential treatment adaptation in the course of fractionated RT [1, 2]. Other fields of application are the assessment of chemotherapy and the application of targeted agents, such as hypoxia-sensitizing or antiangiogenic drugs [3, 4]. Both positron emission tomography (PET) and magnetic resonance imaging (MRI) may provide functional information beneficial for personalized treatment strategies. PET imaging using [ 18F]-fluorodeoxyglucose (FDG) can be used to monitor glucose metabolism, whereas the hypoxic status of the tumor can be assessed using dedicated tracers such as [ 18F]-fluoromisonidazole (FMISO). Diffusion weighted MRI (DW-MRI) provides the possibility to quantify the diffusion of water molecules, which is related to cellular density [5]. Dynamic contrast-enhanced MRI (DCE-MRI) yields a temporally varying signal due to the distribution of contrast agent in blood pool and tissue. By compartmental modeling estimates of quantitative physiological parameters can be derived [6]. With the advent of combined PET/MR imaging [7, 8] the acquisition of simultaneous, intrinsically registered PET and MR data has become possible. This facilitates the comparison and combined analysis of PET- and MR-derived functional imaging data. Simultaneous PET/MR may thus be of high potential for treatment individualization [9, 10]. Recent studies have associated different functional imaging information with RT outcome for head and neck (HN) cancer. This applies to FDG-PET [11, 12], static as well as dynamic FMISO-PET [13–16], apparent diffusion coefficients (ADCs) inferred by DW-MRI [17], as well as DCE-MRI [18, 19]. These studies provide a rationale to adapt RT treatment plans according to functional imaging information. It is not clear yet if datasets from different functional imaging modalities are completely complementary, or if information is to some extent redundant. Initial analyses of correlations between different functional datasets have already been performed in recent studies. The studies of Rajendran et al. [20] and Thorwarth et al. [21] revealed good voxel-by-voxel correlation of FDG and FMISO in some HN tumors, whereas others showed no clear correlation. The biological basis of the observed correlations may be the hypoxia-inducible factor 1 α (HIF 1 α) [20]. Similar results were obtained by Zegers et al. [22] comparing uptake of FDG and the hypoxia PET tracer [ 18F]-HX4 in patients with non–small cell lung cancer. Houweling et al. [23] quantified correlations between FDG and ADC maps of HN tumors on a voxel level, and found a negative correlation in most patients. Both Newbold et al. [24] and Donaldson et al. [25] found correlations between hypoxia derived from pimonidazole staining and DCE-derived parameter maps on a region-of-interest (ROI) level. A study by Jansen et al. [26] found that neck nodal metastases with positive FMISO uptake differed significantly in median Ktrans values from those with no FMISO uptake. Earlier studies have shown that a dynamic imaging protocol may be superior compared to a single time frame for hypoxia quantification using FMISO-PET [16]. However, in addition to a late static scan several hours post injection (p.i.), such a dynamic protocol requires a PET acquisition during tracer wash-in in the first minutes p.i. [27], which may hamper its usage in clinical routine. A positive correlation result between early FMISO and DCE information would potentially provide the possibility to infer early FMISO information from DCE, which would facilitate its clinical usage. To address the question if available functional information of PET/MR is complementary or to some extend redundant, this study extends beyond existing studies by considering a comprehensive set of functional data. Correlations of various functional datasets are quantified on a voxel as well as on a regional level within HN tumors by means of the Spearman correlation coefficient. For the analysis, FDG-PET, FMISO-PET acquired in the wash-in, as well as in the retention phase, ADC maps extracted from DW-MRI, and DCE-MRI derived maps are taken into account. The study is a first explorative, hypothesis generating approach to investigate the utilization of integrated PET/MR for personalized treatment strategies.

Positron emission tomography (PET) using radiolabeled biomolecules is a translational molecular imaging technology that is increasingly used in support of drug development. Current methods for radiolabeling biomolecules with fluorine-18 are laborious and require multistep procedures with moderate labeling yields. The Al18F-labeling strategy involves chelation in aqueous medium of aluminum mono[18F]fluoride ({Al18F}2+) by a suitable chelator conjugated to a biomolecule. However, the need for elevated temperatures (100-120 °C) required for the chelation reaction limits its widespread use. Therefore, we designed a new restrained complexing agent (RESCA) for application of the AlF strategy at room temperature.Methods. The new chelator RESCA was conjugated to three relevant biologicals and the constructs were labeled with {Al18F}2+ to evaluate the generic applicability of the one-step Al18F-RESCA-method.Results. We successfully labeled human serum albumin with excellent radiochemical yields in less than 30 minutes and confirmed in vivo stability of the Al18F-labeled protein in rats. In addition, we efficiently labeled nanobodies targeting the Kupffer cell marker CRIg, and performed µPET studies in healthy and CRIg deficient mice to demonstrate that the proposed radiolabeling method does not affect the functional integrity of the protein. Finally, an affibody targeting HER2 (PEP04314) was labeled site-specifically, and the distribution profile of (±)-[18F]AlF(RESCA)-PEP04314 in a rhesus monkey was compared with that of [18F]AlF(NOTA)-PEP04314 using whole-body PET/CT.Conclusion. This generic radiolabeling method has the potential to be a kit-based fluorine-18 labeling strategy, and could have a large impact on PET radiochemical space, potentially enabling the development of many new fluorine-18 labeled protein-based radiotracers.

DHP107 is a newly developed lipid‐based oral formulation of paclitaxel. We evaluated the in vivo tissue pharmacokinetics (PKs) of DHP107 in mice and patients using positron emission tomography (PET). Radioisotope‐labeled [3H]DHP107 and [18F]DHP107 for oral administration were formulated in the same manner as the manufacturing process of DHP107. In vivo tissue PK were assessed in healthy ICR mice and breast cancer xenografted SCID mice. Two patients with metastatic breast cancer were clinically evaluated for absorption at the target lesion after internal absorbed dose estimation. Whole‐body PET/computed tomography data were acquired in healthy and xenografted mice and in patients up to 10–24 h after administration. Tissue [18F]DHP107 signals were plotted against time and PK parameters were determined. The amounts of radioactivity in various organs and excreta were determined using a beta‐counter and are expressed as the percentage of injected dose (ID). Oral [18F]DHP107 was well‐absorbed and reached the target lesion in mice and patients with breast cancer. Significant amounts of radioactivity were found in the stomach, intestine, and liver after oral administration of [3H]‐ and [18F]DHP107 in healthy mice. The [18F]DHP107 reached a peak distribution of 0.7–0.8%ID in the tumor at 5.6–7.3 h in the xenograft model. The [18F]DHP107 distribution in patients with metastatic breast cancer was the highest at 3–4 h postadministration. Systemic exposures after administration of a DHP107 therapeutic dose were comparable with those in previous studies. PET using radioisotope‐labeled drug candidates is useful for drug development and can provide valuable information that can complement plasma PK data, particularly in early phase clinical trials.