[Ga]ABY-028: an albumin-binding domain (ABD) protein-based imaging tracer for positron emission tomography (PET) studies of altered vascular permeability and predictions of albumin-drug conjugate transport.

Background: Albumin is commonly used as a carrier platform for drugs to extend their circulatory half-lives and influence their uptake into tissues that have altered permeability to the plasma protein. The albumin-binding domain (ABD) protein, which binds in vivo to serum albumin with high affinity, has proven to be a versatile scaffold for engineering biopharmaceuticals with a range of binding capabilities. In this study, the ABD protein equipped with a mal-DOTA chelator (denoted ABY-028) was radiolabeled with gallium-68 (Ga).

Irreversible inhibition of cytosolic thioredoxin reductase 1 as a mechanistic basis for anticancer therapy.

Cancer cells adapt to their inherently increased oxidative stress through activation of the glutathione (GSH) and thioredoxin (TXN) systems. Inhibition of both of these systems effectively kills cancer cells, but such broad inhibition of antioxidant activity also kills normal cells, which is highly unwanted in a clinical setting. We therefore evaluated targeting of the TXN pathway alone and, more specifically, selective inhibition of the cytosolic selenocysteine-containing enzyme TXN reductase 1 (TXNRD1).

β-Adrenergically induced glucose uptake in brown adipose tissue is independent of UCP1 presence or activity: Mediation through the mTOR pathway.

Objective: Today, the presence and activity of brown adipose tissue (BAT) in adult humans is generally equated with the induced accumulation of [2-F]2-fluoro-2-deoxy-d-glucose ([F]FDG) in adipose tissues, as investigated by positron emission tomography (PET) scanning. In reality, PET-FDG is currently the only method available for quantification of BAT activity in adult humans. The underlying assumption is that the glucose uptake reflects the thermogenic activity of the tissue.

Preclinical PET imaging of EGFR levels: pairing a targeting with a non-targeting Sel-tagged Affibody-based tracer to estimate the specific uptake.

Background: Though overexpression of epidermal growth factor receptor (EGFR) in several forms of cancer is considered to be an important prognostic biomarker related to poor prognosis, clear correlations between biomarker assays and patient management have been difficult to establish. Here, we utilize a targeting directly followed by a non-targeting tracer-based positron emission tomography (PET) method to examine some of the aspects of determining specific EGFR binding in tumors.

Methods: The EGFR-binding Affibody molecule ZEGFR:2377 and its size-matched non-binding control ZTaq:3638 were recombinantly fused with a C-terminal selenocysteine-containing Sel-tag (ZEGFR:2377-ST and ZTaq:3638-ST).

A method for comparing intra-tumoural radioactivity uptake heterogeneity in preclinical positron emission tomography studies.

Background: Non-uniformity influences the interpretation of nuclear medicine based images and consequently their use in treatment planning and monitoring. However, no standardised method for evaluating and ranking heterogeneity exists. Here, we have developed a general algorithm that provides a ranking and a visualisation of the heterogeneity in small animal positron emission tomography (PET) images.

[11C]MADAM Used as a Model for Understanding the Radiometabolism of Diphenyl Sulfide Radioligands for Positron Emission Tomography (PET).

In quantitative PET measurements, the analysis of radiometabolites in plasma is essential for determining the exact arterial input function. Diphenyl sulfide compounds are promising PET and SPECT radioligands for in vivo quantification of the serotonin transporter (SERT) and it is therefore important to investigate their radiometabolism. We have chosen to explore the radiometabolic profile of [11C]MADAM, one of these radioligands widely used for in vivo PET-SERT studies.

Evaluation of efficacy of a new MEK inhibitor, RO4987655, in human tumor xenografts by [(18)F] FDG-PET imaging combined with proteomic approaches.

Background: Inhibition of mitogen-activated protein kinase (MEK, also known as MAPK2, MAPKK), a key molecule of the Ras/MAPK (mitogen-activated protein kinase) pathway, has shown promising effects on B-raf-mutated and some RAS (rat sarcoma)-activated tumors in clinical trials. The objective of this study is to examine the efficacy of a novel allosteric MEK inhibitor RO4987655 in K-ras-mutated human tumor xenograft models using [(18)F] FDG-PET imaging and proteomics technology.

Methods: [(18)F] FDG uptake was studied in human lung carcinoma xenografts from day 0 to day 9 of RO4987655 therapy using microPET Focus 120 (CTI Concorde Microsystems, Knoxville, TN, USA).

Imaging of a clinically relevant stroke model: glucose hypermetabolism revisited.

Background And Purpose: Ischemic stroke has been shown to cause hypermetabolism of glucose in the ischemic penumbra. Experimental and clinical data indicate that infarct-related systemic hyperglycemia is a potential therapeutic target in acute stroke. However, clinical studies aiming for glucose control in acute stroke have neither improved functional outcome nor reduced mortality.

Comparison of methods for evaluating radiolabelled Annexin A5 uptake in pre-clinical PET oncological studies.

Purpose: The uptakes of radiolabel led AnnexinA5 (AnxA5) and a size-matched control protein in experimental tumours were evaluated by kinetic analyses and compared with standard uptake values (SUVs) to investigate whether the method of analysis may impact on the conclusions that can be drawn.

Procedures: PET scans of the (11)C-labelled proteins performed in untreated and doxorubicin-treated mice with head and neck carcinoma xenografts were retrospectively analysed. The appropriateness of using the Logan graphical analyses for reversibly binding radiotracers in these models was evaluated and confirmed.

Visualization of angiogenesis during cancer development in the polyoma middle T breast cancer model: molecular imaging with (R)-[11C]PAQ.

Background: Vascular endothelial growth factor receptor 2 (VEGFR2) is a crucial mediator of tumour angiogenesis. High expression levels of the receptor have been correlated to poor prognosis in cancer patients. Reliable imaging biomarkers for stratifying patients for anti-angiogenic therapy could therefore be valuable for increasing treatment success rates.

Selective intra-arterial administration of ¹⁸F-FDG to the rat brain -- effects on hemispheric uptake.

Introduction: The purpose of this study was to investigate the radioligand uptake and iodine contrast distribution in the intra- and extracranial circulation of the rat, after intra-arterial injections to the common carotid artery and different parts of the internal carotid artery.

Methods: All animal experiments were carried out in accordance with Karolinska Institutet's guidelines and were approved by the local laboratory animal ethics committee. We used clinical neurointerventional systems to place microcatheters in the extra- or intracranial carotid artery of 15 Sprague-Dawley rats.

[18 F]FDG-PET imaging is an early non-invasive pharmacodynamic biomarker for a first-in-class dual MEK/Raf inhibitor, RO5126766 (CH5126766), in preclinical xenograft models.

Background: Positron emission tomography (PET) with [2-18 F]-2-fluoro-2-deoxy-D-glucose ([18 F]FDG-PET) was acquired at multiple time-points a) to monitor the early response to RO5126766 (CH5126766) in xenograft models b) to evaluate non-invasive small animal [18 F]FDG-PET imaging as a biomarker for MEK inhibitors for translation into dose-finding studies in cancer patients and c) to explore the underlying mechanism related to FDG uptake in tumors treated with RO5126766.

Methods: [18 F]FDG uptake was studied in HCT116 (K-ras), COLO205 (B-raf) mutants and COLO320DM (wild type) xenografts from day 0 to 3 of RO5126766 treatment using a microPET Focus 120 and complemented with in vitro incubations, ex-vivo phosphor imaging and immunohistochemical (IHC) analyses.

Results: In the HCT116 (K-ras) and COLO205 (B-raf) mutant xenografts, significant decreases in [18 F]FDG uptake were detected in vivo on day 1 with 0.

Metabolism of epidermal growth factor receptor targeting probe [11C]PD153035: impact on biodistribution and tumor uptake in rats.

Unlabelled: Several tracers have been evaluated as probes for noninvasive epidermal growth factor receptor (EGFR) quantification with PET. One of the most promising candidates is the (11)C-labeled analog of the EGFR tyrosine kinase inhibitor PD153035. However, previous in vitro studies indicated extensive metabolism of the tracer, which could be disadvantageous for the assessment of receptor density in vivo.

Site-specifically 11C-labeled Sel-tagged annexin A5 and a size-matched control for dynamic in vivo PET imaging of protein distribution in tissues prior to and after induced cell death.

Background: Radiolabeled annexin A5 (AnxA5) is widely used for detecting phosphatidylserine exposed on cell surfaces during apoptosis. We describe here a new method for labeling AnxA5 and a size-matched control protein with short-lived carbon-11, for probing the specificity of in vivo cell death monitoring using positron emission tomography (PET) imaging.

Methods: AnxA5 and the control protein were recombinantly expressed with a C-terminal "Sel-tag", the tetrapeptide -Gly-Cys-Sec-Gly-COOH.

Targeting VEGF-B as a novel treatment for insulin resistance and type 2 diabetes.

The prevalence of type 2 diabetes is rapidly increasing, with severe socioeconomic impacts. Excess lipid deposition in peripheral tissues impairs insulin sensitivity and glucose uptake, and has been proposed to contribute to the pathology of type 2 diabetes. However, few treatment options exist that directly target ectopic lipid accumulation.

HER2-positive tumors imaged within 1 hour using a site-specifically 11C-labeled Sel-tagged affibody molecule.

Unlabelled: A rapid, reliable method for distinguishing tumors or metastases that overexpress human epidermal growth factor receptor 2 (HER2) from those that do not is highly desired for individualizing therapy and predicting prognoses. In vivo imaging methods are available but not yet in clinical practice; new methodologies improving speed, sensitivity, and specificity are required.

Methods: A HER2-binding Affibody molecule, Z(HER2:342), was recombinantly fused with a C-terminal selenocysteine-containing tetrapeptide Sel-tag, allowing site-specific labeling with either (11)C or (68)Ga, followed by biodistribution studies with small-animal PET.

Combining [11C]-AnxA5 PET imaging with serum biomarkers for improved detection in live mice of modest cell death in human solid tumor xenografts.

Background: In vivo imaging using Annexin A5-based radioligands is a powerful technique for visualizing massive cell death, but has been less successful in monitoring the modest cell death typically seen in solid tumors after chemotherapy. Here we combined dynamic positron emission tomography (PET) imaging using Annexin A5 with a serum-based apoptosis marker, for improved sensitivity and specificity in assessment of chemotherapy-induced cell death in a solid tumor model.

Methodology/principal Findings: Modest cell death was induced by doxorubicin in a mouse xenograft model with human FaDu head and neck cancer cells.

Brief Report: alterations in cerebral blood flow as assessed by PET/CT in adults with autism spectrum disorder with normal IQ.

Specific biological markers for autism spectrum disorder (ASD) have not yet been established. Functional studies have shown abnormalities in the anatomo-functional connectivity of the limbic-striatal "social" brain. This study aimed to investigate regional cerebral blood flow (rCBF) at rest.

Radiolabelled receptor-tyrosine-kinase targeting drugs for patient stratification and monitoring of therapy response: prospects and pitfalls.

Transmembrane receptor tyrosine kinases (RTKs) are overexpressed in many malignancies. RTK signalling triggers cell proliferation, suppression of apoptosis, increased motility, and recruitment of neovasculature. Overexpressed RTKs are the molecular targets for an increasing number of anticancer drugs.

Vascular endothelial growth factor B controls endothelial fatty acid uptake.

The vascular endothelial growth factors (VEGFs) are major angiogenic regulators and are involved in several aspects of endothelial cell physiology. However, the detailed role of VEGF-B in blood vessel function has remained unclear. Here we show that VEGF-B has an unexpected role in endothelial targeting of lipids to peripheral tissues.

Radiolabelled proteins for positron emission tomography: Pros and cons of labelling methods.

Background: Dynamic biomedical research is currently yielding a wealth of information about disease-associated molecular alterations on cell surfaces and in the extracellular space. The ability to visualize and quantify these alterations in vivo could provide important diagnostic information and be used to guide individually-optimized therapy. Biotechnology can provide proteinaceous molecular probes with highly specific target recognitions.

Synthesis and preclinical evaluation of [(11)C]PAQ as a PET imaging tracer for VEGFR-2.

Purpose: (R,S)-N-(4-Bromo-2-fluorophenyl)-6-methoxy-7-((1-methyl-3-piperidinyl)methoxy)-4-quinazolinamine (PAQ) is a tyrosine kinase inhibitor with high affinity for the vascular endothelial growth factor receptor 2 (VEGFR-2), which plays an important role in tumour angiogenesis. The aim of this work was to develop and evaluate in mice the (11)C-labelled analogue as an in vivo tracer for VEGFR-2 expression in solid tumours.

Methods: [(11)C]PAQ was synthesized by an N-methylation of desmethyl-PAQ using [(11)C]methyl iodide.

On the selection of a tracer for PET imaging of HER2-expressing tumors: direct comparison of a 124I-labeled affibody molecule and trastuzumab in a murine xenograft model.

Unlabelled: Human epidermal growth factor receptor type 2 (HER2) is a tyrosine kinase, which is often overexpressed in many carcinomas. Imaging HER2 expression in malignant tumors can provide important prognostic and predictive diagnostic information. The use of anti-HER2 tracers labeled with positron-emitting radionuclides may increase the sensitivity of HER2 imaging.

Tagging recombinant proteins with a Sel-tag for purification, labeling with electrophilic compounds or radiolabeling with 11C.

Selenocysteine (Sec; U in one-letter code) is the twenty-first naturally occurring amino acid, with a selenium atom that gives this cysteine (Cys) homolog unique biochemical properties, including a high nucleophilicity and significant reactivity with electrophilic agents. This can be used in biotechnological Sec-dependent applications. Here, we describe how Sec can be introduced into a carboxy-terminal tetrapeptide motif (-Gly-Cys-Sec-Gly-COOH, known as a Sel-tag) for recombinant proteins by tailoring the encoding gene to become compatible with the Escherichia coli selenoprotein synthesis machinery.

The tyrosine kinase inhibitor PD153035: implication of labeling position on radiometabolites formed in vitro.

Introduction: The epidermal growth factor receptor is highly expressed in several types of cancers. Molecules with high affinity to its intracellular tyrosine kinase domain are being developed as in vivo imaging probes. The 4-anilinoquinazoline PD153035 has promising in vitro and in vivo properties for development as a reversible radioligand.