Imaging of EGFR and EGFR Tyrosine Kinase Overexpression in Tumors by Nuclear Medicine Modalities

Protein tyrosine kinases (PTKs) play a pivotal role in signal transduction pathways and in the development and maintenance of various cancers. They are involved in multiple processes such as transcription, cell cycle progression, proliferation, angiogenesis and inhibition of apoptosis. Among the PTKs, the EGFR is one of the most widely studied and has emerged as a promising key target for the treatment of cancer. Indeed, several drugs directed at this receptor are FDA-approved and many others are at various stages of development. However, thus far, the therapeutic outcome of EGFR-targeted therapy is suboptimal and needs to be refined. Quantitative PET molecular imaging coupled with selective labelled biomarkers may facilitate in vivo EGFR-targeted drug efficacy by noninvasively assessing the expression of EGFR in tumor, guiding dose and regime by measuring target drug binding and receptor occupancy as well as potentially detecting the existence of a primary or secondary mutation leading to either drug interaction or failure of EGFR recognition by the drug. This review describes the attempts to develop labelled EGFR molecular imaging agents that are based either on low molecular weight tyrosine kinase inhibitors or monoclonal antibodies directed to the extracellular binding domain of the receptor to be used in nuclear medicine modalities

Gating, enhanced gating, and beyond: information utilization strategies for motion management, applied to preclinical PET

BACKGROUND: Respiratory gating and gate optimization strategies present solutions for overcoming image degradation caused by respiratory motion in PET and traditionally utilize hardware systems and/or employ complex processing algorithms. In this work, we aimed to advance recently emerging data-driven gating methods and introduce a new strategy for optimizing the four-dimensional data based on information contained in that data. These algorithms are combined to form an automated motion correction workflow. METHODS: Software-based gating methods were applied to a nonspecific population of 84 small-animal rat PET scans to create respiratory gated images. The gated PET images were then optimized using an algorithm we introduce as ‘gating+’ to reduce noise and optimize signal; the technique was also tested using simulations. Gating+ is based on a principle of only using gated information if and where it adds a net benefit, as evaluated in temporal frequency space. Motion-corrected images were assessed quantitatively and qualitatively. RESULTS: Of the small-animal PET scans, 71% exhibited quantifiable motion after software gating. The mean liver displacement was 3.25 mm for gated and 3.04 mm for gating+ images. The (relative) mean percent standard deviations measured in background ROIs were 1.53, 1.05, and 1.00 for the gated, gating+, and ungated values, respectively. Simulations confirmed that gating+ image voxels had a higher probability of being accurate relative to the corresponding ungated values under varying noise and motion scenarios. Additionally, we found motion mapping and phase decoupling models that readily extend from gating+ processing. CONCLUSIONS: Raw PET data contain information about motion that is not currently utilized. In our work, we showed that through automated processing of standard (ungated) PET acquisitions, (motion-) information-rich images can be constructed with minimal risk of noise introduction. Such methods have the potential for implementation with current PET technology in a robust and reproducible way

Mice Deficient in Ribosomal Protein S6 Phosphorylation Suffer from Muscle Weakness that Reflects a Growth Defect and Energy Deficit

BACKGROUND: Mice, whose ribosomal protein S6 cannot be phosphorylated due to replacement of all five phosphorylatable serine residues by alanines (rpS6(P-/-)), are viable and fertile. However, phenotypic characterization of these mice and embryo fibroblasts derived from them, has established the role of these modifications in the regulation of the size of several cell types, as well as pancreatic beta-cell function and glucose homeostasis. A relatively passive behavior of these mice has raised the possibility that they suffer from muscle weakness, which has, indeed, been confirmed by a variety of physical performance tests. METHODOLOGY/PRINCIPAL FINDINGS: A large variety of experimental methodologies, including morphometric measurements of histological preparations, high throughput proteomic analysis, positron emission tomography (PET) and numerous biochemical assays, were used in an attempt to establish the mechanism underlying the relative weakness of rpS6(P-/-) muscles. Collectively, these experiments have demonstrated that the physical inferiority appears to result from two defects: a) a decrease in total muscle mass that reflects impaired growth, rather than aberrant differentiation of myofibers, as well as a diminished abundance of contractile proteins; and b) a reduced content of ATP and phosphocreatine, two readily available energy sources. The abundance of three mitochondrial proteins has been shown to diminish in the knockin mouse. However, the apparent energy deficiency in this genotype does not result from a lower mitochondrial mass or compromised activity of enzymes of the oxidative phosphorylation, nor does it reflect a decline in insulin-dependent glucose uptake, or diminution in storage of glycogen or triacylglycerol (TG) in the muscle. CONCLUSIONS/SIGNIFICANCE: This study establishes rpS6 phosphorylation as a determinant of muscle strength through its role in regulation of myofiber growth and energy content. Interestingly, a similar role has been assigned for ribosomal protein S6 kinase 1, even though it regulates myoblast growth in an rpS6 phosphorylation-independent fashion

Labeled EGFRTK irreversible inhibitor (ML03). In vitro and in vivo properties, potential as PET biomarker for cancer and feasibility as anticancer drug

Radiosynthesis of ML03 (N- {4 Key words: carbon-11; cancer; biodistribution; PET; EGFr Growth factors mediate their pleiotropic actions by binding to and activating receptor tyrosine kinases. Epidermal growth factor receptor (EGFr, erb-B1) belongs to a family of proteins involved in the proliferation of normal and malignant cells. 1,2 The binding of activating ligands such as EGF, TGF ␣, AR, BTC or HB-EGF to the EGFr results in activation of the cytosolic kinase domain. Overexpression of EGFr is the hallmark of many human tumors such as breast cancer, glioma, laryngeal cancer, squamous cell carcinoma of the head and neck and prostate cancer. In our previous work, 15 we synthesized, labeled and evaluated 4-(fluoroanilino)quinazoline derivatives as EGFrTK PET biomarkers. These molecules bind reversibly to the ATP binding site of the receptor and inhibit the autophosphorylation of the EGFrTK. Competition with intracellular ATP results in their fast dissociation from the EGFr kinase site, however, making these compounds ineffective as PET reporter probes. We therefore concluded that irreversible EGFr tyrosine kinase inhibitors labeled with carbon-11 might be more effective as PET markers for tumors overexpressing EGFr. A group of compounds (6-acrylamido-4-anilinoquinazolines) that bind irreversibly to the EGFr have been described recently. 16 -20 The ligand binds covalently to the cys-773, which is proximal to the ATP binding site

Mice deficient in ribosomal protein S6 phosphorylation suffer from muscle weakness that reflects a growth defect and energy deficit. PLoS One

Abstract Background: Mice, whose ribosomal protein S6 cannot be phosphorylated due to replacement of all five phosphorylatable serine residues by alanines (rpS6 P2/2 ), are viable and fertile. However, phenotypic characterization of these mice and embryo fibroblasts derived from them, has established the role of these modifications in the regulation of the size of several cell types, as well as pancreatic b-cell function and glucose homeostasis. A relatively passive behavior of these mice has raised the possibility that they suffer from muscle weakness, which has, indeed, been confirmed by a variety of physical performance tests

Evaluation of Modified PEG-Anilinoquinazoline Derivatives as Potential Agents for EGFR Imaging in Cancer by Small Animal PET

Purpose: The in vivo evaluation of three modified polyethylene glycol (PEG)-anilinoquinazoline derivatives labeled with 124 I, 18 F, and 11 C as potential positron emission tomography (PET) bioprobes for visualizing epidermal growth factor receptor (EGFR) in cancer using small animal PET. Procedures: Xenograft mice with the human glioblastoma cell lines U138MG (lacking EGFR expression) and U87MG.wtEGFR (transfected with an overexpressing human wild-type EGFR gene) were used. Static and dynamic PET imaging was conducted for all three PEGylated compounds. Tumor necrosis, microvessel density, and EGFR levels were evaluated by histopathology and enzyme-linked immunosorbent assay. Results: Nineteen animal models were generated (two U138MG, three U87MG, 14 with both U138MG and U87MG bilateral masses). In static images, a slight increase in tracer uptake was observed in tumors, but in general, there was no retention of tracer uptake over time and no difference in uptake between U138MG and U87MG masses. In addition, no significant uptake was demonstrated in dynamic scans of the 18 F-PEG tracer. No necrosis was present except in four animals. MVD was 9.6 and 48 microvessels/×400 field in the U138GM and U87GM masses