Galith Abourbeh

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.

Cancer molecular imaging: radionuclide-based biomarkers of the epidermal growth factor receptor (EGFR).

Overexpression of the epidermal growth factor receptor tyrosine kinase (EGFR-TK) has been documented in numerous human cancers of epithelial origin, and was found to correlate with resistance to treatment and poor prognosis. Recognizing the central role that this receptor plays in cancer development and progression, various approaches have been developed to target it in order to more specifically eradicate cancer cells. These methods include, among others, low-molecular weight inhibitors of the TK domain that are commonly designed to treat those tumors that overexpress the EGFR. Nevertheless, no currently available assay provides non-invasive, longitudinal and sensitive quantitation of receptor levels in tumors so as to better identify candidate patients for EGFR-targeted therapies. Hence, attempts have been made to develop radiolabeled molecular imaging agents as potential bioprobes to quantitatively monitor treatment efficiency. Such EGFR-targeted bioprobes could not only improve patient selection and treatment monitoring, but also allow a direct delivery of radionuclides for radiotherapy. In this review, the role that EGFR plays in cancer development and therapy is briefly presented, followed by a short review of prominent milestones in the development of EGFR-TK inhibitors. These inhibitors constitute the fundamental core structure for the development of radiolabeled probes to visualize the EGFR in vivo. The considerations that need to be taken into account for the development of such probes will be presented, along with a critical examination on the progress that has been made thus far in the field.

PolyIC GE11 polyplex inhibits EGFR‐overexpressing tumors

Phage display has identified the dodecapeptide YHWYGYTPQNVI (GE11) as a ligand that binds to the epidermal growth factor receptor (EGFR) but does not activate the receptor. Here, we compare the EGFR binding affinities of GE11, EGF, and their polyethyleneimine‐polyethyleneglycol (PEI‐PEG) conjugates. We found that although GE11 by itself does not exhibit measurable affinity to the EGFR, tethering it to PEI‐PEG increases its affinity markedly, and complex formation with polyinosine/cytosine (polyIC) further enhances the affinity to the submicromolar range. PolyIC/PPGE11 has a similar strong antitumor effect against EGFR overexpressing tumors in vitro and in vivo, as polyIC/polyethyleneimine‐polyetheleneglycol‐EGF (polyIC/PP‐EGF). Absence of EGFR activation, as previously shown by us and easier production of GE11 and GE11 conjugates, confer polyIC/PPGE11 a significant advantage over similar EGF‐based polyplexes as a potential therapy of EGFR overexpressing tumors.

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

BackgroundRespiratory 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.MethodsSoftware-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.ResultsOf 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.ConclusionsRaw 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.

Identifying erlotinib-sensitive non-small cell lung carcinoma tumors in mice using [(11)C]erlotinib PET.

BackgroundNon-small cell lung carcinoma (NSCLC) represents approximately 80% of lung cancer cases, and over 60% of these tumors express the epidermal growth factor receptor (EGFR). Activating mutations in the tyrosine kinase (TK) domain of the EGFR are detected in 10% to 30% of NSCLC patients, and evidence of their presence is a prerequisite for initiation of first-line therapy with selective TK inhibitors (TKIs), such as gefitinib and erlotinib. To date, the selection of candidate patients for first-line treatment with EGFR TKIs requires an invasive tumor biopsy to affirm the mutational status of the receptor. This study was designed to evaluate whether positron emission tomography (PET) of NSCLC tumor-bearing mice using [11C]erlotinib could distinguish erlotinib-sensitive from erlotinib-insensitive or erlotinib-resistant tumors.MethodsFour human NSCLC cell lines were employed, expressing either of the following forms of the EGFR: (i) the wild-type receptor (QG56 cells), (ii) a mutant with an exon 19 in-frame deletion (HCC827 cells), (iii) a mutant with the exon 21 L858R point mutation (NCI-H3255 cells), and (iv) a double mutant harboring the L858R and T790M mutations (NCI-H1975 cells). Sensitivity of each cell line to the anti-proliferative effect of erlotinib was determined in vitro. In vivo PET imaging studies following i.v. injection of [11C]erlotinib were carried out in nude mice bearing subcutaneous (s.c.) xenografts of the four cell lines.ResultsCells harboring activating mutations in the EGFR TK domain (HCC827 and NCI-H3255) were approximately 1,000- and 100-fold more sensitive to erlotinib treatment in vitro, respectively, compared to the other two cell lines. [11C]Erlotinib PET scans could differentiate erlotinib-sensitive tumors from insensitive (QG56) or resistant (NCI-H1975) tumors already at 12 min after injection. Nonetheless, the uptake in HCC827 tumors was significantly higher than that in NCI-H3255, possibly reflecting differences in ATP and erlotinib affinities between the EGFR mutants.Conclusions[11C]Erlotinib imaging in mice differentiates erlotinib-sensitive NSCLC tumors from erlotinib-insensitive or erlotinib-resistant ones.

Differentiating Between Cancer and Inflammation: A Metabolic-Based Method for Functional Computed Tomography Imaging

One of the main limitations of the highly used cancer imaging technique, PET-CT, is its inability to distinguish between cancerous lesions and post treatment inflammatory conditions. The reason for this lack of specificity is that [(18)F]FDG-PET is based on increased glucose metabolic activity, which characterizes both cancerous tissues and inflammatory cells. To overcome this limitation, we developed a nanoparticle-based approach, utilizing glucose-functionalized gold nanoparticles (GF-GNPs) as a metabolically targeted CT contrast agent. Our approach demonstrates specific tumor targeting and has successfully distinguished between cancer and inflammatory processes in a combined tumor-inflammation mouse model, due to dissimilarities in angiogenesis occurring under different pathologic conditions. This study provides a set of capabilities in cancer detection, staging and follow-up, and can be applicable to a wide range of cancers that exhibit high metabolic activity.

Structure–Activity Relationship and Preclinical Evaluation of Carbon-11-Labeled Ammonium Salts as PET–Myocardial Perfusion Imaging Agents

BackgroundDue to the limited availability of suitable positron emission tomography (PET) tracers, the majority of myocardial perfusion imaging (MPI) scans is performed using SPECT rather than PET.AimThe aim of this study is to design and synthesize carbon-11-labeled ammonium salt derivatives and explore their structure–activity relationship (SAR) and their potential as PET–MPI agents.Methods and ResultsThree carbon-11-labeled ammonium salts were developed. SAR of the labeled compounds were explored vis-à-vis the effects of charge density and lipophilicity on the distribution kinetics in mice. These studies pointed at [11C]4 as the lead compound. Comparative microPET/CT scans in healthy rats, using both [11C]4 and [13 N]–NH3, substantiated the potential of [11C]4 ([11C]-DMDPA). A proof of concept for the potential of radiolabeled ammonium salts as MPI agents has been demonstrated in a newly developed swine model of permanent partial coronary artery occlusion.ConclusionsSAR studies of 11C-labeled ammonium salts suggest that both lipophilicity and charge density affect the performance of these compounds as MPI probes. In a swine model, the labeled lead successfully visualized the defect regions in the myocardium. The data presented call for the development of fluorine-18 analogues, to increase clinical impact.

Rat Imaging and In Vivo Stability Studies using [11C]-Dimethyl-Diphenyl Ammonium, a Candidate Agent for PET-Myocardial Perfusion Imaging

BACKGROUND PET myocardial perfusion imaging (MPI) holds several advantages over SPECT for diagnosing coronary artery disease. The short half-lives of prevailing PET-MPI agents hamper wider clinical application of PET in nuclear cardiology; prompting the development of novel PET-MPI agents. We have previously reported on the potential of radiolabeled ammonium salts, and particularly on that of [(11)C]dimethyl-diphenyl-ammonium ([(11)C]DMDPA), for cardiac PET imaging. This study was designed to improve the radiosynthesis and increase the yield of [(11)C]DMDPA, characterize more meticulously the kinetics of radioactivity distribution after its injection via micro-PET/CT studies, and further explore its potential for PET-MPI. METHODS The radiosynthetic procedure of [(11)C]DMDPA was improved with respect to the previously reported one. The kinetics of radioactivity distribution following injection of [(11)C]DMDPA were investigated in juvenile and young adult male SD rats using microPET/CT, and compared to those of [(13)N]NH3. Furthermore, the metabolic fate of [(11)C]DMDPA in vivo was examined after its injection into rats. RESULTS Following a radiosynthesis time of 25-27 min, 11.9 ± 1.1 GBq of [(11)C]DMDPA was obtained, with a 43.7% ± 4.3% radiochemical yield (n = 7). Time activity curves calculated after administration of [(11)C]DMDPA indicated rapid, high and sustained radioactivity uptake in hearts of both juvenile and young adult rats, having a two-fold higher cardiac radioactivity uptake compared to [(13)N]NH3. Accordingly, at all time points after injection to both juvenile and young adult rats, image quality of the left ventricle was higher with [(11)C]DMDPA compared to [(13)N]NH3. In vivo stability studies of [(11)C]DMDPA indicate that no radioactive metabolites could be detected in plasma, liver and urine samples of rats up to 20 min after injection, suggesting that [(11)C]DMDPA is metabolically stable in vivo. CONCLUSIONS This study further illustrates that [(11)C]DMDPA holds, at least in part, essential qualities required from a PET-MPI probe. Owing to the improved radiosynthetic procedure reported herein, [(11)C]DMDPA can be produced in sufficient amounts for clinical use.

PET molecular imaging of angiogenesis with a multiple tyrosine kinase receptor-targeted agent in a rat model of myocardial infarction.

PurposeAngiogenesis plays a major role in tissue remodeling and repair after myocardial infarction (MI), and imaging it could provide information on the healing process. During angiogenesis, vascular endothelial growth factor receptors (VEGFRs), platelet-derived growth factor receptors (PDGFRs), and Tie receptors are upregulated, and this study aimed to develop a C-11 positron emission tomography (PET) agent for imaging angiogenesis by targeting these receptors.ProceduresA VEGFR-2/Tie-2/PDGFRα inhibitor (N-(6-{4-[3-(2-fluoro-5-trifluoromethyl-phenyl)-ureido]-phenoxy}-1H-benzoimidazol-2-yl)-2-(4-methyl-piperazin-1-yl)-acetamide (ATV-1)) was synthesized and labeled with C-11. MicroPET imaging of a rat MI model was compared to proteins expression by immunohistochemistry.Results[11C]ATV-1 specifically accumulated in the infracted region of the left ventricular (LV) lateral wall more than in the interventricular septal wall, but not in sham-operated or healthy animals. Moreover, [11C]ATV-1 uptake in the LV significantly correlated with Tie-2, VEGFR-2, and PDGFRα expression.ConclusionImaging angiogenesis in MI rats using [11C]ATV-1 and PET has been demonstrated. These results merit further research and development of more hydrophilic modified [11C]ATV-1 as a PET tracer.

Glucose-functionalized gold nanoparticles as a metabolically targeted CT contrast agent for distinguishing tumors from non-malignant metabolically active processes

The highly used cancer imaging technique, [18F]FDG-PET, is based on the increased glucose metabolic activity in tumors. However, since there are other biological processes that exhibit increased metabolic activity, in particular inflammation, this methodology is prone to non-specificity for cancer. Herein we describe the development of a novel nanoparticle-based approach, utilizes Glucose-Functionalized Gold Nanoparticles (GF-GNPs) as a metabolically targeted CT contrast agent. Our method has demonstrated specific tumor targeting and has successfully differentiated between cancer and inflammation in a combined tumor-inflammation mouse model, due to dissimilarities in vasculatures in different pathologic conditions. This novel approach provides new capabilities in cancer imaging, and can be applicable to a wide range of cancers.