Experimental results and related clinical implications of PET detection of epidermal growth factor receptor (EGFr) in cancer

PET and SPECT Imaging of the EGFR Family (RTK Class I) in Oncology

The human epidermal growth factor receptor family (EGFR-family, other designations: HER family, RTK Class I) is strongly linked to oncogenic transformation. Its members are frequently overexpressed in cancer and have become attractive targets for cancer therapy. To ensure effective patient care, potential responders to HER-targeted therapy need to be identified. Radionuclide molecular imaging can be a key asset for the detection of overexpression of EGFR-family members. It meets the need for repeatable whole-body assessment of the molecular disease profile, solving problems of heterogeneity and expression alterations over time. Tracer development is a multifactorial process. The optimal tracer design depends on the application and the particular challenges of the molecular target (target expression in tumors, endogenous expression in healthy tissue, accessibility). We have herein summarized the recent preclinical and clinical data on agents for Positron Emission Tomography (PET) and Single Photon Emission Tomography (SPECT) imaging of EGFR-family receptors in oncology. Antibody-based tracers are still extensively investigated. However, their dominance starts to be challenged by a number of tracers based on different classes of targeting proteins. Among these, engineered scaffold proteins (ESP) and single domain antibodies (sdAb) show highly encouraging results in clinical studies marking a noticeable trend towards the use of smaller sized agents for HER imaging.

Influence of composition of cysteine-containing peptide-based chelators on biodistribution of 99mTc-labeled anti-EGFR affibody molecules

Epidermal growth factor receptor (EGFR) is overexpressed in a number of cancers and is the molecular target for several anti-cancer therapeutics. Radionuclide molecular imaging of EGFR expression should enable personalization of anti-cancer treatment. Affibody molecule is a promising type of high-affinity imaging probes based on a non-immunoglobulin scaffold. A series of derivatives of the anti-EGFR affibody molecule ZEGFR:2377, having peptide-based cysteine-containing chelators for conjugation of ^99mTc, was designed and evaluated. It was found that glutamate-containing chelators Gly-Gly-Glu-Cys (GGEC), Gly-Glu-Glu-Cys (GEEC) and Glu-Glu-Glu-Cys (EEEC) provide the best labeling stability. The glutamate containing conjugates bound to EGFR-expressing cells specifically and with high affinity. Specific targeting of EGFR-expressing xenografts in mice was demonstrated. The number of glutamate residues in the chelator had strong influence on biodistribution of radiolabeled affibody molecules. Increase of glutamate content was associated with lower uptake in normal tissues. The ^99mTc-labeled variant containing the EEEC chelator provided the highest tumor-to-organ ratios. In conclusion, optimizing the composition of peptide-based chelators enhances contrast of imaging of EGFR-expression using affibody molecules.

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 Z_EGFR:2377 and its size-matched non-binding control Z_Taq:3638 were recombinantly fused with a C-terminal selenocysteine-containing Sel-tag (Z_EGFR:2377-ST and Z_Taq:3638-ST). The proteins were site-specifically labeled with DyLight488 for flow cytometry and ex vivo tissue analyses or with ¹¹C for in vivo PET studies. Kinetic scans with the ¹¹C-labeled proteins were performed in healthy mice and in mice bearing xenografts from human FaDu (squamous cell carcinoma) and A431 (epidermoid carcinoma) cell lines. Changes in tracer uptake in A431 xenografts over time were also monitored, followed by ex vivo proximity ligation assays (PLA) of EGFR expressions.

Results

Flow cytometry and ex vivo tissue analyses confirmed EGFR targeting by Z_EGFR:2377-ST-DyLight488. [Methyl-¹¹C]-labeled Z_EGFR:2377-ST-CH₃ and Z_Taq:3638-ST-CH₃ showed similar distributions in vivo, except for notably higher concentrations of the former in particularly the liver and the blood. [Methyl-¹¹C]-Z_EGFR:2377-ST-CH₃ successfully visualized FaDu and A431 xenografts with moderate and high EGFR expression levels, respectively. However, in FaDu tumors, the non-specific uptake was large and sometimes equally large, illustrating the importance of proper controls. In the A431 group observed longitudinally, non-specific uptake remained at same level over the observation period. Specific uptake increased with tumor size, but changes varied widely over time in individual tumors. Total (membranous and cytoplasmic) EGFR in excised sections increased with tumor growth. There was no positive correlation between total EGFR and specific tracer uptake, which, since Z_EGFR:2377 binds extracellularly and is slowly internalized, indicates a discordance between available membranous and total EGFR expression levels.

Conclusions

Same-day in vivo dual tracer imaging enabled by the Sel-tag technology and ¹¹C-labeling provides a method to non-invasively monitor membrane-localized EGFR as well as factors affecting non-specific uptake of the PET ligand.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-016-0213-8) contains supplementary material, which is available to authorized users.

Comparison of two site-specifically (18)F-labeled affibodies for PET imaging of EGFR positive tumors

The epidermal growth factor receptor (EGFR) serves as an attractive target for cancer molecular imaging and therapy. Our previous positron emission tomography (PET) studies showed that the EGFR-targeting affibody molecules ⁶⁴Cu-DOTA-Z_EGFR:1907 and ¹⁸F-FBEM-Z_EGFR:1907 can discriminate between high and low EGFR-expression tumors and have the potential for patient selection for EGFR-targeted therapy. Compared with ⁶⁴Cu, ¹⁸F may improve imaging of EGFR-expression and is more suitable for clinical application, but the labeling reaction of ¹⁸F-FBEM-Z_EGFR:1907 requires a long synthesis time. The aim of the present study is to develop a new generation of ¹⁸F labeled affibody probes (Al¹⁸F-NOTA-Z_EGFR:1907 and ¹⁸F-CBT-Z_EGFR:1907) and to determine whether they are suitable agents for imaging of EGFR expression. The first approach consisted of conjugating Z_EGFR:1907 with NOTA and radiolabeling with Al¹⁸F to produce Al¹⁸F-NOTA-Z_EGFR:1907. In a second approach the prosthetic group ¹⁸F-labeled-2-cyanobenzothiazole (¹⁸F-CBT) was conjugated to Cys-Z_EGFR:1907 to produce ¹⁸F-CBT-Z_EGFR:1907. Binding affinity and specificity of Al¹⁸F-NOTA-Z_EGFR:1907 and ¹⁸F-CBT-Z_EGFR:1907 to EGFR were evaluated using A431 cells. Biodistribution and PET studies were conducted on mice bearing A431 xenografts after injection of Al¹⁸F-NOTA-Z_EGFR:1907 or ¹⁸F-CBT-Z_EGFR:1907 with or without coinjection of unlabeled affibody proteins. The radiosyntheses of Al¹⁸F-NOTA-Z_EGFR:1907 and ¹⁸F-CBT-Z_EGFR:1907 were completed successfully within 40 and 120 min with a decay-corrected yield of 15% and 41% using a 2-step, 1-pot reaction and 2-step, 2-pot reaction, respectively. Both probes bound to EGFR with low nanomolar affinity in A431 cells. Although ¹⁸F-CBT-Z_EGFR:1907 showed instability in vivo, biodistribution studies revealed rapid and high tumor accumulation and quick clearance from normal tissues except the bones. In contrast, Al¹⁸F-NOTA-Z_EGFR:1907 demonstrated high in vitro and in vivo stability, high tumor uptake, and relative low uptake in most of the normal organs except the liver and kidneys at 3 h after injection. The specificity of both probes for A431 tumors was confirmed by their lower uptake on coinjection of unlabeled affibody. PET studies showed that Al¹⁸F-NOTA-Z_EGFR:1907 and ¹⁸F-CBT-Z_EGFR:1907 could clearly identify EGFR positive tumors with good contrast. Two strategies for ¹⁸F-labeling of affibody molecules were successfully developed as two model platforms using NOTA or CBT coupling to affibody molecules that contain an N-terminal cysteine. Al¹⁸F-NOTA-Z_EGFR:1907 and ¹⁸F-CBT-Z_EGFR:1907 can be reliably obtained in a relatively short time. Biodistribution and PET studies demonstrated that Al¹⁸F-NOTA-Z_EGFR:1907 is a promising PET probe for imaging EGFR expression in living mice.

Preparation of clinical-grade (89) Zr-panitumumab as a positron emission tomography biomarker for evaluating epidermal growth factor receptor-targeted therapy

Panitumumab is a fully human monoclonal antibody approved for the treatment of epidermal growth factor receptor (EGFR) positive colorectal cancer. Recently, panitumumab has been radiolabeled with (89) Zr and evaluated for its potential to be used as immuno-positron emission tomography (PET) probe for EGFR positive cancers. Interesting preclinical results published by several groups of researchers have prompted us to develop a robust procedure for producing clinical-grade (89) Zr-panitumumab as an immuno-PET probe to evaluate EGFR-targeted therapy. In this process, clinical-grade panitumumab is bio-conjugated with desferrioxamine chelate and subsequently radiolabeled with (89) Zr resulting in high radiochemical yield (>70%, n = 3) and purity (>98%, n = 3). All quality control (QC) tests were performed according to United States Pharmacopeia specifications. QC tests showed that (89) Zr-panitumumab met all specifications for human injection. Herein, we describe a step-by-step method for the facile synthesis and QC tests of (89) Zr-panitumumab for medical use. The entire process of bioconjugation, radiolabeling, and all QC tests will take about 5 h. Because the synthesis is fully manual, two rapid, in-process QC tests have been introduced to make the procedure robust and error free.

EGFR mutations are associated with favorable intracranial response and progression-free survival following brain irradiation in non-small cell lung cancer patients with brain metastases

BACKGROUND

The presence of epidermal growth factor receptor (EGFR) mutations in non-small cell lung cancer (NSCLC) is associated with increased radiosensitivity in vitro. However, the results from clinical studies regarding the radiosensitivity in NSCLC with mutant EGFR are inconclusive. We retrospectively analyzed our NSCLC patients who had been regularly followed up by imaging studies after irradiation for brain metastases, and investigated the impact of EGFR mutations on radiotherapy (RT).

METHODS

Forty-three patients with brain metastases treated with RT, together with EGFR mutation status, demographics, smoking history, performance status, recursive partitioning analysis (RPA) class, tumor characteristics, and treatment modalities, were included. Radiological images were taken at 1 to 3 months after RT, and 3 to 6 months thereafter. Radiographic response was evaluated by RECIST criteria version 1.1 according to the intracranial images before and after RT. Log-rank test and Cox regression model were used to correlate EGFR mutation status and other clinical features with intracranial radiological progression-free survival (RPFS) and overall survival (OS).

RESULTS

The median follow-up duration was 15 months. Patients with mutant EGFR had higher response rates to brain RT than those with wild-type EGFR (80% vs. 46%; p = 0.037). Logistic regression analysis showed that EGFR mutation status is the only predictor for treatment response (p = 0.032). The median intracranial RPFS was 18 months (95% CI = 8.33-27.68 months). In Cox regression analysis, mutant EGFR (p = 0.025) and lower RPA class (p = 0.026) were associated with longer intracranial RPFS. EGFR mutation status (p = 0.061) and performance status (p = 0.076) had a trend to predict OS.

CONCLUSIONS

Mutant EGFR in NSCLC patients is an independent prognostic factor for better treatment response and longer intracranial RPFS following RT for brain metastases.

PET of EGFR expression with an 18F-labeled affibody molecule

Epidermal growth factor receptor (EGFR) is often overexpressed in a variety of human cancers, and its expression is associated with poor prognosis for many cancer types. However, an accurate technique to noninvasively image EGFR expression in vivo is not available in the clinical setting. In this research, an Affibody analog, anti-EGFR Ac-Cys-Z(EGFR:1907), was successfully site-specifically (18)F-labeled for PET of EGFR expression.

METHODS

The prosthetic group N-[2-(4-(18)F-fluorobenzamido) ethyl] maleimide ((18)F-FBEM) was conjugated to Ac-Cys-Z(EGFR:1907) under mild conditions (pH 7) to produce the probe (18)F-FBEM-Cys-Z(EGFR:1907). The binding affinity and specificity tests of (18)F-FBEM-Cys-Z(EGFR:1907) to EGFR were conducted using A431 cancer cells. Small-animal PET and biodistribution studies were conducted on various mice tumor xenograft models with EGFR overexpression (6 types) after injection of approximately 2.0 MBq of (18)F-FBEM-Cys-Z(EGFR:1907) with or without coinjection of unlabeled Ac-Cys-Z(EGFR:1907) for up to 3 h after injection. A correlation study between (18)F-FBEM-Cys-Z(EGFR:1907) small- animal PET quantification and ex vivo Western blot analysis of tumor EGFR expression was conducted in those 6 types of tumor models.

RESULTS

(18)F-FBEM-Cys-Z(EGFR:1907) binds to EGFR with low nanomolar affinity (37 nM) in A431 cells. (18)F-FBEM-Cys-Z(EGFR:1907) rapidly accumulated in the tumor and cleared from most of the normal organs except the liver and kidneys at 3 h after injection, allowing excellent tumor-to-normal tissue contrast to be obtained. In the A431 tumor xenograft model, coinjection of the PET probe with 45 μg of Ac-Cys-Z(EGFR:1907) was able to improve the tumor uptake (3.9 vs. 8.1 percentage of the injected radioactive dose per gram of tissue, at 3 h after injection) and tumor imaging contrast, whereas coinjection with 500 μg of Ac-Cys-Z(EGFR:1907) successfully blocked the tumor uptake significantly (8.1 vs. 1.0 percentage of the injected radioactive dose per gram of tissue, at 3 h after injection, 88% inhibition, P < 0.05). Moderate correlation was found between the tumor tracer uptake at 3 h after injection quantified by PET and EGFR expression levels measured by Western blot assay (P = 0.007, R = 0.59).

CONCLUSION

(18)F-FBEM-Cys-Z(EGFR:1907) is a novel protein scaffold-based PET probe for imaging EGFR overexpression of tumors, and its ability to differentiate tumors with high and low EGFR expression in vivo holds promise for future clinical translation.

Exploring molecular genetics of bladder cancer: lessons learned from mouse models

Urothelial cell carcinoma (UCC) of the bladder is one of the most common malignancies worldwide, causing considerable morbidity and mortality. It is unusual among the epithelial carcinomas because tumorigenesis can occur by two distinct pathways: low-grade, recurring papillary tumours usually contain oncogenic mutations in FGFR3 or HRAS, whereas high-grade, muscle-invasive tumours with metastatic potential generally have defects in the pathways controlled by the tumour suppressors p53 and retinoblastoma (RB). Over the past 20 years, a plethora of genetically engineered mouse (GEM) models of UCC have been developed, containing deletions or mutations of key tumour suppressor genes or oncogenes. In this review, we provide an up-to-date summary of these GEM models, analyse their flaws and weaknesses, discuss how they have advanced our understanding of UCC at the molecular level, and comment on their translational potential. We also highlight recent studies supporting a role for dysregulated Wnt signalling in UCC and the development of mouse models that recapitulate this dysregulation.

The emerging era of personalized therapy in squamous cell carcinoma of the head and neck

Over the past three decades there has been a move toward organ preservation protocols in the management of locally advanced mucosal head and neck squamous cell carcinomas (LAHNSCC) with combinations of radiotherapy (RT), chemotherapy and, more recently, biological agents. Current standard chemoradiation strategies have reached the upper limits of toxicity. In addition, the traditional one size fits all approach of grouping patients according to traditional clinicopathological features fails to take into account the vast underlying biological heterogeneity of tumors and their host. A number of recent advances such as highly conformal RT, molecular profiling and targeted agents, and improvements in treatment response assessment have set the scene for a fundamental paradigm shift toward greater tailoring of therapy with the aim of improving outcomes and reducing the burden of survivorship. This review focuses on the recognition of the prognostic value of tumor human papillomavirus (HPV) status, the incorporation of biologically targeted therapies and the evolving role of molecular imaging in predicting tumor response and prognosis in the curative management of LAHNSCC.

Molecular detection of epidermal growth factor receptor in colorectal cancer: does it still make sense?

AIM

The aim of the study was to detect and compare the epidermal growth factor receptor (EGFr) content using different methods, to establish whether the quantitative detection and functional study of EGFr in colorectal cancer, using methods other than immunohistochemistry (IHC), are appropriate.

METHOD

Analysis of EGFr by IHC was performed in 230 colorectal cancer patients using monoclonal anti-EGFr. Total and activated EGFr (pY1068) contents were determined in 92 patients and real-time PCR, to determine the level of EGFr messenger RNA, was carried out in 60 patients.

RESULTS

There was no association between EGFr IHC groups and the mean total EGFr levels measured using ELISA.

CONCLUSION

The study shows that the results of different EGFr detection methods do not correlate with each other. Hence, the real role of EGFr in colorectal cancer remains unsettled. Clinically, the receptor itself does not seem to be important and it would be better to focus on EGFr signalling in downstream pathways.

Metabolic stability of 6,7-dialkoxy-4-(2-, 3- and 4-[18F]fluoroanilino)quinazolines, potential EGFR imaging probes

Epidermal growth factor receptors (EGFR), upregulated in many tumor types, have been a target for therapeutic development and molecular imaging. The objective of this study was to evaluate the distribution and metabolic characteristics of fluorine-18 labeled anilinoquinazolines as potential imaging agents for EGFR tyrosine kinase expression. Fluorine-18 labeled fluoronitrobenzenes were prepared by reaction of potassium cryptand [(18)F]fluoride with 1,2- and 1,4-dinitrobenzenes, and 3-nitro-N,N,N-trimethylanilinium triflate in 5min. Decay-corrected radiochemical yields of [(18)F]fluoride incorporation into the nitro-aromatic compounds were 81±2%, 44±4% and 77±5% (n=3-5) for the 2-, 3- and 4-fluoro isomers, respectively. Sodium borohydride reduction to the corresponding [(18)F]fluoroanilines was achieved with greater than 80% conversion in 5min. Coupling of [(18)F]fluoroaniline-hydrochlorides to 6,7-dimethoxy-4-chloro-quinazoline gave the corresponding 6,7-dimethoxy-4-(2-, 3- and 4-[(18)F]fluoroanilino)quinazolines in 31±5%, 17±2% and 55±2% radiochemical yield, respectively, while coupling to the 6,7-diethoxy-4-chloro-quinazoline produced 6,7-diethoxy-4-(2-, 3- and 4-[(18)F]fluoroanilino)quinazolines in 19±6%, 9±3% and 36±6% radiochemical yield, respectively, in 90min to end of synthesis from [(18)F]fluoride. Biodistribution of 2- and 4-[(18)F]fluoroanilinoquinazolines was conducted in tumor-bearing mice (MDA-MB-435 and MDA-MB-468 xenografts). Low tumor uptake (<1% injected dose per gram (ID/g) of tissue up to 3h postinjection of the radiotracers) was observed. High bone uptake (5-15% ID/g) was noted with the 4-[(18)F]fluoroanilinoquinazolines. The metabolic stabilities of radiolabeled quinazolines were further evaluated by incubation with human female cryopreserved isolated hepatocytes. Rapid degeneration of the 4-fluoro-substituted compounds to baseline polar metabolites was observed by radio-TLC, whereas, the 2- and 3-[(18)F]fluoroaniline derivatives were significantly more stable, up to 2h, corroborating the in vivo biodistribution studies. para-Substituted [(18)F]fluoroanilines, a common structural motif in radiopharmaceuticals, are highly susceptible to metabolic degradation.

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 ¹²⁴I, ¹⁸F, and ¹¹C 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 ¹⁸F-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, respectively (p = 0.00008). Similarly, the microvessel grades were generally higher in the U87GM group (p = 0.002). Total EGFR amount was higher in U87MG than U138MG masses (p = 0.001), but the ratio of activated (pY1068) to total EGFR did not differ (p = 0.95).

Conclusions

PEGylated tracers labeled with ¹¹C, ¹²⁴I, and ¹⁸F showed no significant difference in uptake between U138MG and U87MG glioblastoma xenograft mice. The tracer binding with EGFR could be influenced by activation of the tyrosine kinase portion of the receptor which was similar in U138MG and U87MG. Despite these results, these tracers should be investigated in animal models with mutant EGFR genes to determine whether aberrant receptor function plays a role in tumor uptake.

Epidermal growth factor receptor in glioma: signal transduction, neuropathology, imaging, and radioresistance

Aberrant epidermal growth factor receptor (EGFR) signaling is common in cancer. Increased expression of wild type and mutant EGFR is a widespread feature of diverse types of cancer. EGFR signaling in cancer has been the focus of intense investigation for decades primarily for two reasons. First, aberrant EGFR signaling is likely to play an important role in the pathogenesis of cancer, and therefore, the mechanisms of EGFR-mediated oncogenic signaling are of interest. Second, the EGFR signaling system is an attractive target for therapeutic intervention. EGFR gene amplification and overexpression are a particularly striking feature of glioblastoma (GBM), observed in approximately 40% of tumors. GBM is the most common primary malignant tumor of the central nervous system in adults. In approximately 50% of tumors with EGFR amplification, a specific EGFR mutant (EGFRvIII, also known as EGFR type III, de2-7, Delta EGFR) can be detected. This mutant is highly oncogenic and is generated from a deletion of exons 2 to 7 of the EGFR gene, which results in an in-frame deletion of 267 amino acids from the extracellular domain of the receptor. EGFRvIII is unable to bind ligand, and it signals constitutively. Although EGFRvIII has the same signaling domain as the wild type receptor, it seems to generate a distinct set of downstream signals that may contribute to an increased tumorigenicity. In this review, we discuss recent progress in key aspects of EGFR signaling in GBM, focusing on neuropathology, signal transduction, imaging of the EGFR, and the role of the EGFR in mediating resistance to radiation therapy in GBM.

Radiolabeled cetuximab: dose optimization for epidermal growth factor receptor imaging in a head-and-neck squamous cell carcinoma model

Noninvasive imaging of the epidermal growth factor receptor (EGFR) in head-and-neck squamous cell carcinoma could be of value to select patients for EGFR-targeted therapy. We assessed dose optimization of (111) Indium-DTPA-cetuximab ((111) In-cetuximab) for EGFR imaging in a head-and-neck squamous cell carcinoma xenograft model. (111) In-cetuximab slowly internalized into FaDu cells in vitro, amounting to 1.0 × 10(4) molecules cetuximab per cell after 24 hr (15.8% of added activity). In nude mice with subcutaneous FaDu xenograft tumors, a protein dose escalation study with (111) In-cetuximab showed highest specific accumulation in tumors at protein doses between 1 and 30 μg per mouse (mean tumor uptake 33.1 ± 3.1%ID/g, 3 days postinjection (p.i.)). The biodistribution of (111) In-cetuximab and (125) I-cetuximab was determined at 1, 3 and 7 days p.i. at optimal protein dose. Tumor uptake was favorable for (111) In-cetuximab compared to (125) I-cetuximab. With pixel-by-pixel analysis, good correlations were found between intratumoral distribution of (111) In-cetuximab as determined by autoradiography and EGFR expression in the same tumor sections as determined immunohistochemically (mean r = 0.74 ± 0.14; all correlations p < 0.0001). Micro Single Photon Emission Computed Tomography (MicroSPECT) scans clearly visualized FaDu tumors from 1 day p.i. onward and tumor-to-background contrast increased until 7 days p.i. (tumor-to-liver ratios 0.58 ± 0.24, 3.42 ± 0.66, 8.99 ± 4.66 and 16.33 ± 11.56, at day 0, day 1, day 3 and day 7 p.i., respectively). Our study suggests that, at optimal cetuximab imaging dose, (111) In-cetuximab can be used for visualization of EGFR expression in head-and-neck squamous cell carcinoma using SPECT.

Radiolabeled small molecule protein kinase inhibitors for imaging with PET or SPECT

Imaging protein kinase expression with radiolabeled small molecule inhibitors has been actively pursued to monitor the clinical potential of targeted therapeutics and treatments as well as to determine kinase receptor density changes related to disease progression. The goal of the present review is to provide an overview of the breadth of radiolabeled small molecules that have been synthesized to target intracellular protein kinases, not only for imaging in oncology, but also for other areas of interest, particularly the central nervous system. Considerable radiotracer development has focused on imaging receptor tyrosine kinases of growth factors, protein kinases A, B and C, and glycogen synthase kinase-3ß. Design considerations, structural attributes and relevant biological results are summarized.

Kinetic analysis of novel mono- and multivalent VHH-fragments and their application for molecular imaging of brain tumours

BACKGROUND AND PURPOSE

The overexpression of epidermal growth factor receptor (EGFR) and its mutated variant EGFRvIII occurs in 50% of glioblastoma multiforme. We developed antibody fragments against EGFR/EGFRvIII for molecular imaging and/or therapeutic targeting applications.

EXPERIMENTAL APPROACH

An anti-EGFR/EGFRvIII llama single-domain antibody (EG(2)) and two higher valency format constructs, bivalent EG(2)-hFc and pentavalent V2C-EG(2) sdAbs, were analysed in vitro for their binding affinities using surface plasmon resonance and cell binding studies, and in vivo using pharmacokinetic, biodistribution, optical imaging and fluorescent microscopy studies.

KEY RESULTS

Kinetic binding analyses by surface plasmon resonance revealed intrinsic affinities of 55 nM and 97 nM for the monovalent EG(2) to immobilized extracellular domains of EGFR and EGFRvIII, respectively, and a 10- to 600-fold increases in apparent affinities for the multivalent binders, V2C-EG(2) and EG(2)-hFc, respectively. In vivo pharmacokinetic and biodistribution studies in mice revealed plasma half-lives for EG(2), V2C-EG(2) and EG(2)-hFc of 41 min, 80 min and 12.5 h, respectively, as well as a significantly higher retention of EG(2)-hFc compared to the other two constructs in EGFR/EGFRvIII-expressing orthotopic brain tumours, resulting in the highest signal in the tumour region in optical imaging studies. Time domain volumetric optical imaging fusion with high-resolution micro-computed tomography of microvascular brain network confirmed EG(2)-hFc selective accumulation/retention in anatomically defined tumour regions.

CONCLUSIONS

Single domain antibodies can be optimized for molecular imaging applications by methods that improve their apparent affinity and prolong plasma half-life and, at the same time, preserve their ability to penetrate tumour parenchyma.

Searching for metachronous tumours in patients with head and neck cancer: the ideal protocol!

PURPOSE OF REVIEW

As treatment changes in the management of head and neck cancer, patients are reportedly living longer; therefore, their death may be due to comorbidity, metastatic disease or the development of a metachronous second primary tumour (MSPT). This review describes recent developments in the identification of MSPTs of head and neck cancer, oesophagus and lung, and suggests/recommends an 'ideal surveillance protocol'.

RECENT FINDINGS

The rate of MSPT development ranges between 6 and 9% annually for life. Improved accuracy in the detection of mucosal asymptomatic premalignant and early cancer has been enhanced by incorporating fluorescence spectroscopy in addition to modern flexible endoscopic techniques in the outpatient setting. Newer imaging has replaced old techniques (chest radiograph, barium swallow, etc.) by using radiotracer PET-computed tomography to detect local tumour activity. Further advances are anticipated in optical diagnostics and the incorporation of radiopharmaceuticals with labelled antibodies to enhance PET imaging, thus making tumour identification more accurate. Genetic classification of head and neck cancer has already identified high-risk patient groups, thereby allowing expensive tumour screening techniques to be used selectively and specifically. Patients who continue to smoke and abuse alcohol must be helped and encouraged to quit.

SUMMARY

It is now possible to review traditional follow-up policy for treated head and neck cancer patients, to encourage the implementation of an evidence-based surveillance protocol, to identify only patients who are at high-risk of developing a MSPT, to incorporate modern targeted expensive tumour screening and to allow treatment of early cancer and effective treatment, thereby improving patients' quality of life and increasing survival.

Are there imaging characteristics associated with epidermal growth factor receptor and KRAS mutations in patients with adenocarcinoma of the lung with bronchioloalveolar features?

PURPOSE

To identify any particular imaging features on computed tomography (CT) in patients with confirmed adenocarcinoma with bronchioloalveolar (ABAC) features and known epidermal growth factor receptor (EGFR) and KRAS mutations.

MATERIALS AND METHODS

Institutional review board approval was obtained for this retrospective study. Seventy-seven pulmonary nodules in 64 patients with a histologic diagnosis of ABAC and known EGFR or KRAS mutation status were assessed. Of these, 23 patients who were negative for both EGFR and KRAS mutations were used as a control group. Lesion size, margins, and density (ground glass versus solid) were assessed. Statistical analysis using the two-tailed Fisher's exact test t test was performed with multiple different variables.

RESULTS

Twenty-one (33%) of 64 patients had EGFR mutations, 20 (31%) of 64 patients had a KRAS mutation, and 23 (36%) had neither. In nine patients with an EGFR mutation, there were 10 nodules with some ground glass opacity (GGO) and in nine patients with a KRAS mutation, there were nine nodules with some GGO. Twenty-six (34%) of the 77 nodules had some GGO, and 12 (46%) of these 26 nodules were entirely GGO. Sixty-two (81%) of the 77 nodules had some solid component, which also included some that were mixed with GGO. Thirty-five (45%) of 77 nodules had air bronchograms. All five nodules (100%) with a high percentage of bronchioloalveolar carcinoma (>75%) had the appearance of GGO only. The presence of GGO on CT was not significantly associated with the presence of an EGFR mutation (p = 0.44) or with the presence of a KRAS mutation (p = 0.77).

CONCLUSIONS

In our sample of patients with ABAC, there was no specific CT appearance, which would correlate with either an EGFR mutation or a KRAS mutation, when compared with a control group of patients who did not have these mutations.

Targeting the EGF receptor for ovarian cancer therapy

Ovarian carcinoma is the leading cause of death from gynecologic malignancy in the US. Factors such as the molecular heterogeneity of ovarian tumors and frequent diagnosis at advanced stages hamper effective disease treatment. There is growing emphasis on the identification and development of targeted therapies to disrupt molecular pathways in cancer. The epidermal growth factor (EGF) receptor is one such protein target with potential utility in the management of ovarian cancer. This paper will discuss contributions of EGF receptor activation to ovarian cancer pathogenesis and the status of EGF receptor inhibitors and EGF receptor targeted therapies in ovarian cancer treatment.

Imaging of EGFR expression in murine xenografts using site-specifically labelled anti-EGFR 111In-DOTA-Z EGFR:2377 Affibody molecule: aspect of the injected tracer amount

INTRODUCTION

Overexpression of epidermal growth factor receptor (EGFR) is a prognostic and predictive biomarker in a number of malignant tumours. Radionuclide molecular imaging of EGFR expression in cancer could influence patient management. However, EGFR expression in normal tissues might complicate in vivo imaging. The aim of this study was to evaluate if optimization of the injected protein dose might improve imaging of EGFR expression in tumours using a novel EGFR-targeting protein, the DOTA-Z(EGFR:2377) Affibody molecule.

METHODS

An anti-EGFR Affibody molecule, Z(EGFR:2377), was labelled with (111)In via the DOTA chelator site-specifically conjugated to a C-terminal cysteine. The affinity of DOTA-Z(EGFR:2377) for murine and human EGFR was measured by surface plasmon resonance. The cellular processing of (111)In-DOTA-Z(EGFR:2377) was evaluated in vitro. The biodistribution of radiolabelled Affibody molecules injected in a broad range of injected Affibody protein doses was evaluated in mice bearing EGFR-expressing A431 xenografts.

RESULTS

Site-specific coupling of DOTA provided a uniform conjugate possessing equal affinity for human and murine EGFR. The internalization of (111)In-DOTA-Z(EGFR:2377) by A431 cells was slow. In vivo, the conjugate accumulated specifically in xenografts and in EGFR-expressing tissues. The curve representing the dependence of tumour uptake on the injected Affibody protein dose was bell-shaped. The highest specific radioactivity (lowest injected protein dose) provided a suboptimal tumour-to-blood ratio. The results of the biodistribution study were confirmed by gamma-camera imaging.

CONCLUSION

The (111)In-DOTA-Z(EGFR:2377) Affibody molecule is a promising tracer for radionuclide molecular imaging of EGFR expression in malignant tumours. Careful optimization of protein dose is required for high-contrast imaging of EGFR expression in vivo.

Strategies for molecular imaging of epidermal growth factor receptor tyrosine kinase in cancer

A wealth of research has focused on developing targeted cancer therapies by specifically inhibiting epidermal growth factor receptor tyrosine kinase (EGFR-TK). However, the outcome of most EGFR-TK-targeted drugs that were approved by the Food and Drug Administration or entered clinical trials has been only moderate. Enhancement of EGFR-targeted therapy hinges on a reliable in vivo quantitative molecular imaging method. Such a method would enable monitoring of receptor drug binding and receptor occupancy in vivo; determination of the duration of EGFR inhibition in vivo; and, potentially, identification of a primary or secondary mutation in EGFR leading to drug interaction or loss of EGFR recognition by the drug. This review analyzes the most recent strategies to visualize and quantify EGFR-TK in cancer by nuclear medicine imaging and describes future directions.