Molecular imaging of therapeutic response to epidermal growth factor receptor blockade in colorectal cancer

Molecular Endoscopy for the Diagnosis and Therapeutic Monitoring of Colorectal Cancer

Colorectal cancer (CRC) is one of the leading causes of cancer related death in the western world. Its successful treatment requires early detection and removal of precursor lesions as well as individualized treatment of advanced disease. During recent years, molecular imaging techniques have shown promising results to improve current clinical practice. For instance, molecular endoscopy resulted in higher detection rates of precursors in comparison to conventional endoscopy in preclinical and clinical studies. Molecular confocal endomicroscopy allowed a further classification of suspect lesions as well as the prediction and monitoring of the therapeutic response. In this review, we summarize recent achievements for molecular imaging of CRC in preclinical studies, initial clinical trials and the remaining challenges for future translation into clinical practice.

Change of Apoptosis and Glucose Metabolism in Lung Cancer Xenografts during Cytotoxic and Anti-Angiogenic Therapy Assessed by Annexin V Based Optical Imaging and 18F-FDG-PET/CT

Methods

For apoptosis imaging, the near-infrared probe Annexin Vivo750 was used in combination with fluorescence molecular tomography and microcomputed tomography (FMT/µCT). Glucose metabolism was assessed using ¹⁸F-FDG-PET/CT. Five groups of nude mice bearing lung cancer xenografts (A549) were investigated: (i) untreated controls and two groups after (ii) cytotoxic (carboplatin) or (iii) anti-angiogenic (sunitinib) treatment for four and nine days, respectively. Imaging data were validated by immunohistochemistry.

Results

In response to carboplatin treatment, an inverse relation was found between the change in glucose metabolism and apoptosis in A549 tumors. Annexin Vivo showed a continually increasing tumor accumulation, while the tumor-to-muscle ratio of ¹⁸F-FDG continuously decreased during therapy. Immunohistochemistry revealed a significantly higher tumor apoptosis (p=0.007) and a minor but not significant reduction in vessel density only at day 9 of carboplatin therapy. Interestingly, during anti-angiogenic treatment there was an early drop in the tumor-to-muscle ratio between days 0 and 4, followed by a subsequent minor decrease (¹⁸F-FDG tumor-to-muscle-ratio: 1.9 ± 0.4; day 4: 1.1 ± 0.2; day 9: 1.0 ± 0.2; p=0.021 and p=0.001, respectively). The accumulation of Annexin Vivo continuously increased over time (Annexin Vivo: untreated: 53.7 ± 36.4 nM; day 4: 87.2 ± 53.4 nM; day 9: 115.1 ± 103.7 nM) but failed to display the very prominent early induction of tumor apoptosis that was found by histology already at day 4 (TUNEL: p=0.0036) together with a decline in vessel density (CD31: p=0.004), followed by no significant changes thereafter.

Conclusion

Both molecular imaging approaches enable visualizing the effects of cytotoxic and anti-angiogenic therapy in A549 tumors. However, the early and strong tumor apoptosis induced by the anti-angiogenic agent sunitinib was more sensitively and reliably captured by monitoring of the glucose metabolism as compared to Annexin V-based apoptosis imaging.

MR cell size imaging with temporal diffusion spectroscopy

Cytological features such as cell size and intracellular morphology provide fundamental information on cell status and hence may provide specific information on changes that arise within biological tissues. Such information is usually obtained by invasive biopsy in current clinical practice, which suffers several well-known disadvantages. Recently, novel MRI methods such as IMPULSED (imaging microstructural parameters using limited spectrally edited diffusion) have been developed for direct measurements of mean cell size non-invasively. The IMPULSED protocol is based on using temporal diffusion spectroscopy (TDS) to combine measurements of water diffusion over a wide range of diffusion times to probe cellular microstructure over varying length scales. IMPULSED has been shown to provide rapid, robust, and reliable mapping of mean cell size and is suitable for clinical imaging. More recently, cell size distributions have also been derived by appropriate analyses of data acquired with IMPULSED or similar sequences, which thus provides MRI-cytometry. This review summarizes the basic principles, practical implementations, validations, and example applications of MR cell size imaging based on TDS and demonstrates how cytometric information can be used in various applications. In addition, the limitations and potential future directions of MR cytometry are identified including the diagnosis of nonalcoholic steatohepatitis of the liver and the assessment of treatment response of cancers.

Regeneration of testis tissue after ectopic implantation of porcine testis cell aggregates in mice: improved consistency of outcomes and in situ monitoring

Ectopic implantation of donor testis cell aggregates in recipient mice results in de novo formation or regeneration of testis tissue and, as such, provides a unique invivo model for the study of testis development. However, currently the results are inconsistent and the efficiency of the model remains low. This study was designed to: (1) examine several factors that can potentially improve the consistency and efficiency of this model and (2) explore the use of ultrasound biomicroscopy (UBM) for the non-invasive invivo evaluation of implants. Testis cell aggregates, containing ~40% gonocytes, from 1-week-old donor piglets were implanted under the back skin of immunodeficient mice through skin incisions using gel matrices or through subcutaneous injection without using gel matrices. The addition of gel matrices led to inconsistent tissue development; gelatin had the greatest development, followed by collagen, whereas agarose resulted in poor development. The results also depended on the implanted cell numbers since implants with 100×106 cells were larger than those with 50×106 cells. The injection approach for cell implantation was less invasive and resulted in more consistent and efficient testis tissue development. UBM provided promising results as a means of non-invasive monitoring of implants.

Photosensitizer Nanoparticles Boost Photodynamic Therapy for Pancreatic Cancer Treatment

Patients with pancreatic cancer (PCa) have a poor prognosis apart from the few suitable for surgery. Photodynamic therapy (PDT) is a minimally invasive treatment modality whose efficacy and safety in treating unresectable localized PCa have been corroborated in clinic. Yet, it suffers from certain limitations during clinical exploitation, including insufficient photosensitizers (PSs) delivery, tumor-oxygenation dependency, and treatment escape of aggressive tumors. To overcome these obstacles, an increasing number of researchers are currently on a quest to develop photosensitizer nanoparticles (NPs) by the use of a variety of nanocarrier systems to improve cellular uptake and biodistribution of photosensitizers. Encapsulation of PSs with NPs endows them significantly higher accumulation within PCa tumors due to the increased solubility and stability in blood circulation. A number of approaches have been explored to produce NPs co-delivering multi-agents affording PDT-based synergistic therapies for improved response rates and durability of response after treatment. This review provides an overview of available data regarding the design, methodology, and oncological outcome of the innovative NPs-based PDT of PCa.

Paradigms in Fluorescence Molecular Imaging: Maximizing Measurement of Biological Changes in Disease, Therapeutic Efficacy, and Toxicology/Safety

Fluorescence molecular imaging (MI) is an important concept in preclinical research that focuses on the visualization of cellular and biological function in a non-invasive fashion to better understand in vivo disease processes and treatment effects. MI differs fundamentally from traditional preclinical imaging strategies in that it generally relies on reporter probes specific for particular targets or pathways that can be used to reveal biological changes in situ, at the site(s) of disease. In contrast, the more established imaging modalities, like magnetic resonance imaging, X-ray, micro X-ray computed tomography, and ultrasound, historically have relied primarily on late-stage anatomical or physiologic changes. The practical application of fluorescence MI, however, has drifted somewhat from the emphasis on quantifying biology, and based on the publication record, it now appears to include any imaging in which a probe or contrast agent is used to non-invasively acquire in vivo endpoint information. Unfortunately, the mere use of a defined biologically specific probe, in the absence of careful study design, does not guarantee that any useful biological information is actually gained, although often useful endpoint results still can be achieved. This review proposes to add subcategories of MI, termed MI biological assessment (or MIBA), that emphasize a focus on obtaining early and clear biological changes associated with disease development, therapeutic efficacy, and drug-induced tissue changes. Proper selection of probes and careful study design are critical for maximizing the non-invasive assessment of in vivo biological changes, and applications of these critical elements are described.

The Potential Targets and Mechanisms of a Carbazole and Pyrazole Containing Anticancer Compound

AIMS

Characterization of a small anticancer compound.

BACKGROUND

The development of small molecules as new anti-cancer therapeutics is necessary to improve anti-tumor efficacy and reduce toxicities, especially for the treatment of brain tumors, where only small molecules can effectively cross the brain-blood barrier. Several novel hits were previously selected by concurrently screening colon and glioma cancer cell lines with a sensorconjugated reporter system. Here, we focused on one of them.

OBJECTIVE

Elucidating the potential target(s) of a novel anticancer compound.

METHODS

Computer-assisted structural and motif analysis (least absolute shrinkage and selection operator or LASSO score) was used to assess compound's targets, then direct kinase activity assays were used for the confirmation; Western blot of phosphorylated kinases, as well as FACS and caspase 3/7 activity assays, were used to decipher the action mechanisms. Finally, the expression profiling of proteins involved in various G-protein pathways by real-time PCR was performed.

RESULTS

The small chemical, (4E)-4-[2-(9-ethyl-9H-carbazol-3-yl)hydrazin-1-ylidene]-3-methyl- 4,5-dihydro-1H-pyrazol-5-one, with a formula C18H17N5O and MW of 319.36, designated as VUGX01, was predicted to be a ligand/inhibitor to receptor tyrosine kinases (RTKs) by computer analysis (least absolute shrinkage and selection operator or LASSO score). However, direct analysis with recombinant kinases showed that it is not an effective inhibitor to the popular receptor kinases at 1μM concentration. This compound can activate caspases in some tumor cell lines but has minimal effects on the cell cycle. Drug treatments lead to the changes in phosphorylation of AKT and c- RAF, as well as the expression level of MAP2K, suggesting this compound may interact with Gprotein coupled receptors (GPCRs). The expression profiling of 82 proteins involved in various Gprotein pathways by real-time PCR showed that the treatment up-regulates the expression of several proteins, including angiotensinogen, angiotensin II receptor, and IP3-kinase catalytic subunit gamma.

CONCLUSION

VUGX01 can effectively block proliferation and induce apoptosis of certain types of cancer cells, even it is predicted by high LASSO score, but it is not an effective RTKs inhibitor, it may inhibit cell growth through acting as a novel ligand to one or several GPCRs.

A Novel Conjugate of Bis[((4-bromophenyl)amino)quinazoline], a EGFR-TK Ligand, with a Fluorescent Ru(II)-Bipyridine Complex Exhibits Specific Subcellular Localization in Mitochondria

The epidermal growth factor receptor (EGFR) is a key target in anticancer research, whose aberrant function in malignancies has been linked to severe irregularities in critical cellular processes, including cell cycle progression, proliferation, differentiation, and survival. EGFR mutant variants, either transmembrane or translocated to the mitochondria and/or the nucleus, often exhibit resistance to EGFR inhibitors. The ability to noninvasively image and quantify EGFR provides novel approaches in the detection, monitoring, and treatment of EGFR-related malignancies. The current study aimed to deliver a new theranostic agent that combines fluorescence imaging properties with EGFR inhibition. This was achieved via conjugation of an in-house-developed ((4-bromophenyl)amino)quinazoline inhibitor of mutant EGFR-TK, selected from a focused aminoquinazoline library, with a [Ru(bipyridine)₃]²⁺ fluorophore. A triethyleneglycol-derived diamino linker featuring (+)-ionizable sites was employed to link the two functional moieties, affording two unprecedented Ru conjugates with 1:1 and 2:1 stoichiometry of aminoquinazoline to the Ru complex (mono-quinazoline-Ru-conjugate and bis-quinazoline-Ru-conjugate, respectively). The bis-quinazoline-Ru-conjugate, which retains an essential inhibitory activity, was found by fluorescence imaging to be effectively uptaken by Uppsala 87 malignant glioma (grade IV malignant glioma) cells. The fluorescence imaging study and a time-resolved fluorescence resonance energy transfer study indicated a specific subcellular distribution of the conjugate that coincides with that of a mitochondria-targeted dye, suggesting mitochondrial localization of the conjugate and potential association with mitochondria-translocated forms of EGFR. Mitochondrial localization was further documented by the specific concentration of the bis-quinazoline-Ru-conjugate in a mitochondrial isolation assay.

Preclinical Imaging in Targeted Cancer Therapies

Preclinical imaging with radiolabeled probes can provide noninvasive tools to test the efficacy of targeted agents in tumors harboring specific genetic alterations and to identify imaging parameters that can be used as pharmacodynamics markers in cancer patients. The present review will primarily focus on preclinical imaging studies that can accelerate the clinical approval of targeted agents and promote the development of imaging biomarkers for clinical applications. Since only subgroups of patients may benefit from treatment with targeted anticancer agents, the identification of a patient population expressing the target is of primary importance for the success of clinical trials. Preclinical imaging studies tested the ability of new radiolabeled compounds to recognize mutant, amplified, or overexpressed targets and some of these tracers were transferred to the clinical setting. More common tracers such as ¹⁸F-Fluorothymidine and ¹⁸F-Fluorodeoxyglucose were employed in animal models to test the inhibition of the target and downstream pathways through the evaluation of early changes of proliferation and glucose metabolism allowing the identification of sensitive and resistant tumors. Furthermore, since the majority of patients treated with targeted anticancer agents will invariably develop resistance, preclinical imaging studies were performed to test the efficacy of reversal agents to overcome resistance. These studies provided consistent evidence that imaging with radiolabeled probes can monitor the reversal of drug resistance by newly designed alternative compounds. Finally, despite many difficulties and challenges, preclinical imaging studies targeting the expression of immune checkpoints proved the principle that it is feasible to select patients for immunotherapy based on imaging findings. In conclusion, preclinical imaging can be considered as an integral part of the complex translational process that moves a newly developed targeted agent from laboratory to clinical application intervening in all clinically relevant steps including patient selection, early monitoring of drug effects and reversal of drug resistance.

In vivo magnetic resonance imaging of treatment-induced apoptosis

Imaging apoptosis could provide an early and specific means to monitor tumor responses to treatment. To date, despite numerous attempts to develop molecular imaging approaches, there is still no widely-accepted and reliable method for in vivo imaging of apoptosis. We hypothesized that the distinct cellular morphologic changes associated with treatment-induced apoptosis, such as cell shrinkage, cytoplasm condensation, and DNA fragmentation, can be detected by temporal diffusion spectroscopy imaging (TDSI). Cetuximab-induced apoptosis was assessed in vitro and in vivo with cetuximab-sensitive (DiFi) and insensitive (HCT-116) human colorectal cancer cell lines by TDSI. TDSI findings were complemented by flow cytometry and immunohistochemistry. Cell cycle analysis and flow cytometry detected apoptotic cell shrinkage in cetuximab-treated DiFi cells, and significant apoptosis was confirmed by histology. TDSI-derived parameters quantified key morphological changes including cell size decreases during apoptosis in responsive tumors that occurred earlier than gross tumor volume regression. TDSI provides a unique measurement of apoptosis by identifying cellular characteristics, particularly cell shrinkage. The method will assist in understanding the underlying biology of solid tumors and predict tumor response to therapies. TDSI is free of any exogenous agent or radiation, and hence is very suitable to be incorporated into clinical applications.

Conformationally Induced Off-On Cell Membrane Chemosensor Targeting Receptor Protein-Tyrosine Kinases for in Vivo and in Vitro Fluorescence Imaging of Cancers

Molecules capable of monitoring receptor protein-tyrosine kinase expression could potentially serve as useful tools for cancer diagnosis due to the overexpression of tyrosine kinases during tumor growth and metastasis. In this work, a conformationally induced "off-on" tyrosine kinase cell membrane fluorescent sensor (SP1) was designed and evaluated for the detection and imaging of receptor protein-tyrosine kinases in vivo and in vitro. SP1 consists of sunitinib and pyrene linked via hexamethylenediamine and displays quenched fluorescence as a dimer. The fluorescence of SP1 is restored in the presence of receptor protein-tyrosine kinases upon strong interaction with SP1 at the target terminal. The unique signal response mechanism enables SP1 use for fluorescence microscopy imaging of receptor protein-tyrosine kinases in the cell membranes of living cells, allowing for the rapid differentiation of cancer cells from normal cells. SP1 can be used to visualize the chick embryo chorioallantoic membrane and mouse model tumors, suggesting its possible application for early cancer diagnosis.

Cholangiocarcinoma: molecular imaging-guided radiofrequency hyperthermia-enhanced intratumoral herpes simplex virus thymidine kinase gene therapy

We investigated the feasibility of using radiofrequency hyperthermia (RFH) to enhance green fluorescent protein (GFP)/herpes simplex virus thymidine kinase (HSV-TK)/ganciclovir (GCV) gene therapy of cholangiocarcinoma. Cholangiocarcinoma cells and mice with cholangiocarcinoma were treated by (i) GFP/HSV-TK/plasmid combined with RFH at 42°C, followed by ganciclovir administration; (ii) HSV-TK alone; (iii) RFH alone; and (iv) saline. The therapeutic effects among different treatments were evaluated by bioluminescent optical imaging and ultrasound imaging. For the technical validation, GFP/HSV-TK/plasmid was intrabiliarily injected into pig common bile duct (CBD) walls using a needle-integrated balloon catheter with or without RFH enhancement. GFP gene expression was evaluated by optical imaging, which was correlated with histology. The results show that combination therapy of HSV-TK plus RFH significantly induced lower cell viabilities and decreased bioluminescence signals compared the other three groups, which were further confirmed by the tumor volume decrease with combination therapy, as measured by ultrasound imaging. Optical imaging of CBD tissues demonstrated an increased GFP expression in the group with RFH enhancement, compared that with non-RFH treatment. We concluded that intratumoral RFH can enhance the therapeutic effect of GFP/HSV-TK/plasmid on cholangiocarcinoma, which may open new avenues for effective treatment of this deadly disease.

Dynamic Biomarkers of Response to Antiangiogenic Therapies in Colorectal Cancer: A Review

Background:

Identification of clinical and molecular biomarkers to predict dynamic response or monitor in real-time the efficacy of antiangiogenic therapy represents a major point in the treatment of patients with advanced colorectal cancer. Several stu-dies have been conduced to identify some predictive biomarkers to select patients who will benefit from bevacizumab, the most widely used antiangiogenic monoclonal anti-body.

Conclusion:

After a decade since the introduction of bevacizumab, no effective predictive biomarkers are available in routine clinical practice. In this review, we summarized the potential candidate dynamic biomarkers that may play a role in this setting.

Detection and characterization of murine colitis and carcinogenesis by molecularly targeted contrast-enhanced ultrasound

AIM

To study mucosal addressin cellular adhesion molecule-1 (MAdCAM-1) and vascular endothelial growth factor (VEGF)-targeted contrast enhanced ultrasound (CEUS) for the assessment of murine colitis and carcinogenesis.

METHODS

C57BL/6 mice were challenged with 3% dextran sodium-sulfate (DSS) for three, six or nine days to study the development of acute colitis. Ultrasound was performed with and without the addition of unspecific contrast agents. MAdCAM-1-targeted contrast agent was used to detect and quantify MAdCAM-1 expression. Inflammatory driven colorectal azoxymethane (AOM)/DSS-induced carcinogenesis was examined on day 42 and 84 using VEGF-targeted contrast agent. Highly specific tissue echogenicity was quantified using specialized software. Sonographic findings were correlated to tissue staining, western blot analysis and immunohistochemistry to quantify the degree of inflammation and stage of carcinogenesis.

RESULTS

Native ultrasound detected increased general bowel wall thickening that correlated with more progressed and more severe DSS-colitis (healthy mice: 0.3 mm ± 0.03 vs six days DSS: 0.5 mm ± 0.2 vs nine days DSS: 0.6 mm ± 0.2, P < 0.05). Moreover, these sonographic findings correlated well with clinical parameters such as weight loss (r² = 0.74) and histological damage (r² = 0.86) (P < 0.01). In acute DSS-induced murine colitis, CEUS targeted against MAdCAM-1 detected and differentiated stages of mild, moderate and severe colitis via calculation of mean pixel contrast intensity in decibel (9.6 dB ± 1.6 vs 12.9 dB ± 1.4 vs 18 dB ± 3.33, P < 0.05). Employing the AOM/DSS-induced carcinogenesis model, tumor development was monitored by CEUS targeted against VEGF and detected a significantly increased echogenicity in tumors as compared to adjacent healthy mucosa (healthy mucosa, 1.6 dB ± 1.4 vs 42 d, 18.2 dB ± 3.3 vs 84 d, 18.6 dB ± 4.9, P < 0.01). Tissue echogenicity strongly correlated with histological analysis and immunohistochemistry findings (VEGF-positive cells in 10 high power fields of healthy mucosa: 1 ± 1.2 vs 42 d after DSS start: 2.4 ± 1.6 vs 84 d after DSS start: 3.5 ± 1.3, P < 0.01).

CONCLUSION

Molecularly targeted CEUS is a highly specific and non-invasive imaging modality, which characterizes murine intestinal inflammation and carcinogenesis in vivo.

Multi-modality imaging-monitored creation of rat orthotopic pancreatic head cancer with obstructive jaundice

Purpose

To investigate the feasibility of using multi-modality imaging to monitor the creation of rat models with orthotopic pancreatic head cancer with obstructive jaundice.

Results

27 of 52 rats (51.92%) developed pancreatic head cancer. The tumor formation rate was significantly higher in the animal group receiving bioluminescent tumor, compared to the group receiving non-bioluminescent donor tumors [78.1% (25/32 rats) vs 10.0% (2/20 rats), P = 0.0001]. Both ultrasound imaging and MRI clearly characterized the orthotopic tumors. Laboratory biochemistry test for those rats with obstructive jaundice showed elevated levels of bilirubin, aspartate transaminase (AST), alkaline phosphatase (ALT) and gamma-glutamyl transpeptidase (λ-GGT), compared with those rats without jaundice (P < 0.05). Correlative pathology confirmed that all tumors were ductal adenocarcinomas, and located in pancreatic head regions.

Materials and Methods

Rat pancreatic adenocarcinoma cells (DSL-6A/C1) were first transfected with lentivirus/mCherry-luciferase genes, and then subcutaneously implanted into flanks of donor immunocompetent Lewis rats, to create pancreatic tumor tissues. The tumor tissues from donor rats with either bioluminescence signal or without the signal were then transplanted into the pancreatic heads of 52 recipient Lewis rats. Bioluminescence optical and ultrasound imaging, as well as magnetic resonance imaging (MRI), were performed to follow up the tumor formation and growth in these tumor-transplanted rats. Physical examination and biochemistry test were used to discern the rats with obstructive jaundice. The rats were euthanized for subsequent histologic correlation and confirmation.

Conclusions

We successfully created a new rat model with orthotopic pancreatic head cancer, which can be accurately monitored and visualized by different imaging modalities.

Optimized Translocator Protein Ligand for Optical Molecular Imaging and Screening

Translocator protein (TSPO) is a validated target for molecular imaging of a variety of human diseases and disorders. Given its involvement in cholesterol metabolism, TSPO expression is commonly elevated in solid tumors, including glioma, colorectal cancer, and breast cancer. TSPO ligands capable of detection by optical imaging are useful molecular tracers for a variety of purposes that range from quantitative biology to drug discovery. Leveraging our prior optimization of the pyrazolopyrimidine TSPO ligand scaffold for cancer imaging, we report herein a new generation of TSPO tracers with superior binding affinity and suitability for optical imaging and screening. In total, seven candidate TSPO tracers were synthesized and vetted in this study; the most promising tracer identified (29, K_d = 0.19 nM) was the result of conjugating a high-affinity TSPO ligand to a fluorophore used routinely in biological sciences (FITC) via a functional carbon linker of optimal length. Computational modeling suggested that an n-alkyl linker of eight carbons in length allows for positioning of the bulky fluorophore distal to the ligand binding domain and toward the solvent interface, minimizing potential ligand-protein interference. Probe 29 was found to be highly suitable for in vitro imaging of live TSPO-expressing cells and could be deployed as a ligand screening and discovery tool. Competitive inhibition of probe 29 quantified by fluorescence and ³H-PK11195 quantified by traditional radiometric detection resulted in equivalent affinity data for two previously reported TSPO ligands. This study introduces the utility of TSPO ligand 29 for in vitro imaging and screening and provides a structural basis for the development of future TSPO imaging ligands bearing bulky signaling moieties.

Preclinical Applications of 3'-Deoxy-3'-[18F]Fluorothymidine in Oncology - A Systematic Review

The positron emission tomography (PET) tracer 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT) has been proposed to measure cell proliferation non-invasively in vivo. Hence, it should provide valuable information for response assessment to tumor therapies. To date, [18F]FLT uptake has found limited use as a response biomarker in clinical trials in part because a better understanding is needed of the determinants of [18F]FLT uptake and therapy-induced changes of its retention in the tumor. In this systematic review of preclinical [18F]FLT studies, comprising 174 reports, we identify the factors governing [18F]FLT uptake in tumors, among which thymidine kinase 1 plays a primary role. The majority of publications (83 %) report that decreased [18F]FLT uptake reflects the effects of anticancer therapies. 144 times [18F]FLT uptake was related to changes in proliferation as determined by ex vivo analyses. Of these approaches, 77 % describe a positive relation, implying a good concordance of tracer accumulation and tumor biology. These preclinical data indicate that [18F]FLT uptake holds promise as an imaging biomarker for response assessment in clinical studies. Understanding of the parameters which influence cellular [18F]FLT uptake and retention as well as the mechanism of changes induced by therapy is essential for successful implementation of this PET tracer. Hence, our systematic review provides the background for the use of [18F]FLT in future clinical studies.

Optical imaging probes in oncology

Cancer is a complex disease, characterized by alteration of different physiological molecular processes and cellular features. Keeping this in mind, the possibility of early identification and detection of specific tumor biomarkers by non-invasive approaches could improve early diagnosis and patient management.Different molecular imaging procedures provide powerful tools for detection and non-invasive characterization of oncological lesions. Clinical studies are mainly based on the use of computed tomography, nuclear-based imaging techniques and magnetic resonance imaging. Preclinical imaging in small animal models entails the use of dedicated instruments, and beyond the already cited imaging techniques, it includes also optical imaging studies. Optical imaging strategies are based on the use of luminescent or fluorescent reporter genes or injectable fluorescent or luminescent probes that provide the possibility to study tumor features even by means of fluorescence and luminescence imaging. Currently, most of these probes are used only in animal models, but the possibility of applying some of them also in the clinics is under evaluation.The importance of tumor imaging, the ease of use of optical imaging instruments, the commercial availability of a wide range of probes as well as the continuous description of newly developed probes, demonstrate the significance of these applications. The aim of this review is providing a complete description of the possible optical imaging procedures available for the non-invasive assessment of tumor features in oncological murine models. In particular, the characteristics of both commercially available and newly developed probes will be outlined and discussed.

Markers of Response to Antiangiogenic Therapies in Colorectal Cancer: Where Are We Now and What Should Be Next?

Despite advances in the treatment of colorectal cancer (CRC), it remains the second most common cause of cancer-related death in the Western world. Angiogenesis is a complex process that involves the formation of new blood vessels from preexisting vessels. It is essential for promoting cancer survival, growth, and dissemination. The inhibition of angiogenesis has been shown to prevent tumor progression experimentally, and several chemotherapeutic targets of tumor angiogenesis have been identified. These include anti-vascular endothelial growth factor (VEGF) treatments, such as bevacizumab (a VEGF-specific binding antibody) and anti-VEGF receptor tyrosine kinase inhibitors, although antiangiogenic therapy has been shown to be effective in the treatment of several cancers, including CRC. However, it is also associated with its own side effects and financial costs. Therefore, the identification of biomarkers that are able to identify patients who are more likely to benefit from antiangiogenic treatment is very important. This article intends to be a concise summary of the potential biomarkers that can predict or prognosticate the benefit of antiangiogenic treatments in CRC, and also what we can expect in the near future.

EGFR is not a major driver for osteosarcoma cell growth in vitro but contributes to starvation and chemotherapy resistance

Background

Enhanced signalling via the epidermal growth factor receptor (EGFR) is a hallmark of multiple human carcinomas. However, in recent years data have accumulated that EGFR might also be hyperactivated in human sarcomas. Aim of this study was to investigate the influence of EGFR inhibition on cell viability and its interaction with chemotherapy response in osteosarcoma cell lines.

Methods

We have investigated a panel of human osteosarcoma cell lines regarding EGFR expression and downstream signalling. To test its potential applicability as therapeutic target, inhibition of EGFR by gefitinib was combined with osteosarcoma chemotherapeutics and cell viability, migration, and cell death assays were performed.

Results

Osteosarcoma cells expressed distinctly differing levels of functional EGFR reaching in some cases high amounts. Functionality of EGFR in osteosarcoma cells was proven by EGF-mediated activation of both MAPK and PI3K/AKT pathway (determined by phosphorylation of ERK1/2, AKT, S6, and GSK3β). The EGFR-specific inhibitor gefitinib blocked EGF-mediated downstream signal activation. At standard in vitro culture conditions, clinically achievable gefitinib doses demonstrated only limited cytotoxic activity, however, significantly reduced long-term colony formation and cell migration. In contrast, under serum-starvation conditions active gefitinib doses were distinctly reduced while EGF promoted starvation survival. Importantly, gefitinib significantly supported the anti-osteosarcoma activities of doxorubicin and methotrexate regarding cell survival and migratory potential.

Conclusion

Our data suggest that EGFR is not a major driver for osteosarcoma cell growth but contributes to starvation- and chemotherapy-induced stress survival. Consequently, combination approaches including EGFR inhibitors should be evaluated for treatment of high-grade osteosarcoma patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-015-0251-5) contains supplementary material, which is available to authorized users.

Monitoring of anti-cancer treatment with (18)F-FDG and (18)F-FLT PET: a comprehensive review of pre-clinical studies

Functional imaging of solid tumors with positron emission tomography (PET) imaging is an evolving field with continuous development of new PET tracers and discovery of new applications for already implemented PET tracers. During treatment of cancer patients, a general challenge is to measure treatment effect early in a treatment course and by that to stratify patients into responders and non-responders. With 2-deoxy-2-[(18)F]fluoro-D-glucose ((18)F-FDG) and 3'-deoxy-3'-[(18)F]fluorothymidine((18)F-FLT) two of the cancer hallmarks, altered energy metabolism and increased cell proliferation, can be visualized and quantified non-invasively by PET. With (18)F-FDG and (18)F-FLT PET changes in energy metabolism and cell proliferation can thereby be determined after initiation of cancer treatment in both clinical and pre-clinical studies in order to predict, at an early time-point, treatment response. It is hypothesized that decreases in glycolysis and cell proliferation may occur in tumors that are sensitive to the applied cancer therapeutics and that tumors that are resistant to treatment will show unchanged glucose metabolism and cell proliferation. Whether (18)F-FDG and/or (18)F-FLT PET can be used for prediction of treatment response has been analyzed in many studies both following treatment with conventional chemotherapeutic agents but also following treatment with different targeted therapies, e.g. monoclonal antibodies and small molecules inhibitors. The results from these studies have been most variable; in some studies early changes in (18)F-FDG and (18)F-FLT uptake predicted later tumor regression whereas in other studies no change in tracer uptake was observed despite the treatment being effective. The present review gives an overview of pre-clinical studies that have used (18)F-FDG and/or (18)F-FLT PET for response monitoring of cancer therapeutics.

Utility of [18 F]FLT-PET to assess treatment response in trastuzumab-resistant and trastuzumab-sensitive HER2-overexpressing human breast cancer xenografts

PURPOSE

The objective of this study was to evaluate 3'-deoxy-3'-[(18) F]fluorothymidine ([(18) F]FLT) positron emission tomography (PET) as an early marker of trastuzumab response in HER2-overexpressing xenografts.

PROCEDURES

Tumor-to-muscle ratios were compared between both trastuzumab-sensitive and trastuzumab-resistant cohorts prior to and after one and two treatments.

RESULTS

A significant difference (P = 0.03) was observed between treated and control trastuzumab-sensitive xenografts after one treatment, which preceded between-group differences in tumor volume. Reduced Ki67 (P = 0.02) and thymidine kinase 1 (TK1) (P = 0.35) immunoreactivity was observed in the treated xenografts. No significant differences in volume, tumor-to-muscle ratio, or immunoreactivity were observed between treated and control trastuzumab-resistant cohorts. A significant difference (P = 0.02) in tumor-to-muscle ratio was observed between trastuzumab-sensitive and trastuzumab-resistant cohorts after two treatments; however, tumor volumes were also different (P = 0.04). Ki67 (P = 0.04) and TK1 (P = 0.24) immunoreactivity was ~50 % less in trastuzumab-sensitive xenografts.

CONCLUSIONS

[(18) F]FLT-PET provided early response assessment in trastuzumab-sensitive xenografts but only differentiated between trastuzumab-resistant and trastuzumab-sensitive xenografts concurrent with differences in tumor size.

Monitoring Cell Death in Regorafenib-Treated Experimental Colon Carcinomas Using Annexin-Based Optical Fluorescence Imaging Validated by Perfusion MRI

Objective

To investigate annexin-based optical fluorescence imaging (OI) for monitoring regorafenib-induced early cell death in experimental colon carcinomas in rats, validated by perfusion MRI and multiparametric immunohistochemistry.

Materials and Methods

Subcutaneous human colon carcinomas (HT-29) in athymic rats (n = 16) were imaged before and after a one-week therapy with regorafenib (n = 8) or placebo (n = 8) using annexin-based OI and perfusion MRI at 3 Tesla. Optical signal-to-noise ratio (SNR) and MRI tumor perfusion parameters (plasma flow PF, mL/100mL/min; plasma volume PV, %) were assessed. On day 7, tumors underwent immunohistochemical analysis for tumor cell apoptosis (TUNEL), proliferation (Ki-67), and microvascular density (CD31).

Results

Apoptosis-targeted OI demonstrated a tumor-specific probe accumulation with a significant increase of tumor SNR under therapy (mean Δ +7.78±2.95, control: -0.80±2.48, p = 0.021). MRI detected a significant reduction of tumor perfusion in the therapy group (mean ΔPF -8.17±2.32 mL/100 mL/min, control -0.11±3.36 mL/100 mL/min, p = 0.036). Immunohistochemistry showed significantly more apoptosis (TUNEL; 11392±1486 vs. 2921±334, p = 0.001), significantly less proliferation (Ki-67; 1754±184 vs. 2883±323, p = 0.012), and significantly lower microvascular density (CD31; 107±10 vs. 182±22, p = 0.006) in the therapy group.

Conclusions

Annexin-based OI allowed for the non-invasive monitoring of regorafenib-induced early cell death in experimental colon carcinomas, validated by perfusion MRI and multiparametric immunohistochemistry.

Application of infrared-based molecular imaging to a mouse model with head and neck cancer

BACKGROUND

This study investigated whether near infrared (NIR) or visible fluorescent molecular imaging produced a better representation of a mouse model with head and neck squamous cell carcinoma (HNSCC). Additionally, the study explored whether epidermal growth factor receptor (EGFR)-targeted probes could play an important role in the diagnosis of HNSCC.

METHODS

An orthotopic mouse model of HNSCC labeled with the NIR fluorophore, infrared fluorescent protein (iRFP), was developed and monitored noninvasively in real time. The tumors were further evaluated using tumor-specific EGFR-targeted probes conjugated with an NIR dye (IRDye800), or a visible fluorescent protein.

RESULTS

The iRFP cell line produced better results than cells emitting visible light when studying local, distant, and deep tumors in the mouse model. The EGFR-targeted probe conjugated with IRDye800 accurately detected tumor perimeters.

CONCLUSION

This model has great potential as a unique tool in the study of HNSCC tumor development. © 2015 Wiley Periodicals, Inc. Head Neck 38: E1351-E1357, 2016.

[(18)F]-FLT PET to predict early response to neoadjuvant therapy in KRAS wild-type rectal cancer: a pilot study

OBJECT

This pilot study evaluated the utility of 3'-deoxy-3'[18F]-fluorothymidine ([(18)F]-FLT) positron emission tomography (PET) to predict response to neoadjuvant therapy that included cetuximab in patients with wild-type KRAS rectal cancers.

METHODS

Baseline [(18)F]-FLT PET was collected prior to treatment initiation. Follow-up [(18)F]-FLT was collected after three weekly infusions of cetuximab, and following a combined regimen of cetuximab, 5-FU, and radiation. Imaging-matched biopsies were collected with each PET study.

RESULTS

Diminished [(18)F]-FLT PET was observed in 3/4 of patients following cetuximab treatment alone and in all patients following combination therapy. Reduced [(18)F]-FLT PET following combination therapy predicted disease-free status at surgery. Overall, [(18)F]-FLT PET agreed with Ki67 immunoreactivity from biopsy samples and surgically resected tissue, and was predictive of treatment-induced rise in p27 levels.

CONCLUSION

These results suggest that [(18)F]-FLT PET is a promising imaging biomarker to predict response to neoadjuvant therapy that included EGFR blockade with cetuximab in patients with rectal cancer.

New whole-body multimodality imaging of gastric cancer peritoneal metastasis combining fluorescence imaging with ICG-labeled antibody and MRI in mice

BACKGROUND

Peritoneal metastasis is the most frequent pattern of recurrence after curative surgery for gastric cancer. However, such a recurrence is difficult to detect by conventional computed tomography (CT) and magnetic resonance imaging (MRI) at an early stage. To improve the sensitivity and specificity of diagnostic imaging for peritoneal metastasis, we developed a new type of multimodality imaging combining fluorescence imaging with near-infrared fluorophore (NIR)-labeled antibodies and MRI.

METHODS

Dual optical imaging of peritoneal metastasis was carried out using luciferase-tagged gastric cancer cell lines and XenoLight CF750 or indocyanine green (ICG)-labeled anti-human epidermal growth factor receptor (EGFR) or CEA antibody as a probe in mice with Ivis in vivo imaging system.

RESULTS

This whole-body fluorescent imaging system sensitively detected metastatic foci <1 mm in diameter in the peritoneal cavity noninvasively. Fluorescence imaging proved to be specific because the fluorescence signal was abolished by blocking with excess unlabeled antibody. Although this fluorescence imaging had higher sensitivity for detection of small-sized peritoneal metastases than MRI, it proved difficult to accurately determine organ distribution of the metastasis. We thus developed a multimodality imaging system by the fusion of the three-dimensional fluorescence image with the MRI image and demonstrated its improved diagnostic accuracy over either method alone.

CONCLUSION

The present results suggest that multimodality imaging consisting of fluorescence imaging with NIR-labeled EGFR or CEA antibody and MRI allows sensitive, specific, and anatomically accurate detection of peritoneal metastasis noninvasively at an early stage.

High-yielding, automated production of 3'-deoxy-3'-[(18)F]fluorothymidine using a modified Bioscan Coincidence FDG reaction module

INTRODUCTION

High-yielding, automated production of a PET tracer that reflects proliferation, 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT), is reported using a modified Bioscan Coincidence FDG reaction module.

METHODS

Production of [(18)F]FLT was implemented through: (1) modification of an original FDG manifold; (2) application of an alternate time sequence; and (3) altered solid-phase extraction (SPE) purification. Quality control testing, including standard radiochemical figures of merit and preclinical positron emission tomography (PET) imaging, was carried out.

RESULTS

High decay-corrected yields of [(18)F]FLT (16-39%) were reproducibly obtained. The product exhibited very high specific activity (4586.9TBq/mmol; 123,969Ci/mmol) and radiochemical purity (>99%). Overall, the [(18)F]FLT produced in this manner was superior to typical productions that utilized a GE TRACERlab FXF-N reaction module. Additionally, purification with SPE cartridges, followed by manual elution, accelerated overall run time and resulted in a two-fold increase in [(18)F]FLT concentration. PET imaging showed the [(18)F]FLT produced by this method was highly suitable for non-invasive tumor imaging in mice.

CONCLUSIONS

The Bioscan Coincidence GE FDG Reaction Module was readily adapted to reproducibly provide [(18)F]FLT in high yield, specific activity, and radiochemical purity. The approach was suitable to provide sufficient amounts of material for preclinical studies.

A low molecular weight zinc2+-dipicolylamine-based probe detects apoptosis during tumour treatment better than an annexin V-based probe

OBJECTIVES

Molecular imaging of apoptosis is frequently discussed for monitoring cancer therapies. Here, we compare the low molecular weight phosphatidylserine-targeting ligand zinc2+-dipicolylamine (Zn2+-DPA) with the established but reasonably larger protein annexin V.

METHODS

Molecular apoptosis imaging with the fluorescently labelled probes annexin V (750 nm, 36 kDa) and Zn2+-DPA (794 nm, 1.84 kDa) was performed in tumour-bearing mice (A431). Three animal groups were investigated: untreated controls and treated tumours after 1 or 4 days of anti-angiogenic therapy (SU11248). Additionally, μPET with 18 F-FDG was performed. Imaging data were displayed as tumour-to-muscle ratio (TMR) and validated by quantitative immunohistochemistry.

RESULTS

Compared with untreated control tumours, TUNEL staining indicated significant apoptosis after 1 day (P < 0.05) and 4 days (P < 0.01) of treatment. Concordantly, Zn2+-DPA uptake increased significantly after 1 day (P < 0.05) and 4 days (P < 0.01). Surprisingly, annexin V failed to detect significant differences between control and treated animals. Contrary to the increasing uptake of Zn2+-DPA, 18 F-FDG tumour uptake decreased significantly at days 1 (P < 0.05) and 4 (P < 0.01).

CONCLUSIONS

Increase in apoptosis during anti-angiogenic therapy was detected significantly better with the low molecular weight probe Zn2+-DPA than with the annexin V-based probe. Additionally, significant treatment effects were detectable as early using Zn2+-DPA as with measurements of the glucose metabolism using 18 F-FDG.

KEY POINTS

• The detection of apoptosis by non-invasive imaging is important in oncology. • A new low molecular weight probe Zn2+-DPA shows promise in depicting anti-angiogenic effects. • The small Zn2+-DPA ligand appears well suited for monitoring therapy. • Treatment effects are detectable just as early with Zn2+-DPA as with 18F-FDG.

Monitoring of tumor response to cisplatin with simultaneous fluorescence and positron emission tomography: a feasibility study

Dual modality molecular imaging can capture concurrent molecular events and evaluate therapeutic efficacy from uniquely different perspectives based on different molecular targets. In this work, dual modality tomographic imaging, (18) F-fluorodeoxyglucose based positron emission tomography and subsurface fluorescence molecular tomography ([(18) F]FDG-PET/subsurface FMT), is proposed to monitor tumor response to cisplatin on a mouse xenograft model in vivo. One mouse was administered with cisplatin (1.0 mg/kg) by intraperitoneal injection once every day for 14 days, and another mouse was administered with saline to serve as the control. Dual modality [(18) F]FDG-PET/subsurface FMT imaging was conducted on days 0, 2, 5, 9, 15, and 22. In vivo imaging and quantitative analysis demonstrated the feasibility of [(18) F]FDG-PET/subsurface FMT imaging in tracking the changes of [(18) F]FDG tumor uptake and amount of red fluorescent protein (RFP) synthesized by tumor cells in the same mouse simultaneously. Dual modality [(18) F]FDG-PET/subsurface FMT imaging may thus provide a powerful tool for better understanding disease progress and treatment evaluation from different perspectives.

3'-Deoxy-3'-[18F]-Fluorothymidine PET imaging reflects PI3K-mTOR-mediated pro-survival response to targeted therapy in colorectal cancer

Biomarkers that predict response to targeted therapy in oncology are an essential component of personalized medicine. In preclinical treatment response studies that featured models of wild-type KRAS or mutant BRAF colorectal cancer treated with either cetuximab or vemurafenib, respectively, we illustrate that [¹⁸F]-FLT PET, a non-invasive molecular imaging readout of thymidine salvage, closely reflects pro-survival responses to targeted therapy that are mediated by PI3K-mTOR activity. Activation of pro-survival mechanisms forms the basis of numerous modes of resistance. Therefore, we conclude that [¹⁸F]-FLT PET may serve a novel and potentially critical role to predict tumors that exhibit molecular features that tend to reflect recalcitrance to MAPK-targeted therapy. Though these studies focused on colorectal cancer, we envision that the results may be applicable to other solid tumors as well.

In vivo near-infrared fluorescence imaging of apoptosis using histone H1-targeting peptide probe after anti-cancer treatment with cisplatin and cetuximab for early decision on tumor response

Early decision on tumor response after anti-cancer treatment is still an unmet medical need. Here we investigated whether in vivo imaging of apoptosis using linear and cyclic (disulfide-bonded) form of ApoPep-1, a peptide that recognizes histone H1 exposed on apoptotic cells, at an early stage after treatment could predict tumor response to the treatment later. Treatment of stomach tumor cells with cistplatin or cetuximab alone induced apoptosis, while combination of cisplatin plus cetuximab more efficiently induced apoptosis, as detected by binding with linear and cyclic form of ApoPep-1. However, the differences between the single agent and combination treatment were more remarkable as detected with the cyclic form compared to the linear form. In tumor-bearing mice, apoptosis imaging was performed 1 week and 2 weeks after the initiation of treatment, while tumor volumes and weights were measured 3 weeks after the treatment. In vivo fluorescence imaging signals obtained by the uptake of ApoPep-1 to tumor was most remarkable in the group injected with cyclic form of ApoPep-1 at 1 week after combined treatment with cisplatin plus cetuximab. Correlation analysis revealed that imaging signals by cyclic ApoPep-1 at 1 week after treatment with cisplatin plus cetuximab in combination were most closely related with tumor volume changes (r2 = 0.934). These results demonstrate that in vivo apoptosis imaging using Apopep-1, especially cyclic ApoPep-1, is a sensitive and predictive tool for early decision on stomach tumor response after anti-cancer treatment.

A peptide-based positron emission tomography probe for in vivo detection of caspase activity in apoptotic cells

PURPOSE

Apoptosis, or programmed cell death, can be leveraged as a surrogate measure of response to therapeutic interventions in medicine. Cysteine aspartic acid-specific proteases, or caspases, are essential determinants of apoptosis signaling cascades and represent promising targets for molecular imaging. Here, we report development and in vivo validation of [(18)F]4-fluorobenzylcarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone ([(18)F]FB-VAD-FMK), a novel peptide-based molecular probe suitable for quantification of caspase activity in vivo using positron emission tomography (PET).

EXPERIMENTAL DESIGN

Supported by molecular modeling studies and subsequent in vitro assays suggesting probe feasibility, the labeled pan-caspase inhibitory peptide, [(18)F]FB-VAD-FMK, was produced in high radiochemical yield and purity using a simple two-step, radiofluorination. The biodistribution of [(18)F]FB-VAD-FMK in normal tissue and its efficacy to predict response to molecularly targeted therapy in tumors was evaluated using microPET imaging of mouse models of human colorectal cancer.

RESULTS

Accumulation of [(18)F]FB-VAD-FMK was found to agree with elevated caspase-3 activity in response to Aurora B kinase inhibition as well as a multidrug regimen that combined an inhibitor of mutant BRAF and a dual PI3K/mTOR inhibitor in (V600E)BRAF colon cancer. In the latter setting, [(18)F]FB-VAD-FMK PET was also elevated in the tumors of cohorts that exhibited reduction in size.

CONCLUSIONS

These studies illuminate [(18)F]FB-VAD-FMK as a promising PET imaging probe to detect apoptosis in tumors and as a novel, potentially translatable biomarker for predicting response to personalized medicine.

Ultrasound targeted apoptosis imaging in monitoring early tumor response of trastuzumab in a murine tumor xenograft model of her-2-positive breast cancer(1.)

OBJECTIVE

Our study aimed to monitor the trastuzumab therapy response of murine tumor xenograft model with human epidermal growth factor receptor 2 (Her-2)-positive breast cancer using ultrasound targeted apoptosis imaging.

METHODS

We prepared targeted apoptosis ultrasound probes by nanobubble (NB) binding with Annexin V. In vitro, we investigated the binding rate of NB-Annexin V with breast cancer apoptotic cells after the trastuzumab treatment. In vivo, tumor-bearing mice underwent ultrasound targeted imaging over 7 days. After imaging was completed, the tumors were excised to determine Her-2 and caspase-3 expression by immunohistochemistry (IHC). The correlation between parameters of imaging and histologic results was then analyzed.

RESULTS

For seeking the ability of targeted NB binding with apoptotic tumor cells (Her-2 positive), we found that binding rate in the treatment group was higher than that of the control group in vitro (P = .001). There were no differences of tumor sizes in all groups over the treatment process in vivo (P = .98). However, when using ultrasound imaging to visualize tumors by targeted NB in vivo, we observed that the mean and peak intensities from NBs gradually increased in the treatment group after trastuzumab therapy (P = .001). Furthermore, these two parameters were significantly associated with caspase-3 expression of tumor excised samples (P = .0001).

CONCLUSION

Ultrasound targeted apoptosis imaging can be a non-invasive technique to evaluate the early breast tumor response to trastuzumab therapy.

Identification and super-resolution imaging of ligand-activated receptor dimers in live cells

Molecular interactions are key to many chemical and biological processes like protein function. In many signaling processes they occur in sub-cellular areas displaying nanoscale organizations and involving molecular assemblies. The nanometric dimensions and the dynamic nature of the interactions make their investigations complex in live cells. While super-resolution fluorescence microscopies offer live-cell molecular imaging with sub-wavelength resolutions, they lack specificity for distinguishing interacting molecule populations. Here we combine super-resolution microscopy and single-molecule Förster Resonance Energy Transfer (FRET) to identify dimers of receptors induced by ligand binding and provide super-resolved images of their membrane distribution in live cells. By developing a two-color universal-Point-Accumulation-In-the-Nanoscale-Topography (uPAINT) method, dimers of epidermal growth factor receptors (EGFR) activated by EGF are studied at ultra-high densities, revealing preferential cell-edge sub-localization. This methodology which is specifically devoted to the study of molecules in interaction, may find other applications in biological systems where understanding of molecular organization is crucial.

A self-internalizing mitochondrial TSPO targeting imaging probe for fluorescence, MRI and EM

Advances in probes for cellular imaging have driven discoveries in biology and medicine. Primarily, antibodies and small molecules have been made for contrast enhancement of specific proteins. The development of new dendrimer-based tools offers opportunities to tune cellular internalization and targeting, image multiple modalities in the same molecule and explore therapeutics. The translocator protein (TSPO) offers an ideal target to develop dendrimer tools because it is well characterized and implicated in a number of disease states. The TSPO-targeted dendrimers reported here, primarily ClPhIQ-PAMAM-Gd-Liss, are cell membrane permeable nanoparticles that enable labeling of TSPO and provide contrast in fluorescence, electron microscopy and magnetic resonance imaging. The molecular binding affinity for TSPO was found to be 0.51 μM, 3 times greater than the monomeric agents previously demonstrated in our laboratory. The relaxivity per Gd³⁺ of the ClPhIQ₂₃-PAMAM-Gd₁₈ dendrimer was 7.7 and 8.0 mM^-1 s^-1 for r ₁ and r ₂ respectively, approximately double that of the clinically used monomeric Gd³⁺ chelates. In vitro studies confirmed molecular selectively for labeling TSPO in the mitochondria of C6 rat glioma and MDA-MB-231 cell lines. Fluorescence co-registration with Mitotracker Green® and increased contrast of osmium-staining in electron microscopy confirmed mitochondrial labeling of these TSPO-targeted agents. Taken collectively these experiments demonstrate the versatility of conjugation of our PAMAM dendrimeric chemistry to allow multi-modality agents to be prepared. These agents target organelles and use complementary imaging modalities in vitro, potentially allowing disease mechanism studies with high sensitivity and high resolution techniques.

Imaging of treatment response to the combination of carboplatin and paclitaxel in human ovarian cancer xenograft tumors in mice using FDG and FLT PET

Introduction

A combination of carboplatin and paclitaxel is often used as first line chemotherapy for treatment of ovarian cancer. Therefore the use of imaging biomarkers early after initiation of treatment to determine treatment sensitivity would be valuable in order to identify responders from non-responders. In this study we describe the non-invasive PET imaging of glucose uptake and cell proliferation using 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) and 3’-deoxy-3’-[¹⁸F]fluorothymidine (FLT) for early assessment of treatment response in a pre-clinical mouse model of human ovarian cancer treated with carboplatin and paclitaxel.

Methods

Invivo uptake of FLT and FDG in human ovarian cancer xenografts in mice (A2780) was determined before treatment with carboplatin and paclitaxel (CaP) and repeatedday 1, 4 and 8 after treatment start. Tracer uptake was quantified using small animal PET/CT. Tracer uptake was compared with gene expression of Ki67, TK1, GLUT1, HK1 and HK2.

Results

Tumors in the CaP group was significantly smaller than in the control group (p=0.03) on day 8. On day 4 FDG SUVmax ratio was significantly lower in the CaP group compared to the control group (105±4% vs 138±9%; p=0.002) and on day 8 the FDG SUVmax ratio was lower in the CaP compared to the control group (125±13% vs 167±13%; p=0.05). On day 1 the uptake of FLT SUVmax ratio was 89±9% in the CaP group and 109±6% in the control group; however the difference was not statistically significant (p=0.08).

Conclusions

Our data suggest that both FDG and FLT PET may be used for the assessment of anti-tumor effects of a combination of carboplatin and paclitaxel in the treatment of ovarian cancer. FLT provides an early and transient signal and FDG a later and more prolonged response. This underscores the importance of optimal timing between treatment and FLT or FDG imaging since treatment response may otherwise be overlooked.

Diffusion-weighted MRI monitoring of pancreatic cancer response to radiofrequency heat-enhanced intratumor chemotherapy

The aim of this study was to evaluate the feasibility of using diffusion-weighted MRI to monitor the early response of pancreatic cancers to radiofrequency heat (RFH)-enhanced chemotherapy. Human pancreatic carcinoma cells (PANC-1) in different groups and 24 mice with pancreatic cancer xenografts in four groups were treated with phosphate-buffered saline (PBS) as a control, RFH at 42 °C, gemcitabine and gemcitabine plus RFH at 42 °C. One day before and 1, 7 and 14 days after treatment, diffusion-weighted MRI and T2 -weighted imaging were applied to monitor the apparent diffusion coefficients (ADCs) of tumors and tumor growth. MRI findings were correlated with the results of tumor apoptosis analysis. In the in vitro experiments, the quantitative viability assay showed lower relative cell viabilities for treatment with gemcitabine plus RFH at 42 °C relative to treatment with RFH only and gemcitabine only (37 ± 5% versus 65 ± 4% and 58 ± 8%, respectively, p < 0.05). In the in vivo experiments, the combination therapy resulted in smaller relative tumor volumes than RFH only and chemotherapy only (0.82 ± 0.17 versus 2.23 ± 0.90 and 1.64 ± 0.44, respectively, p = 0.003). In vivo, 14-T MRI demonstrated a remarkable decrease in ADCs at day 1 and increased ADCs at days 7 and 14 in the combination therapy group. The apoptosis index in the combination therapy group was significantly higher than those in the chemotherapy-only, RFH-only and PBS treatment groups (37 ± 6% versus 20 ± 5%, 8 ± 2% and 3 ± 1%, respectively, p < 0.05). This study confirms that it is feasible to use MRI to monitor RFH-enhanced chemotherapy in pancreatic cancers, which may present new options for the efficient treatment of pancreatic malignancies using MRI/RFH-integrated local chemotherapy.

[18F]FDG and [18F]FLT positron emission tomography imaging following treatment with belinostat in human ovary cancer xenografts in mice

BACKGROUND

Belinostat is a histone deacetylase inhibitor with anti-tumor effect in several pre-clinical tumor models and clinical trials. The aim of the study was to evaluate changes in cell proliferation and glucose uptake by use of 3'-deoxy-3'-[(18)F]fluorothymidine ([18F]FLT) and 2-deoxy-2-[(18)F]fluoro-D-glucose ([18F]FDG) positron emission tomography (PET) following treatment with belinostat in ovarian cancer in vivo models.

METHODS

In vivo uptake of [18F]FLT and [18F]FDG in human ovary cancer xenografts in mice (A2780) were studied after treatment with belinostat. Mice were divided in 2 groups receiving either belinostat (40 mg/kg ip twice daily Day 0-4 and 6-10) or vehicle. Baseline [18F]FLT or [18F]FDG scans were made before treatment (Day 0) and repeated at Day 3, 6 and 10. Tracer uptake was quantified using small animal PET/CT.

RESULTS

Tumors in the belinostat group had volumes that were 462 ± 62% (640 mm(3)) at Day 10 relative to baseline which was significantly different (P = 0.011) from the control group 769 ± 74% (926 mm(3)). [18F]FLT SUVmax increased from baseline to Day 10 (+30 ± 9%; P = 0.048) in the control group. No increase was observed in the treatment group. [18F]FDG SUVmean was significantly different in the treatment group compared to the control group (P = 0.0023) at Day 10. Within treatment groups [18F]FDG uptake and to a lesser extent [18F]FLT uptake at Day 3 were significantly correlated with tumor growth at Day 10.

CONCLUSIONS

[18F]FDG uptake early following treatment initiation predicted tumor sizes at Day 10, suggesting that [18F]FDG may be a valuable biomarker for non-invasive assessment of anti-tumor activity of belinostat.

Limits of [18F]-FLT PET as a biomarker of proliferation in oncology

Background

Non-invasive imaging biomarkers of cellular proliferation hold great promise for quantifying response to personalized medicine in oncology. An emerging approach to assess tumor proliferation utilizes the positron emission tomography (PET) tracer 3’-deoxy-3’[¹⁸F]-fluorothymidine, [¹⁸F]-FLT. Though several studies have associated serial changes in [¹⁸F]-FLT-PET with elements of therapeutic response, the degree to which [¹⁸F]-FLT-PET quantitatively reflects proliferative index has been continuously debated for more that a decade. The goal of this study was to elucidate quantitative relationships between [¹⁸F]-FLT-PET and cellular metrics of proliferation in treatment naïve human cell line xenografts commonly employed in cancer research.

Methods and Findings

[¹⁸F]-FLT-PET was conducted in human cancer xenograft-bearing mice. Quantitative relationships between PET, thymidine kinase 1 (TK1) protein levels and immunostaining for proliferation markers (Ki67, TK1, PCNA) were evaluated using imaging-matched tumor specimens. Overall, we determined that [¹⁸F]-FLT-PET reflects TK1 protein levels, yet the cell cycle specificity of TK1 expression and the extent to which tumors utilize thymidine salvage for DNA synthesis decouple [¹⁸F]-FLT-PET data from standard estimates of proliferative index.

Conclusions

Our findings illustrate that [¹⁸F]-FLT-PET reflects tumor proliferation as a function of thymidine salvage pathway utilization. Unlike more general proliferation markers, such as Ki67, [¹⁸F]-FLT PET reflects proliferative indices to variable and potentially unreliable extents. [¹⁸F]-FLT-PET cannot discriminate moderately proliferative, thymidine salvage-driven tumors from those of high proliferative index that rely primarily upon de novo thymidine synthesis. Accordingly, the magnitude of [¹⁸F]-FLT uptake should not be considered a surrogate of proliferative index. These data rationalize the diversity of [¹⁸F]-FLT-PET correlative results previously reported and suggest future best-practices when [¹⁸F]-FLT-PET is employed in oncology.

3'-Deoxy-3'-18F-fluorothymidine PET predicts response to (V600E)BRAF-targeted therapy in preclinical models of colorectal cancer

Selective inhibition of oncogenic targets and associated signaling pathways forms the basis of personalized cancer medicine. The clinical success of (V600E)BRAF inhibition in melanoma, coupled with the emergence of acquired resistance, underscores the importance of rigorously validating quantitative biomarkers of treatment response in this and similar settings. Because constitutive activation of BRAF leads to proliferation in tumors, we explored 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) PET to noninvasively quantify changes in tumor proliferation that are associated with pharmacologic inhibition of (V600E)BRAF downstream effectors and that precede changes in tumor volume.

METHODS

Human colorectal cancer (CRC) cell lines expressing (V600E)BRAF were used to explore relationships between upregulation of p27 and phosphorylation of BRAF downstream effectors on small-molecule (V600E)BRAF inhibitor exposure. Athymic nude mice bearing (V600E)BRAF-expressing human CRC cell line xenografts were treated with a small-molecule (V600E)BRAF inhibitor (or vehicle) daily for 10 d. Predictive (18)F-FLT PET was conducted before changes in tumor volume occurred. Correlations were evaluated among PET, inhibition of phosphorylated MEK (p-MEK) and phosphorylated-ERK (p-ERK) by Western blot, tumor proliferation by histology, and small-molecule exposure by matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS).

RESULTS

Treatment of CRC cell lines with PLX4720 reduced proliferation associated with target inhibition and upregulation of p27. In vivo, PLX4720 treatment reduced (18)F-FLT uptake, but not (18)F-FDG uptake, in Lim2405 xenografts before quantifiable differences in xenograft volume. Reduced (18)F-FLT PET reflected a modest, yet significant, reduction of Ki67 immunoreactivity, inhibition of p-MEK and p-ERK, and elevated tumor cell p27 protein levels. Both (18)F-FLT PET and (18)F-FDG PET accurately reflected a lack of response in HT-29 xenografts, which MALDI imaging mass spectrometry suggested may have stemmed from limited PLX4720 exposure.

CONCLUSION

We used preclinical models of CRC to demonstrate (18)F-FLT PET as a sensitive predictor of response to (V600E)BRAF inhibitors. Because (18)F-FLT PET predicted reduced proliferation associated with attenuation of BRAF downstream effectors, yet (18)F-FDG PET did not, these data suggest that (18)F-FLT PET may represent an alternative to (18)F-FDG PET for quantifying clinical responses to BRAF inhibitors.

[18F]FLT PET for non-invasive assessment of tumor sensitivity to chemotherapy: studies with experimental chemotherapy TP202377 in human cancer xenografts in mice

Aim

3′-deoxy-3′-[¹⁸F]fluorothymidine ([18F]FLT) is a tracer used to assess cell proliferation in vivo. The aim of the study was to use [18F]FLT positron emission tomography (PET) to study non-invasively early anti-proliferative effects of the experimental chemotherapeutic agent TP202377 in both sensitive and resistant tumors.

Methods

Xenografts in mice from 3 human cancer cell lines were used: the TP202377 sensitive A2780 ovary cancer cell line (n = 8–16 tumors/group), the induced resistant A2780/Top216 cell line (n = 8–12 tumors/group) and the natural resistant SW620 colon cancer cell line (n = 10 tumors/group). In vivo uptake of [18F]FLT was studied at baseline and repeated 6 hours, Day 1, and Day 6 after TP202377 treatment (40 mg/kg i.v.) was initiated. Tracer uptake was quantified using small animal PET/CT.

Results

TP202377 (40 mg/kg at 0 hours) caused growth inhibition at Day 6 in the sensitive A2780 tumor model compared to the control group (P<0.001). In the A2780 tumor model TP202377 treatment caused significant decrease in uptake of [18F]FLT at 6 hours (-46%; P<0.001) and Day 1 (-44%; P<0.001) after treatment start compared to baseline uptake. At Day 6 uptake was comparable to baseline. Treatment with TP202377 did not influence tumor growth or [18F]FLT uptake in the resistant A2780/Top216 and SW620 tumor models. In all control groups uptake of [18F]FLT did not change. Ki67 gene expression paralleled [18F]FLT uptake.

Conclusion

Treatment of A2780 xenografts in mice with TP202377 (single dose i.v.) caused a significant decrease in cell proliferation assessed by [18F]FLT PET after 6 hours. Inhibition persisted at Day 1; however, cell proliferation had returned to baseline at Day 6. In the resistant A2780/Top216 and SW620 tumor models uptake of [18F]FLT did not change after treatment. With [18F]FLT PET it was possible to distinguish non-invasively between sensitive and resistant tumors already 6 hours after treatment initiation.

[18F]FLT-PET to predict pharmacodynamic and clinical response to cetuximab therapy in Ménétrier's disease

Molecular imaging biomarkers of proliferation hold great promise for quantifying response to personalized medicine. One such approach utilizes the positron emission tomography (PET) tracer 3'-deoxy-3'[18F]-fluorothymidine ([18F]FLT), an investigational agent whose uptake reflects thymidine salvage-dependent DNA synthesis. The goal of this study was to evaluate [18F]FLT-PET in the setting of Ménétrier's disease (MD), a rare, premalignant hyperproliferative disorder of the stomach treatable with cetuximab therapy. Over 15 months, a patient with confirmed MD underwent cetuximab therapy and was followed with sequential [18F]FLT-PET. For comparison to MD, an [18F]FLT-PET study was conducted in another patient to quantify uptake in a normal stomach. Prior to cetuximab therapy, stomach tissue in MD was easily visualized with [18F]FLT-PET, with pre-treatment uptake levels exceeding normal stomach uptake by approximately fourfold. Diminished [18F]FLT-PET in MD was observed following the initial and subsequent doses of cetuximab and correlated with clinical resolution of the disease. To our knowledge, this study reports the first clinical use of [18F]FLT-PET to assess proliferation in a premalignant disorder. We illustrate that the extent of MD involvement throughout the stomach could be easily visualized using [18F]FLT-PET, and that response to cetuximab could be followed quantitatively and non-invasively in sequential [18F]FLT-PET studies. Thus, [18F]FLT-PET appears to have potential to monitor response to treatment in this and potentially other hyperproliferative disorders.

Single tumor imaging with multiple antibodies targeting different antigens

Antibodies are important drugs for treating cancer and there is strong rationale for using multiple antibodies to improve outcomes. We labeled two breast cancer binding antibodies, anti-ErbB2 and anti-EpCAM, with infrared fluorescence dyes of different wavelengths and determined their in vivo distribution in a breast cancer xenograft model using a near-infrared (NIR) fluorescence imaging system. Our data show that these two antibodies can be readily assessed simultaneously in mouse xenograft model. This will help guide design of dosing strategies for multiple antibodies and identify potential interaction that could affect pharmacokinetics and possible side effects.

Monitoring of tumor response to cisplatin by subsurface fluorescence molecular tomography

Subsurface fluorescence molecular tomography (FMT) has promising potential for noninvasive characterization of molecular and cellular activities in small animals by tomographic means in reflectance geometry. In this work, subsurface FMT is employed to monitor the therapeutic response of cisplatin in tumor-bearing mice in vivo. The localization and quantification accuracy of subsurface FMT are demonstrated in phantom. In the in vivo study, the red fluorescent protein activities not only on the surface but in the interior tumor are tracked three-dimensionally during the antitumor treatment.

Predicting cetuximab accumulation in KRAS wild-type and KRAS mutant colorectal cancer using 64Cu-labeled cetuximab positron emission tomography

Overexpression of epidermal growth factor receptor (EGFR) is common in colorectal cancer. However, cetuximab as an EGFR-targeting drug is useful only for a subset of patients and currently no single predictor other than V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation status has been established. In the present study, we investigated cetuximab accumulation in colorectal tumors and major organs using (111)In-DOTA-cetuximab. We also evaluated the potential of positron emission tomography (PET) imaging of (64)Cu-DOTA-cetuximab. Colorectal tumor xenografts with a different EGFR expression level and KRAS mutation status were subjected to in vivo biodistribution study and PET imaging at 48 h post-injection of radiolabeled cetuximab. The EGFR expression levels on colorectal tumors were determined by ex vivo immunoblotting and ELISA. We found that KRAS wild-type tumors had significantly higher (111)In-DOTA-cetuximab accumulation than KRAS mutant tumors (P < 0.001). Based on KRAS mutation status, a strong correlation was found between (111)In-DOTA-cetuximab tumor uptake and EGFR expression level (KRAS wild type: r = 0.988; KRAS mutant: r = 0.829), and between (64)Cu-DOTA-cetuximab tumor uptake with EGFR expression level (KRAS wild type: r = 0.838; KRAS mutant: r = 0.927). Significant correlation was also found between tumor uptake of (111)In-DOTA-cetuximab and (64)Cu-DOTA-cetuximab (r = 0.920). PET imaging with (64)Cu-DOTA-cetuximab allowed clear visualization of tumors. Both radiolabeled cetuximab had effectively visualized cetuximab accumulation in colorectal tumors with a wide variety of EGFR expression levels and different KRAS mutation status as commonly encountered in the clinical setting. Our findings suggest that this radioimmunoimaging therefore can be clinically translated as an in vivo tool to predict cetuximab accumulation in colorectal cancer patients prior to cetuximab therapy.

Protein expression signatures for inhibition of epidermal growth factor receptor-mediated signaling

Analysis of cellular signaling networks typically involves targeted measurements of phosphorylated protein intermediates. However, phosphoproteomic analyses usually require affinity enrichment of phosphopeptides and can be complicated by artifactual changes in phosphorylation caused by uncontrolled preanalytical variables, particularly in the analysis of tissue specimens. We asked whether changes in protein expression, which are more stable and easily analyzed, could reflect network stimulation and inhibition. We employed this approach to analyze stimulation and inhibition of the epidermal growth factor receptor (EGFR) by EGF and selective EGFR inhibitors. Shotgun analysis of proteomes from proliferating A431 cells, EGF-stimulated cells, and cells co-treated with the EGFR inhibitors cetuximab or gefitinib identified groups of differentially expressed proteins. Comparisons of these protein groups identified 13 proteins whose EGF-induced expression changes were reversed by both EGFR inhibitors. Targeted multiple reaction monitoring analysis verified differential expression of 12 of these proteins, which comprise a candidate EGFR inhibition signature. We then tested these 12 proteins by multiple reaction monitoring analysis in three other models: 1) a comparison of DiFi (EGFR inhibitor-sensitive) and HCT116 (EGFR-insensitive) cell lines, 2) in formalin-fixed, paraffin-embedded mouse xenograft DiFi and HCT116 tumors, and 3) in tissue biopsies from a patient with the gastric hyperproliferative disorder Ménétrier's disease who was treated with cetuximab. Of the proteins in the candidate signature, a core group, including c-Jun, Jagged-1, and Claudin 4, were decreased by EGFR inhibitors in all three models. Although the goal of these studies was not to validate a clinically useful EGFR inhibition signature, the results confirm the hypothesis that clinically used EGFR inhibitors generate characteristic protein expression changes. This work further outlines a prototypical approach to derive and test protein expression signatures for drug action on signaling networks.

Gamma camera and optical imaging with a fusion reporter gene using human sodium/iodide symporter and monomeric red fluorescent protein in mouse model

PURPOSE

Multimodality imaging contributes to the activation of translational research by compensating for its weak points. Herein, we developed a noninvasive dual-reporter gene system for nuclear and optical imaging.

MATERIALS AND METHODS

We constructed a fusion reporter vector concurrently expressing the human sodium/iodide symporter (hNIS) and monomeric red fluorescent protein (mCherry), and evaluated the function of this fusion reporter system under in vitro and in vivo conditions.

RESULTS

The expression of hNIS/mCherry fusion gene was confirmed in transfected cells using reverse transcription polymerase chain reaction (RT-PCR) and Western blotting. As the numbers of cells increased, the fluorescence and 125I uptake increased in the hNIS/mCherry-transfected cells, and a high correlation between fluorescence intensity and radioactivity was noted. The fluorescence intensities and radioactivity signals were also well-correlated in HT-29-hNIS/mCherry tumors (R2=0.9304) in in vivo fluorescence and gamma camera imaging.

CONCLUSIONS

The dual-reporter imaging method using hNIS and mCherry genes reflected tumor extent as well as viable cell numbers, and correlated well with one another. This suggests that the hNIS/mCherry dual-reporter system can be a useful tool for multi-modal imaging.