Translational molecular imaging for cancer

Magnetic Resonance Imaging for Translational Research in Oncology

The translation of results from the preclinical to the clinical setting is often anything other than straightforward. Indeed, ideas and even very intriguing results obtained at all levels of preclinical research, i.e., in vitro, on animal models, or even in clinical trials, often require much effort to validate, and sometimes, even useful data are lost or are demonstrated to be inapplicable in the clinic. In vivo, small-animal, preclinical imaging uses almost the same technologies in terms of hardware and software settings as for human patients, and hence, might result in a more rapid translation. In this perspective, magnetic resonance imaging might be the most translatable technique, since only in rare cases does it require the use of contrast agents, and when not, sequences developed in the lab can be readily applied to patients, thanks to their non-invasiveness. The wide range of sequences can give much useful information on the anatomy and pathophysiology of oncologic lesions in different body districts. This review aims to underline the versatility of this imaging technique and its various approaches, reporting the latest preclinical studies on thyroid, breast, and prostate cancers, both on small laboratory animals and on human patients, according to our previous and ongoing research lines.

Multimodality reporter gene imaging: Construction strategies and application

Molecular imaging has played an important role in the noninvasive exploration of multiple biological processes. Reporter gene imaging is a key part of molecular imaging. By combining with a reporter probe, a reporter protein can induce the accumulation of specific signals that are detectable by an imaging device to provide indirect information of reporter gene expression in living subjects. There are many types of reporter genes and each corresponding imaging technique has its own advantages and drawbacks. Fused reporter genes or single reporter genes with products detectable by multiple imaging modalities can compensate for the disadvantages and potentiate the advantages of each modality. Reporter gene multimodality imaging could be applied to trace implanted cells, monitor gene therapy, assess endogenous molecular events, screen drugs, etc. Although several types of multimodality imaging apparatus and multimodality reporter genes are available, more sophisticated detectors and multimodality reporter gene systems are needed.

Small-animal PET imaging analysis with [18 F]FHBG in a mouse model of HSV1-tk gene expression in melanoma

The purpose of this study was to establish a small-animal model for molecular imaging and to acquire basic data on assessing the efficacy of candidate melanoma drugs using small-animal PET imaging analysis with [¹⁸ F]FHBG for herpes simplex virus 1-thymidine kinase (HSV1-tk) gene expression in a melanoma mouse model. The B16 melanoma cell line was transduced with a recombinant lentiviral vector containing the HSV1-tk gene and inoculated into the back skin of C57BL/6J mice. [¹⁸ F]FHBG PET imaging showed better contrast for HSV1-tk(+) melanomas compared to brain, heart, gall bladder, intestine and kidney than did [¹⁸ F]FDG PET imaging.

Phage display-derived oligopeptide-functionalized probes for in vivo specific photoacoustic imaging of osteosarcoma

Specific detection of various tumor types remains crucial for designing effective treatment strategies. We demonstrate photoacoustic imaging (PAI) using high-affinity and high-specificity peptide-based probes for accurate and specific diagnosis of osteosarcoma. Herein, two new tumor-specific oligopeptides, termed PT6 and PT7, were identified using phage display-based screening on an osteosarcoma cell line (UMR-106). The identified oligopeptides were able to detect clinical osteosarcoma samples on tissue microarrays. Oligopeptide-conjugated PEGylated gold nanorods (PGNR) were designed to specifically target UMR-106 cells. More importantly, PAI revealed that both PGNR-PT6 and PGNR-PT7 could bind selectively to subcutaneous UMR-106 xenografts after systemic administration and enhance the contrast of osteosarcoma images by 170% and 230%, respectively, compared to tumor-bearing mice injected with PGNRs conjugated to scrambled oligopeptides. PAI employing PGNRs conjugated to specifically designed nanoprobes may provide a new method for tumor type-specific diagnosis of osteosarcoma.

Meeting the challenges of PET-based molecular imaging in cancer

As personalized medicine becomes a reality, there is a need for specific imaging agents that reflect molecular characteristics of a cancer. Fluorodeoxyglucose is an important advance because of its sensitivity. Newer molecular imaging probes offer higher specificity and are categorized as: radiolabeled biomimetics; antibody-antibody fragments and drug-drug-like compounds. Biomimetics have high sensitivity but tend to be less specific as they often engage natural transporters and metabolic pathways. Antibodies and their fragments are specific but may be limited by slow clearance. Labeled drugs and drug-like compounds offer good specificity but may be limited in sensitivity. There are numerous challenges facing molecular imaging related to their complexity. Additionally, fear of ionizing radiation and regulatory constraints have somewhat inhibited clinical translation. However, there is reason for optimism due to economies of scale and a changing health care system, which places a premium on diagnostic accuracy. Although molecular imaging is not likely to become mainstream in the near future, its long-term prospects for doing so are excellent.

Strategies for imaging androgen receptor signaling pathway in prostate cancer: implications for hormonal manipulation and radiation treatment

Prostate cancer (Pca) is a heterogeneous disease; its etiology appears to be related to genetic and epigenetic factors. Radiotherapy and hormone manipulation are effective treatments, but many tumors will progress despite these treatments. Molecular imaging provides novel opportunities for image-guided optimization and management of these treatment modalities. Here we reviewed the advances in targeted imaging of key biomarkers of androgen receptor signaling pathways. A computerized search was performed to identify all relevant studies in Medline up to 2013. There are well-known limitations and inaccuracies of current imaging approaches for monitoring biological changes governing tumor progression. The close integration of molecular biology and clinical imaging could ease the development of new molecular imaging agents providing novel tools to monitor a number of biological events that, until a few years ago, were studied by conventional molecular assays. Advances in translational research may represent the next step in improving the oncological outcome of men with Pca who remain at high risk for systemic failure. This aim may be obtained by combining the anatomical properties of conventional imaging modalities with biological information to better predict tumor response to conventional treatments.

Peptides as targeting probes against tumor vasculature for diagnosis and drug delivery

Tumor vasculature expresses a distinct set of molecule signatures on the endothelial cell surface different from the resting blood vessels of other organs and tissues in the body. This makes them an attractive target for cancer therapy and molecular imaging. The current technology using the in vivo phage display biopanning allows us to quickly isolate and identify peptides potentially homing to various tumor blood vessels. Tumor-homing peptides in conjugation with chemotherapeutic drugs or imaging contrast have been extensively tested in various preclinical and clinical studies. These tumor-homing peptides have valuable potential as targeting probes for tumor molecular imaging and drug delivery. In this review, we summarize the recent advances about the applications of tumor-homing peptides selected by in vivo phage display library screening against tumor vasculature. We also introduce the characteristics of the latest discovered tumor-penetrating peptides in their potential clinical applications.

Advancing molecular imaging: a chairman's perspective on how radiology can meet the challenge

To date, most molecular imaging techniques applied clinically have offered relatively general information about the metabolism and physiology of diseased cells and tissues. However, due to recent scientific and technological advances, much more specifically targeted molecular imaging probes (e.g., reporter gene probes, whole cell-tracking probes, and probes for localizing specific biomolecules) are now being used in preclinical research and, in some cases, translated to the clinical setting. As a result, the imaging community is poised to help lead a revolution in personalized, molecularly targeted medicine. This article considers the importance of molecular imaging for advancing research and clinical care both within individual institutions and across the medical field. It outlines specific steps that leaders in academic radiology can take to hasten progress in molecular imaging and explains why they must have the courage to reach across traditional interdisciplinary boundaries and advocate for major investments in equipment, education, and personnel.

Optical molecular imaging of epidermal growth factor receptor expression to improve detection of oral neoplasia

BACKGROUND

The development of noninvasive molecular imaging approaches has the potential to improve management of cancer.

METHODS

In this study, we demonstrate the potential of noninvasive topical delivery of an epidermal growth factor-Alexa 647 (EGF-Alexa 647) conjugate to image changes in epidermal growth factor receptor expression associated with oral neoplasia. We report a series of preclinical analyses to evaluate the optical contrast achieved after topical delivery of EGF-Alexa 647 in a variety of model systems, including cells, three-dimensional tissue cultures, and intact human tissue specimens using wide-field and high-resolution fluorescence imaging. Data were collected from 17 different oral cancer patients: eight pairs of normal and abnormal biopsies and nine resected tumors were examined.

RESULTS

The EGF-dye conjugate can be uniformly delivered throughout the oral epithelium with a penetration depth exceeding 500 microm and incubation time of less than 30 minutes. After EGF-Alexa 647 incubation, the presence of oral neoplasia is associated with a 1.5- to 6.9-fold increase in fluorescence contrast compared with grossly normal mucosa from the same patient with both wide-field and high-resolution fluorescence imaging.

CONCLUSIONS

Results illustrate the potential of EGF-targeted fluorescent agents for in vivo molecular imaging, a technique that may aid in the diagnosis and characterization of oral neoplasia and allow real-time detection of tumor margins.

Use of radionuclides in cancer research and treatment

Cancer occurs as a result of misregulation of cell growth, which appears to be a consequence of alteration in the function of oncogenes and tumour suppressor genes. Ionising radiation has been used, since the discovery of X-rays in 1896 by Roentgen, both in cancer research and treatment of the disease. The main purpose of cancer research is to understand the molecular alterations involved in the development and progression of the disease in order to improve diagnosis and develop personalised therapies, by focusing on the features of the tumoral cell and the biological events associated to carcinogenesis. Radioisotopic techniques have been used routinely for in vitro research in the molecular and cellular biology of cancer for more than 20 years and are in the process of being substituted by alternative non-radioactive techniques. However in vivo techniques such as irradiation of cells in culture and/or experimental animal models and radioactive labelling are in development, due in part to advances in molecular imaging technologies. The objective of this review is to analyse in an integrative way the applications of ionising radiation in cancer research and therapy. It had been divided into two parts. The first one will approach the techniques applied to cancer research and the second will summarise how ionising radiation is applied to the treatment of neoplastic disease.

Toward quantitative small animal pinhole SPECT: assessment of quantitation accuracy prior to image compensations

PURPOSE

We assessed the quantitation accuracy of small animal pinhole single photon emission computed tomography (SPECT) under the current preclinical settings, where image compensations are not routinely applied.

PROCEDURES

The effects of several common image-degrading factors and imaging parameters on quantitation accuracy were evaluated using Monte-Carlo simulation methods. Typical preclinical imaging configurations were modeled, and quantitative analyses were performed based on image reconstructions without compensating for attenuation, scatter, and limited system resolution.

RESULTS

Using mouse-sized phantom studies as examples, attenuation effects alone degraded quantitation accuracy by up to -18% (Tc-99m or In-111) or -41% (I-125). The inclusion of scatter effects changed the above numbers to -12% (Tc-99m or In-111) and -21% (I-125), respectively, indicating the significance of scatter in quantitative I-125 imaging. Region-of-interest (ROI) definitions have greater impacts on regional quantitation accuracy for small sphere sources as compared to attenuation and scatter effects. For the same ROI, SPECT acquisitions using pinhole apertures of different sizes could significantly affect the outcome, whereas the use of different radii-of-rotation yielded negligible differences in quantitation accuracy for the imaging configurations simulated.

CONCLUSIONS

We have systematically quantified the influence of several factors affecting the quantitation accuracy of small animal pinhole SPECT. In order to consistently achieve accurate quantitation within 5% of the truth, comprehensive image compensation methods are needed.

Molecular imaging of glucose uptake in oral neoplasia following topical application of fluorescently labeled deoxy-glucose

The clinical value of assessing tumor glucose metabolism via F-18 fluorodeoxyglucose (FDG) PET imaging in oncology is well established; however, the poor spatial resolution of PET is a significant limitation especially for early stage lesions. An alternative technology is optical molecular imaging, which allows for subcellular spatial resolution and can be effectively used with topical contrast agents for imaging epithelial derived cancers. The goal of this study was to evaluate the potential of optical molecular imaging of glucose metabolism to aid in early detection of oral neoplasia. Fluorescently labeled deoxyglucose (2-NBDG (2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose)) was applied topically to tissue phantoms, fresh oral biopsies (n = 32) and resected tumors specimens (n = 2). High-resolution imaging results show that 2-NBDG can be rapidly delivered to oral epithelium using topical application. In normal epithelium, the uptake of 2-NBDG is limited to basal epithelial cells. In contrast, high-grade dysplasia and cancers show uptake of 2-NBDG in neoplastic cells throughout the lesion. Following 2-NBDG labeling, the mean fluorescence intensity of neoplastic tissue averages 3.7 times higher than that of matched nonneoplastic oral biopsies in samples from 20 patients. Widefield fluorescence images of 8-paired oral specimens were obtained pre and postlabeling with 2-NBDG. Prior to labeling, neoplastic samples showed significantly lower autofluorescence than nonneoplastic samples. The fluorescence of neoplastic samples increased dramatically after labeling; the differential increase in fluorescence was on average 30 times higher in neoplastic samples than in normal samples. Topical application of 2-NBDG can therefore provide image contrast in both widefield and high-resolution fluorescence imaging modalities, highlighting its potential in early detection of oral neoplasia.

Molecular imaging with nanoparticles: giant roles for dwarf actors

Molecular imaging, first developed to localise antigens in light microscopy, now encompasses all imaging modalities including those used in clinical care: optical imaging, nuclear medical imaging, ultrasound imaging, CT, MRI, and photoacoustic imaging. Molecular imaging always requires accumulation of contrast agent in the target site, often achieved most efficiently by steering nanoparticles containing contrast agent into the target. This entails accessing target molecules hidden behind tissue barriers, necessitating the use of targeting groups. For imaging modalities with low sensitivity, nanoparticles bearing multiple contrast groups provide signal amplification. The same nanoparticles can in principle deliver both contrast medium and drug, allowing monitoring of biodistribution and therapeutic activity simultaneously (theranostics). Nanoparticles with multiple bioadhesive sites for target recognition and binding will be larger than 20 nm diameter. They share functionalities with many subcellular organelles (ribosomes, proteasomes, ion channels, and transport vesicles) and are of similar sizes. The materials used to synthesise nanoparticles include natural proteins and polymers, artificial polymers, dendrimers, fullerenes and other carbon-based structures, lipid-water micelles, viral capsids, metals, metal oxides, and ceramics. Signal generators incorporated into nanoparticles include iron oxide, gadolinium, fluorine, iodine, bismuth, radionuclides, quantum dots, and metal nanoclusters. Diagnostic imaging applications, now appearing, include sentinal node localisation and stem cell tracking.

Targeted molecular imaging in oncology: focus on radiation therapy

Anatomically based technologies (computed tomography scans, magnetic resonance imaging, and so on) are in routine use in radiotherapy for planning and assessment purposes. Even with improvements in imaging, however, radiotherapy is still limited in efficacy and toxicity in certain applications. Further advances may be provided by technologies that image the molecular activities of tumors and normal tissues. Possible uses for molecular imaging include better localization of tumor regions and early assay for the radiation response of tumors and normal tissues. Critical to the success of this approach is the identification and validation of molecular probes that are suitable in the radiotherapy context. Recent developments in molecular-imaging probes and integration of functional imaging with radiotherapy are promising. This review focuses on recent advances in molecular imaging strategies and probes that may aid in improving the efficacy of radiotherapy.

New markers of pancreatic cancer identified through differential gene expression analyses: claudin 18 and annexin A8

BACKGROUND

New markers to distinguish benign reactive glands from infiltrating ductal adenocarcinoma of the pancreas are needed.

DESIGN

The gene expression patterns of 24 surgically resected primary infiltrating ductal adenocarcinomas of the pancreas were compared with 18 non-neoplastic samples using the Affymetrix U133 Plus 2.0 Arrays and the Gene Logic GeneExpress Software System. Gene fragments from 4 genes (annexin A8, claudin 18, CXCL5, and S100 A2) were selected from the fragments found to be highly expressed in infiltrating adenocarcinomas when compared with normal tissues. The protein expression of these genes was examined using immunohistochemical labeling of tissue microarrays.

RESULTS

Claudin 18 labeled infiltrating carcinomas in a membranous pattern. When compared with normal and reactive ducts, claudin 18 was overexpressed, at least focally, in 159 of 166 evaluable carcinomas (96%). Strong and diffuse claudin 18 overexpression was most often seen in well-differentiated carcinomas (P=0.02). Claudin 18 was overexpressed in 51 of 52 cases (98%) of pancreatic intraepithelial neoplasia. Annexin A8 was at least focally overexpressed in 149 of 154 evaluable infiltrating carcinomas (97%). S100 A2 was at least focally overexpressed in 118 of 154 evaluable infiltrating carcinomas (77%). Non-neoplastic glands also frequently expressed S100 A2 diminishing its potential diagnostic utility. Immunolabeling with antibodies directed against CXCL5 did not reveal any significant differences in protein expression between infiltrating adenocarcinomas and normal pancreatic ducts.

CONCLUSIONS

Claudin 18 and annexin A8 are frequently highly overexpressed in infiltrating ductal adenocarcinomas when compared with normal reactive ducts, suggesting a role for these molecules in pancreatic ductal adenocarcinomas. Furthermore, these may serve as diagnostic markers, as screening tests and as therapeutic targets.

Noninvasive molecular neuroimaging using reporter genes: part II, experimental, current, and future applications

SUMMARY

In this second article, we review the various strategies and applications that make use of reporter genes for molecular imaging of the brain in living subjects. These approaches are emerging as valuable tools for monitoring gene expression in diverse applications in laboratory animals, including the study of gene-targeted and trafficking cells, gene therapies, transgenic animals, and more complex molecular interactions within the central nervous system. Further development of more sensitive and selective reporters, combined with improvements in detection technology, will consolidate the position of in vivo reporter gene imaging as a versatile technique for greater understanding of intracellular biologic processes and underlying molecular neuropathology and will potentially establish a future role in the clinical management of patients with neurologic diseases.

Molecular imaging of reporter gene expression in prostate cancer: an overview

Prostate cancer remains an important and growing health problem. Advances in imaging of prostate cancer may help to achieve earlier and more accurate diagnosis and treatment. We review the various strategies using reporter genes for molecular imaging of prostate cancer. These approaches are emerging as valuable tools for monitoring gene expression in laboratory animals and humans. Further development of more sensitive and selective reporters, combined with improvements in detection technology, will consolidate the position of reporter gene imaging as a versatile method for understanding of intracellular biological processes and the underlying molecular basis of prostate cancer, as well as potentially establishing a future role in the clinical management of patients afflicted with this disease.

Molecular imaging: the vision and opportunity for radiology in the future

Molecular imaging is being hailed as the next great advance for imaging. This introductory article in the molecular imaging series to be published over the next several months in Radiology sets the stage for the subsequent set of articles by providing relevant definitions and background information and traces the evolution of molecular imaging to its current state of research and clinical practice. It discusses in detail the evolution of molecular imaging and the role that the National Cancer Institute and the National Institutes of Health have had in the funding and development of many of the important molecular imaging research programs that are in existence today. The article also provides basic information about the complex biology of the cell and details of the pathogenesis of cancer and how molecular imaging will be critical for earlier detection and management of cancer in the future. The article lays the foundation for the subsequent articles in the series and describes how and why molecular imaging will be critical and integral for clinical care of patients in the future. The introductory article also discusses the relevance of molecular imaging to clinical radiology practice and why it is critical for the practicing radiologist to understand these evolving techniques, as they will be the future of imaging.

Metastasis suppressor proteins: discovery, molecular mechanisms, and clinical application

Clinically and experimentally, primary tumor formation and metastasis are distinct processes — locally growing tumors can progress without the development of metastases. This observation prompted the hypothesis that the molecular processes regulating tumorigenicity and metastasis are distinguishable and could be targeted therapeutically. During the process of transformation and subsequent progression to a malignant phenotype, both genetic and epigenetic alterations alter a cell’s ability to perceive and respond to signals that regulate normal tissue homeostasis. A minority of tumorigenic cells accrue the full complement of alterations that enables them to disseminate from the primary tumor, survive insults from the immune system and biophysical forces, and respond to growth-promoting and/or inhibitory signals from the distant tissues and thrive there. Identification of genes and proteins that specifically inhibit the ability of cells to form metastases (e.g., metastasis suppressors) is providing new insights into the molecular mechanisms that regulate this complex process. This review will highlight: (a ) the functional identification of metastasis suppressors, (b ) the signaling cascades and cellular phenotypes which are controlled or modulated by metastasis suppressors, and (c ) op portunities for translation and clinical trials that are based on mechanistic studies regarding metastasis suppressors.