Antibody-fluorescein conjugates for photoimmunodiagnosis of human colon carcinoma in nude mice

The Use of Fluorescent Anti-CEA Antibodies to Label, Resect and Treat Cancers: A Review

A major barrier to the diagnosis and effective treatment of solid-tumor cancers is the difficulty in detection and visualization of tumor margins in primary and metastatic disease. The use of fluorescence can augment the surgeon's ability to detect cancer and aid in its resection. Several cancer types express carcinoembryonic antigen (CEA) including colorectal, pancreatic and gastric cancer. Antibodies to CEA have been developed and tagged with near-infrared fluorescent dyes. This review article surveyed the use of CEA antibodies conjugated to fluorescent probes for in vivo studies since 1990. PubMed and Google Scholar databases were queried, and 900 titles and abstracts were screened. Fifty-nine entries were identified as possibly meeting inclusion/exclusion criteria and were reviewed in full. Forty articles were included in the review and their citations were screened for additional entries. A total of 44 articles were included in the final review. The use of fluorescent anti-CEA antibodies has been shown to improve detection and resection of tumors in both murine models and clinically. The cumulative results indicate that fluorescent-conjugated anti-CEA antibodies have important potential to improve cancer diagnosis and surgery. In an emerging technology, anti-CEA fluorescent antibodies have also been successfully used for photoimmunotherapy treatment for cancer.

A Fluorescence-Based Wireless Capsule Endoscopy System for Detecting Colorectal Cancer

Wireless capsule endoscopy (WCE) has been widely used in gastrointestinal (GI) diagnosis that allows the physicians to examine the interior wall of the human GI tract through a pain-free procedure. However, there are still several limitations of the technology, which limits its functionality, ultimately limiting its wide acceptance. Its counterpart, the wired endoscopic system is a painful procedure that demotivates patients from going through the procedure, and adversely affects early diagnosis. Furthermore, the current generation of capsules is unable to automate the detection of abnormality. As a result, physicians are required to spend longer hours to examine each image from the endoscopic capsule for abnormalities, which makes this technology tiresome and error-prone. Early detection of cancer is important to improve the survival rate in patients with colorectal cancer. Hence, a fluorescence-imaging-based endoscopic capsule that automates the detection process of colorectal cancer was designed and developed in our lab. The proof of concept of this endoscopic capsule was tested on porcine intestine and liquid phantom. The proposed WCE system offers great possibilities for future applicability in selective and specific detection of other fluorescently labelled cancers.

Les anticorps, outils de choix pour la chirurgie guidée par fluorescence

La chirurgie guidée par fluorescence se développe en clinique depuis plusieurs années. Si l’utilisation de colorants non ciblés peut être utile dans certaines pathologies, des agents de contraste spécifiques sont indispensables en oncologie. Comme le montrent les dernières études cliniques, les anticorps monoclonaux ont toutes les caractéristiques pour jouer un rôle majeur dans ce domaine d’imagerie médicale, à condition que la cible antigénique soit pertinente.

High resolution combined molecular and structural optical imaging of colorectal cancer in a xenograft mouse model

With the emergence of immunotherapies for cancer treatment, there is a rising clinical need to visualize the tumor microenvironment (TME) non-invasively in detail, which could be crucial to predict the efficacy of therapy. Nuclear imaging techniques enable whole-body imaging but lack the required spatial resolution. Conversely, near-infrared immunofluorescence (immuno-NIRF) is able to reveal tumor cells and/or other cell subsets in the TME by targeting the expression of a specific membrane receptor with fluorescently labeled monoclonal antibodies (mAb). Optical coherence tomography (OCT) provides three-dimensional morphological imaging of tissues without exogenous contrast agents. The combination of the two allows molecular and structural contrast at a resolution of ~15 µm, allowing for the specific location of a cell-type target with immuno-NIRF as well as revealing the three-dimensional architectural context with OCT. For the first time, combined immuno-NIRF and OCT of a tumor is demonstrated in situ in a xenograft mouse model of human colorectal cancer, targeted by a clinically-safe fluorescent mAb, revealing unprecedented details of the TME. A handheld scanner for ex vivo examination and an endoscope designed for imaging bronchioles in vivo are presented. This technique promises to complement nuclear imaging for diagnosing cancer invasiveness, precisely determining tumor margins, and studying the biodistribution of newly developed antibodies in high detail.

The development of fluorescence guided surgery for pancreatic cancer: from bench to clinic

INTRODUCTION

Surgeons face major challenges in achieving curative R0 resection for pancreatic cancers. When the lesion is localized, they must appropriately visualize the tumor, determine appropriate resection margins, and ensure complete tumor clearance. Real-time surgical navigation using fluorescence-guidance has enhanced the ability of surgeons to see the tumor and has the potential to assist in achieving more oncologically complete resections. When there is metastatic disease, fluorescence enhancement can help detect these lesions and prevent unnecessary and futile surgeries. Areas covered: This article reviews different approaches for delivery of a fluorescence signal, their pre-clinical and clinical developments for fluorescence guided surgery, the advantages/challenges of each, and their potential for advancements in the future. Expert commentary: A variety of molecular imaging techniques are available for delivering tumor-specific fluorescence signals. Significant advancements have been made in the past 10 years due to the large body of literature on targeted therapies and this has translated into rapid developments of tumor-specific probes.

Combining Near Infrared Fluorescent Imaging for Calcification and Inflammation in Vascular Tissue Samples Ex Vivo

Quantification of vascular lesions in models of vascular calcification is crucial for testing novel treatments, but remains a challenging endeavor. Conventional methods include Oil-Red-O staining of whole tissue samples, calcium quantification in incinerated samples, or stereoisometric histologic processing. While most techniques offer fairly high levels of reliability, all of them share the fact that samples are not available for other assays following the analysis, as tissue is altered or destroyed in the course of the procedure. Furthermore, none is capable of measuring both calcification and inflammation at the same time. Here we present a novel technique for the simultaneous quantification of vascular inflammation and calcification, after which samples are still available for further histologic processing.

Preclinical evaluation of a novel CEA-targeting near-infrared fluorescent tracer delineating colorectal and pancreatic tumors

Surgery is the cornerstone of oncologic therapy with curative intent. However, identification of tumor cells in the resection margins is difficult, resulting in nonradical resections, increased cancer recurrence and subsequent decreased patient survival. Novel imaging techniques that aid in demarcating tumor margins during surgery are needed. Overexpression of carcinoembryonic antigen (CEA) is found in the majority of gastrointestinal carcinomas, including colorectal and pancreas. We developed ssSM3E/800CW, a novel CEA-targeted near-infrared fluorescent (NIRF) tracer, based on a disulfide-stabilized single-chain antibody fragment (ssScFv), to visualize colorectal and pancreatic tumors in a clinically translatable setting. The applicability of the tracer was tested for cell and tissue binding characteristics and dosing using immunohistochemistry, flow cytometry, cell-based plate assays and orthotopic colorectal (HT-29, well differentiated) and pancreatic (BXPC-3, poorly differentiated) xenogeneic human-mouse models. NIRF signals were visualized using the clinically compatible FLARE™ imaging system. Calculated clinically relevant doses of ssSM3E/800CW selectively accumulated in colorectal and pancreatic tumors/cells, with highest tumor-to-background ratios of 5.1 ± 0.6 at 72 hr postinjection, which proved suitable for intraoperative detection and delineation of tumor boarders and small (residual) tumor nodules in mice, between 8 and 96 hr postinjection. Ex vivo fluorescence imaging and pathologic examination confirmed tumor specificity and the distribution of the tracer. Our results indicate that ssSM3E/800CW shows promise as a diagnostic tool to recognize colorectal and pancreatic cancers for fluorescent-guided surgery applications. If successfully translated clinically, this tracer could help improve the completeness of surgery and thus survival.

Antibody-based imaging strategies for cancer

Although mainly developed for preclinical research and therapeutic use, antibodies have high antigen specificity, which can be used as a courier to selectively deliver a diagnostic probe or therapeutic agent to cancer. It is generally accepted that the optimal antigen for imaging will depend on both the expression in the tumor relative to normal tissue and the homogeneity of expression throughout the tumor mass and between patients. For the purpose of diagnostic imaging, novel antibodies can be developed to target antigens for disease detection, or current FDA-approved antibodies can be repurposed with the covalent addition of an imaging probe. Reuse of therapeutic antibodies for diagnostic purposes reduces translational costs since the safety profile of the antibody is well defined and the agent is already available under conditions suitable for human use. In this review, we will explore a wide range of antibodies and imaging modalities that are being translated to the clinic for cancer identification and surgical treatment.

Inert coupling of IRDye800CW and zirconium-89 to monoclonal antibodies for single- or dual-mode fluorescence and PET imaging

IRDye800CW and zirconium-89 ((89)Zr) have very attractive properties for optical imaging and positron emission tomography (PET) imaging, respectively. Here we describe a procedure for dual labeling of mAbs with IRDye800CW and (89)Zr in a current good manufacturing practice (cGMP)-compliant way. IRDye800CW and (89)Zr are coupled inertly, without impairment of immunoreactivity and pharmacokinetics of the mAb. Organ and whole-body distribution of the final product can be assessed by optical and PET imaging, respectively. For this purpose, a minimal amount of the chelate N-succinyldesferrioxamine (N-sucDf) is first conjugated to the mAb. Next, N-sucDf-mAb is conjugated with IRDye800CW, after which the N-sucDf-mAb-IRDye800CW is labeled with (89)Zr. After each of these three steps, the product is purified by gel filtration. The sequence of this process avoids unnecessary radiation exposure to personnel and takes about 5 h. The process can be scaled up by the production of large batches of premodified mAbs that can be dispensed and stored until they are labeled with (89)Zr.

Inert coupling of IRDye800CW to monoclonal antibodies for clinical optical imaging of tumor targets

Background

Photoimmunodetection, in which monoclonal antibodies [mAbs] are labeled with fluorescent dyes, might have clinical potential for early detection and characterization of cancer. For this purpose, the dye should be coupled in an inert way to mAb. In this study, different equivalents of IRDye800CW, a near-infrared fluorescent dye, were coupled to ⁸⁹Zr-labeled cetuximab and bevacizumab, and conjugates were evaluated in biodistribution studies. Radiolabeled mAbs were used to allow accurate quantification for assessment of the number of dye groups that can be coupled to mAbs without affecting their biological properties.

Methods

⁸⁹Zr-cetuximab and ⁸⁹Zr-bevacizumab, containing 0.5 ⁸⁹Zr-desferal group per mAb molecule, were incubated with 1 to 10 eq IRDye800CW at pH 8.5 for 2 h at 35°C, and ⁸⁹Zr-mAb-IRDye800CW conjugates were purified by a PD10 column using 0.9% NaCl as eluent. HPLC analysis at 780 nm was used to assess conjugation efficiency. In vitro stability measurements were performed in storage buffer (0.9% NaCl or PBS) at 4°C and 37°C and human serum at 37°C. ⁸⁹Zr-mAb-IRDye800CW conjugates and ⁸⁹Zr-mAb conjugates (as reference) were administered to nude mice bearing A431 (cetuximab) or FaDu (bevacizumab) xenografts, and biodistribution was assessed at 24 to 72 h after injection.

Results

Conjugation efficiency of IRDye800CW to ⁸⁹Zr-mAbs was approximately 50%; on an average, 0.5 to 5 eq IRDye800CW was conjugated. All conjugates showed optimal immunoreactivity and were > 95% stable in storage buffer at 4°C and 37°C and human serum at 37°C for at least 96 h. In biodistribution studies with ⁸⁹Zr-cetuximab-IRDye800CW, enhanced blood clearance with concomitant decreased tumor uptake and increased liver uptake was observed at 24 to 72 h post-injection when 2 or more eq of dye had been coupled to mAb. No significant alteration of biodistribution was observed 24 to 48 h after injection when 1 eq of dye had been coupled. ⁸⁹Zr-bevacizumab-IRDye800CW showed a similar tendency, with an impaired biodistribution when 2 eq of dye had been coupled to mAb.

Conclusion

Usage of ⁸⁹Zr-mAbs allows accurate quantification of the biodistribution of mAbs labeled with different equivalents of IRDye800CW. Alteration of biodistribution was observed when more than 1 eq of IRDye800CW was coupled to mAbs.

Site-specific protein labeling with amine-containing molecules using Lactobacillus plantarum sortase

Modification of proteins with small molecules is a widely used and powerful tool in biological research. Enzymatic approaches are particularly promising because substrate specificity allows for site-specific modification. Sortase A, a transpeptidase from Staphylococcus aureus, cleaves between the T and G residues in the sequence LPXTG, and subsequently links the carboxyl group of the T residue to an amino group of N-terminal glycine oligomers by a native peptide bond. Although Gram-positive bacteria have several kinds of sortases, there are few reports concerning their expression and substrate specificity. Here, we demonstrate site-specific protein modification with primary amine-containing molecules catalyzed by Lactobacillus plantarum sortase. Enhanced green fluorescent protein (EGFP) was employed as a model protein, and an amine-containing biotin molecule was site-specifically conjugated with LPQTSEQ-tagged EGFP. We developed a novel Lactobacillus plantarum sortase that has different substrate specificity compared to Staphylococcus aureus sortase. Amine-directed protein modification was achieved using the Lactobacillus plantarum sortase ''LPQTSEQ'' sequence original recognition tag. Our results demonstrate a promising method for expanding the capabilities of site-specific protein-small molecule modification.

mTHPC--a drug on its way from second to third generation photosensitizer?

5,10,15,20-Tetrakis(3-hydroxyphenyl)chlorin (mTHPC, Temoporfin) is a widely investigated second generation photosensitizer. Its initial use in solution form (Foscan®) is now complemented by nanoformulations (Fospeg®, Foslip®) and new chemical derivatives related to the basic hydroxyphenylporphyrin framework. Advances in formulation, chemical modifications and targeting strategies open the way for third generation photosensitizers and give an illustrative example for the developmental process of new photoactive drugs.

Photodynamic therapy using an anti-EGF receptor antibody complexed with verteporfin nanoparticles: a proof of concept study

Photodynamic therapy (PDT) is a noninvasive optical treatment method in which the topical or systemic delivery of photosensitizing drugs is followed by irradiation with broadband red light. Coupling photosensitizers with a specific antibody may allow this approach to target specific cancers. This study determines the antitumor efficacy of coupling verteporfin (Visudyne(®)), a hydrophobic polyporphryin oligomer, with an antiepidermal growth factor receptor (anti-EGFR) antibody. Poly[2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate-co-p-nitrophenylcarbonyloxyethyl methacrylate] (PMBN) was conjugated with an anti-EGFR antibody and mixed with verteporfin (verteporfin-PMBN-antibody complex). Tumor-bearing mice were intravenously injected with the verteporfin-PMBN-antibody complex or verteporfin plus PMBN without the antibody. Irradiation was conducted at 640 nm with a dose of 75 J/cm(2). The fluorescence intensity in A431 cells in vitro was threefold higher after exposure to verteporfin-PMBN-antibody complex than after exposure to verteporfin-PMBN. In A431 tumor-bearing mice, the intratumor concentration of verteporfin was 9.4 times higher than that of the skin, following administration of the verteporfin-PMBN-antibody complex. Tumor size significantly decreased within 8 days in mice treated with verteporfin-PMBN-antibody complex compared with those treated with verteporfin-PMBN. PDT using a PMBN-verteporfin-antibody complex offers a promising anticancer therapy.

Antibody-based vascular tumor targeting

The inhibition of angiogenesis represents a major step toward a more selective and better-tolerated therapy of cancer. An alternative way to take advantage of a tumor's absolute dependence on a functional neovasculature is illustrated by the strategy of "antibody-based vascular tumor targeting." This technology aims at the selective delivery of bioactive molecules to the tumor site by their conjugation to a carrier antibody reactive with a tumor-associated vascular antigen. A number of high-affinity monoclonal antibodies are nowadays available which have demonstrated a remarkable ability to selectively localize to the tumor vasculature. Indeed, some of them have already progressed from preclinical animal experiments to clinical studies in patients with cancer, acting as vehicles for the site-specific pharmacodelivery of proinflammatory cytokines or radionuclides.In this chapter, we present a selection of well-characterized markers of angiogenesis which have proven to be suitable targets for antibody-based vascular targeting approaches. Furthermore, different transcriptomic and proteomic methodologies for the discovery of novel vascular tumor markers are described. In the last two sections, we focus on the discussion of antibody-based vascular tumor targeting strategies for imaging and therapy applications in oncology.

Identification of new accessible tumor antigens in human colon cancer by ex vivo protein biotinylation and comparative mass spectrometry analysis

One of the most promising new strategies for the development of efficacious cancer therapies relies on the targeted delivery of biopharmaceutical to the tumor environment by the use of selective and specific antibodies. The identification of accessible perivascular proteins selectively overexpressed in cancer tissue may facilitate the development of antibody-based biopharmaceutical administration. This approach is potentially highly selective and specific, combining the presence of tumor biomarkers readily accessible from the blood vessels and the high rate of angiogenesis characteristic of cancer tissues. We performed ex vivo perfusions of surgically resected human colon cancer using a reactive ester derivative of biotin, thus achieving a selective covalent modification of accessible proteins in vascular structures and stroma. After extraction and purification, biotinylated proteins were digested and the resulting peptides submitted to a comparative mass spectrometry-based proteomic analysis, revealing quantitative differences between normal and cancer colon. Sixty-seven of the total 367 proteins identified were found to be preferentially expressed at the tumor site. We generated human monoclonal antibodies against 2 potential tumor targets, NGAL and GW112, and we proved their selective expression in cancer colon and not or barely in healthy tissues. This article presents the first proteomic analysis of human colorectal cancer structures readily accessible from the tumor vasculature, revealing the overexpression of novel tumor antigens which may serve as selective targets for antibody-based imaging and therapeutic biomolecular strategies.

In vivo optical molecular imaging of vascular endothelial growth factor for monitoring cancer treatment

PURPOSE

Vascular endothelial growth factor (VEGF) expression is a critical component in tumor growth and metastasis. Capabilities to monitor VEGF expression in vivo can potentially serve as a useful tool for diagnosis, prognosis, treatment planning, monitoring, and research. Here, we present the first report of in vivo hyperspectral molecular imaging strategy capable of monitoring treatment-induced changes in VEGF expression.

EXPERIMENTAL DESIGN

VEGF was targeted with an anti-VEGF antibody conjugated with a fluorescent dye and was imaged in vivo using a hyperspectral imaging system. The strategy was validated by quantitatively monitoring VEGF levels in three different tumors as well as following photodynamic treatment. Specificity of the molecular imaging strategy was tested using in vivo competition experiments and mathematically using a quantitative pharmacokinetic model.

RESULTS

The molecular imaging strategy successfully imaged VEGF levels quantitatively in three different tumors and showed concordance with results from standard ELISA. Changes in tumoral VEGF concentration following photodynamic treatment and Avastin treatment were shown. Immunohistochemistry shows that (a) the VEGF-specific contrast agent labels both proteoglycan-bound and unbound VEGF in the extracellular space and (b) the bound VEGF is released from the extracellular matrix in response to photodynamic therapy. In vivo competition experiments and quantitative pharmacokinetic model-based analysis confirmed the high specificity of the imaging strategy.

CONCLUSION

This first report of in vivo quantitative optical molecular imaging-based monitoring of a secreted cytokine in tumors may have implications in providing tools for mechanistic investigations as well as for improved treatment design and merits further investigation.

Imaging in the era of molecular oncology

New technologies for imaging molecules, particularly optical technologies, are increasingly being used to understand the complexity, diversity and in vivo behaviour of cancers. 'Omic' approaches are providing comprehensive 'snapshots' of biological indicators, or biomarkers, of cancer, but imaging can take this information a step further, showing the activity of these markers in vivo and how their location changes over time. Advances in experimental and clinical imaging are likely to improve how cancer is understood at a systems level and, ultimately, should enable doctors not only to locate tumours but also to assess the activity of the biological processes within these tumours and to provide 'on the spot' treatment.

Optical adjuncts for enhanced colonoscopic diagnosis

Background

Optical techniques using previously unexploited properties of light interaction with tissue may be valuable in the detection, diagnosis and staging of colorectal neoplasia.

Methods

A Medline search (1990 to present) was conducted on optical diagnostics in the detection of colorectal neoplasia. The reference list of each identified article was reviewed for further relevant papers.

Results and conclusion

Chromoendoscopy is the only optical adjunct to colonoscopy that has been tested in large randomized clinical trials. It improves the detection of small and flat colorectal adenomas, and of neoplasia in chronic ulcerative colitis and hereditary non-polyposis colorectal cancer. All other techniques are the subject of ongoing research and the practicality of population screening with any of the methods has yet to be established. Optical techniques may, however, permit immediate clinical diagnosis, removing the need for histological analysis. They may also improve the diagnosis of early colonic neoplasia.

Optimal labeling condition of antibodies available for immunofluorescence endoscopy

PURPOSE

In recent years, labeled antibodies have been used for diagnostic imaging in many studies. In this study, we investigated the mode of binding in antibodies labeled with ICG derivatives newly developed for the diagnosis of microcarcinomas, and evaluated the optimal binding molar ratio between the labeling compounds and antibody.

METHODS

MUC 1 antibody and ICG derivatives (ICG-ATT and ICG-sulfo-OSu) were used. ICG derivatives non-covalently bound to the antibody were removed with ethyl acetate, and the ratio of ICG derivatives covalently bound to the labeled antibody was confirmed. During purification of the labeled antibody, the amount of each labeling compound reacting with 1 molecule of the antibody varied as follows: 4, 8, 16, and 32 molar equivalents. Subsequently, the intensity of fluorescence was evaluated by spectroscopy and infrared fluoroscopy.

RESULTS

The ratio of residual ICG derivative labeling the antibody was 67.4% for ICG-ATT and 65.0% for ICG-sulfo-OSu. When fluorescent antibody labeled with ICG-ATT at an F/P ratio of 2.94 or 4.18 was used, specific and clear fluorescent images of the antigen were obtained. When ICG-ATT-labeled antibody at an F/P ratio of 6.50 or 6.75 was used, the fluorescence intensity decreased and the fluorescent images of antigen became unclear.

CONCLUSIONS

It was found that the ICG-ATT-labeled antibody was a more specific and sensitive marker than ICG-sulfo-OSu-labeled antibody, and that lower binding molar ratios of ICG-ATT were more useful for labeling the antibody.

Targeting small-cell lung cancer with novel fluorescent analogs of somatostatin

Early, accurate detection of small-cell lung cancer (SCLC), before it becomes systemic, is essential for successful treatment. Fluorescence-based imaging provides safe, sensitive detection of malignancies. Targeted delivery of fluorophores increases sensitivity of endoscopic imaging. We synthesized novel somatostatin analogs, based on backbone cyclic peptides, and conjugated them with fluorescent agents. Nineteen conjugates differing in core peptide, length of alkyl linker and fluorescence moiety (rhodamine and fluorescein) were tested in vitro, using a receptor binding assay, and nine of the more promising conjugates were tested in vivo by fiber-optic spectrofluorimetry and quantitative spectral imaging, on an H69 human SCLC tumor mouse xenograft model. The lead compound showed exceptional tumor/normal tissue ratios, ranging from 9 to 90, and has potential for targeting SCLC overexpressing somatostatin receptors.

Fluorescence optical diffusion tomography using multiple-frequency data

A method is presented for fluorescence optical diffusion tomography in turbid media using multiple-frequency data. The method uses a frequency-domain diffusion equation model to reconstruct the fluorescent yield and lifetime by means of a Bayesian framework and an efficient, nonlinear optimizer. The method is demonstrated by using simulations and laboratory experiments to show that reconstruction quality can be improved in certain problems through the use of more than one frequency. A broadly applicable mutual information performance metric is also presented and used to investigate the advantages of using multiple modulation frequencies compared with using only one.

Fluorescence optical diffusion tomography

A nonlinear, Bayesian optimization scheme is presented for reconstructing fluorescent yield and lifetime, the absorption coefficient, and the diffusion coefficient in turbid media, such as biological tissue. The method utilizes measurements at both the excitation and the emission wavelengths to reconstruct all unknown parameters. The effectiveness of the reconstruction algorithm is demonstrated by simulation and by application to experimental data from a tissue phantom containing the fluorescent agent Indocyanine Green.

Sensitivity and depth penetration of continuous wave versus frequency-domain photon migration near-infrared fluorescence contrast-enhanced imaging

The development of near-infrared fluorescent contrast agents and imaging techniques depends on the deep penetration of excitation light through several centimeters of tissue and the sensitive collection of the re-emitted fluorescence. In this contribution, the sensitivity and depth penetration of various fluorescence-enhanced imaging studies is surveyed and compared with current studies using continuous wave (CW) and frequency-domain photon migration (FDPM) measurements with planar wave illumination of modulated excitation light at 100 MHz and area collection of reemitted fluorescent light using a previously developed modulated intensified charge-coupled device camera system. Fluorescence was generated from nanomolar to micromolar solutions of indocyanine green (ICG) in a 100 microL volume submerged at 1-4 cm depths in a 1% Liposyn solution to mimic tissue scattering properties. Enhanced depth penetration and sensitivity are achieved with optimal filter rejection of excitation light, and FDPM rejection of background light is not achieved using CW methods. We show the ability to detect as few as 100 fmol of ICG from area illumination of 785 nm light (5.5 mW/cm2) and FDPM area collection of 830 nm fluorescent light generated from 3 cm below the phantom surface. The lowered noise floor of FDPM measurements enables greater sensitivity and penetration depth than comparable CW measurements.

Small animal imaging. current technology and perspectives for oncological imaging

Advances in the biomedical sciences have been accelerated by the introduction of many new imaging technologies in recent years. With animal models widely used in the basic and pre-clinical sciences, finding ways to conduct animal experiments more accurately and efficiently becomes a key factor in the success and timeliness of research. Non-invasive imaging technologies prove to be extremely valuable tools in performing such studies and have created the recent surge in small animal imaging. This review is focused on three modalities, PET, MR and optical imaging which are available to the scientist for oncological investigations in animals.

Fluorescence-enhanced, near infrared diagnostic imaging with contrast agents

The deep tissue propagation of near-infrared (NIR) light between 700-900 nm offers new opportunities for diagnostic imaging when employing sensitive detection techniques and NIR excitable fluorescent agents that target and report disease and metabolism. Herein, we highlight approaches for illuminating tissues and monitoring the re-emitted fluorescence for tomographic reconstruction, strategies for developing fluorescent dye constructs, and clinical opportunities for fluorescence-enhanced NIR optical imaging.

Synthesis, in vitro receptor binding, and in vivo evaluation of fluorescein and carbocyanine peptide-based optical contrast agents

Site-specific delivery of drugs and contrast agents to tumors protects normal tissues from the cytotoxic effects of drugs and enhances the contrast between normal and pathologic tissues. One approach to achieve selectivity is to target overexpressed receptors on the membranes of tumor cells and to visualize the tumors by a noninvasive optical imaging method. Accordingly, we conjugated fluorescein and carbocyanine dyes to somatostatin and bombesin receptor-avid peptides and examined their receptor binding affinities. We also prepared potential dual imaging probes consisting of a bioactive peptide for tumor targeting, a biocompatible dye for optical imaging, and a radioactive or paramagnetic metal chelator for scintigraphic or magnetic resonance imaging of tumors. Using these approaches, the resulting carbocyanine derivatives of somatostatin and bombesin analogues retained high binding for their respective receptors. Further evaluation of representative molecules in rats bearing somatostatin- and bombesin-positive tumors showed selective uptake of the agents by the tumor cells. Unlike carbocyanine derivatives, the receptor binding of fluorescein-somatostatin peptide conjugates was highly sensitive to the type of linker and the site of fluorescein attachment on the nonreceptor binding region of the peptide. In general, the presence of flexible linkers disrupted binding affinity, possibly due to the interaction of the linker's thiourea group with the peptide's cyclic disulfide bond. While the receptor binding affinity of the dual probes was not dependent on the type of chelating group examined, it was affected by the relative positions of fluorescein and chelator on the lysine linker. For somatostatin compounds, best results were obtained when the chelator was on the alpha-amino lysine linker and fluorescein was on the epsilon-amino group. In contrast, conjugation of the chelator to epsilon- and fluorescein to the alpha-amino lysine linker of bombesin peptides resulted in high receptor binding. These findings indicate that despite their small size, conjugation of dyes to truncated somatostatin and bombesin peptide analogues results in promising diagnostic agents that retain high receptor binding activity in vitro. The results further show that these contrast agents can selectively and specifically localize in receptor-positive tumors in rat models.

New optical technologies for earlier endoscopic diagnosis of premalignant gastrointestinal lesions

Gastrointestinal malignancies continue to be the second leading cause of cancer-related deaths in the developed world. The early detection and treatment of gastrointestinal preneoplasms has been demonstrated to significantly improve patient survival. Conventional screening tools include standard white light endoscopy (WLE) and frequent surveillance with biopsy. Well-defined endoscopic surveillance biopsy protocols aimed at early detection of dysplasia and malignancy have been undertaken for groups at high risk. Unfortunately, the poor sensitivity associated with WLE is a significant limitation. In this regard, major efforts continue in the development and evaluation of alternative diagnostic techniques. This review will focus on notable developments made at the forefront of research in modern gastrointestinal endoscopy based on novel optical endoscopic modalities, which rely on the interactions of light with tissues. Here we present the 'state-of-the-art' in fluorescence endoscopic imaging and spectroscopy, Raman spectroscopy, optical coherence tomography, light scattering spectroscopy, chromoendoscopy, confocal fluorescence endoscopy, and immunofluorescence endoscopy. These new developments may offer significant improvements in the diagnosis of early lesions by allowing for targeted mucosal excisional biopsies, and perhaps may even provide 'optical biopsies' of equivalent histological accuracy. This enhancement of the endoscopist's ability to detect subtle preneoplastic changes in the gastrointestional mucosa in real time and improved staging of lesions could lead to curative endoscopic ablation of these lesions and, in the long term, improve patient survival and quality of life.

Internalisation enhances photo-induced cytotoxicity of monoclonal antibody-phthalocyanine conjugates

Immunophototherapy of cancer combines the specificity of a monoclonal antibody (MAb) to an overexpressed tumor marker with the phototoxic properties of the conjugated dye. To analyze the potential role of internalisation of the dye on photo-induced cytotoxicity, we compared two target antigens, carcinoembryonic antigen (CEA) that does not internalise and ErbB2 that does. Human ovarian carcinoma SKOv3 cells that express a high level of ErbB2 were transfected with the CEA cDNA. Using FACS analysis, the resulting cell line, SKOv3-CEA-1B9, demonstrated comparable levels of expression of the two target antigens. Aluminium tetrasulfophthalocyanine (AlPcS(4)) was covalently coupled to anti-CEA MAb 35A7, anti-ErbB2 MAb FSP77 and a non-specific MAb PX, via a five-carbon sulfonamide spacer chain (A(1)) at molar ratios ranging from 6 to 9 moles of AlPcS(4) per mole of MAb. The 35A7-(AlPcS(4)A(1))(8) conjugate induced 68% growth inhibition of the SKOv3-CEA-1B9 cell line after a 20 h incubation at 2.50 microg/ml (based on AlPcS(4)A(1) content) following light exposure. However, the FSP77-(AlPcS(4)A(1))(6) conjugate gave a 51% growth inhibition for an AlPcS(4)A(1) concentration as low as 0.04 microg/ml after the same incubation time and exposure to the same light dose. At a 1.25 microg/ml AlPcS(4)A(1) concentration, the FSP77-(AlPcS(4)A(1))(6) conjugate gave a 67% growth inhibition after an incubation time as short as 1 h, reaching a 96% inhibition after an 8 h incubation time. Using an unique cell line that expresses two different target antigens, we demonstrated a clear advantage of an internalising over a non-internalising MAb-dye conjugate in terms of phototoxic efficacy. In vivo evaluation of the photodynamic properties of the conjugates is in progress.

Noninvasive localization of tumors by immunofluorescence imaging using a single chain Fv fragment of a human monoclonal antibody with broad cancer specificity

BACKGROUND

A single chain antibody fragment, NovoMAb-G2-scFv, derived from a human anti-tumor monoclonal antibody recognizes tumor antigen molecules expressed on a wide variety of human cancers including melanoma, breast carcinoma, colon adenocarcinoma, squamous cell carcinoma, lung carcinoma, and prostate carcinoma. This study was designed to evaluate the use of a NovoMab-G2-scFv/cyanine fluorochrome (Cy5.5.18) conjugate as diagnostic tool for in vivo imaging of tumors.

METHODS

The NovoMab-G2-scFv-Cy5 complex was administered to athymic mice injected subcutaneously with human melanoma tumor cells, and the distribution of fluorescence was imaged noninvasively using a charge-coupled device camera. Images were acquired 2, 6, 12, 24, 48, and 72 hours after injection.

RESULTS

Fluorescence was detected at the tumor site after injection of NovoMab-G2-scFv-Cy5 but not after injection of a labeled irrelevant control antibody fragment. Fluorescence from the tumor site peaked 2 hours after injection and gradually declined, reaching a minimum 72 hours after injection. Fluorescence was also apparent in the kidneys, indicating clearance of the complex through the kidneys. Results suggest that 16% and 73% of the antibody is located in the tumor and kidneys, respectively. Imaging of isolated organs confirmed the presence of the NovoMab-G2-scFv-Cy5 complex in tumors, kidneys, and liver. No fluorescence was observed in other organs.

CONCLUSIONS

Specific binding of the antibody-dye complex to the tumor was observed, and the kinetics of binding to tumors and kidneys were determined. These results suggest that the NovoMab-G2-scFv-Cy5.5 complex may be used for noninvasive tumor localization.

Long circulating half-life and high tumor selectivity of the photosensitizer meta-tetrahydroxyphenylchlorin conjugated to polyethylene glycol in nude mice grafted with a human colon carcinoma

In a mode of nude mice bearing a human colon carcinoma xenograft, the biodistribution and tumor localization of metatetrahydroxyphenylchlorin (m-THPC) coupled to polyethylene glycol (PEG) were compared with those of the free form of this photosensitizer used in photodynamic therapy (PDT). At different times after i.v. injection of both forms of 125I-labeled photosensitizer, m-THPC-PEG gave on average a 2-fold higher tumor uptake than free m-THPC. In addition, at early times after injection, m-THPC-PEG showed a 2-fold longer blood circulating half-life and a 4-fold lower liver uptake than free m-THPC. The tumor to normal tissue ratios of radioactivity concentrations were always higher for m-THPC-PEG than for free m-THPC at any time point studied from 2 to 96 hr post-injection. Significant coefficients of correlation between direct fluorescence measurements and radioactivity counting were obtained within each organ tested. Fluorescence microscopy studies showed that m-THPC-PEG was preferentially localized near the tumor vessels, whereas m-THPC was more diffusely distributed inside the tumor tissue. To verify whether m-THPC-PEG conjugate remained phototoxic in vivo, PDT experiments were performed 72 hr after injection and showed that m-THPC-PEG was as potent as free m-THPC in the induction of tumor regression provided that the irradiation does for m-THPC-PEG conjugate was adapted to a well-tolerated 2-fold higher level. The overall results demonstrate first the possibility of improving the in vivo tumor localization of a hydrophobic dye used for PDT by coupling it to PEG and second that a photosensitizer conjugated to a macromolecule can remain phototoxic in vivo.

Immunoscopy--a technique combining endoscopy and immunofluorescence for diagnosis of colorectal carcinoma

BACKGROUND

Colorectal carcinoma is a common malignant disease with a high mortality rate. It arises most frequently in adenomas of the colorectum with different grades of dysplasia. Endoscopy and biopsy are among the most reliable diagnostic tools currently available. Diagnosis of malignancy at an early stage is sometimes difficult. This study reports on a new method, "immunoscopy", that combines endoscopy and immunofluorescent diagnostic procedures; it is the first reported use of locally applied fluorescein-labeled antibodies for detection of colorectal carcinomas.

METHODS

A monoclonal antibody against carcinoembryonic antigen was fluorescein labeled. In phase I, formalin-fixed tissue samples, and in phase II, postoperative fresh tissue samples from tumorous and nontumorous areas of resected colorectal carcinomas were studied. After being incubated for 10 minutes, specific fluorescence was visualized with a conventional endoscope whose range was increased by means of two narrow band filters.

RESULTS

Because of high levels of autofluorescence, evaluation of immunoscopic investigations using formalin fixed tissue (phase I) was not carried out. Immunoscopic investigation with postoperative fresh tissue samples could differentiate between tumorous and nontumorous areas (p < 0.001). Immunoscopic results were compared with data from immunohistochemical investigations with anti-carcinoembryonic antigen on the same tissue samples.

CONCLUSIONS

Immunoscopy can differentiate between malignant and benign mucosal areas in fresh tissue samples. The high sensitivity of immunoscopy could potentially make it a useful diagnostic complement to routine endoscopy.

Cyanine fluorochrome-labeled antibodies in vivo: assessment of tumor imaging using Cy3, Cy5, Cy5.5, and Cy7

Monoclonal antibodies to two different targetable antigens were conjugated to each of four commercially available cyanine fluorochromes. Equal amounts of all four antibodies were coinjected into tumor-bearing animals and imaged. Small, superficial tumors were adequately labeled using all four fluorochromes. Large tumors were labeled well only by Cy7, probably due to self-masking and dilution effects. Cy7 was superior to other cyanine fluorochromes for visualizing structures located deep within the animal.

Serum albumin as a vehicle for zinc phthalocyanine: photodynamic activities in solid tumour models

Zinc phthalocyanine (ZnPc) is a second-generation photosensitiser for the photodynamic therapy (PDT) of cancer. Unsubstituted ZnPc is, however, highly insoluble in most common solvents, and for clinical applications the material needs to be incorporated in liposomes. We report a simple, alternative procedure to formulate ZnPc through non-covalent binding to bovine serum albumin (BSA). Intravenous administration of ZnPc-BSA preparations, at a molar ratio of 11:1 and at a ZnPc dose equivalent to 0.5 mol kg-1, to tumour-bearing mice followed 24 h later by PDT was shown to provide tumour control in two different models, the EMT-6 tumour in Balb/c mice and the human colon T380 carcinoma in nude mice. Analysis of serum fractions from treated animals showed that ZnPc readily redistributes over the serum high-density lipoprotein (HDL) fraction. We also demonstrated the absence of hepatic toxicity of the ZnPc-BSA preparation by monitoring the hepatic cytochrome P450 activity in treated animals and the viability of human cultured hepatocytes.

Tumor labeling in vivo using cyanine-conjugated monoclonal antibodies

Far-red-emitting cyanine fluorochromes have many properties desirable for in vivo imaging: absorption and emission at wavelengths where blood and tissue are relatively transparent, high quantum yields, and good solubility even at high molar ratios of fluorochrome to antibody. Potentially, conjugation by multiple linkages should minimize hydrolysis in vivo. We conjugated two tumor-targeting monoclonal antibodies: anti-SSEA-1 (IgM, kappa) at ratios of 1.2-35 mol dye/mol antibody and 9.2.27 (IgG2a, kappa) at 0.6-6 mol dye/mol antibody, using the cyanine fluorochromes Cy3.18, Cy5.18, and Cy5.5.18. Nude mice were inoculated using the SSEA-1-expressing MH-15 teratocarcinoma or the 9.2.27 antigen-expressing SK-MEL-2 melanoma to give tumors at several sites. Conjugated antibody was injected, and mice were imaged immediately after injection and at appropriate intervals thereafter using a standard camera lens, dissecting microscope, or endoscopes. Images were acquired using either an image-intensified video camera or cooled CCD cameras. Immediately after injection, major blood vessels and the heart, liver, and kidneys were readily visualized. After 1 day, tumor-targeting antibody conjugates were concentrated in tumors and there was little circulating conjugate; however, the bladder and kidneys were still visible. Tumors labeled by specific antibody were the most fluorescent tissues at 2 days after injection, but non-specific antibody conjugates did not concentrate in the tumors. The small intestine was weakly visualized by both specific and non-specific antibody conjugates. These data support the possibility of visualizing tumor metastasis by optical means, including currently available endoscopes.

Clinical pharmacokinetic studies of photofrin by fluorescence spectroscopy in the oral cavity, the esophagus, and the bronchi

BACKGROUND

To optimize photodynamic therapy (PDT) and photodetection of cancer, two important variables that must be considered are the uptake of the dye and the dye contrast between normal and neoplastic tissue after injection.

METHODS

To study these variables in a clinical context, an apparatus based on a noninvasive optical fiber that detects the dye by light-induced fluorescence (LIF) was constructed.

RESULTS

Studies on the pharmacokinetics of the fluorescent fraction of Photofrin in patients with early squamous cell carcinoma in the oral cavity, esophagus or bronchi show a signal contrast ranging from 1.5 to 3.5 a short time after intravenous injection that rapidly decreases and tends to unity (one) about 12 hours later. The magnitude of this contrast appears to correlate with the staging of the cancer, the more invasive tumors showing the highest contrast. The more invasive tumors also show the highest uptake. The oral cavity pharmacokinetics are similar to those found in the esophagus and the bronchi.

CONCLUSIONS

The oral cavity appears to be a good model, with easy access for optimizing photodetection and PDT in the esophagus and the bronchi. These pharmacokinetics can be used directly for optimizing photodetection. However, complementary information on the detailed localization of the drug by fluorescence microscopy and a correlation of these data with tumor necrosis efficacy are necessary to optimize PDT timing and therapeutic gain.

Immunophotodiagnosis of colon carcinomas in patients injected with fluoresceinated chimeric antibodies against carcinoembryonic antigen

Based on previous experiments in nude mice, showing that fluoresceinated monoclonal antibodies against carcinoembryonic antigen localized specifically in human carcinoma xenografts and could be detected by laser-induced fluorescence, we performed a feasibility study to determine whether this immunophotodiagnosis method could be applied in the clinic. Six patients, with known primary colorectal carcinoma, received an i.v. injection of 4.5 or 9 mg of mouse-human chimeric anti-carcinoembryonic antigen monoclonal antibody coupled with 0.10-0.28 mg of fluorescein (molar ratio 1/10 to 1/14). The monoclonal antibody was also labeled with 0.2-0.4 mCi of 125I (1 Ci = 37 GBq). Photodetection of the tumor was done ex vivo on surgically resected tissues for the six patients and in vivo by fluorescence rectosigmoidoscopy for the sixth patient. Upon laser irradiation, clearly detectable heterogeneous green fluorescence from the dye-antibody conjugate was visually observed on all six tumors; almost no such fluorescence was detectable on normal mucosa. The yellowish tissue autofluorescence, which was emitted from both tumor and normal mucosa, could be subtracted by real-time image processing. Radioactivity measurements confirmed the specificity of tumor localization by the conjugate; tissue concentrations of up to 0.059% injected dose per g of tumor and 10 times less (0.006%) per g of normal mucosa were found. The overall results demonstrate the feasibility of tumor immunophotodiagnosis at the clinical level.

Imaging and therapy with monoclonal antibodies in non-hematopoietic tumors

Although radiolabelled monoclonal antibodies are useful in tumor imaging, in our opinion their most important role is in the evaluation of the capacity of newly developed monoclonal antibodies to localize in tumors specifically. Intravenous injections of monoclonal antibody fragments, labelled with beta-emitting radionuclides, can completely eradicate large human colon carcinoma xenografts in nude mice whereas this is not achieved by unconjugated monoclonal antibodies. New strategies are being developed to make radioimmunotherapy applicable to carcinoma patients.