Comparison of Two Tricarbocyanine-Based Dyes for Fluorescence Optical Imaging

Fluorescence Imaging of Breast Tumors and Gastrointestinal Cancer

Optical imaging offers a high potential for noninvasive detection and therapy of cancer in humans. Recent advances in instrumentation for diffuse optical imaging have led to new capabilities for the detection of cancer in highly scattering tissue such as the female breast. In particular, fluorescence imaging was made applicable as a sensitive technique to image molecular probes in vivo. We review recent developments in the detection of breast cancer and fluorescence-guided surgery of the breast by contrast agents available for application on humans. Detection of cancer has been investigated with the unspecific contrast agents "indocyanine green" and "omocianine" so far. Hereby, indocyanine green was found to offer high potential for the differentiation of malignant and benign lesions by exploiting vessel permeability for macromolecules as a cancer-specific feature. Tumor-specific molecular targeting and activatable probes have been investigated in clinical trials for fluorescence-guided tumor margin detection. In this application, high spatial resolution can be achieved, since tumor regions are visualized mainly at the tissue surface. As another example of superficial tumor tissue, imaging of lesions in the gastrointestinal tract is discussed. Promising results have been obtained on high-risk patients with Barrett´s esophagus and with ulcerative colitis by administering 5-aminolevulinic acid which induces accumulation of protoporphyrin IX serving as a tumor-specific fluorescent marker. Time-gated fluorescence imaging and spectroscopy are effective ways to suppress underlying background from tissue autofluorescence. Furthermore, recently developed tumor-specific molecular probes have been demonstrated to be superior to white-light endoscopy offering new ways for early detection of malignancies in the gastrointestinal tract.

Indocyanine green fluorescence-guided surgery after IV injection in metastatic colorectal cancer: A systematic review

OBJECTIVE

Indocyanine green fluorescence-guided surgery (ICG-FGS) has emerged as a potential new imaging modality for improving the detection of hepatic, lymph node (LN), and peritoneal metastases in colorectal cancer (CRC) patients. The aim of this paper is to review the available literature in the clinical setting of ICG-FGS for tumoral detection in various fields of metastatic colorectal disease.

METHODS

PubMed and Medline literature databases were searched for original articles on the use of ICG in the setting of clinical studies on colorectal cancer. The search terms used were "near-infrared fluorescence", "intraoperative imaging", "indocyanine green", "human" and "colorectal cancer".

RESULTS

ICG fluorescence imaging (ICG-FI) is clearly supported as an intraoperative technique that allows the detection of additional superficial hepatic metastases of CRC. Data on the role of ICG-FI in the intraoperative detection of peritoneal metastases and LN metastases are scarce but encouraging and ICG-FI could potentially improve the staging and treatment of these patients.

CONCLUSION

ICG-FI is a promising imaging technique in the detection of small infraclinic LN, hepatic, and peritoneal metastatic deposits that may allow better staging and more complete surgical resection with a potential prognostic benefit for patients.

Anetumab ravtansine: a novel mesothelin-targeting antibody-drug conjugate cures tumors with heterogeneous target expression favored by bystander effect

Mesothelin is a tumor differentiation antigen frequently overexpressed in tumors such as mesothelioma, ovarian, pancreatic, and lung adenocarcinomas while showing limited expression in nonmalignant tissues. Mesothelin is therefore an attractive target for cancer therapy using antibody-drug conjugates (ADC). This study describes the detailed characterization of anetumab ravtansine, here referred to as BAY 94-9343, a novel ADC consisting of a human anti-mesothelin antibody conjugated to the maytansinoid tubulin inhibitor DM4 via a disulfide-containing linker. Binding properties of the anti-mesothelin antibody were analyzed using surface plasmon resonance, immunohistochemistry, flow cytometry, and fluorescence microscopy. Effects of BAY 94-9343 on cell proliferation were first studied in vitro and subsequently in vivo using subcutaneous, orthotopic, and patient-derived xenograft tumor models. The antibody binds to human mesothelin with high affinity and selectivity, thereby inducing efficient antigen internalization. In vitro, BAY 94-9343 demonstrated potent and selective cytotoxicity of mesothelin-expressing cells with an IC(50) of 0.72 nmol/L, without affecting mesothelin-negative or nonproliferating cells. In vivo, BAY 94-9343 localized specifically to mesothelin-positive tumors and inhibited tumor growth in both subcutaneous and orthotopic xenograft models. In addition, BAY 94-9343 was able to induce a bystander effect on neighboring mesothelin-negative tumor cells. Antitumor efficacy of BAY 94-9343 correlated with the amount of mesothelin expressed and was generally superior to that of standard-of-care regimen resulting in complete tumor eradication in most of the models. BAY 94-9343 is a selective and highly potent ADC, and our data support its development for the treatment of patients with mesothelin-expressing tumors.

In vivo therapy monitoring of experimental rheumatoid arthritis in rats using near-infrared fluorescence imaging

An in vivo near-infrared fluorescence (NIRF) imaging technique is described for therapy monitoring of ankle joints affected by collagen-induced arthritis, a model of human rheumatoid arthritis. Arthritis was induced in rats by intradermal injections of collagen and Freund's incomplete adjuvant. For in vivo imaging, the nonspecific NIR dye tetrasulfocyanine (TSC) was used. Prior to and after treatment with a nonsteroidal anti-inflammatory drug, meloxicam, or analgesic drug, tramadol hydrochloride (which served as no-therapy control), normalized fluorescence intensities of each ankle joint were measured. Additionally, each ankle joint was characterized by clinical arthritis scoring and histopathology. Over a 3-week treatment period, a significant difference in disease progression between animals treated with meloxicam and tramadol hydrochloride was detected. A statistically significant improvement in ankle joint pathology from high- or moderate-grade to moderate- or low-grade upon meloxicam therapy, as determined by clinical evaluation, translated into a significant decrease in fluorescence intensity. In contrast, all arthritic joints of the no-therapy control group deteriorated to high-grade arthritis with high-fluorescence intensities in NIRF imaging.

Cyanine dyes as contrast agents for near-infrared imaging in vivo: acute tolerance, pharmacokinetics, and fluorescence imaging

We compare pharmacokinetic, tolerance, and imaging properties of two near-IR contrast agents, indocyanine green (ICG) and 1,1(')-bis-(4-sulfobutyl) indotricarbocyanine-5,5(')-dicarboxylic acid diglucamide monosodium salt (SIDAG). ICG is a clinically approved imaging agent, and its derivative SIDAG is a more hydrophilic counterpart that has recently shown promising imaging properties in preclinical studies. The rather lipophilic ICG has a very short plasma half-life, thus limiting the time available to image body regions during its vascular circulation (e.g., the breast in optical mammography where scanning over several minutes is required). In order to change the physicochemical properties of the indotricarbocyanine dye backbone, several derivatives were synthesized with increasing hydrophilicity. The most hydrophilic dye SIDAG is selected for further biological characterization. The acute tolerance of SIDAG in mice is increased up to 60-fold compared to ICG. Contrary to ICG, the pharmacokinetic properties of SIDAG are shifted toward renal elimination, caused by the high hydrophilicity of the molecule. N-Nitrosomethylurea (NMU)-induced rat breast carcinomas are clearly demarcated, both immediately and 24 h after intravenous administration of SIDAG, whereas ICG shows a weak tumor contrast under the same conditions. Our findings demonstrate that SIDAG is a high potential contrast agent for optical imaging, which could increase the sensitivity for detection of inflamed regions and tumors.

In vitro affinity maturation of HuCAL antibodies: complementarity determining region exchange and RapMAT technology

Monoclonal antibodies gain ever-increasing importance in the treatment of human diseases across a broad range of indications. Diverse technologies currently exist, which are used to generate recombinant therapeutic antibodies that are basically indistinguishable from naturally occurring human immunoglobulins. We describe how human combinatorial antibody libraries are used together with unique optimization techniques to produce such therapeutically relevant proteins, for instance in the areas of oncology and inflammation.

A multichannel time-domain scanning fluorescence mammograph: performance assessment and first in vivo results

We present a scanning time-domain fluorescence mammograph capable to image the distribution of a fluorescent contrast agent within a female breast, slightly compressed between two parallel glass plates, with high sensitivity. Fluorescence of the contrast agent is excited using a near infrared picosecond diode laser module. Four additional picosecond diode lasers with emission wavelengths between 660 and 1066 nm allow to measure the intrinsic optical properties of the breast tissue. By synchronously moving a source fiber and seven detection fiber bundles across the breast, distributions of times of flight of photons are recorded simultaneously for selected source-detector combinations in transmission and reflection geometry either at the fluorescence wavelength or at the selected laser wavelengths. To evaluate the performance of the mammograph, we used breastlike rectangular phantoms comprising fluorescent and absorbing objects using the fluorescent dye Omocyanine as contrast agent excited at 735 nm. We compare two-dimensional imaging of the phantom based on transmission and reflection data. Furthermore, we developed an improved tomosynthesis algorithm which permits three-dimensional reconstruction of fluorescence and absorption properties of lesions with good spatial resolution. For illustration, we present fluorescence mammograms of one patient recorded 30 min after administration of the contrast agent indocyanine green showing the carcinoma at high contrast originating from fluorescence of the extravasated dye, excited at 780 nm.

Optical imaging of mammary and prostate tumors in living animals using a synthetic near infrared zinc(II)-dipicolylamine probe for anionic cell surfaces

In vivo optical imaging shows that a fluorescent imaging probe, comprised of a near-infrared fluorophore attached to an affinity group containing two zinc(II)-dipicolylamine (Zn-DPA) units, targets prostate and mammary tumors in two different xenograft animal models. The tumor selectivity is absent with control fluorophores whose structures do not have appended Zn-DPA targeting ligands. Ex vivo biodistribution and histological analyses indicate that the probe is targeting the necrotic regions of the tumors, which is consistent with in vitro microscopy showing selective targeting of the anionic membrane surfaces of dead and dying cells.

Late-fluorescence mammography assesses tumor capillary permeability and differentiates malignant from benign lesions

Using scanning time-domain instrumentation we recorded fluorescence projection mammograms on few breast cancer patients prior, during and after infusion of indocyanine green (ICG), while monitoring arterial ICG concentration by transcutaneous pulse densitometry. Late-fluorescence mammograms recorded after ICG had been largely cleared from the blood by the liver, showed invasive carcinomas at high contrast over a rather homogeneous background, whereas benign lesions did not produce (focused) fluorescence contrast. During infusion, tissue concentration contrast and hence fluorescence contrast is determined by intravascular contributions, whereas late-fluorescence mammograms are dominated by contributions from protein-bound ICG extravasated into the interstitium, reflecting relative microvascular permeabilities of carcinomas and normal breast tissue. We simulated intravascular and extravascular contributions to ICG tissue concentration contrast within a two-compartment unidirectional pharmacokinetic model.

Nonlinear reconstruction of absorption and fluorescence contrast from measured diffuse transmittance and reflectance of a compressed-breast-simulating phantom

We report on the nonlinear reconstruction of local absorption and fluorescence contrast in tissuelike scattering media from measured time-domain diffuse reflectance and transmittance of laser as well as laser-excited fluorescence radiation. Measurements were taken at selected source-detector offsets using slablike diffusely scattering and fluorescent phantoms containing fluorescent heterogeneities. Such measurements simulate in vivo data that would be obtained employing a scanning, time-domain fluorescence mammograph, where the breast is gently compressed between two parallel glass plates, and source and detector optical fibers scan synchronously at various source-detector offsets, allowing the recording of laser and fluorescence mammograms. The diffusion equations modeling the propagation of the laser and fluorescence radiation were solved in frequency domain by the finite element method simultaneously for several modulation frequencies using Fourier transformation and preprocessed experimental data. To reconstruct the concentration of the fluorescent contrast agent, the Born approximation including higher-order reconstructed photon densities at the excitation wavelength was used. Axial resolution was determined that can be achieved by various detection schemes. We show that remission measurements increase the depth resolution significantly.

Chlorin-bacteriochlorin energy-transfer dyads as prototypes for near-infrared molecular imaging probes: controlling charge-transfer and fluorescence properties in polar media

The photophysical properties of two energy-transfer dyads that are potential candidates for near-infrared (NIR) imaging probes are investigated as a function of solvent polarity. The dyads (FbC-FbB and ZnC-FbB) contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. The dyads were studied in toluene, chlorobenzene, 1,2-dichlorobenzene, acetone, acetonitrile and dimethylsulfoxide (DMSO). In both dyads, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of approximately (5-10 ps)(-1) and a yield of >99% in nonpolar and polar media. In toluene, the fluorescence yields (Phif=0.19) and singlet excited-state lifetimes (tau approximately 5.5 ns) are comparable to those of the benchmark bacteriochlorin. The fluorescence yield and excited-state lifetime decrease as the solvent polarity increases, with quenching by intramolecular electron (or hole) transfer being greater for FbC-FbB than for ZnC-FbB in a given solvent. For example, the Phif and tau values for FbC-FbB in acetone are 0.055 and 1.5 ns and in DMSO are 0.019 and 0.28 ns, whereas those for ZnC-FbB in acetone are 0.12 and 4.5 ns and in DMSO are 0.072 and 2.4 ns. The difference in fluorescence properties of the two dyads in a given polar solvent is due to the relative energies of the lowest energy charge-transfer states, as assessed by ground-state redox potentials and supported by molecular-orbital energies derived from density functional theory calculations. Controlling the extent of excited-state quenching in polar media will allow the favorable photophysical properties of the chlorin-bacteriochlorin dyads to be exploited in vivo. These properties include very large Stokes shifts (85 nm for FbC-FbB, 110 nm for ZnC-FbB) between the red-region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (lambdaf=760 nm), long bacteriochlorin excited-state lifetime (approximately 5.5 ns), and narrow (<or=20 nm) absorption and fluorescence bands. The latter will facilitate selective excitation/detection and multiprobe applications using both intensity- and lifetime-imaging techniques.

Differentiation of angiogenic burden in human cancer xenografts using a perfusion-type optical contrast agent (SIDAG)

INTRODUCTION

Use of fluorescence imaging in oncology is evolving rapidly, and nontargeted fluorochromes are currently being investigated for clinical application. Here, we investigated whether the degree of tumour angiogenesis can be assessed in vivo by planar and tomographic methods using the perfusion-type cyanine dye SIDAG (1,1'-bis- [4-sulfobutyl]indotricarbocyanine-5,5'-dicarboxylic acid diglucamide monosodium).

METHOD

Mice were xenografted with moderately (MCF7, DU4475) or highly vascularized (HT1080, MDA-MB435) tumours and scanned up to 24 hours after intravenous SIDAG injection using fluorescence reflectance imaging. Contrast-to-noise ratio was calculated for all tumours, and fluorochrome accumulation was quantified using fluorescence-mediated tomography. The vascular volume fraction of the xenografts, serving as a surrogate marker for angiogenesis, was measured using magnetic resonance imaging, and blood vessel profile (BVP) density and vascular endothelial growth factor expression were determined.

RESULTS

SIDAG accumulation correlated well with angiogenic burden, with maximum contrast to noise ratio for MDA-MB435 (P < 0.0001), followed by HT1080, MCF7 and DU4475 tumours. Fluorescence-mediated tomography revealed 4.6-fold higher fluorochrome concentrations in MDA-MB435 than in DU4475 tumours (229 +/- 90 nmol/l versus 49 +/- 22 nmol/l; P < 0.05). The vascular volume fraction was 4.5-fold (3.58 +/- 0.9% versus 0.8 +/- 0.53%; P < 0.01), blood vessel profile density 5-fold (399 +/- 36 BVPs/mm2 versus 78 +/- 16 BVPs/mm2) and vascular endothelial growth factor expression 4-fold higher for MDA-MB435 than for DU4475 tumours.

CONCLUSION

Our data suggest that perfusion-type cyanine dyes allow assessment of angiogenesis in vivo using planar or tomographic imaging technology. They may thus facilitate characterization of solid tumours.

Optical agents

Optical imaging is an emerging modality in the growing field of biomedical diagnostics. The past decade has witnessed the development of a variety of promising strategies for optical imaging techniques. Fundamental to these techniques is the design and application of novel fluorescent markers to allow molecular level in-vivo studies of disease in animal models in the laboratory and eventually in human clinical studies. This review surveys the range of fluorophores employed in these probes and the alternative probe systems in which they are used: non-specific, targeted and activatable; recent developments in the area of fluorescent nanoprobes and multimodality constructs are also reviewed.

Novel near-infrared fluorescent integrin-targeted DFO analogue

Desferrioxamine (DFO), a siderophore initially isolated from Streptomyces pilosus, possesses extraordinary metal binding properties with wide biomedical applications that include chelation therapy, nuclear imaging, and antiproliferation. In this work, we prepared a novel multifunctional agent consisting of (i) a near-infrared (NIR) fluorescent probe-cypate; (ii) an integrin alpha vbeta3 receptor (ABIR)-avid cyclic RGD peptide, and (iii) a DFO moiety, DFO-cypate-cyclo[RGDfK(approximately)] (1, with approximately representing the cypate conjugation site at the side chain of lysine; f is d-phenylalanine). Compound 1 and two control compounds, cypate-cyclo[RGDfK(approximately)] ( 2) and cypate-DFO ( 3), were synthesized by modular assembly of the corresponding protected RGD peptide cyclo[R(Pbf)GD(OBut)fK] and DFO on the dicarboxylic acid-containing cypate scaffold in solution. The three compounds exhibited similar UV-vis and emission spectral properties. Metal binding analysis shows that DFO as well as 1 and 3 exhibited relatively high binding affinity with Fe(III), Al(III), and Ga(III). In contrast to Ga(III), the binding of Fe to 1 and 3 quenched the fluorescence emission of cypate significantly, suggesting an efficient metal-mediated approach to perturb the spectral properties of NIR fluorescent carbocyanine probes. In vitro, 1 showed a high ABIR binding affinity (10 (-7) M) comparable to that of 2 and the reference peptide cyclo(RGDfV), indicating that both DFO and cypate motifs did not interfere significantly with the molecular recognition of the cyclic RGD motif with ABIR. Fluorescence microscopy showed that internalization of 1 and 2 in ABIR-positive A549 cells at 1 h postincubation was higher than 3 and cypate alone, demonstrating that incorporating ABIR-targeting RGD motif could improve cellular internalization of DFO analogues. The ensemble of these findings demonstrate the use of multifunctional NIR fluorescent ABIR-targeting DFO analogues to modulate the spectral properties of the NIR fluorescent probe by the chelating properties of DFO and visualize intracellular delivery of DFO by receptor-specific peptides. These features provide a strategy to explore the potential of 1 in tumor imaging and treatment as well as some molecular recognition processes mediated by metal ions.

Crystallization and molecular-replacement solution of a diagnostic fluorescent dye in complex with a specific Fab fragment

Tetrasulfocyanine (TSC) has been described as a fluorescent probe for tumour imaging. The complex of TSC and the Fab antibody fragment MOR03268 has been crystallized in three different crystal forms. MOR03268 was identified from the HuCAL GOLD library and further optimized to bind TSC with high affinity (Kd = 0.6 nM). For two of the three crystal forms (forms 1 and 2), data sets could be collected to 2.8 and 2.85 A resolution, respectively. Form 1 belongs to space group I222, with unit-cell parameters a = 72, b = 99, c = 154 A. Form 2 belongs to space group P4(3)2(1)2, with unit-cell parameters a = b = 77, c = 379 A. Form 3 only diffracted to 8 A and was not analyzed further. Molecular-replacement solutions for forms 1 and 2 were found and rebuilding and refinement is in progress. Form 1 contains one Fab molecule per asymmetric unit, while form 2 harbours two. Judging from the green colour of the crystals, both forms contain the Fab molecule bound to the green TSC dye and in both the hydrolysis-sensitive dye molecule is protected from degradation for several weeks to months. The structures should reveal the molecular basis of the high-affinity recognition of TSC by the Fab molecule MOR03268.