D-galactose receptor-targeted in vivo spectral fluorescence imaging of peritoneal metastasis using galactosamin-conjugated serum albumin-rhodamine green

Artificial Glycoproteins as a Scaffold for Targeted Drug Therapy

Akin to a cellular "fingerprint," the glycocalyx is a glycan-enriched cellular coating that plays a crucial role in mediating cell-to-cell interactions. To gain a better understanding of the factors that govern in vivo recognition, artificial glycoproteins were initially created to probe changes made to the accumulation and biodistribution of specific glycan assemblies through biomimicry. As a result, the organ-specific accumulation for a variety of glycoproteins decorated with simple and/or complex glycans was identified. Additionally, binding trends with regard to cancer cell selectivity were also investigated. To exploit the knowledge gained from these studies, numerous groups thus became engaged in developing targeted drug methodologies based on the use of artificial glycoproteins. This has either been done through adopting the glycoprotein scaffold as a drug carrier, or to directly glycosylate therapeutic proteins/enzymes to localize their biological activity. The principle aim of this Review is to present the foundational research that has driven artificial glycoprotein-based targeting and subsequent adaptations with potential therapeutic applications.

Synthesis, cytotoxicity and liver targeting of 3-O-β-D-Galactosylated Resveratrol

OBJECTIVES

Resveratrol (Res), a naturally occurring polyphenol, has shown pharmacological activities in treatment of liver diseases. However, the application of Res was limited by its poor bioavailability and liver targeting. Herein, 3-O-β-D-Galactosylated Resveratrol (Gal-Res) was synthesized by structural modification of Res to enhance bioavailability and liver targeting.

METHODS

The Gal-Res was characterized by IR, ¹ H-NMR spectra and MS. The in vitro antitumour experiments, in vivo pharmacokinetics and biodistribution studies were evaluated.

RESULTS

Gal-Res was successfully synthesized in our study. Compared to Res, Gal-Res resulted in enhanced cytotoxicity in HepG2 cells. After intravenous injection of normal SD rats, Gal-Res significantly improved the bioavailability of Res and the C_max and AUC_0-t of Gal-Res were 3.186 and 3.929 time than that of Res. In addition, in the study of liver targeting, the relative uptake rate (R_e ) of Gal-Res in the liver (2.006) is the largest. The drug targeting efficiency (T_e ; 38.924%) of Gal-Res was greater than that of Res. These showed that Gal-Res could significantly improve the distribution ability of Res in liver.

CONCLUSIONS

On the whole, Gal-Res increased cellular uptake to HepG2 cells, bioavailability and liver targeting, providing its future clinical application in the treatment of liver diseases.

Activatable Near-Infrared Fluorescence Imaging Using PEGylated Bacteriochlorin-Based Chlorin and BODIPY-Dyads as Probes for Detecting Cancer

Near infrared (NIR) fluorescent probes are attractive tools for biomedical in vivo imaging due to the relatively deeper tissue penetration and lower background autofluorescence. Activatable probes are turned on only after binding to their target, further improving target to background ratios. However, the number of available activatable NIR probes is limited. In this study, we introduce two types of activatable NIR fluorophores derived from bacteriochlorin: chlorin-bacteriochlorin energy-transfer dyads and boron-dipyrromethene (BODIPY)-bacteriochlorin energy-transfer dyads. These fluorophores are characterized by multiple narrow excitation bands with relatively strong emission in the NIR. Targeted bacteriochlorin-based antibody or peptide probes have been previously limited by aggregation after conjugation. Polyethylene glycol (PEG) chains were added to improve the hydrophilicity without altering pharmacokinetics of the targeting moieties. These PEGylated bacteriochlorin-based activatable fluorophores have potential as targeted activatable, multicolor NIR fluorescent probes for in vivo applications.

Ultrasensitive (Co)polymers Based on Poly(methacrylamide) Structure with Fining-Tunable pH Responsive Value

Novel pH responsive copolymers with tertiary amine groups were prepared by free radical polymerization with 2-(dialkylamino)ethyl methacrylate monomers. These polymers were pH sensitive with the ability to be responsively fine-tuned in aqueous solution, which was proven through titration, transmittance measurements, and proton nuclear magnetic resonance spectroscopy. The polymers were soluble in water at low pH values, induced by electrostatic repulsion between amine groups, and aggregated above their pKa value due to the hydrophobic effect of the alkyls. The pH responsive values were precisely tuned from 7.4 to 4.8 by increasing the hydrophobic monomer ratio. Our work provides a novel approach for the development of ultrasensitive pH-responsive polymers for application in biomedical materials.

A topically-sprayable, activatable fluorescent and retaining probe, SPiDER-βGal for detecting cancer: Advantages of anchoring to cellular proteins after activation

SPiDER-βGal is a newly-developed probe that is activated by β-galactosidase and is then retained within cells by anchoring to intracellular proteins. Previous work has focused on gGlu-HMRG, a probe activated by γ-glutamyltranspeptidase, which demonstrated high sensitivity for the detection of peritoneal ovarian cancer metastases in an animal model. However, its fluorescence, after activation by γ-glutamyltranspeptidase, rapidly declines over time, limiting the actual imaging window and the ability to define the border of lesions. The purpose of this study is to compare the fluorescence signal kinetics of SPiDER-βGal with that of gGlu-HMRG using ovarian cancer cell lines in vitro and ex vivo tissue imaging. In vitro removal of gGlu-HMRG resulted in a rapid decrease of fluorescence intensity followed by a more gradual decrease up to 60 min while there was a gradual increase in fluorescence up to 60 min after removal of SPiDER-βGal. This is most likely due to internalization and retention of the dye within cells. This was also confirmed ex vivo tissue imaging using a red fluorescence protein (RFP)-labeled tumor model in which the intensity of fluorescence increased gradually after activation of SPiDER-βGal. Additionally, SPiDER-βGal resulted in intense enhancement within the tumor due to the high target-to-background ratio, which extended up to 60 min after activation. In contrast, gGlu-HMRG fluorescence resulted in decreasing fluorescence over time in extracted tumors. Thus, SPiDER-βGal has the advantages of higher signal with more signal retention, resulting in improved contrast of the tumor margin and suggesting it may be an alternative to existing activatable probes.

Near-infrared photoimmunotherapy with galactosyl serum albumin in a model of diffuse peritoneal disseminated ovarian cancer

Near-infrared photoimmunotherapy (NIR-PIT) is a highly cell-selective cancer therapy based on an armed antibody conjugated with a phthalocyanine-based photo-absorber, IRDye700DX (IR700). NIR-PIT can quickly kill target cells that express specific proteins on the cellular membrane but only when the antibody-IR700 conjugate binds to the cell membrane and is then exposed to NIR light. NIR-PIT is highly selective based on the specificity of the antibody. Galactosyl serum albumin (GSA) is composed of albumin decorated with galactose molecules conjugated to the carboxyl groups of albumin. GSA binds to beta-D-galactose receptors, a surface lectin, which are overexpressed on the cell surface of many cancers, including ovarian cancers and is quickly internalized after binding. Here, we demonstrate the feasibility of NIR-PIT in a model of disseminated peritoneal ovarian cancer (SHIN3 cells) using GSA-IR700 that binds to beta-D-galactose receptors. GSA-IR700 bound quickly to SHIN3 cells, then accumulated in the endo-lysosomes. Cell-specific killing was observed in vitro, yet a relatively large dose of NIR light exposure was required for cell killing compared to antibody-IR700 conjugates. To evaluate in vivo therapeutic effects of GSA-IR700 NIR-PIT, peritoneal disseminated SHIN3 tumor-bearing mice were separated into four groups: no treatment; NIR light only; GSA-IR700 only; and GSA-IR700 NIR-PIT. Repeated NIR-PIT showed significant suppression of tumor based on bioluminescence compared to the other groups (p < 0.05). Thus, repeated NIR-PIT using GSA-IR700 can achieve efficient antitumor effects, although GSA-IR700 NIR-PIT was less effective than antibody-IR700 NIR-PIT conjugates likely due to the rapid internalization of GSA-IR700.

Dynamic fluorescent imaging with the activatable probe, γ-glutamyl hydroxymethyl rhodamine green in the detection of peritoneal cancer metastases: Overcoming the problem of dilution when using a sprayable optical probe

Optical fluorescence-guided imaging is increasingly used to guide surgery and endoscopic procedures. Activatable probes are particularly useful because of high target-to-background ratios that increase sensitivity for tiny cancer foci. However, green fluorescent activatable probes suffer from interference from autofluorescence found in biological tissue. The purpose of this study was to determine if dynamic imaging can be used to differentiate specific fluorescence arising from an activated probe in a tumor from autofluorescence in background tissues especially when low concentrations of the dye are applied. Serial fluorescence imaging was performed using various concentrations of γ-glutamyl hydroxymethyl rhodamine green (gGlu-HMRG) which was sprayed on the peritoneal surface with tiny implants of SHIN3-DsRed ovarian cancer tumors. Temporal differences in signal between specific green fluorescence in cancer foci and non-specific autofluorescence in background tissue were measured at 5, 10, 20 and 30 min after application of gGlu-HMRG and were processed into three kinetic maps reflecting maximum fluorescence signal (MF), wash-in rate (WIR), and area under the curve (AUC), respectively. Using concentrations up to 10 μM of gGlu-HMRG, the fluorescence intensity of cancer foci was significantly higher than that of small intestine but only at 30 min. However, on kinetic maps derived from dynamic fluorescence imaging, the signal of cancer foci was significantly higher than that of small intestine after only 5 min even at concentrations as low as 2.5 μM of gGlu-HMRG (p < 0.01). At lower concentrations, kinetic maps derived from dynamic fluorescence imaging were superior to unprocessed images for cancer detection.

Characteristics of ovarian cancer detection by a near-infrared fluorescent probe activated by human NAD(P)H: quinone oxidoreductase isozyme 1 (hNQO1)

Near-infrared (NIR) fluorescent probes are ideal for in vivo imaging, because they offer deeper tissue penetration by the light and lower background autofluorescence than fluorophores that emit in the visible range. Q₃STCy is a newly synthesized, NIR light-emitting probe that is activated by an enzyme commonly overexpressed in tumor cells, human nicotinamide adenine dinucleotide (phosphate): quinone oxidoreductase isozyme 1, known as hNQO1 or DT-diaphorase. The purpose of this study is to compare the sensitivity of detecting peritoneal ovarian cancer metastasis (POCM) with Q₃STCy and gGlu-HMRG, a green fluorescent probe, upon their surface application. In vitro uptake of Q₃STCy was significantly higher than that of gGlu-HMRG. Using a red fluorescence protein (RFP)-labeled in vivo tumor model of POCM, the Q₃STCy probe provided high sensitivity (96.9%) but modest specificity (61.0%), most likely the result of albumin-probe interactions and non-specific activation in nearby altered but healthy cells. Three types of kinetic maps based on maximum fluorescence signal (MF), wash-in rate (WIR), and area under the curve (AUC) allowed for differentiation of the activated fluorescence signal associated with POCM from the background signal of the small intestine, thereby significantly improving the specificity of Q₃STCy to 80%, 100%, and 100% for MF, WIR, and AUC, as well yielding a moderate improvement in sensitivity (100% for all approaches) that is comparable to that with gGlu-HMRG, but with the added advantages of NIR fluorescence as the transduction modality. Such a new methodology has the potential to afford identification of cancerous lesions deeper within tissue.

Exploring the glycan interaction in vivo: Future prospects of neo-glycoproteins for diagnostics

Herein the biodistributions and in vivo kinetics of chemically prepared neoglycoproteins are reviewed. Chemical methods can be used to conjugate various mono- and oligosaccharides onto a protein surface. The kinetics and organ-specific accumulation profiles of these glycoconjugates, which are introduced through intravenous injections, have been analyzed using conventional dissection studies as well as noninvasive methods such as single photon emission computed tomography, positron emission tomography and fluorescence imaging. These studies suggest that glycan-dependent protein distribution kinetics may be useful for pharmacological and diagnostic applications.

Chemically synthesized glycoconjugates on proteins: effects of multivalency and glycoform in vivo

The biodistributions and in vivo kinetics of chemically prepared glycoconjugates on proteins are reviewed.

Redox-responsive nanocarrier based on heparin end-capped mesoporous silica nanoparticles for targeted tumor therapy in vitro and in vivo

This study reports a smart controlled drug release system based on mesoporous silica nanoparticles (MSNs) for targeted drug delivery. The system was fabricated by employing heparin as an end-capping agent to seal the mesopores of MSNs via disulfide bonds as intermediate linkers for intracellular glutathione triggered drug release. Lactobionic acid molecules were then coupled to heparin end-capped MSNs that serve as targeting motifs for facilitating the uptake of doxorubicin (DOX) loaded MSNs by HepG2 cells and tumors, respectively. Detailed investigations demonstrated that the fabricated drug delivery systems could deliver DOX to cancer cells to induce cell apoptosis in vitro and tumor tissue for the inhibition of tumor growth in vivo with minimal side effects. The study affords a promising nanocarrier for redox-responsive cargo delivery with high curative efficiency for cancer therapy.

Endoscopic molecular imaging of cancer

White light endoscopy has proven to be a very powerful tool in oncology. There is still, however, a need for better endoscopic techniques to overcome the current limitations of white light optics. New technologies that allow higher sensitivity, improved microanatomy and molecular characterization have been available for in vitro microscopy and are now being translated into in vivo endoscopy. Endoscopic molecular imaging is still in its infancy but holds the promise for enhancing sensitivity for early lesions, thus allowing earlier diagnosis and enabling early image-guided endoscopic intervention. A key feature of endoscopic molecular imaging is its increased sensitivity and specificity, which will be illustrated in this article, as well as describing perspectives on its future use in oncologic surgery.

Activatable organic near-infrared fluorescent probes based on a bacteriochlorin platform: synthesis and multicolor in vivo imaging with a single excitation

Near infrared (NIR) fluorescent probes are ideal for in vivo imaging because they offer deeper tissue penetration and lower background autofluorescence. Although most fluorophores in this range are cyanine-based dyes, several new classes of fluorescent NIR probes have been developed. In this study, we developed organic bacteriochlorin derivatives, NMP4 and NMP5, which are excited with a single green light and emit different narrow, well-resolved bands in the NIR (peak of 739 and 770 nm for NMP4 and NMP5, respectively). When conjugated to galactosyl-human serum albumin (hGSA) or glucosyl-human serum albumin (glu-HSA), both targeting H-type lectins, including the β-d-galactose receptor expressing on ovarian cancer, these agents become targeted, activatable, single excitation, multicolor NIR fluorescence probes. After conjugation to either glu-HSA or hGSA, substantial quenching of fluorescence occurs that is reversed after cell binding and internalization. In vitro studies showed higher cancer cell uptake with NMP4 or NMP5 conjugated to hGSA compared to the same conjugates with glu-HSA. In vivo single excitation two-color imaging was performed after intraperitoneal injection of these agents into mice with disseminated ovarian cancer. Excited with a single green light, distinct NIR emission spectra from each fluorophore were detected and could be distinguished with spectral unmixing. In vivo results using a red fluorescence protein (RFP) labeled tumor model of disseminated ovarian cancer demonstrated high sensitivity and specificity for all probes. The success of single excitation, 2-color NIR fluorescence imaging with a new class of bacteriochlorin-based activatable fluorophores, NMP4 and NMP5, paves the way for further exploration of noncyanine dye-based NIR fluorophores.

A molecular probe for recognizing the size of hydrophobic cavities based on near-infrared absorbing diradical-Pt(II) complexes

A diradical-platinum(II) complex was able to recognize the subtle difference in cavity size between β- and γ-cyclodextrin with on-off switching of intense near-infrared absorption. This provides a new probe for identifying the size of hydrophobic cavities, which has been successfully applied here to differentiate human serum albumin from α-chymotrypsin.

A portable fluorescence camera for testing surgical specimens in the operating room: description and early evaluation

PURPOSE

Clinical translation of novel optical probes requires testing of human specimens ex vivo to ensure efficacy. However, it may be difficult to remove human tissue from the operating room due to regulatory/privacy issues. Therefore, we designed a portable fluorescence camera to test targeted optical imaging probes on human specimens in the operating room.

PROCEDURES

A compact benchtop fluorescence camera was designed and built in-house. A mouse xenograft model of ovarian cancer with an activatable imaging probe based on rhodamine green was used to test the device. Comparison was made to commercially available imaging systems.

RESULTS

The prototype camera produced images comparable to images acquired with commercially available, non-portable imaging systems.

CONCLUSION

We demonstrate the feasibility of a specimen-based portable fluorescence camera for use in the operating room. Its small size ensures that tissue excised from patients can be tested promptly for fluorescence within the operating room environment, thus expediting the testing of novel imaging probes.

The use of fluorescent proteins for developing cancer-specific target imaging probes

Target-specific imaging probes represent a promising tool in the molecular imaging of human cancer. Fluorescently-labeled target-specific probes are useful in imaging cancers because of their ability to bind a target receptor with high sensitivity and specificity. The development of probes relies upon preclinical testing to validate the sensitivity and specificity of these agents in animal models. However, this process involves both conventional histology and immunohistochemistry, which require large numbers of animals and samples with costly handling. In this chapter, we describe a novel validation tool that takes advantage of genetic engineering technology, whereby cell lines are transfected with genes that induce the target cell to produce fluorescent proteins with characteristic emission spectra, thus enabling their easy identification as cancer cells in vivo. Combined with multicolor fluorescence imaging, this can provide rapid validation of newly-developed exogenous probes that fluoresce at different wavelengths. For example, the plasmid containing the gene encoding red fluorescent protein (RFP) was transfected into cell lines previously developed to either express or not express specific cell surface receptors. Various antibody-based or ligand-based optical-contrast agents, with green fluorophores were developed to concurrently target cancer cells and validate their positive and negative controls, such as the β-D: -galactose receptor, HER1, and HER2 in a single animal/organ. Spectrally-resolved multicolor fluorescence imaging was used to detect separate fluorescence emission spectra from the exogenous green fluorophore and RFP. Here, we describe the use of "co-staining" (matching the exogenous fluorophore and the endogenous fluorescent protein to the positive control cell line) and "counter-staining" (matching the exogenous fluorophore to the positive control and the endogenous fluorescent protein to the negative control cell line) to validate the sensitivity and specificity of target-specific probes. Using these in vivo imaging techniques, we are able to determine the sensitivity and specificity of target-specific optical contrast agents in several distinct animal models of cancer in vivo, thus exemplifying the versatility of our technique, while reducing the number of animals needed to conduct these experiments.

Impact of albumin on drug delivery--new applications on the horizon

Over the past decades, albumin has emerged as a versatile carrier for therapeutic and diagnostic agents, primarily for diagnosing and treating diabetes, cancer, rheumatoid arthritis and infectious diseases. Market approved products include fatty acid derivatives of human insulin or the glucagon-like-1 peptide (Levemir(®) and Victoza(®)) for treating diabetes, the taxol albumin nanoparticle Abraxane(®) for treating metastatic breast cancer which is also under clinical investigation in further tumor indications, and (99m)Tc-aggregated albumin (Nanocoll(®) and Albures(®)) for diagnosing cancer and rheumatoid arthritis as well as for lymphoscintigraphy. In addition, an increasing number of albumin-based or albumin-binding drugs are in clinical trials such as antibody fusion proteins (MM-111) for treating HER2/neu positive breast cancer (phase I), a camelid albumin-binding nanobody anti-HSA-anti-TNF-α (ATN-103) in phase II studies for treating rheumatoid arthritis, an antidiabetic Exendin-4 analog bound to recombinant human albumin (phase I/II), a fluorescein-labeled albumin conjugate (AFL)-human serum albumin for visualizing the malignant borders of brain tumors for improved surgical resection, and finally an albumin-binding prodrug of doxorubicin (INNO-206) entering phase II studies against sarcoma and gastric cancer. In the preclinical setting, novel approaches include attaching peptides with high-affinity for albumin to antibody fragments, the exploitation of albumin-binding gadolinium contrast agents for magnetic resonance imaging, and physical or covalent attachment of antiviral, antibacterial, and anticancer drugs to albumin that are permanently or transiently attached to human serum albumin (HSA) or act as albumin-binding prodrugs. This review gives an overview of the expanding field of preclinical and clinical drug applications and developments that use albumin as a protein carrier to improve the pharmacokinetic profile of the drug or to target the drug to the pathogenic site addressing diseases with unmet medical needs.

Biodistribution and excretion of monosaccharide-albumin conjugates measured with in vivo near-infrared fluorescence imaging

Target specific small molecules as modulators of drug delivery may play a significant role in the future development of therapeutics. Small molecules can alter the in vivo pharmacokinetics of therapeutic macromolecules leading to more efficient drug delivery with less systemic toxicity. The potential of creating a more effective drug delivery system through glycosylation has led, for instance, to the addition of galactose to increase drug delivery to the liver. However, there are many other monosaccharides with potentially useful targeting properties that require further characterization. Here, we investigate the potential of glycosylation to guide molecular therapies using five different monosaccharides conjugated to human serum albumin (HSA). Additionally, we investigate how the amount of glycosylation may alter the pharmacokinetic profile of HSA. We introduce the use of in vivo near-infrared optical imaging to characterize the effect of differential glycosylation on the pharmacokinetics of macromolecules.

Two-step synthesis of galactosylated human serum albumin as a targeted optical imaging agent for peritoneal carcinomatosis

An optical probe, RG-(gal)(28)GSA, was synthesized to improve the detection of peritoneal implants by targeting the beta-d-galactose receptors highly expressed on the cell surface of a wide variety of cancers arising from the ovary, pancreas, colon, and stomach. Evaluation of RG-(gal)(28)GSA, RG-(gal)(20)GSA, glucose-analogue RG-(glu)(28)GSA, and control RG-HSA demonstrates specificity for the galactose, binding to several human adenocarcinoma cell lines, and cellular internalization. Studies using peritoneally disseminated SHIN3 xenografts in mice also confirmed a preference for galactose with the ability to detect submillimeter size lesions. Preliminary toxicity study for RG-(gal)(28)GSA using Balb/c mice reveal no toxic effects up to 100x of the standard imaging dose of 1 mg/kg administered either intraperitoneally or intravenously. These data indicate that RG-(gal)(28)GSA can selectively target a variety of human adenocarcinomas, can improve intraoperative or endoscopic tumor detection and resection, and may have little or no toxic in vivo effects; hence, it may be clinically translatable.

Pre-clinical whole-body fluorescence imaging: Review of instruments, methods and applications

Fluorescence sampling of cellular function is widely used in all aspects of biology, allowing the visualization of cellular and sub-cellular biological processes with spatial resolutions in the range from nanometers up to centimeters. Imaging of fluorescence in vivo has become the most commonly used radiological tool in all pre-clinical work. In the last decade, full-body pre-clinical imaging systems have emerged with a wide range of utilities and niche application areas. The range of fluorescent probes that can be excited in the visible to near-infrared part of the electromagnetic spectrum continues to expand, with the most value for in vivo use being beyond the 630 nm wavelength, because the absorption of light sharply decreases. Whole-body in vivo fluorescence imaging has not yet reached a state of maturity that allows its routine use in the scope of large-scale pre-clinical studies. This is in part due to an incomplete understanding of what the actual fundamental capabilities and limitations of this imaging modality are. However, progress is continuously being made in research laboratories pushing the limits of the approach to consistently improve its performance in terms of spatial resolution, sensitivity and quantification. This paper reviews this imaging technology with a particular emphasis on its potential uses and limitations, the required instrumentation, and the possible imaging geometries and applications. A detailed account of the main commercially available systems is provided as well as some perspective relating to the future of the technology development. Although the vast majority of applications of in vivo small animal imaging are based on epi-illumination planar imaging, the future success of the method relies heavily on the design of novel imaging systems based on state-of-the-art optical technology used in conjunction with high spatial resolution structural modalities such as MRI, CT or ultrasound.

Molecular probes for the in vivo imaging of cancer

Advancements in medical imaging have brought about unprecedented changes in the in vivo assessment of cancer. Positron emission tomography, single photon emission computed tomography, optical imaging, and magnetic resonance imaging are the primary tools being developed for oncologic imaging. These techniques may still be in their infancy, as recently developed chemical molecular probes for each modality have improved in vivo characterization of physiologic and molecular characteristics. Herein, we discuss advances in these imaging techniques, and focus on the major design strategies with which molecular probes are being developed.

Fluorophore-quencher based activatable targeted optical probes for detecting in vivo cancer metastases

In vivo molecularly targeted fluorescence imaging of tumors has been proposed as a strategy for improving cancer detection and management. Activatable fluorophores, which increased their fluorescence by 10-fold after binding tumor cells, result in much higher target to background ratios than conventional fluorophores. We developed an in vivo targeted activatable optical imaging probe based on a fluorophore-quencher pair, bound to a targeting moiety. With this system, fluorescence is quenched by the fluorophore-quencher interaction outside cancer cells, but is activated within the target cells by dissociation of the fluorophore-quencher pair. We selected the TAMRA (fluorophore)-QSY7 (quencher) pair and conjugated it to either avidin (targeting the D-galactose receptor) or trastuzumab (a monoclonal antibody against the human epithelial growth factor receptor type2 (HER2/neu)) and evaluated their performance in mouse models of cancer. Two probes, TAMRA-QSY7 conjugated avidin (Av-TM-Q7) and trastuzumab (Traz-TM-Q7) were synthesized. Both demonstrated better than similar self-quenching probes. In vitro fluorescence microscopic studies of SHIN3 and NIH/3T3/HER2+ cells demonstrated that Av-TM-Q7 and Traz-TM-Q7 produced high intracellular fluorescent signal. In vivo imaging with Av-TM-Q7 and Traz-TM-Q7 in mice enabled the detection of small tumors. This molecular imaging probe, based on a fluorophore-quencher pair conjugated to a targeting ligand, successfully detected tumors in vivo due to its high activation ratio and low background signal. Thus, these activatable probes, based on the fluorophore-quencher system, hold promise clinically for "see and treat" strategies of cancer management.

Multi-targeted multi-color in vivo optical imaging in a model of disseminated peritoneal ovarian cancer

Commonly used in flow cytometry, multiplexed optical probes can diagnose multiple types of cell surface marker, potentially leading to improved diagnosis accuracy in vivo. Herein, we demonstrate the targeting of two different tumor markers in models of disseminated ovarian cancer. Two ovarian cancer cell lines (SKOV3 and SHIN3) were employed; both overexpress D-galactose receptor (D-galR), but only SKOV3 overexpresses HER2/neu. Additionally, fusion tumors composed of SKOV3 and SHIN3/RFP were evaluated. Both galactosyl serum albumin-rhodamine green (GSA-RhodG), which binds D-galR, and trastuzumab-Alexa680, which binds HER2/neu, were administered to tumor-bearing mice for in vivo fluorescence imaging and in situ fluorescence microscopy. In vivo fluorescence imaging depicted 64 of 69 SKOV3 tumors (94.2%) based on their dual spectra corresponding to both RhodG and Alexa680, while all 71 SHIN3 tumors (100%) were detected based on their single spectrum corresponding only to RhodG. All 59 SHIN3 and 36 SKOV3 tumors were correctly diagnosed with in situ microscopy. Additionally, in the mixed tumor model, all tumors could be depicted using the RhodG spectrum, but only SKOV3 components also showed the Alexa680 spectrum. In conclusion, multitargeted multicolor optical imaging enabled specific in vivo diagnosis of tumors expressing distinct patterns of receptors, leading to improved diagnostic accuracy.

Selective molecular imaging of viable cancer cells with pH-activatable fluorescence probes

A long-term goal of cancer diagnosis is to develop tumor-imaging techniques that have sufficient specificity and sensitivity. To achieve this goal, minimizing the background signal originating from nontarget tissues is crucial. Here we achieve highly specific in vivo cancer visualization by using a newly designed targeted 'activatable' fluorescent imaging probe. This agent is activated after cellular internalization by sensing the pH change in the lysosome. Novel acidic pH-activatable probes based on the boron-dipyrromethene fluorophore were synthesized and then conjugated to a cancer-targeting monoclonal antibody. As proof of concept, ex vivo and in vivo imaging of human epidermal growth factor receptor type 2-positive lung cancer cells in mice was performed. The probe was highly specific for tumors with minimal background signal. Furthermore, because the acidic pH in lysosomes is maintained by the energy-consuming proton pump, only viable cancer cells were successfully visualized. The design concept can be widely adapted to cancer-specific, cell surface-targeting molecules that result in cellular internalization.

Determination of optimal rhodamine fluorophore for in vivo optical imaging

Optical imaging has the potential to improve the efficacy of surgical and endoscopic approaches to cancer treatment; however, the optimal type of fluorescent probe has not yet been established. It is well-known that rhodamine-core-derived fluorophores offer a combination of desirable properties such as good photostability, high extinction coefficient, and high fluorescence quantum yield. However, despite the ubiquitous use of rhodamine fluorophores for in vivo optical imaging, it remains to be determined if unique chemical properties among individual rhodamine core family members affect fluorophore parameters critical to in vivo optical imaging applications. These parameters include preserved fluorescence intensity in low pH environments, similar to that of the endolysosome; efficient fluorescence signal despite conformational changes to targeting proteins as may occur in harsh subcellular environments; persistence of fluorescence after cellular internalization; and sufficient signal-to-background ratios to permit the identification of fluorophore-targeted tumors. In the present study, we conjugated 4 common rhodamine-core based fluorescent dyes to a clinically feasible and quickly internalizing D-galactose receptor targeting reagent, galactosamine serum albumin (GmSA), and conducted a series of in vitro and in vivo experiments using a metastatic ovarian cancer mouse model to determine if differences in optical imaging properties exist among rhodamine fluorophores and if so, which rhodamine core possesses optimal characteristics for in vivo imaging applications. Herein, we demonstrate that the rhodamine-fluorophore, TAMRA, is the most robust of the 4 common rhodamine fluorophores for in vivo optical imaging of ovarian cancer metastases to the peritoneum.

A self-quenched galactosamine-serum albumin-rhodamineX conjugate: a "smart" fluorescent molecular imaging probe synthesized with clinically applicable material for detecting peritoneal ovarian cancer metastases

PURPOSE

Fluorophore activation after cellular internalization of a targeted fluorescently labeled conjugate is an effective molecular imaging strategy to increase target-to-background ratios. The D-galactose receptor on ovarian cancer cells has been used to target self-quenched avidin-rhodamineX conjugates in which the avidin component binds to D-galactose receptor and the rhodamines are optically activated by dequenching only after cellular internalization. As a nonimmunogenic alternative of avidin, galactosamine-conjugated serum albumin (GmSA) targets the D-galactose receptor with higher binding affinity and has more conjugation sites available for rhodamineX than avidin.

EXPERIMENTAL DESIGN

GmSA was conjugated with 20 rhodamineX molecules (GmSA-20ROX) to create a self-quenching complex, which was compared with a conjugate consisting of GmSA and a single rhodamineX (GmSA-1ROX) in ex vivo chemical activation characteristics, intracellular activation, and in vivo molecular imaging for detecting peritoneal micrometastases of SHIN3 ovarian cancer.

RESULTS

GmSA-20ROX was five times brighter than GmSA-1ROX when incubated with SHIN3 ovarian cancer cells for 3 h. Submillimeter SHIN3 ovarian cancer implants in the peritoneal cavity were clearly visualized in vivo with spectral fluorescence imaging due to the high tumor-to-background ratio. The sensitivity and specificity of GmSA-20ROX for implant detection were determined by colocalization of the rhodamineX emission with red fluorescent protein expressed constitutively in the SHIN3 tumor implants. Among 336 lesions, sensitivity and specificity were 99%/99%, respectively, for GmSA-20ROX, whereas the results for GmSA-1ROX were only 24%/100% (n = 388), respectively, for lesions approximately 0.8 mm or greater in diameter.

CONCLUSION

Self-quenched GmSA-20ROX is more efficient than previous d-galactose-targeted fluorescent conjugates.

Targeted optical fluorescence imaging of human ovarian adenocarcinoma using a galactosyl serum albumin-conjugated fluorophore

Achieving maximal cytoreduction during surgery is a critical prognostic factor for women with advanced-stage ovarian cancer. Targeting optical imaging agents directly to ovarian cancer cells by attaching them to galactosyl (galactosamine-conjugated) serum albumin, whose sugar residues bind surface lectins that are expressed in certain ovarian adenocarcinomas, may improve metastatic tumor identification and resection. Thus, we sought to demonstrate that galactosyl serum albumin-conjugated fluorophores would be a robust mechanism through which to target ovarian cancer by evaluating its tumor-targeting capability in nine human ovarian adenocarcinoma cell lines. The optical fluorophore rhodamine green was conjugated to galactosyl serum albumin, a non-immunogenic targeting molecule. Galactosyl serum albumin-rhodamine green's ability to target nine human ovarian adenocarcinoma cell lines was evaluated by flow cytometry, fluorescence microscopy and in vivo optical fluorescence imaging using female athymic nu/nu mice. All nine cell lines tested bound galactosyl serum albumin-rhodamine green more effectively than non-glycosylated controls (P < 0.0001). Fluorescence microscopy demonstrated that galactosyl serum albumin-rhodamine green was internalized into each cell line in a galactosamine-dependent manner. In vivo optical fluorescence images of intraperitoneal tumor-bearing mice acquired 3 h after intraperitoneal injection of galactosyl serum albumin-rhodamine green successfully differentiated between tumor and normal tissue. This technique also allowed the visualization of submillimeter-sized ovarian tumor implants. These results indicate that galactosyl serum albumin-rhodamine green can selectively target a variety of human ovarian adenocarcinomas for optical fluorescence imaging and thus may improve intraoperative tumor detection and resection.