A new optical and nuclear dual-labeled imaging agent targeting interleukin 11 receptor alpha-chain

Peptide-based diagnostic and therapeutic agents: Where we are and where we are heading?

Peptides are increasingly present in all branches of medicine as innovative drugs, imaging agents, theragnostic, and constituent moieties of other sophisticated drugs such as peptide-drug conjugates. Due to new developments in chemical synthesis strategies, computational biology, recombinant technology, and chemical biology, peptide drug development has made a great progress in the last decade. Numerous natural peptides and peptide mimics have been obtained and studied, covering multiple therapeutic areas. Even though peptides have been investigated across the wide therapeutic spectrum, oncology, metabolism, and endocrinology are the most frequent medical indications of them. This review summarizes the current use of and the emerging new opportunities of peptides for diagnosis and treatment of various diseases.

Dual-Labelling Strategies for Nuclear and Fluorescence Molecular Imaging: Current Status and Future Perspectives

Molecular imaging offers the possibility to investigate biological and biochemical processes non-invasively and to obtain information on both anatomy and dysfunctions. Based on the data obtained, a fundamental understanding of various disease processes can be derived and treatment strategies can be planned. In this context, methods that combine several modalities in one probe are increasingly being used. Due to the comparably high sensitivity and provided complementary information, the combination of nuclear and optical probes has taken on a special significance. In this review article, dual-labelled systems for bimodal nuclear and optical imaging based on both modular ligands and nanomaterials are discussed. Particular attention is paid to radiometal-labelled molecules for single-photon emission computed tomography (SPECT) and positron emission tomography (PET) and metal complexes combined with fluorescent dyes for optical imaging. The clinical potential of such probes, especially for fluorescence-guided surgery, is assessed.

Evaluating the Photodynamic Biocidal Activity and Investigating the Mechanism of Thiazolium Cyanine Dyes

In order to develop ideal photosensitizers for photodynamic therapy (PDT), a thiazolium group was introduced in cyanine dyes to possess the advantages of intense absorption in the visible region and anti-microbial activity. We evaluated the anti-bacterial activity of the three thiazolium cyanine dyes against Staphylococcus aureus (Gram-positive bacteria) and Escherichia coli (Gram-negative bacteria) in vitro. This is the first time that such kinds of cyanine dyes are applied in the photodynamic antibiotic area. Cyanines display excellent anti-bacterial activity to S. aureus and E. coli exposed to white light irradiation, and the corresponding light-induced biocidal efficacy of cyanines increased with irradiation time and concentration. At the same time, there was no observation of dark anti-bacterial abilities. Especially, cyanines show low cell cytotoxicity and excellent biocompatibility. These results suggest that thiazolium cyanine could work as a photosensitizer in PDT with great promise and broad applications for killing bacteria. Mechanistic studies suggest that the reactive oxygen species (ROS) is the vital factor for combating bacteria exposure to white light conditions, whereas it is not the only determining factor of the biocidal activity. The interaction of the cyanine to the cell membrane also plays a critical role in killing bacteria, which has exhibited a synergic effect of electrostatic and hydrophobic interactions. It influences the cell uptake and the membrane perturbation activity of the cyanines, which indirectly affects the biocidal activity.

Near-Infrared Fluorescent Activated Polymeric Probe for Imaging Intraluminal Colorectal Cancer Tumors

Detection and removal of preneoplastic tumors is crucial for successful colorectal cancer (CRC) therapy. Here we describe the design of a Cathepsin B (CB)-activated polymeric probe, P-(GGFLGK-IR783), for imaging CRC tumors established by intrarectal or subcutaneous (s.c.) implantation of human colon cancer cells (SW-480 and HT-29) in mice. Multiple copies of the near-infrared fluorescent (NIRF) dye IR783 were attached to a single HPMA copolymer backbone via a CB-cleavable linker (GFLG), and the influence of the dye loading on the fluorescence quenching and activation by CB was assessed in vitro, ex vivo, and in vivo. The optimal dose and dosing regimen of P-(GGFLGK-IR783) for colonic tumor detection was determined. Increasing the IR783 loading in the copolymer from 2.5 to 20 mol % resulted in quenching of the fluorescence signal that was activated in vitro by the action of CB from different origins. Following intravenous administration, P-(GGFLGK-IR783)_7.5% preferentially accumulated in intrarectal and s.c. implanted tumors, allowing tumor visualization after 4 h and even 48 h postadministration. Activation of P-(GGFLGK-IR783)_7.5% by CB was clearly detected in s.c. implanted tumors, revealing about a 4-fold increase in the fluorescence signal in tumors vs healthy colon tissue. The probe containing the CB-cleavable linker produced higher fluorescence signal intensity in tumors, relative to the noncleavable probe. These results indicate that P-(GGFLGK-IR783)_7.5% may aid in detecting CRC tumors and can help to guide selective removal of polyps during colonoscopic procedures.

Combination of PET and CXCR4-Targeted Peptide Molecule Agents for Noninvasive Tumor Monitoring

Precision medicine is emphasizing not only at individual but also at disease molecule level in modern medicine. Therefore, target-specific molecular agents are crucial for precise diagnosis and treatment. We developed a peptide agent that binds a critical chemokine receptor-CXCR4 and could be used to detect tumor status. Confocal images showed binding of the peptide agent to human osteosarcoma cells. Clinical gold-standard molecular imaging agent PET showed tumors had high glucose metabolism, CT showed that these xenograft tumors were calcified and displayed hypervascularity. Peptide imaging demonstrated that these tumors were CXCR4 positive. However, Western blot protein analysis revealed a discordance between the tumor and the CXCR4 targeted agent, suggesting that small changes in peptide sequences have profound effect on binding to their targets. We also demonstrated the molecular screening by modifying the peptide sequence and thereby altering the binding properties of the agent. In conclusion, this study demonstrates that small molecule peptide agents can be used as an additional diagnostic tool for precision medicine.

Optical and nuclear imaging of glioblastoma with phosphatidylserine-targeted nanovesicles

Multimodal tumor imaging with targeted nanoparticles potentially offers both enhanced specificity and sensitivity, leading to more precise cancer diagnosis and monitoring. We describe the synthesis and characterization of phenol-substituted, lipophilic orange and far-red fluorescent dyes and a simple radioiodination procedure to generate a dual (optical and nuclear) imaging probe. MALDI-ToF analyses revealed high iodination efficiency of the lipophilic reporters, achieved by electrophilic aromatic substitution using the chloramide 1,3,4,6-tetrachloro-3α,6α-diphenyl glycoluril (Iodogen) as the oxidizing agent in an organic/aqueous co-solvent mixture. Upon conjugation of iodine-127 or iodine-124-labeled reporters to tumor-targeting SapC-DOPS nanovesicles, optical (fluorescent) and PET imaging was performed in mice bearing intracranial glioblastomas. In addition, tumor vs non-tumor (normal brain) uptake was compared using iodine-125. These data provide proof-of-principle for the potential value of SapC-DOPS for multimodal imaging of glioblastoma, the most aggressive primary brain tumor.

Radioiodination of BODIPY and its application to a nuclear and optical dual functional labeling agent for proteins and peptides

In molecular imaging research, the development of multimodal imaging probes has recently attracted much attention. In the present study, we prepared radioiodinated BODIPY and applied it as a nuclear and optical dual functional labeling agent for proteins and peptides. We designed and synthesized [¹²⁵I]BODIPY with a N-hydroxysuccinimide (NHS) ester, and evaluated its utility as a nuclear and fluorescent dual labeling agent for proteins and peptides. In the radioiodination reaction of BODIPY-NHS with [¹²⁵I]NaI, [¹²⁵I]BODIPY-NHS was obtained at a 48% radiochemical yield. When we carried out the conjugation reaction of [¹²⁵I]BODIPY-NHS with bovine serum albumin (BSA) and RGD (Arg-Gly-Asp) peptide as a model protein and peptide, respectively, [¹²⁵I]BODIPY-BSA and [¹²⁵I]BODIPY-RGD peptide were successfully prepared at 98 and 82% radiochemical yields, respectively. Furthermore, we prepared [¹²³I]BODIPY-trastuzumab by this conjugation reaction and successfully applied it to single photon emission computed tomography (SPECT) imaging studies using tumor-bearing mice, suggesting that radioiodinated BODIPY-NHS serves as a dual functional labeling agent for proteins and peptides. Since iodine has various radioisotopes that can be used for SPECT and positron emission tomography (PET) imaging, biological research, and radiotherapy, the radioiodinated BODIPY may be extensively applicable from basic to clinical research.

High-Throughput Approaches to the Development of Molecular Imaging Agents

Molecular imaging allows for the visualization of changes at the cellular level in diseases such as cancer. A successful molecular imaging agent must rely on disease-selective targets and ligands that specifically interact with those targets. Unfortunately, the translation of novel target-specific ligands into the clinic has been frustratingly slow with limitations including the complex design and screening approaches for ligand identification, as well as their subsequent optimization into useful imaging agents. This review focuses on combinatorial library approaches towards addressing these two challenges, with particular focus on phage display and one-bead one-compound (OBOC) libraries. Both of these peptide-based techniques have proven successful in identifying new ligands for cancer-specific targets and some of the success stories will be highlighted. New developments in screening methodology and sequencing technology have pushed the bounds of phage display and OBOC even further, allowing for even faster and more robust discovery of novel ligands. The combination of multiple high-throughput technologies will not only allow for more accurate identification, but also faster affinity maturation, while overall streamlining the process of translating novel ligands into clinical imaging agents.

Technetium(I) Complexes of Bathophenanthrolinedisulfonic Acid

Bathophenanthrolinedisulfonate (BPS) complexes of technetium(I) of the type [Tc(CO)₃(BPS)(L)]ⁿ (L = imidazole derivatives) were synthesized and evaluated both in vitro and in vivo. [^99mTc(CO)₃(BPS)(MeIm)]^- (MeIm = 1-methyl-1H-imidazole) was prepared in near-quantitative yield using a convenient two-step, one-pot labeling procedure. A targeted analogue capable of binding regions of calcium turnover associated with bone metabolism was also prepared. Here, a bisphosphonate was linked to the metal through an imidazole ligand to give [^99mTc(CO)₃(BPS)(ImAln)]^2- (ImAln = an imidazole-alendronate ligand) in high yield. The technetium(I) complexes were stable in vitro, and in biodistribution studies, [^99mTc(CO)₃(BPS)(ImAln)]^2- exhibited rapid clearance from nontarget tissues and significant accumulation in the shoulder (7.9 ± 0.2% ID/g) and knees (15.1 ± 0.9% ID/g) by 6 h, with the residence time in the skeleton reaching 24 h. A rhenium analogue, which is luminescent and has the same structure, was also prepared and used for fluorescence labeling of cells in vitro. The data reported demonstrate the potential of this class of compounds for use in creating isostructural optical and nuclear probes.

Tumor-targeting peptides from combinatorial libraries

Cancer is one of the major and leading causes of death worldwide. Two of the greatest challenges in fighting cancer are early detection and effective treatments with no or minimum side effects. Widespread use of targeted therapies and molecular imaging in clinics requires high affinity, tumor-specific agents as effective targeting vehicles to deliver therapeutics and imaging probes to the primary or metastatic tumor sites. Combinatorial libraries such as phage-display and one-bead one-compound (OBOC) peptide libraries are powerful approaches in discovering tumor-targeting peptides. This review gives an overview of different combinatorial library technologies that have been used for the discovery of tumor-targeting peptides. Examples of tumor-targeting peptides identified from each combinatorial library method will be discussed. Published tumor-targeting peptide ligands and their applications will also be summarized by the combinatorial library methods and their corresponding binding receptors.

Inhibition of CD44v3 and CD44v6 function blocks tumor invasion and metastatic colonization

The prevention of cancer cell dissemination and secondary tumor formation are major goals of cancer therapy. Here, we report on the development of a new CD44-targeted copolymer carrying multiple copies of the A5G27 peptide, known for its ability to bind specifically to CD44v3 and CD44v6 on cancer cells and inhibit tumor cell migration, invasion, and angiogenesis. We hypothesized that conjugation of A5G27 to N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer would enhance tumor tissue accumulation, promote selective binding to cancer cells, with concomitant increased inhibition of cancer cell invasiveness and migration. Fluorescein-5-isothiocyanate or the near-infrared fluorophore IR783 were attached to the copolymer backbone through a non-cleavable linkage to assess in vitro binding to cancer cells and biodistribution of the polymer in 4T1 murine mammary adenocarcinoma-bearing mice, respectively. The anti-migratory activity was evaluated both in vitro and in vivo. The binding of the targeted copolymer to cancer cells correlated well with the level of CD44 expression, with the polymer being internalized more efficiently by cancer cells. Pre-treatment of mice with polymer-bound A5G27 significantly inhibited lung colonization of migrating 4T1 cells in vivo, with the targeted copolymer accumulating preferentially in subcutaneous 4T1 tumors, when compared to a non-targeted system. As such, the HPMA copolymer-A5G27 conjugate is a promising candidate for inhibiting cancer cell migration and can also be used as a drug or imaging probe carrier for detection and treatment of cancer.

Fluorescent chemical probes for accurate tumor diagnosis and targeting therapy

This review focuses on small molecular ligand-targeted fluorescent imaging probes and fluorescent theranostics, including their design strategies and applications in clinical tumor treatment.

Ligand-targeted theranostic nanomedicines against cancer

Nanomedicines have significant potential for cancer treatment. Although the majority of nanomedicines currently tested in clinical trials utilize simple, biocompatible liposome-based nanocarriers, their widespread use is limited by non-specificity and low target site concentration and thus, do not provide a substantial clinical advantage over conventional, systemic chemotherapy. In the past 20years, we have identified specific receptors expressed on the surfaces of tumor endothelial and perivascular cells, tumor cells, the extracellular matrix and stromal cells using combinatorial peptide libraries displayed on bacteriophage. These studies corroborate the notion that unique receptor proteins such as IL-11Rα, GRP78, EphA5, among others, are differentially overexpressed in tumors and present opportunities to deliver tumor-specific therapeutic drugs. By using peptides that bind to tumor-specific cell-surface receptors, therapeutic agents such as apoptotic peptides, suicide genes, imaging dyes or chemotherapeutics can be precisely and systemically delivered to reduce tumor growth in vivo, without harming healthy cells. Given the clinical applicability of peptide-based therapeutics, targeted delivery of nanocarriers loaded with therapeutic cargos seems plausible. We propose a modular design of a functionalized protocell in which a tumor-targeting moiety, such as a peptide or recombinant human antibody single chain variable fragment (scFv), is conjugated to a lipid bilayer surrounding a silica-based nanocarrier core containing a protected therapeutic cargo. The functionalized protocell can be tailored to a specific cancer subtype and treatment regimen by exchanging the tumor-targeting moiety and/or therapeutic cargo or used in combination to create unique, theranostic agents. In this review, we summarize the identification of tumor-specific receptors through combinatorial phage display technology and the use of antibody display selection to identify recombinant human scFvs against these tumor-specific receptors. We compare the characteristics of different types of simple and complex nanocarriers, and discuss potential types of therapeutic cargos and conjugation strategies. The modular design of functionalized protocells may improve the efficacy and safety of nanomedicines for future cancer therapy.

Binding Specificity of Radiolabeled Cyclic Peptide 153Sm-DTPA-c(CGRRAGGSC) to MHCC97-H Human Liver Cancer Cells and its Antitumor Effects in vivo

Objective:

This objective of this study is to investigate the effects of the radiolabeled cyclic peptide 153Sm-DTPA-c(CGRRAGGSC) on MHCC97-H human liver cancer cells in vitro and in vivo.

Methods:

The protein expression levels were examined by Western blot analysis. Biological activity of 153Sm-DTPA-c(CGRRAGGSC) was assessed with the radioligand binding assay and competitive inhibition experiment. Subcellular localization of the cyclic peptide was observed by fluorescence microscopy. Animals were implanted with MHCC97-H cells and administered with 153Sm-DTPA-c(CGRRAGGSC). Hematoxylin and eosin staining, electron microscopy, and immunohistochemistry were performed to evaluate the effects of 153Sm-DTPA-c(CGRRAGGSC) on implanted tumors.

Result:

The expression levels of interleukin 11 receptor were significantly elevated, by 2-to 5-fold, in tumor cell lines, especially for MHCC97-H cells. Characterization of 153Sm-DTPA-c(CGRRAGGSC) showed that the biological activity of the cyclic peptide was not altered after labeling, and the radiolabeled cyclic peptide exhibited sufficient binding affinity to interleukin 11 receptor . The cyclic peptide of c(CGRRAGGSC) was mainly distributed in the cytoplasm and on the cell membrane of MHCC97-H cells. The in vivo experiments showed that the tumor growth was significantly inhibited by the treatment of 153Sm-DTPA-c(CGRRAGGSC). The inhibitory effect of 153Sm-DTPA-c(CGRRAGGSC) on tumor growth was further confirmed by Hematoxylin and eosin staining, electron microscopy, and immunohistochemistry. Moreover, the expression levels of interleukin 11 receptor in implanted tumors were significantly decreased in the treatment groups.

Conclusion:

153Sm-DTPA-c (CGRRAGGSC) could specifically bind to interleukin 11 receptor on MHCC97-H liver tumor cells, inhibiting the cell proliferation and inducing cellular apoptosis. These findings provide experimental evidence for the development of individual treatment of liver cancers, as well as recurrence and metastasis.

Small flexible structure for targeted delivery of therapeutic and imaging moieties in precision medicine

The goals of precision medicine are to link diagnostic and therapeutic agents, improve clinical outcomes, and minimize side effects. We present a simple, small, flexible three-armed core structure that can be conjugated to targeting, imaging, and therapeutic moieties. The targeting molecule can be a peptide, protein, or chemical compound. The diagnostic reporter can be optical and/or nuclear in nature, and can be replaced by chemo- and/or radiotherapeutic compounds for treatment using a single targeting molecule. Imaging components can be used to detect disease biomarkers, monitor treatment response, and guide surgery in real-time to create a tumor-free margin. Isotope impurity can be exploited to visualize whole-body distribution of therapeutic agents. The one-to-one ratio of targeting component to therapeutic agents facilitates dose calculation. The simple synthesis and flexible, modular nature of the agent facilitate high-purity, large-scale production. The core capacity to "seek, treat, and see" may advance precision medicine in the future.

Multimodal imaging probe for targeting cancer cells using uMUC-1 aptamer

For adequate cancer therapy, newer imaging modalities with more specific ligands for unique targets are crucial. Underglycosylated mucin-1 (uMUC-1) antigen is an early marker of tumor development and is widely overexpressed on most tumors. A combination of nanotechnology with optical, radionuclide, and magnetic resonance (MR) imaging has great potential to improve cancer diagnosis and therapy. In this study, a multimodal nanoparticle imaging system was developed that can be used for optical, MR and positron emission tomography (PET) imaging. Cobalt ferrite magnetic nanoparticles surrounded by fluorescent rhodamine (designated MF) within a silica shell matrix were conjugated with an aptamer targeting uMUC-1 (designated MF-uMUC-1) and further labeled by (68)Ga (designated MFR-uMUC-1) with the help of a p-SCN-bn-NOTA chelating agent, resulting in single multimodal nanoparticles. The resultant nanoparticles are spherical and monodispersed, as revealed by transmission electron microscopy. The MFR-uMUC-1 nanoparticle showed specific and dose-dependent fluorescent, radioisotope and MR signals targeting BT-20 cells expressing uMUC-1. In vivo targeting and multimodal imaging in tumor-bearing nude mice also showed great specificity for targeting cancers with MFR-uMUC-1. The MFR-uMUC-1 probe could be used as a single multimodal probe to visualize cancer cells by means of optical, radionuclide and MR imaging.

The status of contemporary image-guided modalities in oncologic surgery

OBJECTIVE

To review the current trends in optical imaging to guide oncologic surgery.

BACKGROUND

Surgical resection remains the cornerstone of therapy for patients with early stage solid malignancies and more than half of all patients with cancer undergo surgery each year. The technical ability of the surgeon to obtain clear surgical margins at the initial resection remains crucial to improve overall survival and long-term morbidity. Current resection techniques are largely based on subjective and subtle changes associated with tissue distortion by invasive cancer. As a result, positive surgical margins occur in a significant portion of tumor resections, which is directly correlated with a poor outcome.

METHODS

A comprehensive review of studies evaluating optical imaging techniques is performed.

RESULTS

A variety of cancer imaging techniques have been adapted or developed for intraoperative surgical guidance that have been shown to improve functional and oncologic outcomes in randomized clinical trials. There are also a large number of novel, cancer-specific contrast agents that are in early stage clinical trials and preclinical development that demonstrate significant promise to improve real-time detection of subclinical cancer in the operative setting.

CONCLUSIONS

There has been an explosion of intraoperative imaging techniques that will become more widespread in the next decade.

Targeting the interleukin-11 receptor α in metastatic prostate cancer: A first-in-man study

BACKGROUND

Receptors in tumor blood vessels are attractive targets for ligand-directed drug discovery and development. The authors have worked systematically to map human endothelial receptors (“vascular zip codes”) within tumors through direct peptide library selection in cancer patients. Previously, they selected a ligand-binding motif to the interleukin-11 receptor alpha (IL-11Rα) in the human vasculature.

METHODS

The authors generated a ligand-directed, peptidomimetic drug (bone metastasis-targeting peptidomimetic-11 [BMTP-11]) for IL-11Rα–based human tumor vascular targeting. Preclinical studies (efficacy/toxicity) included evaluating BMTP-11 in prostate cancer xenograft models, drug localization, targeted apoptotic effects, pharmacokinetic/pharmacodynamic analyses, and dose-range determination, including formal (good laboratory practice) toxicity across rodent and nonhuman primate species. The initial BMTP-11 clinical development also is reported based on a single-institution, open-label, first-in-class, first-in-man trial (National Clinical Trials number NCT00872157) in patients with metastatic, castrate-resistant prostate cancer.

RESULTS

BMTP-11 was preclinically promising and, thus, was chosen for clinical development in patients. Limited numbers of patients who had castrate-resistant prostate cancer with osteoblastic bone metastases were enrolled into a phase 0 trial with biology-driven endpoints. The authors demonstrated biopsy-verified localization of BMTP-11 to tumors in the bone marrow and drug-induced apoptosis in all patients. Moreover, the maximum tolerated dose was identified on a weekly schedule (20-30 mg/m²). Finally, a renal dose-limiting toxicity was determined, namely, dose-dependent, reversible nephrotoxicity with proteinuria and casts involving increased serum creatinine.

CONCLUSIONS

These biologic endpoints establish BMTP-11 as a targeted drug candidate in metastatic, castrate-resistant prostate cancer. Within a larger discovery context, the current findings indicate that functional tumor vascular ligand-receptor targeting systems may be identified through direct combinatorial selection of peptide libraries in cancer patients. Cancer 2015;121:2411–2421. © 2015 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society.

The authors report on the development of a new ligand-directed peptidomimetic (termed bone metastasis-targeting peptidomimetic-11) for interleukin-11 receptor-based human vascular targeting, including the translation from preclinical studies to a first-in-class, first-in-man clinical trial in patients with metastatic, castrate-resistant prostate cancer.

Interleukin-11 receptor α is overexpressed in human osteosarcoma, and near-infrared-labeled IL-11Rα imaging agent could detect osteosarcoma in mouse tumor xenografts

IL-11Rα is an important cytokine receptor that links oxidative stress and compensatory proliferation. Mounting evidence has demonstrated that IL-11Rα regulates autoimmune demyelination and the invasion and proliferation of cancer cells, making it an important therapeutic target for molecular targeted therapy. Moreover, overexpression of IL-11Rα indicates a poor long-term prognosis in cancer patients. However, the expression status and its potential as a biomarker for diagnosis, tumor imaging, and prognosis in osteosarcoma remain to be determined. We report here that IL-11Rα is highly expressed in osteosarcoma and near-infrared (NIR)-labeled IL-11Rα imaging agent could detect osteosarcoma in mouse tumor xenografts. In a panel of human osteosarcoma specimens, IL-11Rα protein was positively stained in most cases by immunohistochemistry. Western blot analysis and flow cytometry showed that IL-11Rα was overexpressed in osteosarcoma SOSP-9607 cells. Cell-binding assay demonstrated specific binding of the IL-11Rα targeted imaging agent to osteosarcoma SOSP-9607 cells in vitro. In addition, administration of an IL-11Rα targeted imaging agent in a nude mice orthotopic model resulted in selective accumulation of NIR fluorescent signals in the bone tumor as well as several metabolic organs. These results indicate that IL-11Rα is a potential target for the development of molecular targeted therapy and noninvasive tumor imaging in human osteosarcoma. Furthermore, NIR-labeled IL-11Rα imaging agent is a promising lead for the development of a tumor in vivo imaging method at the molecular level in the management of human osteosarcoma.

Targeted multimodal imaging modalities

Molecular imaging non-invasively visualizes and characterizes the biologic functions and mechanisms in living organisms at a molecular level. In recent years, advances in imaging instruments, imaging probes, assay methods, and quantification techniques have enabled more refined and reliable images for more accurate diagnoses. Multimodal imaging combines two or more imaging modalities into one system to produce details in clinical diagnostic imaging that are more precise than conventional imaging. Multimodal imaging offers complementary advantages: high spatial resolution, soft tissue contrast, and biological information on the molecular level with high sensitivity. However, combining all modalities into a single imaging probe involves problems yet to be solved due to the requirement of high dose contrast agents for a component of imaging modality with low sensitivity. The introduction of targeting moieties into the probes enhances the specific binding of targeted multimodal imaging modalities and selective accumulation of the imaging agents at a disease site to provide more accurate diagnoses. An extensive list of prior reports on the targeted multimodal imaging probes categorized by each modality is presented and discussed. In addition to accurate diagnosis, targeted multimodal imaging agents carrying therapeutic medications make it possible to visualize the theranostic effect and the progress of disease. This will facilitate the development of an imaging-guided therapy, which will widen the application of the targeted multimodal imaging field to experiments in vivo.

Dual-modality micro-positron emission tomography/computed tomography and near-infrared fluorescence imaging of EphB4 in orthotopic glioblastoma xenograft models

PURPOSE

In glioblastoma, EphB4 receptors, a member of the largest family of receptor tyrosine kinases, are overexpressed in both tumor cells and angiogenic blood vessels. The purpose of this study was to examine whether the EphB4-binding peptide TNYL-RAW labeled with both (64)Cu and near-infrared fluorescence dye Cy5.5 could be used as a molecular imaging agent for dual-modality positron emission tomography/computed tomography [PET/CT] and optical imaging of human glioblastoma in orthotopic brain tumor models.

MATERIALS AND METHODS

TNYL-RAW was conjugated to Cy5.5 and the radiometal chelator 1,4,7,10-tetraazadodecane-N,N',N″,N‴-tetraacetic acid. The conjugate was then labeled with (64)Cu for in vitro binding and in vivo dual μPET/CT and optical imaging studies in nude mice implanted with EphB4-expressing U251 and EphB4-negative U87 human glioblastoma cells. Tumors and brains were removed at the end of the imaging sessions for immunohistochemical staining and fluorescence microscopic examinations.

RESULTS

μPET/CT and near-infrared optical imaging clearly showed specific uptake of the dual-labeled TNYL-RAW peptide in both U251 and U87 tumors in the brains of the nude mice after intravenous injection of the peptide. In U251 tumors, the Cy5.5-labeled peptide colocalized with both tumor blood vessels and tumor cells; in U87 tumors, the tracer colocalized only with tumor blood vessels, not with tumor cells.

CONCLUSIONS

Dual-labeled EphB4-specific peptide could be used as a noninvasive molecular imaging agent for PET/CT and optical imaging of glioblastoma owing to its ability to bind to both EphB4-expressing angiogenic blood vessels and EphB4-expressing tumor cells.

Intra-colonic administration of a polymer-bound NIRF probe for improved colorectal cancer detection during colonoscopy

There is increasing interest in the use of nanoparticle imaging probes for cancer diagnosis. However, various biological barriers limit the efficient delivery of nanoparticles to tumors following parenteral administration. We have investigated the applicability of a water-soluble polymeric imaging probe for improving the detection of gastrointestinal (GI) tumors after intra-luminal (colonic) administration. N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers bearing either fluorescein-isothiocyanate (FITC) or near-infrared fluorescence (NIRF) dye (IR-783) were conjugated with EPPT1 peptide, derived from the CDR3 Vh region of a monoclonal antibody (ASM2) raised against human epithelial cancer cells, for targeting under-glycosylated mucin-1 (uMUC-1) expressed in neoplastic tissues. The targeted FITC-labeled copolymer, P-(EPPT1)-FITC, was investigated for its ability to bind human CRC cells and tissue specimens in vitro. The uMUC-1-targeted NIRF-labeled copolymer, P-(EPPT1)-IR783, was assessed for its ability to detect colonic lesions in vivo. P-(EPPT1)-FITC demonstrated superior binding to colorectal cancer (CRC) cells that over-express the uMUC-1 antigen and exhibited selectivity towards human CRC tissue specimens, as compared to adjacent normal tissues from the same patient. When applied intra-colonically, P-(EPPT1)-IR783 significantly accumulated in cancerous tissue, relative to the adjacent normal mucosa of HT29 and LS174T tumor-bearing mice, and demonstrated higher signal intensities in colonic tumors, as compared to the non-targeted P-(GG-OH)-IR783 probe (i.e., without EPPT1). We found that P-(GG-OH)-IR783 can also accumulate specifically at tumor sites. The cancer-specific uptake and retention of P-(GG-OH)-IR783 was not mediated by organic anion transporting peptides (OATPs). Our findings indicate that the polymer-bound NIRF probe can successfully detect solid tumors in the GI tract following intra-colonic administration, and could be used in conjunction with colonoscopic procedures to improve the sensitivity of colonoscopies for polyp detection.

Multi-modality imaging to determine the cellular heterogeneity of nasopharyngeal carcinoma components

Nasopharyngeal carcinoma (NPC) is an endemic public health problem in South and Southeast Asian countries. The disease components at the molecular level are unclear and need exploration for the development of future individualized molecular medicine. The purpose of this study was to test the feasibility of target-specific agents to detect different components of NPC. The binding capability of human NPC cell lines was determined by incubation with either agents that specifically target the metabolic status, host cytokines, and stroma. Mice bearing human NPC xenografts were injected with the same test agents plus a clinical molecular imaging agent (18F-fluorodeoxyglucose) and computer tomography (CT) contrast agent. In vitro cell studies have demonstrated that target-specific agents bind to NPC cells with significantly higher signal intensities. Those agents not only bound to the cell membrane but also penetrated into the cytosol and cell nuclei. In vivo imaging demonstrated that the human NPC xenografts revealed high glucose uptake and a profound vasculature in the tumor. All agents were bound to the tumor regions with a high tumor-to-muscle ratio. Finally, all imaging data were validated by histopathological results. Multiple, target-specific agents determine the dynamic and heterogeneous components of NPC at the molecular level.

Bimodal imaging probes for combined PET and OI: recent developments and future directions for hybrid agent development

Molecular imaging—and especially positron emission tomography (PET)—has gained increasing importance for diagnosis of various diseases and thus experiences an increasing dissemination. Therefore, there is also a growing demand for highly affine PET tracers specifically accumulating and visualizing target structures in the human body. Beyond the development of agents suitable for PET alone, recent tendencies aim at the synthesis of bimodal imaging probes applicable in PET as well as optical imaging (OI), as this combination of modalities can provide clinical advantages. PET, due to the high tissue penetration of the γ-radiation emitted by PET nuclides, allows a quantitative imaging able to identify and visualize tumors and metastases in the whole body. OI on the contrary visualizes photons exhibiting only a limited tissue penetration but enables the identification of tumor margins and infected lymph nodes during surgery without bearing a radiation burden for the surgeon. Thus, there is an emerging interest in bimodal agents for PET and OI in order to exploit the potential of both imaging techniques for the imaging and treatment of tumor diseases. This short review summarizes the available hybrid probes developed for dual PET and OI and discusses future directions for hybrid agent development.

Rational design of fluorophores for in vivo applications

Several classes of small organic molecules exhibit properties that make them suitable for fluorescence in vivo imaging. The most promising candidates are cyanines, squaraines, boron dipyrromethenes, porphyrin derivatives, hydroporphyrins, and phthalocyanines. The recent designing and synthetic efforts have been dedicated to improving their optical properties (shift the absorption and emission maxima toward longer wavelengths and increase the brightness) as well as increasing their stability and water solubility. The most notable advances include development of encapsulated cyanine dyes with increased stability and water solubility, squaraine rotaxanes with increased stability, long-wavelength-absorbing boron dipyrromethenes, long-wavelength-absorbing porphyrin and hydroporphyrin derivatives, and water-soluble phthalocyanines. Recent advances in luminescence and bioluminescence have made self-illuminating fluorophores available for in vivo applications. Development of new types of hydroporphyrin energy-transfer dyads gives the promise for further advances in in vivo multicolor imaging.

Multiple target-specific molecular agents for detection and image analysis of breast cancer characteristics in mice

Breast cancer is a heterogenetic tumor at the cellular level with multiple factors and components. The inconsistent expression of molecular markers during disease progression reduces the accuracy of diagnosis and efficacy of target-specific therapy. Single target-specific imaging agents can only provide limited tumor information at one time point. In contrast, multiple target-specific imaging agents can increase the accuracy of diagnosis. The aim of this study was to demonstrate the ability of multi-agent imaging to discriminate such differences in single tumor. Mice bearing human cancer cell xenografts were tested to determine individual differences under optimal experimental conditions. Neovasculature agent (RGD peptide), tumor stromal agent (matrix metalloproteinase), and tumor cell markers (epidermal growth factor, Her-2, interleukin 11) imaging agents were labeled with reporters. 18F-Fluorodeoxyglucose was used to evaluate the tumor glucose status. Optical, X-ray, positron emission tomography, and computer tomography imaging modalities were used to determine tumor characteristics. Tumor size and imaging data demonstrated that individual differences exist under optimal experimental conditions. The target-specific agents used in the study bind to human breast cancer cell lines in vitro and xenografts in vivo. The pattern of binding corresponds to that of tumor markers. Multi-agent imaging had complementary effects in tumor detection. Multiple noninvasive imaging agents and modalities are complementary in the interrogation of unique biological information from each individual tumor. Such multi-agent approaches provide methods to study several disease components simultaneously. In addition, the imaging results provide information on disease status at the molecular level.

Heptamethine cyanine based (64)Cu-PET probe PC-1001 for cancer imaging: synthesis and in vivo evaluation

PURPOSE

Development of a heptamethine cyanine based tumor-targeting PET imaging probe for noninvasive detection and diagnosis of breast cancer.

METHODS

Tumor-specific heptamethine-cyanine DOTA conjugate complexed with Cu-64 (PC-1001) was synthesized for breast cancer imaging. In vitro cellular uptake studies were performed in the breast cancer MCF-7 and noncancerous breast epithelial MCF-10A cell lines to establish tumor specificity. In vivo time-dependent fluorescence and PET imaging of breast tumor xenografts in mice were performed. Blood clearance, biodistribution, and tumor-specific uptake and plasma binding of PC-1001 were quantified. Tumor histology (H&E staining) and fluorescence imaging were examined.

RESULTS

PC-1001 displayed similar fluorescence properties (ε=82,880cm(-1)M(-1), Ex/Em=750/820nm) to the parental dye. Time-dependent cellular accumulation indicated significantly higher probe uptake (>2-fold, 30min) in MCF-7 than MCF-10A cells and the uptake was observed to be mediated by organic anion transport peptides (OATPs) system. In vivo studies revealed that PC-1001 has desirable accumulation profile in tumor tissues, with tumor versus muscle uptake of about 4.3 fold at 24h and 5.8 fold at 48h post probe injections. Blood half-life of PC-1001 was observed to be 4.3±0.2h. Microscopic fluorescence imaging of harvested tumor indicated that the uptake of PC-1001 was restricted to viable rather than necrotic tumor cells.

CONCLUSIONS

A highly efficient tumor-targeting PET/fluorescence imaging probe PC-1001 is synthesized and validated in vitro in MCF-7 breast cancer cells and in vivo in mice breast cancer xenograft model.

Synthesis and characterization of near IR fluorescent albumin nanoparticles for optical detection of colon cancer

Near IR (NIR) fluorescent human serum albumin (HSA) nanoparticles hold great promise as contrast agents for tumor diagnosis. HSA nanoparticles are considered to be biocompatible, non-toxic and non-immunogenic. In addition, NIR fluorescence properties of these nanoparticles are important for in vivo tumor diagnostics, with low autofluorescence and relatively deep penetration of NIR irradiation due to low absorption of biomatrices. The present study describes the synthesis of new NIR fluorescent HSA nanoparticles, by entrapment of a NIR fluorescent dye within the HSA nanoparticles, which also significantly increases the photostability of the dye. Tumor-targeting ligands such as peanut agglutinin (PNA) and anti-carcinoembryonic antigen antibodies (anti-CEA) were covalently conjugated to the NIR fluorescent albumin nanoparticles, increasing the potential fluorescent signal in tumors with upregulated corresponding receptors. Specific colon tumor detection by the NIR fluorescent HSA nanoparticles was demonstrated in a chicken embryo model and a rat model. In future work we also plan to encapsulate cancer drugs such as doxorubicin within the NIR fluorescent HSA nanoparticles for both colon cancer imaging and therapy.

The binding characteristics of a cyclic nonapeptide, c(CGRRAGGSC), in LNCaP human prostate cancer cells

Previous studies have demonstrated that interleukin-11 (IL-11) and the IL-11 receptor (IL-11R) are associated with the regulation of tumor progression and may play a significant role in bone metastases. The nonapeptide structure c(CGRRAGGSC) is a phage display-selected IL-11 mimic, which binds to IL-11R. The aim of this study is to investigate the binding characteristics of a cyclic nonapeptide c(CGRRAGGSC) in LNCaP human prostate cancer cells. To investigate its binding and uptake effects, c(CGRRAGGSC) was labeled with a fluorescent dye, LSS670. The binding location of LSS670 cyclic nonapeptide in LNCaP cells was investigated by fluorescence microscopy. Flow cytometry was used to detect the fluorescence of LSS670-c(CGRRAGGSC) in LNCaP cells. The binding of LSS670-c(CGRRAGGSC) in LNCaP cells was inhibited by unlabeled cyclic nonapeptide, depending on the varying density of c(CGRRAGGSC) and different time points. The molecular probe bound to the LNCaP cell membrane and cytoplasm through fluorescence tracing. In the saturation experiments performed in vitro, the K(d) value was 3.2±0.02 nM and the B(max) value was 754±34 fmol/mg.pro. The 50% inhibiting concentration (IC(50)) was 6.31±0.12 nmol/l and the K(i) value was 2.11±0.14 nmol/l in competitive inhibition experiments. Our results suggest that c(CGRRAGGSC) is able to specifically bind to LNCaP cells through a receptor-mediated pathway.

Dual-labeling strategies for nuclear and fluorescence molecular imaging: a review and analysis

Molecular imaging is used for the detection of biochemical processes through the development of target-specific contrast agents. Separately, modalities such as nuclear and near-infrared fluorescence (NIRF) imaging have been shown to non-invasively monitor disease. More recently, merging of these modalities has shown promise owing to their comparable detection sensitivity and benefited from the development of dual-labeled imaging agents. Dual-labeled agents hold promise for whole-body and intraoperative imaging and could bridge the gap between surgical planning and image-guided resection with a single, molecularly targeted agent. In this review, we summarized the literature for dual-labeled antibodies and peptides that have been developed and have highlighted key considerations for incorporating NIRF dyes into nuclear labeling strategies. We also summarized our findings on several commercially available NIRF dyes and offer perspectives for developing a toolkit to select the optimal NIRF dye and radiometal combination for multimodality imaging.

DOTAGA-anhydride: a valuable building block for the preparation of DOTA-like chelating agents

A DOTA derivative that contains an anhydride group was readily synthesized by reacting DOTAGA with acetic anhydride and its reactivity was investigated. Opening the anhydride with propylamine led to the selective formation of one of two possible regioisomers. The structure of the obtained isomer was unambiguously determined by 1D and 2D NMR experiments, including COSY, HMBC, and NOESY techniques. This bifunctional chelating agent offers a convenient and attractive approach for labeling biomolecules and, more generally, for the synthesis of a large range of DOTA derivatives. The scope of the reaction was extended to prepare DOTA-like compounds that contained various functional groups, such as isothiocyanate, thiol, ester, and amino acid moieties. This versatile building block was also used for the synthesis of a bimodal tag for SPECT or PET/optical imaging.

Developing fluorescent hyaluronan analogs for hyaluronan studies

Two kinds of fluorescent hyaluronan (HA) analogs, one serving as normal imaging agent and the other used as a biosensitive contrast agent, were developed for the investigation of HA uptake and degradation. Our approach of developing HA imaging agents depends on labeling HA with varying molar percentages of a near-infrared (NIR) dye. At low labeling ratios, the hyaluronan uptake can be directly imaged while at high labeling ratios, the fluorescent signal is quenched and signal generation occurs only after degradation. It is found that the conjugate containing 1%-2% NIR dye can be used as a normal optical imaging agent, while bioactivable imaging agents are formed at 6% to 17% dye loading. It was determined that the conjugation of dye to HA with different loading percentages does not impact HA biodegradation by hyaluronidase (Hyal). The feasibility of using these two NIR fluorescent hyaluronan analogs for HA investigation was evaluated in vivo with optical imaging. The data demonstrates that the 1% dye loaded fluorescent HA can be used to monitor the behavior of HA and its fragments, whereas bioactivatable HA imaging agent (17% dye in HA) is more suitable for detecting HA fragments.

Imaging prostate cancer lymph node metastases with a multimodality contrast agent

BACKGROUND

Methods to detect lymph node (LN) metastases in prostate cancer (PCa) are limited. Pelvic LN dissection is commonly performed during prostatectomy, but often followed by morbid complications. More refined methods for detecting LN invasion are needed.

METHODS

We developed a dual-labeled targeting agent having a near-infrared (NIR) fluorophore for intraoperative guidance, and a conventional radiotracer for detection of LN metastasis. Nu/Nu mice were orthotopically implanted with DsRed-expressing human PCa (PC3) cells. Antibody (Ab) specific for epithelial cell adhesion molecule was conjugated to DOTA, IRDye 800CW, and radiolabeled with (64) Cu. Dual-labeled Ab was administered intravenously at 10-12 weeks post-implantation, and positron emission tomography/computed tomography (PET/CT) and fluorescence imaging were performed within 18-24 hr.

RESULTS

Metastasis to lumbar LNs was detected by DsRed fluorescence imaging, as well as pathology, in 75% of mice having pathology-confirmed primary prostate tumors. These metastases were also detected by NIR fluorescence imaging. In some cases, metastases to sciatic, medial, renal, and axillary nodes were also detected. For all LNs examined, no significant differences were found between the percentages of metastases detected by NIR imaging (63%) and µPET/CT (64%) (P = 0.93), or between those detected by DsRed imaging (25%) and pathological examination (19%) (P = 0.12).

CONCLUSION

This study demonstrates that a multimodality contrast agent is useful for early detection of metastatic disease, and has applications for intraoperative PCa treatment. Further agent optimization is necessary to enhance specificity, and provide validation for prostate and other LN metastasizing epithelial cancers.

Genetically modified T cells targeting interleukin-11 receptor α-chain kill human osteosarcoma cells and induce the regression of established osteosarcoma lung metastases

The treatment of osteosarcoma pulmonary metastases remains a challenge. T cells genetically modified to express a chimeric antigen receptor (CAR), which recognizes a tumor-associated antigen, have shown activity against hematopoietic malignancies in clinical trials, but this requires the identification of a specific receptor on the tumor cell. In the current study, we found that interleukin (IL)-11Rα was selectively expressed on 14 of 16 osteosarcoma patients' lung metastases and four different human osteosarcoma cell lines, indicating that IL-11Rα may be a novel target for CAR-specific T-cell therapy. IL-11Rα expression was absent or low in normal organ tissues, with the exception of the gastrointestinal tract. IL-11Rα-CAR-specific T cells were obtained by non-viral gene transfer of Sleeping Beauty DNA plasmids and selectively expanded ex vivo using artificial antigen-presenting cells derived from IL-11Rα + K562 cells genetically modified to coexpress T-cell costimulatory molecules. IL-11Rα-CAR(+) T cells killed all four osteosarcoma cell lines in vitro; cytotoxicity correlated with the level of IL-11Rα expression on the tumor cells. Intravenous injection of IL-11Rα-CAR(+) T cells into mice resulted in the regression of osteosarcoma pulmonary metastases with no organ toxicity. Together, the data suggest that IL-11Rα-CAR T cells may represent a new therapy for patients with osteosarcoma pulmonary metastases.

Rational chemical design of the next generation of molecular imaging probes based on physics and biology: mixing modalities, colors and signals

In recent years, numerous in vivo molecular imaging probes have been developed. As a consequence, much has been published on the design and synthesis of molecular imaging probes focusing on each modality, each type of material, or each target disease. More recently, second generation molecular imaging probes with unique, multi-functional, or multiplexed characteristics have been designed. This critical review focuses on (i) molecular imaging using combinations of modalities and signals that employ the full range of the electromagnetic spectra, (ii) optimized chemical design of molecular imaging probes for in vivo kinetics based on biology and physiology across a range of physical sizes, (iii) practical examples of second generation molecular imaging probes designed to extract complementary data from targets using multiple modalities, color, and comprehensive signals (277 references).

NEAR-INFRARED DYES: Probe Development and Applications in Optical Molecular Imaging

The recent emergence of optical imaging has brought forth a unique challenge for chemists: development of new biocompatible dyes that fluoresce in the near-infrared (NIR) region for optimal use in biomedical applications. This review describes the synthesis of NIR dyes and the design of probes capable of noninvasively imaging molecular events in small animal models.

A review of NIR dyes in cancer targeting and imaging

The development of multifunctional agents for simultaneous tumor targeting and near infrared (NIR) fluorescence imaging is expected to have significant impact on future personalized oncology owing to the very low tissue autofluorescence and high tissue penetration depth in the NIR spectrum window. Cancer NIR molecular imaging relies greatly on the development of stable, highly specific and sensitive molecular probes. Organic dyes have shown promising clinical implications as non-targeting agents for optical imaging in which indocyanine green has long been implemented in clinical use. Recently, significant progress has been made on the development of unique NIR dyes with tumor targeting properties. Current ongoing design strategies have overcome some of the limitations of conventional NIR organic dyes, such as poor hydrophilicity and photostability, low quantum yield, insufficient stability in biological system, low detection sensitivity, etc. This potential is further realized with the use of these NIR dyes or NIR dye-encapsulated nanoparticles by conjugation with tumor specific ligands (such as small molecules, peptides, proteins and antibodies) for tumor targeted imaging. Very recently, natively multifunctional NIR dyes that can preferentially accumulate in tumor cells without the need of chemical conjugation to tumor targeting ligands have been developed and these dyes have shown unique optical and pharmaceutical properties for biomedical imaging with superior signal-to-background contrast index. The main focus of this article is to provide a concise overview of newly developed NIR dyes and their potential applications in cancer targeting and imaging. The development of future multifunctional agents by combining targeting, imaging and even therapeutic routes will also be discussed. We believe these newly developed multifunctional NIR dyes will broaden current concept of tumor targeted imaging and hold promise to make an important contribution to the diagnosis and therapeutics for the treatment of cancer.