Evaluation of 64Cu- and 125I-Radiolabeled Bitistatin as Potential Agents for Targeting αvβ3 Integrins in Tumor Angiogenesis

Biological Effects of Animal Venoms on the Human Immune System

Venoms are products of specialized glands and serve many living organisms to immobilize and kill prey, start digestive processes and act as a defense mechanism. Venoms affect different cells, cellular structures and tissues, such as skin, nervous, hematological, digestive, excretory and immune systems, as well as the heart, among other structures. Components of both the innate and adaptive immune systems can be stimulated or suppressed. Studying the effects on the cells and molecules produced by the immune system has been useful in many biomedical fields. The effects of venoms can be the basis for research and development of therapeutic protocols useful in the modulation of the immunological system, including different autoimmune diseases. This review focuses on the understanding of biological effects of diverse venom on the human immune system and how some of their components can be useful for the study and development of immunomodulatory drugs.

Structure-Function Relationship of the Disintegrin Family: Sequence Signature and Integrin Interaction

Disintegrins are small cysteine-rich proteins found in a variety of snake venom. These proteins selectively modulate integrin function, heterodimeric receptors involved in cell-cell and cell-matrix interaction that are widely studied as therapeutic targets. Snake venom disintegrins emerged from the snake venom metalloproteinase and are classified according to the sequence size and number of disulfide bonds. Evolutive structure and function diversification of disintegrin family involves a stepwise decrease in the polypeptide chain, loss of cysteine residues, and selectivity. Since the structure elucidation of echistatin, the description of the structural properties of disintegrins has allowed the investigation of the mechanisms involved in integrin-cell-extracellular matrix interaction. This review provides an analysis of the structures of all family groups enabling the description of an expanded classification of the disintegrin family in seven groups. Each group presents a particular disulfide pattern and sequence signatures, facilitating the identification of new disintegrins. The classification was based on the disintegrin-like domain of the human metalloproteinase (ADAM-10). We also present the sequence and structural signatures important for disintegrin-integrin interaction, unveiling the relationship between the structure and function of these proteins.

South American snake venoms with abundant neurotoxic components. Composition and toxicological properties. A literature review

In South America there are three snake genera with predominantly neurotoxic venoms: Crotalus, Micrurus and Hydrophis, which include nine species/subspecies, 97 species and a single marine species, respectively. Although accidents with neurotoxic venoms are less frequent than those with anticoagulant, cytotoxic or necrotic venoms (e.g. from Bothrops), they are of major public health importance. Venoms from genus Crotalus have been extensively studied, while data on the venoms from the other two genera are very limited, especially for Hydrophis. The venoms of North and South American Crotalus species show biochemical and physiopathological differences. The former species cause bothrops-like envenomation symptoms, while the latter mainly have neurotoxic and myotoxic effects, leading to respiratory paralysis and, occasionally, renal failure by myoglobinuria and death, often with no local lesions. Micrurus and Hydrophis also cause neurotoxic envenomations. Many studies have isolated, identified and characterized new enzymes and toxins, thus expanding the knowledge of snake venom composition. The present review summarizes the currently available information on neurotoxic venoms from South American snakes, with a focus on protein composition and toxicological properties. It also includes some comments concerning potential medical applications of elapid and crotalic toxins.

Biomedical applications of snake venom: from basic science to autoimmunity and rheumatology

Snake venoms have components with diverse biological actions that are extensively studied to identify elements that may be useful in biomedical sciences. In the field of autoimmunity and rheumatology, various findings useful for the study of diseases and potential drug development have been reported. The study of disintegrins, proteins that block the action of integrins, has been useful for the development of antiplatelet agents and principles for the development of immunosuppressants and antineoplastics. Several proteins in snake venoms act on the coagulation cascade, activating factors that have allowed the development of tests for the study of coagulation, including Russell's viper venom time, which is useful in the diagnosis of antiphospholipid syndrome. Neurotoxins with either pre- or postsynaptic effects have been used to study neurogenic synapses and neuromuscular plaques and the development of analgesics, muscle relaxants and drugs for neurodegenerative diseases. Various components act by inhibiting cells and proteins of the immune system, which will allow the development of anti-inflammatory and immunosuppressive drugs. This review summarizes the usefulness of the components of snake venoms in the fields of autoimmunity and rheumatology, which can serve as a basis for diverse translational research.

Efficient 125I-radiolabeling of biomolecules using a strain-promoted oxidation-controlled cyclooctyne-1,2-quinone cycloaddition reaction

We report a novel 1,2-catechol based radioiodinated precursor for radioiodination of bicyclo[6.1.0]nonyne (BCN) installed biologically active molecules using a strain-promoted oxidation-controlled cyclooctyne-1,2-quinone cycloaddition reaction (SPOCQ) under ambient conditions. Compared to the reported methodologies, the new strategy demonstrates some clear advantages, including high in vitro and in vivo stability, high radiochemical yield, and exceptionally fast reaction kinetics at micro-molar concentration.

The Application of Nanotechnology in the Codelivery of Active Constituents of Plants and Chemotherapeutics for Overcoming Physiological Barriers during Antitumor Treatment

Antitumor therapy using a combination of drugs has shown increased clinical efficacy. Active constituents derived from plants can offer several advantages, such as high efficiacy, low toxicity, extensive effects, and multiple targets. At present, the combination of plants' active constituents and chemotherapeutic drugs has attracted increased attention. Nanodrug delivery systems (NDDSs) have been widely used in tumor-targeted therapy because of their efficacy of delivering antitumor drugs. The in vivo process of tumor-targeted NDDSs has several steps. They include blood circulation, tumor accumulation and penetration, target cell internalization and uptake, and drug release and drug response. In each step, NDDSs encounter multiple barriers that prevent their effective delivery to target sites. Studies have been performed to find alternative strategies to overcome these barriers. We reviewed the recent progress of codelivery of active constituents of plants and chemotherapeutics using NDDSs. Progress into transversing the physiological barriers for more effective in vivo antitumor delivery will be discussed in this review.

Copper-64 Radiopharmaceuticals for Oncologic Imaging

The positron emitting radionuclide (64)Cu has a radioactive half-life of 12.7 hours. The decay characteristics of (64)Cu allow for PET images that are comparable in quality to those obtained using (18)F. Given the longer radioactive half-life of (64)Cu compared with (18)F and the versatility of copper chemistry, copper is an attractive alternative to the shorter-lived nuclides for PET imaging of peptides, antibodies, and small molecules that may require longer circulation times. This article discusses a number of copper radiopharmaceuticals, such as Cu-ATSM, that have been translated to the clinic and new developments in copper-based radiopharmaceuticals.

Disintegrins from snake venoms and their applications in cancer research and therapy

Integrins regulate diverse functions in cancer pathology and in tumor cell development and contribute to important processes such as cell shape, survival, proliferation, transcription, angiogenesis, migration, and invasion. A number of snake venom proteins have the ability to interact with integrins. Among these are the disintegrins, a family of small, non-enzymatic, and cysteine-rich proteins found in the venom of numerous snake families. The venom proteins may have a potential role in terms of novel therapeutic leads for cancer treatment. Disintegrin can target specific integrins and as such it is conceivable that they could interfere in important processes involved in carcinogenesis, tumor growth, invasion and migration. Herein we present a survey of studies involving the use of snake venom disintegrins for cancer detection and treatment. The aim of this review is to highlight the relationship of integrins with cancer and to present examples as to how certain disintegrins can detect and affect biological processes related to cancer. This in turn will illustrate the great potential of these molecules for cancer research. Furthermore, we also outline several new approaches being created to address problems commonly associated with the clinical application of peptide-based drugs such as instability, immunogenicity, and availability.

PEGylation of cationic, shell-crosslinked-knedel-like nanoparticles modulates inflammation and enhances cellular uptake in the lung

The airway provides a direct route for administration of nanoparticles bearing therapeutic or diagnostic payloads to the lung, however optimization of nanoplatforms for intracellular delivery remains challenging. Poly(ethylene glycol) (PEG) surface modification improves systemic performance but less is known about PEGylated nanoparticles administered to the airway. To test this, we generated a library of cationic, shell crosslinked knedel-like nanoparticles (cSCKs), including PEG (1.5 kDa PEG; 2, 5, 10 molecules/polymer arm) on the outer shell. Delivery of PEGylated cSCK to the mouse airway showed significantly less inflammation in a PEG dose-dependent manner. PEGylation also enhanced the entry of cSCKs in lung alveolar epithelial cells and improved surfactant penetration. The PEGylation effect could be explained by the altered mechanism of endocytosis. While non-PEGylated cSCKs used the clathrin-dependent route for endocytosis, entry of PEGylated cSCK was clathrin-independent. Thus, nanoparticle surface modification with PEG represents an advantageous design for lung delivery.

FROM THE CLINICAL EDITOR

In this study, the effects of PEGylation were studied on cross linked knedel-like nanoparticles in drug delivery through the lungs, demonstrating less airway inflammation in the studied model than with non-PEGylated nanoparticles, which suggests an overall favorable profile of PEGylated nanoparticles for alveolar delivery.

Radioluminescent gold nanocages with controlled radioactivity for real-time in vivo imaging

Cerenkov luminescence imaging based on light emission from the decay of radionuclides has recently drawn great interest in molecular imaging. In this paper, we report for the first time the Cerenkov luminescence phenomenon of (198)Au isotope, as well as a facile route to the preparation of radioluminescent Au nanocages without additional radiolabeling or dye conjugation. The specific radioactivity of the Au nanocages could be easily and precisely controlled by varying the concentration of H(198)AuCl(4) precursor used for the galvanic replacement reaction. The direct incorporation of (198)Au atoms into the structure of Au nanocages enabled the ability of accurate analysis and real-time imaging in vivo. Furthermore, under biological conditions the radioactive Au nanocages were shown to emit light with wavelengths in the visible and near-infrared regions, enabling luminescence imaging of the whole mice in vivo, as well as the organs ex vivo. When combined with their favorable scattering and absorption properties in the near-infrared region, the radioactive Au nanocages can serve as a new platform for multimodality imaging and will have a significant impact on both small animal and clinical imaging.

Evaluating the pharmacokinetics and in vivo cancer targeting capability of Au nanocages by positron emission tomography imaging

Gold nanocages have recently emerged as a novel class of photothermal transducers and drug carriers for cancer treatment. However, their pharmacokinetics and tumor targeting capability remain largely unexplored due to the lack of an imaging modality for quick and reliable mapping of their distributions in vivo. Herein, Au nanocages were prepared with controlled physicochemical properties and radiolabeled with (64)Cu in high specific activities for in vivo evaluation using positron emission tomography (PET). Our pharmacokinetic studies with femtomolar administrations suggest that 30 nm nanocages had a greatly improved biodistribution profile than 55 nm nanocages, together with higher blood retention and lower hepatic and splenic uptakes. In a murine EMT-6 breast cancer model, the small cages also showed a significantly higher level of tumor uptake and a greater tumor-to-muscle ratio than the large cages. Quantitative PET imaging confirmed rapid accumulation and retention of Au nanocages inside the tumors. The ability to directly and quickly image the distribution of Au nanocages in vivo allows us to further optimize their physicochemical properties for a range of theranostic applications.

Development of a chimeric recombinant disintegrin as a cost-effective anti-cancer agent with promising translational potential

Vicrostatin (VCN) is a chimeric recombinant disintegrin generated in Origami B (DE3) Escherichia coli as a genetic fusion between the C-terminal tail of a viperid disintegrin echistatin and crotalid disintegrin contortrostatin (CN). The therapeutic modulation of multiple integrin pathways via soluble disintegrins was previously shown by us and others to elicit potent anti-angiogenic and anti-metastatic effects in several animal cancer models. Despite these favorable attributes, these polypeptides are notoriously difficult to produce recombinantly in significant quantity due to their structure which requires the correct pairing of multiple disulfide bonds for biological activity. In this report, we show that VCN can be reliably produced in large amounts (yields in excess of 200 mg of active purified disintegrin per liter of bacterial culture) in Origami B (DE3), an E. coli expression strain engineered to support the folding of disulfide-rich heterologous proteins directly in its oxidative cytoplasmic compartment. VCN retains the integrin binding specificity of both parental molecules it was derived from, but with a different binding affinity profile. While competing for the same integrin receptors that are preferentially upregulated in the tumor microenvironment, VCN exerts a potent inhibitory effect on endothelial cell (EC) migration and tube formation in a dose-dependent manner, by forcing these cells to undergo significant actin cytoskeleton reorganization when exposed to this agent in vitro. Moreover, VCN has a direct effect on breast cancer cells inhibiting their in vitro motility. In an effort to address our main goal of developing a clinically relevant delivery method for recombinant disintegrins, VCN was efficiently packaged in liposomes (LVCN) and evaluated in vivo in an animal breast cancer model. Our data demonstrate that LVCN is well tolerated, its intravenous administration inducing a significant delay in tumor growth and an increase in animal survival, results that can be partially explained by potent tumor apoptotic effects.

Advances in imaging angiogenesis and inflammation in atherosclerosis

Advances in imaging technology have provided powerful tools for dissecting the angiogenic and inflammatory aspects of atherosclerosis. Improved technology along with multi-modal approaches has expanded the utilisation of imaging. Recent advances provide the ability to better define structure and development of angiogenic vessels, identify relationships between inflammatory mediators and the vessel wall, validate biological effects of anti-inflammatory and anti-angiogenic drugs, delivery and/or targeting specific molecules to inflammatory regions of atherosclerotic plaques.

Theragnostics for tumor and plaque angiogenesis with perfluorocarbon nanoemulsions

Molecular imaging agents are extending the potential of noninvasive medical diagnosis from basic gross anatomical descriptions to complicated phenotypic characterizations based upon the recognition of unique cell-surface biochemical signatures. Although originally the purview of nuclear medicine, "molecular imaging" is now studied in conjunction with all clinically relevant imaging modalities. Of the myriad of particles that have emerged as prospective candidates for clinical translation, perfluorocarbon nanoparticles offer great potential for combining targeted imaging with drug delivery, much like the "magic bullet" envisioned by Paul Ehrlich 100 years ago. Perfluorocarbon nanoparticles, once studied in Phase III clinical trials as blood substitutes, have found new life for molecular imaging and drug delivery. The particles have been adapted for use with all clinically relevant modalities and for targeted drug delivery. In particular, their intravascular constraint due to particle size provides a distinct advantage for angiogenesis imaging and antiangiogenesis therapy. As perfluorocarbon nanoparticles have recently entered Phase I clinical study, this review provides a timely focus on the development of this platform technology and its application for angiogenesis-related pathologies.

Cell-targeting and cell-penetrating peptides for delivery of therapeutic and imaging agents

This review will discuss the basic concepts concerning the use of cell-targeting peptides (CTPs) and cell-penetrating peptides (CPPs) in the context of nanocarrier technology. It deals with the discovery and subsequent evolution of CTPs and CPPs, issues concerning their interactions with cells and their biodistribution in vivo, and their potential advantages and disadvantages as delivery agents. The article also briefly discusses several specific examples of the use of CTPs or CPPs to assist in the delivery of nanoparticles, liposomes, and other nanocarriers.

High sensitivity: high-resolution SPECT-CT/MR molecular imaging of angiogenesis in the Vx2 model

OBJECTIVES

The use of antiangiogenic therapy in conjunction with traditional chemotherapy is becoming increasingly in cancer management, but the optimal benefit of these targeted pharmaceuticals has been limited to a subset of the population treated. Improved imaging probes that permit sensitive detection and high-resolution characterization of tumor angiogenesis could improve patient risk-benefit stratification. The overarching objective of these experiments was to develop a dual modality alpha(nu)beta3-targeted nanoparticle molecular imaging agent that affords sensitive nuclear detection in conjunction with high-resolution MR characterization of tumor angiogenesis.

MATERIALS AND METHODS

In part 1, New Zealand white rabbits (n = 21) bearing 14d Vx2 tumor received either alpha(nu)beta3-targeted 99mTc nanoparticles at doses of 11, 22, or 44 MBq/kg, nontargeted 99mTc nanoparticles at 22 MBq/kg, or alpha(nu)beta3-targeted 99mTc nanoparticles (22 MBq/kg) competitively inhibited with unlabeled alpha(nu)beta3-nanoparticles. All animals were imaged dynamically over 2 hours with a planar camera using a pinhole collimator. In part 2, the effectiveness of alpha(nu)beta3-targeted 99mTc nanoparticles in the Vx2 rabbit model was demonstrated using clinical SPECT-CT imaging techniques. Next, MR functionality was incorporated into alpha(nu)beta3-targeted 99mTc nanoparticles by inclusion of lipophilic gadolinium chelates into the outer phospholipid layer, and the concept of high sensitivity - high-resolution detection and characterization of tumor angiogenesis was shown using sequential SPECT-CT and MR molecular imaging with 3D neovascular mapping.

RESULTS

alpha(nu)beta3-Targeted 99mTc nanoparticles at 22 MBq/kg produced the highest tumor-to-muscle contrast ratio (8.56 +/- 0.13, TMR) versus the 11 MBq/kg (7.32 +/- 0.12) and 44 MBq/kg (6.55 +/- 0.07) doses, (P < 0.05). TMR of nontargeted particles at 22.2 MBq/kg (5.48 +/- 0.09) was less (P < 0.05) than the equivalent dosage of alpha(nu)beta3-targeted 99mTc nanoparticles. Competitively inhibition of 99mTc alpha(nu)beta3-integrin-targeted nanoparticles at 22.2 MBq/kg reduced (P < 0.05) TMR (5.31 +/- 0.06) to the nontargeted control contrast level. Multislice CT imaging could not distinguish the presence of Vx2 tumor implanted in the popliteal fossa from lymph nodes in the same fossa or in the contralateral leg. However, the use of 99mTc alpha(nu)beta3-nanoparticles with SPECT-CT produced a clear neovasculature signal from the tumor that was absent in the nonimplanted hind leg. Using alpha(nu)beta3-targeted 99mTc-gadolinium nanoparticles, the sensitive detection of the Vx2 tumor was extended to allow MR molecular imaging and 3D mapping of angiogenesis in the small tumor, revealing an asymmetrically distributed, patchy neovasculature along the periphery of the cancer.

CONCLUSION

Dual modality molecular imaging with alpha(nu)beta3-targeted 99mTc-gadolinium nanoparticles can afford highly sensitive and specific localization of tumor angiogenesis, which can be further characterized with high-resolution MR neovascular mapping, which may predict responsiveness to antiangiogenic therapy.

Molecular imaging of vessels in mouse models of disease

Vascular imaging of angiogenesis in mouse models of disease requires multi modal imaging hardware capable of targeting both structure and function at different physical scales. The three dimensional (3D) structure and function vascular information allows for accurate differentiation between biological processes. For example, image analysis of vessel development in angiogenesis vs. arteriogenesis enables more accurate detection of biological variation between subjects and more robust and reliable diagnosis of disease. In the recent years a number of micro imaging modalities have emerged in the field as preferred means for this purpose. They provide 3D volumetric data suitable for analysis, quantification, validation, and visualization of results in animal models. This review highlights the capabilities of microCT, ultrasound and microPET for multimodal imaging of angiogenesis and molecular vascular targets in a mouse model of tumor angiogenesis. The basic principles of the imaging modalities are described and experimental results are presented.

Auger processes in the 21st century

PURPOSE

The extreme radiotoxicity of Auger electrons and their exquisite capacity to irradiate specific molecular sites has prompted scientists to extensively investigate their radiobiological effects. Their efforts have been punctuated by quadrennial international symposia that have focused on biophysical aspects of Auger processes. The latest meeting, the 6th International Symposium on Physical, Molecular, Cellular, and Medical Aspects of Auger Processes, was held 5-6 July 2007 at Harvard Medical School in Boston, Massachusetts, USA. This article provides a review of the research in this field that was published during the years 2004-2007, the period that has elapsed since the previous meeting.

CONCLUSION

The field has advanced considerably. A glimpse of the potential of this unique form of ionizing radiation to contribute to future progress in a variety of fields of study is proffered.

The Role of Integrins in Cancer and the Development of Anti-Integrin Therapeutic Agents for Cancer Therapy

Integrins have been reported to mediate cell survival, proliferation, differentiation, and migration programs. For this reason, the past few years have seen an increased interest in the implications of integrin receptors in cancer biology and tumor cell aggression. This review considers the potential role of integrins in cancer and also addresses why integrins are present attractive targets for drug design. It discusses of the several properties of the integrin-based chemotherapeutic agents currently under consideration clinically and provides an insight into cancer drug development using integrin as a target.

Minute dosages of alpha(nu)beta3-targeted fumagillin nanoparticles impair Vx-2 tumor angiogenesis and development in rabbits

Fumagillin suppresses angiogenesis in cancer models and clinical trials, but it is associated with neurotoxicity at systemic doses. In this study, alpha(nu)beta(3)-targeted fumagillin nanoparticles were used to suppress the neovasculature and inhibit Vx-2 adenocarcinoma development using minute drug doses. Tumor-bearing rabbits were treated on days 6, 9, and 12 postimplantation with alpha(nu)beta(3)-targeted fumagillin nanoparticles (30 microg/kg), alpha(nu)beta(3)-targeted nanoparticles without drug, nontargeted fumagillin nanoparticles (30 microg/kg) or saline. On day 16, MRI was performed with alpha(nu)beta(3)-targeted paramagnetic nanoparticles to quantify tumor size and assess neovascularity. Tumor volume was reduced among rabbits receiving alpha(nu)beta(3)-targeted fumagillin nanoparticles (470+/-120 mm(3)) compared with the three control groups: nontargeted fumagillin nanoparticles (1370+/-300 mm(3), P<0.05), alpha(nu)beta(3)-targeted nanoparticles without drug (1080+/-180 mm(3), P<0.05) and saline (980+/-80 mm(3), P<0.05). MR molecular imaging of control rabbits (no fumagillin) revealed a predominant peripheral distribution of neovascularity representing 7.2% of the tumor rim volume, which decreased to 2.8% (P<0.05) with alpha(nu)beta(3)-targeted fumagillin nanoparticle treatment. Microscopically, the tumor parenchyma tended to show T-cell infiltration after targeted fumagillin treatment, which was not appreciated in control animals. These results suggest that alpha(nu)beta(3)-targeted fumagillin nanoparticles could provide a safe and effective means to deliver MetAP2 inhibitors alone or in combination with cytotoxic or immunotherapy.

Differences in binding of (99m)Tc-disintegrins to integrin alphavbeta3 on tumor and vascular cells

Disintegrins, which contain an Arg-Gly-Asp sequence in their binding domains are antagonists of integrins such as alphavbeta3. The purpose of this study was to compare a range of disintegrins with different integrin selectivities for their binding behavior in vitro to vascular endothelial cells bearing alphavbeta3 and to cultured tumor cells which express alphavbeta3.

METHODS

Five disintegrins (bitistatin, kistrin, flavoridin, VLO4 and echistatin) and a cyclic pentapeptide, c[RGDyK], were radiolabeled with (99m)Tc and tested for binding to cells in vitro.

RESULTS

(99m)Tc-Kistrin, flavoridin and VLO4 had the highest binding, (99m)Tc-echistatin had moderate binding, and (99m)Tc-bitistatin and (99m)Tc-c[RGDyK] had low binding to cells. The observed binding was attributed to alphavbeta3 to various extents: echistatin, bitistatin>kistrin>flavoridin>VLO4. Cancer cells internalized bound disintegrins after binding, but endothelial cells did not. After binding to endothelial cells, (99m)Tc-kistrin was not displaced by competing peptide or plasma proteins.

CONCLUSIONS

These data suggest that radiolabeled kistrin, flavoridin and VLO4 may have advantages over labeled bitistatin and small cyclic peptides for targeting alphavbeta3 in vivo. Since receptor-bound radioligand is not internalized by endothelial cells, disintegrins may provide an advantage for targeting alphavbeta3 on vasculature because they bind strongly to surface receptors and are not readily displaced.

Imaging of Vx-2 rabbit tumors with alpha(nu)beta3-integrin-targeted 111In nanoparticles

Earlier tumor detection can improve 5-year survival of patients, particularly among those presenting with cancers less than 1 cm in diameter. alpha(nu)beta(3)-Targeted (111)In nanoparticles (NP) were developed and studied for detection of tumor angiogenesis. Studies were conducted in New Zealand white rabbits implanted 12 days earlier with Vx-2 tumor. alpha(nu)beta(3)-Targeted (111)In/NP bearing approximately 10 (111)In/NP vs. approximately 1 (111)In/NP nuclide payloads were compared to nontargeted radiolabeled control particles. In vivo competitive binding studies were used to assess ligand-targeting specificity. alpha(nu)beta(3)-Integrin-targeted NP with approximately 10 (111)In/NP provided better (p < 0.05) tumor-to-muscle ratio contrast (6.3 +/- 0.2) than approximately 1 (111)In/NP (5.1 +/- 0.1) or nontargeted particles with approximately 10 (111)In/NP (3.7 +/- 0.1) over the initial 2-hr postinjection. At 18 hr, mean tumor activity in rabbits receiving alpha(nu)beta(3)-integrin-targeted NP was 4-fold higher than the nontargeted control. Specificity of the NP for the tumor neovasculature was supported by in vivo competition studies and by fluorescence microscopy of alpha(nu)beta(3)-targeted fluorescent-labeled NP. Biodistribution studies revealed that the primary clearance organ in rabbits as a %ID/g tissue was the spleen. Circulatory half-life (t(1/2)beta) was estimated to be approximately 5 hr using a 2-compartment model. alpha(nu)beta(3)-Targeted (111)In perfluorocarbon NP may provide a clinically useful tool for sensitively detecting angiogenesis in nascent tumors, particularly in combination with secondary high-resolution imaging modalities, such as MRI.

Functional expression of bitistatin, a disintegrin with potential use in molecular imaging of thromboembolic disease

Bitistatin is a single-chain disintegrin which contains 83 amino acids and is internally crosslinked with seven disulfide bonds. This platelet aggregation inhibitor, which binds with high affinity to the alphaIIbbeta3 integrin, has potential use as the basis for a radiotracer to locate thrombi and emboli by scintigraphic imaging. A method amenable to large-scale, consistent production of bitistatin was sought. A synthetic gene coding for bitistatin was inserted into two different Escherichia coli expression vectors. One vector expressed recombinant bitistatin (rBitistatin) as a cleavable fusion protein and the other expressed rBitistatin as an isolated protein. In both cases, rBitistatin contained an additional amino acid (Gly) at the N-terminus compared with the native protein. The fusion protein was purified by affinity chromatography, then cleaved enzymatically to release rBitistatin, which was purified by reversed-phase high performance liquid chromatography (HPLC) to a single active form. The rBitistatin produced as an isolated protein was purified from cell lysate by HPLC in a reduced form, then refolded, and purified again by HPLC. Yields of active rBitistatin averaged 12 mg/L for expression as an isolated protein, 10 times as high as when the fusion protein was employed. Structural assays confirmed the expected mass and sequence of the product. Functional assays (inhibition of platelet aggregation in vitro, equilibrium binding to platelets in vitro, and binding of labeled protein to experimental thrombi and emboli in vivo) confirmed that rBitistatin retained the functional characteristics of native bitistatin.