LOADED TARGET-SPECIFIC VESICLES, METHOD OF PRODUCING THE VESICLES AND

THEIR USE IN MEDICAL IMAGING

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application no. 60/943,949, filed June 14, 2007, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to novel target-specific vesicles for medical imaging and methods for producing and using the same. The vesicles generally comprises a contrast yielding substance that can provide a signal, e.g., in magnetic resonance imaging (MRI) and fluorescence imaging.

BACKGROUND OF THE INVENTION

Different imaging techniques are currently being used to obtain anatomical images of physiological and pathological tissues and functional information on the pathogenesis of inflammation, cancer, or ischemic diseases (stroke, heart infarction). To enhance the gained information, contrast agents have been introduced to clinical practice and help to detect and visualize pathological processes.

The current contrast agents for imaging of cellular or subcellular compartments by medical imaging techniques, such as MRI, often lack a satisfactory signal-to-noise ratio and acceptable target specificity. The agents used in MRI are mainly based on a) chelated gadolinium atoms or b) superparamagnetic iron oxide nanoparticles.

Traditional agents for contrast-enhanced MRI are based on the paramagnetic properties of the gadolinium (III) ion, a rare earth metal with 7 unpaired f electrons. Gadolinium decreases the T1 relaxation time of the surrounding hydrogen nuclei, resulting in an increase of signal strength. To prevent toxic effects on liver, spleen, and bone marrow upon injection, the gadolinium ions are typically administered as high stability complexes with chelators such as diethylentriaminepentaacetic acid (DTPA) or tetraazacyclododecanetetraacetic acid (DOTA) [Wedeking et al. 1992]. Due to the low

amount of gadolinium atoms compared to the total mass of the chelated construct, the signal-to-noise ratio is insufficient for cellular or subcellular imaging with these contrast agents [Wilensky et al. 2006]. The use of contrast agents based on chelated gadolinium (III) is therefore limited to imaging of organ function, organ perfusion, inflammation, and other water accumulations [Constantine et al. 2004]. In addition, it is difficult to functionalize this group of contrast agents for targeting of specific cellular receptors or structures.

Chelated gadolinium atoms are and have been in clinical use for many years and there exist several commercial products (e.g. Gadovist 1.0 ®, Schering AG; Magnevist ®, Schering AG) for imaging of blood distribution and organ perfusion. Several research groups couple chelated gadolinium to lipid- or to polymer-based nanostructures such as micelles, nanoparticles, or liposomes, thus ensuring a higher signal yield and target specificity per targeted structure. Nonetheless, the results achieved with these concepts are generally insufficient for practical use due to the limited amount of gadolinium atoms per total mass.

New contrast agents, in particular superparamagnetic iron oxide nanoparticles (SPIO), have been developed more recently that are aimed, among others, at addressing shortcomings described above. Based on the physicochemical properties of nanoparticulate Fe ₂ θ ₃ , the SPIOs are potent contrast agents for MRI with predominant T2 effect, leading to a negative contrast enhancement in standard imaging sequences. Their T2 predominance is a serious obstacle that does not allow for the widespread use of SPIOs for cellular imaging with MRI, since it does not help the radiologist or clinician when a desired target structure produces a negative signal instead of a positive that would be clearly visible.

The most prominent example are polymer (mostly dextran) - coated superparamagnetic iron oxide (SPIO) nanoparticles with diameters ranging roughly from 5 nm to 200 nm. They have shown to be beneficial for detection of liver tumors in clinical practice and are currently being modified for improved targeting and detection

applications, e.g. for cancer or atherosclerosis. However, their predominant effect on T2/T2 ^* relaxation times and consequently a negative contrast enhancement in standard MRI sequences impede a wide application of this contrast agent for standard clinical molecular imaging.

In contrast to SPIO-based contrast agents, gadolinium-based agents show a decrease of T1 relaxation times, resulting in a positive contrast enhancement in standard MRI sequences. Most ongoing research in the field of target-specific contrast agents with predominant T1 effect relies on the above mentioned chelated gadolinium ions.

The use of crystalline gadolinium complexes promises to be an important step forward in the field of cellular or subcellular diagnostics with MRI, but problems with toxicity, water solubility, and stability need to be solved to fulfill the promises [McDonald et al. 2006].

Supramolecular nanometer-sized structures such as particles, micelles, or vesicles built from synthetic polymeric materials have aroused enormous interest in recent years and promise to be useful for novel or improved biomedical applications [Putham (2006), Uchegbu (2006)]. The common goal of these projects is the development of well-defined, self-assembled, highly organized, multifunctional, biocompatible, non-immunogenic, and target-specific tools.

Nanometer-sized polymer vesicles self-assembled in aqueous solution from the amphiphilic triblock copolymer (poly(2-methyloxazoline)-/>poly(dimethylsiloxane)-/> poly(2-methyloxazoiine) (PMOXA-PDMS-PMOXA) are one example of such supramolecular structures [Nardin et al. 2000, Nardin et al. 2002, Broz et al. 2005, Broz et al. 2006]. The copolymer has shown to build highly stable and homogenous unilamellar vesicles with a predictable and controlled diameter (mostly defined by the chain lengths and the proportions of the individual polymer blocks) when introduced into an aqueous environment, thereby enclosing a defined proportion of the solution into the

aqueous core of the vesicle [Nardin et al. 2000, Rigler et al. 2006]. The end group of the PMOXA polymer building block allows chemical modifications of the vesicle surface, e.g. with biotin-avidin-biotin coupled oligonucleotide ligands for specific cell receptor targeting [Broz et al. 2005]. Furthermore, the fully synthetic vesicles can be equipped with biological transmembrane proteins such as OmpF, LamB, Tsx, and FhuA to enable a size-, charge-, or molecule-specific transmembrane transport [Broz et al. 2006, Meier et al. 2000, Graff et al. 2002, Ranquin et al. 2005, Nallani et al. 2006]. Encapsulated enzymes of bacterial or plant origin finally create an organized nanometer-sized bioreactor that can be used for activation of prodrugs or pH- controllable hydrolysis of phosphatase substrates [Broz et al. 2006, Raquin et al. 2005, Onaca et al. 2006].

U.S. Patent No. 6,916,488 and European Patent Office DE60026742T describe the creation and the possible fields of application of polymeric vesicles based on amphiphilic membranes, none of which, however, include production of substrate such as gadolinium salts inside those vesicles or their use as MRI contrast agents. European Patent Office Publication WO2006113556 describes a type of gadolinium-exchanged carboxylate-alumoxane nanoparticles. Several other patent publications describe a variety of other methods of gadolinium nanoparticle production, e.g. CN1709615, CN 1704379, or CN 1692947.

The publications and other materials, including patents, used herein to illustrate the invention and, in particular, to provide additional details respecting the practice are incorporated by reference in their entirety. These publications and other materials are integrated into the text or, for convenience, numbered and listed in the appended Bibliography.

There exists a need in the art for improvements in medical imaging, in particular providing methods and devices to improve the overall quality of imaging for in vivo and in vitro medical imaging and in particular imaging of specific cell types and cellular compartments.

SUMMARY OF THE INVENTION

Generally speaking, this invention addresses the above-described and other needs in the art that will become apparent when reading this disclosure by providing vesicles and methods employing these vesicles that allowing bringing a number of relevant atoms to a target. In particular, these atoms yield a signal in magnetic resonance imaging, X-ray computed tomography, scintigraphic imaging, single photon emission tomography, positron emission tomography and/or fluorescence imaging. The vesicles and methods preferably do not rely on chelated gadolinium atoms. The invention is also direct to the use of these vesicles in clinical medicine, e.g., to obtain images of defined populations of cancer cells, stem cells, or white blood cells and even of subcellular constituents, but also to obtain images of organ function, organ perfusion, inflammation, and other water accumulations. Images are obtained for in vivo evaluation of an organism as well as for in vitro testing.

In one embodiment, the present invention is directed at a method for producing a target-specific vesicle for medical imaging comprising: providing:

(a) copolymer building blocks,

(b) at least one a transmembrane channel or transmembrane carrier,

(c) at least one enzyme, so that a porous vesicle encapsulating said enzyme is formed, adding to said porous vesicle:

(d) at least one soluble anion forming substrate,

(e) at least one soluble cationic substrate (e.g., a soluble MR contrast yielding cationic substrate), wherein said enzyme in (c) causes (d) and (e) to form a stable substrate within said vesicle, and functionalizing said porous vesicle for a target to form said target-specific vesicle.

Said at least one soluble anion forming substrate of (d) may comprise phosphate, chromate, carbonate, sulfite, hydroxide, formate, acetate, propionate, butyrate, valerate, caproate, caprylate, caprate, dodecanoate, tetradecanoate, hexadecanoate, octadecanoiate, eicosanoate, enanthate, myristoleate, palmitoleate, oleate, linoleate, aspartate, glutamate, lactate, citrate, pyruvate, acetoacetate, benzoate, salicylate, aldarate, oxalate, oxalacetate, malate, malonate, succinate, ketoglutarate, oxalosuccinate, isocitrate, cis-aconitate, fumarate, glutarate, glucuronic acid, acrylate.nucleotide monophosphate, nucleotide diphosphate, nucleotide triphosphat and/or oxide and wherein said at least one soluble cationic substrate in (e) may comprise at least one lanthanide group element such as La, Ce, Pr, Nd, Pm, Sm, Du, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu, and/or alkali metal such as Rb, Cs, and/or alkaline earth metal such as Mg, Ca, Sr or Ba, and/or transition metal such as Mg, Re, Co, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au or Hg, and/or actinide element such as Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No or Lr.

Said at least one enzyme may cleave said substrate in (d) and may be a member of EC 3.1.3 (Phosphoric Monoester Hydrolases), a member of EC 3.1.4 (Phosphoric Diester Hydrolases), a member of EC 3.1.5. (Triphosphoric Monoester Hydrolases), a hydrogen peroxide-forming oxidase, or another enzyme leading to release of phosphate, chromate, carbonate, sulfite, sulphide, hydroxide, or oxide from said substrate. (For EC numbers, see, for example, ExPASy

Proteomics Server (2007), which is incorporated herein by reference).

Said at least one enzyme may, in one preferred embodiment, be a hydrolase such as a phosphohydrolase.

Said phosphohydrolase may release phosphate from said anion forming substrate, e.g., glucose 1 -phosphate, and said phosphate may form the stable substrate with the substrate in (e).

The porous vesicle of the invention may be a functionalized via a targeting moiety.

The targeting moiety may be attached to the vesicle covalently or via biotinavidin-biotin bonds.

Said copolymer building blocks of the invention may be amphiphilic and self- assembling.

The at least one transmembrane channel or transmembrane carrier of the present invention might be size-selective, charge selective and/or substrate selective.

The at least one soluble anion forming substrate of (d) and the at least one soluble cationic substrate of (e) may reach the inside of the porous vesicle via said channels in (b), preferably, by passive diffusion.

The invention is also directed at a target-specific vesicle for medical imaging comprising:

(a) a membrane, preferably an amphiphilic membrane, comprising polymerized copolymer building blocks,

(b) a stable substrate, wherein said stable substrate is encapsulated by said membrane, and

(c) at least one targeting moiety attached at said membrane, wherein said targeting moiety targets at least one target, such as a target molecule.

Said copolymer building blocks of said target specific vesicle may be triblock copolymers such as amphiphilic PMOXA PDMS PMOXA triblock copolymers.

Said copolymer building blocks of said target specific vesicle may be one of, triblock copolymers and diblock copolymers, each comprising at least one hydrophobic group and at least one hydrophilic group.

Said hydrophobic group may be, e.g., polyalkylacrylate, polydiene, polybutadiene, polyisoprene, polyoefine, polylactone, polycaprolactone, polylactide, polyoxirane, polyproxpyleneoxide, polyethyleneoxide, polyisobutylene, polystyrene, polysiloxane, polymethylsiloxane, polydimethylsiloxane, polyethylmethylsiloxane, polystyrene, polymethylstyrene, polymethoxysterne, polyvinylnaphtalene, polypyridine, polyvinylpyridinie, polyvinylpyridinium, polyvinylpyrrolidone, polyacrylonitrile, polycarbonate, polyisobutylene, polysulfoneether, polyvinylanthracene, polyvinylcarbazole, polyvinylimidazole, polyvinylnaphthalene, polyvinylphenanthrene, polymethyloxazoline, polyvinylcaprolactam, polyadipicanhydride or polyvinylacetate.

Said hydrophilic group may be, e.g., polyacrylic acid, poly alkyl acrylic acid and its salt, polyethacrylic acid polymethacrylic acid, polyacrylamide, poly dimethyl acrylamide, poly isopropyl acrylamide, polyethyleneglycol, polyethyleneoxide, polymethylvinylether, polystyrenesulfonic acid, polyvinyl alcohol, polyvinylmethylpyridiniumiodide, polyvinylimidazole quatemized with CH3I, polyethyleneimine, polyvinylamine, poly vinyl carboxylic acid amine, methyloxazoline, ethyloxazoline, polylysine, carbohydrate, glucose, glucosamine, glucuronic acid, iduronic acid, deoxy acetamido glucopyranosyl, deoxy sulfamido glucopyranosyl, deoxy sulfamide glucopyranosyl sulfate, monosaccharide, disaccharide, heparine, fondaparinux, glucosamineglycan, heparan sulfate or sulfated disacharide.

Said membrane of the target-specific vesicle may further comprise at least one transmembrane channel, such as a synthetic channel, e.g., polymer channel or a pore protein, e.g., a pore protein of bacterial origin such as an ompF pore protein from E. coli or a transmembrane carrier proteins Polymer channels include, but are not limited to, PET (polyethylene terephthalate) and PET/silica channels, pristine and hybrid PETE channels and other channels described in Zeng et al. (2005) whose disclosure of

nanoscale polymer channels is specifically incorporated herein by reference (see also Habaue et al. (2002)). Transmembrane carrier proteins include, but are not limited to, Ca-channels, including I, t, n, and p type calcium channels, and Ion channels. Bacterial porines or pore proteins, include, but are not limted to, OmpF, OmpG, FhuA, LamB. See also the description in Lomize et al (2006), whose disclosure of membrane proteins is specifically incorporated herein by reference. However, any structure that will allow entry, preferably by diffusion, of the at least one of substrates discussed herein is within the scope of the present invention.

The targeting moiety of said target-specific vesicle may be a lipid, peptide, protein, nucleic acid, lectin, a combination or an association thereof. Said targeting moiety may, in particular, be polyguanylic acid, acetylated LDL, oxidized LDL, maleylated LDL, LPS, AGE, AGE-LDL, dextran sulphate, polyinosic acid and/or lipoteichoic acid.

Said at least one target molecule of said target-specific vesicle may be an antigen or an receptor, e.g., macrophage scavenger receptor A1 , or another protein or peptide associated with at least one cell surface.

The target-specific vesicle of the present invention may have a diameter of less than about 300 nm, less than about 200 nm, less then about 100 nm, less than about 90, less than about 80, less than about 70, less than about 60, less than about 50 or about or less than about 40 nms.

Said stable substrate of said target-specific vesicle may form a nanoparticle having a diameter of more than about 1 nm, more than about 2 nms, more than about 3 nms, more than about 4, more than about 5, more than about 6, more than about 7, more than about 8, more than about 9, more than about 10 nms, more than about 15 nms, more than about 20 nms, more than about 25 nms, more than about 30 nms, more than about 35 nms, more than about 40 nms, more than about 45 nms, more than about or about 50 nms.

The target-specific vesicle may be non-toxic.

Said stable substrate of the present invention may be crystalline.

Said stable substrate may be radioactive.

The target-specific vesicle of the present invention may induce a change in T1 and/or T2 and/ or T2 star relaxation time and/or proton density and/or diffusion weighted imaging signal measured by MR.

The target-specific vesicle of the present invention may induce a change in X-ray absorption.

The target-specific vesicle of the present invention may emit radiation detectable by a gamma camera and/or a scintillation camera and/or a camera sensitive to one of, electron emission and positron emission.

The target-specific vesicle of the present invention may emit fluorescence signal upon illumination.

The invention is also directed at a method for medical imaging comprising: providing a target-specific vesicle described herein, wherein said vesicle comprises at least about 200, at least about 300, at least about 400, at least about 500, at least about 600, at least about 700, at least about 800, at least about 900, at least about 1000, at least about 2000, at least about 3000, at least about 4000, at least about 5000, at least about 6000, at least about 7000, at least about 8000, at least about 9000, at least about 10000 atoms that yield a signal in one of, magnetic resonance imaging, X-ray computed tomography, scintigraphic imaging, single photon emission tomography, positron emission tomography or fluorescence imaging.

The stable substrate of the methods and vesicles of the present invention may be a precipitated water-insoluble substrate or a complexed substrate, wherein said complexed substrate will remain within the vesicle due to its size and/or charge.

The stable substrate of the methods and vesicles of the present invention may be one of, a MRI contrast agent, a X-ray contrast agent, a radiation emitting agent or a fluorescent agent.

The MRI contrast agent may induce a change of at least one of: T1 and/or T2 and/or T2 star relaxation times and/or proton density and/or diffusion weighted imaging in MRI.

The X-ray contrast agent may induce a change of X-ray absorption in computed tomography.

The radiation emitting agent may emit radiation detactable by a gamma camera and/or a scintillation camera and/or a camera to one of, electron emission and positron emission.

The fluorescent agent may emit a fluorescence signal detectable by a camera.

Certain examples of the invention are described below with respect to certain non-limiting embodiments thereof as illustrated in the following drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an illustration of a schematic visualization of the nanoparticle precipitation concept.

Figure 2 is a photographic illustration of cryogenic transmission electron microscopy of the targetable vesicle of the present invention yielding a contrast and a control population of targetable vesicles filled only with acid phosphatase.

Figure 3 is a photographic illustration of the same samples as in Figure 2 studied with atomic force microscopy in tapping mode after drying on a mica layer.

Figure 4 is a photographic illustration of confocal microscopy imaging of THP-1 macrophages treated with fluorescence-labeled polymer vesicles and unlabeled vesicles.

Figure 5 is an illustration showing MRI measurements of gradient echo with inversion recovery (IR=1500ms, TR=4000ms) and linear fitting of 1/T1 values for relaxivity measurement.

Figure 6 is a chart showing an assessment of toxicity of gadolinium phosphate containing vesicles on THP-1 macrophages with a standard cell death assay.

DETAILED DESCRIPTION OF VARIOUS AND PREFERRED EMBODIMENTS

For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description of various illustrative and non-limiting embodiments thereof.

Presented herein are target-specific vesicles, a method of producing them as well as their application.

The vesicles can be used in the context of a wide variety of imaging methods, including, but not limited to, magnetic resonance imaging, X-ray computed tomography, scintigraphic imaging, single photon emission tomography, positron emission tomography and fluorescence imaging.

The vesicles can be employed in the imaging of cellular or subcellular targets in vivo (in organisms) and in the context of in vitro testing in medial fields such as cardiology, neurology, interventional radiology, and angiology.

Depending on the targeting moiety of the vesicle, the vesicle can be used to target a wide array of target molecules such antigens or receptors expressed on specific cells. The provision of a certain targeting moiety is also referred to herein as "functionalization." The target molecule targeted by the targeting moiety of the vesicle may be a macrophage receptor specific for highly active macrophages, typically found in inflamed tissues and atherosclerotic plaques in blood vessels. Thus, targeting this target molecule via the targeting moiety of the vesicle allow for the detection of such highly inflamed so-called vulnerable plaques in arteries that are at high risk of rupture, leading to serious diseases such as heart infarction, stroke, or gut ischemia. Other targeting moieties, can be used for the detection of diseases such as cancer or further inflammatory conditions. In a preferred embodiment, the vesicles are used for the detection of low numbers of cancer cells, e.g., in the treatment of cancer or cancer metastases.

In one example, target-specific vesicles, which are administered, over well known routes such as injection, to an organism in an effective target molecule/ target cell binding amount in vivo targets via targeting moiety or moieties displayed at the surface of the vesicle the targeting molecule of the target cell, such as a metastatic cancer cell. Each vesicle contains more than 3000 atoms, such as gadolinium atoms, allowing the effective imaging of the target cell, e.g., in MRI imaging.

The vesicles described herein in more detail comprise amphiphilic triblock copolymer membranes having a core of, e.g., precipitated gadolinium-phosphate as contrast agents, which here constitutes the stable substrate, for cellular imaging with, e.g., MRI, X-ray computed tomography, scintigraphic imaging, single photon emission tomography, positron emission tomography or fluorescence imaging. The imaging method and vesicles preferably do not rely on chelated gadolinium atoms and thus allow for substantially more gadolinium atoms per total mass. A total amount of, e.g., about 5500 gadolinium atoms per vesicle are within the range of certain embodiments of the invention. This number opens the doors for cellular or subcellular imaging with, e.g., MRI. Compared to SPIOs, the vesicles can have a predominant T1 effect, resulting

in a positive contrast enhancement in standard imaging sequences. Apart from precipitated gadolinium-phosphate, a range of other crystals/precipitates can be produced within the vesicles, including, but not limited to, iron phosphates and iron oxides.

A wide array of enzymes can be employed for catalyzing cleave of the soluble anion forming substrate, which eventually leads to the formation of the stable substrate of the present invention that in turn provide for the imaging signal. These enzymes include, but are not limited to, phosphoric monoester hydrolases, phosphoric diester hydrolases, triphosphoric monoester hydrolases, hydrogen peroxide-forming oxidases, or other enzymes leading to release of phosphate, chromate, carbonate, sulfite, sulphide, hydroxide, or oxide from the substrate. Phosphoric Monoester Hydrolases of the present invention include in particular, but are not limited to, members of EC 3.1.3; phosphoric diester hydrolases include in particular, but are not limited to, members of EC 3.1.4; triphosphoric monoester hydrolases include in particular, but are not limited to, members of EC 3.1.5. The EC number referenced herein are, for example, explained in ExPASy Proteomics Server (2007), which is incorporated herein by reference.

For, example, the following enzyme entries belong to class 3.1.3: Alkaline phosphatase, Acid phosphatase, Phosphoserine phosphatase, Phosphatidate phosphatase, 5'-nucleotidase, 3'-nucleotidase, 3'(2'),5'-bisphosphate nucleotidase, 3- phytase, Glucose-6-phosphatase, Glucose-1 -phosphatase, Fructose-bisphosphatase, Trehalose-phosphatase, Bisphosphoglycerate phosphatase, Methylphosphothioglycerate phosphatase, Histidinol-phosphatase, Phosphoprotein phosphatase,[Phosphorylase] phosphatase, Phosphoglycolate phosphatase, Glycerol- 2-phosphatase, Phosphoglycerate phosphatase, Glycerol- 1 -phosphatase, Mannitol-1 - phosphatase, Sugar-phosphatase, Sucrose-phosphatase, Inositol-phosphate phosphatase, 4-phytase, Phosphatidylglycerophosphatase, ADP-phosphoglycerate phosphatase, N-acylneuraminate-9-phosphatase, Nucleotidase, Polynucleotide 3'- phosphatase, Polynucleotide 5'-phosphatase, Deoxynucleotide 3'-phosphatase.

Thymidylate 5'-phosphatase, Phosphoinositide 5-phosphatase, Sedoheptulose- bisphosphatase, 3-phosphoglycerate phosphatase, Streptomycin-6-phosphatase. Guanidinodeoxy-scyllo-inositol-4-phosphatase, 4-nitrophenylphosphatase. [Glycogen-synthase-D] phosphatase, [Pyruvate dehydrogenase (acetyl-transferring)]- phosphatase, [Acetyl-CoA carboxylasej-phosphatase, 3-deoxy-manno-octulosonate-8- phosphatase, Fructose-2,6-bisphosphate 2-phosphatase, [Hydroxymethylglutaryl-CoA reductase (NADPH)]-phosphatase, Protein-tyrosine-phosphatase, [Pyruvate kinase]- phosphatase, Sorbitol-6-phosphatase, Dolichyl-phosphatase, [3-methyl-2-oxobutanoate dehydrogenase (2-methylpropanoyl-transferring)]-phosphatase, [Myosin-light-chain] phosphatase, Fructose-2,6-bisphosphate 6-phosphatase, Caldesmon-phosphatase. Inositol-polyphosphate 5-phosphatase, lnositol-1 ,4-bisphosphate 1 -phosphatase. Sugar-terminal-phosphatase, Alkylacetylglycerophosphatase, Phosphoenolpyruvate phosphatase, Multiple inositol-polyphosphate phosphatase, 2-carboxy-D-arabinitol-1 - phosphatase, Phosphatidylinositol-3-phosphatase, Phosphatidylinositol-3,4- bisphosphate 4-phosphatase, Phosphatidylinositol-3,4,5-trisphosphate 3-phosphatase, 2-deoxyglucose-6-phosphatase, Glucosylglycerol 3-phosphatase, Mannosyl-3- phosphoglycerate phosphatase, 2-phosphosulfolactate phosphatase, 5-phytase. Alpha-ribazole phosphatase, Pyridoxal phosphatase,

Phosphoethanolamine/phosphocholine phosphatase, Lipid-phosphate phosphatase and Acireductone synthase.

For, example, the following enzyme entries belong to class 3.1.4.: Phosphodiesterase I, Glycerophosphocholine phosphodiesterase, phospholipase C, Phospholipase D, Phosphoinositide phospholipase C, Sphingomyelin phosphodiesterase, Serine-ethanolaminephosphate phosphodiesterase, [acyl-carrier- protein] phosphodiesterase, Adenylyl-[glutamate — ammonia ligase] and hydrolase, 2',3'-cyclic-nucleotide 2'-phosphodiesterase, 3',5'-cyclic-nucleotide phosphodiesterase, 3',5'-cyclic-GMP phosphodiesterase, 2',3'-cyclic-nucleotide 3'-phosphodiesterase, Glycerophosphocholine cholinephosphodiesterase, Alkylglycerophosphoethanolamine phosphodiesterase, CMP-λ/-acylneuraminate phosphodiesterase, Sphingomyelin phosphodiesterase D, Glycerol-1 ^-cyclic-phosphate 2-phosphodiesterase, Glycerophosphoinositol, Inositolphosphodiesterase, Glycerophosphoinositol

Glycerophosphodiesterase, λ/-acetylglucosamine-1 -phosphodiester α-λ/- acetylglucosaminidase, Glycerophosphodiester phosphodiesterase, Dolichylphosphate- glucose phosphodiesterase, Dolichylphosphate-mannose phosphodiesterase, Glycosylphosphatidylinositol phospholipase D, Glucose-1 -phospho-D- mannosylglycoprotein phosphodiesterase or Cyclic-guanylate-specific phosphodiesterase.

DGTPase is an example of an enzyme entity belonging to class 3.1.5.

Figure 1 shows the production of a vesicle according to the present invention. In particular, the Figure provides a schematic visualization of the nanoparticle precipitation concept. The depicted triblock copolymer vesicles are functionalized with transmembrane OmpF pore proteins and the tracking ligand (targeting moiety) polyguanylic acid. Fluorescence-labeled streptavidin is being used to couple the ligand to the vesicle surface via biotin interaction. The pH-triggerable enzyme acid phosphatase is encapsulated inside the vesicle to create a nanometer-sized bioreactor (A). In a second step, glucose- 1 -phosphate and gadolinium chloride are added and processed to insoluble gadolinium phosphate precipitates by enzymatic action (B). The final targetable polymer vesicle is packed with multiple gadolinium phosphate nanoparticles (stable substrate) (C).

Figure 2 depicts the presence of electron-dense particles inside the polymer vesicles. In A) a cryogenic transmission electron microscopy of the final targetable vesicle is shown. The image shows a homogenous population of vesicles with a mean diameter of slightly less than 50 nm and polyparticulate content with high density. In B), a control population of polymer vesicles filled only with acid phosphatase shows similar mean diameter, but a homogenous content with no dense particles.

In Figure 3 the same samples as Figure 2 were employed. However, the images were created via atomic force microscopy in tapping mode after drying on a mica layer.

Polymer vesicles with precipitated gadolinium phosphate nanoparticles (A-D) show a continuous layer of retracted polymer material and islands with a defined hexagonal pattern (detail can be seen in 3C and 3D) of a hard material in phase imaging. In 3E and 3F, control polymer vesicles filled only with acid phosphatase show similar layers of polymer material, but no hexagonal pattern in-between. The images show the presence of hard matter, most likely gadolinium phosphate nanoparticles, that build an organized pattern upon drying of the vesicle solution.

Macrophage imaging can be used to, e.g., visualize plaques associated with vessel thrombosis. Figure 4 depicts confocal microscopy imaging of THP-1 macrophages treated with fluorescence-labeled vesicles of the invention (A) and unlabeled vesicles (B). The images show the intracellular localization of the fluorescence labeled gadolinium phosphate containing polymer vesicles after an incubation time of 1 hour. The targeting ligand polyguanylic acid which serves as targeting moiety allows the vesicles to be taken up by scavenger receptor expressing, active macrophages in high numbers. Cells without scavenger receptor expression do not take up the polymer vesicles. The results demonstrate the use of the vesicles for bimodal imaging of macrophages with fluorescence detection methods.

Figure 5 depicts MRI measurements of vesicles according to one embodiment of the invention. 5.A) depicts a gradient echo with inversion recovery (IR=1500ms, TR=4000ms). Below the samples, the respective concentration of polymer vesicles/ml is provided. 5.B) depicts the linear fitting of 1/T1 values for relaxivity measurement. The results demonstrate the linear positive signal enhancement when increasing the vesicle concentration in the solution. The polymer vesicle contrast agent shows a gadolinium typical predominant T1 effect.

Figure 6 depicts an assessment of the toxicity of gadolinium phosphate containing polymer vesicles according to the invention on THP-1 macrophages with a standard cell death assay (see Methods below for details). Macrophages were incubated with increasing concentrations of polymer vesicles for 24h and tested for membrane integrity

with an automated microplate based assay. No significant increase of cell death could be detected during the observation period, indicating that gadolinium phosphate loaded polymer vesicles are not cytotoxic (error bars represent the standard deviation over a series of experiments).

EXAMPLES

Enzyme "nanoreactors" built of self-assembled triblock copolymer membranes [Broz et al. (2006)] with size-selective pores were incubated with GdCI ₃ and a phosphatase substrate, resulting in the enzyme-triggered biomineralization of highly insoluble gadolinium-phosphate inside the tracking ligand-functionalized polymeric vesicle [Broz et al. (2005)].

Synthesis of gadolinium phosphate containing polymer vesicles

Nanoreactors based on polymer vesicles from (poly(2-methyloxazoline)--> poly(dimethylsiloxane)-/>poly(2-methyloxazoline) (PMOXA-PDMS-PMOXA) triblock copolymer building blocks (JW05, total M _n 7090 g/mol, 10% with biotin-modified end- groups) were produced as described previously [Broz et al. 2006].

In particular, amphiphilic PMOXA-PDMS-PMOXA triblock copolymer building blocks (10% with biotin-modified end-groups) were first dissolved in ethanol and mixed with bacterial ompF pore proteins from Escherichia coli. This solution was added drop wise to an aqueous solution of the pH-sensitive enzyme acid phosphatase, resulting in the self-assembled creation of pore-containing nanometer-sized vesicles with encapsulated acid phosphatase. In the next step, 33 mmol/L glucose-1 -phosphate (Sigma-Aldrich) and 100 mmol/L gadolinium chloride (GdCI ₃ ) (Sigma-Aldrich) were added and the solution was adjusted to pH 5 with 1 mol/L hydrochloric acid. Both constituents reached the interior of the polymer vesicles across the pore proteins driven by passive diffusion, whereas the glucose-1 -phosphate was hydrolyzed by the acid phosphatase. The resulting free phosphate groups (or phosphoric acid, respectively) and the gadolinium (III) ions now precipitated inside the vesicles as highly insoluble

gadolinium phosphate phosphate (GdPO ₄ -XH ₂ O) [Lessing et al. 2003]. Figure 1 shows a two dimensional outline and visualization of one specific embodiment of a gadolinium nanovesicle. The vesicle comprises biotinylated triblock copolymer building blocks with streptavidin-coupled polyguanylic acid (ligand for macrophage scavenger receptor A1 ). In the embodiment shown OmpF pore proteins situate themselves in the polymeric membrane, the precipitated gadolinium phosphate is packed inside the vesicle. Finally (see also Figure 1), the surface of the complete vesicle was further functionalized by attaching the macrophage scavenger receptor A1 (SRA1 ) ligand polyguanylic acid (biotin-avidin-biotin bond). In particular, after 24 h, the surface of the complete vesicle was further functionalized by attaching the SRA-1 ligand polyguanylic acid (Microsynth, Balgach, CH; 23 G, 3 ^' modified with biotin) as described previously [Broz et al. 2005]. Streptavidin-Alexa Fluor® 610 (Invitrogen, Basel, CH) was used as a coupling molecule to label the vesicles fluorescently. The final vesicles were then purified from non- encapsulated and non-bound molecules by gel chromatography (Sepharose® 4B, Sigma-Aldrich, Buchs, CH in a 37 cm column with 1 cm inner diameter, Bio-Rad, Reinach, CH)..

The main features are encapsulated acid phosphatase (total molecular weight 55 kDa; Sigma-Aldrich, Buchs, CH) and OmpF pore proteins (total molecular weight 110 kDa) that integrate into the polymer membrane.

Tools for the characterization of vesicles, their localization, toxology and imaging

Physicochemical characterization of these vesicles was performed by laser light scattering, cryogenic transmission electron microscopy (cryo-TEM) and magnetometry/atomic force microscopy (AFM). Localization and toxicology experiments were performed in cell cultures of human THP- 1 macrophages and analyzed by confocal laser microscopy (with additional fluorescence-labeling of vesicles) and a light absorption microassay. MR experiments were performed on a 1.5T human imaging scanner (Magnetom Avanto, Siemens Medical Solutions, Erlangen, Germany).

For characterization, the vesicles were imaged by cryogenic transmission electron microscopy (LEO 910, Carl Zeiss AG, Feldbach, CH) and atomic force microscopy (Agilent 5100, Molecular Imaging, Tempe, USA). Cryo-TEM was performed

according to standard methods. For AFM, the vesicle solution was dropped on a mica layer and dried in a desiccator for 2 hours. The samples were analyzed in tapping mode with a silicon cantilever (fr = 300 kHz). Magnetic resonance experiments were performed on a 1.5T human imaging scanner (Magnetom Avanto, Siemens Medical Solutions, Erlangen, Germany) on 1 ml vials filled with a solution in water of the sample at different concentrations (5x10 ¹² , 3,75x10 ¹² , 2.5x10 ¹² , 5x10 ¹¹ nanovesicles/ml) submerged in water to provide enough signal for gradient shimming. Standard Spin- Echo sequences with different echo times (TE = 10, 30, 50 ms, Repetition Time TR = 4 s) and Gradient-Echo with Inversion Recovery magnetization preparation (Inversion Times IR = 150, 300, 500, 750, 1000, 1500 ms, Echo Time TE = 3.61 ms, TR = 4 s) were used as a source of data for the exponential fitting needed to calculate T1 and T2 values of the solutions. The same sequence protocol was also used to compare the magnetic properties of the samples with different concentrations (1 mmol/L, 250 μmol/L, 50 μmol/L) of a commercially available gadobutrol contrast agent (Gadovist®, Schering, Berlin, Germany) and to analyze the suspended cell samples. Figure 5A shows one image from the acquired dataset (IR=1500ms) and is further discussed below.

Results

Characteristics of the vesicles

The resulting vesicles had a mean diameter of about 60 nm and distinguishable polyparticulate content in cryo-TEM. In particular, the resulting vesicles had a mean diameter of about 46 nm +/- 9 nm and distinguishable polyparticulate, high density content in cryo-TEM. Control vesicles that contained only acid phosphatase but did not undergo the nanoparticle producing reaction had a diameter in the same range, but homogenous low density content (Figure 2). The images indicate the presence of multiple particles with high electron density and a size in the range of 5 nm inside the polymer vesicles that did undergo the gadolinium phosphate precipitating reaction.

The magnetometric measurements indicated a total amount of 5500 Gd atoms per vesicle, corresponding to a bulk nanoparticle of 7 nm. The target cells showed a rapid uptake of the ligand-functionalized and fluorescence-labeled vesicles within 5

minutes and a steady increase of fluorescence intensity over 3 hours. As discussed below, toxicity was absent over the observation period of 24 hours. 45 μM [Gd] nanovesicles (corresponding to 8 nM vesicles) showed a Ti relaxation time of 949 ms and a T ₂ relaxation time of 367 ms. It has to be remarked that the T ₂ value calculation was much more affected by noise. Similar values were achieved with 50 μM [Gd] Gadovist. Control vesicles without pores, enzymes, gadolinium, or phosphate showed no significant change in relaxation times compared to free water. T ₁ relaxivity was determined by a linear fitting of the calculated Ti values for different concentrations, and a value of 9.1x10 ¹⁷ ml/(msec x number of vesicles) was found (Figure 5B). First samples with 5(VOOO nanovesicle-treated target cells in a suspension of 1 ml showed detectable increase of signal compared to untreated cells and free water.

As discussed in more detail below, the same polymer vesicles (gadolinium phosphate containing and the control) were then dried on a mica layer for AFM. Measurements in tapping mode in air with a silicon cantilever revealed characteristic aggregations of soft, most probably polymeric material as seen in Figure 3 in phase imaging and islands with a regular, hexagonal pattern of hard material between the soft aggregations. The control vesicles did not produce the hexagonal pattern after drying on the mica layer. The regular pattern of hard material is most likely a deposition of the water-insoluble gadolinium phosphate nanoparticles, while the water-soluble polymer is retracted into the aggregates during the drying process.

Discussion

The Examples describe a medical imaging device and the process of its production according to the invention. The device is a receptor-targetable nanovesicle built from coblock polymers which preferably contain in-situ precipitated nonsoluble, MRI-visible nanocristals produced by in-situ precipitation using enzymatic cleavage from soluble precursors. The method of production is characterized by equipping the vesicle wall with, e.g., ion- and substrate-permeable pores, enclosing a suitable enzyme within the vesicle during a process such as self-assembly, and starting, e.g., crystallinisation of the core crystals by adding an enzyme-cleavable soluble substrate yielding a suited

anion upon cleavage, and a MR contrast-yielding cation. The combination of the anion and the cation (also referred to herein as "stable substrate") is characterised by low solubility, while the initial combination of enzyme substrate and cation have a high solubility. The dense packaging of molecules in the crystal structure results in strong paramagnetic properties of each vesicle, compared to contrast agents in solution. Further, the invention is also directed at the use of such devices for receptor- and cell- specific MR imaging in organisms and for in vitro testing. The enzyme nanoreactor system based on polymeric biomimetic membranes was used to control the precipitation of gadolinium salts, to target a specific cell line, and to protect the target cell from toxic effects of gadolinium. The system's uses include imaging of cellular or subcellular targets in modern biomedicine.

Targeting

The invention is, in one embodiment, intended to be used as a contrast agent for MRI. The exemplary ligand (targeting moiety) used is specific for highly active macrophages, typically found in inflamed tissues and atherosclerotic plaques in blood vessels. Therefore this functionalization allows, in this embodiment, the detection of highly inflamed so-called vulnerable plaques in arteries that are at high risk of rupture, leading to serious diseases such as heart infarction, stroke, or gut ischemia.

By changing the tracking ligand ("targeting moiety"), the same contrast agent can be used for the detection of other diseases such as cancer or inflammatory conditions. A preferred embodiment is directed at the precise detection of low numbers of cancer cells, e.g., in the treatment of cancer or cancer metastases.

Characterization of the vesicles functionality

As a model to demonstrate the use of the novel polymer vesicle based agent, cell cultures of highly active macrophages were employed [Broz et al 2005]. Macrophages are phagocytic monocyte-derived cells of the innate immune system and play a key role in major diseases such as atherosclerosis, cancer, and autoimmune disorders. In the case of atherosclerosis, macrophages are main constituents of type V vulnerable

plaques that are in risk of shear-induced rupture that in the case of coronary arteries leads to heart infarction [Stary et al. 1995]. The macrophages represent up to 20% of total cell amount of the fibrous cap of vulnerable plaques and weaken the mechanical resistance of the cap mainly by producing potent matrix metalloproteinases and attracting lymphocytes [Tearney et al. 2003; Moreno et al. 1994]. A high percentage and activity of the plaque macrophages correlates significantly with the risk of plaque rupture and therefore vessel thrombosis and heart infarction. For a successful prevention of this disease, it is vital to detect high risk plaques and treat them specifically. Most concepts for vulnerable plaque detection such as intracoronary thermography, radionuclide imaging, and targeted SPIOs represent basically the macrophage distribution and their activity state, but have several limitations until now [Madjid et al. 2006; Davies et al. 2006; Jaffer et al. 2006; MacNeill et al 2003].

Synthesis of gadolinium phosphate containing polymer vesicles

(see above)

Tools for the characterization of vesicles, their localization, toxology and imaging

(see above)

As described above, acid phosphatase containing, macrophage targeted ligand functionalized nanoreactors built from self-assembled triblock copolymer membranes with size-selective OmpF pores were incubated with gadolinium chloride (GdCI ₃ ) and a phosphatase substrate that is able to reach the interior of the vesicles [Broz et al. 2006]. Inside the polymer vesicles, the hydrolysis of the phosphatase substrate by the encapsulated enzyme results in the production of free phosphate groups (phosphoric acid, respectively), followed by a rapid precipitation of the highly water-insoluble hydrated gadolinium phosphate (GdPO ₄ -XH ₂ O) (Figure 1) [Lessing et al. 2003].

Characterization of vesicles functionality and toxicity Cell culture experiments

THP-1 cells (ECACC, Salisbury, UK) were cultured as recommended by the manufacturer. Differentiation into functional adherent macrophages was initiated 72 hours prior to experiment with 100 nmol/L phorbol 12-myristate 13-acetate (PMA) (Sigma-Aldrich) in 24-well multiwell plates (Becton-Dickinson, Basel, Switzerland) with glass cover slips (12 mm diameter), resulting in a mean cell density of approximately 1.25 ⁵ cells/cm ² . For vesicle uptake experiments, macrophages were incubated with 4 nmol/L vesicles for 1 h. After washing with PBS, the cells were fixed in 4% paraformaldehyde for 20 min at room temperature. Fixed cells were mounted with an anti-bleaching glycerol-based mounting medium (Sigma-Aldrich) on glass slides. For MRI scans, the cells were detached from the glass cover slips with 0.5% trypsin (Sigma- Aldrich) after the incubation period and resuspended in cell culture medium. Cell numbers were determined using standard microscope cell counting chambers. The treated cell population was compared to untreated cells and free water. To assess the toxicity of the gadolinium phosphate containing polymeric vesicles, a colorimetric LDH release assay (Sigma-Aldrich) was performed in 96-well multiwell plates. Dead cells release intracellular LDH into the serum-free medium, where it is detected with a standard method based on the NADH-mediated conversion of a tetrazolium dye. The dye was detected with an automated microplate absorption reader (MPP 4001 , Mikrotek, Overath, Germany) at a wavelength of 490 nm. Ratio of living cells in the sample compared to the cell number in an untreated control was taken as cell survival parameter.

Results

As discussed above, the resulting vesicles had a mean diameter of about 46 nm +/- 9 nm and distinguishable polyparticulate, high density content in cryo-TEM. Control vesicles that contained only acid phosphatase but did not undergo the nanoparticle producing reaction had a diameter in the same range, but homogenous low density content (Figure 2). The images indicate the presence of multiple particles with high electron density and a size in the range of 5 nm inside the polymer vesicles that did undergo the gadolinium phosphate precipitating reaction.

In cell cultures of active macrophages, the polymer vesicle contrast agent was tested for fluorescence imaging. By using a fluorescence labeled streptavidin for ligand coupling, the vesicles can be easily tagged with a variety of stable and bright dyes. The targeting moiety polyguanylic acid guarantees the specific delivery of the polymer vesicles to active, scavenger receptor expressing macrophages Broz et al. 2005]. After 1 h incubation time, the ligand functionalized fluorescent polymeric vesicles could be found in high numbers inside macrophages (Figure 4A). Macrophages treated with control vesicles without the fluorescence labeled streptavidin showed no significant intracellular fluorescence (Figure 4B). A confocal microscopy z-stack analysis of macrophages that were treated with the polymer vesicles revealed several hundreds to thousands of distinguishable signals in vesicular shape inside the cells. The results demonstrate the potential of the polymeric vesicles as high signal imaging contrast agents for fluorescence detection.

In MRI, an aqueous solution with 8 nmol/L vesicles showed a T1 relaxation time of 949 ms and a T2 relaxation time of 367 ms. Similar values were achieved with 50 μmol/L [Gd] gadobutrol, whereas free water resulted in a T1 relaxation time of 1879 ms and T2 relaxation time of 414 ms. Following control vesicles did not generate a significant change in relaxation times compared to free water: 1 ) no pore proteins in the membrane; 2) no encapsulated acid phosphatase; 3) no GdCb during the synthesis; 4) no glucose-1 -phosphate during the synthesis. T1 relaxivity was determined by a linear fitting of the calculated T1 values for different concentrations and a value of 9.1 e-17 ml/(msec x number of vesicles) was found (Figure 5). Based on mol [vesicles], this corresponds to 3.5 ¹⁰ L x s ^"1 x mmol ^"1 . Samples with 50 ^' 0OO polymer vesicle-treated macrophages (same as in Figure 4) in a suspension of 1 ml phosphate buffered saline showed a detectable increase of signal compared to untreated cells and free water. The relative grey value intensity of the treated cells was 56% higher than the signal of the untreated cells and 47% higher than the signal of free water.

Gadolinium ions are known to exhibit strong toxic effects on cells [Shellock et al. 1999], therefore we performed a standard cytotoxicity testing using the LDH release assay as

described above. Macrophages were treated with increasing doses of gadolinium phosphate containing polymer vesicles for 24 hours and tested for membrane integrity compared to populations of untreated cells. Up to a concentration of 7 nmol/L vesicles in the cell culture medium, there was no significant increase of cell death in the treated macrophage cultures (Figure 6). The results indicate that the vesicle based bimodal contrast agent does not exhibit acute toxicity in cell cultures.

Discussion

The environment-reactive enzyme nanoreactor system based on polymeric biomimetic membranes can be used to control the precipitation of gadolinium minerals locally and temporally, to target a specific cell line, and to protect the target cells from toxic effects of gadolinium. The gadolinium phosphate nanoparticles are protected inside the polymer vesicles and can be transported to a defined cellular receptor or surface structure. The polymer vesicles exhibit a gadolinium typical decrease of T1 relaxation time and are taken up by active macrophages in high numbers. The T1 relaxivity of 3.5 ¹⁰ L x s ^'1 x mmol ^'1 [vesicle] is significantly higher than the T1 relaxivity of commercially available MRI contrast agents (e.g. 3.6 L x S ¹ X mmol ^'1 for gadobutrol in water). This extremely strong T1 relaxivity per single vesicle opens the door for cellular and molecular imaging with standard MRI scanners. A small number of 50 ^" 0OO macrophages can be detected with MRI when using the targetable vesicles. Unwanted acute toxic effects of gadolinium on the targeted cells are absent and should not endanger the use of the novel polymer vesicles based contrast agent for molecular imaging of macrophages, e.g. in inflamed atherosclerotic plaques. The use of stable, biocompatible and protein-repellent triblock copolymer vesicles with a biological targeting function solves the stability and solubility problems of gadolinium minerals in an elegant way.

Compared to superparamagnetic iron oxide nanoparticles, the polymer vesicle system discussed above is preferably based on the predominant T1 effect of gadolinium and produces a positive increase of signal when using a standard MRI scanner for humans. No additional imaging hardware or software is necessary for the detection of injected

gadolinium phosphate containing polymer vesicles, a clear advantage compared to other nanotechnologica! contrast agent approaches. Furthermore, by exchanging the tracking ligand on the vesicles surface, the whole system could be used for bimodal MR and fluorescence imaging of other diseases such as cancer or infections.

Once given the above disclosure of the methods and vesicles of the instant invention, many other features, modifications, and improvements will become apparent to the skilled artisan. Such features, modifications, and improvements are therefore considered to be part of this invention, without limitation imposed by the example embodiments described herein. Moreover, any word, term, phrase, feature, example, embodiment, or part or combination thereof, unless unequivocally set forth as expressly uniquely defined or as otherwise limiting, is not intended to impart a narrowing scope to the invention in contravention of the ordinary meaning of the claim terms by which the scope of the patent property rights shall otherwise be determined:

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