JP2008037856A - Mri probe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new MRI probe which can be easily synthesized and purified. <P>SOLUTION: The MRI probe is composed of particles of metal salts shown by a general formula A<SB>m</SB>B<SB>n</SB>(A represents a specific metal and B represents a specific anion) such as GdPO<SB>4</SB>-1.5H<SB>2</SB>O or particles obtained by coating the metal salt particles with a hydrophilic substance. The MRI probe can be easily synthesized and purified from easily available starting materials, and can be prepared at a low cost. In addition, the particles obtained by coating particles of the metal salt or its hydrate with a hydrophilic substance are excellent in dispersibility in water, has an increased relaxivity in water and can also be utilized as a MRI probe also usable as a positive contrast agent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a probe used for MRI (magnetic resonance imaging).

  Image diagnostic methods in the medical field are indispensable medical techniques from the viewpoint of early detection of lesions, preoperative diagnosis, postoperative follow-up diagnosis, and the like. Currently, CT (computed tomography), MRI (magnetic resonance imaging), and PET (positron emission tomography) are widely used as diagnostic imaging methods in medical practice. However, exposure to X-rays in CT and exposure to γ-rays in PET cannot be avoided, and multi-section imaging has become possible due to the recent advancement of high-functionality equipment. Increasing the amount of radiation exposure caused by this is an additional burden on patients. On the other hand, MRI is a noninvasive diagnostic imaging method without radiation exposure, and has an advantage of obtaining an arbitrary cross-sectional image.

MRI contrast agents are widely used to improve MRI sensitivity. Currently, as contrast agents for MRI that are routinely used in the medical field, gadolinium complex type Magnevist (registered trademark) and ProHance (registered trademark), and iron oxide (Fe ₂ O ₃ ) _m (FeO) _n Examples of such a supermagnetic particle type Resovist (registered trademark) and Feridex (registered trademark). When supermagnetic particles are administered into the body by intravenous injection or the like, they are accumulated specifically in the liver due to metabolic pathways, undergo glucuronidation and the like, and are excreted bile.

  In recent years, contrast agents having better contrast ability have been developed by increasing the relaxivity R of contrast agents for MRI. For positive contrast agents, high R1 values can be obtained by introducing gadolinium complexes with conventional multidentate ligands such as DTPA and gadolinium ions into the main and side chains of dendrimers, micelles, liposomes, and various polymers. Has been studied. In addition to the fact that there are many gadolinium complexes in one molecule, the R1 value per molecule increases, and in addition, gadolinium complexes are bonded to macromolecules such as polymers. High R1 values are achieved because the correlation time between the complex and water molecules increases, resulting in an increase in R1 per gadolinium complex molecule. On the other hand, iron oxide particles are mainly used for negative contrast agents. This iron oxide particle has a property as super magnetism, and has a large magnetism in an environment where an external magnetic field exists, and the magnetic field around the iron oxide particle is disturbed by this magnetism, and a large R2 value can be obtained. To ensure water dispersibility and biocompatibility, supermagnetic particles are often coated with water-soluble polymers.

  The value of R2 / R1 is often used to determine whether a certain MRI contrast medium is used as a positive contrast medium or as a negative contrast medium.Roughly, if R2 / R1> 5 to 3, a negative contrast medium is used. If “R2 / R1 <5-3”, it is used as a positive contrast agent. In the case of iron oxide particles, AMI-25 (Advanced Magnetics, Cambridge, Mass.) Is 4.0 and SH U 555 A (Schering, Berlin, Germany) is 6.0, which is a negative contrast agent. As an exception, AMI-227 (Advanced Magnetics), which is a small iron oxide particle (Ultrasmall Paramagnetic Iron Oxides), is 2.2 and is also used as a positive contrast agent (Eur. Radiol. 8, 1198-1204 (1998). )).

  When exogenous particles are administered into the blood, their pharmacokinetics are generally determined by the particle size and degree of hydrophilicity. Those having a large particle size are recognized by the phagocytic cell line as foreign matter and are excreted mainly from the liver. On the other hand, low molecular weight drugs and highly hydrophilic drugs are mainly excreted from the liver. When the particle size is around 100 nm, a cancer tissue accumulation effect called EPR (Enhanced Permeability and Retention) effect appears. This is because cancer tissue always proliferates more rapidly than normal cells, and blood vessel formation is always occurring. This is because, in cancer tissues, lymphatic vessels having an excretory function are not yet developed, and it is said that what is normally excreted from here remains as a result for a long time.

  At present, gadolinium complexes are mainly used as positive contrast agents, and in order to increase R1 and molecular weight, a method of binding to dendrimers, micelles, liposomes, polymers, etc. is used. This complicates synthesis and purification, and has the disadvantage that many organic molecules constituting a high molecular weight must be used as a drug. On the other hand, when performing image diagnosis by MRI, a positive contrast agent that produces a contrast that makes the lesion site specifically white is clearly easier to diagnose, and when a negative contrast agent is used, the site It is necessary to discriminate whether it is specifically dark or whether it is dark on the image because the MR signal intensity of the part is accidentally low.

  On the other hand, known MRI positive contrast agents mainly composed of inorganic compounds are mainly composed of metal oxides. Known MRI positive contrast agents mainly composed of such inorganic compounds have particles with magnetism, which increases the R2 value, which increases the R2 / R1 value, making it difficult to use as a positive contrast agent. It has the problem of becoming. In addition, there are particles (AMI-227 (Advanced Magnetics)) with R2 / R1 value of 2.2, but because they are supermagnetic particles, the particles have magnetism under an external static magnetic field. It is difficult to suppress, and it is considered difficult to produce particles having an R2 / R1 value extremely close to 1 found in the present invention.

Japanese Patent Publication No.62-42934 Japanese Patent Publication No.63-290832 EP0210043 A2 US 2005/0260137 A1 US006638494 B1 US 2004/0101564 A1 US005698271 A US006120856 A WO96 / 02235 US2005 / 0220714 A1 WO99 / 06849 WO98 / 11922

  An object of the present invention is to provide a novel MRI probe that can be easily synthesized and purified. Another object of the present invention is to provide a novel MRI probe that can be easily synthesized and purified, has a high degree of relaxation, and can be used as a positive contrast agent.

  As a result of intensive studies, the inventors of the present application can use, as an MRI probe, particles that are easily prepared and that are composed of a metal salt or a hydrate thereof, or particles that are coated with a hydrophilic substance. As a result, the present invention has been completed.

  That is, the present invention provides an MRI probe comprising particles composed of a compound represented by the following general formula (1) or a hydrate thereof.

A _m B _n (1)
(However, A is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Y, Mn, Cr, Fe, Co, Ni, and Cu. Represents an ion of at least one metal selected from the group consisting of: B is selected from the group consisting of phosphate ion, sulfonate ion, carboxylate ion, borate ion, citrate ion, nitrate ion and halide ion Represents at least one anion, and m and n independently of each other represent a positive number).

  Furthermore, the present invention provides an MRI probe comprising particles obtained by coating the particles with a hydrophilic substance.

  The present invention provides a novel MRI probe that can be easily synthesized and purified. Since the MRI probe of the present invention can be easily synthesized and purified from readily available starting materials, it can be produced at low cost. In addition, particles made by coating metal salts or their hydrates with hydrophilic substances are particularly excellent in dispersibility in water, have a high degree of relaxation, and can be used as positive contrast agents. It can be used as a probe.

  As described above, the MRI probe of the present invention comprises particles made of the metal salt represented by the above general formula (1) or a hydrate thereof, or the particles.

  In the general formula (1), A is a metal ion as described above, and among these, Gd, Fe, Mn, and Cu ions are preferable metal ions from the viewpoint of the degree of relaxation. In particular, Gd ions are preferred. A may be one type of metal ion or a combination of a plurality of metal ions.

  In the general formula (1), B is an anion as described above, and among these, from the viewpoint of the degree of relaxation and the ease of particle formation, phosphate ions and sulfonate ions are preferable as anions. In particular, phosphate ions are preferable. B may be one type of anion or a combination of a plurality of anions.

  In the general formula (1), m and n each independently represent a positive number. This positive number is often an integer or half-integer (such as 0.5, 1.5, 2.5, etc., where the first decimal place is 5 and ends with the first decimal place). Other decimal numbers may be used, and in the case of a decimal, it is usually a decimal up to the first decimal place. From the viewpoint of ease of preparation, m is preferably a number in the range of 0.5 to 2.0, and more preferably in the range of 0.8 to 1.2. N is preferably a number in the range of 0.5 to 2.0, and more preferably in the range of 0.8 to 1.2. However, since the metal salt is substantially electrically neutral, the ratio between the product of metal ion valence and m and the product of anion valence and n is substantially 1: 1. is there.

  The metal salt represented by the general formula (1) may be hydrated. When hydrated, the number of water molecules bound to the metal salt is usually in the range of 0.1 to 5.0. This number is also an integer or a half integer, like m and n above, but may be a decimal other than an integer or a half integer, and in the case of a decimal, it is usually a decimal up to the first decimal place. . Note that the metal salt is not necessarily hydrated.

  The average particle diameter of the particles composed of the metal salt represented by the general formula (1) or a hydrate thereof easily diffuses into the tissue when used as an MRI probe, and has excellent performance as a contrast agent. In order to achieve this, it is preferably 0.3 nm or more and 5000 nm or less, more preferably 0.5 nm or more and 500 nm or less, further preferably 1 nm or more and 150 nm or less, and further preferably 4 nm or more and 100 nm or less. The particles are not limited to a spherical shape such as a cylindrical shape or an oval sphere, but in the case of a shape other than the spherical shape, it means the average of the long diameter (longest diameter). Here, the average particle diameter is measured by observing the particles with an electron microscope and taking the arithmetic average.

  The particles composed of the metal salt represented by the general formula (1) or a hydrate thereof are known per se and can be produced by the known methods described below. In addition, there are many commercially available products, and when there are commercially available products, commercially available products can be used.

  As a raw material of the metal ion A in the metal salt represented by the general formula (1), metal complexes such as metal A alkoxide, acetylacetonate and oxine complex; acetate, oxalate and carboxylate Organic acid salts; inorganic acid salts such as nitrates, sulfates, carbonates and chlorides; metal oxides; and other various metal compounds can be used. On the other hand, as a raw material of the anion B, an organic acid, an inorganic acid, an ester compound (for example, a methoxylated product, an ethoxylated product, a tert-butoxylated product, etc.) containing B or capable of releasing B upon reaction. Ammonium salts, hydrogen ammonium salts, salts with various metals, and other various compounds can be used.

  The metal salt represented by the above general formula (1) or a hydrate thereof can be produced by subjecting the raw materials of A and B described above to a known hydrothermal synthesis method or solvothermal method. Hereinafter, these will be described.

Hydrothermal synthesis method The hydrothermal synthesis method is a step of preparing a mixed aqueous solution of metal ions A and anions B in the general formula (1), and the pH of the mixed solution is made basic with, for example, an aqueous sodium hydroxide solution. It is a method comprising a step of adjusting and forming a hydroxide, and a step of hydrothermally synthesizing a liquid mixture containing the hydroxide at a predetermined temperature and pressure. Further, the hydrothermal synthesis method may not form precipitates derived from hydroxide or the like, and in this case, a step of preparing a mixed aqueous solution of metal ions A and anions B in the general formula (1) And adjusting the pH of the mixed solution, and hydrothermal synthesis of the mixed solution at a predetermined temperature and pressure. The metal ion A has a pH that forms precipitates such as hydroxides depending on the type, but is generally 9.0 or less, preferably 6.0 or less, more preferably 5.0 or less. Although the pH of the aqueous solution of the raw material mixture can be set to an arbitrary value, when hydrothermal treatment is performed by precipitating a hydroxide, the metal ion A forms a hydroxide depending on the type, but the raw material The pH of the solution is generally 9.0 or higher, preferably 10.0 or higher, more preferably 11.0 to 13.0, and most preferably 12.0 to 12.9. In addition, in the pH adjustment step in the case where precipitates derived from hydroxide or the like are not formed, the pH is usually adjusted to a range of 1.0 to 5.0. The concentration of metal ion A in the mixed aqueous solution of metal ion A and anion B is usually about 1 to 3000 mM, and the concentration of anion B is about 0.8 to 1.2 times the stoichiometric amount with respect to metal A. It is.

  Next, hydrothermal treatment is performed on the raw material mixture whose pH has been adjusted. The hydrothermal treatment method is a method in which a raw material solution is subjected to high temperature and high pressure treatment for a certain time to synthesize a compound by utilizing the high reactivity and dissolution / precipitation action of the solution under high temperature and high pressure, and to grow crystals. Specifically, the raw material solution is put in a corrosion-resistant and heat-resistant reaction vessel, which is loaded into a high-pressure vessel such as an autoclave, and hydrothermal treatment is performed using an electric furnace or an oil bath. Specifically, the raw material solution may be placed in a corrosion-resistant, heat-resistant, pressure-resistant reaction vessel and hydrothermally treated using an electric furnace or an oil bath. The hydrothermal treatment temperature is generally in the range of 100 ° C to 500 ° C. Below 100 ° C the product yield is very low, and even below 120 ° C the product yield is poor. Since it becomes very high pressure above 500 ° C., the size of the reactor is limited. Preferably, it is in the range of 120 ° C to 300 ° C. More preferably, it is in the range of 140 ° C to 250 ° C. Most preferably, it is in the range of 180 ° C to 220 ° C. The treatment time is generally in the range of 0.1 to 100 hours, preferably in the range of 0.1 to 24 hours. More preferably in the range of 0.5 to 6 hours, most preferably in the range of 1.5 to 3 hours.

  By the hydrothermal treatment, particles of a metal salt or a hydrate thereof are formed. It is preferable to further refine the particles in order to remove unreacted raw materials adhering to the particles and impurities such as salts that are insufficiently grown into the particles. This purification is carried out by ionizing impurities by stirring for about 12 to 48 hours with a strong acid such as nitric acid for about 12 to 48 hours, and then washing the particles with water and collecting the particles by centrifugation. be able to.

Solvothermal method The solvothermal method is a technique for synthesizing a target material having high crystallinity by dissolving a starting material in a solvent containing an organic solvent and reacting at a temperature equal to or higher than the boiling point of the solvent. In this method, a solvent is generally used at a temperature of 100 ° C. to 1000 ° C. and a pressure of 1 to 10,000 atm to a high level. Here, when water is used as a solvent, it is particularly called a hydrothermal synthesis method, and when glycol is used as a solvent, it is particularly called a glycothermal method. Since the hydrothermal synthesis method has been described above, this section describes the solvothermal method using a solvent other than water.

  The solvothermal method is a method comprising a step of preparing a mixed solution of metal ions A, anions B and a solvent in the general formula (1), and a step of synthesizing the mixed solution at a predetermined temperature and pressure. Here, in preparing the mixed solution at room temperature and atmospheric pressure, the metal ions A and the anions B in the general formula (1) do not necessarily have to be dissolved. The solvent in the solvothermal method is generally selected from various alcohols (for example, methanol, ethanol, 1-propanol, 2-propanol, butanol, etc.), acetone, hexane, various ethers, and each group. There are those using a mixture of at least two or more solvents as a reaction solvent, and those using a mixture of the organic solvent and water as a reaction solvent. Preferably, those using ethanol, methanol, glycol, or a solvothermal method using a mixed solvent thereof with water, more preferably those using ethanol, or a solvothermal method using a mixed solvent thereof with water, Most preferred is a solvothermal method using a mixed solvent of water and ethanol in a volume ratio of 1: 1. The concentration of metal ion A in the mixed aqueous solution of metal ion A and anion B is usually about 1 to 3000 mM, and the concentration of anion B is about 0.8 to 1.2 times the stoichiometric amount with respect to metal A. It is.

  Next, the raw material mixture is subjected to heat treatment. The heat treatment method is a method in which a raw material solution is subjected to high-temperature and high-pressure treatment for a certain time to synthesize a compound by utilizing the high reactivity and dissolution / precipitation action of the solution under high temperature and high pressure, and to grow crystals. Specifically, the raw material solution is put in a corrosion-resistant and heat-resistant reaction vessel, which is loaded into a high-pressure vessel such as an autoclave, and heat treatment is performed using an electric furnace or an oil bath. Specifically, the raw material solution may be put in a corrosion-resistant, heat-resistant, pressure-resistant reaction vessel, and this may be heat-treated using an electric furnace or an oil bath. The heat treatment temperature is generally in the range of 100 ° C to 500 ° C. Below 100 ° C the product yield is very low, and even below 120 ° C the product yield is poor. Since it becomes very high pressure above 500 ° C., the size of the reactor is limited. Preferably, it is in the range of 120 ° C to 300 ° C. More preferably, it is in the range of 130 ° C to 170 ° C. Most preferably, it is in the range of 131 ° C to 149 ° C. The treatment time is generally in the range of 0.1 to 300 hours, preferably in the range of 0.1 to 24 hours. More preferably in the range of 0.5 to 6 hours, most preferably in the range of 1.5 to 3 hours.

  The obtained metal salt or hydrate particles are preferably purified by the same method as in the hydrothermal synthesis method.

  The particles obtained by the above method can be used as they are as an MRI probe, but it is preferable to coat the particles with a hydrophilic substance in order to further improve dispersibility and biocompatibility in water (body fluid). . By increasing the dispersibility in water, the degree of relaxation becomes larger, and even better performance as an MRI probe can be exhibited. Moreover, it becomes possible to stay in the blood for a long time by improving biocompatibility. In addition, although the particle | grains obtained by the said method are electrically neutral fundamentally, a part of surface metal ion or anion may be missing and may be charged (refer Example 3 below). . Since water is highly polar, when the particles are charged, the dispersibility in water is high, and good dispersibility can be obtained without coating with a hydrophilic substance. When the particles are electrically neutral and have low dispersibility in water, it is particularly preferable to coat with a hydrophilic substance. Here, the “hydrophilic substance” is a substance that is soluble in water, and by coating electrically neutral particles with this, the dispersibility of the particles in water is more than in the case of not coating. It is a substance that also increases. The solubility of the hydrophilic substance in water (water 100 g, 20 ° C.) is preferably 0.01 g or more, more preferably 1 g or more. The dispersibility of the particles in water can be examined by measuring the average particle size of the particles present in water using a particle size distribution measuring device or an electron microscope.

  The following can be mentioned as an example of the said hydrophilic substance. Condensation products with divalent and polyvalent inorganic ions and organic acids such as arginic acid. Orthophosphoric acid or metaphosphoric acid having a phosphoric acid group, and their condensation products such as pyrophosphoric acid, polyphosphoric acid, cyclophosphoric acid and their heterocondensation products. Organic substance consisting of carbohydrates having phosphoric acid group, diphosphoric acid group, polyphosphoric acid group, thiophosphoric acid group, phosphonic acid group, thiophosphonic acid group, carboxyl group, sulfo group, sulfonic acid group, thiol group, mercapto group, silanetriol group And its derivatives. Monosaccharides and oligosaccharides having phosphoric acid groups, diphosphoric acid groups, polyphosphoric acid groups, thiophosphoric acid groups, phosphonic acid groups, thiophosphonic acid groups, carboxyl groups, sulfo groups, sulfonic acid groups, mercapto groups, thiol groups, silanetriol groups Organic substances and their derivatives consisting of sucrose and polysaccharides. Oligomers and polymers such as polyalkylene glycol, alkyl polyethylene glycol, aryl polyethylene glycol, alkyl aryl polyethylene glycol, and derivatives thereof. Nucleotides having phosphate groups and their oligomers and polymers. Nitrogen-containing polysaccharides and their derivatives, such as mucopolysaccharides, glycoprotides, and titines. Ribonucleic acid, deoxyribonucleic acid and the like. Also a mixture of these.

  Specifically, phosphate esters such as ascorbic acid and ascorbic acid-2-phosphate, aspartic acid, pyruvic acid, glutamic acid, glycine, alanine, serine, threonine, valine, leucine, isoleucine, cysteine, methionine, phenylalanine , Tyrosine, proline, tryptophan, lysine, arginine, histidine, tartaric acid, lactic acid, butyric acid, malic acid, citric acid, etc. and their derivatives, and their forms are either monomers, dimers, oligomers or multimers good. Phytic acid, phytic acid, neuraminic acid, N-acetylneuraminic acid, N-glycolylneuraminic acid, galacturonic acid, uronic acid, aldaric acid, aldonic acid, alditol, and their derivatives, and their forms are monomers and Any of dimer, oligo-body and multimer may be used. Glucose-6-phosphate, glucose-1-phosphate, fructose-6-phosphate, fructose-1,6-bisphosphate, etc. and their derivatives, and their forms are monomers, dimers, oligos, Any of multimers may be used. Ribose, deoxyribose, xylose, arabinose, glucose, fructose (fructose), galactose, mannose, maltose (maltose), lactose (lactose), sucrose (sucrose), etc. and their derivatives. Any of a polymer, an oligomer and a multimer may be used, and the molecular weight thereof may be any. Dextran, sulfated dextran, carboxylated dextran, dextrin, sulfated dextrin, carboxylated dextrin, cyclodextrin, sulfated cyclodextrin, carboxylated cyclodextrin, chondroitin sulfate, hyaluronic acid, cellulose, starch, glycogen, inulin, heparin, pectin , Starch and derivatives thereof, and the form thereof may be any of monomer, dimer, oligo, and multimer, and the molecular weight may be any. Polyethylene glycol derivatives such as polyethylene glycol, polyethylene glycol-4-nonylphenyl-3-sulfopropyl ether, polyacrylic acid, poly (4-styrene sulfate), poly (4-styrene sulfate-co-maleic acid), polydiallyl di ester Methyl ammonium, polyphosphoric acid and the like and derivatives thereof, and the molecular weight thereof may be any. Proteins such as albumin and globulin, their derivatives, and their molecular weights may be used.

  Of these hydrophilic substances, polysaccharides such as dextran are preferable from the viewpoint of dispersibility in water and biocompatibility. In the case of polysaccharides, the molecular weight is not particularly limited, but is usually about 1,000 to 100,000, preferably about 1,000 to 30,000.

  Coating with a hydrophilic substance is performed by bringing particles into contact with the hydrophilic substance by adding the hydrophilic substance to the aqueous dispersion of particles or adding the particles or the aqueous dispersion of particles to an aqueous solution of the hydrophilic substance. The subsequent particles can be easily collected by collecting the particles by centrifugation or the like. In this case, the contact may be performed at room temperature and is preferably performed with stirring. The contact time is not particularly limited, but may usually be about 1 minute to 60 minutes. The final concentration of the hydrophilic substance upon contact is usually 0.001 to 5% by weight, preferably about 0.01 to 0.5% by weight, and the weight ratio of the particles to the hydrophilic substance is hydrophilic to the particles 1. The active substance is usually about 0.0001 to 100, preferably about 0.001 to 10.

  Alternatively, when the hydrophilic substance is stable to heat and acid and base, such as dextran, by performing the hydrothermal synthesis method or solvothermal method described above in the presence of the hydrophilic substance. It is also possible to coat the particles with a hydrophilic substance. That is, a hydrophilic substance is allowed to coexist in a mixed aqueous solution containing metal ions A and anions B used in the hydrothermal synthesis method or solvothermal method, and the hydrothermal synthesis method or solvothermal method is performed as described above. it can. In this case, the final concentration of the hydrophilic substance in the mixed aqueous solution is usually about 0.001 to 90% by weight, preferably about 1 to 50% by weight.

  The MRI probe of the present invention can be used in the same manner as a conventional MRI probe used conventionally. That is, an MRI probe of the present invention in an amount effective for imaging is administered to a living body, and an image is taken by an MRI apparatus using this as a contrast agent. Usually, an aqueous solution or aqueous dispersion having a concentration of about 100 mM to 1000 mM is injected into an organ or tissue to be injected intravenously or observed at about 0.01 mL / kg to 1 mL / kg, and this is used as a contrast agent. An image is taken with an MRI apparatus.

  Hereinafter, the present invention will be described more specifically based on examples. However, the present invention is not limited to the following examples.

1. Preparation of GdPO ₄ · 1.5H ₂ O Particles 1.35 g of gadolinium nitrate hexahydrate was dissolved in 5 mL of water, and 10 mL of 1M aqueous sodium hydroxide solution was added thereto. Further, a solution of 0.356 g of ammonium hydrogen phosphate and 10 mL of water was added. The pH of this white turbid solution was adjusted to 12.5 with 4M aqueous sodium hydroxide solution. This was transferred to a glass tube, sealed, and stirred at 200 ° C. for 2 hours at 600 rpm. After the reaction, the reaction solution was returned to room temperature and centrifuged at 3200 rpm for 10 minutes. The supernatant was removed, 10 mL of 0.1 M nitric acid aqueous solution was added to the precipitate, and the mixture was stirred for 1 day while maintaining the pH at 1 with 1 M nitric acid aqueous solution. One day later, the supernatant was removed by centrifugation at 3200 rpm for 5 minutes. Pure water (trade name: milli Q water) was added to the precipitate, and the mixture was centrifuged at 3200 rpm for 5 minutes, and the supernatant was collected four times. The collected supernatants were combined and centrifuged at 5500 rpm for 20 minutes. The precipitate was collected and subjected to longitudinal relaxation time T1 measurement, transverse relaxation time T2 measurement, transmission electron microscope TEM observation, and XRD measurement.

2. Shape and size of particles The fine particles synthesized in 1 of this example were observed with a transmission electron microscope. The result is shown in FIG. As can be seen from FIG. 1, fine particles having a major axis of about 50 nm are generated.

3. Physicochemical Properties and Composition of Particles XRD (X-ray diffraction) measurement was performed on the fine particles synthesized in 1 of this example. The result is shown in FIG. The measurement results are as follows.
Particle composition: GdPO ₄・ 1.5H ₂ O

4). Performance as an MRI probe The fine particles synthesized in 1 of this example were measured for longitudinal relaxation time T1 and transverse relaxation time T2. The measurement conditions were as follows.
・ Particle concentration (gadolinium concentration): 26.6 mM
・ Solvent: 0.5% agarose gel aqueous solution ・ Measuring device: NMS 120 minispec NMR ANALYZER manufactured by BRUKER (external static magnetic field with permanent magnet is 40 MHz, longitudinal relaxation / transverse relaxation time measuring device)
・ Measurement temperature: 40 ℃

The results were as follows.
T1: 370 msec
T2: 92.7 msec

  Since the longitudinal relaxation time and the transverse relaxation time were measurable, it was found that the obtained particles can be used as an MRI probe. In measuring the longitudinal relaxation time and transverse relaxation time of the fine particles synthesized in 1 of this example, since the dispersibility of the fine particles in water was not good, a solution in which agarose gel was added to water was used.

1. Preparation of GdPO ₄ · 1.5H ₂ O Particles Coated with Dextran 0.675 g of gadolinium nitrate hexahydrate was dissolved in 3 mL of water, and 5 mL of 1M aqueous sodium hydroxide solution was added thereto. Further, a solution of 0.178 g ammonium hydrogen phosphate and 5 mL water was added. There, 3.90g of Dextran-40 was added. The pH of this white turbid solution was adjusted to 12.5 with 4M aqueous sodium hydroxide solution. This was transferred to a glass tube, sealed, and stirred at 200 ° C. for 2 hours at 600 rpm. After the reaction, the reaction solution was returned to room temperature and centrifuged at 3200 rpm for 10 minutes. The supernatant was removed, 10 mL of 0.1 M nitric acid aqueous solution was added to the precipitate, and the mixture was stirred for 1 day while maintaining the pH at 1 with 1 M nitric acid aqueous solution. One day later, the supernatant was removed by centrifugation at 3200 rpm for 5 minutes. Pure water (trade name: milli Q water) was added to the precipitate, and the mixture was centrifuged at 3200 rpm for 5 minutes, and the supernatant was collected four times. The collected supernatants were combined and centrifuged at 5500 rpm for 20 minutes. The supernatant is collected, longitudinal relaxation time T1 measurement, transverse relaxation time T2 measurement, transmission electron microscope TEM observation, inductively coupled plasma emission spectroscopy (ICP-AES), dynamic light scattering particle size distribution measurement, zeta potential Measurement and MRI imaging were performed.

2. Shape and size of particles The shape of the particles synthesized in 1 of Example 2 was observed with a transmission electron microscope. The result is shown in FIG. From this, it can be seen that the fine particles synthesized in Example 2 are rod-shaped particles having a major axis of about 20 to 40 nm and a minor axis of about 5 to 10 nm, and particles having a uniform particle size and particle shape are generated. In addition, although the X-ray analysis was not performed about the particle | grains synthesize | combined in Example 2, since the hydrothermal synthesis method similar to Example 1 is only performed in the presence of dextran, It is considered that particles of GdPO ₄ · 1.5H ₂ O were formed and the particles were coated with dextran.

3. Particle size distribution The particle size distribution was measured for the transparent solution in which the particles synthesized in Example 1 above were dispersed. The measurement conditions were as follows.
・ Solvent: Pure water (trade name: milli Q)
・ Measuring device: PAR-3 dynamic light scattering particle size distribution measuring device manufactured by Otsuka Electronics ・ Measuring temperature: 19.9 ℃

The results were as follows.
・ Average particle size: 236.8 nm
This result was larger than the result of “5 to 10 nm fine particles” in the TEM observation image. This is considered to be because the generated fine particles of 5 to 10 nm gather in water to form particles having an average particle size of about the average particle size obtained with a dynamic light scattering particle size distribution analyzer.

4). Particle Composition The gadolinium concentration of the transparent solution in which the fine particles synthesized in 1 of Example 2 were dispersed was measured. As a pretreatment, 0.1 mL of the transparent solution in which the particles synthesized in Example 1 above were dispersed and 0.9 mL of aqua regia (concentrated hydrochloric acid: concentrated nitric acid = 3: 1) were mixed and placed in a glass container equipped with a cooling tube. Heated at 100 ° C. with stirring for 12 hours. This solution was returned to room temperature and further diluted 1000 times with aqua regia to be used as a sample for ICP-AES measurement. The measurement conditions were as follows.
・ Solvent: Aqua regia ・ Detection wavelength: Gd: 342.247nm
・ Equipment: Shimadzu ICPS-8000 ICP-AES equipment

The results were as follows.
Gd: 3.43 μM

The concentration of gadolinium was found for the transparent solution in which the fine particles synthesized in Example 1 above were dispersed, and the X-ray analysis was not performed on the particles synthesized in Example 2, but in the presence of dextran, Since only the same hydrothermal synthesis method is performed, it is considered that particles of GdPO ₄ .1.5H ₂ O are formed and coated with dextran as in Example 1.

5. Performance as MRI probe For the particles synthesized in 1 of Example 2 above, longitudinal relaxation time T1 and transverse relaxation time T2 were measured. The measurement conditions were as follows.
・ Particle concentration (gadolinium concentration): 3.43 mM (This concentration was determined by ICP-AES measurement)
・ Solvent: Pure water (trade name: milli Q)
・ Measuring equipment: NMS 120 minispec NMR ANALYZER (BRUKER) (external static magnetic field by permanent magnet is 40MHz, longitudinal relaxation / transverse relaxation time measuring device)
・ Measurement temperature: 40 ℃

The results were as follows.
T1: 39.0 msec
T2: 34.4 msec

  As is clear from this result, by coating the particles with dextran, both the longitudinal relaxation time T1 and the transverse relaxation time T2 are significantly shortened compared to Example 1, and a larger contrast is obtained when used as an MRI probe. It can be seen that a clear image can be obtained. Further, from this result, R1 = 7.48 and R2 = 8.48 have a very large value as a contrast agent for MRI, and the fine particles synthesized in 1 of Example 2 are effective as a contrast agent for MRI. confirmed. Further, the R1 / R2 value is R1 / R2 = 1.13, which is very close to 1. The fine particles synthesized in the above 1 of Example 2 are excellent not only as a negative contrast agent but also as a positive contrast agent. I understand that

6). Zeta potential The zeta potential of the transparent solution in which the fine particles synthesized in 1 of Example 2 were dispersed was measured. The measurement conditions were as follows.
・ Solvent: Pure water (trade name: milli Q)
・ Measuring device: ELS-6000 manufactured by Otsuka Electronics Co., Ltd.

The results were as follows.
Zeta potential: 4.35 mV
From this result, it can be seen that the fine particles synthesized in 1 of Example 2 are slightly positively charged.

7). MRI imaging
(1) Spin echo method T ₁ weighted image Place the sample solution prepared as follows in a glass tube, put it on a tapper containing agar, and spin using a 1.5T MR scanner (Signa Horzon LX, GE Yokogawa Medical Systems) It was obtained echo method T ₁ -weighted images. The first row from the top is only Magnevist (registered trademark) from the left, 1.0, 0.1, 0.01 mM, and the second row is from the left, only the transparent solution in which the fine particles synthesized in Example 1 above are dispersed is 2, 0.4, 0.08 mM (Gd Concentration), the third row from the left is Resovist (registered trademark) only 1.0, 0.1, 0.01 mM, and the fourth row is pure water (trade name milli Q water). The solution from the first stage to the third stage was diluted with pure water (trade name: milli Q water).

The results are shown in FIG. First stage of FIG. 4, but in which varying concentrations of Magnevist (R) is 0.01 to 1.0 mm, with an increase in density, the image turns white in T ₁ -weighted images, Magnevist (R) It can be seen that it works as a positive contrast agent for MRI. Second stage of FIG. 4, but in which varying concentrations of dispersed clear solution of fine particles synthesized above 1 of Example 2 0.08～2MM, with an increase in density, the image in T ₁ -weighted images It turned out to be white and the fine particles synthesized in 1 of Example 2 were confirmed to be effective as a contrast agent for MRI, and also acted as a positive contrast agent in the same manner as Magnevist (registered trademark) in the first stage. I understand.

(2) Fast spin echo method T ₂ weighted image Place the sample solution prepared in the glass tube as shown below, stand on a tapper with agar, and use 1.5T MR scanner (Signa Horzon LX, GE Yokogawa Medical Systems) to obtain a fast spin echo method T ₂ -weighted images. The first row from the top is only Magnevist (registered trademark) from the left, 1.0, 0.1, 0.01 mM, and the second row is from the left, only the transparent solution in which the fine particles synthesized in Example 1 above are dispersed is 2, 0.4, 0.08 mM (Gd Concentration), the third row from the left is Resovist (registered trademark) only 1.0, 0.1, 0.01 mM, and the fourth row is pure water (trade name milli Q water). The solution from the first stage to the third stage was diluted with pure water (trade name: milli Q water).

The results are shown in FIG. Third stage from the top in FIG. 5, but in which varying concentrations of Resovist (registered trademark) to 0.01 to 1.0 mm, with an increase in density, the image becomes dark in the T ₂ -weighted images, Resovist (registered It can be seen that (Trademark) acts as a negative contrast agent for MRI. The second row in FIG. 5 shows a case where the concentration of the transparent solution in which the fine particles synthesized in Example 1 of Example 2 are dispersed is changed to 0.08 to ₂ mM. It was confirmed that the fine particles synthesized in 1 of Example 2 were effective as a contrast agent for MRI, and also worked as a negative contrast agent as in the third stage Resovist (registered trademark). I understand that. However, it can be seen that the function as a negative contrast agent is weaker than that of the third-stage Resovist (registered trademark), and the function as a positive contrast agent is stronger. This agrees with the fact that the R2 / R1 value of the fine particles synthesized in Example 1 above is very close to 1.

1. Preparation of GdPO ₄ Particles 4.06 g of gadolinium acetate tetrahydrate, 1.40 g of trimethyl phosphate and 40 mL of water: ethanol = 1: 1 solution were placed in a glass tube, sealed and stirred at 135-140 ° C. for 2 hours. The obtained colloidal solution was transferred to a dialysis cellulose tube having a pore diameter of 5 nm, and dialyzed for 1 day while constantly changing the external solution of the dialysis cellulose tube. Using the resulting transparent solution, transmission electron microscope TEM observation, inductively coupled plasma emission spectroscopy (ICP-AES), longitudinal relaxation time T1 measurement, transverse relaxation time T2 measurement, dynamic light scattering particle size distribution measurement, Zeta potential measurement and MRI imaging were performed.

2. Shape and size of particles The shape of the particles synthesized in 1 of Example 3 was observed with a transmission electron microscope. The result is shown in FIG. From this, it can be seen that particles having a diameter of about 5 to 7 nm are generated and gathered together.

3. Particle size distribution The particle size distribution of the transparent solution in which the particles synthesized in Example 1 above were dispersed was measured. The measurement conditions were as follows.
・ Solvent: Pure water (trade name: milli Q)
・ Measuring equipment: PAR-3 dynamic light scattering particle size distribution measuring equipment manufactured by Otsuka Electronics ・ Measuring temperature: 19.9 ℃

The results were as follows.
・ Average particle size: 167.4 nm
This result was larger than the result of “5 to 7 nm fine particles” in the TEM observation image. This is considered to be because the generated fine particles of 5 to 7 nm gather in water to form particles having an average particle size of about the average particle size determined by a dynamic light scattering particle size distribution analyzer.

4). Particle Composition The gadolinium and phosphorus concentrations of the transparent solution in which the fine particles synthesized in 1 of Example 3 were dispersed were measured. As a pretreatment, 0.1 mL of a transparent solution in which the particles synthesized in Example 1 above were dispersed and 0.9 mL of aqua regia (concentrated hydrochloric acid: concentrated nitric acid = 3: 1) were mixed and placed in a glass container equipped with a condenser. Heated at 100 ° C. with stirring for 12 hours. This solution was returned to room temperature and further diluted 1000 times with aqua regia to be used as a sample for ICP-AES measurement. The measurement conditions were as follows.
・ Solvent: Aqua regia ・ Detection wavelength: Gd: 342.247nm
P: 178.287nm
・ Equipment: Shimadzu ICPS-8000 ICP-AES equipment

The results were as follows.
Gd: 3.278 μM
P: 2.967 μM

From the point that the ratio of Gd to P is approximately 1: 1 and the above synthesis method, the composition of the particles is considered to be GdPO ₄ or a hydrate thereof. The reason why the Gd concentration is slightly higher than the P concentration is thought to be due to the loss of some of the PO _{4 on} the particle surface. It has become.

5. Zeta potential The zeta potential of the transparent solution in which the fine particles synthesized in 1 of Example 3 were dispersed was measured. The measurement conditions were as follows.
・ Solvent: Pure water (trade name: milli Q)
・ Measuring device: ELS-6000 manufactured by Otsuka Electronics Co., Ltd.

The results were as follows.
Zeta potential: 10.67 mV
From this result, it can be seen that the fine particles synthesized in 1 of Example 3 are positively charged.

6). Performance as MRI probe The longitudinal relaxation time T1 and the transverse relaxation time T2 of the transparent solution in which the fine particles synthesized in Example 1 of Example 3 were dispersed were measured. The measurement conditions were as follows.
・ Particle concentration (gadolinium concentration): 1.6 mM (This concentration was determined by ICP-AES measurement)
・ Solvent: Pure water (trade name: milli Q)
・ Measuring equipment: NMS 120 minispec NMR ANALYZER (BRUKER) (external static magnetic field by permanent magnet is 40MHz, longitudinal relaxation / transverse relaxation time measuring device)
・ Measurement temperature: 40 ℃

The results were as follows.
・ T1: 68.0 msec
・ T2: 67.2 msec

  From this result, R1 = 9.0 and R2 = 9.1 have a very large value as a contrast agent for MRI, and it was confirmed that the fine particles synthesized in Example 1 of Example 3 are effective as a contrast agent for MRI. It was. The R1 / R2 value is R1 / R2 = 1.01, which is very close to 1, and the fine particles synthesized in the above 1 of Example 3 are excellent not only as a negative contrast agent but also as a positive contrast agent. I understand that

7). MRI imaging
(1) Spin echo method T ₁ weighted image Place the sample solution prepared as follows in a glass tube, put it on a tapper containing agar, and spin using a 1.5T MR scanner (Signa Horzon LX, GE Yokogawa Medical Systems) It was obtained echo method T ₁ -weighted images. The first stage is 1.0, 0.1, 0.01 mM from the left only for Magnevist (registered trademark), and the second stage is only 2.3, 0.23, 0.046 mM (Gd concentration) from the left for only the transparent solution containing fine particles synthesized in Example 1 above. From the left, the third row is Resovist (registered trademark) only 1.0, 0.1, 0.01 mM, and the fourth row is pure water (trade name milli Q water). The solution from the first stage to the third stage was diluted with pure water (trade name: milli Q water).

The results are shown in FIG. First stage from top of FIG. 7, but in which varying concentrations of Magnevist (R) is 0.01 to 1.0 mm, with an increase in density, the image turns white in T ₁ -weighted images, Magnevist (R ) Works as a positive contrast agent for MRI. The second row in FIG. 7 shows a case where the concentration of the transparent solution in which the fine particles synthesized in 1 of Example 3 are dispersed is changed to 0.046 to 2.3 mM. In the T ₁ weighted image as the concentration increases. The image becomes white, and it is confirmed that the fine particles synthesized in 1 of Example 3 are effective as a contrast agent for MRI, and also works as a positive contrast agent like the first-stage Magnevist (registered trademark). I understand that.

(2) Fast spin echo method T ₂ weighted image Place the sample solution in a glass tube as shown below, place it on a tapper containing agar, and use a 1.5T MR scanner (Signa Horzon LX, manufactured by GE Yokogawa Medical Systems) to obtain a fast spin echo method T ₂ -weighted images. The first stage is 1.0, 0.1, 0.01 mM from the left only for Magnevist (registered trademark), and the second stage is only 2.3, 0.23, 0.046 mM (Gd concentration) from the left for only the transparent solution in which the fine particles synthesized in Example 1 above are dispersed. From the left, the third row is Resovist (registered trademark) only 1.0, 0.1, 0.01 mM, and the fourth row is pure water (trade name milli Q water). The solution from the first stage to the third stage was diluted with pure water (trade name: milli Q water).

The results are shown in FIG. Third stage from the top in FIG. 8, but in which varying concentrations of Resovist (registered trademark) to 0.01 to 1.0 mm, with an increase in density, the image becomes dark in the T ₂ -weighted images, Resovist (registered It can be seen that (Trademark) acts as a negative contrast agent for MRI. The second row in FIG. 8 shows the case where the concentration of the transparent solution in which the fine particles synthesized in Example 1 of Example 3 are dispersed is changed to 0.046 to 2.3 mM. In the T ₂ weighted image as the concentration increases. The image becomes dark and the fine particles synthesized in 1 of Example 3 are confirmed to be effective as a contrast agent for MRI, and also works as a negative contrast agent as in the third stage Resovist (registered trademark). I understand that However, it can be seen that the function as a negative contrast agent is weaker than that of the third-stage Resovist (registered trademark), and the function as a positive contrast agent is stronger. This agrees with the fact that the R2 / R1 value of the fine particles synthesized in Example 1 above is very close to 1.

  The fine particles synthesized in Example 3 were coated. First, sodium polyphosphate, sodium dextran sulfate (m.w.25000), sodium dextran sulfate (m.w.4000), and dextran-40 were used as coating agents. Sodium polyphosphate, sodium dextran sulfate (m.w.25000), and sodium dextran sulfate (m.w.4000) were added in an amount of 0.1 wt% to the water in which the fine particles synthesized in Example 3 were dispersed.

1. Preparation of coated GdPO ₄ · 1.5H ₂ O particles with dextran
The same operation as in Example 2 was performed except that the stirring time at 200 ° C. and 600 rpm in the sealed glass tube was changed to 2.5 hours after adding Dextran-40 and adjusting the pH to 12.5 with an aqueous sodium hydroxide solution. GdPO4 · 1.5H2O particles coated with dextran were prepared. Supernatant liquid after centrifugation at 5500 rpm for 20 minutes is collected, transmission electron microscope TEM observation, XRD (X-ray diffraction) measurement, dynamic light scattering particle size distribution measurement, Fourier transform infrared (FT-IR) spectroscopy measurement, induction Coupled radio frequency plasma emission spectroscopy (ICP-AES), longitudinal relaxation time T1 measurement, transverse relaxation time T2 measurement, SQUID (magnetic susceptibility) measurement, and MRI imaging were performed.

2. Shape and size of particles The shape of the particles synthesized in Example 1 above in Example 1 was observed with a transmission electron microscope. The result is shown in FIG. Measuring devices: TECNAI F20 (acceleration voltage: 200 kV), TECNAI 12 (acceleration voltage: 120 kV) manufactured by FEI Company. In FIG. 9, a large photograph is a photograph at an acceleration voltage of 200 kV, and a lower right inset is a photograph at an acceleration voltage of 120 kV.

  From the photograph at an acceleration voltage of 200 kV, the fine particles synthesized in Example 5 are rod-like particles having a major axis of about 20 to 40 nm and a minor axis of about 5 to 15 nm, and particles having a uniform particle size and particle shape are generated. I understand that. In addition, it can be seen from the photograph at an acceleration voltage of 120 kV that there are substances that cannot be seen at the acceleration voltage of 200 kV on the surface of the rod-like particles, that is, a substance that is difficult to X-ray diffraction. Since this is not visible at 200 kV, this substance is considered to be an organic substance, and is considered to be dextran coating rod-shaped particles. This is also supported by the results of the following Fourier transform infrared (FT-IR) spectroscopic measurement.

3. Physicochemical properties and composition of particles XRD (X-ray diffraction) measurement was performed on the fine particles synthesized in 1 of the present example. The result is shown in FIG. The measurement results are as follows. This shows that GdPO ₄ H ₂ O is mixed with GdPO ₄ 1.5H ₂ O. Particle composition: GdPO ₄・ 1.5H ₂ O ＋ GdPO ₄・ H ₂ O

4). Particle size distribution The particle size distribution of the transparent solution in which the particles synthesized in Example 1 above were dispersed was measured. The measurement conditions were as follows.
・ Solvent: Pure water (trade name: milli Q)
・ Measuring device: PAR-3 dynamic light scattering particle size distribution measuring device manufactured by Otsuka Electronics ・ Measuring temperature: 25.2 ℃

The results were as follows.
・ Average particle size: 23.2 ± 7.8 nm
This result was the same scale as the result of a TEM observation image of “rod-like particles having a major axis of about 20 to 40 nm and a minor axis of about 5 to 15 nm”. From this, it can be seen that the particles synthesized in 1 of Example 5 are monodispersed and no aggregation occurs.

5. Fourier Transform Infrared (FT-IR) Spectroscopic Measurement For the transparent solution in which the particles synthesized and purified in 1 of Example 5 were dispersed, the solvent water was removed under reduced pressure to obtain a white powder. The white powder was subjected to Fourier transform infrared (FT-IR) spectroscopy. The measurement conditions were as follows.
・ Method: KBr method ・ Measuring equipment: FT / IR-600 plus by JASCO

  From this, it can be seen that the particles synthesized and purified in 1 of Example 5 contain dextran. Since the particles synthesized and purified in 1 of Example 5 were purified by centrifugation, this dextran is considered to be integrated with the particles. Further, from the transmission electron micrograph of the acceleration voltage of 120 kV in 2 above, dextran is present on the particle surface, suggesting that the particles synthesized in 1 of Example 5 are coated.

6). Gadolinium Ion Concentration The gadolinium concentration of the transparent solution in which the fine particles synthesized in Example 1 of Example 5 were dispersed was measured. As a pretreatment, 0.1 mL of a transparent solution in which the particles synthesized in Example 1 above were dispersed and 0.9 mL of aqua regia (concentrated hydrochloric acid: concentrated nitric acid = 3: 1) were mixed and placed in a glass container equipped with a condenser. Heated at 100 ° C. with stirring for 12 hours. This solution was returned to room temperature and further diluted 1000 times with aqua regia to be used as a sample for ICP-AES measurement. The measurement conditions were as follows.
・ Solvent: Aqua regia ・ Detection wavelength: Gd: 342.247nm
・ Equipment: Shimadzu ICPS-8000 ICP-AES equipment

The results were as follows.
Gd: 2.17 mM (concentration of gadolinium ions in the transparent solution in which the fine particles synthesized in Example 1 above were dispersed)

7). Performance as MRI probe The longitudinal relaxation time T1 and the transverse relaxation time T2 of the transparent solution in which the fine particles synthesized in Example 1 of Example 5 were dispersed were measured. The measurement conditions were as follows.
・ Particle concentration (gadolinium concentration): 2.17 mM (this concentration was determined by ICP-AES measurement)
・ Solvent: Pure water (trade name: milli Q)
・ Measuring equipment: NMS 120 minispec NMR ANALYZER (BRUKER) (external static magnetic field by permanent magnet is 40MHz, longitudinal relaxation / transverse relaxation time measuring device)
・ Measurement temperature: 40 ℃

The results were as follows (FIG. 13).
R1: 13.9 mM ^-1 sec ^-1
R2: 15.0 mM ^-1 sec ^-1

  From this result, the transparent solution in which the fine particles synthesized in Example 1 of Example 5 are dispersed has very large values as a contrast agent for MRI of R1 = 13.9 and R2 = 15.0. It was confirmed that the microparticles synthesized in 1) are effective as a contrast agent for MRI. It can be seen that the longitudinal relaxation time shortening effect R1 and the lateral relaxation time shortening effect R2 are larger than those of the transparent solution in which the fine particles synthesized in Example 1 above are dispersed, and a larger contrast is obtained when used as an MRI probe. It can be seen that a clear image can be obtained. This is considered to be because the formation of particles sufficiently progressed by increasing the reaction time.

  The R2 / R1 value was R2 / R1 = 1.08, which is closer to 1 than the transparent solution in which the fine particles synthesized in Example 1 were dispersed, and the fine particles synthesized in Example 1 above. Is very good as a positive contrast agent.

8). SQUID (Magnetic Susceptibility) Measurement For the transparent solution in which the particles synthesized in 1 of Example 5 were dispersed, the solvent water was removed under reduced pressure to obtain a white powder. This white powder was measured for SQUID (magnetic susceptibility). The measurement conditions were as follows.
・ Measuring device: 7 T Quantum Design SQUID magnetometer manufactured by Quantum Design Japan
・ Measurement temperature: 300 K

  The results are shown in FIG. From this, it was found that the particles synthesized in 1 of Example 5 were paramagnetic. This proves that the particles synthesized in 1 of Example 5 have an R2 / R1 value very close to 1 as shown in 7 of Example 5. This is because when the particles are not paramagnetic but ferromagnetic or superparamagnetic, R2 increases and R2 / R1 increases in MRI where a strong external magnetic field exists. When R2 / R1 value is large, it is effective as a negative contrast agent. It can be seen that the fine particles synthesized in 1 of Example 5 are very excellent as a positive contrast agent.

9. MRI imaging
(1) Spin echo method T1-weighted image Place the sample solution prepared in the following into a glass tube, stand on a tapper with agar, and spin echo using a 1.5T MR scanner (Signa Horzon LX, GE Yokogawa Medical Systems) Method T1-weighted images were obtained. The first row from the top is only Magnevist (registered trademark) from the left, 5.0, 1.0, 0.5, 0.1, 0.01 mM, and the second row is from the left only the transparent solution in which the fine particles synthesized in the above 1 of Example 5 are dispersed is 2.2, 1.1, 0.5, 0.2, 0.04 mM (Gd concentration), the third row is Resovist (registered trademark) only from the left 5.0, 1.0, 0.5, 0.1, 0.01 mM (Fe concentration), the fourth row is pure water (trade name milli Q Water). The solution from the first stage to the third stage was diluted with pure water (trade name: milli Q water).

  The results are shown in FIG. The first row in FIG. 15 is obtained by changing the concentration of Magnevist (registered trademark) to 0.01 to 5.0 mM, but as the concentration increases, the image becomes white in the T1-weighted image, and Magnevist (registered trademark) becomes MRI. It can be seen that it works as a positive contrast medium for The second row of FIG. 15 shows the case where the concentration of the transparent solution in which the fine particles synthesized in Example 1 of Example 5 are dispersed is changed to 0.04 to 2.2 mM. It turned out that the fine particles synthesized in Example 1 of Example 5 were effective as a contrast agent for MRI, and also acted as a positive contrast agent in the same manner as Magnevist (registered trademark) in the first stage. I understand.

(2) Fast spin echo method T2-weighted image Place the sample solution prepared in a glass tube as shown below, stand on a tapper containing agar, and fast using a 1.5T MR scanner (Signa Horzon LX, GE Yokogawa Medical Systems). Spin echo T2-weighted images were obtained. The first row from the top is 5.0, 1.0, 0.5, 0.1, 0.01 mM only from the left, and the second row is only the transparent solution in which the fine particle Magnevist (registered trademark) synthesized in Example 1 of Example 5 is dispersed from the left 2.2, 1.1, 0.5, 0.2, 0.04 mM (Gd concentration), the third row is Resovist (registered trademark) only from the left 5.0, 1.0, 0.5, 0.1, 0.01 mM (Fe concentration), the fourth row is pure water (trade name milli Q Water). The solution from the first stage to the third stage was diluted with pure water (trade name: milli Q water).

  The results are shown in FIG. The third row from the top of FIG. 16 is obtained by changing the concentration of Resovist (registered trademark) to 0.01 to 5.0 mM. As the concentration increases, the image becomes darker in the T2-weighted image, and Resovist (registered trademark) ) Works as a negative contrast agent for MRI. The second row in FIG. 16 is the one in which the concentration of the transparent solution in which the fine particles synthesized in Example 1 of Example 5 are dispersed is changed to 0.04 to 2.2 mM. It was confirmed that the fine particles synthesized in 1 of Example 5 were effective as a contrast agent for MRI, and also acted as a negative contrast agent as in the third stage Resovist (registered trademark). I understand that. However, the function as a negative contrast agent is weaker than that of the third-stage Resovist (registered trademark), and it can be seen that, like the first-stage Magnevist (registered trademark), the function as a positive contrast agent is stronger. This coincides with the fact that the R2 / R1 value of the fine particles synthesized in 1 of Example 5 is very close to 1.

10. MRI imaging (in vivo)
VX2 cancer-bearing rabbits were used as the tumor-bearing animals, and the fine particles synthesized in 1 of Example 5 were administered from the posterior auricular vein. From left, T1-weighted images before administration, 5 minutes after administration, 10 minutes after administration, 30 minutes after administration, and 24 hours after administration.

  The results are shown in FIG. It can be seen that the cancer tissue in the center of the image is drawn white as time passes after administration. This is because angiogenesis is actively performed in cancer tissues, macromolecules in blood leak into cancer tissues, and since the drainage pathway is underdeveloped, macromolecules leaked into cancer tissues remain in cancer tissues (EPR) Since the Enhanced Permeation and Retention) effect is occurring, it is considered that the fine particles synthesized in Example 1 above, which are fine particles having a diameter of 100 nm or less, were accumulated in the cancer tissue. It was shown that the fine particles synthesized in 1 of Example 5 are effective not only as a normal contrast agent for MRI but also as a contrast agent that specifically shows cancer tissue.

  VX2 cancer-bearing rabbits were used as tumor-bearing animals, and Magnevist (registered trademark) was administered from the posterior auricular vein. From left, T1-weighted images before administration, 5 minutes after administration, 10 minutes after administration, 30 minutes after administration, and 24 hours after administration.

  The results are shown in FIG. When Magnevist (registered trademark) is used, it can be seen that a specific contrast increase of the cancer tissue in the center of the image does not occur. This is considered to be because Magnevist (registered trademark) has a small molecular size and cannot be accumulated in cancer tissue using the EPR effect like the fine particles synthesized in Example 1 above.

2 is a transmission electron micrograph of particles produced in Example 1. FIG. The scale bar is 10 nm. 2 is a diagram showing the results of XRD (X-ray diffraction) measurement of particles produced in Example 1. FIG. 2 is a transmission electron micrograph of particles produced in Example 2. FIG. The scale bar is 20 nm. A dispersion of particles produced in Example 2 is T ₁ weighted image obtained by MRI imaging. 4 is a T ₂ weighted image obtained by MRI imaging of a particle dispersion prepared in Example 2. FIG. 4 is a transmission electron micrograph of particles produced in Example 3. The scale bar is 0.1 μm. A dispersion of particles produced in Example 3 is T ₁ weighted image obtained by MRI imaging. A dispersion of particles produced in Example 3 is T ₂ weighted images obtained by MRI imaging. 6 is a transmission electron micrograph of particles produced in Example 5. FIG. 6 is a view showing an XRD pattern of particles produced in Example 5. FIG. It is a figure which shows the result of the dynamic light-scattering type particle size distribution measurement of the particle produced in Example 5. It is a figure which shows the infrared spectrum of the particle | grains produced in Example 5, and dextran. It is a figure which shows the result of having measured the longitudinal relaxation time T1 and the lateral relaxation time T2 of the particle | grains produced in Example 5. FIG. It is a figure which shows the result of having measured SQUID (magnetic susceptibility) of the particle | grains produced in Example 5. FIG. 7 is a T1-weighted image of spin echo method particles produced in Example 5. FIG. 6 is a T2-weighted image of the spin echo method particles produced in Example 5. FIG. FIG. 6 is a T1-weighted image of a VX2 cancer-bearing rabbit administered with particles prepared in Example 5. FIG. It is a T1-weighted image of a VX2 cancer-bearing rabbit administered with Magnevist (registered trademark).

Claims (10)

An MRI probe comprising particles composed of a compound represented by the following general formula (1) or a hydrate thereof.
A _m B _n (1)
(However, A is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Y, Mn, Cr, Fe, Co, Ni, and Cu. Represents an ion of at least one metal selected from the group consisting of: B is selected from the group consisting of phosphate ion, sulfonate ion, carboxylate ion, borate ion, citrate ion, nitrate ion and halide ion Represents at least one anion, and m and n independently of each other represent a positive number).   The MRI probe according to claim 1, wherein m and n each independently represent a number of 0.5 to 2.0.   The MRI probe according to claim 1 or 2, wherein the A is a Gd ion and the B is a phosphate ion.   The MRI probe according to any one of claims 1 to 3, wherein an average particle diameter of the particles is 0.3 nm or more and 5000 nm or less.   The MRI probe according to claim 4, wherein an average particle diameter of the particles is 0.5 nm or more and 500 nm or less.   An MRI probe comprising particles obtained by coating the particles according to any one of claims 1 to 3 with a hydrophilic substance.   The MRI probe according to claim 6, wherein the hydrophilic substance is a polysaccharide.   The MRI probe according to claim 7, wherein the polysaccharide is dextran.   The MRI probe according to any one of claims 6 to 8, wherein an average particle size of the coated particles is 0.3 nm or more and 500 nm or less. The MRI probe according to claim 9, wherein the average particle diameter of the coated particles is 0.5 nm or more and 500 nm or less.

Images