JP2021085016A - pH-RESPONSIVE POLYMER COMPOUND - Google Patents

Abstract

To provide a pH-responsive polymer compound that undergoes a volume phase transition sharply in response to a pH change in particular in a slightly acidic range.SOLUTION: The polymer compound is obtained by copolymerization of a cross-linking agent and a polymerizable monomer. The polymerizable monomer includes one or more selected from the group consisting of methacrylic acid, acrylic acid, allylamine, 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl methacrylate, 2-(diisopropylamino)ethyl methacrylate, acrylamide, N-isopropylacrylamide, N-vinylpyrrolidone and 4-vinylpyridine. The cross-linking agent comprises a compound represented by the general formula (1) in the figure, where R represents a hydrogen atom or methyl group, and n represents an integer from 2 to 4.)SELECTED DRAWING: None

Description

The present invention relates to pH responsive polymer compounds and their use.

Magnetic resonance imaging (MRI) is a useful imaging method that enables non-invasive visualization of living tissues with excellent spatial and temporal resolution, and is one of the important methods in diagnosing tumors and the like. .. In MRI, the density and state of hydrogen nuclei per unit volume placed in a predetermined magnetic field (longitudinal relaxation time T ₁ , horizontal relaxation time T ₂ , flow v) are adjusted by adjusting values such as repetition time and echo time. And image it. MRI contrast agents are widely used in the medical field because they improve the contrast of images by shortening _{T 1} and T _{2 of hydrogen nuclei and enable clear tissue viewing.} The shortening efficiency of T ₁ and T ₂ is expressed as their relaxation ability (r ₁ , r ₂ ), and the higher these are, the more sensitive the MRI contrast agent becomes, and the MRI signal intensity changes significantly.
Conventionally, a chelated heavy metal such as gadolinium has been used as an MRI contrast agent, but since there are problems such as limited imaging ability and side effects, an alternative contrast agent is required.

The extracellular pH is usually maintained at about 7.2, but it is known that it is as low as about pH 6.4 in malignant tumors. If high contrast can be obtained in the range of pH 6.4 to 7.2 in MRI, it can be very useful for discriminating tumor tissue. Therefore, a substance that can be applied to an MRI contrast agent whose relaxation time changes in response to pH has been searched for.
For example, Non-Patent Document 1, there is a manganese ions have been described pH probe encapsulated in a polymer compound, T ₁ imaging capability is changed four times in PH7.4～6.5.
There are also examples of finding pH responsiveness in crosslinkable polymer compounds. For example, Patent Document 1 and Non-Patent Documents 2 to 3 describe polymer compounds in which methacrylic acid is crosslinked with a cross-linking agent such as methylene bisacrylamide or ethylene glycol dimethacrylate, and these are volumes in response to pH. It is disclosed that a phase transition occurs. In particular, it is disclosed that a polymer compound copolymerized with methacrylic acid and methylenebisacrylamide exhibits a wide range of gradual T ₂ changes at pH 4 to 7 (Non-Patent Documents 2 to 3).
However, the relationship between the type and degree of cross-linking of the cross-linking polymer compound and the pH responsiveness and NMR relaxation time related to the volume phase transition has not been investigated in detail.

US2017 / 0152334

Nature Nanotechnology, 11, 724-730 (2016) Dalton Transactions, 42, 15864-15867 (2013) Bioorganic & Medicinal Chemistry 20, 769-774 (2012)

An object of the present invention is to provide a pH-responsive polymer compound that sharply undergoes a volume phase transition in response to a pH change, particularly a pH change in a weakly acidic range, and the polymer compound. Further, it is an object to provide an MRI contrast agent which is excellent in MRI imaging capability, in particular _{T 2} imaging capability.

As a result of intensive studies to solve the above problems, the present inventors have found that a crosslinkable polymer compound crosslinked with a specific crosslinking agent causes a sharp volume phase transition with respect to a change in pH, and that the value is high. It was found to have a T ₂ imaging capability molecular compound excellent. We also came up with the idea that the pH responsiveness can be adjusted by changing the degree of cross-linking, and have completed the present invention.

That is, one aspect of the present invention is a polymer compound obtained by copolymerizing a polymerizable monomer and a cross-linking agent, wherein the polymerizable monomer is methacrylic acid, acrylic acid, allylamine, 2- (dimethylamino). One or more selected from the group consisting of ethyl methacrylate, 2- (diisopropylamino) ethyl methacrylate, 2- (diisopropylamino) ethyl methacrylate, acrylamide, N-isopropylacrylamide, N-vinylpyrrolidone, and 4-vinylpyridine. The cross-linking agent is a polymer compound containing a compound represented by the following general formula (1).

（一般式（１）中、Ｒは水素原子又はメチル基を表し、ｎは２〜４の整数を表す。）

(In the general formula (1), R represents a hydrogen atom or a methyl group, and n represents an integer of 2 to 4).

In this embodiment, the degree of cross-linking by the cross-linking agent is preferably 30 mol% or more with respect to the entire polymer compound.
In this embodiment, the cross-linking agent preferably contains a compound of n = 2 in the general formula (1).
The polymer compound of this embodiment can be preferably included in the MRI contrast agent.
The polymeric compound of this embodiment can be preferably included in the drug carrier.
The polymer compound of this embodiment can be preferably included in the reagent for spectrophotometry.

Another aspect of the present invention is a method for producing a polymer compound, which comprises copolymerizing a polymerizable monomer and a cross-linking agent, wherein the polymerizable monomer is methacrylic acid, acrylic acid, allylamine, 2-(. One selected from the group consisting of dimethylamino) ethyl methacrylate, 2- (diethylamino) ethyl methacrylate, 2- (diisopropylamino) ethyl methacrylate, acrylamide, N-isopropylacrylamide, N-vinylpyrrolidone, and 4-vinylpyridine or It is a production method containing two or more kinds, and the cross-linking agent contains a compound represented by the general formula (1).
In this embodiment, the molar ratio of the polymerizable monomer to the cross-linking agent is preferably 70:30 to 2:98.
In this embodiment, the cross-linking agent preferably contains a compound of n = 2 in the general formula (1).

Another aspect of the present invention is a method of measuring the pH of a target, which is a step of bringing the target into contact with the polymer compound of the present invention and a step _{of measuring the T 2} relaxation time of the target in contact with the polymer compound. , And a step of comparing _{the measured value of the T 2} relaxation time with a calibration curve prepared in advance to determine the pH of the target.
In this embodiment, the target is preferably a biological sample.

The polymer compound of the present invention sharply undergoes a volumetric phase transition in which it contracts on the low pH side and swells on the high pH side due to a change in hydrophobic interaction in a narrow pH range of weak acidity. As a result, the motility of the water molecules that hydrate the polymer compound changes significantly, and the lateral relaxation time T ₂ changes sharply in response to pH, so that excellent T ₂ imaging ability can be exhibited. Therefore, the polymer compound of the present invention can be a main component of a paramagnetic metal-free MRI contrast agent.
In addition, the polymer compound of the present invention can be used as a drug carrier capable of selectively delivering tumor tissue by utilizing the sharp volume phase transition in response to a change in pH.

The conceptual diagram which shows _{the behavior of the T 2} relaxation time by the volume phase transition of the pH responsive polymer compound and the corresponding MR image (T _{2 emphasis image).} The graph which shows the _{T 2} measurement value in each pH condition of the polymer compound 1-6. Graph showing imaging capability _{r 2} at each pH condition of the polymer compound 1-6. Appearance photograph of polymer compounds 1 to 6 under each pH condition. Transmission electron micrographs of polymer compounds 1 to 6 (scale bar: 200 nm).

The polymer compound of the present invention is a polymer compound obtained by copolymerizing a polymerizable monomer and a cross-linking agent, and the polymerizable monomer is methacrylic acid, acrylic acid, allylamine, 2- (dimethylamino) ethyl methacrylate. , 2- (diisopropylamino) ethyl methacrylate, 2- (diisopropylamino) ethyl methacrylate, acrylamide, N-isopropylacrylamide, N-vinylpyrrolidone, and 4-vinylpyridine. , The cross-linking agent is a polymer compound containing a compound represented by the following general formula (1).

（一般式（１）中、Ｒは水素原子又はメチル基を表し、ｎは２〜４の整数を表す。）

(In the general formula (1), R represents a hydrogen atom or a methyl group, and n represents an integer of 2 to 4).

The polymerizable monomer in the present invention is methacrylic acid, acrylic acid, allylamine, 2- (dimethylamino) ethyl methacrylate, 2- (diethylamino) ethyl methacrylate, 2- (diisopropylamino) ethyl methacrylate, acrylamide, N-isopropylacrylamide, N. -One or more selected from the group consisting of vinylpyrrolidone and 4-vinylpyridine. The polymerizable monomer preferably contains methacrylic acid, more preferably composed of methacrylic acid, but is not particularly limited.

The cross-linking agent in the present invention contains the compound represented by the general formula (1). In the general formula (1), n represents an integer of 2 to 4, preferably containing a compound of n = 2 from the viewpoint of responsiveness in the range of pH 6.4 to 7.2, and a compound of n = 2 alone. It is more preferable to include in. Further, in the general formula (1), R represents a hydrogen atom or a methyl group, and is preferably a methyl group.
In the general formula (1), the compound in which R is a methyl group and n = 2 is diethylene glycol dimethacrylate (DEGDMA), the compound in which R is a methyl group and n = 3 is triethylene glycol dimethacrylate (TEGDMA), and R is a methyl group. The compound with n = 4 is tetraethylene glycol dimethacrylate (TETEGDMA).
As long as the cross-linking agent in the present invention contains the compound represented by the general formula (1), it is not hindered to contain other cross-linking agents, but it is preferable that the cross-linking agent is substantially free of other cross-linking agents. Examples of other cross-linking agents include methylene bisacrylamide (MBAA), ethylene glycol dimethacrylate (EGDMA) and the like.

The polymer compound of the present invention is a copolymer of the above-mentioned polymerizable monomer and a cross-linking agent.
The average degree of polymerization is not particularly limited.
The polymer compound of the present invention usually has a three-dimensional structure, and is preferably spherical (including substantially spherical) particles. The three-dimensional structure can hold water molecules inside. The particle size is not particularly limited, but is preferably 10 to 1000 nm.
Here, the particle size can be measured by a transmission electron microscope, a scanning electron microscope, an atomic force microscope, a size exclusion chromatography method, a dynamic or static light scattering method, or the like.

In the polymer compound of the present invention, the degree of cross-linking by the cross-linking agent is preferably 30 mol% or more, more preferably 35 mol% or more, still more preferably 40 mol% or more with respect to the entire polymer compound. The upper limit of the degree of cross-linking is preferably 98 mol% or less, 95 mol% or less, 90 mol% or less, 85 mol% or less, 80 mol% or less, 75 mol% or less, 70 mol% or less, 65 mol% or less, 60 mol% or less, or 55 mol%. It may be:
Here, the degree of cross-linking refers to the molar ratio of the cross-linking agent to the total molar amount of the polymerizable monomer and the cross-linking agent.
By setting the degree of cross-linking in such a range, the polymer compound undergoes a volume phase transition in the range of pH 6.4 to 7.2.

The polymer compound of the present invention can be produced by copolymerizing the above-mentioned polymerizable monomer and a cross-linking agent.
The copolymerization can be carried out by a conventional method, and is preferably carried out by, for example, precipitation polymerization. According to the precipitation polymerization, the reaction is easy to proceed, and the particle size of the obtained polymer compound is easy to be uniform. It is preferable that the particle size is uniform because it is easy to handle and the pH response of the polymer compound becomes sharp. As described above, the polymer compound of the present invention is usually in the form of spherical (including substantially spherical) particles.
The reaction conditions are arbitrary and may be appropriately adjusted by those skilled in the art based on well-known techniques.
A core-shell structure with a polymer shell may be formed by a well-known method.

In the copolymerization reaction, a polymerization initiator may be used.
Examples of the polymerization initiator include 2,2'-azobis (isobutyronitrile) (AIBN), 2,2'-azobis-2-methylbutyronitrile (AMBN), 2,2'-azobis-2, 4-Dimethylvaleronitrile (ADVN), 4,4'-azobis-4-cyanovaleric acid (AVCA), 2,2'-azobis (2-methylpropionic acid) dimethyl ester, 2,2'-azobis (2-) Methylpropionamidine) dihydrochloride (AAPH), 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride and the like can be mentioned, but are not particularly limited.

In the reaction system of the copolymerization reaction, the molar ratio of the polymerizable monomer to the cross-linking agent is preferably 70:30 to 2:98. The lower limit of the molar ratio range is more preferably 65:35, even more preferably 60:40. The upper limit of the molar ratio range is 95: 5, 90:10, 85:15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45, 50:50. , Or 45:55. By setting the so-called charge amount in this way, the above-mentioned degree of cross-linking in the obtained polymer compound becomes a preferable range.

The polymer compound of the present invention causes a sharp volume phase transition in a weakly acidic pH range, particularly in the pH range of 6.4 to 7.2. More specifically, it usually shrinks at pH 6.4 or less, more preferably pH 6.6 or less, still more preferably pH 6.8 or less, and gives a cloudy appearance, usually at 7.0 or more, more preferably 7.2 or more. It swells and has a transparent appearance (Fig. 1).
In the contracted state of the polymer compound, the motility of the molecules of the hydrated water is greatly suppressed and the T ₂ relaxation time is shortened, so that the T ₂ emphasized image has a low signal and a black image. On the other hand, in the swollen state of the polymer compound, the motility of the molecules of the hydrated water increases and the T ₂ relaxation time becomes long, so that the T ₂ emphasized image has a high signal and a white image. _{When the T 2} relaxation time suddenly changes (jumps) due to the difference in pH as described above, the contrast of the image becomes large and a clear image can be obtained. Therefore, the high pH of the present invention having a sharp pH responsiveness. The molecular compound is suitable as a component of an MRI contrast agent having excellent contrast ability.

That is, the polymer compound of the present invention can be preferably included in the MRI contrast agent.
The content of the polymer compound of the present invention in the MRI contrast agent is not particularly limited, but can be, for example, 25 to 99.9% by weight of the entire contrast agent as the concentration at the time of use.
Water and components that can be normally contained may be optionally coexisted in the MRI contrast agent. Further, it may be supported on particles (beads) such as a metal such as gadolinium or a resin.
Since the MRI contrast agent containing the polymer compound of the present invention has excellent contrast ability corresponding to pH, it is expected that malignant tumors and the like can be clearly detected.

In addition, the polymer compound of the present invention can be preferably included in the drug carrier.
As described above, since the polymer compound of the present invention sharply undergoes a volume phase transition depending on pH, the drug can be selectively delivered to a target site, particularly a tissue under a low pH environment. By adjusting the cross-linking agent, the degree of cross-linking, etc. in the polymer compound, the volume phase transition can be controlled according to the change in pH, so that it is possible to design the release of the carried drug at the target site.

In addition, the polymer compound of the present invention can be preferably included in the reagent for spectrophotometry. Examples of the reagent for the spectrophotometric method include a fluorescent probe reagent used for the fluorescence measurement method, a color-developing reagent, and the like, but the reagent is not particularly limited.
As described above, since the polymer compound of the present invention causes a sharp volume phase transition depending on the pH, for example, a fluorescent compound or a dye compound may be included in the polymer compound of the present invention to be measured. The intensity of fluorescence and color development will change depending on the pH of the compound.

As described above, the polymer compound of the present invention yields a sharp volume phase transition in response to the pH, T ₂ relaxation time changes rapidly (jump) for, measuring the pH of the subject by utilizing the property It is also possible.
That is, the step of contacting with the polymer compound of the present invention, the step of measuring _{the T 2 relaxation time of the object with which the polymer compound is in contact, and the measurement value of the T 2} relaxation time are compared with the calibration curve prepared in advance. The pH of the target can be measured by at least performing the step of determining the pH of the target.
In addition, "measurement" includes quantitative and qualitative ones, and also includes grasping an approximate pH range.

_{Here, the calibration curve may be paraphrased as a standard curve, and may include a T 2} relaxation time measured in advance under at least two known pH conditions for a sample containing the polymer compound of the present invention.
In this method, the object to be measured is usually a biological sample. Specifically, this method is in
When the method is performed in vivo, a liquid or tissue in the living body is mentioned, and when the method is performed in vitro, a liquid or solid sample collected from the living body or a sample such as a tissue or a cell is mentioned. The living body may be an animal or a plant, but is usually an animal, preferably a mammal, and more preferably a human.
The object to be measured may be a sample other than a biological sample, and includes, for example, an artificially prepared aqueous solution, an aqueous solution collected from the sea, a river, or the like. By using the method of the present invention, even a sample to which it is difficult to apply the method for measuring absorbance or fluorescence can be measured.
This method makes it possible to infer, for example, the state of the tissue corresponding to the measured pH value, for example, the presence of a malignant tumor.

Hereinafter, the present invention will be described in more detail with reference to specific experimental examples, but the present invention is not limited to the following aspects.

(1) Synthesis of Polymer Compounds Polymer compounds 1 to 6 were synthesized by copolymerizing the polymerizable monomer shown in Table 1 with a cross-linking agent. A specific synthesis method will be described later.
The abbreviations are as follows.
MAA: Methacrylic acid MBAA: Methylene bisacrylamide EGDMA: Ethylene glycol dimethacrylate DEFDMA: Diethylene glycol dimethacrylate AIBN: 2,2'-azobisisobutyronitrile

(1-1) Synthesis of Polymer Compound 1 In a 100 mL three-necked flask, MAA 490 mg (5.69 mmol), MBAA 220 mg (1.42 mmol), AIBN 13 mg (0.08 mmol), and acetonitrile 80 mL. Was added, and the mixture was refluxed for 60 minutes in a nitrogen atmosphere with stirring. After immersing the three-necked flask in an ice bath, centrifugation was performed at 20000 g for 10 minutes to remove the supernatant. After adding 40 mL of acetonitrile and dispersing the precipitate by ultrasonic waves, washing was performed by removing the supernatant liquid by the same centrifugation operation. This cleaning operation was performed a total of 3 times. After air drying for 1 hour, it was vacuum dried for 24 hours. Approximately 200 mg of white powder was obtained.
Elemental analysis (C: 49.42%, H: 6.32%, N: 7.27%).

(1-2) Synthesis of Polymer Compound 2 In order to remove the polymerization inhibitor, EGDMA was purified by performing basic alumina column chromatography in advance.
MAA 368 mg (4.27 mmol) in a 100 mL three-necked flask, EGDMA
564 mg (2.85 mmol), 13 mg (0.08 mmol) of AIBN, and 80 mL of acetonitrile were added, and the mixture was refluxed under a nitrogen atmosphere for 60 minutes with stirring. After immersing the three-necked flask in an ice bath, centrifugation was performed at 20000 g for 10 minutes to remove the supernatant. After adding 40 mL of acetonitrile and dispersing the precipitate by ultrasonic waves, washing was performed by removing the supernatant liquid by the same centrifugation operation. This cleaning operation was performed a total of 3 times. After air drying for 1 hour, it was vacuum dried for 24 hours. Approximately 100 mg of white powder was obtained.
Elemental analysis (C: 54.35%, H: 7.31%, N: 0.25%).

(1-3) Synthesis of Polymer Compounds 3 to 6 In order to remove the polymerization inhibitor, DEGDMA was purified by performing basic alumina column chromatography in advance.
In a 100 mL three-necked flask, MAA [(7.12-X) x 86.09] mg (7.12-X mmol), DEFDMA [X x 242.27] mg (X mmol), AIBN 13 mg (0. 08 mmol) and 80 mL of acetonitrile were added, and the mixture was refluxed for 60 minutes under a nitrogen atmosphere with stirring. X is 1.42, 2.14, 2.85, and 3.20 in the synthesis of the polymers 3, 4, 5, and 6, respectively. After immersing the three-necked flask in an ice bath, centrifugation was performed at 20000 g for 10 minutes to remove the supernatant. After adding 40 mL of acetonitrile and dispersing the precipitate by ultrasonic waves, washing was performed by removing the supernatant liquid by the same centrifugation operation. This cleaning operation was performed a total of 3 times. After air drying for 1 hour, it was vacuum dried for 24 hours. Approximately 150 mg of white powder was obtained.
Elemental analysis was performed on polymer 3 (C: 54.38%, H: 7.26%, N: 0.27%), polymer 4 (C: 54.67%, H: 7.71%, N:). 0.24%), polymer 5 (C: 55.41%, H: 7.62%, N: 0.13%), polymer 6 (C: 56.24%,
H: 7.79%, N: 0.15%).

(2) Characteristic evaluation of synthesized polymer compound (2-1) Lateral relaxation time T ₂ measurement 100 mM phosphate buffer (pH 6.0, 6.2, 6.4, 6.6, 6.8, For each sample in which the polymer compounds 1 to 6 were dissolved in 7.0, 7.2, or 7.4) so as to be 0.5 wt%, the transverse relaxation time T ₂ was set by NMR under the following conditions. measured, to calculate the transverse relaxivity r _2.
Measurement temperature: 28.5 ° C
Nuclear magnetic resonance frequency: 43 MHz (equivalent to 1 tesla as magnetic field strength)
T ₂ measurement sequence and parameters: Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence, acquisition time = 0.8 s, repetition time = 4 s, CPMG echo time = 1 ms, final echo time = 2 s, number of steps = 20.
The horizontal relaxivity r ₂ is defined by the following equation.
r2 = (1 / T _{2, obs} -1 / T _{2, d} ) / [P]
_{(T 2, obs:} measurement of a sample containing a polymer _{compound, T 2, d: T 2} = 1.7~1.8 buffer without polymer compound, [P]: polymer concentration = 0.5 wt%)

_{FIG. 2 shows the T 2} measured values of each polymer compound solution under each pH condition. The polymer compounds 1 and 2 showed a gradual _{decrease in T 2} at pH 7.4 to 6.0, while the polymer compounds 3 to 6 showed a jump in _{which T 2 decreased sharply in a narrow pH range.} In particular, the polymer compounds 5 and 6 showed a _{T 2} change of about 2-fold at pH 6.4 to 6.8. This corresponds to a change of nearly 100 times when converted to the lateral relaxation ability r ₂ (wt% ^-1 s ^-1 _{), which is the T 2} shortening ability per unit concentration (Fig. 3).
_{Table 2 shows T 2 of the} polymer compounds 5 and 6 to pH 6.4 and 6.8 in FIG. 2 and the rate of decrease thereof, and r ₂ of pH 6.4 and 6.8 in FIG. 3 and the rate of increase thereof. Each is shown.

(2-2) Observation of volume phase transition by dynamic light scattering 100 mM phosphate buffer (pH 6.0, 6.2, 6.4, 6.6, 6.8, 7.0, 7.2 , Or 7.4), each of the polymer compounds 1 to 6 was dissolved so as to be 0.01 wt%, each sample was prepared, and the particle size of each polymer compound was measured by a dynamic light scattering method. .. The measurement temperature was 25 ° C.
Table 3 shows the cumulant average particle size (nm) of each polymer compound. The polymer compounds 5 and 6 showed a rapid change in particle size at pH 6.4 to 6.6.

(2-3) Appearance observation of volume phase transition 100 mM phosphate buffer (pH 6.0, 6.2, 6.4, 6.6, 6.8, 7.0, 7.2, or 7. In 4), each of the polymer compounds 1 to 6 was dissolved so as to be 0.5 wt%, and the image was taken with a digital camera.
FIG. 4 shows an external photograph of each polymer compound under each pH condition. For the polymer compounds 3 to 6, changes in a narrow pH range between the cloudy state and the transparent state of the solution were visually observed. In particular, the polymer compounds 5 and 6 showed a clear change in appearance at pH 6.4 to 6.8.

(2-4) Morphological Observation with Transmission Electron Microscope In a mixed solution of acetonitrile and ultrapure water, polymer compounds 1 to 6 were dissolved in 0.01 wt% each and added dropwise to a 5 μL form bar support film. After that, the sample was prepared by vacuum drying. The sample was observed using a transmission electron microscope at a measurement voltage of 200 kV.
FIG. 5 shows a transmission electron micrograph of each polymer compound.

From these test results, it can be seen that the polymer compound of the present invention contracts and aggregates due to hydrophobic interaction as the pH decreases, and the motility of water molecules hydrated in the polymer compound is greatly suppressed. As a result, the transverse relaxation time T ₂ shortening caused was suggested.

INDUSTRIAL APPLICABILITY The present invention provides a pH-responsive polymer compound that sharply causes a volume phase transition of contracting on the low pH side and swelling on the high pH side due to a change in hydrophobic interaction in a narrow pH range of weak acidity. To. The polymer compound of the present invention, and MRI contrast agents with superior T ₂ imaging capability, since that can be preferably applied to tumor tissue selectively delivering drug carrier, it is industrially very useful.

Claims (11)

A polymer compound obtained by copolymerizing a polymerizable monomer and a cross-linking agent.
The polymerizable monomer is methacrylic acid, acrylic acid, allylamine, 2- (dimethylamino) ethyl methacrylate, 2- (diethylamino) ethyl methacrylate, 2- (diisopropylamino) ethyl methacrylate, acrylamide, N-isopropylacrylamide, N-vinyl. Containing one or more selected from the group consisting of pyrrolidone and 4-vinylpyridine.
A polymer compound in which the cross-linking agent contains a compound represented by the following general formula (1).

(In the general formula (1), R represents a hydrogen atom or a methyl group, and n represents an integer of 2 to 4). The polymer compound according to claim 1, wherein the degree of cross-linking by the cross-linking agent is 30 mol% or more with respect to the entire polymer compound. The polymer compound according to claim 1 or 2, wherein the cross-linking agent contains a compound having n = 2 in the general formula (1). An MRI contrast agent containing the polymer compound according to any one of claims 1 to 3. A drug carrier comprising the polymer compound according to any one of claims 1 to 3. A reagent for spectrophotometry, which comprises the polymer compound according to any one of claims 1 to 3. A method for producing a polymer compound, which comprises copolymerizing a polymerizable monomer and a cross-linking agent.
The polymerizable monomer is methacrylic acid, acrylic acid, allylamine, 2- (dimethylamino) ethyl methacrylate, 2- (diethylamino) ethyl methacrylate, 2- (diisopropylamino) ethyl methacrylate, acrylamide, N-isopropylacrylamide, N-vinyl. Containing one or more selected from the group consisting of pyrrolidone and 4-vinylpyridine.
A production method, wherein the cross-linking agent contains a compound represented by the following general formula (1).

(In the general formula (1), R represents a hydrogen atom or a methyl group, and n represents an integer of 2 to 4). The production method according to claim 7, wherein the molar ratio of the polymerizable monomer to the cross-linking agent is 70:30 to 2:98. The production method according to claim 7 or 8, wherein the cross-linking agent contains a compound having n = 2 in the general formula (1). A method of measuring the pH of a subject
The step of bringing the object into contact with the polymer compound according to any one of claims 1 to 3.
_{A method including a step of measuring the T 2} relaxation time of a target with which the polymer compound is in contact, and a step of comparing _{the measured value of the T 2} relaxation time with a calibration curve prepared in advance to determine the pH of the target. .. The method according to claim 10, wherein the subject is a biological sample.

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