JP2014001159A - Surface-modified iron oxide nanoparticle carrying medicine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an agent-carrier complex stably carrying an anticancer agent.SOLUTION: An iron oxide nanoparticle, as a carrier, having its surface covered with polyethylene glycol-b-poly(vinylbenzyl phosphonate), carries an anticancer agent.

Description

  The present invention relates to a surface-modified iron oxide nanoparticle carrying a low molecular weight anticancer agent, more specifically, an iron oxide nanoparticle surface-modified with a specific block copolymer and an anticancer agent having a positively charged group and a hydrophobic moiety. The present invention relates to a composite and a method for producing the same.

  When low-molecular-weight drugs are administered into the blood, most of them disappear from the body due to metabolism by the liver and excretion into the urine. Therefore, in order to exert a therapeutic effect, it is necessary to administer a large amount of drug, but this causes a problem of side effects on normal tissues. In order to solve this problem, a method of encapsulating a drug in a carrier such as a specific lipid-derived liposome or a block copolymer-derived polymeric micelle has been studied. Thus, in the latter case, for example, one block of the block copolymer is made of polyethylene glycol that is hydrophilic, nonionic, and biocompatible, and the other is made of a polymer having hydrophobicity or specific properties. Moreover, drug-carrier conjugates (or complexes) that can be used for clinical use have been developed by devising how to encapsulate drugs (see, for example, Patent Document 1). Through research in this technical field including these studies, it has been found that by controlling the size of the conjugate to several tens of nanometers, the drug can be retained in the blood for a long time. It is also known that it tends to accumulate in inflammatory sites (for example, see Non-Patent Document 1).

Japanese Patent No. 2517760

Y. Matsumura, et al. , Cancer Res. 46 (1986) 6387-6392

  However, in the prior art, generally, when a drug conjugate is administered to an individual, the conjugate is disintegrated and excreted from the glomerulus by exposure to a harsh biological environment such as a high salt concentration. There is a problem that a large aggregate is formed by adsorption of serum protein and is phagocytosed by liver Kupffer cells. In addition, there is a problem that sufficient drug delivery cannot be performed because the efficiency of loading the drug on the above-described polymer micelle or the like is not necessarily high, and leakage occurs during the retention in the blood.

In addition to the development of the above-described drug carrier, the present inventors modified the surface of a biodevice or quantum dot utilizing the above-described properties of polyethylene glycol (hereinafter also referred to as “PEG”) with polyethylene glycol (or “PEGylation”). ") Has been proposed to do. For example, some of the inventors used polyethylene glycol-b-poly (vinyl benzyl phosphonate) (hereinafter also referred to as “PEG-b-PVBP”) to PEGylate iron oxide nanoparticles. When coated on the surface, PEG exhibits extremely high immobilization stability and results in surface-modified iron oxide nanoparticles coated with a relatively high density of PEG, such iron oxide nanoparticles staying in the blood for a long time In addition, it has been reported that it can be confirmed to promote tumor accumulation without a targeting ligand in a mouse tumor model (Y. Nagasaki, et al., Colloids and surface).
s. B, Biointerfaces 2011, 88, 771-778, hereinafter, Nagasaki, et al. That's it. This document is incorporated herein by reference in its entirety. ). Such surface-modified iron oxide nanoparticles themselves are expected to be used in technical fields such as hyperthermia of tumors. However, if the drug can be efficiently introduced into the surface-modified iron oxide nanoparticles, and if it does not adversely affect the characteristics such as long-term blood retention and tumor accumulation, such drug introduction The provision of iron oxide nanoparticles will contribute to solving the above-mentioned problems.

  Now, if the iron oxide nanoparticles whose surface is coated with PEG-b-PVBP is efficient and is an anticancer agent having a positively charged group and a hydrophobic portion such as doxorubicin, it is easily supported on the iron oxide nanoparticles. In addition, the inventors have found that the characteristics of the nanoparticles can be substantially maintained.

  Therefore, the present invention provides iron oxide nanoparticles carrying a drug, wherein the drug is an anticancer agent having a positively charged group and a hydrophobic moiety, and the iron oxide nanoparticles are polyethylene glycol-b-poly (vinyl benzyl phospho). The iron oxide nanoparticles (hereinafter also referred to as “nanocomposite”) having a surface coated with natto and having dispersibility in phosphate buffered saline (PBS), and a method for producing the same provide.

More specific embodiments of the present invention are as follows:
A drug-supported iron oxide nanoparticle, the drug is an antitumor agent having a positively charged group and a hydrophobic moiety, and the iron oxide nanoparticle is polyethylene glycol-b-poly (vinylbenzyl phosphonate) surface And the iron oxide nanoparticles represented by the following formula (I).

Where
R represents an unsubstituted or substituted C ₁ -C ₁₂ alkyl group, and when substituted, the substituent represents a formyl group or a group of formula R ¹ R ² CH—, where R ¹ and R ² _{independently,} C 1 -C ₄ alkoxy or ^{R 1} and ^{R 2} are -OCH ₂ CH ₂ O together _{-, - O (CH 2)} 3 O- or -O _{(CH 2)} 4 O- and Represent,
L represents a linking group,
m is an integer of 14 to 5,000,
n is an integer of 2 to 1,000,
However, in the poly (vinyl benzyl phosphonate) segment, in place of the vinyl benzyl phosphonate repeating unit, a repeating unit selected from the group consisting of vinyl benzyl hydroxy and vinyl benzyloxy C ₁ -C ₄ alkyl is randomly or It can contain up to 30% as a block.

<Detailed Description of the Invention>
Hereinafter, terms, descriptions and the like used to define the present invention will be described.
The iron oxide referred to as “iron oxide nanoparticles” can be obtained by any manufacturing method, and can be in any form as long as it meets the object of the present invention. However, although it is not limited, preferred are iron oxides such as magnetite steel (Fe ₃ O _{4 and the} like), ferric trioxide (Fe ₂ O ₃ ) α state, γ state, more preferably γ state iron oxide. Can be mentioned. Nanoparticles mean particles whose average diameter is on the order of nm, and these diameters are those determined by measuring the diameter from each electron microscopic image of at least 100 particles or present in an aqueous medium. In this state, a hydrodynamic diameter by dynamic light scattering (DLS) measurement is used as a reference. Specifically, the particles of iron oxide itself are not limited, but the number average particle diameter is 3 to 100 nm, and the iron oxide nanoparticles are made of polyethylene glycol-b-poly (vinyl benzyl phospho). In the particles whose surface is coated with natto (also referred to as “surface-modified iron oxide nanoparticles”), the hydrodynamic diameter is not limited, but is 10 to 200 nm, preferably 20 to 20 nm. 60 nm.

“Iron oxide nanoparticles are coated with polyethylene glycol-b-poly (vinyl benzyl phosphonate) (PEG-b-PVBP)” means that the interpretation of the technical scope of the present invention is limited by theory. Although not described, Nagasaki, et al. PEG-b-PVBP is bonded to the iron oxide surface through multipoint anchoring of phosphonate groups in a plurality of PVBP segments of PEG-b-PVBP. I understand. In addition, as it is known in the art that the phosphonate group has the ability to bind to various metal oxides including iron oxide, the main chain structure of the PVBP segment made of polystyrene is hydrophobic. Thus, it is understood that the binding of PEG-b-PVBP to the iron oxide surface allows the PEG chain to be firmly and densely immobilized on the surface. The surface PEG chain density of the surface-modified iron oxide nanoparticles used as a drug carrier in the present invention is the same as the preparation, the weight ratio of PEG-b-PVBP and iron salt for forming iron oxide at the time of production of the particles. By varying the zeta potential, it is preferable to use one prepared to 0.43 to 0.81 PEG chains, for example, up to a density of approximately 0.8 PEG chains per nm ² .

  Such surface-modified iron oxide nanoparticles easily carry the drug by contacting the drug with a positively charged group and an anticancer drug having a hydrophobic moiety in an aqueous medium of deionized water or an appropriately buffered aqueous solution. Surface-modified iron oxide nanoparticles (nanocomposites) can be provided. As can be understood from the above, the surface-modified iron oxide nanoparticles can be understood as having a phosphonate group and a hydrophobic domain on the surface. It is understood that it is chemically bonded and immobilized or supported on the surface-modified iron oxide nanoparticles via action and / or hydrophobic bonds. As will be described later, the nanocomposite according to the present invention thus obtained has a stable blood equivalent to the surface-modified iron oxide nanoparticles that do not carry a drug even though the drug is carried on the surface-modified iron oxide nanoparticles. It exhibits moderate retention and also exhibits significantly reduced cytotoxicity compared to the cytotoxicity of the drug itself.

  Such stability is maintained even when the drug weight is 22% based on the total weight of the surface-modified iron oxide nanoparticles carrying the drug. Accordingly, the nanocomposites that can be provided according to the present invention can include, but are not limited to, 5% to 40%, preferably 10% to 40% drug by weight, based on the total weight.

PEG-b-PVBP is capable of interacting with the iron oxide nanoparticle surface as described above, the molecular weight of each block, and additional minor (can account for up to 5% of the total molecular weight) repeating units, Substituents and the like may be included. However, a typical example of PEG-b-PVBP includes a block copolymer represented by the following formula (I).

Where
R represents an unsubstituted or substituted C ₁ -C ₁₂ alkyl group, and when substituted, the substituent represents a formyl group or a group of formula R ¹ R ² CH—, where R ¹ and R ² _{independently,} C 1 -C ₄ alkoxy or ^{R 1} and ^{R 2} are -OCH ₂ CH ₂ O together _{-, - O (CH 2)} 3 O- or -O _{(CH 2)} 4 O- and Represent,
L represents a linking group,
m is an integer of 14 to 5,000, preferably 90 to 1200;
n is an integer of 2 to 1,000, preferably 10 to 100;
However, in the poly (vinyl benzyl phosphonate) segment, in place of the vinyl benzyl phosphonate repeating unit, a repeating unit selected from the group consisting of vinyl benzyl hydroxy and vinyl benzyloxy C ₁ -C ₄ alkyl is randomly or The block may contain up to 30%, preferably up to 10%, more preferably up to 5%, particularly preferably 0%.

The repeating unit in the above proviso can usually be included by the production method of PEG-b-PVBP.
C ₁ -C ₁₂ alkyl group or an alkyl group referred to in _C 1 -C ₄ alkyl are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s- butyl, t- butyl, pentyl, isopentyl, neopentyl, hexyl, isohexyl, Includes heptyl, dodecyl and the like.
The linking group L may be any group as long as it does not adversely affect the above-described interaction between PEG-b-PVBP and iron oxide nanoparticles, but — (CH ₂ ) _c S—, —CO (CH ₂ ) _c S—, —COO (CH ₂ ) _c S—, —COC (CH ₃ ) ₂ —, are selected, where c can be an integer from 1 to 5. Incidentally, wherein the direction of the binding of these linking groups in (I) is a forward described, for example, - (CH ₂₎ When c _S- of poly through a S (vinylbenzyl phosphonate) Means to join segments.

Since it can be understood that the drug is supported on the surface-modified iron oxide nanoparticles by the above-mentioned mechanism of action, any drug can be included as long as it is a low-molecular anticancer drug having a positively charged group and a hydrophobic moiety. The positively charged group means a nitrogen atom-containing group such as an amino group or an imino group, and the hydrophobic part is saturated or partially contains one or two nitrogen atoms or oxygen atoms. This means a moiety containing an unsaturated condensed hydrocarbon ring, and a low molecular weight anticancer agent is a protein,
It is used as a concept for polypeptide and nucleic acid anticancer agents. Such drugs include, but are not limited to, at least one selected from the group consisting of an anthracycline anticancer agent, a quinoline alkaloid anticancer agent, and a vinca alkaloid anticancer agent, which is a concept commonly used in the art. It can be an anticancer agent. In the present invention, two or more types of anticancer agents can be simultaneously supported on each nanoparticle. Examples of the anthracycline anticancer agent include, but are not limited to, doxorubicin, epirubicin, idarubicin, and pirarubicin. The quinoline alkaloid anticancer agent includes, but is not limited to, topotecan, irinotecan, and camptothecin. Examples of vinca alkaloid anticancer agents include, but are not limited to, vinblastine, vincristine, vinorelbine, and eribulin.

  The nanocomplex loaded with these drugs exhibits long-term stability in a PBS solution containing fetal bovine serum (FBS) in a high-concentration PBS-containing solution, which will be described later, and the cytotoxicity of the loaded drug. Can be understood that a dense PEG chain brush is formed on the surface in an aqueous medium. In addition, the hydrodynamic particle size does not significantly change that of the surface-modified iron oxide nanoparticles, and can be adjusted to approximately 50 nm or less, so that it accumulates in the tumor or cancer tissue via the EPR (enhanced permeability and retention) effect. Considering that such a tissue has a pH that is generally on the acidic side, a drug having a positively charged group carried by the mechanism as described above can be used in the tissue. The probability of selective release is considered high. Thus, it can be understood that the nanocomposites according to the present invention have utility beyond conventional drug-carrier conjugates (or complexes).

  Such a nanocomposite is a surface modification having the above characteristics even if it is produced by any method such as a coprecipitation method using iron salt and PEG-b-PVBP, thermal decomposition method, hydrothermal treatment method, etc. It can be produced by contacting iron oxide nanoparticles and a drug in an aqueous medium. Therefore, according to the present invention, as means for solving the above-mentioned problems, an iron oxide nanoparticle-containing solution whose surface is coated with PEG-b-PVBP is converted into an anticancer agent-containing solution having a positively charged group and a hydrophobic portion. There is also provided a method for producing iron oxide nanoparticles carrying an anticancer agent, comprising the steps of mixing and recovering the formed iron oxide nanoparticles carrying the anticancer agent. A solution containing iron oxide nanoparticles whose surface is coated with PEG-b-PVBP is prepared as an aqueous solution adjusted in pH with an appropriate buffer, if necessary. An aqueous solution adjusted in pH as described above is prepared from the hydrochloride, and both aqueous solutions are mixed, and stirred at room temperature protected from light as necessary to form surface-modified iron oxide nanoparticles carrying a drug. Stirring may be performed for 12 hours to 32 hours. The nanocomposite thus formed can be recovered by separating it from a drug or the like that has not been supported by a recovery method known per se, for example, centrifugal ultrafiltration.

It is a graph which shows the result of the test 1 and shows the stability of the PEGylated iron oxide nanoparticle in PBS and 10% FBS solution. The vertical axis represents the hydrodynamic particle size (nm), and the horizontal axis represents the test time (days). It is a graph showing the result of having fractionated the particle-drug mixed solution in Example 1 through SEC and measuring the absorbance of each fraction. The vertical axis represents the absorbance due to the drug (481 nm), and the horizontal axis represents the elution fraction. The black square data is the free drug solution, and the black circle data is the particle-drug complex solution. It is a graph showing the result of having measured the cell viability with respect to the change of the drug concentration in Test 2. FIG. The vertical axis represents cell viability and the horizontal axis represents drug concentration (μM). The black square data is the free drug solution, and the black circle data is the particle-drug complex solution.

Hereinafter, the present invention will be described in more detail with reference to specific examples, but it is not intended to limit the present invention thereto.
Iron oxide nanoparticles whose surface is coated with PEG-b-PVBP are described in Nagasaki, et al. Nanoparticles with various copolymer coverages can be produced by the method described in 1), but typical examples are shown below. When the temperature was not described in the following production examples and tests, the treatment was performed at room temperature (25 ° C.).

Reference Example Production Example 1 Synthesis of Polyethylene Glycol-b-Polychloromethylstyrene (PEG-b-PCMS) Block Copolymer PEG-b-PCMS was synthesized according to the following synthesis scheme 1:

Polyethylene glycol (PEG-SH) having a methoxy group at the α-terminal and a thiol group at the ω-terminal (M _n = 5,000 g / mol; 0.2 mmol, 1.0 g) and azobisisobutyronitrile (0 0.1 mmol, 16.5 mg) was added to the reaction vessel. Next, after the inside of the reaction vessel was evacuated, the operation of blowing nitrogen gas was repeated three times to make the inside of the reaction vessel a nitrogen atmosphere. 10 mL of toluene and chloromethylstyrene (10 mmol, 1.38 mL) were added to the reaction vessel, heated to 60 ° C., and stirred for 24 hours. The reaction mixture was washed three times using polyethyl ether which is a good solvent for polychloromethylstyrene homopolymer, and then freeze-dried with benzene to obtain a white powder. The yield was 1.4 g and the yield was 96%. The acquisition of the target PEG-b-PCMS block copolymer was confirmed by examining the spectrum by size exclusion chromatography (SEC) measurement and ¹ H NMR measurement.

Reference Production Example 2 Synthesis of PEG Block Copolymer (PEG-b-PVBP) Having Multiple Phosphite Groups and Benzene Skeleton NaH (5.25 mmol, 126 mg), NaI (ca. 40 mg), reaction solvent under nitrogen atmosphere After adding 5 mL of THF, diethyl phosphite (2.55 mmol, 0.33 mL) was added in an ice bath. Further, PEG-b-PCMS (500 mg) was dissolved in 5 mL of THF in a reaction vessel under another nitrogen atmosphere. The latter was slowly added dropwise to the former with a syringe and reacted overnight at room temperature to introduce a diethyl phosphite group into CMS (PEG-b-PDEVBPBP). After evaporating the solvent of the product, methanol dialysis (MWCO 3500) was performed, and the product was dissolved in benzene and freeze-dried, and then the powder was recovered. The structural analysis was performed by ¹ H, ³¹ P-NMR measurement. ^{From 1} H NMR, the appearance of a peak derived from diethyl phosphite and a high magnetic field shift of the peak derived from the benzyl position were confirmed, and the introduction of a diethyl phosphite group could be confirmed. In addition, a single peak that seems to be derived from diethyl phosphite was confirmed from ³¹ P-NMR (26.91 ppm), confirming that the target reaction had progressed. The yield was 532 mg and the yield was 88%.

Subsequently, PEG-b-PDEVBP (430 mg) and 5 mL of dichloromethane as a reaction solvent were added under a nitrogen atmosphere, bromotrimethylsilane (0.47 mL, 3.55 mmol) was then added, and the mixture was removed in an oil bath at 45 ° C. for 2 hours. Fluxed. After the reaction, the solvent was evaporated, methanol was added, and the mixture was stirred at room temperature for 15 hours, then dialyzed with methanol (MWCO 3500), dissolved in benzene, freeze-dried, and the powder was collected. The structural analysis was performed by ¹ H, ³¹ P-NMR measurement. ^{From 1} H NMR, the disappearance of the peak derived from the diethyl phosphite group due to the progress of methanol decomposition was observed. Furthermore, since the ³¹ P NMR peak was shifted by a high magnetic field compared with PEG-b-PDEVBPBP (26.91 → 24.17 ppm), the synthesis of PEG-b-PVBP could be confirmed. The yield was 384 mg and the yield was 85%.

Reference Production Example 3 Synthesis of PEGylated Iron Oxide Nanoparticles To each reaction vessel, 75 μL each of 0.05 M FeCl ₂ aqueous solution and 0.1 M FeCl ₃ aqueous solution were added, and 27 mg / mL PEG-b-PVBP aqueous solution was added. Was added and stirred for 5 minutes. Thereafter, 504 μL of 28% NH ₄ OH solution was added while the reaction vessel was immersed in a water tank in which ultrasonic waves were generated, and stirred for 2 hours. The solution after the reaction was subjected to water dialysis (MWCO 12-14,000) to remove excess NH ₄ OH. When dynamic light scattering (DLS) measurement was performed using the obtained solution, it was confirmed that particles having a unimodal distribution with an average particle diameter of 25-30 nm could be synthesized.

<Test 1> Dispersion Stability of PEGylated Iron Oxide Nanoparticles Particles in PBS solution or PBS solution containing 10% FBS were added to the synthesized particle solution with a 10-fold concentrated PBS solution or fetal bovine serum (FBS). The change in the average particle size was recorded by dynamic light scattering (DLS) measurement. In either case, the average particle size of the particles did not change for a long time, suggesting that the in vivo stability is high (FIG. 1).

<Example 1> Synthesis of PEGylated iron oxide nanoparticle-doxorubicin complex The pH of the PEGylated iron oxide nanoparticle solution was adjusted to 7.4 by dialysis in a 10 mM HEPES buffer. Thereto, a HEPES solution (pH 7.4) of doxorubicin (hereinafter also referred to as “DOX”) hydrochloride was added to a final concentration of 1 mg / mL or 2 mg / mL, and it was kept in a light-shielded environment (25 ° C.) for 1 day. Stir. When the unsupported drug in the particle-drug mixed solution was separated using a centrifugal ultrafiltration device (MWCO 30,000) and the absorbance of the separated solution was measured, the drug loading efficiency and the loaded amount were calculated. Samples with a DOX final concentration of 1 mg / mL are 98.3 ± 0.9% and 12.0 ± 0.1%, respectively, and samples with a DOX final concentration of 2 mg / mL are 99.0 ± 0.7%, respectively. 21.5 ± 0.1%. Moreover, the average particle diameters by DLS measurement were 33.7 ± 6 nm and 44.0 ± 9 nm, respectively. Further, the particle-drug mixed solution was separated by passing through SEC, and the absorbance of each fraction was measured. As a result, no absorbance from unreacted DOX was detected, and it was confirmed that most of the DOX was supported on the particles. (See FIG. 2).

<Test 2> Cytotoxicity test using particle-DOX mixed solution The DOX solution or particle-DOX mixed solution was brought into contact with PC3 cells for 48 hours, and the cell viability was measured by MTT assay. The results are shown in FIG. When compared with the DOX concentration in the cell culture medium, the cytotoxicity of the particle-DOX mixed solution was smaller than that of the DOX solution, which suggests that the drug is supported on the particles. It is also suggested that no DOX is released from the particle-DOX for at least 48 hours under the cell culture conditions.

Since the present invention provides surface-modified iron oxide nanoparticles that stably carry a specific anticancer agent, it can be used, for example, in the pharmaceutical manufacturing industry.

Claims (7)

Iron oxide nanoparticles carrying a drug, the drug is an anticancer drug having a positively charged group and a hydrophobic moiety, and the surface is coated with polyethylene glycol-b-poly (vinylbenzyl phosphonate). The iron oxide nanoparticles that are dispersed in phosphate buffered saline (PBS). Iron oxide nanoparticles carrying a drug, the drug is an anticancer drug having a positively charged group and a hydrophobic moiety, and the surface is coated with polyethylene glycol-b-poly (vinylbenzyl phosphonate). And the iron oxide nanoparticles wherein the block copolymer is represented by the following formula (I).

Where
R represents an unsubstituted or substituted C ₁ -C ₁₂ alkyl group, and when substituted, the substituent represents a formyl group or a group of formula R ¹ R ² CH—, where R ¹ and R ² _{independently,} C 1 -C ₄ alkoxy or ^{R 1} and ^{R 2} are -OCH ₂ CH ₂ O together _{-, - O (CH 2)} 3 O- or -O _{(CH 2)} 4 O- and Represent,
L represents a linking group,
m is an integer of 14 to 5,000,
n is an integer of 2 to 1,000,
However, in the poly (vinyl benzyl phosphonate) segment, in place of the vinyl benzyl phosphonate repeating unit, a repeating unit selected from the group consisting of vinyl benzyl hydroxy and vinyl benzyloxy C ₁ -C ₄ alkyl is randomly or It can contain up to 30% as a block. Wherein the linking group is selected from the group consisting of — (CH ₂ ) _c S—, —CO (CH ₂ ) _c S—, —COO (CH ₂ ) _c S—, —COC (CH ₃ ) ₂ —, The iron oxide nanoparticles according to claim 2, wherein c is an integer of 1 to 5. The iron oxide nanoparticles according to any one of claims 1 to 3, wherein the drug is at least one anticancer agent selected from the group consisting of an anthracycline anticancer agent, a quinoline alkaloid anticancer agent, and a vinca alkaloid anticancer agent. The drug is an anthracycline anticancer drug selected from doxorubicin, epirubicin, idarubicin, pirarubicin, or a quinoline alkaloid anticancer drug selected from topotecan, irinotecan, camptothecin, or vincaine selected from vinblastine, vincristine, vinorelbine, eribulin The iron oxide nanoparticles according to any one of claims 1 to 3, which is an alkaloid anticancer agent. The iron oxide nanoparticle which carry | supported the chemical | medical agent of Claim 2 which has dispersibility in phosphate buffered saline (PBS). Mixing an iron oxide nanoparticle-containing solution, the surface of which is coated with polyethylene glycol-b-poly (vinylbenzyl phosphonate), with an anticancer agent-containing solution having a positively charged group and a hydrophobic moiety, and the formed anticancer agent A method for producing iron oxide nanoparticles carrying an anticancer agent, comprising the step of recovering iron oxide nanoparticles carrying iron.

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