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Definitions

• Iron oxide nanoparticles are useful as contrast agents for magnetic resonance imaging (MRI) because of their chemical stability and suitable magnetization.
• Magnetite (Fe 3 O 4 ) and maghemite ( ⁇ -Fe 2 O 3 ) are two examples of superparamagnetic iron oxide nanoparticles.
• iron oxide nanoparticles are capable of conjugating with biocompatible polymers to form biocompatible magnetic materials, e.g., MRI contrast agents.
• Fe 3 O 4 magnetic nanoparticles are synthesized by using a mixture of Fe(II) and Fe(III) salts.
• Fe 3 O 4 magnetic nanoparticles contain about 33% Fe(II) ions relative to the total iron ions.
• ⁇ -Fe 2 O 3 magnetic nanoparticles contain 0% Fe(II) ions.
• Fe 3 O 4 provides stronger T 2 shortening effect, i.e., higher relaxivity r2, than ⁇ -Fe 2 O 3 .
• Fe 3 O 4 nanoparticles are significantly more effective in producing hydroxyl radicals than ⁇ -Fe 2 O 3 nanoparticles and, as a result, Fe 3 O 4 may induce higher toxicity compared to ⁇ -Fe 2 O 3 in clinical applications. See, e.g., Park et al., Arch Toxicol., 2014, 88(8):1607-1618; and Wu et al., Journal of Food and Drug Analysis, 2014, 22, 86-94.
• the present invention relates to certain biocompatible magnetic materials that can be used as MRI contrast agents with high relaxivity and low toxicity.
• biocompatible magnetic materials that contain an iron oxide nanoparticle and one or more biocompatible polymers, each having formula (I) below, covalently bonded to the iron oxide nanoparticle:
• R is H, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 3 -C 10 cycloalkyl, C 1 -C 10 heterocycloalkyl, aryl, heteroaryl, a C 1 -C 10 carbonyl group, or a C 1 -C 10 amine group;
• L is a linker; x is 1 to 10; and y is 5 to 1000.
• the biocompatible magnetic materials each contain 4-15% Fe(II) ions relative to the total iron ions.
• the iron oxide nanoparticle can have a Fe(II) content the same as or different from that contained in a biocompatible magnetic material.
• An exemplary iron oxide nanoparticle contains 4-15% (e.g., 4-10% and 4-8%) Fe(II) ions relative to the total iron ions in it.
• the linker L can be O, S, Si, C 1 -C 6 alkylene, a carbonyl moiety containing two carbonyl groups and 2-20 carbon atoms, or a group having one of the following formulas:
• each of m, n, p, q, and t, independently, is 1-6;
• W is O, S, or NR b ;
• each of L 1 , L 3 , L 5 , L 7 , and L 9 , independently, is a bond, O, S, or NR c ;
• each of L 2 , L 4 , L 6 , L 8 , and L 10 , independently, is a bond, O, S, or NR d ;
• V is OR e , SR f , or NR g R h , each of R a , R b , R c , R d , R e , R f , R g , and R h , independently, being H, OH, a C 1 -C 10 alkyl, a C 1 -C 10 heteroalkyl, a C 3 -C 10 cycloalkyl, a C 1 -C 10 heterocycloalky
• alkyl herein refers to a saturated, linear or branched hydrocarbon moiety, such as methyl, ethyl, propyl, butyl, pentyl, and hexyl.
• alkenyl refers to a linear or branched hydrocarbon moiety that contains at least one double bond, such as —CH ⁇ CH-CH 3 and —CH ⁇ CH-CH 2 —.
• alkynyl refers to a linear or branched hydrocarbon moiety that contains at least one triple bond, such as —C ⁇ C-CH 3 and —C ⁇ C-CH 2 —.
• cycloalkyl refers to a saturated, cyclic hydrocarbon moiety, such as cyclohexyl and cyclohexylene.
• heterocycloalkyl refers to a saturated, cyclic hydrocarbon moiety containing at least one heteroatom selected from N, O, P, B, S, Si, Sb, Al, Sn, As, Se, and Ge, such as piperazinyl and piperidinyl.
• heteroalkyl refers to an aliphatic moiety containing at least one heteroatom selected from N, O, P, B, S, Si, Sb, Al, Sn, As, Se, and Ge.
• heteroalkyl include methoxymethyl and methylaminoethyl.
• aryl herein refers to a C 6 monocyclic, C 10 bicyclic, C 14 tricyclic, C 20 tetracyclic, or C 24 pentacyclic aromatic ring system.
• aryl groups include phenyl, phenylene, naphthyl, naphthylene, anthracenyl, anthrcenylene, pyrenyl, and pyrenylene.
• heteroaryl herein refers to an aromatic 5-8 membered monocyclic, 8-12 membered bicyclic, 11-14 membered tricyclic, and 15-20 membered tetracyclic ring system having one or more heteroatoms (such as O, N, S, or Se).
• heteroaryl groups include furyl, furylene, fluorenyl, fluorenylene, pyrrolyl, pyrrolylene, thienyl, thienylene, oxazolyl, oxazolylene, imidazolyl, imidazolylene, benzimidazolyl, benzimidazolylene, thiazolyl, thiazolylene, pyridyl, pyridylene, pyrimidinyl, pyrimidinylene, quinazolinyl, quinazolinylene, quinolinyl, quinolinylene, isoquinolyl, isoquinolylene, indolyl, and indolylene.
• alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, heteroalkyl, aryl, and heteroaryl mentioned herein include both substituted and unsubstituted moieties.
• cycloalkyl, cycloalkylene, cycloalkenyl, cycloalkenylene, cycloalkynyl, cycloalkynylene, heterocycloalkyl, heterocycloalkylene, heterocycloalkenyl, heterocycloalkenylene, aryl, and heteroaryl include, but are not limited to, C 1 -C 10 alkyl, C 2 -C 10 alkenyl, C 2 -C 10 alkynyl, C 3 -C 20 cycloalkyl, C 3 -C 20 cycloalkenyl, C 3 -C 20 heterocycloalkyl, C 3 -C 20 heterocycloalkenyl, C 1 -C 10 alkoxy, aryl, aryloxy, heteroaryl, heteroaryloxy, amino, C 1 -C 10 alkylamino, C 2 -C 20 dialkylamino, arylamino, diarylamino, C 1 -
• substituents on aliphatic, heteroaliphatic, oxyaliphatic, alkyl, alkylene, alkenyl, alkenylene, alkynyl, and alkynylene include all of the above-recited substituents except C 1 -C 10 alkyl.
• Cycloalkyl, cycloalkylene, cycloalkenyl, cycloalkenylene, heterocycloalkyl, heterocycloalkylene, heterocycloalkenyl, heterocycloalkenylene, aryl, and heteroaryl can also be fused with each other.
• the method includes four steps: (i) providing a first solution that contains an iron oxide nanoparticle in a first organic solvent, the iron oxide nanoparticle containing 4-15% Fe(II) ions relative to the total iron ions; (ii) providing a second solution that contains a biocompatible polymer of formula (I) in a second organic solvent; (iii) mixing the first solution and the second solution to afford a mixed solution; and (iv) adding water to the mixed solution and stirring the resulting solution for at least 20 hours to obtain a biocompatible magnetic material.
• the iron oxide nanoparticle is formed by mixing a hydroxide solution with an iron solution that contains a Fe(II) salt under an inert gas atmosphere.
• a biocompatible magnetic material that contains an iron oxide nanoparticle and one or more biocompatible polymers covalently bonded to the iron oxide nanoparticle.
• the iron oxide nanoparticle can be a superparamagnetic core having a particle size of 1 to 100 nm (e.g., 2 to 50 nm and 5 to 25 nm). Preparation of a superparamagnetic core is well known in the art. See Laurent et al., Chem. Rev., 2008, 108, 2064-2110.
• the iron oxide nanoparticle is typically formed of an organic acid or a salt thereof.
• organic acid or salt include, but are not limited to, oleic acid and a salt thereof.
• the iron oxide nanoparticle preferably contains 4-15% Fe(II) ions relative to the total iron ions in it.
• An exemplary iron oxide nanoparticle contains 4-10% or 4-8% Fe(II) ions relative to the total iron ions.
• the content of Fe(II) ions in an iron oxide nanoparticle is important for a biocompatible magnetic material to exert high relaxivity and low toxicity. More specifically, a low Fe(II) content, e.g., less than 4% Fe(II) ions relative to the total iron ions, typically exhibits low relaxivity. On the other hand, a high Fe(II) content, e.g., greater than 15% Fe(II) ions relative to the total iron ions, can cause high toxicity.
• the biocompatible magnetic material also contains one or more biocompatible polymers to enhance its biocompatibility.
• biocompatible polymers has formula (I) below:
• the iron oxide nanoparticle is covalently bonded to one or more biocompatible polymers each having the following formula:
• R 1 is H, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 3 -C 10 cycloalkyl, C 1 -C 10 heterocycloalkyl, aryl, heteroaryl, a C 1 -C 10 carbonyl group, or a C 1 -C 10 amine group
• R 2 is H, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 3 -C 10 cycloalkyl, C 1 -C 10 heterocycloalkyl, aryl, or heteroaryl
• x is 1 to 10
• y is 5 to 1000.
• R 1 is C 1 -C 6 alkyl, a C 1 -C 10 carbonyl group, or a C 1 -C 10 amine group
• R 2 is H or C 1 -C 6 alkyl.
• R 1 is methyl (—CH 3 ), carboxyl (—COOH), or amino (—NH 2 ), and R 2 is H.
• the carboxyl-terminated or amine-terminated biocompatible polymer can be coupled with a biological molecule, e.g., folic acid.
• folic acid allows coupling with an amine-terminated biocompatible polymer by forming a —CONH— linkage.
• the biocompatible magnetic material of this invention can be coupled to a specific targeting agent for biological applications.
• a specific targeting agent include, but art not limited to, an antibody, a protein, a peptide, an enzyme, a carbohydrate, a glycoprotein, a nucleotide, and a lipid.
• R 1 is coupled to an antibody (e.g., My10).
• the method includes the following steps: providing a first solution that contains an iron oxide nanoparticle in a first organic solvent, in which the iron oxide nanoparticle contains 4-15% Fe(II) ions relative to the total iron ions; providing a second solution that contains biocompatible polymers of formula (I) in a second organic solvent; mixing the first solution and the second solution to afford a mixed solution; and adding water to the mixed solution and stirring the resulting solution for at least 20 hours to obtain a biocompatible magnetic material.
• the iron oxide nanoparticle used in the method is typically formed by mixing a hydroxide solution with an iron solution that contains a Fe(II) salt under an inert gas atmosphere.
• An exemplary iron solution contains a Fe(II) salt (e.g., FeCl 2 ) and a Fe(III) salt (e.g., FeCl 3 ), in which the mole ratio of Fe(III)/Fe(II) is 1.70 or higher (e.g., 1.75 or higher, 1.80 or higher, and 1.90 or higher).
• the hydroxide solution can be a sodium hydroxide solution having a concentration of 2 N or lower (e.g., 1.5 N or lower and 1 N or lower).
• inert gas examples include, but are not limited to, nitrogen and argon.
• the iron oxide nanoparticle can be formed of an organic acid or a salt thereof.
• An exemplary organic acid or salt is oleic acid or a salt thereof.
• oleic acid When oleic acid is used, it can be present in an amount of 100 mL or less (e.g., 90 mL or less, 70 mL or less, and 50 mL or less) per mole iron.
• the iron oxide nanoparticle is formed from oleic acid and an iron solution containing FeCl 2 and FeCl 3 , affording an iron oxide-oleic acid nanoparticle or IO-OA.
• This exemplary iron oxide nanoparticle can be prepared as follows: mixing FeCl 2 and FeCl 3 in a solvent (e.g., water), adding a sodium hydroxide solution (e.g., 1 N) under nitrogen to the above mixture, and treating the solution thus obtained with oleic acid to form an IO-OA nanoparticle.
• the iron oxide nanoparticle is preferably collected, after the treatment with an organic acid or a salt thereof, by removing water, dissolving it in toluene, and centrifuging the liquid thus obtained to eliminate certain large particles.
• biocompatible polymers used in the method include the polymers themselves, as well as their salts and solvates, if applicable.
• a salt for example, can be formed between an anion and a positively charged group (e.g., amino) on a polymer.
• Suitable anions include chloride, bromide, iodide, sulfate, nitrate, phosphate, citrate, methanesulfonate, trifluoroacetate, acetate, malate, tosylate, tartrate, fumurate, glutamate, glucuronate, lactate, glutarate, and maleate.
• a salt can also be formed between a cation and a negatively charged group (e.g., carboxylate) on a polymer.
• Suitable cations include sodium ion, potassium ion, magnesium ion, calcium ion, and an ammonium cation such as tetramethylammonium ion.
• the polymers also include those salts containing quaternary nitrogen atoms.
• a solvate refers to a complex formed between a polymer and a pharmaceutically acceptable solvent. Examples of a pharmaceutically acceptable solvent include water, ethanol, isopropanol, ethyl acetate, acetic acid, and ethanolamine.
• Scheme (I) below shows a process of preparing an exemplary silane-containing biocompatible polymer.
• alkoxyl-polyethylene glycol (molecular weight 2000) reacts with succinic anhydride in the presence of a base (e.g., dimethylaminopyridine) to form mPEG-COOH, which is subsequently converted to mPEG-COCl using thionyl chloride.
• a base e.g., dimethylaminopyridine
• a first solution containing the above-described iron oxide nanoparticle is formed in a first organic solvent, and a second solution containing the above-described biocompatible polymers is provided in a second organic solvent.
• Each of the first organic solvent and the second organic solvent can be toluene, aliphatic hydrocarbon, tetrahydrofuran, ketone, alcohol, alkyl ester, or a combination thereof.
• both organic solvents are toluene.
• the iron oxide nanoparticle used in the method contains 4-15% Fe(II) ions relative to the total iron ions in it.
• a biocompatible magnetic material thus obtained typically contains 4-15% Fe(II) ions relative to the total iron ions.
• the biocompatible polymer synthesized in Scheme (I) above is useful in that it can chemically modify the surface of the iron oxide nanoparticle to increase biocompatibility.
• the biocompatible polymer is useful in that it can label particles (e.g., nanoparticles, magnetic particles, magnetic nanoparticles, and superparamagnetic particles), to render the particles to be further reactive toward one or more targeting, fluorescent, therapeutic, or diagnostic agents.
• the targeting agent is preferably coupled to the biocompatible polymer via covalent bonds.
• targeting agents include an antibody, a protein, a peptide, an enzyme, a carbohydrate, a glycoprotein, a nucleotide, and a lipid.
• the biocompatible magnetic material may have a diameter of about 3-500 nm after coupling with the targeting agent.
• folic acid can be used to specify breast cancer cells with a folate receptor.
• the structure of the folic acid allows coupling with an amine-terminated or carboxy-terminated biocompatible polymer.
• the folic acid allows coupling with the amine-terminated biocompatible polymer by forming a —CONH— linkage.
• the water was removed after the pH of the water solution was adjusted to a pH value of 1 to 2 with hydrochloric acid (3 N). 12 L toluene was then added to the remaining dark paste to suspend crude IO-OA nanoparticles in the toluene solution. The crude IO-OA nanoparticles in toluene were centrifuged at 6000 rpm for 15 minutes to obtain IO-OA nanoparticles in toluene.
• a biocompatible polymer mPEG-silane-750 was prepared as follows. A mixture of 300 g (0.4 moles) of methoxy-PEG (mPEG, molecular weight 750), succinic anhydride (48 g; 0.48 moles) and 4-dimethylamino-pyridine (DMAP; 19.5 g; 0.159 moles) were allowed to sit in a 1000-mL round bottom flask under vacuum (20 Torrs) for 2 hours. 600 mL of toluene was added to the mixture, which was then stirred at 30° C. for one day to form mPEG-COOH.
• DMAP 4-dimethylamino-pyridine
• a solid product was collected by filtration, re-dissolved in 500 mL of toluene, and centrifuged at 5000 rpm for 5 minutes to collect a supernatant, to which was added 9 L of isopropyl ether.
• a brown oily liquid was separated from the isopropyl ether and dried under vacuum to obtain the biocompatible polymer mPEG-silane-750.
• a biocompatible polymer mPEG-silane-2000 was prepared as follows. Methoxy-PEG (mPEG, molecular weight 2000) (3 kg) was added to a 20 L reaction vessel, equipped with a Dean-Stark Trap. 15 L toluene was added to the reaction vessel and the reaction mixture was stirred at 150 ⁇ °rpm with a mechanical stirrer. The reaction was conducted at 120° C. and refluxed for 60 minute. Succinic anhydride (SA, 180 g) and 4-Dimethylaminopyridine (DMAP, 70g) were then added to the reaction vessel and the reaction was continued for 20 hours at 65° C. to form mPEG-COOH.
• SA Succinic anhydride
• DMAP 4-Dimethylaminopyridine
• a biocompatible polymer COOH-mPEG-silane-2000 was prepared following the same procedure described above using a mixture of 800 g (0.4 moles) of PEG (PEG, molecular weight 2000), succinic anhydride (88 g; 0.88 moles), and 4-dimethylamino-pyridine (DMAP; 19.5 g; 0.16 moles).
• a biocompatible magnetic material was prepared by conjugating mPEG-silane-2000 with an iron oxide nanoparticle, i.e., IO-OA nanoparticle, in toluene as follows.
• a toluene solution of IO-OA nanoparticle (6 mg Fe/mL, 700 mL) and a toluene solution of mPEG-silane-2000 (160 mg/mL, 500 mL) were mixed in a 2 L round bottom flask with water being added to the resulting solution. After 24 hours reaction, mPEG-silane-2000 conjugated iron oxide nanoparticles were extracted by water, and filtration to remove large particles to afford an clear aqueous solution. The resulting aqueous solution was purified and concentrated with an ultra-filtration device to obtain a biocompatible magnetic material labeled as IO-OA/mPEG-silane-2000.
• Fe(II)/Fe(III) ion ratios of iron oxide nanoparticles and biocompatible magnetic materials were measured by Iron Test kit (Spectroquant 1.00796.0001, Merck). The reagent in the test kit, i.e., 1.10-plenanthroline, was sensitive for Fe(II) ion but not Fe(III) ion. In a buffered medium, the Fe(II) ions reacted with 1.10-plenanthroline to form a red complex that was determined photometrically. The test iron oxide nanoparticles or biocompatible magnetic materials were first degraded to iron ions by adding sulfur acid and the pH of the resulting solution was adjusted to 2 to 8 by using 0.8 M NaHCO 3 .
• biocompatible magnetic materials of this invention unexpectedly exhibited a much higher Fe(II) content as compared to Feraheme.
• FIGS. 1-2 show the XRPD patterns for IO-OA (batch 4) and IO-OA/mPEG-silane-2000 (batch 2).
• Iron oxide solutions were prepared at various concentrations (0.1, 0.2, 0.3, 0.4, and 0.5 mM).
• T2 relaxation time of each solution was measured by Minispec mq 20 from the Bruker Corporation.
• a linear relationship was established between the reciprocal of the relaxation time as the ordinate axis and the concentration of the solution as the abscissa axis.
• the slope of the linear relationship was determined as the r2 relaxivity. Results are shown in Table 2 below.
• biocompatible magnetic materials of this invention unexpectedly exhibited much higher r2 relaxivity as compared to Feraheme.
• Described below are protocols for coupling a biocompatible magnetic material of this invention with a specific targeting agent.
• IO-OA/COOH-PEG-silane-2000 (4.48 mg Fe/mL) was mixed with 5 mL of cold deionized water and kept on ice-bath.
• 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (10 ⁇ 6 mole) was added to the solution and stirred for 30 minutes.
• N-hydroxysuccinimide (10 ⁇ 6 mole) was then added to the mixture and stirred for another 30 minutes.
• Antibody My10 (1 mL, 2 ⁇ g/mL) was added to the resulting mixture and reacted for 2 hours.
• the solution thus obtained was purified by passing through a magnetic sorting device to obtain a biocompatible magnetic material coupled with an antibody, i.e., My10-conjugated IO-OA/COOH-PEG-silane-2000.

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