Contrast agents for collagen and fibrin imaging

Abstract

This disclosure relates to fibrin- and collagen-specific imaging agents comprising metal oxide nanoparticles.

Description

[0001] CONTRAST AGENTS FOR COLLAGEN AND FIBRIN IMAGING

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of priority of U.S. Provisional Application No. 63 / 488,642, filed March 6, 2023, which is incorporated herein by reference in its entirety.

[0004] TECHNICAL FIELD

[0005] This disclosure relates to fibrin- and collagen-specific imaging agents comprising metal oxide nanoparticles.

[0006] BACKGROUND

[0007] Diagnostic imaging techniques, such as magnetic resonance imaging (MRI), X- ray, nuclear radiopharmaceutical imaging, ultraviolet-visible-infrared light imaging, and ultrasound, are often used in medical diagnosis. Complexes of paramagnetic metal oxide ions (e.g., gadolinium oxide, iron oxide, manganese oxide) and ligands are widely used to enhance and improve imaging contrast. Small metal oxide particles can be used to aid kidney elimination and interstitial tissue extravasation of the metal oxide-ligand complexes following acquisition of the diagnostic image.

[0008] SUMMARY

[0009] The present application describes fibrin- and collagen-specific imaging agents comprising extremely small metal oxide nanoparticles, as well as pharmaceutical compositions comprising the imaging agents described herein. Also provided herein are methods for imaging fibrin and collagen in a mammal.

[0010] All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. To the extent publications and patents or patent applications incorporated by reference contradict the disclosure contained in the specification, the specification is intended to supersede and / or take precedence over any such contradictory material.

[0011] Other features and advantages of the disclosure will be apparent from the following detailed description and figures, and from the claims.

[0012] DESCRIPTION OF DRAWINGS

[0013] FIG. 1 shows the structure of SNIO-CBP.

[0014] FIG. 2 shows SAXS profile of SNIO-CBP in the q range corresponding to singlenanometer range in the real space; scattering profile was fitted into spherical particles with a log-normal distribution at a mean diameter of 1 .47 nm.

[0015] FIG. 3 shows gel filtration chromatogram of SNIO-CBP showing its size purity and hydrodynamic diameter.

[0016] FIG. 4 shows gel filtration chromatograms of SNIO-CBP incubated with FBS and FBS alone, showing minimal degree of non-specific binding of SNIO-CBP in plasma. Red and orange peaks: binding products; bottom peaks: native species in FBS.

[0017] FIG. 5 shows binding affinity of SNIO-CBP towards human type I collagen.

[0018] FIG. 6 shows T1 -weighted MRI study of SNIO-CBP clearance in normal mice (i.v. injection, 2 nmol / g based on CBP concentration).

[0019] FIG. 7 shows comparison of SNIO-CBP (2 nmol / g CBP) and CM-101 (5 nmol / g CBP) in mice treated with 12 wk CCh or olive oil vehicle (00), and similar contrast-to- noise ratio in liver were obtained (n = 6 for each group). Representative microscopy images of the adjacent liver tissues from CCh (disease) and 00 (control) mice, stained with Sirius Red and Prussian Blue, show the presence of fibrosis in CCh mice and the accumulation of SNIO-CBP in the fibrosis band.

[0020] FIG. 8 shows MR imaging of liver fibrosis in a mouse model of non-alcoholic steatohepatitis using SNIO-CBP (2 nmol / g CBP). Mice fed with choline-deficient, lamino acid-defined, high-fat diet (CDAHFD) for 14 weeks (n = 6) act as a disease group. Mice that received 14 weeks of standard chow (SD, n = 6) were used as control. Significant enhanced liver signal was observed in the CDAHFD group imaged with SNIO-CBP. Corresponding liver histology revealed the fibrosis and retention of the probe in the disease group. FIG. 9 shows a schematic representation of nanoparticle synthesis.

[0021] FIG. 10 shows zeta potential of SNIO-CBP.

[0022] FIG. 11 shows the stability of SNIO-CBP.

[0023] FIG. 12 shows the binding affinity of SNIO-CBP to type I collagen.

[0024] FIG. 13 shows longitudinal relaxivity (n).

[0025] FIG. 14 shows SNIO-CBP pharmacokinetics in normal mice.

[0026] FIG. 15 shows CCh induced liver fibrosis model.

[0027] FIG. 16 shows ex vivo characterizations (CCh model).

[0028] FIG. 17 shows diet-induced liver fibrosis.

[0029] DETAILED DESCRIPTION

[0030] Collagens are a class of extracellular matrix proteins that represent about 30% of total body protein and contribute to the structure of tendons, bones, and connective tissues. Abnormal accumulation of collagen in various organs can lead to fibrosis, for example, myocardial fibrosis, heart failure, nonalcoholic steatohepatitis (NASH), liver cirrhosis, and primary biliary cirrhosis; lesions in the vasculature or breasts; collagen- induced arthritis; muscular dystrophy; scleroderma; Dupuytren's disease; and rheumatoid arthritis, among other debilitating conditions. Fibrin is a fibrillary protein derived from the soluble plasma protein fibrinogen. Fibrin is a major component of blood clots and is present in all thrombi, regardless of thrombus age or bodily location. Valued in part for high specificity and sensitivity, both fibrin- and collagen-binding compounds can be used for diagnostic imaging.

[0031] Provided herein are protein-binding imaging agents having paramagnetic metal oxide ions and ligands to enhance image contrast and aid analysis. These imaging agents are readily eliminated from the patient by utilizing paramagnetic metal oxide ions having smaller particle sizes while still producing high resolution images.

[0032] Definitions

[0033] Commonly used chemical abbreviations that are not explicitly defined in this disclosure may be found in The American Chemical Society Style Guide, Second Edition, American Chemical Society, Washington, D.C. (1997); “2001 Guidelines for Authors” J. Org. Chem. 66(1), 24A (2001); and “A Short Guide to Abbreviations and Their Use in Peptide Science” J. Peptide Sci. 5, 465-471 (1999).

[0034] As used herein, the term “peptide” refers to a chain of amino acids that is about 2 to about 25 amino acid residues in length. All peptide sequences herein are written from the N- to C-terminus. For any of the peptides described herein that contain two or more cysteine residues, it is understood that the cysteine residues can form one or more disulfide bonds under non-reducing conditions. Formation of a disulfide bond can result in the formulation of a cyclic peptide.

[0035] As used herein, the terms “natural” or “naturally occurring” amino acid refers to one of the twenty most common amino acids occurring in nature. Natural amino acids modified to provide a label for detection purposes (e.g., radioactive labels, optical labels, or dyes) are considered to be natural amino acids. Natural L amino acids are referred to by their standard one- or three-letter abbreviations. D amino acids are referred to using the lower-case convention for standard one-letter abbreviations, and the “D-” prefix convention for standard three-letter abbreviations.

[0036] As used herein, the terms “target binding” and “binding” refer to non-covalent interactions of a peptide or composition within a target. These non-covalent interactions are independent from one another and may be, inter alia, hydrophobic, hydrophilic, dipole-dipole, pi-stacking, hydrogen bonding, electrostatic associations, and / or Lewis acid-base interactions. The binding affinity for a target is expressed in terms of the equilibrium dissociation constant “Kd” to the target under a defined set of conditions.

[0037] As used herein, the term “relaxivity” refers to the increase in either of the magnetic resonance imaging (MRI) quantities 1 / T1 or 1 / T2 per millmolar (mM) concentration of paramagnetic ion, contrast agent, or compound, wherein T1 is the longitudinal or spin-lattice, relaxation time, and T2 is the transverse or spin-spin relaxation time of water protons or other imaging or spectroscopic nuclei, including protons found in molecules other than water. Relaxivity is expressed in units of mM’1s’1.

[0038] As used herein, the term “purified” refers to a peptide or compound that has been separated from either naturally occurring organic molecules with which it normally associates or, for a chemically-synthesized molecule, separated from other organic molecules present in the chemical synthesis. Typically, the polypeptide or compound is considered “purified” when it is at least 70% (e.g., at least 70%, at least 80%, at least 90%, at least 95%, or at least 99%), by dry weight, free from any other proteins or organic molecules. The terms “purified” and isolated” are used interchangeably herein.

[0039] Where values are described as ranges, it will be understood that such disclosure includes the disclosure of all possible sub-ranges within such ranges, as well as specific numerical values that fall within such ranges irrespective of whether a specific numerical value or specific sub-range is expressly stated.

[0040] Collagen-Binding Imaging Agents

[0041] Provided herein are imaging agents of Formula I:

[0042] [NP]-[C]m-[L]n-[CP]o (I) or a pharmaceutically acceptable salt thereof, wherein NP is a nanoparticle metal oxide core comprising iron oxide, manganese oxide, or gadolinium oxide;

[0043] C is a metal oxide-binding ligand;

[0044] L is a linker moiety;

[0045] CP is a collagen-binding peptide; n is an integer selected from 0 to 10; and m and o are each integers independently selected from 1 to 5.

[0046] In some embodiments of the imaging agent of Formula I, n is 0, n is 1, n is 2, n is

[0047] 3, n is 4, or n is 5. In some embodiments of the imaging agents of Formula I, m is 1 or m is 2. In some embodiments of the imaging agents of Formula I, o is 1 or o is 2.

[0048] In some embodiments of the imaging agents of Formula I, NP is a nanoparticle metal oxide comprising iron oxide. In some embodiments of the imaging agent of Formula I, NP is a nanoparticle metal oxide comprising manganese oxide. In some embodiments of the imaging agents of Formula I, NP is a nanoparticle metal oxide core comprising gadolinium oxide. In some embodiments of the imaging agents of Formula I, NP is a nanoparticle metal oxide core comprising iron oxide, manganese oxide, gadolinium oxide, or a combination thereof. For example, the nanoparticle core can comprise iron oxide and manganese oxide. For example, the nanoparticle core can comprise iron oxide and gadolinium oxide. For example, the nanoparticle core can comprise manganese oxide and gadolinium oxide. For example, the nanoparticle core can comprise iron oxide, manganese oxide, and gadolinium oxide.

[0049] In some embodiments of the imaging agents of Formula I, the nanoparticle metal oxide core comprises about 5 to about 200 metal ions. For example, about 5 to about 175, about 5 to about 150, about 5 to about 125, about 5 to about 100, about 5 to about 75, about 5 to about 50, about 5 to about 25, or about 5 to about 10 metal ions. In some embodiments, the nanoparticle metal oxide core comprises about 10 to about 200, about 25 to about 200, about 50 to about 200, about 75 to about 200, about 100 to about 200, about 125 to about 200, about 150 to about 200, or about 175 to about 200 metal ions. In some embodiments, the nanoparticle metal oxide core comprises about 5 to about 15, about 10 to about 15, about 10 to about 20, about 10 to about 25, about 10 to about 30, about 10 to about 35, about 10 to about 40, about 10 to about 45, about 10 to about 50, about 25 to about 50, about 50 to about 100, about 75 to about 100, about 100 to about 125, about 125 to about 150, or about 150 to about 175 metal ions.

[0050] In some embodiments, the nanoparticle metal oxide core is about 2.0 to about 10.0 nm in diameter. For example, about 2.0 to about 9.0, about 2.0 to about 8.0, about 2.0 to about 7.5, about 2.0 to about 7.0, about 2.0 to about 6.5, about 2.0 to about 6.0, about 2.0 to about 5.5, about 2.0 to about 5.0, about 2.0 to about 4.5, about 2.0 to about 3.5, or about 2.0 to about 3.0 nm in diameter. In some embodiments, the nanoparticle metal oxide core is about 2.5 to about 10.0, about 3.0 to about 10.0, about 3.5 to about 10.0, about 4.0 to about 10.0, about 4.5 to about 10.0, about 5.0 to about 10.0, about 5.5 to about 10.0, about 6.0 to about 10.0, about 6.5 to about 10.0, about 7.0 to about 10.0, about 7.5 to about 10.0, about 8.0 to about 10.0, about 8.5 to about 10.0, or about 9.0 to about 10.0 nm in diameter. In some embodiments, the nanoparticle metal oxide core is about 3.0 to about 5.0 nm in diameter. For example, about 3.0 to about 4.8, about 3.0 to about 4.5, about 3.0 to about 4.2, about 3.0 to about 4.0, or about 3.0 to about 3.8 nm in diameter. For example, about 3.2 to about 5.0, about 3.5 to about 5.0, about 3.8 to about 5.0, about 4.0 to about 5.0, or about 4.2 to about 5.0 nm in diameter. In some embodiments, the nanoparticle metal oxide core is about 3.4 to about 4.5 nm in diameter. In some embodiments, the nanoparticle metal oxide core is about 0.5 to 1.5 nm in diameter. In some embodiments, the nanoparticle metal oxide core is about 1.0 nm in diameter.

[0051] In some embodiments, the hydrodynamic size of the coated nanoparticle metal oxide core is about 2.0 to about 25 nm in diameter. For example, about 2.0 to about 23, about 2.0 to about 21, about 2.0 to about 20, about 2.0 to about 18, about 2.0 to about 15, about 2.0 to about 12, about 2.0 to about 10, about 2.0 to about 8, about 2.0 to about 6, or about 2.0 to about 4 nm in diameter. In some embodiments, the hydrodynamic size of the coated nanoparticle metal oxide core is about 2.5 to about 25, about 3.0 to about 25, about 3.5 to about 25, about 4.0 to about 25, about 4.5 to about 25, about 5.0 to about 25, about 5.0 to about 25, about 5.5 to about 25, about 6.0 to about 25, about 6.5 to about 25, about 7.0 to about 25, about 8.0 to about 25, about 8.5 to about 25, about 9.0 to about 25, about 9.5 to about 25, about 10 to about 25, about 12 to about 25, about 15 to about 25, about 17 to about 25, about 20 to about 25, or about 22 to about 25 nm in diameter. In some embodiments, the hydrodynamic size of the coated nanoparticle metal oxide core is about 2.9 to about 21 nm in diameter.

[0052] In some embodiments of the imaging agents of Formula I, the metal oxidebinding ligand is a benzenediol or a hydroxy carboxylic acid. In some embodiments of the imaging agents of Formula I, the metal oxide-binding ligand is a benzenediol. In some embodiments of the imaging agents of Formula I, the metal oxide-binding ligand is a hydroxy carboxylic acid.

[0053] In some embodiments of the imaging agents of Formula I, the benzenediol has the formula: wherein X and Y are independently selected from CR8and N;

[0054] R1is selected from the group consisting of-CFFCFbCOOH, -CH2CH2NH2,

[0055] -CH2CH2SH, -(CH2CH2O)XN3- -(CH2CH20)XOC- -(CH2CH2O)XSCN-, x is an integer selected from 1-9; R2is H or an electron withdrawing group; and

[0056] R8is selected from the group consisting of H and Ci-Ce alkyl.

[0057] In some embodiments of the imaging agents of Formula I, the benzenediol has the formula:

[0058] CH2CH2C(=O)NH-; x is an integer selected from 1-9;

[0059] R2is H or an electron withdrawing group; and

[0060] R8is selected from the group consisting of H and Ci-Ce alkyl wherein indicates the points of attachment of the specified group to the nanoparticle metal oxide core.

[0061] In some embodiments of the imaging agents of Formula I, R1is - CH2CH2NHC(=O)- or -CH2CH2C(=O)NH-

[0062] In some embodiments of the imaging agents of Formula I, the benzenediol is indicates the points of attachment of the specified group to the linker.

[0063] In some embodiments of the imaging agents of Formula I, X is CR8, wherein R8is selected from the group consisting of H and Ci-Ce alkyl. For example, X can be CH, CMe, and CEt. In some embodiments of the imaging agents of Formula I, X is N.

[0064] In some embodiments of the imaging agents of Formula I, R2is H. In some embodiments of the imaging agents of Formula I, R2is an electron withdrawing group. For example, R2can be -NO2, -SO3H, -SOiNa, -CF3, -SO2CF3, or - CN.

[0065] In some embodiments of the imaging agents of Formula I, Y is CR8, wherein R8is selected from the group consisting of H and Ci-Ce alkyl. For example, Y can be CH, CMe, and CEt. In some embodiments of the imaging agents of Formula I, Y is N.

[0066] In some embodiments of the imaging agents of Formula I, the hydroxy carboxylic acid is an a-hydroxy carboxylic acid. For example, the hydroxy carboxylic acid can be lactic acid or glycolic acid. In some embodiments of the imaging agents of Formula I, the hydroxy carboxylic acid is a -hydroxy carboxylic acid. For example, the hydroxy carboxylic acid can be tropic acid or citric acid.

[0067] In some embodiments of the imaging agents of Formula I, the hydroxy carboxylic acid has the formula: wherein p is an integer selected from 1-4;

[0068] R3is selected from the group consisting of H, -(CH2)qC(0)-, and -(CH2)qNH-; q is an integer selected from 1-5; or a pharmaceutically acceptable salt thereof.

[0069] In some embodiments of the imaging agents of Formula I, the hydroxy carboxylic acid has the formula: wherein indicates the points of attachment of the specified group to the nanoparticle metal oxide core. In some embodiments of the imaging agents of Formula I, R3is -(CH2)qC(O)- or -(CH2)qNH-.

[0070] In some embodiments of the imaging agents of Formula I, the hydroxy carboxylic wherein \ indicates the points of attachment of the specified group to the linker.

[0071] In some embodiments of the imaging agents of Formula I, the linker moiety has a molecular weight of about 200 to about 800 amu. For example, about 200 to about 750, about 200 to about 700, about 200 to about 650, about 200 to about 600, about 200 to about 550, about 200 to about 500, about 200 to about 450, about 200 to about 400, about 200 to about 350, about 200 to about 300, or about 200 to about 250 amu. In some embodiments of the imaging agent of Formula I, the linker has a molecular weight of about 250 to about 800, about 300 to about 800, about 350 to about 800, about 400 to about 800, about 450 to about 800, about 500 to about 800, about 550 to about 800, about 600 to about 800, about 650 to about 800, about 700 to about 800, or about 750 to about 800 amu. In some embodiments of the imaging agent of Formula I, the linker moiety has a molecular weight of about 250 to about 600, about 300 to about 650, about 350 to about 700, or about 400 to about 750 amu.

[0072] In some embodiments of the imaging agents of Formula I, the linker moiety is selected from the group consisting of-NHCH(R4)CO-, -NH(CH2)sC(O)-, -NHCH2CH2OCH2CH2CH2C(O)- -NHCH2CH2OCH2CH2OCH2CH2C(O)- NHCH2C6H4CH2NH-, -NH(CH2)tNH- -NHCH2OCH2NH-, -NHCH2CH2OCH2CH2NH-, -NHCH2CH2OCH2CH2OCH2CH2NH-, -N3(CH2CH2O)UC(O)-, -C=C(CH2CH2O)UC(O)-, -SCN(CH2CH2O)UC(O)- wherein s is an integer selected from 1-6; R4is an amino acid side chain; t is an integer selected from 2-6; u is an integer selected from 2-10; and the linker can be read either right-to-left or left-to-right; wherein the indicates the points of attachment of the specified group to the collagen-binding peptide.

[0073] In some embodiments of the imaging agents of Formula I, the linker moiety is selected from the group consisting of-CH2CH2OC(=O)-, -CH2CH2OCH2CH2OC(=O)- -CH2CH2O(CH2CH2O)2C(=O)- -CH2CH2O(CH2CH2O)3C(=O)- - CH2CH2O(CH2CH2O)4C(=O)- and -CH2CH2O(CH2CH2O)5C(=O)-.

[0074] In some embodiments of the imaging agents of Formula I, the linker moiety is selected from the group consisting of -CH2CH2O-, -CH2CH2OCH2CH2O-, - CH2CH2O(CH2CH2O)2-, -CH2CH2O(CH2CH2O)3-, -CH2CH2O(CH2CH2O)4-, and - CH2CH2O(CH2CH2O)5-.

[0075] In some embodiments of the imaging agents of Formula I, the linker moiety is n someembodiments of the imaging agents of

[0076] Formula I, the collagen-binding peptide is about 2 to about 25 amino acid residues in length. For example, about 2 to about 23, about 2 to about 20, about 2 to about 18, about 2 to about 15, about 2 to about 12, about 2 to about 10, about 2 to about 8, about 2 to about 5, or about 2 to about 4 amino acid residues in length. In some embodiments of the imaging agents of Formula I, the collagen-binding peptide is about 5 to about 25, about 8 to about 25, about 10 to about 25, about 12 to about 25, about 15 to about 25, about 18 to about 25, about 20 to about 25, or about 22 to about 25 amino acid residues in length. In some embodiments of the imaging agents of Formula I, the collagen-binding peptide is about 5 to about 10, about 5 to about 15, about 10 to about 12, about 10 to about 15, about 10 to about 20, about 15 to about 18, or about 15 to about 20 amino acid residues in length.

[0077] In some embodiments of the imaging agents of Formula I, the collagen-binding peptide has the formula:

[0078]

[0079] In some embodiments of the imaging agents of Formula I, the imaging agents has the formula:

[0080] wherein a nanoparticle metal oxide core comprising iron oxide, manganese oxide, gadolinium oxide, or a combination thereof;

[0081] X and Y are independently selected from CH and N;

[0082] R2is selected from the group consisting of H, -NO2, -CF3, -SO3H, SChNa, -CHCHSOiNa; and n is an integer selected from 1-6.

[0083] In some embodiments of the imaging agents of Formula I, the imaging agents further comprises an additional metal oxide-binding ligand. In some embodiments, the additional metal oxide-binding ligand wherein indicates the points of attachment of the specified group to the nanoparticle metal oxide core.

[0084] In some embodiments, the metal oxide-binding ligand and the additional metal oxide-binding ligand cover about 1-10%, 10-20%, 20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90%, or 90-100% of the surface of the nanoparticle metal oxide core. In some embodiments, the metal oxide-binding ligand covers about 1-10%, 10- 20%, 20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90%, or 90-100% of the surface of the nanoparticle metal oxide core. In some embodiments, the additional metal oxide-binding ligand cover about 1-10%, 10-20%, 20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90%, or 90-100% of the surface of the nanoparticle metal oxide core. In some embodiments, the ratio of the metal oxide-binding ligand to the additional metal oxide-binding ligand on the surface of the nanoparticle metal oxide core of about 1 : 1, 1 :5, 1 : 10, 1 :15, 1 :20, 20: 1, 15: 1, 10: 1, or 5: 1. In some embodiments, the ratio is about 1.1. In some embodiments, the ratio is about 1.5. In some embodiments, the ratio is about 1.10. In some embodiments, the ratio is about 1.15. In some embodiments, the ratio is about 1.20. In some embodiments, the ratio is about 20: 1. In some embodiments, the ratio is about 15: 1. In some embodiments, the ratio is about 10: 1. In some embodiments, the ratio is about 5: 1.

[0085] In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is CH, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is CH, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is CH, and R2is selected from the group consisting of -SO3H and -SChNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is CH, and R2is -CHCHSChNa.

[0086] In some embodiments, the nanoparticle metal oxide core is iron oxide, X is N, Y is CH, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is N, Y is CH, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is N, Y is CH, and R2is selected from the group consisting of -SO3H and -SChNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is N, Y is CH, and R2is -CHCHSChNa.

[0087] In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is N, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is N, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is N, and R2is selected from the group consisting of -SO3H and -SC Na. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is N, and R2is -CHCHSChNa.

[0088] In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is CH, Y is CH, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is CH, Y is CH, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is CH, Y is CH, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is CH, Y is CH, and R2is -CHCHSChNa.

[0089] In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is N, Y is CH, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is N, Y is CH, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is N, Y is CH, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is N, Y is CH, and R2is -CHCHSChNa.

[0090] In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is CH, Y is N, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is CH, Y is N, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is CH, Y is N, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, X is CH, Y is N, and R2is -CHCHSChNa.

[0091] In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is CH, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is CH, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is CH, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, X is CH, Y is CH, and R2is -CHCHSChNa.

[0092] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, X is N, Y is CH, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, X is N, Y is CH, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, X is N, Y is CH, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, X is N, Y is CH, and R2is -CHCHSChNa.

[0093] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, X is CH, Y is N, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, X is CH, Y is N, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, X is CH, Y is N, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, X is CH, Y is N, and R2is -CHCHSChNa.

[0094] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is lactic acid, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid is lactic acid, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is lactic acid, and R2is selected from the group consisting of- SO3H and -SOsNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is lactic acid, and R2is -CHCHSChNa.

[0095] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is glycolic acid, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid is glycolic acid, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is glycolic acid, and R2is selected from the group consisting of-SC H and -SChNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is glycolic acid, and R2is -CHCHSChNa.

[0096] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is citric acid, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid is citric acid, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is citric acid, and R2is selected from the group consisting of -SO3H and -SC Na. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is citric acid, and R2is -CHCHSChNa.

[0097] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is H, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid i integer selected from 1-4, R3is H, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is

[0098] H, and R2is selected from the group consisting of -SO3H and -SChNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is H, and R2is

[0099] -CHCHSC Na.

[0100] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is - (CH2)qC(O)- , q is an integer selected from 0-5, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid is integer selected from 1-4, R3is -(CH2)qC(O)-, q is an integer selected from 0-5, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is -(CH2)qC(O)-, q is an integer selected from 0-5, and R2is selected from the group consisting of -SChH and -SOaNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is -(CH2)qC(O)-, q is an integer selected from 0-5, and R2is -CHCHSChNa

[0101] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is

[0102] -(CH2)qNH-, q is an integer selected from 0-5, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid is integer selected from 1-4, R3is -(CH2)qNH-, q is an integer selected from 0-5, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is -(CH2)qNH-, q is an integer selected from 0-5, and R2is selected from the group consisting of -SChH and -SOaNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is -(CH2)qNH-, q is an integer selected from 0-5, and R2is -CHCHSOiNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is lactic acid, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid is lactic acid, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is lactic acid, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is lactic acid, and R2is - CHCHSChNa.

[0103] In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is glycolic acid, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid is glycolic acid, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is glycolic acid, and R2is selected from the group consisting of -SChH and -SC Na. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is glycolic acid, and R2is -CHCHSChNa.

[0104] In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is citric acid, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid is citric acid, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is citric acid, and R2is selected from the group consisting of-SChH and -SC Na. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is citric acid, and R2is -CHCHSChNa.

[0105] In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is H, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid i integer selected from 1-4,

[0106] R3is H, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is H, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is H, and R2is -

[0107] CHCHSChNa.

[0108] In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is - (CH2)qC(O)- , q is an integer selected from 0-5, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid is integer selected from 1-4, R3is -(CH2)qC(O)-, q is an integer selected from 0-5, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i selected from 1-4, R3is -(CH2)qC(O)-, q is an integer selected from 0-5, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is integer selected from 1-4, R3is -(CH2)qC(O)-, q is an integer selected from 0-5, and R2is -CHCHSChNa.

[0109] In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is -(CH2)qNH-, q is an integer selected from 0-5, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid is integer selected from 1-4, R3is -(CH2)qNH- q is an integer selected from 0-5, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is -(CH2)qNH-, q is an integer selected from 0-5, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is integer selected from 1-4, R3is -(CH2)qNH-, q is an integer selected from 0-5, and R2is -CHCHSC Na. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is lactic acid, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid is lactic acid, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is lactic acid, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is lactic acid, and R2is -CHCHSOiNa.

[0110] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is glycolic acid, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid is glycolic acid, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is glycolic acid, and R2is selected from the group consisting of -SChH and -SC Na. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is glycolic acid, and R2is -CHCHSChNa.

[0111] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is citric acid, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid is citric acid, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is citric acid, and R2is selected from the group consisting of-SChH and -SC Na. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is citric acid, and R2is -CHCHSChNa.

[0112] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is H, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid i integer selected from 1-4,

[0113] R3is H, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is H, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is

[0114] H, and R2is -CHCHSChNa.

[0115] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is -(CH2)qC(O)-, q is an integer selected from 0-5, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid is integer selected from 1-4, R3is -(CH2)qC(O)-, q is an integer selected from 0-5, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i selected from 1-4, R3is -(CH2)qC(O)-, q is an integer selected from 0-5, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is integer selected from 1-4, R3is -(CH2)qC(O)-, q is an integer selected from 0-5, and R2is -CHCHSChNa.

[0116] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is

[0117] -(CH2)qNH-, q is an integer selected from 0-5, and R2is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid is integer selected from 1-4, R3is -(CH2)qNH- q is an integer selected from 0-5, and R2is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R3is -(CH2)qNH-, q is an integer selected from 0-5, and R2is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is integer selected from 1-4, R3is -(CH2)qNH-, q is an integer selected from 0-5, and R2is -CHCHSC Na. Collagen-Binding Imaging Agents

[0118] Collagen-binding peptides as described herein have an affinity for the extracellular matrix protein collagen, including human and other animal Collagen Type I. Collagens are particularly useful extracellular matrix proteins to target. For example, collagens I and III are the most abundant components of the extracellular matrix of myocardial tissue, representing over 90% of total myocardial collagen and about 5% of dry myocardial weight. The ratio of collagen I to collagen III in the myocardium in approximately 2:1, and their total concentration is approximately 100 pM in the extracellular matrix. Human collagen type l is a trimer of two chains with an [al(I)]2 [a2(I)] stoichiometry characterized by a repeating G-X-Y sequence motif, where X is most frequently proline and Y is frequently hydroxyproline. In some embodiments, a compound described herein can have an affinity for human, rat, and / or dog collagen type I.

[0119] In some embodiments, the compounds described herein comprise a collagen binding peptide linked directly to one or more metal oxide-binding ligands. In some embodiments, the compounds described herein comprise a collagen binding peptide linked indirectly to one or more metal oxide-binding ligands via a linking moiety. Peptides useful for inclusion in the compounds and compositions described herein include natural amino acids and the unnatural amino acid L-4,4’-biphenylalanine (Bip). The peptides can be synthesized according to standard synthesis methods such as those disclosed in, e.g., WO 01 / 09188 and WO 01 / 08712. Amino acids with many different protecting groups appropriate for immediate use in the solid-phase synthesis of peptides are commercially available.

[0120] Peptides can be assayed for affinity to the appropriate extracellular matrix protein by methods as disclosed in WO 01 / 09188 and WO 01 / 08712, and as described below. For example, peptides can be screened for binding to an extracellular matrix protein by methods well known in the art, including pull-down assays, equilibrium dialysis, affinity chromatography, and inhibition or displacement of probes bound to the matrix protein. For example, peptides can be evaluated for their ability to bind to collagen, such as dried human, rat or dog collagen type I. In some embodiments, a collagen binding peptide can bind human collagen with a dissociation constant of less than 25 pM, less than 10 pM, less than 5 pM, less than 1 pM, or less than 100 nM. In some embodiments the collagen binding peptide can bind rat collagen with a dissociation constant of less than 25 pM, less than 10 pM, less than 5 pM, less than 1 pM, or less than 100 nM. In some embodiments the collagen binding peptide can bind dog collagen with a dissociation constant of less than 25 pM, less than 10 pM, less than 5 pM, less than 1 pM, or less than 100 nM.

[0121] Peptides may be synthesized directly using conventional techniques, including solid-phase peptide synthesis, solution-phase synthesis, etc. See, for example, Stewart et al., Solid-Phase peptide Synthesis (1989), W.H. Freeman Co., San Francisco; Merrifield, J. Am. Chem. Soc., 1963 85:2149-2145; and Bodanszky and Bodanszky, The Practice of Peptide Synthesis (1984), Springer-Verlag, New York. Peptides may also be prepared or purchased commercially. Automated peptide synthesis machines, such as manufactured by Perkin-Elmer Applied Biosystems, may also be used.

[0122] The collagen binding peptide can be purified once it has been isolated or synthesized by either chemical or recombinant techniques. For purification purposes, there are many standard methods that may be employed including reversed-phase high- pressure liquid chromatography (RP-HPLC) using an alkylated silica column such as C4-, Cs- or Cis-silica. A gradient mobile phase of increasing organic content is generally used to achieve purification, for example, acetonitrile in an aqueous buffer. In some embodiments, the mobile phase can also include a small amount of trifluoroacetic acid. Ion-exchange chromatography can also be used to separate peptides based on their charge. The degree of purity of the collagen binding peptide may be determined by various methods, including identification of a major large peak on HPLC. In some embodiments, the peptide produces a single peak that is at least 95% of the input material on an HPLC column. In some embodiments, the peptide produces a single peak that is at least 97%, at least 98%, at least 99% or even 99.5% of the input material on an HPLC column.

[0123] MR compounds can exhibit high relaxivity as a result of binding to collagen, which can lead to better image resolution. In some embodiments, the increase in relaxivity upon binding is 1.5-fold or more (e.g., at least a 2, 3, 4, 5, 6, 7, 8, 9, or 10 fold increase in relaxivity). For example, targeted MR compounds can increase the relaxivity upon binding by 7-8 fold, 9-10 fold, or even greater than 10 fold. In some embodiments, relaxivity is measured using an NMR spectrometer. In some embodiments, the relaxivity of an MRI compound at 20 MHz and 37 °C is at least 8 mM’1s'1per paramagnetic metal ion (e.g., at least 10, 15, 20, 25, 30, 35, 40, or 60 mM'1s'1per paramagnetic metal ion). In some embodiments, the MR compounds have a relaxivity greater than 60 mM'ls'1at 20 MHz and 37 °C.

[0124] As described herein, targeted MR compounds can be taken up selectively by areas in the body having higher concentrations of collagen relative to other areas. Selectivity of uptake of targeted agents can be determined by comparing the uptake of the agents by myocardium as compared to the uptake by blood. The selectivity of targeted compounds also can be demonstrated using MRI and observing enhancement of myocardial signal as compared to blood signal.

[0125] Fibrin-Binding Imaging Agents

[0126] Provided herein are imaging agents of Formula II:

[0127] [NP]-[C]a-[L]b-[FP]e (II) or a pharmaceutically acceptable salt thereof, wherein NP is a nanoparticle metal oxide core comprising iron oxide, manganese oxide, or gadolinium oxide;

[0128] C is a metal oxide-binding ligand;

[0129] L is a linker moiety;

[0130] FP is a fibrin-binding peptide; b is an integer selected from 0 to 10; and a and c are each integers independently selected from 1 to 5.

[0131] In some embodiments of the imaging agents of Formula II, a is 0, a is 1, a is 2, a is 3, a is 4, or a is 5. In some embodiments of the imaging agents of Formula II, b is 1 or b is 2. In some embodiments of the imaging agents of Formula II, c is 1 or c is 2.

[0132] In some embodiments of the imaging agents of Formula II, NP is a nanoparticle metal oxide comprising iron oxide. In some embodiments of the imaging agents of Formula II, NP is a nanoparticle metal oxide comprising manganese oxide. In some embodiments of the imaging agents of Formula II, NP is a nanoparticle metal oxide core comprising gadolinium oxide. In some embodiments of the imaging agents of Formula II, NP is a nanoparticle metal oxide core comprising iron oxide, manganese oxide, gadaolinium oxide, or a combination thereof. For example, the nanoparticle core can comprise iron oxide and manganese oxide. For example, the nanoparticle core can comprise iron oxide and gadolinium oxide. For example, the nanoparticle core can comprise manganese oxide and gadolinium oxide. For example, the nanoparticle core can comprise iron oxide, manganese oxide, and gadolinium oxide.

[0133] In some embodiments of the imaging agents of Formula II, the nanoparticle metal oxide core comprises about 5 to about 200 metal ions. For example, about 5 to about 175, about 5 to about 150, about 5 to about 125, about 5 to about 100, about 5 to about 75, about 5 to about 50, about 5 to about 25, or about 5 to about 10 metal ions. In some embodiments, the nanoparticle metal oxide core comprises about 10 to about 200, about 25 to about 200, about 50 to about 200, about 75 to about 200, about 100 to about 200, about 125 to about 200, about 150 to about 200, or about 175 to about 200 metal ions. In some embodiments, the nanoparticle metal oxide core comprises about 5 and about 15, about 10 and about 15, about 10 and about 20, about 10 and about 25, about 10 and about 30, about 10 and about 35, about 10 and about 40, about 10 and about 45, about 10 and about 50, about 25 and about 50, about 50 and about 100, about 75 and about 100, about 100 and about 125, about 125 to about 150, or about 150 to about 175 metal ions.

[0134] In some embodiments, the nanoparticle metal oxide core is about 2.0 to about 10.0 nm in diameter. For example, about 2.0 to about 9.0, about 2.0 to about 8.0, about 2.0 to about 7.5, about 2.0 to about 7.0, about 2.0 to about 6.5, about 2.0 to about 6.0, about 2.0 to about 5.5, about 2.0 to about 5.0, about 2.0 to about 4.5, about 2.0 to about 3.5, or about 2.0 to about 3.0 nm in diameter. In some embodiments, the nanoparticle metal oxide core is about 2.5 to about 10.0, about 3.0 to about 10.0, about 3.5 to about 10.0, about 4.0 to about 10.0, about 4.5 to about 10.0, about 5.0 to about 10.0, about 5.5 to about 10.0, about 6.0 to about 10.0, about 6.5 to about 10.0, about 7.0 to about 10.0, about 7.5 to about 10.0, about 8.0 to about 10.0, about 8.5 to about 10.0, or about 9.0 to about 10.0 nm in diameter. In some embodiments, the nanoparticle metal oxide core is about 3.0 to about 5.0 nm in diameter. For example, about 3.0 to about 4.8, about 3.0 to about 4.5, about 3.0 to about 4.2, about 3.0 to about 4.0, or about 3.0 to about 3.8 nm in diameter. For example, about 3.2 to about 5.0, about 3.5 to about 5.0, about 3.8 to about 5.0, about 4.0 to about 5.0, or about 4.2 to about 5.0 nm in diameter. In some embodiments, the nanoparticle metal oxide core is about 3.4 to about 4.5 nm in diameter.

[0135] In some embodiments, the hydrodynamic size of the coated nanoparticle metal oxide core is about 2.0 to about 25 nm in diameter. For example, about 2.0 to about 23, about 2.0 to about 21, about 2.0 to about 20, about 2.0 to about 18, about 2.0 to about 15, about 2.0 to about 12, about 2.0 to about 10, about 2.0 to about 8, about 2.0 to about 6, or about 2.0 to about 4 nm in diameter. In some embodiments, the hydrodynamic size of the coated nanoparticle metal oxide core is about 2.5 to about 25, about 3.0 to about 25, about 3.5 to about 25, about 4.0 to about 25, about 4.5 to about 25, about 5.0 to about 25, about 5.0 to about 25, about 5.5 to about 25, about 6.0 to about 25, about 6.5 to about 25, about 7.0 to about 25, about 8.0 to about 25, about 8.5 to about 25, about 9.0 to about 25, about 9.5 to about 25, about 10 to about 25, about 12 to about 25, about 15 to about 25, about 17 to about 25, about 20 to about 25, or about 22 to about 25 nm in diameter. In some embodiments, the hydrodynamic size of the coated nanoparticle metal oxide core is about 2.9 to about 21 nm in diameter.

[0136] In some embodiments of the imaging agents of Formula II, the metal oxi debinding ligand is a benzenediol or a hydroxy carboxylic acid. In some embodiments of the imaging agents of Formula II, the metal oxide-binding ligand is a benzenediol. In some embodiments of the imaging agents of Formula II, the metal oxide-binding ligand is a hydroxy carboxylic acid.

[0137] In some embodiments of the imaging agents of Formula II, the benzenediol has the formula: wherein A and B are independently selected from CR9and N;

[0138] R?is selected from the group consisting of-CH2CH2COOH, -CH2CH2NH2, -CH2CH2SH, -(CH2CH2O)dN3-, -(CH2CH2O)dC=C-, -(CH2CH2O)dSCN-, d is an integer selected from 1-9; R6is H or an electron withdrawing group; and

[0139] R9is selected from the group consisting of H and Ci-Ce alkyl.

[0140] In some embodiments of the imaging agents of Formula II, the benzenediol has the formula:

[0141] CH2CH2C(=O)NH-; d is an integer selected from 1-9;

[0142] R6is H or an electron withdrawing group; and

[0143] R9is selected from the group consisting of H and Ci-Ce alkyl wherein indicates the points of attachment of the specified group to the nanoparticle metal oxide core.

[0144] In some embodiments of the imaging agents of Formula II, R5is - CH2CH2NHC(=O)- or -CH2CH2C(=O)NH-

[0145] In some embodiments of the imaging agents of Formula II, the benzenediol is indicates the points of attachment of the specified group to the linker.

[0146] In some embodiments of the imaging agents of Formula II, X is CR9, wherein R9is selected from the group consisting of H and Ci-Ce alkyl. For example, X can be CH, CMe, and CEt. In some embodiments of the imaging agents of Formula II, X is N.

[0147] In some embodiments of the imaging agents of Formula II, R6is H. In some embodiments of the imaging agents of Formula II, R6is an electron withdrawing group. For example, R6can be -NO2, -SO3H, -SChNa, -CF3, -SO2CF3, or -CN.

[0148] In some embodiments of the imaging agents of Formula II, the hydroxy carboxylic acid is an a-hydroxy carboxylic acid. For example, the hydroxy carboxylic acid can be lactic acid or glycolic acid. In some embodiments of the imaging agents of Formula II, the hydroxy carboxylic acid is a P-hydroxy carboxylic acid. For example, the hydroxy carboxylic acid can be tropic acid or citric acid.

[0149] In some embodiments of the imaging agents of Formula II, the hydroxy carboxylic acid has the formula: wherein e is an integer selected from 1-4;

[0150] R7is selected from the group consisting of H, -(CH2)IC(O)-, and -(CH2)fNH-; f is an integer selected from 0-5; or a pharmaceutically acceptable salt thereof.

[0151] In some embodiments of the imaging agents of Formula II, the hydroxy carboxylic acid has the formula: wherein '''’1 indicates the points of attachment of the specified group to the nanoparticle metal oxide core.

[0152] In some embodiments of the imaging agents of Formula II, R7is -(CH2)fC(O)- or -(CH2)fNH-. In some embodiments of the imaging agents of Formula II, the hydroxy carboxylic acid wherein indicates the points of attachment of the specified group to the linker.

[0153] In some embodiments of the imaging agents of Formula II, the linker moiety has a molecular weight of about 200 to about 800 amu. For example, about 200 to about 750, about 200 to about 700, about 200 to about 650, about 200 to about 600, about 200 to about 550, about 200 to about 500, about 200 to about 450, about 200 to about 400, about

[0154] 200 to about 350, about 200 to about 300, or about 200 to about 250 amu. In some embodiments of the imaging agent of Formula II, the linker has a molecular weight of about 250 to about 800, about 300 to about 800, about 350 to about 800, about 400 to about 800, about 450 to about 800, about 500 to about 800, about 550 to about 800, about 600 to about 800, about 650 to about 800, about 700 to about 800, or about 750 to about

[0155] 800 amu. In some embodiments of the imaging agent of Formula II, the linker moiety has a molecular weight of about 250 to about 600, about 300 to about 650, about 350 to about 700, or about 400 to about 750 amu.

[0156] In some embodiments of the imaging agents of Formula II, the linker moiety is selected from the group consisting of-NHCH(R4)CO-, -NH(CH2)gC(O)-, NHCH2CH2OCH2CH2CH2C(O)-, -NHCH2CH2OCH2CH2OCH2CH2C(O)-, NHCH2C6H4CH2NH-, -NH(CH2)hNH- -NHCH2OCH2NH-, -NHCH2CH2OCH2CH2NH-, -NHCH2CH2OCH2CH2OCH2CH2NH-

[0157] -N3(CH2CH2O)iC(O)-, -C=C(CH2CH2O)iC(O)-, -SCN(CH2CH2O)iC(O)-, wherein g is an integer selected from 1-6;

[0158] R4is an amino acid side chain; h is an integer selected from 2-6; i is an integer selected from 2-10; and the linker can be read either right-to-left or left-to-right; wherein the indicates the points of attachment of the specified group to the fibrin-binding peptide.

[0159] In some embodiments of the imaging agents of Formula II, the linker moiety is selected from the group consisting of-CH2CH2OC(=O)-, -CH2CH2OCH2CH2OC(=O)-, -CH2CH2O(CH2CH2O)2C(=O)-, -CH2CH2O(CH2CH2O)3C(=O)-, - CH2CH2O(CH2CH2O)4C(=O)-, and -CH2CH2O(CH2CH2O)5C(=O)-.

[0160] In some embodiments of the imaging agents of Formula II, the linker moiety is selected from the group consisting of -CH2CH2O-, -CH2CH2OCH2CH2O-, - CH2CH2O(CH2CH2O)2-, -CH2CH2O(CH2CH2O)3-, -CH2CH2O(CH2CH2O)4-, and - CH2CH2O(CH2CH2O)s-.

[0161] In some embodiments of the imaging agents of Formula II, the linker moiety is

[0162] In some embodiments of the imaging agents of Formula II, the fibrin-binding peptide is about 2 to about 25 amino acid residues in length. For example, about 2 to about 23, about 2 to about 20, about 2 to about 18, about 2 to about 15, about 2 to about 12, about 2 to about 10, about 2 to about 8, about 2 to about 5, or about 2 to about 4 amino acid residues in length. In some embodiments of the imaging agents of Formula II, the fibrin-binding peptide is about 5 to about 25, about 8 to about 25, about 10 to about 25, about 12 to about 25, about 15 to about 25, about 18 to about 25, about 20 to about 25, or about 22 to about 25 amino acid residues in length. In some embodiments of the imaging agents of Formula II, the fibrin-binding peptide is about 5 to about 10, about 5 to about 15, about 10 to about 12, about 10 to about 15, about 10 to about 20, about 15 to about 18, or about 15 to about 20 amino acid residues in length.

[0163] In some embodiments of the imaging agents of Formula II, the fibrin-binding peptide has the formula:

[0164] wherein X1is selected from the group consisting of:

[0165] X2is selected from the group consisting of:

[0166] X3is selected from the group consisting of H and OH;

[0167] X4is selected from the group consisting of H, I, Br, and Cl;

[0168] X5is selected from the group consisting of H and CH2COOH;

[0169] X6is selected from the group consisting of:

[0170] X7is selected from the group consisting of CH2CH2C(O)NH2 and CH2CH(CH3)2; wherein the indicates the point of attachment of the specified group to the fibrin- binding peptide.

[0171] In some embodiments of the imaging agents of Formula II, the imaging agents has the formula:

[0172] wherein an iron oxide, manganese oxide, or gadolinium oxide nanoparticle;

[0173] A and B are independently selected from CH and N;

[0174] R6is selected from the group consisting of -H, -NO2, -CF3, -SO3H, -SChNa,

[0175] -CHCHSChNa; and n is an integer selected from 1-6.

[0176] In some embodiments of the imaging agents of Formula II, the imaging agents further comprises an additional metal oxide-binding ligand. In some embodiments, the additional metal oxide-binding ligand indicates the points of attachment of the specified group to the nanoparticle metal oxide core.

[0177] In some embodiments, the metal oxide-binding ligand and the additional metal oxide-binding ligand cover about 1-10%, 10-20%, 20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90%, or 90-100% of the surface of the nanoparticle metal oxide core. In some embodiments, the metal oxide-binding ligand covers about 1-10%, 10- 20%, 20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90%, or 90-100% of the surface of the nanoparticle metal oxide core. In some embodiments, the additional metal oxide-binding ligand cover about 1-10%, 10-20%, 20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90%, or 90-100% of the surface of the nanoparticle metal oxide core.

[0178] In some embodiments, the ratio of the metal oxide-binding ligand to the additional metal oxide-binding ligand on the surface of the nanoparticle metal oxide core of about 1 : 1, 1 :5, 1 : 10, 1 :15, 1 :20, 20: 1, 15: 1, 10: 1, or 5: 1. In some embodiments, the ratio is about 1.1. In some embodiments, the ratio is about 1.5. In some embodiments, the ratio is about 1.10. In some embodiments, the ratio is about 1.15. In some embodiments, the ratio is about 1.20. In some embodiments, the ratio is about 20: 1. In some embodiments, the ratio is about 15: 1. In some embodiments, the ratio is about 10: 1. In some embodiments, the ratio is about 5: 1.

[0179] In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is CH, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is CH, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is CH, and R6is selected from the group consisting of-SC H and -SChNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is CH, and R6is -CHCHSChNa.

[0180] In some embodiments, the nanoparticle metal oxide core is iron oxide, A is N, B is CH, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, A is N, B is CH, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, A is N, B is CH, and R6is selected from the group consisting of -SO3H and -SChNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, A is N, B is CH, and R6is -CHCHSChNa.

[0181] In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is N, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is N, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is N, and R6is selected from the group consisting of -SO3H and -SChNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is N, and R6is -CHCHSChNa.

[0182] In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is CH, B is CH, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is CH, B is CH, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is CH, B is CH, and R6is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is CH, B is CH, and R6is -CHCHSChNa.

[0183] In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is N, B is CH, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is N, B is CH, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is N, B is CH, and R6is selected from the group consisting of-SOiH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is N, B is CH, and R6is -CHCHSChNa.

[0184] In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is CH, B is N, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is CH, B is N, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is CH, B is N, and R6is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, A is CH, B is N, and R6is -CHCHSChNa.

[0185] In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is CH, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is CH, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is CH, and R6is selected from the group consisting of-SChH and -SChNa In some embodiments, the nanoparticle metal oxide core is iron oxide, A is CH, B is CH, and R6is -CHCHSChNa.

[0186] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, A is N, B is CH, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, A is N, B is CH, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, A is N, B is CH, and R6is selected from the group consisting of-SOsH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, A is N, B is CH, and R6is -CHCHSChNa.

[0187] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, A is CH, B is N, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, A is CH, B is N, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, A is CH, B is N, and R6is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, A is CH, B is N, and R6is -CHCHSChNa.

[0188] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is lactic acid, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid is lactic acid, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is lactic acid, and R6is selected from the group consisting of-

[0189] SO3H and -SOsNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is lactic acid, and R6is -CHCHSChNa.

[0190] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is glycolic acid, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid is glycolic acid, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is glycolic acid, and R6is selected from the group consisting of-SC H and -SChNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is glycolic acid, and R6is -CHCHSChNa.

[0191] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is citric acid, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid is citric acid, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is citric acid, and R6is selected from the group consisting of- SO3H and -SOsNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid is citric acid, and R6is -CHCHSChNa.

[0192] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is H, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid i integer selected from 1-4, R7is H, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is

[0193] H, and R6is selected from the group consisting of -SO3H and -SChNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is H, and R6is

[0194] -CHCHSC Na.

[0195] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid is integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is selected from the group consisting of -SChH and -SOaNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is -CHCHSChNa

[0196] In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is

[0197] -(CH2)fNH- f is an integer selected from 0-5, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxlic acid is integer selected from 1-4, R7is -(CH2)fNH- f is an integer selected from 0-5, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)fNH-, f is an integer selected from 0-5, and R6is selected from the group consisting of -SChH and -SOaNa. In some embodiments, the nanoparticle metal oxide core is iron oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)rNH- f is an integer selected from 0-5, and R6is -CHCHSChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is lactic acid, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid is lactic acid, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is lactic acid, and R6is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is lactic acid, and R6is -CHCHSOiNa.

[0198] In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is glycolic acid, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid is glycolic acid, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is glycolic acid, and R6is selected from the group consisting of -SChH and -SC Na. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is glycolic acid, and R6is -CHCHSChNa.

[0199] In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is citric acid, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid is citric acid, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is citric acid, and R6is selected from the group consisting of-SChH and -SC Na. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is citric acid, and R6is -CHCHSChNa.

[0200] In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is H, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid i integer selected from 1-4,

[0201] R7is H, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is H, and R6is selected from the group consisting of -SOaH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is H, and R6is -CHCHSC Na.

[0202] In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid is integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid is integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is -CHCHSChNa.

[0203] In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)fNH- f is an integer selected from 0-5, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxlic acid is integer selected from 1-4, R7is -(CH2)fNH-, f is an integer selected from 0-5, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)fNH- f is an integer selected from 0-5, and R6is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is manganese oxide, the hydroxy carboxylic acid i is an integer selected from 1-4, R7is -(CH2)rNH- f is an integer selected from 0-5, and R6is -CHCHSOiNa In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is lactic acid, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid is lactic acid, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is lactic acid, and R6is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is lactic acid, and R6is -CHCHSOiNa.

[0204] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is glycolic acid, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid is glycolic acid, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is glycolic acid, and R6is selected from the group consisting of -SChH and -SC Na. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is glycolic acid, and R6is -CHCHSChNa.

[0205] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is citric acid, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid is citric acid, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is citric acid, and R6is selected from the group consisting of-SChH and -SC Na. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is citric acid, and R6is -CHCHSChNa.

[0206] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is H, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid i integer selected from 1-4,

[0207] R7is H, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is H, and R6is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is

[0208] H, and R6is -CHCHSChNa.

[0209] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid is integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid is integer selected from 1-4, R7is -(CH2)fC(O)-, f is an integer selected from 0-5, and R6is -CHCHSChNa.

[0210] In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is

[0211] -(CH2)fNH- f is an integer selected from 0-5, and R6is -NO2. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxlic acid is integer selected from 1-4, R7is -(CH2)fNH-, f is an integer selected from 0-5, and R6is -CF3. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i integer selected from 1-4, R7is -(CH2)fNH- f is an integer selected from 0-5, and R6is selected from the group consisting of-SChH and -SChNa. In some embodiments, the nanoparticle metal oxide core is gadolinium oxide, the hydroxy carboxylic acid i is an integer selected from 1-4, R7is -(CH2)rNH- f is an integer selected from 0-5, and R6is -CHCHSOiNa Fibrin-Binding Imaging Agents

[0212] Fibrin-binding peptides as described herein have an affinity for fibrin (e.g., thrombi, solid tumors, and atherosclerotic plaques) within a mammal. Any peptide capable of binding fibrin may be used. For example, the peptides disclosed in WO 2008 / 071679, U.S. Patent Nos. 6,984,373; 6,991,775; and 7,238,341 and U.S. Patent Application No. 2005 / 0261472 may be used.

[0213] The ability of peptides to bind fibrin can be assessed by known methodology. For example, affinity of the peptide for fibrin can be assessed using the DD(E) fragment of fibrin, which contains subunits of 55 kD (Fragment E) and 190 kD (Fragment DD). The DD(E) fragment can be biotinylated and immobilized via avidin to a solid substrate (e.g., a multi-well plate). Peptides can be incubated with the immobilized DD(E) fragment in a suitable buffer and biding detected using known methodology. See, for example, WO 2001 / 09188.

[0214] Binding can also be assessed in a blood plasma-derived clot assay (see e.g., Overoye-Chan et al. J. Am. Chem. Soc. 2008 130:6025-39). Here, known concentrations of peptide are incubated in blood plasma (human or other species), and thrombin is added to induce clot formation. The clot is separated from the serum, and the concentration of the peptide in the serum ([peptide]free) is determined (e.g., by HPLC or if the peptide is labeled with a fluorophore by fluorescence, or if labeled by a radionuclide concentration is determined by radioactivity). The concentration of fibrin-bound peptide ([peptide]bound) is calculated by subtraction ([peptide]bound) = [peptide]total - [peptide]free).

[0215] Binding can also be assessed by a dried fibrin assay. Here, purified fibrinogen (2.5 mg / mL; 7 / M fibrin) is clotted with thrombin and dried to a thin film in wells of a microtiter plate. The resulting clots bind to the plate without loss of protein. The clots are rehydrated with buffer containing known concentrations of peptide. After incubation at 37 °C for 2 hr, the concentration of peptide in the supernatant ([peptide]free) is determined (e.g., by HPLC or if the peptide is labeled with a fluorophore by fluorescence, or if labeled by a radionuclide concentration is determined by radioactivity). The concentration of fibrin-bound peptide ([peptide]bound) is calculated by subtraction ([peptide]bound) = [peptide]total - [peptide]free). A dissociation constant (Kd) for fibrin binding can be determined by fitting a plot of [peptide]bound versus [peptide]free to either a stoichiometric (see e.g. Nair et al., Angew. Chem. Int. Ed. 200847:4918-21) or equivalent binding sites model (see e.g. Overoye-Chan et al. J. Am. Chem. Soc. 2008 130:6025-39).

[0216] Peptides may be synthesized directly using conventional techniques, including solid-phase peptide synthesis, solution-phase synthesis, etc. See, for example, Stewart et al., Solid-Phase peptide Synthesis (1989), W.H. Freeman Co., San Francisco; Merrifield, J. Am. Chem. Soc., 1963 85:2149-2145; Bodanszky and Bodanszky, The Practice of Peptide Synthesis (1984), Springer-Verlag, New York. Peptides may also be prepared or purchased commercially. Automated peptide synthesis machines, such as manufactured by Perkin-Elmer Applied Biosystems, may also be used.

[0217] In some embodiments, the fibrin binding peptide is purified once it has been isolated or synthesized by either chemical or recombinant techniques. For purification purposes, there are many standard methods that may be employed including reversed- phase high-pressure liquid chromatography (RP-HPLC) using an alkylated silica column such as C4-, Cs- or Cis-silica. A gradient mobile phase of increasing organic content is generally used to achieve purification, for example, acetonitrile in an aqueous buffer, usually containing a small amount of trifluoroacetic acid. Ion-exchange chromatography can also be used to separate peptides based on their charge. The degree of purity of the fibrin binding peptide may be determined by various methods, including identification of a major large peak on HPLC. In some embodiments, the peptide produces a single peak that is at least 95% of the input material on an HPLC column. In some embodiments, the peptide produces a single peak that is at least 97%, at least 98%, at least 99% or at least 99.5% of the input material on an HPLC column.

[0218] Pharmaceutically Acceptable Derivatives and Compositions

[0219] In some embodiments, the imaging agents of the present disclosure can be formulated as a pharmaceutical composition in accordance with routine procedures. In some embodiments, a pharmaceutical composition comprises a compound of Formula I, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable excipient. In some embodiments, a pharmaceutical composition comprises a compound of Formula II, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable excipient.

[0220] As used herein, the imaging agents can include pharmaceutically acceptable derivatives thereof. "Pharmaceutically acceptable" means that the compound or composition can be administered to an animal without unacceptable adverse effects. A "pharmaceutically acceptable derivative" means any pharmaceutically acceptable salt, ester, salt of an ester, or other derivative of the imaging agents of the present disclosure that, upon administration to a recipient, is capable of providing (directly or indirectly) the imaging agents or an active metabolite or residue thereof.

[0221] Other derivatives are those that increase the bioavailability of the imaging agents when such compounds are administered to a mammal (e.g., by allowing an orally administered compound to be more readily absorbed into the blood), or which enhance delivery of the parent compound to a biological compartment (e.g., the brain or lymphatic system) thereby increasing the exposure relative to the parent species.

[0222] Pharmaceutically acceptable salts of the imaging agents of the present disclosure include counter ions derived from pharmaceutically acceptable inorganic and organic acids and bases known in the art. For example, alkali and alkaline earth metal cations; sodium; primary, secondary and tertiary amines such as ethanolamine, diethanolamine, morpholine, glucamine, N,N-dimethylglucamine, N-methylglucamine; and amino acids such as lysine, arginine and ornithine.

[0223] Pharmaceutical compositions described herein can be administered by any route, including both oral and parenteral administration. Parenteral administration includes, but is not limited to, subcutaneous, intravenous, intraarterial, interstitial, intrathecal, and intracavity administration. When administration is intravenous, pharmaceutical compositions may be given as a bolus, as two or more closes separated in time, or as a constant or non-linear flow infusion. Thus, compositions of the present disclosure can be formulated for any route of administration.

[0224] Typically, compositions for intravenous administration are solutions in sterile isotonic aqueous buffer. Where necessary, the composition may also include a solubilizing agent, a stabilizing agent, and a local anesthetic such as lidocaine to ease pain at the site of the injection. The composition for intravenous administration may include 80 millimolar sucrose. In some embodiments, the ingredients will be supplied either separately, e.g. in a kit, or mixed together in a unit dosage form, for example, as a dry lyophilized powder or water free concentrate. The composition may be stored in a hermetically sealed container such as an ampule or sachette indicating the quantity of active agent in activity units. Where the composition is administered by infusion, it can be dispensed with a 10 infusion bottle containing sterile pharmaceutical grade "water for injection," saline, or other suitable intravenous fluids. Where the composition is to be administered by injection, an ampule of sterile water for injection or saline may be provided so that the ingredients may be mixed prior 15 to administration. Pharmaceutical compositions of the present disclosure comprise the imaging agents described herein and pharmaceutically acceptable salts thereof, with any pharmaceutically acceptable ingredient, excipient, carrier, adjuvant or vehicle.

[0225] In some embodiments, the compositions of the present disclosure are administered to the patient in the form of an injectable composition. In some embodiments, the method of administering a compound is parenterally, meaning intravenously, intra-arterially, intrathecally, interstitially or intracavitarilly. Pharmaceutical compositions of this disclosure can be administered to animals including humans in a manner similar to other diagnostic or therapeutic agents. The dosage to be administered, and the mode of administration will depend on a variety of factors including age, weight, sex, condition of the patient and genetic factors, and will ultimately be decided by medical personnel subsequent to experimental determinations of varying dosage followed by imaging as described herein.

[0226] Methods for Imaging Collagen

[0227] In some embodiments, a method for imaging collagen in a mammal comprises administering to the mammal an effective amount of an imaging agents of Formula I, or a pharmaceutically acceptable salt thereof; acquiring an image of the collagen of the mammal using a nuclear imaging technique and acquiring an image of the mammal using magnetic resonance imaging; and overlaying said images to localize the collagen within the anatomical image of the mammal. In some embodiments of the method for imaging collagen, the image of the collagen of the mammal using a nuclear imaging technique and the image of the mammal using magnetic resonance imaging are acquired simultaneously. In some embodiments of the method for imaging collagen, the image of the collagen of the mammal using a nuclear imaging technique is acquired first, and the image of the mammal using magnetic resonance imaging is acquired second. In some embodiments of the method for imaging collagen, the imagine of the mammal using magnetic resonance imaging is acquired first, and the image of the collagen of the mammal using a nuclear imaging technique is acquired second.

[0228] In some embodiments, a method for imaging collagen in a mammal comprises administering to the mammal an effective amount of an imaging agents of Formula I, or a pharmaceutically acceptable salt thereof; then acquiring an image of the collagen of the mammal using a nuclear imaging technique and acquiring an image of the mammal using computed tomography; then overlaying said images to localize the collagen within the anatomical image of the mammal.

[0229] In some embodiments of the method for imaging collagen, the image of the collagen of the mammal using a nuclear imaging technique and the image of the mammal using computed tomography are acquired simultaneously. In some embodiments of the method for imaging collagen, the image of the collagen of the mammal using a nuclear imaging technique is acquired first, and the image of the mammal using computed tomography is acquired second. In some embodiments of the method for imaging collagen, the image of the mammal using computed tomography is acquired first, and the image of the collagen of the mammal using a nuclear imaging technique is acquired second.

[0230] In some embodiments of the method for imaging collagen, the nuclear imaging technique is single photon emission, computed tomography, or a combination thereof. In some embodiments of the method for imaging collagen, the mammal is a human. In some embodiments of the method for imaging collagen, the mammal is a rat. In some embodiments of the method for imaging collagen, the mammal is a dog. In some embodiments of the method for imaging collagen, the method further comprises administering to the mammal an effective amount of a second imaging agents. In some embodiments, the second imaging agents does not target collagen.

[0231] In some embodiments, the second imaging agents comprises an MRI imaging agents. In some embodiments, the second imaging agents is an MRI imaging agents. For example, gadoteridol, gadopentetate, gadobenate, gadoxetic acid, gadodiamide, gadoversetamide, and gadofosveset; or a CT imaging agents selected from the group consisting of iopamidol, iohexol, ioxilan, iopromide, iodixanol, ioxaglate, metrizoate, and diatrizoate.

[0232] Methods for Imaging Fibrin

[0233] In some embodiments, a method for imaging fibrin in a mammal comprises administering to the mammal an effective amount of an imaging agents of Formula I, or a pharmaceutically acceptable salt thereof; acquiring an image of the fibrin of the mammal using a nuclear imaging technique and acquiring an image of the mammal using magnetic resonance imaging; and overlaying said images to localize the fibrin within the anatomical image of the mammal.

[0234] In some embodiments of the method for imaging fibrin, the image of the fibrin of the mammal using a nuclear imaging technique and the image of the mammal using magnetic resonance imaging are acquired simultaneously. In some embodiments of the method for imaging fibrin, the image of the fibrin of the mammal using a nuclear imaging technique is acquired first, and the image of the mammal using magnetic resonance imaging is acquired second. In some embodiments of the method for imaging fibrin, the image of the mammal using magnetic resonance imaging is acquired first, and the image of the fibrin of the mammal using a nuclear imaging technique is acquired second.

[0235] In some embodiments, a method for imaging fibrin in a mammal comprises administering to the mammal an effective amount of an imaging agents of Formula I, or a pharmaceutically acceptable salt thereof; then acquiring an image of the fibrin of the mammal using a nuclear imaging technique and acquiring an image of the mammal using computed tomography; then overlaying said images to localize the fibrin within the anatomical image of the mammal. In some embodiments of the method for imaging fibrin, the image of the fibrin of the mammal using a nuclear imaging technique and the image of the mammal using computed tomography are acquired simultaneously. In some embodiments of the method of imaging fibrin, the image of the fibrin of the mammal using a nuclear imaging technique is acquired first, and the image of the mammal using computed tomography is acquired second. In some embodiments of the method for imaging fibrin, the image of the mammal using computed tomography is acquired first, and the image of the fibrin of the mammal using a nuclear imaging technique is acquired second.

[0236] In some embodiments of the method for imaging fibrin, the nuclear imaging technique is single photon emission, computed tomography, or a combination thereof.

[0237] In some embodiments of the method for imaging fibrin, the mammal is a human. In some embodiments of the method for imaging fibrin, the mammal is a rat. In some embodiments of the method for imaging fibrin, the mammal is a dog.

[0238] In some embodiments of the method for imaging fibrin, the method further comprises administering to the mammal an effective amount of a second imaging agents. In some embodiments, the second imaging agents does not target fibrin.

[0239] In some embodiments, the second imaging agents comprises an MRI imaging agents. In some embodiments, the second imaging agents is an MRI imaging agents. For example, gadoteridol, gadopentetate, gadobenate, gadoxetic acid, gadodiamide, gadoversetamide, and gadofosveset; or a CT imaging agents selected from the group consisting of iopamidol, iohexol, ioxilan, iopromide, iodixanol, ioxaglate, metrizoate, and diatrizoate.

[0240] Image Overlay

[0241] Overlaying of images can be done by various means known in the art. See, for example, U.S. Patent Nos. 7,412,279; 7,110616; 6,898,331; 6,549,798; and 5,672,877; Rudd, J.HF. et al., J. Nucl. Med. 2008 49(6): 871-878; Slomka, P.J. et al., J. Nucl. Med. 2009 50: 1621-1630; and Jupp, B. and O’Brien, T.J., Epilepsia 2007 49: 82-89. In some embodiments, the first and second image data sets can be overlaid to determine the presence of the collagen or fibrin within the mammal. For example, the first and second image data sets can be combined to produce a third data set that includes an image of the collagen or the fibrin target and an image of anatomical region where the collagen or the fibrin is located. The third data set is capable of indicating the location of the collagen or the fibrin, if present, within the mammal. If desired, the third data set may be displayed on a display device in order to indicate the location of the stationary target within the vascular system. The third data set may also indicate the size of the stationary target within the mammal.

[0242] EXAMPLES

[0243] The disclosure is further described in the following examples, which do not limit the scope of the disclosure described in the claims.

[0244] EXAMPLE 1: Synthesis of exceedingly small FexOynanoparticles with citrate coating using microwave irradiation

[0245] Iron oxide nanoparticles coated with citrate were synthesized according to a known procedure (Pellico et al., Langmuir 2017, 33, 10239-10247). The size of the nanoparticle and the thickness of the coating was controlled by varying the reaction temperature. The size of the iron oxide core varies from 3.4-4.5 nm in diameter. The hydrodynamic size of the citrate-coated nanoparticle varies from 2.9-21 nm in diameter.

[0246] To a mixture of FeCh-bLLO and citric acid trisodium salt in water was added hydrazine monohydrate. The mixture was treated with microwave irradiation and heated at 240W for 10 min with stirring. Temperatures ranged from 60-140 °C. Upon reaction completion, the resulting nanoparticles were purified by gel filtration chromatography (PD10).

[0247] EXAMPLE 2: Synthesis of exceedingly small FexOynanoparticles with catecholbased coating

[0248]

[0249] Iron oxide nanoparticles coated with catechol -based metal oxide-binding ligands were synthesized according to a known procedure (Wei et al. Nano Lett. 2012, 22, 22- 25). The iron oxide particles were first synthesized with an oleic acid surface and the catechol derivatives were synthesized separately.

[0250] Catechol derivatives

[0251] To a solution of 3-(3,4-dihydroxyphenyl)propanoic acid in dichloromethane was added A-hydroxy succinimide (NHS) and N,N ’-di cyclohexylcarbodiimide (DCC). The resulting NHS-ester in dichloromethane was treated with an amino-based bifunctional linking moiety and / VW ’-di isopropyl ethyl amine (DIPEA) to afford the catechol derivative.

[0252] To the iron oxide nanoparticles coated with oleic acid ligands in ethanol was added 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEAA). MEAA was used as an intermediate ligand to improve solubility of the iron oxide particles in DMF / DI water, as well as to facilitate ligand exchange to generate the final particles. The intermediate MEAA-based particle was treated with a solution of the catechol derivative in DMF / DI water, precipitated, then purified by dialysis to afford the iron oxide nanoparticles coated with catechol-based metal oxide-binding ligands.

[0253] To obtain iron oxide particles coated with structurally distinct catechols, which can be used for further derivatization, a similar procedure was carried out using a mixture of different catechol -based compounds in pre-calculated ratios.

[0254] EXAMPLE 3:

[0255] Superparamagnetic iron oxide nanoparticles (SPION) have been studied for their applications in 72 weighted MRI, as SPIONs have larger r2 / rl ratio than Gd(IIl). However, the high r2 / rl also leads to more significant signal loss of SPIONs in positive contrast 71 -weighted imaging. In addition, most SPIONs have long circulation in the blood stream and / or high liver accumulation due to their large, >10 nm sizes and because they are phagocytosed by macrophages. As a result, targeted imaging with SPIONs takes hours to days for sufficient probe accumulation at target and background washout, and targeted imaging of the liver is precluded by high background signal. It was shown that single-nanometer iron oxide (SNIO) nanoparticles are potent probes for 71 -weighted imaging in vivo, with fast blood clearance and low liver uptake. SNIOCBP is an SNIO nanoparticle functionalized with a type I collagen-binding peptide for the detection of liver fibrosis, which is the outcome of most chronic hepatic injury including viral hepatitis B or C infection, autoimmune and biliary diseases or alcoholic and nonalcoholic steatohepatitis.

[0256] SNIO-CBP was prepared via conjugation of alkyne-functionalized SNIO (SNIO- alkyne) with type I collagen binding peptide CBP-azide via copper-catalyzed alkyneazide reaction (FIG. 1). Small-angle X-ray scattering (SAXS) established that the iron oxide core of SNIOCBP had a mean diameter of 1.5 nm (FIG. 2). Gel filtration chromatography showed a mean hydrodynamic diameter of 3.8 nm (FIG. 3). SNIO-CBP has near-zero zeta potential and exhibited minimal non-specific binding in plasma after incubation with fetal bovine serum (FBS) (FIG. 4). The SNIO / CBP ratio was determined to be 1 / 1.2, according to56Fe ICP-MS and7-amino acid quantification. SNIO-CBP shows a dissociation constant of 23.2 / M in binding with type-I collagen (FIG. 5). Longitudinal relaxivity (rl) of SNIO-CBP was measured to be 4.5 s'1(mM Fe)'1at 1.41 T and 37 °C, or 145 s-1(mM peptide)1.

[0257] Dynamic 7i-weighted MRI following intravenous administration (2 nmol / g based on CBP concentration), showed immediate blood pool enhancement with a blood elimination half-life of 5.7 min, followed by rapid renal elimination. Importantly, SNIO- CBP showed only transient and slight liver enhancement consistent with an extracellular distribution and renal clearance (FIG. 6). Then the ability of SNIO-CBP to detect liver fibrosis in two different mouse models: CCh induced liver fibrosis and choline-deficient, L-amino acid defined, high fat diet (CDAHFD) model was investigated. SNIO-CBP enhanced T1 -weighted MRI could specifically and robustly detect liver fibrosis in both toxin- (FIG. 7) and dietary-induced (FIG. 8) mouse models. The change in ACNR of fibrotic liver induced by SNIO-CBP was in good agreement with the increasing hydroxyproline content and elevated collagen proportional area (CPA) in liver. Prussian blue staining showed localization of SNIO-CBP in fibrotic regions. Importantly, the sensitivity of SNIO-CBP was compared in detecting liver fibrosis in CCh mice with CM- 101, a CBP modified gadolinium based contrast agent. We found that SNIO-CBP provided equivalent enhancement of fibrotic liver compared to CM-101, even at a 2.5- fold lower dose, indicating the higher sensitivity of the gadolinium-free SNIO-CBP.

[0258] It was shown that SNIO-CBP has ideal properties as a targeted Zi-weighted contrast agent: good affinity to type I collagen, minimal nonspecific binding to plasma biomolecules, fast blood elimination, and minimal nonspecific liver enhancement. These properties enabled rapid (minutes post injection) detection and quantification of liver fibrosis in two different mouse models with higher sensitivity than the state of the art Gd based probe. Taken together, SNIO-CBP is a promising candidate as a gadolinium free contrast agent for sensitive detection of liver fibrosis.

[0259] OTHER EMBODIMENTS

[0260] It is to be understood that while the disclosure has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the disclosure, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. An imaging agent of Formula I, or a pharmaceutically acceptable salt thereof:[NP]-[C]m-[L]„-[CP]o (I) wherein NP is a nanoparticle metal oxide core comprising iron oxide, manganese oxide, or gadolinium oxide;C is a metal oxide-binding ligand;L is a linker moiety;CP is a collagen-binding peptide; n is an integer selected from 0-10; and m and o are each integers independently selected from 1-5.

2. The imaging agent of claim 1, wherein the nanoparticle metal oxide core comprises about 5 to about 200 metal ions.

3. The imaging agent of claim 2, wherein the nanoparticle metal oxide core comprises about 5 to about 100 metal ions.

4. The imaging agent of claim 3, wherein the nanoparticle metal oxide core comprises about 10 to about 50 metal ions.

5. The imaging agent of any one of claims 1-4, wherein the nanoparticle metal oxide core comprises iron oxide.

6. The imaging agent of any one of claims 1-4, wherein the nanoparticle metal oxide core comprises manganese oxide.

7. The imaging agent of any one of claims 1-4, wherein the nanoparticle metal oxide core comprises gadolinium oxide.

8. The imaging agent of any one of claims 1-7 wherein the metal oxidebinding ligand is selected from a benzenediol or a hydroxycarboxylic acid.

9. The imaging agent of claim 8, wherein the benzenediol has the formula:wherein X and Y are independently selected from CH and N;R1is selected from -CH2CH2COOH, -CH2CH2NH2, -CH2CH2SH, -(CH2CH2O)xN3- -(CH2CH2O)XC=C- -(CH2CH2O)XSCN- -(CH2CH2O)XSH-x is an integer selected from 1-9; andR2is H or an electron withdrawing group.

10. The imaging agent of claim 9, wherein R2is an electron withdrawing group selected from the group consisting of-NCh, -SO3H, SO Na, and -CF3.

11. The imaging agent of claim 8, wherein the metal oxide-binding ligand is an a-hydroxy carboxylic acid.

12. The imaging agent of claim 11, wherein the a-hydroxy carboxylic acid is selected from lactic acid or glycolic acid.

13. The imaging agent of claim 8, wherein the hydroxy carboxylic acid has the formula:wherein p is an integer selected from 1-4;R3is selected from the group consisting of H, -(CH2)qC(O)-, and -(CH2)qNH-;q is an integer selected from 1-5; or a pharmaceutically acceptable salt thereof.

14. The imaging agent of any one of claims 1-13, wherein the linker, if present, has a molecular weight of about 200 to about 800 amu.

15. The imaging agent of claim 14, wherein the linker has a molecular weight of about 250 to about 600 amu.

16. The imaging agent of claim 15, wherein each linker is independently selected from the group consisting of-NHCH(R4)CO- -NH(CH2)sC(0)-, - NHCH2CH2OCH2CH2CH2C(O)-, -NHCH2CH2OCH2CH2OCH2CH2C(O)- NHCH2C6H4CH2NH-, -NH(CH2)tNH- -NHCH2OCH2NH- - NHCH2CH2OCH2CH2NH-, -NHCH2CH2OCH2CH2OCH2CH2NH- - N3(CH2CH2O)UC(O)-, -C=C(CH2CH2O)UC(O)-, -SCN(CH2CH2O)UC(O)-, -wherein s is an integer selected from 1-6;R4is an amino acid side chain; and t is an integer selected from 2-6; and u is an integer selected from 2-10.

17. The imaging agent of any one of claims 1-16, wherein the collagen- binding peptide is about 2 to about 25 amino acid residues in length.

18. The imaging agent of claim 17, wherein the collagen-binding peptide is about 10 to about 20 amino acid residues in length.

19. The imaging agent of claim 18, wherein the collagen-binding peptide has the formula:

20. An imaging agent of Formula II, or a pharmaceutically acceptable salt thereof:[NP]-[C]a-[L]b-[FP]e (II) wherein NP is a nanoparticle metal oxide core comprising iron oxide, manganese oxide, or gadolinium oxide;C is a metal oxide-binding ligand;L is a linker moiety;FP is a fibrin-binding peptide; b is an integer selected from 0-10; and a and c are each integers independently selected from 1-5.

21. The imaging agent of claim 20, wherein the nanoparticle metal oxide core comprises about 5 to about 200 metal ions.

22. The imaging agent of claim 21, wherein the nanoparticle metal oxide core comprises about 5 to about 100 metal ions.

23. The imaging agent of claim 22, wherein the nanoparticle metal oxide core comprises about 10 to about 50 metal ions.

24. The imaging agent of any one of claims 20-23, wherein the nanoparticle metal oxide core comprises iron oxide.

25. The imaging agent of any one of claims 20-23, wherein the nanoparticle metal oxide core comprises manganese oxide.

26. The imaging agent of any one of claims 20-23, wherein the nanoparticle metal oxide core comprises gadolinium oxide.

27. The imaging agent of any one of claims 20-26, wherein the metal oxidebinding ligand is selected from a benzenediol or a hydroxy carboxylic acid.

28. The imaging agent of claim 27, wherein the benzenediol has the formula:wherein A and B are independently selected from CH and N;R5is selected from the group consisting of-CH2CH2COOH, -CH2CH2NH2, -CH2CH2SH, -(CH2CH2O)dN3-, -(CH2CH2O dC=C- -(CH2CH2O)dSCN-, -d is an integer selected from 1-9; and R6is H or an electron withdrawing group.

29. The imaging agent of claim 28, wherein R6is an electron withdrawing group selected from the group consisting of-NCh, -SO3H, -SOiNa, and -CF3.

30. The imaging agent of claim 27, wherein the metal oxide-binding ligand is an ex-hydroxy carboxylic acid.

31. The imaging agent of claim 30, wherein the a-hydroxy carboxylic acid is selected from lactic acid or glycolic acid.

32. The imaging agent of claim 27, wherein the hydroxy carboxylic acid has the formula:wherein e is an integer selected from 1-4;R7is selected from H, -(CH2)fC(O)-, and -(CH2)rNH-; f is an integer selected from 1-5; or a pharmaceutically acceptable salt thereof.

33. The imaging agent of any one of claims 20-32, wherein the linker, if present, has a molecular weight between about 200 and about 800 amu.

34. The imaging agent of claim 33, wherein the linker has a molecular weight between about 250 to about 600 amu.

35. The imaging agent of claim 34, wherein the linker is independently selected from the group consisting of-NHCH(R)CO-, -NH(CH2)gC(O)-, -NHCH2CH2OCH2CH2CH2C(O)-, -NHCH2CH2OCH2CH2OCH2CH2C(O)-NHCH2C6H4CH2NH-, -NH(CH2)hNH-, -NHCH2OCH2NH-, -NHCH2CH2OCH2CH2NH-, -NHCH2CH2OCH2CH2OCH2CH2NH-, -N3(CH2CH2O)!C(O)-, -C=C(CH2CH2O)iC(O)-, -SCN(CH2CH2O)iC(O)-, -wherein g is an integer selected from 1-6; R is any amino acid side chain; and h is an integer selected from 2-6; and i is an integer selected from 2-1036. The imaging agent of any one of claims 20-35, wherein the fibrin-binding peptide is between 2 and 25 amino acid residues in length.

37. The imaging agent of claim 36, wherein the fibrin-binding peptide is between about 10 and 20 amino acid residues in length.

38. The imaging agent of claim 37, wherein the fibrin-binding peptide has the formula:wherein X1is selected from the group consisting of:X2is selected from the group consisting of:X3is selected from the group consisting of H and OH;X4is selected from the group consisting of H, I, Br, and Cl;X5is selected from the group consisting of H and CH2COOH;X6is selected from the group consisting of:X7is selected from the group consisting of CH2CH2C(O)NH2 and CH2CH(CH3)2.

39. A pharmaceutical composition comprising a compound of Formula I, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable excipient.

40. A pharmaceutical composition comprising a compound of Formula II, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable excipient.

41. A method for imaging collagen in a mammal, the method comprising: a) administering to the mammal an effective amount of an imaging agent of Formula I, or a pharmaceutically acceptable salt thereof; b) acquiring an image of the collagen of the mammal using a nuclear imaging technique; c) acquiring an anatomical image of the mammal using magnetic resonance imaging or computed tomography; and d) overlaying the images of steps b) and c) to localize the image of collagen within the anatomical image of the mammal.

42. The method of claim 41, wherein the nuclear imaging technique is selected from single photon emission computed tomography and positron emission tomography.

43. The method of claim 41, wherein the images of steps b) and c) are acquired simultaneously.

44. The method of claim 41, wherein the method further comprises administering to the mammal an effective amount of a second imaging agent, wherein the second imaging agent does not target collagen.

45. The method of claim 44, wherein the second imaging agent is an MRI imaging agent selected from the group consisting of: gadoteridol, gadopentetate, gadobenate, gadoxetic acid, gadodiamide, gadoversetamide, and gadofosveset; or a CTimaging agent selected from the group consisting of iopamidol, iohexol, ioxilan, iopromide, iodixanol, ioxaglate, metrizoate, and diatrizoate.

46. A method for imaging fibrin in a mammal, the method comprising: a) administering to the mammal an effective amount of an imaging agent of Formula II, or a pharmaceutically acceptable salt thereof; b) acquiring an image of the fibrin of the mammal using a nuclear imaging technique; c) acquiring an anatomical image of the mammal using magnetic resonance imaging or computed tomography; and d) overlaying the images of steps b) and c) to localize the image of fibrin within the anatomical image of the mammal.

47. The method of claim 46, wherein the nuclear imaging technique is selected from single photon emission computed tomography and positron emission tomography.

48. The method of claim 46, wherein the images of steps b) and c) are acquired simultaneously.

49. The method of claim 46, wherein the method further comprises administering to the mammal an effective amount of a second imaging agent, wherein the second imaging agent does not target fibrin.

50. The method of claim 49, wherein the second imaging agent is an MRI imaging agent selected from the group consisting of: gadoteridol, gadopentetate, gadobenate, gadoxetic acid, gadodiamide, gadoversetamide, and gadofosveset; or a CT imaging agent selected from the group consisting of iopamidol, iohexol, ioxilan, iopromide, iodixanol, ioxaglate, metrizoate, and diatrizoate.

Images