Compound and application thereof in contrast agent

Abstract

The invention belongs to the technical field of nuclear magnetic resonance contrast agents, and particularly relates to a contrast agent. According to the research, two sodium polyacrylate derivatives, namely PAA-EOB-GdA and PAA-EOB-GdB, are successfully synthesized. Wherein the chiral derivative PAA-EOB-GdA shows an abnormally high relaxation rate, and the r1 value reaches 37.87 mM <-1 >. S <-1 > and is further increased to 43.23 mM <-1 >. S <-1 > after acting with HSA. The reagent has a remarkable effect in blood vessel and tumor imaging, the enhancement value is better than that of Gd-DOTA, and the dosage of a contrast agent is expected to be reduced. Besides, the PAA-EOB-GdA still keeps good biocompatibility and cell viability under the high Gd (III) concentration, and due to the enhanced metal ion dissociation stability of the PAA-EOB-GdA, the free gadolinium ion release related toxicity risk can be remarkably reduced. Compared with PAA-EOB-GdB, PAA-EOB-GdA shows clearer imaging capability and longer in-vivo retention time due to enhanced hydrophobicity of a chiral group, and an imaging window is expanded. The polymer-based macromolecular Gd (III) contrast agent has a wide clinical application prospect in arterial vein mapping, delayed steady-state imaging and tissue blood volume and perfusion measurement.

Description

Technical Field

[0001] This application belongs to the technical field of magnetic resonance contrast agents, and particularly relates to a compound and its application in contrast agents. Background Art

[0002] Magnetic resonance imaging (MRI), as one of the most superior non-invasive diagnostic tools in modern biomedical imaging, has significant advantages in detecting soft tissue lesions due to its excellent soft tissue contrast ability. To improve the diagnostic ability of MRI, contrast agents (CAs) are widely used, which enhance the signal intensity by interacting with water protons. Among numerous contrast agents, gadolinium-based contrast agents (GBCAs) are particularly prominent, especially those derived from Gd-DOTA and Gd-DTPA complexes. These GBCAs are indispensable in various diagnostic applications due to their high magnetic moment and the property of prolonging T1 relaxation time.

[0003] Although gadolinium-based contrast agents (GBCAs) are widely used in magnetic resonance imaging (MRI), conventional GBCAs characterized by small molecular weights have some significant limitations. First, their in vivo clearance rate is fast, making it difficult to maintain a long imaging window, which is particularly obvious in applications such as angiography and long-term monitoring. Second, the relaxation rate of conventional GBCAs is relatively low (usually 3 - 5 mM -1 s -1 ), which means that in practical applications, continuous high-dose (0.1 mmol·kg -1 body weight) injection is required to achieve the desired imaging effect. However, high-dose injection not only exacerbates safety issues but also increases the risk of gadolinium-related toxicity. For example, in patients with renal insufficiency, conventional GBCAs may cause nephrogenic systemic fibrosis (NSF); in addition, the deposition of gadolinium in the brain tissue also brings potential long-term health risks. These problems pose great challenges to the clinical application of conventional GBCAs, and there is an urgent need to develop safer and more efficient alternative solutions.

[0004] To address the technical problems existing in the application of conventional gadolinium-based contrast agents (GBCAs), researchers have proposed innovative solutions. For example, integrating DOTA or DTPA ligands with dendrimers, polymeric compounds, or polypeptides to construct multinuclear lanthanide complexes. This strategy significantly prolongs the rotational correlation time by increasing the molecular size and rigidity of the complex, thereby greatly enhancing the relaxation rate. The higher relaxation rate enables these novel contrast agents to achieve imaging effects comparable to or even better than those of conventional GBCAs at lower doses, effectively reducing the toxicity risks associated with high-dose administration of traditional GBCAs, such as nephrogenic systemic fibrosis (NSF) and gadolinium deposition in the brain. In addition, due to their large molecular weight and specific structural design, multinuclear lanthanide complexes exhibit a longer blood circulation time in vivo. This property not only reduces the need for frequent dosing but also confers significant advantages in application scenarios requiring long-term monitoring, such as magnetic resonance angiography (MRA). Summary of the Invention

[0005] The purpose of this application is to provide a novel compound. The compound has a high relaxation rate, can be used to prepare contrast agents, and is applicable to vascular imaging and application scenarios requiring long-term monitoring. Specifically, it is achieved through the following technical solutions. A compound, characterized in that the structural formula of the compound is:

[0006] Or where m is selected from 12 to 14, n is selected from 3 to 4, and P is selected from 36 to 39.

[0007] Preferably, the particle size of the compound is 20 - 30 nm.

[0008] Preferably, the potential of the compound of formula (I) is -45.4 mV.

[0009] Preferably, the potential of the compound of formula (II) is -37.8 mV.

[0010] Preferably, at 1.4 T and 37 °C, the transverse relaxation time T1 of the compound of formula (I) is 37.87 ± 0.43 mM -1 ·s -1 , and the transverse relaxation time T2 is 50.0 ± 0.39 mM -1 s -1 .

[0011] Preferably, at 1.4 T and 37 °C, the transverse relaxation time T1 of the compound of formula (II) is 25.75 ± 0.28 mM -1 ·s -1 , and the transverse relaxation time T2 is 32.4 ± 0.3 mM -1 s-1 。

[0012] Preferably, the preparation process of the compound includes: the preparation of PAA-EOB-NH2, and the preparation route of PAA-EOB-NH2 is as follows:

[0013]

[0014] As a further preference, in the above preparation route of PAA-EOB-NH2, m is selected from 12 to 14, and o is selected from 39 to 44.

[0015] Preferably, the preparation process of the compound further includes: PAA-EOB-NH2 undergoes an amidation reaction with GdA to obtain the compound of formula (I); PAA-EOB-NH2 undergoes an amidation reaction with GdB to obtain the compound of formula (II).

[0016] This application also proposes the use of the above compound in a contrast agent.

[0017] Preferably, the contrast agent is used for magnetic resonance angiography or tumor imaging.

[0018] Compared with the prior art, this application has the following beneficial effects:

[0019] In this study, two polyacrylate derivatives PAA-EOB-GdA and PAA-EOB-GdB were successfully synthesized. Among them, the chiral derivative PAA-EOB-GdA exhibits an abnormally high relaxation rate, with an r1 value of 37.87 mM -1 ·s -1 (about 12 times that of the commonly used Gd-DOTA currently), and it further increases to 43.23 mM after acting with HSA -1 ·s -1 。This reagent has a significant effect in vascular and tumor imaging, has a better enhancement value compared to Gd-DOTA, and is expected to reduce the dosage of the contrast agent. In addition, PAA-EOB-GdA still maintains good biocompatibility and cell viability at high Gd(III) concentrations. Due to its enhanced metal ion dissociation stability, it can significantly reduce the toxicity risk related to the release of free gadolinium ions. Compared with PAA-EOB-GdB, PAA-EOB-GdA shows clearer imaging ability and longer in vivo retention time due to the enhanced hydrophobicity of the chiral group, expanding the imaging window. This polymer-based macromolecular Gd(III) contrast agent has broad clinical application prospects in arterial-venous mapping, delayed steady-state imaging, and tissue blood volume and perfusion measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] To clearly introduce the examples, the following will briefly introduce the drawings:

[0021] Figure 1 1H NMR spectrum of Compound 1;

[0022] Figure 2 1H NMR spectrum of Compound 2;

[0023] Figure 3 1H NMR spectrum of PAA;

[0024] Figure 4 1H NMR spectrum of PAA-EOB;

[0025] Figure 5 1H NMR spectrum of PAA-EOB-Boc;

[0026] Figure 6 1H NMR spectrum of PAA-EOB-NH2;

[0027] Figure 7 Synthesis route diagram of PAA-EOB-GdA and PAA-EOB-GdB in Example 1;

[0028] Figure 8 Hydrodynamic diameter diagram of PAA-EOB-GdA and PAA-EOB-GdB;

[0029] Figure 9 Electron microscopy diagram of PAA-EOB-GdA and PAA-EOB-GdB;

[0030] Figure 10 Zeta potential diagram of PAA-EOB-GdA and PAA-EOB-GdB;

[0031] Figure 11 T1 relaxation rate of the sample in aqueous solution in the absence of HSA;

[0032] Figure 12 T1 relaxation rate of the sample in aqueous solution in the presence of HSA;

[0033] Figure 13 T2 relaxation rate of the sample in aqueous solution in the absence of HSA;

[0034] Figure 14 T2 relaxation rate of the sample in aqueous solution in the presence of HSA;

[0035] Figure 15 Cytotoxicity test diagram of PAA-EOB-GdA;

[0036] Figure 16 Cytotoxicity test diagram of PAA-EOB-GdB;

[0037] Figure 17 These are magnetic resonance angiography images of PAA-EOB-GdA and PAA-EOB-GdB;

[0038] Figure 18 These are magnetic resonance imaging images of PAA-EOB-GdA;

[0039] Figure 19 These are magnetic resonance imaging images of Gd-DOTA;

[0040] Figure 20 These are graphs of the changes in the normalized signal-to-noise ratio (nSNR) values within the tumor;

[0041] Figure 21 These are T1-weighted axial MR images of subcutaneous tumor-bearing mice at different time points after injection of PAA-EOB-GdA;

[0042] Figure 22 These are graphs of the changes in the normalized signal-to-noise ratio (nSNR) values of the liver of mice injected with PAA-EOB-GdA;

[0043] Figure 23 These are graphs of the changes in the normalized signal-to-noise ratio (nSNR) values of the kidneys of mice injected with PAA-EOB-GdA;

[0044] Figure 24 These are the biodistributions of Gd in BALB / c mice after injection of PAA-EOB-GdA;

[0045] Figure 25 These are the biodistributions of Gd in BALB / c mice after injection of PAA-EOB-GdB;

[0046] Figure 26 These are the biodistributions of Gd in BALB / c mice after injection of Gd-DOTA;

[0047] Figure 27 These are the concentrations of the contrast agent in the blood at 5 min and 24 h;

[0048] Figure 28 These are the comparisons of the total uptake of the contrast agent in the liver and kidneys at 5 min and 24 h after injection; ns, p>0.05 *p<0.05 **p<0.01 ***p<0.001 ****p<0.0001;

[0049] Figure 29 These are H&E stained sections of mouse liver and kidney tissues;

[0050] Figure 30 These are graphs of the blood biochemical indices of normal BALB / c mice. Detailed implementation manners

[0051] The present application will be further described by way of specific embodiments below. Those of ordinary skill in the art will be able to implement the present application based on these descriptions. In addition, the embodiments of the present application involved in the following description are generally only a part of the embodiments of the present application, rather than all of the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts should fall within the scope of protection of the present application.

[0052] The material information involved in the following examples is as follows: Gadolinium(III) chloride (GdCl3·6H2O, 99.99%-Gd) (REO), 4-methoxyaniline (purity: 99%), N-Boc-ethylenediamine (purity: 96%), 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (purity: 96%) and 2-(2-(2-(tert-butoxycarbonylamino)ethoxy)ethoxy)acetic acid (purity: 97%) were purchased from Energy Chemical. Sodium polyacrylate (average molecular weight measured by GPC is 5100, powder) and human serum albumin (HSA, lyophilized powder, purity ≥96%) were purchased from Sigma Aldrich. DMEM, RPMI1640, trypsin (containing EDTA), penicillin-streptomycin were purchased from Gibco. Dialysis membrane (standard, RC, 3.5 kDa) was purchased from Beyotime. All animals were purchased from Zhejiang Laboratory Animal Center.

[0053] Example 1 Synthesis of PAA-EOB-GdA and PAA-EOB-GdB

[0054] The present example discloses a preparation method of a contrast agent, which specifically includes the following steps:

[0055] Synthesis of Compound 1. Under N2, 2-[2-(tert-butoxycarbonylamino)ethoxy]ethoxyacetic acid (3.0 g, 11.39 mmol, 1 eq) and p-ethoxyaniline (1.72 g, 12.53 mmol, 1.1 eq) were dissolved in 30 mL of methanol, and then DMTMM (3.69 g, 12.53 mmol, 1.1 eq) was added. After stirring at room temperature for 2 h, the solvent was removed by rotary evaporation. The solid was dissolved in EA (there was a white insoluble matter), washed with saturated NaHCO3 solution (the insoluble matter dissolved), and bubbles were generated. The organic phase was dried and purified by column chromatography (PE∶EA = 2∶1) to obtain 3.0 g (yield ~69%) of a yellow oily compound 1. The nuclear magnetic resonance hydrogen spectrum was used to determine its structural formula, as shown in Figure 1 .

[0056] Synthesis of Compound 2. Under N2, in an ice bath, Compound 1 was dissolved in 3 mL of TFA and stirred for 1 h. The solvent was removed by rotary evaporation to obtain 2.7 g of Compound 2 as a yellow oil. The structural formula was determined by 1H NMR spectrum, see Figure 2 .

[0057] Synthesis of PAA-EOB. Under N2, sodium polyacrylate PAA (3.33 g, 35.44 mmol, 1 eq) was dissolved in 20 mL of H2O, and Compound 2 (2.0 g, 7.088 mmol, 0.2 eq) was dissolved in 10 mL of methanol. Finally, a methanol solution (10 mL) of DMTMM (11.49 g, 38.98 mmol, 1.1 eq) was added and stirred for 12 h. The reaction was stopped, and methanol was removed by rotary evaporation to obtain a liquid containing insoluble matter. Then, the pH was adjusted to 8 with 1 M NaOH and dialyzed (MWCO: 3.5 kDa) for 48 h (H2O, methanol) to obtain 2.6 g of white solid PAA-EOB. The structural formula was determined by 1H NMR spectrum, see Figure 4 .

[0058] Synthesis of PAA-EOB-Boc. Under N2, PAA-EOB (2.6 g, 0.35 mmol, 1 eq), N-tert-butoxycarbonyl-1,2-ethylenediamine (2.41 g, 15.05 mmol, 43 eq), and DMTMM (4.44 g, 15.05 mmol, 43 eq) were dissolved in 30 mL of methanol and stirred for about 4 h. Most of the solvent was removed by rotary evaporation, and dialysis (MWCO: 3.5 kDa) was carried out for 48 h (H2O, methanol) to obtain 5 g of white solid PAA-EOB-Boc. The structural formula was determined by 1H NMR spectrum, see Figure 5 .

[0059] Synthesis of PAA-EOB-NH2. Under N2, PAA-EOB-Boc was dissolved in a mixed solution (TFA:DCM = 1:1, 20 mL) and stirred for 2 h. Then, the reaction was stopped, the solvent was removed by rotary evaporation, and dialysis (MWCO: 3.5 kDa) was carried out for 48 h (H2O, methanol) to obtain 2.5 g of PAA-EOB-NH2. The structural formula was determined by 1H NMR spectrum, see Figure 6 .

[0060] Synthesis of PAA-EOB-GdA. Under N2, PAA-EOB-NH2 (0.04 g) was dissolved in 5 mL of methanol solution, GdA (0.208 g) was dissolved in 10 mL of H2O, and DMTMM (0.11 g) was dissolved in 5 mL of methanol. Then they were mixed and stirred overnight at room temperature. After removing most of the methanol solution by rotary evaporation, it was purified by dialysis (MWCO: 3.5 kDa) for 48 h (H2O, methanol) to obtain the nanoparticles PAA-EOB-GdA.

[0061] Synthesis of PAA-EOB-GdB. Under N2, PAA-EOB-NH2 (0.04 g) was dissolved in 5 mL of methanol solution, GdB (0.186 g) was dissolved in 10 mL of H2O, and DMTMM (0.11 g) was dissolved in 5 mL of methanol. Then they were mixed and stirred overnight at room temperature. After removing most of the methanol solution by rotary evaporation, it was purified by dialysis (MWCO: 3.5 kDa) for 48 h (H2O, methanol) to obtain the nanoparticles PAA-EOB-GdB.

[0062] Example 2, In Vitro Characterization of PAA-EOB-GdA and PAA-EOB-GdB

[0063] To analyze the properties of the PAA-EOB-GdA and PAA-EOB-GdB polymers prepared in Example 1, dynamic light scattering (DLS) was used in this example to evaluate the hydrated particle size distribution of the polymers. See Figure 8 , PAA-EOB-GdA and PAA-EOB-GdB showed similar particle sizes, approximately 20 - 30 nm. Further, transmission electron microscopy (TEM) was used to test the morphology and particle size of the polymers. As Figure 9 shown, both PAA-EOB-GdA and PAA-EOB-GdB exhibited a uniform spherical morphology with a relatively uniform particle size distribution. The particle size observed by TEM was consistent with the results of DLS analysis, confirming that these polymers have a nanoscale size structure.

[0064] In this example, dynamic light scattering (DLS) was also used to measure the ζ potential of the polymers to evaluate the surface charge changes at each modification stage. As Figure 10 shown, both PAA-EOB-GdA and PAA-EOB-GdB presented negative potentials, indicating that the surface was negatively charged due to the presence of Gd(III) complexes. The absolute values of the ζ potential of both particles were greater than 30 mV (the particles repelled each other), indicating that the particles were stable under the test conditions. The morphology and consistent size of these nanoparticles indicated successful modification of the polymers and functionalization with Gd(III) complexes. In addition, it should be noted that although this example was carried out in accordance with the attachedFigure 7 The synthetic route diagrams were used to prepare PAA-EOB-GdA and PAA-EOB-GdB. However, NMR and ICP-MS characterizations revealed that in the compounds, m was selected from 12 to 14, n was selected from 3 to 4, and P was selected from 36 to 39.

[0065] Example 3: Determination of the longitudinal (T1) and transverse (T2) relaxation times of PAA-EOB-GdA and PAA-EOB-GdB

[0066] The two samples from Example 1 and Gd-DTPA were respectively dissolved in deionized water and a series of solutions with different Gd 3+ concentrations were prepared. Then, the relaxation times of these solutions were measured in NMR tubes. Further, to observe the change in relaxation rate to study the interaction between the samples and proteins, 4.5% (w / v) human serum albumin HSA was added to the NMR tubes. After incubation at 37 °C for 30 min, the relaxation times were re-measured and the relaxation rates were calculated.

[0067] The method for measuring the relaxation time was to measure the T1 and T2 relaxation times of the samples before and after interaction with HSA using a 1.4T MR magnet (60 MHz, Huantong NMR, China). The pulse durations of 90° and 180° were 40 μS and 80 μS respectively. The duration of 10 inversion recovery experiments was 0.05×T1 to 5×T1. The repetition time for T1 measurement was 10.0 s. For T2, the Carr-Purcell-Meiboom-Gill pulse sequence was used, the echo spacing was 3.0 mS, the repetition time was 10.0 s, and the number of accumulations was 5 times. The relaxation rates r1 and r2 were determined by calculating the slope of the linear relationship between 1 / T1 or 1 / T2 and the Gd concentration (mM).

[0068] Please refer to Figure 11 , in the absence of HSA, PAA-EOB-GdA exhibited the highest T1 relaxation rate, which was 37.87 ± 0.43 mM -1 ·s -1 , followed by PAA-EOB-GdB, which was 25.75 ± 0.28 mM -1 ·s -1 . Both of these values were significantly higher than that of Gd-DOTA (3.19 ± 0.029 mM -1 s -1 ). This enhancement was attributed to the improvement of the rotational correlation time, which was due to the polymer effect, especially for PAA-EOB-GdA, the additional chiral ethyl group on the DOTA ring. Figure 12 Among them, in the presence of HSA, the relaxation rate of PAA-EOB-GdA further increased to 43.23 ± 0.57 mM -1 s -1, while the relaxation rate of PAA-EOB-GdB increased to 28.18 ± 0.54 mM - 1 s -1 . The increase in the relaxation rate is mainly due to the binding of HSA, which restricts molecular motion. In contrast, the relaxation rate of Gd-DOTA only slightly increased to 3.76 ± 0.06 mM -1 s -1 .

[0069] Figure 13 and 14 , in the transverse relaxation time (T2), PAA-EOB-GdA also showed the highest relaxation rate. After incubation with 4.5% HSA, the relaxation rate of PAA-EOB-GdA increased from 50.0 ± 0.39 mM -1 s -1 to 58.87 ± 0.78 mM -1 s -1 . Similarly, the relaxation rate of PAA-EOB-GdB increased from 32.4 ± 0.3 mM -1 s -1 to 34.49 ± 0.79 mM -1 s -1 . Both molecules showed much higher transverse relaxation rates than Gd-DOTA: the relaxation rate of Gd-DOTA in 4.5% HSA was 3.95 ± 0.09 mM -1 s -1 .

[0070] Example 4. Cytotoxicity Test of PAA-EOB-GdA and PAA-EOB-GdB

[0071] The CCK-8 kit was selected to evaluate the toxicity of the contrast agent prepared in Example 1 at the cellular level. Since the contrast agent is mainly metabolized through the liver and kidney pathways. Human normal hepatocytes (LX-2) and human normal renal cells (293T) were selected for testing, and hepatocarcinoma cells (HepG2) and glioma cells (U87MG) were also selected. See Figure 15 and 16, The results showed that both PAA-EOB-GdA and PAA-EOB-GdB exhibited very low cytotoxicity within the Gd(III) concentration range of 0 - 0.5 mM. Specifically, for PAA-EOB-GdA, a slight inhibitory effect on the activity of HepG2 cells was observed at concentrations above 0.2 mM. Similar trends of slightly reduced survival rates were shown in LX-2 and 293T cells, while the survival rate of U87MG cells remained stable. However, even at the highest concentration tested (c(Gd) = 0.5 mM), the cell survival rates of all four cell lines remained above 90%. These results demonstrated that both polymers had good biocompatibility, providing a strong theoretical basis for their further evaluation in vivo.

[0072] Example 5, Magnetic Resonance Angiography of PAA-EOB-GdA and PAA-EOB-GdB

[0073] In this example, PAA-EOB-GdA and PAA-EOB-GdB were applied to angiography of SD rats. PAA-EOB-GdA (0.05 mmol kg -1 ), PAA-EOB-GdB (0.05 mmol kg -1 ), and Gd-DOTA (0.1 mmol kg -1 ) were injected into the tail vein of rats, and MRA images were acquired within 1 - 30 min. As Figure 17 shown, for the rats injected with PAA-EOB-GdA, the arterial vessels, venous vessels, cerebral vessels, and heart were clearly visible. Although the signal intensity showed signs of weakening at 30 min, the main vessel contours were still very clear. The vascular signals of the rats injected with PAA-EOB-GdB were also enhanced, with the clearest images 1 min after administration, and then the signals significantly weakened and had been largely metabolized at 30 min, and obvious bright signals were visible in the bladder. Given the low relaxation rate of Gd-DOTA, we increased the administration dose to 0.1 mmol kg -1 , but even so, only a vaguely visible vascular margin could be observed at 1 min, and by 5 min, the clear contours could no longer be distinguished. Compared with the rats injected with PAA-EOB-GdB, the slower metabolism observed in the rats injected with PAA-EOB-GdA was mainly attributed to the poor hydrophilicity of the chiral Gd(III) molecules. This property prolonged the circulation time of the complex in the bloodstream, which was beneficial for extending the time window of angiography.

[0074] Example 6, Magnetic Resonance Imaging of PAA-EOB-GdA

[0075] In this example, PAA-EOB-GdA was applied to magnetic resonance imaging in BALB / c mice. AsFigure 18 As shown, after tail vein injection of PAA-EOB-GdA (0.1 mmol·kg -1 ), an immediate enhancement of signal intensity was observed at the tumor margin. It is worth noting that Figure 20 in, from 2 to 32 min after injection, the normalized signal-to-noise ratio (nSNR) value remained stable, about 2, always maintaining a high enhancement value, indicating that PAA-EOB-GdA could be retained at the tumor margin for a long time, thus providing the possibility for long-term diagnostic evaluation. In contrast, Figure 19 in the control group Gd-DOTA did not show obvious signal enhancement after injection, which was also illustrated by the corresponding nSNR values. To investigate the in vivo metabolism of the contrast agent in depth, normal BALB / c mice were injected with 0.1 mmol kg -1 of PAA-EOB-GdA via the tail vein, with Gd-DOTA as the control. MR images were acquired at time intervals from 2 to 32 min after injection. The research results showed that PAA-EOB-GdA was mainly metabolized through the kidneys. Specifically, see Figure 21 , at 32 min after injection, the gallbladder showed enhanced signal, and the renal pelvis changed from dark signal to bright signal within the first 2 min after injection. In contrast, Gd-DOTA with small molecule characteristics was quickly eliminated from the body. In addition, Figure 22 and 23 , nSNR indicated that this polymeric contrast agent could be retained in the body for a longer time and showed higher signal values compared with Gd-DOTA. The extended imaging window provided a greater diagnostic space.

[0076] Example 7. Biodistribution of PAA-EOB-GdA and PAA-EOB-GdB in Mice

[0077] In this example, the clinically used contrast agent Gd-DOTA was used as the control to study the biodistribution of PAA-EOB-GdA and PAA-EOB-GdB in mice. These reagents were injected into the tail veins of BALB / c mice at a dose of 0.1 mmol kg -1 , and the Gd concentration in various tissues was quantified by inductively coupled plasma mass spectrometry (ICP-MS) 5 min and 24 h after injection. The tissues tested included liver, kidney, heart, spleen, lung, brain, intestine, muscle and blood. The biodistribution profiles of each drug at different times are shown in Figures 24 - 26As shown, after tail vein injection, Gd was mainly detected in the kidneys and blood within 5 min after administration. As the main metabolic organ, the Gd content in the kidneys after injection of PAA-EOB-GdA, PAA-EOB-GdB, and Gd-DOTA was 252.66 μg / g tissue, 148.79 μg / g tissue, and 115.68 μg / g tissue, respectively. The small molecule Gd-DOTA was almost completely cleared through urine or feces after 24 h. The macromolecular complexes of the present application had a relatively long retention time in vivo. And more than 60% of the metal metabolism occurred after 24 h. It should be noted that the contrast agents of the present application showed a relatively high concentration in the blood. Specifically, please refer to Figure 27 , the Gd content in the blood of mice injected with PAA-EOB-GdA and PAA-EOB-GdB was 81.90 μg / g tissue and 55.18 μg / g tissue, respectively, at 5 min, while that of Gd-DOTA was 28.2 μg / g tissue, which was increased by about 2 times and 1 time, respectively. In addition, please refer to Figure 28 , compared with Gd-DOTA, PAA-EOB-GdA showed better liver uptake. This result provides valuable inspiration for the development of innovative long-acting and targeted contrast agents.

[0078] Example 8. Toxicity Experiment

[0079] To evaluate the potential toxicity of the contrast agents of the present application in vivo, PBS and Gd-DOTA were used as negative and positive controls, respectively, to evaluate the toxicity of the complexes. BALB / c mice (n = 3) were randomly assigned to the acute or subacute group. In the acute group, the drug was injected once, and the mice were anesthetized 24 h after injection. After euthanasia by decapitation, blood was collected from the orbital cavity for serum chemical analysis. Then the main organs were taken and stained with hematoxylin and eosin (H&E) for histological examination. In the subacute group, the mice received four injections in total, once a week for one month. 24 h after the last administration, they were anesthetized and euthanized, and blood and main organs were collected for analysis. As Figure 29 shown, histological examinations of liver sections in both groups showed a normal hepatic lobule structure centered on the central vein, without fibrosis in the hepatic sinus or aggregation of hepatocytes. The hepatocyte morphology was normal, the cell nuclei were round and located in the center, and some binucleated hepatocytes were observed. There was no sign of cholestasis in the interlobular bile ducts. The renal tissue sections of both groups showed normal glomerular size and morphology, with clear boundaries and no infiltration of inflammatory cells in the renal interstitium.

[0080] Please refer to Figure 30, biochemical analysis of liver function serum markers including alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and albumin (ALB) showed that there were no significant differences between the test group and the control group in acute or subacute studies, indicating that the contrast agent did not cause liver injury. Similarly, compared with the control group, the serum urea nitrogen (BUN) and creatinine (CR) levels in the experimental group indicated no kidney injury. Creatine kinase (CK) and lactate dehydrogenase (LDH) levels are used to diagnose bone and heart diseases as well as liver diseases, and no significant changes in CK or LDH levels were observed in the acute or subacute experimental groups, indicating that the contrast agent does not cause myocardial or skeletal muscle injury. In addition, normal levels of liver and kidney function markers further confirmed the integrity of these organs. Taken together, these findings support the good safety of the synthesized contrast agent in vivo.

Claims

1. A compound, characterized in that, The structural formula of the compound is as follows: or wherein m is selected from 12 to 14, n is selected from 3 to 4, and P is selected from 36 to 39.

2. A compound according to claim 1, wherein The particle size of the compound is 20 to 30 nm.

3. A compound according to claim 1, wherein The potential of the compound of formula (I) is -45.4 mV.

4. A compound according to claim 1, characterized in that, The potential of the compound of formula (II) is -37.8 mV.

5. A compound according to claim 1, wherein At 1.4 T and 37 °C, the transverse relaxation time T1 of the compound of formula (I) is 37.87 ± 0.43 mM -1 ·s -1 , and the transverse relaxation time T2 is 50.0 ± 0.39 mM -1 s -1 .

6. A compound according to claim 1, wherein At 1.4 T and 37 °C, the transverse relaxation time T1 of the compound of formula (II) is 25.75 ± 0.28 mM -1 ·s -1 , and the transverse relaxation time T2 is 32.4 ± 0.3 mM -1 s -1 .

7. A compound according to claim 1, characterized in that, The preparation process of the compound includes: the preparation of PAA-EOB-NH2, and the preparation route of the PAA-EOB-NH2 is shown as follows: wherein, m is selected from 12 to 14, and o is selected from 39 to 44.

8. A compound according to claim 7, wherein The preparation process of the compound further includes: PAA-EOB-NH2 undergoes an amidation reaction with GdA to obtain the compound of formula (I); PAA-EOB-NH2 undergoes an amidation reaction with GdB to obtain the compound of formula (II).

9. Use of the compound according to any one of claims 1 to 8 in a contrast agent.

10. The application according to claim 9, wherein The contrast agent is used for magnetic resonance angiography or tumor imaging.

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