TUMOR STROMA IMAGING AGENT AND PREPARATION METHOD THEREOF

Abstract

A tumor stroma imaging agent with a chemical structural formula (I):

##STR00001##

is provided, where R is hydrogen or fluorine. Compared with the prior art, the tumor stroma imaging agent exhibits significant affinity for fibroblast activation protein (FAP), high uptake for a malignant tumor with high FAP expression in a tumor stroma, and high sensitivity and specificity for the diagnosis of a malignant tumor, and is not prone to false positives. Therefore, the tumor stroma imaging agent can be effectively and safely used for the diagnosis and treatment of various malignant tumors with a prolonged half-life and an extended window period, which is conducive to clinical application.

Claims

1. A tumor stroma imaging agent with a chemical structural formula as follows: ##STR00015## wherein R is hydrogen or fluorine.

2. The tumor stroma imaging agent according to claim 1, wherein the tumor stroma imaging agent has a chemical structural formula as follows: ##STR00016##

3. The tumor stroma imaging agent according to claim 1, wherein the tumor stroma imaging agent has a chemical structural formula selected from the group consisting of ##STR00017##

4. A preparation method of the tumor stroma imaging agent according to claim 1, comprising: mixing an .sup.18F.sup.−-containing acetic acid-sodium acetate buffer with a labeling precursor, a solvent, and an AlCl.sub.3 aqueous solution to allow a labeling reaction; and subjecting a product of the labeling reaction to a post-treatment, wherein the labeling precursor has a chemical structural formula as follows: ##STR00018## or the labeling precursor is a salt of ##STR00019##

5. The preparation method according to claim 4, wherein the .sup.18F.sup.−-containing acetic acid-sodium acetate buffer has an activity of 110 mCi to 135 mCi.

6. The preparation method according to claim 4, wherein the .sup.18F.sup.−-containing acetic acid-sodium acetate buffer has a pH of 4.2.

7. The preparation method according to claim 4, wherein the labeling reaction is conducted at 80° C. to 120° C. for 5 min to 10 min.

8. The preparation method according to claim 5, wherein a volume-mass ratio of the .sup.18F.sup.−-containing acetic acid-sodium acetate buffer to the labeling precursor is 1:(0.9-1.6) mL/mg; the .sup.18F.sup.−F-containing acetic acid-sodium acetate buffer, the solvent, and the AlCl.sub.3 aqueous solution are in a volume ratio of (45-30):75:5; the AlCl.sub.3 aqueous solution has a concentration of 0.4 M; and the solvent is selected from the group consisting of acetonitrile, N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), and polyethylene glycol (PEG).

9. The preparation method according to claim 4, wherein the post-treatment comprises: adding water to quench the labeling reaction and allowing a resulting reaction solution to pass through an Al.sub.2O.sub.3 column to obtain a filtrate; and allowing the filtrate to pass through a C.sub.18-Plus column, rinsing the C.sub.18-Plus column with ethanol and normal saline (NS) successively, and allowing an eluate to pass through a sterile filtration membrane to obtain an injection of the tumor stroma imaging agent.

10. The preparation method according to claim 9, wherein the injection has an activity of 50.3 mCi to 72.3 mCi.

11. The preparation method according to claim 4, wherein the labeling precursor has a chemical structural formula as follows: ##STR00020## or the labeling precursor is a salt of ##STR00021##

12. The preparation method according to claim 4, wherein the tumor stroma imaging agent has a chemical structural formula as follows: ##STR00022##

13. The preparation method according to claim 4, wherein the tumor stroma imaging agent has a chemical structural formula selected from the group consisting of ##STR00023##

14. The preparation method according to claim 5, wherein the .sup.18F.sup.−-containing acetic acid-sodium acetate buffer has a pH of 4.2.

15. The preparation method according to claim 5, wherein the labeling reaction is conducted at 80° C. to 120° C. for 5 min to 10 min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1A shows a high-performance liquid chromatography (HPLC) spectrum of (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 prepared in Example 1.

[0035] FIG. 1B shows an HPLC spectrum of (S)—AlF-NOTA-Bn-FAPI-4 control prepared in Example 11.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The present disclosure is further described in detail below in conjunction with specific examples and by referring to data. It should be understood that the examples are provided to merely illustrate the present disclosure and do not limit the scope of the present disclosure in any way.

Example 1

[0037] Preparation of (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4

##STR00008##

[0038] An .sup.18O(p, n).sup.18F reaction was conducted with a proton cyclotron to produce .sup.18F.sup.− with an activity of 150 mCi. The generated .sup.18F.sup.− was transported through a pipe to an anion exchange column QMA (QMA was a refillable column) for capture. After the capture was completed, the QMA was blow-dried with N.sub.2 and then rinsed with 0.45 mL of an acetic acid-sodium acetate buffer at a pH of 4.2 for elution to obtain an .sup.18F-containing buffer with an activity of 135 mCi.

[0039] 469.7 μg of a labeling precursor (S)-NOTA-Bn-FAPI-4, 0.75 mL of acetonitrile, and 0.05 mL of a 0.4 M AlCl.sub.3 aqueous solution were added to 0.45 mL of the .sup.18F-containing buffer to allow a reaction at 80° C. for 10 min, and 5 mL of deionized water was added to quench the reaction. The resulting reaction solution was allowed to pass through an Al.sub.2O.sub.3 column to obtain a filtrate.

[0040] The filtrate was allowed to pass through a C.sub.18-Plus column for enrichment, and the column was rinsed with 2 mL of ethanol and 10 mL of NS successively. An eluate was allowed to pass through a sterile filtration membrane to obtain an injection of a tumor stroma diagnostic imaging agent (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 with an activity of 72.3 mCi and a labeling rate of 48.2%.

[0041] The retention time and radiochemical purity of (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 were tested by HPLC, and test results are shown in FIGS. 1A-1B. The peak time of (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 is 16.112 min, which is consistent with a retention time of the (S)—AlF-NOTA-Bn-FAPI-4 control, and the radiochemical purity is still as high as 99% after labeling.

Example 2

[0042] An .sup.18O(p, n).sup.18F reaction was conducted with a proton cyclotron to produce .sup.18F.sup.− with an activity of 150 mCi. The generated .sup.18F.sup.− was transported through a pipe to an anion exchange column QMA (QMA was a refillable column) for capture. After the capture was completed, the QMA was blow-dried with N.sub.2 and rinsed with 0.3 mL of an acetic acid-sodium acetate buffer at a pH of 4.2 for elution to obtain an .sup.18F.sup.−-containing buffer with an activity of 125 mCi.

[0043] 469.7 μg of a labeling precursor (S)-NOTA-Bn-FAPI-4, 0.75 mL of acetonitrile, and 0.05 mL of a 0.4 M AlCl.sub.3 aqueous solution were added to 0.3 mL of the .sup.18F.sup.−-containing buffer to allow a reaction at 80° C. for 10 min, and 5 mL of deionized water was added to quench the reaction. The resulting reaction solution was allowed to pass through an Al.sub.2O.sub.3 column to obtain a filtrate.

[0044] The filtrate was allowed to pass through a C.sub.18-Plus column for enrichment, and the column was rinsed with 2 mL of ethanol and 10 mL of NS successively. An eluate was allowed to pass through a sterile filtration membrane to obtain an injection of a tumor stroma diagnostic imaging agent (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 with an activity of 67.5 mCi.

Example 3

[0045] An .sup.18O(p, n).sup.18F reaction was conducted with a proton cyclotron to produce .sup.18F.sup.− with an activity of 160 mCi. The generated .sup.18F.sup.− was transported through a pipe to an anion exchange column QMA (QMA was a refillable column) for capture. After the capture was completed, the QMA was blow-dried with N.sub.2 and rinsed with 0.45 mL of an acetic acid-sodium acetate buffer at a pH of 4.2 for elution to obtain an .sup.18F.sup.−-containing buffer with an activity of 135 mCi.

[0046] 469.7 μg of a labeling precursor (S)-NOTA-Bn-FAPI-4, 0.75 mL of acetonitrile, and 0.05 mL of a 0.4 M AlCl.sub.3 aqueous solution were added to 0.45 mL of the .sup.18F.sup.−-containing buffer to allow a reaction at 80° C. for 10 min, and 5 mL of deionized water was added to quench the reaction. The resulting reaction solution was allowed to pass through an Al.sub.2O.sub.3 column to obtain a filtrate.

[0047] The filtrate was allowed to pass through a Cis-Plus column for enrichment, and the column was rinsed with 2 mL of ethanol and 10 mL of NS successively. An eluate was allowed to pass through a sterile filtration membrane to obtain an injection of a tumor stroma diagnostic imaging agent (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 with an activity of 72 mCi.

Example 4

[0048] An .sup.18O(p, n).sup.18F reaction was conducted with a proton cyclotron to produce .sup.18F.sup.− with an activity of 150 mCi. The generated .sup.18F.sup.− was transported through a pipe to an anion exchange column QMA (QMA was a refillable column) for capture. After the capture was completed, the QMA was blow-dried with N.sub.2 and rinsed with 0.45 mL of an acetic acid-sodium acetate buffer at a pH of 4.2 for elution to obtain an .sup.18F.sup.−-containing buffer with an activity of 135 mCi.

[0049] 469.7 μg of a labeling precursor (S)-NOTA-Bn-FAPI-4, 0.75 mL of acetonitrile, and 0.05 mL of a 0.4 M AlCl.sub.3 aqueous solution were added to 0.45 mL of the .sup.18F.sup.−-containing buffer to allow a reaction at 100° C. for 10 min, and 5 mL of deionized water was added to quench the reaction. The resulting reaction solution was allowed to pass through an Al.sub.2O.sub.3 column to obtain a filtrate.

[0050] The filtrate was allowed to pass through a Cis-Plus column for enrichment, and the column was rinsed with 2 mL of ethanol and 10 mL of NS successively. An eluate was allowed to pass through a sterile filtration membrane to obtain an injection of a tumor stroma diagnostic imaging agent (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 with an activity of 70 mCi.

Example 5

[0051] An .sup.18O(p, n).sup.18F reaction was conducted with a proton cyclotron to produce .sup.18F.sup.− with an activity of 120 mCi. The generated .sup.18F.sup.− was transported through a pipe to an anion exchange column QMA (QMA was a refillable column) for capture. After the capture was completed, the QMA was blow-dried with N.sub.2 and rinsed with 0.45 mL of an acetic acid-sodium acetate buffer at a pH of 4.2 for elution to obtain an .sup.18F.sup.−-containing buffer with an activity of 110 mCi.

[0052] 469.7 μg of a labeling precursor (S)-NOTA-Bn-FAPI-4, 0.75 mL of acetonitrile, and 0.05 mL of a 0.4 M AlCl.sub.3 aqueous solution were added to 0.45 mL of the .sup.18F.sup.−-containing buffer to allow a reaction at 80° C. for 10 min, and 5 mL of deionized water was added to quench the reaction. The resulting reaction solution was allowed to pass through an Al.sub.2O.sub.3 column to obtain a filtrate.

[0053] The filtrate was allowed to pass through a C.sub.18-Plus column for enrichment, and the column was rinsed with 2 mL of ethanol and 10 mL of NS successively. An eluate was allowed to pass through a sterile filtration membrane to obtain an injection of a tumor stroma diagnostic imaging agent (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 with an activity of 53.9 mCi.

Example 6

[0054] Preparation of (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-2

##STR00009##

[0055] An .sup.18O(p, n).sup.18F reaction was conducted with a proton cyclotron to produce .sup.18F.sup.− with an activity of 120 mCi. The generated .sup.18F.sup.− was transported through a pipe to an anion exchange column QMA (QMA was a refillable column) for capture. After the capture was complete, the QMA was blow-dried with N.sub.2 and rinsed with 0.45 mL of an acetic acid-sodium acetate buffer at a pH of 4.2 for elution to obtain an .sup.18F.sup.−-containing buffer with an activity of 110 mCi.

[0056] 433.7 μg of a labeling precursor (S)-NOTA-Bn-FAPI-2, 0.75 mL of DMSO, and 0.05 mL of a 0.4 M AlCl.sub.3 aqueous solution were added to 0.45 mL of the .sup.18F.sup.−-containing buffer to allow a reaction at 100° C. for 8 min, and 5 mL of deionized water was added to quench the reaction. The resulting reaction solution was allowed to pass through an Al.sub.2O.sub.3 column to obtain a filtrate.

[0057] The filtrate was allowed to pass through a C.sub.18-Plus column for enrichment, and the column was rinsed with 2 mL of ethanol and 10 mL of NS successively. An eluate was allowed to pass through a sterile filtration membrane to obtain an injection of a tumor stroma diagnostic imaging agent (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-2 with an activity of 50.5 mCi.

Example 7

[0058] Preparation of [.sup.18F]—AlF-NOTA-Bn-FAPI-2

##STR00010##

[0059] An .sup.18O(p, n).sup.18F reaction was conducted with a proton cyclotron to produce .sup.18F.sup.− with an activity of 120 mCi. The generated .sup.18F.sup.− was transported through a pipe to an anion exchange column QMA (QMA was a refillable column) for capture, and after the capture was completed, the QMA was blow-dried with N.sub.2 and then rinsed with 0.45 mL of an acetic acid-sodium acetate buffer at a pH of 4.2 for elution to obtain an .sup.18F-containing buffer with an activity of 110 mCi.

[0060] 469.7 μg of a labeling precursor NOTA-Bn-FAPI-2, 0.75 mL of DMF, and 0.05 mL of a 0.4 M AlCl.sub.3 aqueous solution were added to 0.45 mL of the .sup.18F.sup.−-containing buffer to allow a reaction at 110° C. for 8 min, then 5 mL of deionized water was added to quench the reaction, and a resulting reaction solution was allowed to pass through an Al.sub.2O.sub.3 column to obtain a filtrate.

[0061] The filtrate was allowed to pass through a C.sub.18-Plus column for enrichment, then the column was rinsed with 2 mL of ethanol and 10 mL of NS successively, and an eluate was allowed to pass through a sterile filtration membrane to obtain an injection of a tumor stroma diagnostic imaging agent [.sup.18F]—AlF-NOTA-Bn-FAPI-2 with an activity of 50.3 mCi.

Example 8

[0062] Preparation of [.sup.18F]—AlF-NOTA-Bn-FAPI-4

##STR00011##

[0063] An .sup.18O(p, n).sup.18F reaction was conducted with a proton cyclotron to produce .sup.18F.sup.− with an activity of 120 mCi, the generated .sup.18F.sup.− was transported through a pipe to an anion exchange column QMA (QMA was a refillable column) for capture. After the capture was complete, the QMA was blow-dried with N.sub.2 and rinsed with 0.45 mL of an acetic acid-sodium acetate buffer at a pH of 4.2 for elution to obtain an .sup.18F.sup.−-containing buffer with an activity of 110 mCi.

[0064] 433.7 Kg of a labeling precursor NOTA-Bn-FAPI-4, 0.75 mL of PEG, and 0.05 mL of a 0.4 M AlCl.sub.3 aqueous solution were added to 0.45 mL of the .sup.18F.sup.−-containing buffer to allow a reaction at 120° C. for 5 min, and 5 mL of deionized water was added to quench the reaction. The resulting reaction solution was allowed to pass through an Al.sub.2O.sub.3 column to obtain a filtrate.

[0065] The filtrate was allowed to pass through a Cis-Plus column for enrichment, and the column was rinsed with 2 mL of ethanol and 10 mL of NS successively. An eluate was allowed to pass through a sterile filtration membrane to obtain an injection of a tumor stroma diagnostic imaging agent [.sup.18F]—AlF-NOTA-Bn-FAPI-4 with an activity of 54.5 mCi.

Example 9

[0066] Preparation of Boc-FAPI-4 and Boc-FAPI-2

##STR00012##

[0067] The preparation of Boc-FAPI-4 and Boc-FAPI-2 may be conducted by referring to: Thomas Lindner et al. Development of Quinoline-Based Theranostic Ligands for the Targeting of Fibroblast Activation Protein. Journal of Nuclear Medicine, 2018, 59 (9), pp. 1415-1422; or may be commercially available. (S)-NOTA-Bn-SCN may be commercially available.

Example 10

[0068] Preparation of (S)-NOTA-Bn-FAPI-4

##STR00013##

[0069] 21.0 mg (33.9 μmol) of Boc-FAPI-4, 2,200 μL of acetonitrile, and 60.0 mg of p-toluenesulfonic acid were added to a 4 mL reaction flask, heated to 45° C., and stirred to allow a reaction for 2 h. The resulting reaction system was subjected to vacuum distillation to remove the solvent, and a residue was dissolved with 1,050 μL of DMSO to obtain a reaction product solution. 15.0 mg (33.2 μmol) of (S)-NOTA-Bn-SCN was dissolved in 110 μL of DMSO and added to the reaction product solution. The resulting mixed solution was subjected to an ultrasonic reaction for 2 h at room temperature, and 1 mL of water in which 20 μL of acetic acid was dissolved was added to quench the reaction.

[0070] After the reaction was complete, 5 μL of a sample was taken and identified by analytical HPLC. Parameters of the analytical HPLC on the Phenomenex Luna C.sub.18 reversed-phase column (5 μm, 250×4.6 mm) were as follows: flow rate: 1 mL/min; phase A: a solution of 0.1% trifluoroacetic acid (TFA) in water; phase B: a solution of 0.1% TFA in acetonitrile; at 2 min to 25 min, decreasing from 95% to 20% in phase A and increasing from 5% to 80% in phase B; and at 25 min to 30 min, maintaining at 20% in phase A. The ultraviolet (UV) absorbance was measured at 214 nm and 254 nm to obtain a retention time of the product NOTA-FAPI-B. The product was then separated through preparative HPLC. The collected product was lyophilized to obtain a fluffy white powder.

[0071] A high-resolution mass spectrometer (HRMS) was used to determine the molecular ion peak of the synthesized product: HRMS: [M+H]+=937.384 (m/z), theoretical calc: 937.3842 (C.sub.44H.sub.54F.sub.2N.sub.10O.sub.9S).

[0072] Nuclear magnetic resonance (NMR) data of the above compound were as follows:

[0073] .sup.1H NMR (400 MHz, D.sub.2O) δ:2.273 (S, 2H), 2.875-3.314 (m, 12H), 3.153-3.351 (m, 6H), 3.694-3.786 (m, 9H), 4.187-4.371 (m, 10H), 5.118-5.138 (s, 1H), 7.178-7.369 (m, 2H), 7.464-7.483 (m, 4H), 7.831-7.898 (t, 1H), 8.721-8.738 (m, 2H).

[0074] Each of NOTA-Bn-FAPI-4, (S)-NOTA-Bn-FAPI-2, and NOTA-Bn-FAPI-2 was prepared according to the above method.

Example 11

[0075] Preparation of an (S)—AlF-NOTA-Bn-FAPI-4 Control

##STR00014##

[0076] In a 1 mL V-reaction flask, a mixed solution of 7 μL of sodium fluoride (3.0 mM) and a sodium acetate buffer (0.1 M, pH 4.0) was added to a mixed solution of 0.2 mL of deionized water, 10 μL of aluminum trichloride (2 mM), and a sodium acetate buffer (0.1 M, pH 4.0). The resulting system was ultrasonically shaken for 1 min and heated to 100° C. to allow a reaction for 10 min. A mixed solution of 5 μL of acetonitrile, 5 μL of (S)-NOTA-Bn-FAPI-4 (2.5 mM), and a sodium acetate buffer (0.1 M, pH 4.0) was added, and the resulting system was further heated to 100° C. to allow a reaction for 10 min.

[0077] After the resulting reaction solution was cooled, 5 μL of a sample was taken and identified by analytical HPLC. Parameters of the analytical HPLC on the Phenomenex Luna C.sub.18 reversed-phase column (5 μm, 250×4.6 mm) were as follows: flow rate: 1 mL/min; phase A: a solution of 0.1% TFA in water; phase B: a solution of 0.1% TFA in acetonitrile; at 2 min to 25 min, decreasing from 95% to 20% in phase A and increasing from 5% to 80% in phase B; and at 25 min to 30 min, maintaining at 20% in phase A. Single components were collected at 15.53 min and 15.72 min and analyzed by LC-MS: molecular ion peaks: [M+H].sup.+=964.371 (m/z), theoretical calc: 964.3717 (C.sub.44H.sub.54AlF.sub.2N.sub.10O.sub.9S) corresponding to (S)—Al-NOTA-Bn-FAPI-4 (Rt=15.53 min) component; and [M+H].sup.+=983.371 (m/z) corresponding to (S)—AlF-NOTA-Bn-FAPI-4 (Rt=15.72 min), theoretical calc: 983.3701 (C.sub.44H.sub.54AlF.sub.3N.sub.10O.sub.9S) component.

[0078] 3 mL of the remaining reaction solution was taken and diluted with water, and the resulting diluted solution was allowed to pass through an Al.sub.2O.sub.3 column to obtain a filtrate. The filtrate was allowed to pass through a C.sub.18-Plus column for enrichment. The column was washed with 3 mL of phosphate-buffered saline (PBS) and 2 mL of water and subjected to elution with 600 μL of a solution of 10 mM hydrochloric acid in ethanol. An eluate was allowed to pass through a sterile filtration membrane to obtain an injection for a tumor stroma diagnostic imaging experiment.

[0079] Each of AlF-NOTA-Bn-FAPI-4, (S)—AlF-NOTA-Bn-FAPI-2, and AlF-NOTA-Bn-FAPI-2 was prepared according to the above method.

Example 12

[0080] 1. A Cell Binding Experiment of (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4

[0081] (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 was adopted as an experimental group, AlF-FAPI-75+(S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 was adopted as a blockage group, and free .sup.18F.sup.− was adopted as a control group.

[0082] A human fibrosarcoma cell HT-1080-FAP (HT-1080-FAP cell line) transfected by an FAP gene was activated to obtain an HT-1080-FAP cell suspension.

[0083] The experimental group: 2 mL of the HT-1080-FAP cell suspension was taken and washed three times with frozen PBS. A complete medium including the imaging agent (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 (2.96 MBq, 80 μCi) was added, and the resulting mixture was incubated for 1 h. The cells were washed three times with frozen PBS, and 0.5 mL of NaOH-sodium dodecyl sulfate (SDS) (1M NaOH, 1% SDS) was added for lysis. The resulting cell lysate was finally collected, placed in a marked γ-counting tube, and subjected to γ-counting.

[0084] The blockage group: 2 mL of the HT-1080-FAP cell suspension was taken and washed three times with frozen PBS. A complete medium including the blocker AlF-FAPI-75 was added, and the resulting mixture was incubated for 0.5 h. A complete medium including the imaging agent (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 (2.96 MBq, 80 μCi) was added, and the resulting mixture was incubated for 1 h. The cells were washed three times with frozen PBS, and 0.5 mL of NaOH-SDS (1 M NaOH, 1% SDS) was added for lysis. The resulting cell lysate was finally collected, placed in a marked γ-counting tube, and subjected to γ-counting.

[0085] The control group: 2 mL of the HT-1080-FAP cell suspension was taken and washed three times with frozen PBS. A complete medium including the free .sup.18F.sup.− (2.96 MBq, 80 μCi) was added, and the resulting mixture was incubated for 1 h. The cells were washed three times with frozen PBS, and 0.5 mL of NaOH-SDS (1 M NaOH, 1% SDS) was added for lysis. The resulting cell lysate was finally collected, placed in a marked γ-counting tube, and subjected to γ-counting. The final volumes of the groups were the same. After 1 h of incubation, a radioactivity count value of cell uptake in each group was shown in Table 1.

TABLE-US-00001 TABLE 1 Radioactivity count values of the cell binding experiment of (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 Grouping for the cell Radioactivity count value binding experiment (γ count value/min) Experimental group 5999.98 ± 864.12 Blockage group 2000.01 ± 113.34 Control group 180.13 ± 34.67

[0086] The above data shows that the absorption of tumor cells for a radiocontrast agent in the experimental group is 3 times that of the blockage group with a statistically significant difference (t=6.713, P<0.05) and the absorption of tumor cells for a radiocontrast agent in the experimental group is 33.31 times that of the control group with a statistically significant difference (t=8.934, P<0.01). It can be seen that the imaging agent (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 shows prominent selective adsorption for tumor cells. Therefore, it can be determined that the contrast agent prepared in the present example exhibits prominent specificity in the diagnosis of FAP overexpression in tumor stroma.

[0087] 2. Biodistribution of (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 in Tumor-Bearing Mice

[0088] Six mice were divided into an experimental group and a blockage group with 3 mice in each group. Mice in the experimental group each were injected with (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 (3.7 MBq, 100 μCi) through a tail vein within 1 min, and 60 min later, the mice each were sacrificed by cutting a carotid artery for bloodletting. Mice in the blockage group each were injected with 100 μg of the blocker AlF-FAPI-75 (1,000 μg/mL) through a tail vein and injected with (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 (3.7 MBq, 100 μCi) through a tail vein 30 min later, and 60 min later, the mice each were sacrificed by cutting a carotid artery for bloodletting. The heart, liver, lung, kidney, spleen, brain, and the like were collected, weighed, and tested for radioactivity. Finally, an (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 radioactivity uptake rate (a percentage of uptake radioactivity per gram of tissue in the injected radioactivity, ID/g) in each of blood and various organs and a radioactivity ratio of a target organ to a non-target organ (T/NT) were calculated at different time points. The final results are shown in Table 2.

TABLE-US-00002 TABLE 2 Distribution of (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 in tumor-bearing mice 1 h after injection, % ID/g Grouping Tissue or organ Experimental group Blockage group Blood 0.10 + 0.04 0.13 ± 0.10 Heart 0.09 + 0.09 0.08 ± 0.05 Liver 0.07 + 0.05 0.08 ± 0.04 Spleen 0.10 + 0.01 0.16 ± 0.14 Kidney 0.94 + 0.20 0.84 ± 0.21 Muscle 0.16 + 0.05 0.09 ± 0.03 Bone 0.15 + 0.03 0.06 ± 0.01 Intestine 0.19 + 0.06 0.16 ± 0.02 Brain 0.02 + 0.01 0.03 ± 0.01 Lung 0.16 + 0.08 0.28 ± 0.19 Tumor 1.12 + 0.06 0.22 ± 0.05

[0089] It can be seen from Table 2 that, according to the biological distribution of (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 in the experimental group and the blockage group 1 h after injection, blood uptake values of the experimental group and the blockage group are (0.10±0.04)% ID/g and (0.13±0.10)% ID/g, respectively, indicating that (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 is quickly cleared in the blood; kidney uptake values of the experimental group and the blockage group are (0.94±0.20)% ID/g and (0.84±0.21)% ID/g, respectively, indicating that the marker is mainly excreted by the kidney; radioactivity uptake values of graft tumors in the experimental group and the blockade group are (1.12±0.06)% ID/g and (0.22±0.05)% ID/g, respectively, with a statistically significant difference (t=2.921, P<0.05); and the distribution of (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 in other organs is significantly lower than that in tumors, indicating that the (S)—[.sup.18F]—AlF-NOTA-Bn-FAPI-4 prepared in the present example exhibits prominent specificity and sensitivity for FAP overexpression in a tumor stroma.

[0090] The examples are described above to facilitate the comprehension and use of the present disclosure by those of ordinary skill in the art. Obviously, those skilled in the art can easily make various modifications to these examples and apply a general principle described herein to other examples without creative efforts. Therefore, the present disclosure is not limited to the above examples. All improvements and modifications made by a person skilled in the art according to the disclosure of the present disclosure should fall within the protection scope of the present disclosure.