Molecular Imaging Probes Based on Matrix Metalloproteinase Inhibitors (MMPIs)

Abstract

Matrix metalloproteinases (MMPs) are a family of zinc- and calcium-dependent endopeptidases which are secreted or anchored in the cell membrane and are capable of degrading the multiple components of the extracellular matrix (ECM). MMPs are frequently overexpressed or highly activated in numerous human diseases. Owing to the important role of MMPs in human diseases, many MMP inhibitors (MMPIs) have been developed as novel therapeutics, and some of them have entered clinical trials. However, so far, only one MMPI (doxycycline) has been approved by the FDA. Therefore, the evaluation of the activity of a specific subset of MMPs in human diseases using clinically relevant imaging techniques would be a powerful tool for the early diagnosis and assessment of the efficacy of therapy. In recent years, numerous MMPIs labeled imaging agents have emerged. This article begins by providing an overview of the MMP subfamily and its structure and function. The latest advances in the design of subtype selective MMPIs and their biological evaluation are then summarized. Subsequently, the potential use of MMPI-labeled diagnostic agents in clinical imaging techniques are discussed, including positron emission tomography (PET), single-photon emission computed tomography (SPECT) and optical imaging (OI). Finally, this article concludes with future perspectives and clinical utility.

Keywords: Matrix metalloproteinases (MMPs); positron emission tomography (PET); single-photon emission computed tomography (SPECT) and optical imaging (OI).

Figure 1

MMP Catalytic subunit. A cartoon representation of the MMP-1 (PDB code 1CGF) showing the different α-helixes and β-sheets with the corresponding coordinated metal ions. The sticks highlight the active site with the three histidines and the catalytic glutamic acid.

Scheme 1

Chemical structure for compounds CGS 25966A, CGS 27023A and 1–14.

Scheme 2

Chemical structure for compounds 15–20.

Scheme 3

Chemical structure for compound 21.

Scheme 4

Chemical structure for compounds 22–26.

Figure 2

Micro-PET images of [¹¹C]26 in a MCF-7 transfected with IL-1α implanted athymic mouse, and a MDA-MB-435 implanted mouse, after an initial 30 min uptake period. Reprinted with permission from [75] Copyright © 2003 Elsevier Inc. All rights reserved.

Scheme 5

Chemical structure for compounds 27–41.

Scheme 6

Synthetic route for [¹⁸F]40–41. Reagents and conditions: (a) (1)C₂H₄(OTs)₂, [¹⁸F]K(K 222)F, 100 °C; (2) MeONa, 120 °C. (b) TFA, CH₃CN, rt. (c) C₂H₄(OTs)₂, K₂CO₃, CH₃CN, 82 °C. (d) (1) [¹⁸F]K(K 222)F, 105 °C; (2) TFA, CH₃CN, rt. (e) Chloroacetylchloride or bromoacetylbromide, DIPEA, DMF. (f) (1) [¹⁸F]K(K 222)F, 130 °C; (2) TFA, CH₃CN, rt.

Figure 3

¹⁸F PET images of the abdomen of nude mice subcutaneously grafted with a human U-87 MG glioblastoma. Red arrows show the tumor in different slices. (A) PET images obtained by sequential administration of [¹⁸F]40 (1a) (upper row) and [¹⁸F]FDG (bottom row), showing colocalization of tracer uptake. The [¹⁸F]40 (1a) scan was acquired 100 min post-tracer injection; [¹⁸F]FDG was injected immediately after completion of the [¹⁸F]40 (1a) scan and the image was acquired 45 min post-[¹⁸F]FDG injection. Both scans were static acquisitions (injected dose 7.4 MBq, acquisition time 30 min). (B) PET images obtained by sequential administration of [¹⁸F]40 (1a) (upper row) and [¹⁸F]FDG (bottom row), in a mouse that received 40 mg/kg of the broad-spectrum MMPI Ilomastat 30 min before injection of [¹⁸F]40 (1a). The timing scheme and injected doses are the same as in panel A. Reprinted with permission form [83] Copyright © 2013 American Chemical Society.

Scheme 7

Chemical structure for compounds 42–47.

Scheme 8

Synthetic route for [¹⁸F]44. Reaction conditions: (a) [¹⁸F]fluoride (potassium 222 cryptate), K₂CO₃, CH₃CN, 84 °C, 15 min; (b) CuSO₄·H₂O, sodium ascorbate, DMF, rt, 8 min.

Scheme 9

Chemical structure for compound 48.

Scheme 10

Chemical structure for compounds 49–50.

Scheme 11

Chemical structure for compound 51.

Scheme 12

Chemical structure for compounds SB-3CT and [¹⁸F]52 and K_i values against several MMPs.

Figure 4

The site of the ligated left common carotid artery (left panel) and a corresponding whole-body coronal slice (0.4 mm thick) through a left carotid lesion (right panel) 4 weeks after ligation and a HC diet in an apoE−/− mouse. The intense uptake of the radiolabeled broad spectrum MMP inhibitor [¹²⁴I]55 in the left carotid lesion (arrow) 30 min after intravenous injection is visible using high-resolution small animal PET. Reprinted with permission from ref [95] Copyright © Springer-Verlag 2007.

Scheme 13

Chemical structure for compounds 56–59.

Figure 5

In vivo imaging of MMP activation in aneurysm. (A) An example of fused micro SPECT/CT images of mouse at 4 weeks after surgery to induce carotid aneurysm. The arrows point to aneurysmal left (L) and control right (R) carotid arteries. (B) The image-derived quantitative analysis of background-corrected [¹¹¹In]56 (RP782) carotid uptake. The background-corrected tracer uptake in left carotid artery peaked at 4 weeks after surgery and was significantly higher than uptake in right carotid artery at every time point studied. n 5 16-18 in each group. * p = 0.01. ** p < 0.001. C 5 coronal slice; S 5 sagittal slice; T 5 transverse slice. Reprinted with permission from [98] copyright © 2010 by the Society of Nuclear Medicine, Inc.

Figure 6

In vivo micro-SPECT/ micro-CT transverse (A) and sagittal (B) zoomed and masked images of the 5 study groups. Compound [^99mTc]58 uptake in atherosclerotic aortic lesions was identified noninvasively in arch and abdominal aorta by micro-SPECT aided by micro-CT; aortic arch calcification was detected by micro-CT. Ch 5 high-cholesterol-fed. Reprinted with permission from [97] copyright © 2009 by the Society of Nuclear Medicine, Inc.

Figure 7

Compound [^99mTc]59 (RYM1) imaging of AAA. (A,B) Examples of fused [^99mTc]59 (RYM1) SPECT/CT images of animals from the low remodeling (A) and aneurysm (B) groups, classified on the basis of a visual in situ analysis of abdominal aorta. Transversal (left), coronal (middle), and sagittal (right) views are shown. Arrows point to areas of maximal tracer uptake in abdominal aorta. (C) Quantification of [^99mTc]59 (RYM1) signal in area of maximal tracer uptake in suprarenal abdominal aorta in low remodeling and AAA groups. * p < 0.05. (D) Correlation between [^99mTc]59 (RYM1) signal in vivo and MMP activity quantified by zymography ex vivo. AU 5 arbitrary units; cpv 5 counts per voxel; LR 5 low remodeling. Reprinted with permission from [99] copyright © 2017 by the Society of Nuclear Medicine and Molecular Imaging.

Scheme 14

Chemical structure for compounds 60–62.

Figure 8

Cy5.5-MMPI 21 tracer signal localizes at sites of perivascular cuffs and gelatinase activity in vivo. (A,B) Five hours after intravenous injection of 21 (4 nmol) in two score 3 EAE mice, the brains were sliced into thick sections (200 mm) and imaged by FRI; color-encoded near infrared fluorescence and white-light images were captured and matched (left images). The same brain slices were then analyzed by in situ zymography for detection of activated gelatinases and subsequently stained with pan-laminin to define vessel borders and with CD45 antibodies to visualize inflammatory infiltrates (right images). Scale bars, 100 mm. (C,D) FRI of thick EAE brain sections (200 mm) at 5 h after intravenous injection of (4 nmol). Overlay of color-encoded near-infrared fluorescence image with significant MMP activity (red) projected onto the white-light image. The same brain slice was subsequently immunofluorescently stained with CD45 antibody; blue signal. 4′,6-diamidino-2- phenylindole (DAPI) staining of nuclei. Two separate brains are shown in (C,D). Scale bars, 100 mm. Reprinted with permission from [103] Copyright © 2016, American Association for the Advancement of Science.

Figure 9

MMPI-PET [¹⁸F]15 and Gd-T1-MRI in MS patients before and after anti-inflammatory treatment. (A) [¹⁸F]15 and Gd-T1-MRI of patient #6 representing an acute attack of RRMS (EDSS 2.0) at baseline (top) and at 35 days after treatment (Tx) (methylprednisolone) (bottom); white dashed circles mark colocalization of the MMPI-PET signal and contrast enhancement in the MRI scan, which resolves by 35 days after treatment, correlating with a residual MMPI-PET signal. Left: Gd-T1-MRI. Middle: [¹⁸F]15 scan 30 to 60 min after injection co-registered to the Gd-T1-MRI scan. Right: An overlay of Gd-T1-MRI and (PET-MRI). (B) Patient #2 represents an acute attack of RRMS. Left: Single co-registered [¹⁸F]15 (30 to 60 min after injection) and Gd-T1-MRI slice at baseline (top) and 28 days after treatment (1 g of methylprednisolone, three times per day) (bottom). Right: Five consecutive PET (upper row) and corresponding MRI (bottom row) slices at baseline (top panel), 7 days after therapy (middle panel, PET only), and 28 days after therapy (bottom panel). Note the intense contrast enhancement in Gd-T1-MRI (maximum, white dashed circle #1) with spatially adjacent but not identical MP activity (black circle #1) at baseline. Reduced MMPI-PET signal at 7 days after therapy (black circle #2), and by 28 days after therapy, the MMPI-PET signal remains low (black circle #3), but the Gd-T1-MRI signal now colocalizes to the original MMP active area from the baseline scan. Reprinted with permission from [103] Copyright © 2016, American Association for the Advancement of Science.

Scheme 15

Chemical structure for compounds 63–66.

Figure 10

In vivo [¹⁸F]45 microPET/CT images of a mouse exposed to cigarette smoke (CS) shown in a sagittal view. The right view indicates the ROIs (Regions Of Interest) drawn in the lung. The microPET images correspond to the sum of all the frames from 12 to 90 min p.i. of [¹⁸F]45. Reprinted with permission from [107] Copyright © World Molecular Imaging Society 2015.

Scheme 16

Chemical structure 67.

Figure 11

Transverse view of transmission CT and PET images at 50-60 min after injection of [¹⁸F]67 IPFP in the (A) Air and (B) CS groups. (C) Maximum intensity projection images of removed lungs (left) and heart (right) from the Air (upper) and CS (lower) groups. Reprinted with permission from [108] copyright © 2018, Springer Nature.

Scheme 17

Chemical structure for compounds 68–73.

Scheme 18

Chemical structure for compounds 74–78.