Simultaneous FAPI PET/MRI Targeting the Fibroblast-Activation Protein for Breast Cancer.

Background Integrated PET/MRI is a promising modality for breast assessment. The most frequently used tracer, fluorine 18 (18F) fluorodeoxyglucose (FDG), is applied for whole-body staging in advanced breast cancer but has limited accuracy in evaluating primary breast lesions. The fibroblast-activation protein (FAP) is abundantly expressed in invasive breast cancer. FAP-directed PET tracers have recently become available, but results in primary breast tumors remain lacking. Purpose To evaluate the use of FAP inhibitor (FAPI) breast PET/MRI in assessing breast lesions and of FAPI whole-body scanning for lymph node (LN) and distant staging using the ligand gallium 68 (68Ga)-FAPI-46. Materials and Methods In women with histologically confirmed invasive breast cancer, all primary 68Ga-FAPI-46 breast and whole-body PET/MRI and PET/CT examinations conducted at the authors' center between October 2019 and December 2020 were retrospectively analyzed. MRI lesion characteristics and standardized uptake values (SUVs) were quantified with dedicated software. Mann-Whitney U tests were used to compare tumor SUVs across different tumor types. The Pearson correlation coefficient was calculated between SUV and measures of MRI morphologic characteristics. Results Nineteen women (mean age, 49 years ± 9 [standard deviation]) were evaluated-18 to complement initial staging and one for restaging after therapy for distant metastases. Strong tracer accumulation was observed in all 18 untreated primary breast malignancies (mean maximum SUV [SUVmax] = 13.9 [range, 7.9-29.9]; median lesion diameter = 26 mm [range, 9-155 mm]), resulting in clear tumor delineation across different gradings, receptors, and histologic types. All preoperatively verified LN metastases in 13 women showed strong tracer accumulation (mean SUVmax= 12.2 [range, 3.3-22.4]; mean diameter = 21 mm [range, 14-35 mm]). Tracer uptake established or supported extra-axillary LN involvement in seven women and affected therapy decisions in three women. Conclusion This retrospective analysis indicates use of 68Ga fibroblast-activation protein inhibitor tracers for breast cancer diagnosis and staging. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Mankoff and Sellmyer in this issue.

Optimizing the Biodistribution of Radiofluorinated Barbiturate Tracers for Matrix Metalloproteinase Imaging by Introduction of Fluorescent Dyes as Pharmacokinetic Modulators.

Dysregulated expression or activation of matrix metalloproteinases (MMPs) is observed in many kinds of life-threatening diseases. Therefore, MMP imaging-for example, with radiolabeled MMP inhibitors (MMPIs)-potentially represents a valuable tool for clinical diagnostics using noninvasive single photon emission computed tomography (SPECT) or positron emission tomography (PET) imaging. Despite numerous preclinical imaging approaches, translation to a clinical setting has not yet been successful. We introduce and oppose three potential radiofluorinated MMP-targeted imaging probes, modified by the introduction of pentamethine cyanine (Cy5) dyes and therefore containing both radio- as well as fluorescent label with respect to their capability to assess MMP activity in vivo by means of scintigraphic (PET) and/or fluorescent (NIRF) imaging. New hybrid MMPI tracer candidates, structurally based on radiofluorinated pyrimidine-2,4,6-triones (barbiturates) from previous approaches, were synthesized by convenient two-step syntheses. In the first step, Cy5 dyes, varying in the number of sulfonate groups (nSO3- = 1, 2, or 4) and bearing an additional "clickable" alkyne moiety, were coupled to the barbiturate MMPI by amide formation. In the second step, the [18F]fluoride radiolabel was introduced into the resulting Cy5 dye conjugates by "radio-click" chemistry. Biodistribution studies of these hybrid tracer candidates were assessed and compared in C57BL/6 mice by PET as well as fluorescence imaging. MMP activity was imaged in a MMP-positive mouse model of irritant contact dermatitis (ICD) by PET and sequential fluorescence reflectance imaging (FRI), respectively. In vivo data were validated by scintillation counting, gelatin zymography, and MMP-histology. Three new potential hybrid MMP imaging probes were prepared, differing essentially in the number of sulfonate groups, introduced by Cy5 dye components. Although the hydrophilicity of these compounds was substantially increased, 10a (nSO3- = 1) and 10b (nSO3- = 2) were still rapidly eliminated via unfavorable hepatobiliary pathways, as observed in earlier approaches. Only 11 (nSO3- = 4) showed delayed in vivo clearance and a shift towards higher renal elimination. In the chosen mouse model of ICD, only 11 (nSO3- = 4) significantly accumulated in the inflamed mouse ear, which could be precisely visualized by means of PET and FRI.

Initial Results of 68Ga-FAPI-46 PET/MRI to Assess Response to Neoadjuvant Chemotherapy in Breast Cancer.

Improving imaging-based response after neoadjuvant chemotherapy (NAC) in breast cancer assessment could obviate histologic confirmation of pathologic complete response (pCR) and facilitate deescalation of chemotherapy or surgery. Fibroblast activation protein inhibitor (FAPI) PET/MRI is a promising novel molecular imaging agent for the tumor microenvironment with intense uptake in breast cancer. We assessed the diagnostic performance of follow-up breast 68Ga-FAPI-46 (68Ga-FAPI) PET/MRI in classifying the response status of local breast cancer and lymph node metastases after completion of NAC and validated this approach immunohistochemically. Methods: In women who completed NAC for invasive breast cancer, follow-up 68Ga-FAPI PET/MRI and corresponding fibroblast activation protein (FAP) immunostainings were retrospectively analyzed. Metrics of 68Ga-FAPI uptake and FAP immunoreactivity in women with or without pCR were compared using the Mann-Whitney U test. Diagnostic performance to detect remnant invasive cancer was calculated for tracer uptake metrics using receiver-operating-characteristic curves and for masked readers' visual assessment categories of PET/MRI and MRI alone. Results: Thirteen women (mean age ± SD, 47 ± 9 y) were evaluated. Seven of the 13 achieved pCR in the breast and 6 in the axilla. FAP immunoreactivity was significantly associated with response status. The 68Ga-FAPI PET/MRI mean breast tumor-to-background ratio was 0.9 (range, 0.6-1.2) for pCR and 2.1 (range, 1.4-3.1) for no pCR (P = 0.001). Integrated PET/MRI could classify breast response correctly in all 13 women based on readers' visual assessment or tumor-to-background ratio. Evaluation of MRI alone resulted in at least 2 false-positives. For lymph nodes, PET/MRI readers had at least 2 false-negative classifications, whereas MRI alone resulted in 2 false-negatives and 1 false-positive. Conclusion: To our knowledge, this was the first analysis of 68Ga-FAPI PET/MRI for response assessment after NAC for breast cancer. The diagnostic performance of PET/MRI in a small study sample trended toward a gain over MRI alone, clearly supporting future prospective studies.

Synthesis and evaluation of a novel hydroxamate based fluorescent photoprobe for imaging of matrix metalloproteinases.

The assessment of matrix metalloproteinase (MMP) activity in vivo is highly desirable in various human diseases such as cancers. Hydroxamic acids based on CGS27023A or CGS25966 are nonpeptidyl lead structures that specifically target activated MMPs in vivo. The aim of this study was the modification and fluorescent labeling of these lead structures to develop a highly affine, nonpeptide MMP inhibitor (MMPI)-ligand for molecular optical imaging of activated MMPs. An 11 step synthesis was developed involving a PEGylated benzyl derivative as a spacer to minimize the interactions between the activated MMP and the dye of conjugate 11 with an azide as a protected amino function. After reducing the azide (Staudinger reaction) and labeling with Cy5.5, we obtained a CGS-based MMP inhibitor 11 with a fluorescent signaling flag. To evaluate the biological properties of this photoprobe, three human cancer cell lines (A-673, HT-1080 and BT-20) were characterized with respect to their MMP-2 and -9 (gelatinases) expression levels (real-time PCR) and protein levels (Western blotting). Initially, fluorogenic inhibition assays were used to assess the MMP inhibition potential. The PEGylated CGS 10 showed complete inhibition of MMP-2 and MMP-9 activities in vitro both for purified MMP-2/-9 (active and pro-forms) and MMP-2/-9 containing cell culture supernatants. To test the imaging potential in biological tissues, gelatinase activity was measured on tumor cryostat sections of the above-mentioned tumor cells using FITC-labeled dye-quenched gelatin. Gelatinase positive tumors revealed strong binding of CGS-Cy5.5 11, while gelatinase negative tumors were not targeted. In conclusion, this new CGS-based MMP photoprobe has a high affinity for MMP-2 and -9 and is thus a promising candidate for sensitive imaging of MMP activity in various diseases in patients.

PET-compatible endothelin receptor radioligands: synthesis and first in vitro and in vivo studies.

The expression and function of endothelin (ET) receptors is abnormal in cardiovascular diseases, tumor progression, and tumor metastasis. In this study, we prepared two [(18)F]-fluorinated derivatives of the non-peptide ET(A) receptor antagonist PD 156707 and evaluated their ET receptor binding potencies. Ex vivo as well as in vivo biodistribution studies in mice were performed, as well as the metabolism of the radiotracer, which was examined by metabolite analysis in mice and rats. All tested derivatives of PD 156707 exhibited potent in vitro pharmacological characteristics with K(i) values comparable to that of the lead compound. The biodistribution studies showed a high accumulation of the tracer in bile and intestine. In vivo we were able to show that the visualization of the heart as a major target organ with high ET(A)R expression is possible.

Synthesis and evaluation of a novel fluorescent photoprobe for imaging matrix metalloproteinases.

The measurement of matrix metalloproteinase (MMP) activity in diseases like inflammation, oncogenesis, or atherosclerosis in vivo is highly desirable. Fine-tuned pyrimidine-2,4,6-triones (barbiturates) offer nonpeptidyl lead structures for developing imaging agents for specifically visualization of activated MMPs in vivo. The aim of this study was to modify a C-5-disubstituted barbiturate and thus design a highly affine, nonpeptidic, optical MMP inhibitor (MMPI)-ligand for imaging of activated MMPs in vivo. A convergent 10 step synthesis was developed, starting with a malonic ester and (4-bromophenoxy)benzene to generate 5-bromo-pyrimidine-2,4,6-trione as the key intermediate. To minimize the interactions between activated MMPs and the dye of the conjugate 6, a PEGylated piperazine derivative was used as a spacer and an azide as a protected amino function. After linking both building blocks, reducing the azide ( Staudinger reaction) and labeling with Cy 5.5, we obtained the nonhydroxamate MMP inhibitor 6 with high affinity (IC 50-value: 48 nM for MMP-2) measured in a fluorogenic assay using commercially available MMP-substrates and the purified enzyme. Zymography revealed an efficient blocking of enzyme activity of purified MMP-2 and MMP-9 and of MMP-containing cell supernatants (HT-1080), (A-673) using the PEGylated barbiturate 5. Fluorescence microscopy studies using a highly (A-673) and a moderate (HT-1080) MMP-2 secreting cell line showed efficient binding of the Cy 5.5 labeled tracer 6 to the MMP-2 positive cells while MMP-2 negative cells (MCF-7) did not bind. Therefore, this new barbiturate-based MMP-probe has a high affinity and specificity toward MMP-2 and -9 and is thus a promising candidate for sensitive MMP detection in vivo.

Novel fluorinated derivatives of the broad-spectrum MMP inhibitors N-hydroxy-2(R)-[[(4-methoxyphenyl)sulfonyl](benzyl)- and (3-picolyl)-amino]-3-methyl-butanamide as potential tools for the molecular imaging of activated MMPs with PET.

An approach to the in vivo imaging of locally upregulated and activated matrix metalloproteinases (MMPs) found in many pathological processes is offered by positron emission tomography (PET). Hence, appropriate PET radioligands for MMP imaging are required. Here, we describe the syntheses of novel fluorinated MMP inhibitors (MMPIs) based on lead structures of the broad-spectrum inhibitors N-hydroxy-2(R)-[[(4-methoxyphenyl)sulfonyl](benzyl)-amino]-3-methyl-butanamide (CGS 25966) and N-hydroxy-2(R)-[[(4-methoxyphenyl)sulfonyl](3-picolyl)-amino]-3-methyl-butanamide (CGS 27023A). Additionally, tailor-made precursor compounds for radiolabeling with the positron-emitter 18F were synthesized. All prepared hydroxamate target compounds showed high in vitro MMP inhibition potencies for MMP-2, MMP-8, MMP-9, and MMP-13. As a consequence, the promising fluorinated hydroxamic acid derivative 1f was resynthesized in its 18F-labeled version via two different procedures yielding the potential PET radioligand [18F]1f. As expected, the biodistribution behavior of this novel compound and that of the more hydrophilic variant [18F]1j, also developed by our group, indicates that there was no tissue specific accumulation in wild-type (WT) mice.

Syntheses of Radioiodinated Pyrimidine-2,4,6-Triones as Potential Agents for Non-Invasive Imaging of Matrix Metalloproteinases.

Dysregulated expression or activation of matrix metalloproteinases (MMPs) is observed in many kinds of live-threatening diseases. Therefore, MMP imaging for example with radiolabelled MMP inhibitors (MMPIs) potentially represents a valuable tool for clinical diagnostics using non-invasive single photon emission computed tomography (SPECT) or positron emission tomography (PET) imaging. This work includes the organic chemical syntheses and in vitro evaluation of five iodinated barbiturate based MMPIs and the selection of derivative 9 for radiosyntheses of isotopologues [123I]9 potentially useful for MMP SPECT imaging and [124I]9 for MMP PET imaging.

5-pyrrolidinylsulfonyl isatins as a potential tool for the molecular imaging of caspases in apoptosis.

Caspases are the unique enzymes responsible for the execution of the cell death program and may represent an exclusive target for the specific molecular imaging of apoptosis in vivo. 5-Pyrrolidinylsulfonyl isatins represent potent nonpeptidyl caspase inhibitors that may be suitable for the development of caspase binding radioligands (CBRs). (S)-5-[1-(2-Methoxymethylpyrrolidinyl)sulfonyl]isatin (7) served as a lead compound for modification of its N-1-position. Corresponding pairs of N-1-substituted 2-methoxymethyl- and 2-phenoxymethylpyrrolidinyl derivatives were examined in vitro by biochemical caspase inhibition assays. All target compounds possess high in vitro caspase inhibition potencies in the nanomolar to subnanomolar range for caspase-3 (Ki=0.2-56.1 nM). As shown for compound (S)-1-(4-(2-fluoroethoxy)benzyl)-5-[1-(2-methoxymethylpyrrolidinyl)sulfonyl]isatin (35), the class of N-1-substituted 5-pyrrolidinylsulfonyl isatins competitively inhibits caspase-3. All caspase inhibitors show selectivity for the effector caspases-3 and -7 in vitro. The 2-methoxymethylpyrrolidinyl versions of the isatins appear to possess superior caspase inhibition potencies in cellular apoptosis inhibition assays compared with the 2-phenoxymethylpyrrolidinyl inhibitors.

Correlation of Intraprostatic Tumor Extent with 68Ga-PSMA Distribution in Patients with Prostate Cancer.

UNLABELLED: We evaluated the diagnostic value and accuracy of prostate-specific membrane antigen (PSMA) PET for the intraprostatic delineation of prostate cancer before prostatectomy. METHODS: We identified 6 patients with biopsy-proven high-risk prostate cancer who were referred for (68)Ga-PSMA PET/CT before radical prostatectomy to rule out metastasis. After prostatectomy, a histologic map of the prostate was reconstructed. The histologic extent and Gleason score of each segment of the prostate were compared with (68)Ga-PSMA PET images resliced to the histologic axis. Sensitivity, specificity, positive and negative predictive value, and positive and negative likelihood ratios were calculated. The SUV of each segment was measured, and median values were compared. RESULTS: Of the 132 segments, 112 were eligible for analysis. The correlation of histologic results with (68)Ga-PSMA PET images showed a specificity and sensitivity of 92%. The positive and negative likelihood ratio and the positive and negative predictive value for detection of prostate cancer on (68)Ga-PSMA PET were 11.5, 0.09, 96%, and 85%, respectively. The median SUVmax of true-positive prostate segments was significantly higher than that of true-negative segments (11.0 ± 7.8 vs. 2.7 ± 0.9, P< 0.001), and a cutoff of 4 revealed a sensitivity and specificity of 86.5% and an accuracy of 87.5%. CONCLUSION: These preliminary results show that the intraprostatic localization and extent of prostate cancer may be estimated by (68)Ga-PSMA PET. This imaging method may be helpful for identifying target lesions before prostate biopsy and may support decision making before focal or radical therapy.

Scintigraphic imaging of matrix metalloproteinase activity in the arterial wall in vivo.

BACKGROUND: Matrix metalloproteinases (MMPs) are enzymes involved in the proteolytic degradation of extracellular matrix. They play an important role in several disease processes, such as inflammation, cancer, and atherosclerosis. METHODS AND RESULTS: In this study, we have used the broad-spectrum MMP inhibitor CGS 27023A to develop the radioligand [123I]I-HO-CGS 27023A for in vivo imaging of MMP activity. Using this radioligand, we were able to specifically image MMP activity by scintigraphy in vivo in the MMP-rich vascular lesions that develop after carotid artery ligation and cholesterol-rich diet in apolipoprotein E-deficient mice. These results were confirmed by gamma counting of lesional tissue (counts per minute per milligram). CONCLUSIONS: Imaging of MMP activity in vivo is feasible using radiolabeled MMP inhibitors. Additional studies are needed to test the potential of this approach as a novel noninvasive clinical diagnostic tool for the management of human MMP-related diseases.

C-5-disubstituted barbiturates as potential molecular probes for noninvasive matrix metalloproteinase imaging.

Studies have demonstrated a positive correlation between inflammation, metastasis, or atherosclerosis and the unbalanced or culminated expression of matrix metalloproteinases (MMPs). The molecular imaging of locally upregulated MMP activity in vivo is a clinical challenge. Actually, radioligands based on nonpeptidyl MMP inhibitors (MMPIs) are currently in development as putative radiopharmaceutical agents for the noninvasive in vivo assessment of activated MMPs. Nonpeptidyl MMPIs bind to the zinc active site of the activated enzyme via mono- (e.g. carboxylate) or bidentate (e.g. hydroxamate) complexation thereby exhibiting a broad-spectrum MMP binding potency. Thus, these mentioned endopeptidase inhibitors should be useable lead compounds for the redevelopment as diagnostic MMPI radiotracers. Recently, the non-hydroxamate C-5-disubstituted pyrimidine-2,4,6-triones were disclosed as subgroup-selective MMP inhibitors. We here describe a set of fine-tuned barbiturates as a new class of MMPI radiotracers for the noninvasive in vivo visualization of activated MMPs using scintigraphic techniques such as SPECT or PET.

Multimodal imaging reveals temporal and spatial microglia and matrix metalloproteinase activity after experimental stroke.

Stroke is the most common cause of death and disability from neurologic disease in humans. Activation of microglia and matrix metalloproteinases (MMPs) is involved in positively and negatively affecting stroke outcome. Novel, noninvasive, multimodal imaging methods visualizing microglial and MMP alterations were employed. The spatio-temporal dynamics of these parameters were studied in relation to blood flow changes. Micro positron emission tomography (µPET) using [(18)F]BR-351 showed MMP activity within the first days after transient middle cerebral artery occlusion (tMCAo), followed by increased [(18)F]DPA-714 uptake as a marker for microglia activation with a maximum at 14 days after tMCAo. The inflammatory response was spatially located in the infarct core and in adjacent (penumbral) tissue. For the first time, multimodal imaging based on PET, single photon emission computed tomography, and magnetic resonance imaging revealed insight into the spatio-temporal distribution of critical parameters of poststroke inflammation. This allows further evaluation of novel treatment paradigms targeting the postischemic inflammation.

Synthesis and preliminary biological evaluation of new radioiodinated MMP inhibitors for imaging MMP activity in vivo.

Non-invasive measurement of matrix metalloproteinase (MMP) activity in vivo is a clinical challenge in many disease processes such as inflammation, tumor metastasis and atherosclerosis. Therefore, radioiodinated analogues of the non-peptidyl broad-spectrum MMP inhibitor (MMPI) CGS 27023A 1a were synthesized for non-invasive detection of MMP activity in vivo using single photon emission computed tomography (SPECT). The compounds Br-CGS 27023A 1b and HO-CGS 27023A 1d were synthesized from the amino acid D-valine and used as precursors for radioiodinated derivatives of CGS 27023A and their non-radioactive references I-CGS 27023A 1c and HO-I-CGS 27023A 1e. Radioiodination of the precursors with [(123)I]NaI or [(125)I]NaI produced the no-carrier-added MMP inhibitors [(123)I]I-CGS 27023A 1f, [(125)I]I-CGS 27023A 1g, HO-[(123)I]I-CGS27023A 1h, and HO-[(125)I]I-CGS 27023A 1i. In vitro studies showed that the non-radioactive analogues of the MMP inhibitors exhibited affinities against gelatinase A (MMP-2) and gelatinase B (MMP-9) in the nanomolar range, comparable to the parent compound CGS 27023A. In vivo biodistribution using HO-[(125)I]I-CGS 27023A 1i in CL57 Bl6 mice showed rapid blood and plasma clearance and low retention in normal tissues. The preliminary biological evaluation warrant further studies of these radioiodinated MMP inhibitors as potential new radiotracers for imaging MMP activity in vivo.

A new generation of radiofluorinated pyrimidine-2,4,6-triones as MMP-targeted radiotracers for positron emission tomography.

Radiolabeled C-5-disubstituted pyrimidine-2,4,6-triones have recently been suggested by our group as a class of potent matrix metalloproteinase (MMP) targeted radiotracers that can noninvasively visualize activated MMPs by means of positron emission tomography (PET). MMPs belong to the zinc- and calcium-dependent endopeptidases which are involved in the proteolytic degradation of components of the extracellular matrix (ECM) but also are capable of processing and releasing bioactive molecules such as growth factors, proteinase inhibitors, and cytokines. Locally increased levels of activated MMPs modulate and contribute to the progression of various diseases, such as cancer, atherosclerosis, stroke, arthritis, and others. Therefore, activated MMPs are suitable biological targets for the specific and noninvasive visualization of aforementioned pathologies in vivo. On the basis of our recent results, we here describe a series of new fluorinated pyrimidine-2,4,6-triones of the second generation with maintained MMP inhibition potencies (IC(50) = 4-605 nM), which are fine-tuned toward more hydrophilic versions, and show the improved biodistribution behavior of one selected radiofluorinated pyrimidine-2,4,6-trione by means of small-animal PET.

Efficient synthesis of a fluorine-18 labeled biotin derivative.

INTRODUCTION: The natural occurring vitamin biotin, also known as vitamin H or vitamin B(7), plays a major role in various metabolic reactions. Caused by its high binding affinity to the protein avidin with a dissociation constant of about 10(-15)M the biotin-avidin system was extensively examined for multiple applications. We have synthesized a fluorine-18 labeled biotin derivative [(18)F]4 for a potential application in positron emission tomography (PET). METHODS: Mesylate precursor 3 was obtained by an efficient two-step reaction via a copper catalyzed azide-alkyne cycloaddition (CuAAC) from easily accessible starting materials. [(18)F]4 was successfully synthesized by a nucleophilic radiofluorination of precursor 3. A biodistribution study by means of small-animal PET imaging in wt-mice was performed and serum stability was examined. RESULTS: Compound [(18)F]4 was obtained from precursor compound 3 with an average specific activity of 16GBq/µmol within 45min and a radiochemical yield of 45±5% (decay corrected). [(18)F]4 demonstrated only negligible decomposition in human serum. A qualitative binding study revealed the high affinity of the synthesized biotin derivative to avidin. Blocking experiments with native biotin showed that binding was site-specific. Biodistribution studies showed that [(18)F]4 was cleared quickly and efficiently from the body by hepatobiliary and renal elimination. CONCLUSION: An efficient synthesis for [(18)F]4 was established. In vivo characteristics were determined and demonstrated the pharmacokinetic behaviour of [(18)F]4.

A new class of highly potent matrix metalloproteinase inhibitors based on triazole-substituted hydroxamates: (radio)synthesis and in vitro and first in vivo evaluation.

In vivo imaging of MMPs is of great (pre)clinical interest and can potentially be realized with modern three-dimensional and noninvasive in vivo molecular imaging techniques such as positron emission tomography (PET). Consequently, MMP inhibitors (MMPIs) radiolabeled with positron emitting nuclides (e.g., (18)F) represent a suitable tool for the visualization of activated MMPs with PET. On the basis of our previous work and results regarding radiolabeled and unlabeled derivatives of the nonselective MMPIs, we discovered a new class of fluorinated MMPIs with a triazole-substituted hydroxamate substructure. These novel MMPIs are characterized by an increased hydrophilicity compared with the lead structures and excellent MMP inhibition potencies for MMP-2, MMP-8, MMP-9, and MMP-13 (IC(50) = 0.006-107 nM). Therefore, one promising fluorinated triazole-substituted hydroxamate (30b) was selected and resynthesised as its (18)F-labeled version to yield the potential PET radioligand [(18)F]30b. The biodistribution behavior of this novel compound was investigated with small animal PET.

The MMP inhibitor (R)-2-(N-benzyl-4-(2-[18F]fluoroethoxy)phenylsulphonamido)-N-hydroxy-3-methylbutanamide: Improved precursor synthesis and fully automated radiosynthesis.

The CGS 25966 derivative (R)-2-(N-Benzyl-4-(2-[(18)F]fluoroethoxy)phenyl-sulphonamido)-N-hydroxy-3-methylbutanamide [(18)F]9 represents a very potent radiolabelled matrix metalloproteinase inhibitor. For first human PET studies it is mandatory to have a fully automated radiosynthesis and a straightforward precursor synthesis available. The realisation of both requirements is reported herein. In particular, the corresponding precursor 8 was obtained in a reliable 7 step synthesis with an overall chemical yield of 2.3%. Furthermore, the target compound [(18)F]9 was prepared with a radiochemical yield of 14.8±3.9% (not corrected for decay).

Radiofluorinated pyrimidine-2,4,6-triones as molecular probes for noninvasive MMP-targeted imaging.

Matrix metalloproteinases (MMPs) are zinc- and calcium-dependent endopeptidases. Representing a subfamily of the metzincin superfamily, MMPs are involved in the proteolytic degradation of components of the extracellular matrix. Unregulated MMP expression, MMP dysregulation and locally increased MMP activity are common features of various diseases, such as cancer, atherosclerosis, stroke, arthritis, and others. Therefore, activated MMPs are suitable biological targets for the specific visualization of such pathologies, in particular by using radiolabeled MMP inhibitors (MMPIs). The aim of this work was to develop a radiofluorinated molecular probe for noninvasive in vivo imaging for the detection of up-regulated levels of activated MMPs in the living organism. Fluorinated MMPIs (26, 31 and 38) based on the pyrimidine-2,4,6-trione lead structure RO 28-2653 (1) were synthesized, and their MMP inhibition potency was evaluated in vitro. The radiosynthesis and the in vivo biodistribution of the first (18)F-labeled prototype, MMP-targeted tracer [(18)F]26, suitable for molecular imaging by means of positron emission tomography (PET) were realized.

A new 18F-labelled derivative of the MMP inhibitor CGS 27023A for PET: radiosynthesis and initial small-animal PET studies.

The CGS 27023A derivative (R)-2-(N-((6-fluoropyridin-3-yl)methyl)-4-methoxyphenyl-sulphonamido)-N-hydroxy-3-methylbutanamide 1a was identified as a very potent matrix metalloproteinase inhibitor. Here, we describe a one-step radiosynthesis of the target compound [(18)F]1a. The syntheses of [(18)F]1a resulted in a radiochemical yield of 12.1+/-5.9% (decay-corrected), a radiochemical purity of 98.8+/-0.6%, and a specific activity of 39+/-27 GBq/micromol at the end of synthesis within 160+/-18 min from the end of radionuclide production (n=5). Initial small-animal PET studies in wild-type mice (C57/BL6) showed no unfavourable tissue accumulation of [(18)F]1a.