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

Discovery of a Novel Small-Molecule Inhibitor Disrupting TRBP-Dicer Interaction against Hepatocellular Carcinoma via the Modulation of microRNA Biogenesis

MicroRNAs (miRNAs) are key players in human hepatocellular carcinoma (HCC) tumorigenesis. Therefore, small molecules targeting components of miRNA biogenesis may provide new therapeutic means for HCC treatment. By a high-throughput screening and structural simplification, we identified a small molecule, CIB-3b, which suppresses the growth and metastasis of HCC in vitro and in vivo by modulating expression profiles of miRNAome and proteome in HCC cells. Mechanistically, CIB-3b physically binds to transactivation response (TAR) RNA-binding protein 2 (TRBP) and disrupts the TRBP-Dicer interaction, thereby altering the activity of Dicer and mature miRNA production. Structure-activity relationship study via the synthesis of 45 CIB-3b derivatives showed that some compounds exhibited a similar inhibitory effect on miRNA biogenesis to CIB-3b. These results support TRBP as a potential therapeutic target in HCC and warrant further development of CIB-3b along with its analogues as a novel therapeutic strategy for the treatment of HCC.

Molecular Imaging Probes Based on Matrix Metalloproteinase Inhibitors (MMPIs)

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.

Developing an Antibody-Drug Conjugate Approach to Selective Inhibition of an Extracellular Protein

Antibody–drug conjugates (ADCs) are a growing class of therapeutics that harness the specificity of antibodies and the cell‐killing potency of small‐molecule drugs. Beyond cytotoxics, there are few examples of the application of an ADC approach to difficult drug discovery targets. Here, we present the initial development of a non‐internalising ADC, with a view to selectively inhibiting an extracellular protein. Employing the wellinvestigated matrix metalloproteinase‐9 (MMP‐9) as our model, we adapted a broad‐spectrum, nonselective MMP inhibitor for conjugation and linked this to a MMP‐9‐targeting antibody. The resulting ADC fully inhibits MMP‐9, and ELISA results suggest antibody targeting can direct a nonselective inhibitor.

Evaluation of [68Ga]Ga-DOTA-TCTP-1 for the Detection of Metalloproteinase 2/9 Expression in Mouse Atherosclerotic Plaques

Background: The expression of matrix metalloproteinases 2/9 (MMP-2/9) has been implicated in arterial remodeling and inflammation in atherosclerosis. We evaluated a gallium-68 labeled peptide for the detection of MMP-2/9 in atherosclerotic mouse aorta. Methods: We studied sixteen low-density lipoprotein receptor deficient mice (LDLR^-/-ApoB^100/100) kept on a Western-type diet. Distribution of intravenously-injected MMP-2/9-targeting peptide, [⁶⁸Ga]Ga-DOTA-TCTP-1, was studied by combined positron emission tomography (PET) and contrast-enhanced computed tomography (CT). At 60 min post-injection, aortas were cut into cryosections for autoradiography analysis of tracer uptake, histology, and immunohistochemistry. Zymography was used to assess MMP-2/9 activation and pre-treatment with MMP-2/9 inhibitor to assess the specificity of tracer uptake. Results: Tracer uptake was not visible by in vivo PET/CT in the atherosclerotic aorta, but ex vivo autoradiography revealed 1.8 ± 0.34 times higher tracer uptake in atherosclerotic plaques than in normal vessel wall (p = 0.0029). Tracer uptake in plaques correlated strongly with the quantity of Mac-3-positive macrophages (R = 0.91, p < 0.001), but weakly with MMP-9 staining (R = 0.40, p = 0.099). Zymography showed MMP-2 activation in the aorta, and pre-treatment with MMP-2/9 inhibitor decreased tracer uptake by 55% (p = 0.0020). Conclusions: The MMP-2/9-targeting [⁶⁸Ga]Ga-DOTA-TCTP-1 shows specific uptake in inflamed atherosclerotic lesions; however, a low target-to-background ratio precluded in vivo vascular imaging. Our results suggest, that the affinity of gelatinase imaging probes should be steered towards activated MMP-2, to reduce the interference of circulating enzymes on the target visualization in vivo.

Synthesis and in vitro Evaluation of ADAM10 and ADAM17 Highly Selective Bioimaging Probes

A disintegrin and metalloproteinase (ADAMs) are membrane-bound metalloproteases responsible for the ectodomain shedding of various transmembrane proteins and play important roles in multiple relevant biological processes. Their altered expression is involved in several pathological conditions, and in particular ADAM10 or ADAM17 overexpression is found in various forms of cancer. To better understand how they are regulated in the cellular context, it is useful to visualize the specific ADAMs pathway by means of molecular imaging techniques. For this purpose, we synthesized bioactive fluorescent probes suitable for cell imaging and that are able to specifically target ADAM10 or ADAM17. Two previously developed ADAM17- and ADAM10-selective inhibitors were chosen for conjugation, respectively, to a Cy5.5 dye and to Cy5.5 and FITC dyes. Herein we also report the synthesis of a gold-labeled compound as an additional bioimaging probe for ADAM10. The newly synthesized ligands were found to be active in vitro on human recombinant ADAM10 and/or ADAM17, showing IC₅₀ values in the nanomolar range and a good selectivity over matrix metalloproteinases (MMPs). Finally, these newly developed probes were successfully used for ADAMs staining on different lymphoma cell lines and lymph node mesenchymal stromal cells.

Matrix Metalloproteinases: A challenging paradigm of cancer management

Matrix metalloproteinases (MMPs) are members of zinc-dependent endopeptidases implicated in a variety of physiological and pathological processes. Over the decades, MMPs have been studied for their role in cancer progression, migration, and metastasis. As a result, accumulated evidence of MMPs incriminating role has made them an attractive therapeutic target. Early generations of broad-spectrum MMP inhibitors exhibited potent inhibitory activities, which subsequently led to clinical trials. Unexpectedly, these trials failed to meet the desired goals, mainly due to the lack of efficacy, poor oral bioavailability, and toxicity. In this review, we discuss the regulatory role of MMPs in cancer progression, current strategies in targeting MMPs for cancer treatment including prodrug design and tumor imaging, and therapeutic value of MMPs as biomarkers in breast, lung, and prostate cancers.

Radiolabeled hydroxamate-based matrix metalloproteinase inhibitors: How chemical modifications affect pharmacokinetics and metabolic stability

INTRODUCTION

Dysregulated MMP expression or activation is associated with several diseases. To study MMP activity in vivo by means of PET a radiolabeled MMP inhibitor (MMPI) functioning as radiotracer has been developed by our group based on the lead structure CGS 25966.

MATERIALS AND METHODS

Aiming at the modification of the pharmacokinetics of this lipophilic model tracer a new class of MMPIs has been discovered, consisting of additional fluorinated hydrophilic substructures, such as mini-PEG and/or 1,2,3-triazole units. To identify the best candidate for further clinical applications, radiofluorinated compounds of each subgroup have been (radio) synthesized and evaluated regarding their biodistribution behavior and their metabolic stability.

RESULTS

Radiosyntheses of different triazole based MMPIs could be realized using two step "click chemistry" procedures. Compared to lead structure [(18)F]FEtO-CGS 25966 ([(18)F]1e, log D(exp) =2.02, IC50=2-50nM) all selected candidates showed increased hydrophilicities and inhibition potencies (log D(exp) =0.23-1.25, IC50=0.006-6nM). Interestingly, despite different hydrophilicities most triazole based MMPIs showed no significant differences in their in vivo biodistribution behavior and were cleared predominantly via the hepatobiliary excretion route. Biostability and metabolism studies in vitro and in vivo revealed significant higher metabolic stability for the triazole moiety compared to the benzyl ring in the lead structure. Cleavage of ethylene glycol subunits of the mini-PEG chain led to a faster metabolism of mini-PEG containing MMPIs.

CONCLUSION

The introduction of hydrophilic groups such as mini-PEG and 1,2,3-triazole units did not lead to a significant shift of the hepatobiliary elimination towards renal clearance. Particularly the introduction of mini-PEG chains led to an intense metabolic decomposition. Substitution of the benzyl moiety in lead structure 1e by a 1,2,3-trizole ring resulted in an increased metabolic stability. Therefore, the 1,2,3-triazole-1-yl-methyl substituted MMPI [(18)F]3a was found to be the most stable candidate in this series and should be chosen for further preclinical evaluation.

Fluorinated matrix metalloproteinases inhibitors--Phosphonate based potential probes for positron emission tomography

Fluorine-containing inhibitors of matrix metalloproteinases (MMPs) can serve as lead structures for the development of (18)F-labeled radioligands. These compounds might be useful as non-invasive imaging probes to characterize pathologies associated with increased MMP activity. Results with a series of fluorinated analogs of a known biphenyl sulfonamide inhibitor have shown that fluorine can be incorporated into two different positions of the molecular scaffold without significant loss of potency in the nanomolar range. Additionally, the potential of a hitherto unknown fluorinated tertiary sulfonamide as MMP inhibitor has been demonstrated.

A comprehensive review on controls in molecular imaging: lessons from MMP-2 imaging

Metalloproteinases (MMPs), including MMP-2, play critical roles in tissue remodeling and are involved in a large array of pathologies, including cancer, arthritis and atherosclerosis. Their prognostic value warranted a large investment or resources in the development of noninvasive detection methods, based on probes for many current clinical and pre-clinical imaging modalities. However, the potential of imaging techniques is only matched by the complexity of the data they generate. This complexity must be properly assessed and accounted for in the early steps of probe design and testing in order to accurately determine the efficacy and efficiency of an imaging strategy. This review proposes basic rules for the evaluation of novel probes by addressing the specific case of MMP targeted probes.

Cell-penetrating peptides and their analogues as novel nanocarriers for drug delivery

INTRODUCTION

The impermeability of biological membranes is a major obstacle in drug delivery; however, some peptides have transition capabilities of biomembranes. In recent decades, cell-penetrating peptides (CPPs) have been introduced as novel biocarriers that are able to translocate into the cells. CPPs are biologically potent tools for non-invasive cellular internalization of cargo molecules. Nevertheless, the non-specificity of these peptides presents a restriction for targeting drug delivery; therefore, a peptidic nanocarrier sensitive to matrix metalloproteinase (MMP) has been prepared, called activatable cell-penetrating peptide (ACPP). In addition to the cell-penetrating peptide dendrimer (DCPP), other analogues of CPPs have been synthesized.

METHODS

In this study, the most recent literature in the field of biomedical application of CPPs and their analogues, ACPP and DCCP, were reviewed.

RESULTS

This review focuses on CPP and its analogues, ACPP and DCPP, as novel nanocarriers for drug delivery. In addition, nanoconjugates and bioconjugates of these peptide sequences are discussed.

CONCLUSION

DCCP, branched CPPs, compared to linear peptides have advantages such as resistance to rapid biodegradation, high loading capacities and large-scale production capability.

Antibody-based imaging strategies for cancer

Although mainly developed for preclinical research and therapeutic use, antibodies have high antigen specificity, which can be used as a courier to selectively deliver a diagnostic probe or therapeutic agent to cancer. It is generally accepted that the optimal antigen for imaging will depend on both the expression in the tumor relative to normal tissue and the homogeneity of expression throughout the tumor mass and between patients. For the purpose of diagnostic imaging, novel antibodies can be developed to target antigens for disease detection, or current FDA-approved antibodies can be repurposed with the covalent addition of an imaging probe. Reuse of therapeutic antibodies for diagnostic purposes reduces translational costs since the safety profile of the antibody is well defined and the agent is already available under conditions suitable for human use. In this review, we will explore a wide range of antibodies and imaging modalities that are being translated to the clinic for cancer identification and surgical treatment.

Development and evaluation of a non-peptidic ligand for the molecular imaging of inflammatory processes using S100A9 (MRP14) as a novel target

We describe the development and first evaluation of a novel S100A9 specific molecular imaging probe (Cy5.5-CES271) for optical imaging of local inflammatory activity in vivo.

In vivo biodistribution of radiolabeled MMP-2/9 activatable cell-penetrating peptide probes in tumor-bearing mice

Matrix metalloproteinases (MMPs) play a pivotal role in cancer progression and present therefore an interesting biomarker for early diagnosis, staging and therapy evaluation. Consequently, MMP-specific molecular imaging probes have been proposed for noninvasive visualization and quantification of MMP activity. An interesting approach is MMP-2/9 activatable cell-penetrating peptides (ACPP) that accumulate in the tumor tissue after activation. However, a recent study revealed that probe activation occurred already in the vasculature followed by nonspecific tumor targeting. In the latter study, biodistribution was determined 6 and 24 h post-ACPP injection. An alternative explanation could still be that the kinetics of tumor-specific activation is faster than that of blood activation plus subsequent nonspecific uptake in tumor. The aim of this study was to assess if tumor-specific ACPP activation occurs in mice with MMP-2/9 positive subcutaneous HT-1080 tumors at 3 h post-injection. As control, we studied the MMP-2/9 sensitive ACPP in mice bearing subcutaneous BT-20 tumors with low MMP-2/9 expression to test if probe cleavage correlates with tumoral MMP expression. Ex vivo biodistribution showed no improved tumoral ACPP activation in HT-1080 tumor-bearing mice at 3 h post-injection compared with previous reported data collected at 24 h post-injection. Furthermore, tumoral uptake and relative tumoral activation for ACPP were similar in both BT-20 and HT-1080 tumor-bearing mice. In conclusion, this study suggests that tumoral ACPP uptake in these tumor models originates from probe activation in the vasculature instead of tumor-specific MMP activation. Novel ACPPs that target tissue-specific proteases without nonspecific activation may unleash the full potential of the elegant ACPP concept.

FRET-based and other fluorescent proteinase probes

The continuous detection of enzyme activities and their application in medical diagnostics is one of the challenges in the translational sciences. Proteinases represent one of the largest groups of enzymes in the human genome and many diseases are based on malfunctions of proteolytic activity. Fluorescent sensors may shed light on regular and irregular proteinase activity in vitro and in vivo and provide a deeper insight into the function of these enzymes and their role in pathophysiological processes. The focus of this review is on Förster resonance energy transfer (FRET)-based proteinase sensors and reporters because these probes are most likely to provide quantitative data. The medical relevance of proteinases are discussed using lung diseases as a prominent example. Probe design and probe targeting are described and fluorescent probe development for disease-relevant proteinases, including matrix-metalloproteinases, cathepsins, caspases, and other selected proteinases, is reviewed.

Chemical biology for understanding matrix metalloproteinase function

The matrix metalloproteinase (MMP) family has long been associated with normal physiological processes such as embryonic implantation, tissue remodeling, organ development, and wound healing, as well as multiple aspects of cancer initiation and progression, osteoarthritis, inflammatory and vascular diseases, and neurodegenerative diseases. The development of chemically designed MMP probes has advanced our understanding of the roles of MMPs in disease in addition to shedding considerable light on the mechanisms of MMP action. The first generation of protease-activated agents has demonstrated proof of principle as well as providing impetus for in vivo applications. One common problem has been a lack of agent stability at nontargeted tissues and organs due to activation by multiple proteases. The present review considers how chemical biology has impacted the progress made in understanding the roles of MMPs in disease and the basic mechanisms of MMP action.

Non-FDG imaging of atherosclerosis: will imaging of MMPs assess plaque vulnerability?

Acute ruptures of atherosclerotic plaques with subsequent occlusion account for the vast majority of clinical events such as myocardial infarction or stroke. New imaging approaches focusing on the visualization of inflammation in the vessel wall could emerge as tools for individualized risk assessment and prevention of events. To this end, PET employing (18)F-fluorodeoxyglucose (FDG) has recently been introduced for the first clinical trials. Although this approach nicely visualizes plaques inflammation questions remain with respect to if and how this inflammatory signal can be employed for predicting individual plaque rupture. Molecular imaging of proteases such as matrix-metalloproteinases (MMPs) involved in several steps in plaque progression driving plaques into vulnerable, rupture-prone states seems a promising alternative approach. This review introduces and discusses the vulnerable plaque concept, animal models with human-like plaque ruptures and the potential of a FDG versus a non-FDG MMP-targeted strategy to image rupture-prone plaques.

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.

Selecting Potential Targetable Biomarkers for Imaging Purposes in Colorectal Cancer Using TArget Selection Criteria (TASC): A Novel Target Identification Tool

Peritoneal carcinomatosis (PC) of colorectal origin is associated with a poor prognosis. However, cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy is available for a selected group of PC patients, which significantly increases overall survival rates up to 30%. As a consequence, there is substantial room for improvement. Tumor targeting is expected to improve the treatment efficacy of colorectal cancer (CRC) further through 1) more sensitive preoperative tumor detection, thus reducing overtreatment; 2) better intraoperative detection and surgical elimination of residual disease using tumor-specific intraoperative imaging; and 3) tumor-specific targeted therapeutics. This review focuses, in particular, on the development of tumor-targeted imaging agents. A large number of biomarkers are known to be upregulated in CRC. However, to date, no validated criteria have been described for the selection of the most promising biomarkers for tumor targeting. Such a scoring system might improve the selection of the correct biomarker for imaging purposes. In this review, we present the TArget Selection Criteria (TASC) scoring system for selection of potential biomarkers for tumor-targeted imaging. By applying TASC to biomarkers for CRC, we identified seven biomarkers (carcinoembryonic antigen, CXC chemokine receptor 4, epidermal growth factor receptor, epithelial cell adhesion molecule, matrix metalloproteinases, mucin 1, and vascular endothelial growth factor A) that seem most suitable for tumor-targeted imaging applications in colorectal cancer. Further cross-validation studies in CRC and other tumor types are necessary to establish its definitive value.

Exogenous Molecular Probes for Targeted Imaging in Cancer: Focus on Multi-modal Imaging

Cancer is one of the major causes of mortality and morbidity in our health care system. Molecular imaging is an emerging methodology for the early detection of cancer, and the development of exogenous molecular probes that can be labeled for multi-modality imaging is critical to this process. Today, molecular imaging is at crossroad, and new targeted imaging agents are expected to broadly expand our ability to detect pre-malignant lesions. This integrated imaging strategy will permit clinicians to not only localize lesions within the body, but also to visualize the expression and activity of specific molecules. This information is expected to have a major impact on diagnosis, therapy, drug development and understanding of basic cancer biology. At this time, a number of molecular probes have been developed by conjugating various labels to affinity ligands for targeting in different imaging modalities. This review will describe the current status of exogenous molecular probes for optical, nuclear and MRI imaging platforms. Furthermore, we will also shed light on how these techniques can be used synergistically in multi-modal platforms and how these techniques are being employed in current research.