High-affinity peptide against MT1-MMP for in vivo tumor imaging

Comparison of 5-aminolevulinic acid and MMP-14 targeted peptide probes in preclinical models of GBM

Rationale: Developing novel pre-operative and intraoperative imaging approaches for glioblastoma multiforme (GBM) could aid therapeutic intervention while sparing healthy normal brain, which remains a significant clinical challenge. 5-aminolevulinic acid (5-ALA) is the only intraoperative imaging agent approved to aid the resection of GBM. Matrix metalloproteinase 14 (MMP14), which is overexpressed in GBM, is an attractive target for preoperative and intraoperative imaging of GBM. Prior studies have shown the feasibility of near-infrared fluorescence (NIRF) imaging and positron emission tomography (PET) imaging of GBM xenografts in mice using MMP-14 targeted peptide probes. The present studies assessed the tumor-specific localization and contrast of these MMP-14 targeted peptides relative to 5-ALA in GBM models. Methods: Fluorescence and PET imaging was performed after i.v. injection of 5-ALA and the MMP-14 targeted peptide probes (non-labeled or radiolabeled with 64Cu) in mice bearing human GBM orthotopic xenografts (U87, D54). Imaging signals were correlated to MMP-14 expression determined by immunofluorescence. Tumor-to-normal brain ratio (TBR) and Dice similarity coefficient (DSC) relative to tumor defined by ex vivo pathology or in vivo magnetic resonance imaging were determined for each imaging agent. Results: NIRF signals from the MMP-14 targeted peptide probes showed comparable TBR (p < 0.05) but significantly higher DSC (p < 0.05) relative to 5-ALA. NIRF signals from the peptide probes significantly correlated with MMP-14 expression (p < 0.05). MMP-14 binding peptide labeled with 64Cu showed moderate DSC (0.45) while PET signals significantly correlated (p < 0.05) with NIRF signals from a co-injected MMP-14 substrate peptide. NIRF and PET signals localized in residual tumor regions in the resection cavity during in situ resection. Conclusions: MMP-14 targeted peptides showed favorable TBR and higher tumor localization than 5-ALA in GBM orthotopic models. Further development of MMP-14 targeted peptide probes could lead to improved pre-operative and intraoperative management of GBM.

Multifunctional nano co-delivery system for efficiently eliminating neuroblastoma by overcoming cancer heterogeneity

The high heterogeneity of neuroblastoma (NB) is currently the main challenge in clinical treatment, impeding the complete eradication of the tumor through monotherapy alone. In this study, we propose a combination strategy using a targeted nano co-delivery system (ADRF@Ag2Se) comprising phototheranostic agents, differentiation inducers and chemotherapy drugs for sequential therapy of NB. Upon intravenous injection, ADRF@Ag2Se demonstrates effective tumor targeting by the specific binding of AF7P to MMP14, which is overexpressed on the surface of NB cells. Subsequent implementation of local photothermal therapy (PTT) leverages the robust photothermal conversion capabilities of the amphiphilic photothermal reagent PF. This is followed by the temperature-triggered release of differentiation-inducing agent 13-cis-retinoic acid and chemo-drug doxorubicin to synergistically eliminate the residual lesions. This nanotherapeutic strategy facilitatesin vivotargeted delivery and PTT under the supervision of NIR-II fluorescence, and it also enhances the chemotherapeutic response through differentiation induction of poorly differentiated cancer cells. In the NB tumor model, this co-delivery strategy effectively inhibited tumor growth and significantly prolonged the survival of the mice.

A Versatile Microfluidic Platform for Extravasation Studies Based on DNA Origami-Cell Interactions

The adhesion of circulating tumor cells (CTCs) to the endothelial lumen and their extravasation to surrounding tissues are crucial in the seeding of metastases and remain the most complex events of the metastatic cascade to study. Integrins expressed on CTCs are major regulators of the extravasation process. This knowledge is primarily derived from animal models and biomimetic systems based on artificial endothelial layers, but these methods have ethical or technical limitations. We present a versatile microfluidic device to study cancer cell extravasation that mimics the endothelial barrier by using a porous membrane functionalized with DNA origami nanostructures (DONs) that display nanoscale patterns of adhesion peptides to circulating cancer cells. The device simulates physiological flow conditions and allows direct visualization of cell transmigration through microchannel pores using 3D confocal imaging. Using this system, we studied integrin-specific adhesion in the absence of other adhesive events. Specifically, we show that the transmigration ability of the metastatic cancer cell line MDA-MB-231 is influenced by the type, distance, and density of adhesion peptides present on the DONs. Furthermore, studies with mixed ligand systems indicate that integrins binding to RGD (arginine-glycine-aspartic acid) and IDS (isoleucine-aspartic acid-serine) did not synergistically enhance the extravasation process of MDA-MB-231 cells.

Development of anti-membrane type 1-matrix metalloproteinase nanobodies as immunoPET probes for triple negative breast cancer imaging

Triple-negative breast cancer (TNBC) is characterized by aggressiveness and high rates of metastasis. The identification of relevant biomarkers is crucial to improve outcomes for TNBC patients. Membrane type 1-matrix metalloproteinase (MT1-MMP) could be a good candidate because its expression has been reported to correlate with tumor malignancy, progression and metastasis. Moreover, single-domain variable regions (VHHs or Nanobodies) derived from camelid heavy-chain-only antibodies have demonstrated improvements in tissue penetration and blood clearance, important characteristics for cancer imaging. Here, we have developed a nanobody-based PET imaging strategy for TNBC detection that targets MT1-MMP. A llama-derived library was screened against the catalytic domain of MT1-MMP and a panel of specific nanobodies were identified. After a deep characterization, two nanobodies were selected to be labeled with gallium-68 (⁶⁸Ga). ImmunoPET imaging with both ([⁶⁸Ga]Ga-NOTA-3TPA14 and [⁶⁸Ga]Ga-NOTA-3CMP75) in a TNBC mouse model showed precise tumor-targeting capacity in vivo with high signal-to-background ratios. (⁶⁸Ga)Ga-NOTA-3CMP75 exhibited higher tumor uptake compared to (⁶⁸Ga)Ga-NOTA-3TPA14. Furthermore, imaging data correlated perfectly with the immunohistochemistry staining results. In conclusion, we found a promising candidate for nanobody-based PET imaging to be further investigated as a diagnostic tool in TNBC.

Analysis of Compositional Bias in a Commercial Phage Display Peptide Library by Next-Generation Sequencing

The principal presumption of phage display biopanning is that the naïve library contains an unbiased repertoire of peptides, and thus, the enriched variants derive from the affinity selection of an entirely random peptide pool. In the current study, we utilized deep sequencing to characterize the widely used Ph.DTM-12 phage display peptide library (New England Biolabs). The next-generation sequencing (NGS) data indicated the presence of stop codons and a high abundance of wild-type clones in the naïve library, which collectively result in a reduced effective size of the library. The analysis of the DNA sequence logo and global and position-specific frequency of amino acids demonstrated significant bias in the nucleotide and amino acid composition of the library inserts. Principal component analysis (PCA) uncovered the existence of four distinct clusters in the naïve library and the investigation of peptide frequency distribution revealed a broad range of unequal abundances for peptides. Taken together, our data provide strong evidence for the notion that the naïve library represents substantial departures from randomness at the nucleotide, amino acid, and peptide levels, though not undergoing any selective pressure for target binding. This non-uniform sequence representation arises from both the M13 phage biology and technical errors of the library construction. Our findings highlight the paramount importance of the qualitative assessment of the naïve phage display libraries prior to biopanning.

Hyaluronidase responsive second near-infrared fluorescent nanocomplex for combined HER2 blockade and chemotherapy of HER2+ breast cancer

The human epidermal growth factor receptor-2-positive (HER2+) type is aggressive and has poor prognosis. Although anti-HER2 therapy alone or in combination with other treatment regimens showed significant improvement in survival outcomes, breast cancer patients are still suffering from tumor relapse and severe dose-limiting side effects. Thus, there is still an unmet challenge to develop effective therapeutic agents for HER2+ breast cancer treatment with minimized side effects. Herein, we produced a stimuli-responsive and tumor-targeted hyaluronic acid (HA) nanocomplex that combined HER2 blockade and chemotherapy for effective HER2+ breast cancer therapy. A hydrophobic NIR-II dye, IR1048, was covalently linked with HA to form a spherical HA-IR1048 nanoparticle (HINP), with Herceptin conjugated on the surface and paclitaxel (PTX) encapsulated inside. The fluorescent signals from the yielding Her-HINP/PTX are quenched originally, but a strong NIR-II signal is generated when HINP is degraded by the hyaluronidase that is overexpressed in breast tumors, thus allowing the tracking and visualization of Herceptin and PTX accumulation. Her-HINP/PTX peaked in HER2+ tumors at 24 h post injection as imaged by NIR-II fluorescent imaging. A significantly improved tumor growth inhibition effect was observed after five systemic treatments compared to single PTX (3.71 ± 0.41 times) or Herceptin (5.98 ± 0.51 times) treatment in a HER2-overexpressed breast cancer mouse model with prolonged survival. Collectively, the designed Her-HINP/PTX presents a new hyaluronidase-responsive and HER2 blockade nanoformulation that can visualize the accumulation of nanocomplexes and release drugs inside tumors for combined HER2+ breast cancer therapy with a great promise for translational study. STATEMENT OF SIGNIFICANCE: The high expressions of a protein called human epidermal growth factor receptor 2 (HER2) in breast tumors make this subtype of cancer aggressive. Currently, chemotherapy combined with a HER2 antibody, Herceptin, is a preferred approach for HER2-positive breast cancer therapy. However, these breast cancer patients still suffer from tumor relapse and severe side effects because various therapeutic agents have inherent different biodistributions, resulting in insufficient treatment effects and unfavorable normal organ uptake of these therapeutic agents. Herein, we produced a nanocomplex carrying both Herceptin and chemotherapy drug to simultaneously deliver two drugs into tumors for efficient HER2+ tumor treatment with minimized side effects, providing new insights for designing a combined therapy strategy.

Qualitative and Quantitative Analysis of Tumor Cell Invasion Using Au Clusters

Tumor invasion/metastasis is still the major cause of death in cancer patients. Membrane type-1 matrix metalloproteinase (MT1-MMP) is directly related to tumor invasion/metastasis. To accurately and quickly distinguish the risk of invasion/metastasis of primary tumor cells, it is urgent to develop a simple and precise quantitative method to distinguish the expression level of MT1-MMP. In this work, we have constructed red fluorescent Au clusters with peroxidase-like properties that could specifically bind to MT1-MMP on human cervical cancer cells. After MT1-MMP was labelled with Au clusters, we could visually see red fluorescence of MT1-MMP on cervical cancer cells via fluorescence microscopy and catalytic color imaging using an ordinary optical microscope. The constructed Au clusters contained 26 Au atoms; thus, the amount of MT1-MMP on cervical cancer cells could be accurately quantified using inductively coupled plasma mass spectrometry (ICP-MS). More importantly, the invasion/metastasis capabilities of the cervical cancer Siha, Caski and Hela cells with different MT1-MMP amounts could be accurately distinguished by fluorescence/catalysis qualitative imaging and ICP-MS quantitative analysis. This method of qualitative/quantitative analysis of tumor-associated proteins on cancer cells has great potential for accurately diagnosing aggressive tumor cells and assessment of their invasion/metastasis risk.

Interference-free SERS nanoprobes for labeling and imaging of MT1-MMP in breast cancer cells

The expression of membrane type-1 matrix metalloproteinase (MT1-MMP) in cancer cells is critical for understanding the development, invasion and metastasis of cancers. In this study, we devised an interference-free surface-enhanced Raman scattering (SERS) nanoprobe with high selectivity and specificity for MT1-MMP. The nanoprobe was comprised of silver core-silica shell nanoparticle with a Raman reporter tag (4-mercaptobenzonitrile) embedded in the interface. Moreover, the nitrile group in 4-mercaptobenzonitrile shows a unique characteristic peak in the Raman-silent region (1800-2800 cm^-1), which eliminates spectral overlapping or background interference in the Raman fingerprint region (500-1800 cm^-1). After surface modification with a targeting peptide, the nanoprobe allowed visualization and evaluation of MT1-MMP in breast cancer cells via SERS spectrometry. This interference-free, peptide-functionalized SERS nanoprobe is supposed to be conducive to early diagnosis and invasive assessment of cancer in clinical settings.

Catalytic Clusterbody for Enhanced Quantitative Protein Immunoblot

To assess low-abundance protein biomarkers associated with tumor progression, we have developed artificial catalytic antibodies based on well-defined metal clusters modified with rationally designed peptides, termed clusterbodies. Such clusterbodies possess favorable integrated features of matched ultrasmall sizes, intrinsic fluorescence, and enzyme-like catalytic and selective recognition properties that are inaccessible to traditional antibodies. Consequently, a quantitative assay with high accuracy and high sensitivity is established by measuring the fluorescence and catalytic chemiluminescence of metal clusters preferentially recognizing the protein biomarker, which is confirmed by the molecular-weight marker references of immunoblotting. The results of quantitative immunoblotting are highly close to that derived from the enzyme-linked immunosorbent assay, implying the reliability of this protocol. Remarkably, the detection limit of the aimed protein achieved is as low as 1.0 pg, one magnitude lower than that of the conventional immunoassay. The significant variation of expression levels of the biomarker in tumor cells evidently indicates their distinguished invasion ability. This platform has potential application in analyzing low-abundance protein biomarkers in complex biological matrixes, which is essential to corroborate tumor malignancy in early stage. It inspires the construction of clusterbody-based precise bioprobes with customized structures and integrative functions for advanced quantitative biosensing.

The development of a Glypican-3-specific binding peptide using in vivo and in vitro two-step phage display screening for the PET imaging of hepatocellular carcinoma

Glypican-3 (GPC3) is a diagnostic biomarker for hepatocellular carcinoma (HCC). Although numerous designs targeting GPC3 have been reported, the HCC diagnostic agents with specific tumor accumulation and low background, particularly in normal liver tissue, are still in need. Peptides have attracted considerable attention as an imaging probe due to their low immunogenicity, short in vivo circulation time, and acceptable production cost. Herein, a two-step phage display screening approach was performed against GPC3-high expression tumor xenografts in vivo, followed by human recombinant GPC3 protein in vitro. A GPC3-specific binding peptide, named TJ12P2, with the sequence of Ser-Asn-Asp-Arg-Pro-Pro-Asn-Ile-Leu-Gln-Lys-Arg (SNDRPPNILQKR) was identified. The apparent Kd value between TJ12P2 and the GPC3 protein was measured as 158.2 ± 26.25 nM. After 18F labeling, 18F-AlF-NOTA-TJ12P2 was found accumulated in the tumors by positron emission tomography (PET) imaging in two HCC subcutaneous tumor models (HepG2 and SMMC-7721) with high GPC3 expression. Static PET imaging revealed that 18F-AlF-NOTA-TJ12P2 accumulation in the HepG2 and SMMC-7721 tumors reached 1.825 ± 0.296 %ID g-1 and 1.575 ± 0.520 %ID g-1, with tumor-to-muscle ratios of 4.14 ± 0.50 and 4.25 ± 0.25, respectively, at 30 min post-injection (p.i.). Much less accumulation (0.533 ± 0.078 %ID g-1) of the 18F-AlF-NOTA-TJ12P2 was found in the control PC3 tumors with low GPC3 expression. More importantly, no obvious normal liver uptake of TJ12P2 was observed in the abovementioned animal models. As a result, a novel peptide targeting GPC3, TJ12P2, with strong affinity and specificity was identified using a two-step phage display screening technique in the present study. The 18F-AlF-NOTA-TJ12P2 may be a promising PET imaging probe with translational potential for accurate HCC diagnosis.

MT1-MMP activatable fluorogenic probes with enhanced specificity via high-affinity peptide conjugation for tumor imaging

Overlapping substrate specificities within the family of matrix metalloproteinases (MMPs), usually caused by their highly conserved structural topology, increase the potential for a substrate to be cleaved by multiple enzymes within this family, which leads to the decrease in the selectivity of MMP substrate-based probes. To resolve this issue, MT1-MMP activatable fluorogenic probes for tumor detection with enhanced specificity were developed by combining a fluorescence resonance energy transfer (FRET) peptide substrate and its specific binding peptide with different lengths of linkers. The specificity of the probes increased profiting from the high affinity of the MT1-MMP specific binding peptide while keeping the ability to amplify the output imaging signals in response to MMP activity with the FRET substrate. Enzyme kinetics analysis clearly demonstrated that the conjugation of P-1 and MT1-AF7p enhanced both the specificity and selectivity of the fluorogenic probes for MT1-MMP, and introducing a linker composed of 12 PEG subunits into these two fragments led to optimized specificity and selectivity of the fluorogenic probe for MT1-MMP. Both in vitro and in vivo results revealed that the imaging probe with the linker composed of 12 PEG subunits based on our designed strategy could be effectively applied for MT1-MMP positive tumor imaging. Since this strategy for enhancing the specificity of protease sensing probes can be applied to other proteases and is not just limited to MT1-MMP, it is an appealing platform to achieve selective tumor imaging.

Phage nanofibers in nanomedicine: Biopanning for early diagnosis, targeted therapy, and proteomics analysis

Display of a peptide or protein of interest on the filamentous phage (also known as bacteriophage), a biological nanofiber, has opened a new route for disease diagnosis and therapy as well as proteomics. Earlier phage display was widely used in protein-protein or antigen-antibody studies. In recent years, its application in nanomedicine is becoming increasingly popular and encouraging. We aim to review the current status in this research direction. For better understanding, we start with a brief introduction of basic biology and structure of the filamentous phage. We present the principle of phage display and library construction method on the basis of the filamentous phage. We summarize the use of the phage displayed peptide library for selecting peptides with high affinity against cells or tissues. We then review the recent applications of the selected cell or tissue targeting peptides in developing new targeting probes and therapeutics to advance the early diagnosis and targeted therapy of different diseases in nanomedicine. We also discuss the integration of antibody phage display and modern proteomics in discovering new biomarkers or target proteins for disease diagnosis and therapy. Finally, we propose an outlook for further advancing the potential impact of phage display on future nanomedicine. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Targeting MMP-14 for dual PET and fluorescence imaging of glioma in preclinical models

PURPOSE

There is a clinical need for agents that target glioma cells for non-invasive and intraoperative imaging to guide therapeutic intervention and improve the prognosis of glioma. Matrix metalloproteinase (MMP)-14 is overexpressed in glioma with negligible expression in normal brain, presenting MMP-14 as an attractive biomarker for imaging glioma. In this study, we designed a peptide probe containing a near-infrared fluorescence (NIRF) dye/quencher pair, a positron emission tomography (PET) radionuclide, and a moiety with high affinity to MMP-14. This novel substrate-binding peptide allows dual modality imaging of glioma only after cleavage by MMP-14 to activate the quenched NIRF signal, enhancing probe specificity and imaging contrast.

METHODS

MMP-14 expression and activity in human glioma tissues and cells were measured in vitro by immunofluorescence and gel zymography. Cleavage of the novel substrate and substrate-binding peptides by glioma cells in vitro and glioma xenograft tumors in vivo was determined by NIRF imaging. Biodistribution of the radiolabeled MMP-14-binding peptide or substrate-binding peptide was determined in mice bearing orthotopic patient-derived xenograft (PDX) glioma tumors by PET imaging.

RESULTS

Glioma cells with MMP-14 activity showed activation and retention of NIRF signal from the cleaved peptides. Resected mouse brains with PDX glioma tumors showed tumor-to-background NIRF ratios of 7.6-11.1 at 4 h after i.v. injection of the peptides. PET/CT images showed localization of activity in orthotopic PDX tumors after i.v. injection of ⁶⁸Ga-binding peptide or ⁶⁴Cu-substrate-binding peptide; uptake of the radiolabeled peptides in tumors was significantly reduced (p < 0.05) by blocking with the non-labeled-binding peptide. PET and NIRF signals correlated linearly in the orthotopic PDX tumors. Immunohistochemistry showed co-localization of MMP-14 expression and NIRF signal in the resected tumors.

CONCLUSIONS

The novel MMP-14 substrate-binding peptide enabled PET/NIRF imaging of glioma models in mice, warranting future image-guided resection studies with the probe in preclinical glioma models.

Glypican-3 (GPC3) targeted Fe3O4 core/Au shell nanocomplex for fluorescence/MRI/photoacoustic imaging-guided tumor photothermal therapy

Low binding affinity and lack of therapy functions limit tumor targeting peptide applications in the biomedical field. Herein, we successfully modified a previous phage display derived Glypican-3 (GPC3) binding peptide (GBP) on the surface of a Fe₃O₄ Core/Au shell nanocomplex (FANP) to improve GBP binding affinity and enhance FANP tumor photothermal therapy (PTT) efficacy. As a result, GBP-FANP showed improved avidity to GPC-3 (Apparent K_d = 396.3 ± 70.8 nM) compared to that of GPB (Apparent K_d = 735.2 ± 53.6 nM). After intravenous administration, GBP-FANP was found specifically accumulated in GPC-3 positive HepG2 tumors and peaked at 24 h post-injection as observed by magnetic resonance imaging (MRI)/photoacoustic (PA)/fluorescent imaging. Moreover, HepG2 tumors that received GBP-FANP treatment were significantly inhibited with laser irradiation (630 nm, 1 W cm^-2, 10 min). In conclusion, our present strategy provides a way of improving peptide ligand avidity with nanotechnology for cancer theranostics applications.

iRGD: A Promising Peptide for Cancer Imaging and a Potential Therapeutic Agent for Various Cancers

Poor penetration into the tumor parenchyma and the reduced therapeutic efficacy of anticancer drugs and other medications are the major problems in tumor treatment. A new tumor-homing and penetrating peptide, iRGD (CRGDK/RGPD/EC), can be effectively used to combine and deliver imaging agents or anticancer drugs into tumors. The different “vascular zip codes” expressed in different tissues can serve as targets for docking-based (synaptic) delivery of diagnostic and therapeutic molecules. αv-Integrins are abundantly expressed in the tumor vasculature, where they are recognized by peptides containing the RGD integrin recognition motif. The iRGD peptide follows a multistep tumor-targeting process: First, it is proteolytically cleaved to generate the CRGDK fragment by binding to the surface of cells expressing αv integrins (αvβ3 and αvβ5). Then, the fragment binds to neuropilin-1 and penetrates the tumor parenchyma more deeply. Compared with conventional RGD peptides, the affinity of iRGD for αv integrins is in the mid to low nanomolar range, and the CRGDK fragment has a stronger affinity for neuropilin-1 than that for αv integrins because of the C-terminal exposure of a conditional C-end Rule (CendR) motif (R/KXXR/K), whose receptor proved to be neuropilin-1. Consequently, these advantages facilitate the transfer of CRGDK fragments from integrins to neuropilin-1 and consequently deeper penetration into the tumor. Due to its specific binding and strong affinity, the iRGD peptide can deliver imaging agents and anticancer drugs into tumors effectively and deeply, which is useful in detecting the tumor, blocking tumor growth, and inhibiting tumor metastasis. This review aims to focus on the role of iRGD in the imaging and treatment of various cancers.

Screening, Identification, and Characterization of an Affinity Peptide Specific to MT1-MMP and Its Application in Tumor Imaging

Membrane type-1 matrix metalloproteinase (MT1-MMP) plays a crucial role in many physiological and pathological processes, especially in tumor invasion and metastasis. Bioimaging of this key molecule may find wide usage in various applications. MT-loop is a unique sequence of MT1-MMP and locates in the surface of the protein. In our previous studies, AF7p, an affinity peptide that targeting the MT-loop domain of MT1-MMP, was identified by screening a phage display (Ph.D.) peptide library. However, the target of AF7p is a synthetic sequence which lacked native conformation of the MT-loop region; thus, the binding affinity and specificity in reality may not be optimal. In this study, we considered the 3-dimensional (3-D) conformation of the MT-loop area in the MT1-MMP molecule and designed a novel strategy to screen the Ph.D. peptide library. The peptide we obtained showed a better binding affinity to WT-MT1-MMP than AF7p as observed through enzyme-linked immunosorbent assay (ELISA) and biolayer interferometry (BLI). The new peptide labeled and attached MT1-MMP expression cell lines HT1080 and did not show any toxicity to cells. Furthermore, for in vivo imaging, HT1080 tumor-bearing mice with higher MT1-MMP expression accumulated more Cy5.5-HS7 than mice with MT1-MMP low-expression cell lines A549 at tumor sites, and the half-life of HS7 was longer than that of AF7p, as confirmed by ex vivo imaging of the main organs. These results suggest the feasibility of using the subtraction biopanning strategy to screen the affinity peptide targeting MT-loop regions and HS7 is a superior probe for noninvasively imaging MT1-MMP expression in MT1-MMP-positive tumor models. It provides impetus for further studies to use HS7 in early diagnosis of tumors and in peptide-mediated drugs.

Quantum dots tethered membrane type 3 matrix metalloproteinase-targeting peptide for tumor optical imaging

Membrane type matrix metalloproteinases (MT-MMPs) play important roles in malignant tumor progression through the degradation of the extracellular matrix and signal transduction. However, a member of the family, MT3-MMP, has attracted the least concern compared with other MT-MMPs. Here, a novel MT3-MMP-targeting peptide with high affinity and specificity has been developed by a phage-display peptide screening technology and multiple biophysics measurements, including single-molecule recognition force spectroscopy and isothermal titration calorimetry. The binding peptides are conjugated on the surface of CdSe/ZnS quantum dots (QDs) and consequently acted as a ligand that specifically targets MT3-MMP overexpressed tumor cells. The imaging nanoprobes used QDs as the photographic developer for optical imaging in vivo. The nanoprobes exhibited a desirable targeting effect and generated good biodistribution profiles for visualization and imaging of MT3-MMP overexpressed tumor. The peptide could be useful to evaluate the distribution and expression of MT3-MMP. Furthermore, the peptide-functionalized QDs show potential application for cancer diagnosis.

The Precise Diagnosis of Cancer Invasion/Metastasis via 2D Laser Ablation Mass Mapping of Metalloproteinase in Primary Cancer Tissue

Cancer invasion and metastasis remain the major causes of over 90% of patient deaths. Molecular imaging methods such as computed tomography (CT)/magnetic resonance imaging (MRI) can precisely assess primary regional lymph node invasion and distant organ metastasis via body scanning; however, such diagnostic methods are often utilized too late for cancer therapy. To date, pathologic methods mainly provide information on differentiation/proliferation and potential drug therapy biomarkers of primary tumors rather than precisely reveal tumor regional invasion and distant metastasis in the body. We hypothesized that quantification of membrane type-1 matrix metalloproteinase (MT1-MMP) levels in primary tumor tissue will provide a precise assessment of tumor regional lymph node invasion and remote organ metastasis. In this work, we developed peptide-coated Au clusters with intrinsic red fluorescence and a specific mass signal. When these clusters labeled MT1-MMP in tumor tissue sections derived from the xenograft lung carcinoma model, human lung carcinoma and human renal carcinoma, we could directly observe MT1-MMP via optical fluorescence microscopy and quantitatively detect the MT1-MMP expression level via laser ablation inductively coupled plasma mass spectrometry 2D mapping (2D-LA-Mass Mapping). By observing and quantifying the MT1-MMP expression level in primary human lung carcinoma and human renal carcinoma tissue sections, we precisely assessed the risk of primary tumor invasion/metastasis. Importantly, the accuracy of this pathologic method was verified by CT/MRI molecular imaging of cancer patients and traditional hematoxylin and eosin (H&E) staining/immunohistochemistry (IHC)/immunofluorescence (IF) pathologic studies of primary tumor tissues.

MMP-2-responsive fluorescent nanoprobes for enhanced selectivity of tumor cell uptake and imaging

It is difficult to develop highly selective substrate-based fluorescent nanoprobes for specific matrix metalloproteinases (MMPs) due to overlapping substrate specificities among the family of MMP enzymes. To resolve this issue, we have developed novel fluorescent nanoprobes that are highly selective for soluble MMP-2. Herein, MMP-2-responsive nanoprobes were prepared by immobilizing fluorescent fusion proteins on nickel ferrite nanoparticles via the His-tag nickel chelation mechanism. The fusion protein consisted of a fluorescent mCherry protein with a cell penetrating peptide (CPP) moiety. An MMP-2 cleavage site was also introduced within the fusion protein, which was directly linked to the nickel ferrite nanoparticles. The selectivity of nanoprobes was modulated by hiding the cleavage site of MMP-2 substrates deeply inside the system, which could result in strong steric hindrance between the nanoprobes and MMPs, especially for membrane-tethered MMPs such as MMP-14. A cell-based assay demonstrated that the nanoprobes could only be activated by tumor cells secreting soluble MMP-2, but not membrane-tethered MMP-14. To further evaluate the contribution of the steric hindrance effect on the nanoprobes, a truncated recombinant MMP-14 was employed to confer their cleavage activity as compared to native membrane-tethered MMP-14. Furthermore, a designed probe with a diminished steric hindrance effect was proved to be activated by membrane-tethered type MMP-14. The results indicated that the design of fluorescent nanoprobes employing the steric hindrance effect can greatly enhance the selectivity of MMP-responsive nanoprobes realizing the specific detection of soluble MMP-2 in a tumor microenvironment. We believe that highly selective MMP-2-responsive fluorescent nanoprobes have broad impacts on biomedical applications including molecular imaging and labeling for tumor detection.

MT1-MMP as a PET Imaging Biomarker for Pancreas Cancer Management

Pancreatic ductal adenocarcinoma (PDAC) continues to be one of the deadliest cancers for which optimal diagnostic tools are still greatly needed. Identification of PDAC-specific molecular markers would be extremely useful to improve disease diagnosis and follow-up. MT1-MMP has long been involved in pancreatic cancer, especially in tumour invasion and metastasis. In this study, we aim to ascertain the suitability of MT1-MMP as a biomarker for positron emission tomography (PET) imaging. Two probes were assessed and compared for this purpose, an MT1-MMP-specific binding peptide (MT1-AF7p) and a specific antibody (LEM2/15), labelled, respectively, with ⁶⁸Ga and with ⁸⁹Zr. PET imaging with both probes was conducted in patient-derived xenograft (PDX), subcutaneous and orthotopic, PDAC mouse models, and in a cancer cell line (CAPAN-2)-derived xenograft (CDX) model. Both radiolabelled tracers were successful in identifying, by means of PET imaging techniques, tumour tissues expressing MT1-MMP although they did so at different uptake levels. The ⁸⁹Zr-DFO-LEM2/15 probe showed greater specific activity compared to the ⁶⁸Ga-labelled peptide. The mean value of tumour uptake for the ⁸⁹Zr-DFO-LEM2/15 probe (5.67 ± 1.11%ID/g, n=28) was 25-30 times higher than that of the ⁶⁸Ga-DOTA-AF7p ones. Tumour/blood ratios (1.13 ± 0.51 and 1.44 ± 0.43 at 5 and 7 days of ⁸⁹Zr-DFO-LEM2/15 after injection) were higher than those estimated for ⁶⁸Ga-DOTA-AF7p probes (of approximately tumour/blood ratio = 0.5 at 90 min after injection). Our findings strongly point out that (i) the in vivo detection of MT1-MMP by PET imaging is a promising strategy for PDAC diagnosis and (ii) labelled LEM2/15 antibody is a better candidate than MT1-AF7p for PDAC detection.

Optimization of a MT1-MMP-targeting Peptide and Its Application in Near-infrared Fluorescence Tumor Imaging

Membrane type 1 metalloproteinase (MT1-MMP) is an important regulator of cancer invasion, growth and angiogenesis, thus making it an attractive target for cancer imaging and therapy. A non-substrate peptide (MT1-AF7p) that bonded to the "MT-Loop" region of MT1-MMP was identified by using a phage-displayed peptide library and was used to image the MT1-MMP expression in vivo through optical imaging. However, the substrate in the screening did not have a 3D structure, thus resulting in a loose bonding of MT1-AF7p. To simulate the real conformation of the "MT-Loop" and improve the performance of MT1-AF7p, molecular simulations were performed, because this strategy provides multiple methods for predicting the conformation and interaction of proteinase in 3D. In view of the binding site of the receptor-ligand interactions, histidine 4 was selected for mutation to achieve an increased affinity effect. The optimized peptides were further identified and conformed by atomic force microscopy, isothermal titration calorimetry, cell fluorescence imaging in vitro, and near-infrared fluorescence tumor optical imaging in vivo. The results revealed that the optimized peptide with a mutation of histidine 4 to arginine has the highest affinity and specificity, and exhibited an increased fluorescence intensity in the tumor site in optical imaging.

Quantitative Analysis of Multiple Proteins of Different Invasive Tumor Cell Lines at the Same Single-Cell Level

Tumor cell invasion is pivotal to the development, metastasis, and prognosis of tumors. It is reported that the invasive ability of tumor cells is mainly dependent on the expression levels of membrane type-1 matrix metalloproteinase (MT1-MMP) and integrin α_V β₃ proteins on cell membranes. To precisely distinguish between tumor cells with different invasive abilities, it is important to establish a highly sensitive and precise quantification method to differentiate the expression levels of MT1-MMP and integrin α_V β₃ in the same single tumor cell at the same time. Herein, two functional peptides to construct red-emissive Au₂₆ clusters and green-emissive Ag₁₂ clusters are reported. Moreover, the Au₂₆ clusters and Ag₁₂ clusters have the ability to specifically target MT1-MMP and integrin α_V β₃ , respectively, in the same single cell at the same time. By utilizing the fluorescent properties and metallic compositions of metal clusters, the MT1-MMP and integrin α_V β₃ levels of the more invasive SiHa cells or the less invasive HeLa cells are simultaneously and quantitatively differentiated via laser ablation inductively coupled plasma mass spectrometry. This method of quantitatively detecting multiple invasive proteins on the same cell is of great value for accurately diagnosing aggressive tumors and monitoring the invasiveness of these tumors.

A hindsight reflection on the clinical studies of poly(l-glutamic acid)-paclitaxel

Chemotherapy for cancer treatment is limited by the excessive toxicity to normal tissues. The design of chemodrug-loaded nanoformulations provides a unique approach to improve the treatment efficacy while minimizing toxicity. Despite the numerous publications of nanomedicine for the last several decades, however, only a small fraction of the developed nanoformulations have entered clinical trials, with even fewer being approved for clinical application. Poly(l-glutamic acid)-paclitaxel (PG-TXL) belongs to the few formulations that reached phase III clinical trials. Unfortunately, the development of PG-TXL stopped in 2016 due to the inability to show significant improvement over current standard care. This review will provide an overview of the preclinical and clinical evaluations of PG-TXL, and discuss lessons to be learned from this ordeal. The precise identification of suitable patients for clinical trial studies, deep understanding of the mechanisms of action, and an effective academic-industry partnership throughout all phases of drug development are important for the successful bench-to-bedside translation of new nanoformulations. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Peptide-Based Structures.

MT1-MMP Responsive Doxorubicin Conjugated Poly(lactic-co-glycolic Acid)/Poly(styrene-alt-maleic Anhydride) Core/Shell Microparticles for Intrahepatic Arterial Chemotherapy of Hepatic Cancer

In this study, we demonstrated that the MT1-MMP-responsive peptide (sequence: GPLPLRSWGLK) and doxorubicin-conjugated poly(lactic-co-glycolic acid/poly(styrene-alt-maleic anhydride) core/shell microparticles (PLGA/pSMA MPs) can be applied for intrahepatic arterial injection for hepatocellular carcinoma (HCC). PLGA/pSMA MPs were prepared with a capillary-focused microfluidic device. The particle size, observed by scanning electron microscopy (SEM), was around 22 ± 3 μm. MT1-MMP-responsive peptide and doxorubicin (DOX) were chemically conjugated with pSMA segments on the shell of MPs to form a PLGA/pSMA-peptide-DOX complex, resulting in high encapsulation efficiency (91.1%) and loading content (2.9%). DOX was released from PLGA/pSMA-peptide-DOX MPs in a pH-dependent manner (∼25% at pH 5.4 and ∼8% at pH 7.4) and accumulated significantly in an MT1-MMP-overexpressing Hep3B cell line. An in vivo intrahepatic injection study showed localization of MPs on the hepatic vessels and hepatic lobes up to 24 h after the injection without any shunting to the lung. Moreover, MPs efficiently inhibited tumor growth of Hep3B hepatic tumor xenografted mouse models. We expect that PLGA/pSMA-peptide-DOX MPs can be utilized as an effective intrahepatic drug delivery system for the treatment of HCC.

Targeting MT1-MMP as an ImmunoPET-Based Strategy for Imaging Gliomas

BACKGROUND

A critical challenge in the management of Glioblastoma Multiforme (GBM) tumors is the accurate diagnosis and assessment of tumor progression in a noninvasive manner. We have identified Membrane-type 1 matrix metalloproteinase (MT1-MMP) as an attractive biomarker for GBM imaging since this protein is actively involved in tumor growth and progression, correlates with tumor grade and is closely associated with poor prognosis in GBM patients. Here, we report the development of an immunoPET tracer for effective detection of MT1-MMP in GBM models.

METHODS

An anti-human MT1-MMP monoclonal antibody (mAb), LEM2/15, was conjugated to p-isothiocyanatobenzyl-desferrioxamine (DFO-NCS) for 89Zr labeling. Biodistribution and PET imaging studies were performed in xenograft mice bearing human GBM cells (U251) expressing MT1-MMP and non-expressing breast carcinoma cells (MCF-7) as negative control. Two orthotopic brain GBM models, patient-derived neurospheres (TS543) and U251 cells, with different degrees of blood-brain barrier (BBB) disruption were also used for PET imaging experiments.

RESULTS

89Zr labeling of DFO-LEM2/15 was achieved with high yield (>90%) and specific activity (78.5 MBq/mg). Biodistribution experiments indicated that 89Zr-DFO-LEM2/15 showed excellent potential as a radiotracer for detection of MT1-MMP positive GBM tumors. PET imaging also indicated a specific and prominent 89Zr-DFO-LEM2/15 uptake in MT1-MMP+ U251 GBM tumors compared to MT1-MMP- MCF-7 breast tumors. Results obtained in orthotopic brain GBM models revealed a high dependence of a disrupted BBB for tracer penetrance into tumors. 89Zr-DFO-LEM2/15 showed much higher accumulation in TS543 tumors with a highly disrupted BBB than in U251 orthotopic model in which the BBB permeability was only partially increased. Histological analysis confirmed the specificity of the immunoconjugate in all GBM models.

CONCLUSION

A new anti MT1-MMP-mAb tracer, 89Zr-DFO-LEM2/15, was synthesized efficiently. In vivo validation showed high-specific-contrast imaging of MT1-MMP positive GBM tumors and provided strong evidence for utility of MT1-MMP-targeted immunoPET as an alternate to nonspecific imaging of GBM.

Radioiodinated Peptidic Imaging Probes for in Vivo Detection of Membrane Type-1 Matrix Metalloproteinase in Cancers

Membrane type-1 matrix metalloproteinase (MT1-MMP) plays pivotal roles in tumor progression and metastasis, and holds great promise as an early biomarker for malignant tumors. Therefore, the ability to evaluate MT1-MMP expression could be valuable for molecular biological and clinical studies. For this purpose, we aimed to develop short peptide-based nuclear probes because of their facile radiosynthesis, chemically uniform structures, and high specific activity, as compared to antibody-based probes, which could allow them to be more effective for in vivo MT1-MMP imaging. To the best of our knowledge, there have been no reports of radiolabeled peptide probes for the detection of MT1-MMP in cancer tissues. In this study, we designed and prepared four probes which consist of a MT1-MMP-specific binding peptide sequence (consisting of L or D amino acid isomers) and an additional cysteine (at the N or C-terminus) for conjugation with N-(m-[(123/125)I]iodophenyl) maleimide. We investigated probe affinity, probe stability in mice plasma, and probe biodistribution in tumor-bearing mice. Finally, in vivo micro single photon emission computed tomography (SPECT) imaging and ex vivo autoradiography were performed. Consequently, [(123)I]I-DC, a D-form peptide probe radioiodinated at the C-terminus, demonstrated greater than 1000-fold higher specific activity than previously reported antibody probes, and revealed comparably moderate binding affinity. [(125)I]I-DC showed higher stability as expected, and [(123)I]I-DC successfully identified MT1-MMP expressing tumor tissue by SPECT imaging. Furthermore, ex vivo autoradiographic analysis revealed that the radioactivity distribution profiles corresponded to MT1-MMP-positive areas. These findings suggest that [(123)I]I-DC is a promising peptide probe for the in vivo detection of MT1-MMP in cancers.

Imaging Matrix Metalloproteinase Activity Implicated in Breast Cancer Progression

Proteolysis has been cited as an important contributor to cancer initiation and progression. One can take advantage of tumor-associated proteases to selectively deliver imaging agents. Protease-activated imaging systems have been developed using substrates designed for hydrolysis by members of the matrix metalloproteinase (MMP) family. We presently describe approaches by which one can optically image matrix metalloproteinase activity implicated in breast cancer progression, with consideration of selective versus broad protease probes.

Hybrid graphene/Au activatable theranostic agent for multimodalities imaging guided enhanced photothermal therapy

Photothermal therapy (PTT) has been increasingly investigated. However, there are still challenges in strategies that can further enhance photoconversion efficiency and improve photothermal tumor ablation effect of current nanomaterials. Herein, we developed a fluorescent/photoacoustic imaging guided PTT agent by seeding Gold (Au) nanoparticles onto graphene oxide (GO). Near infrared dye (Cy5.5) labeled-matrix metalloproteinase-14 (MMP-14) substrate (CP) was conjugated onto the GO/Au complex (GA) forming tumor targeted theranostic probe (CPGA), whereCy5.5 fluorescent signal is quenched by Surface Plasmon Resonance (SPR) capacity from both GO and Au, yet it can boost strong fluorescence signals after degradation by MMP-14. The photothermal effect of GA hybrid was found significantly elevated compared with Au or GO alone. After intravenous administration of CPGA into SCC7 tumor-bearing mice, high fluorescence and PA signals were observed in the tumor area over time, which peaked at the 6 h time point (tumor-to-normal tissue ratio of 3.64 ± 0.51 for optical imaging and 2.5 ± 0.27 for PA imaging). The tumors were then irradiated with a laser, and an excellent tumor inhibition was observedwithoutrecurrence. Our studies further encourage applications of the hybrid nanocomposite for image-guided enhanced PTT in biomedical applications, especially in cancer theranostics.

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.

Development of a Radiolabeled Peptide-Based Probe Targeting MT1-MMP for Breast Cancer Detection

Breast cancer is one of the most frequent and aggressive primary tumors among women of all races. Matrix metalloproteinase (MMPs), a family of zinc- and calcium-dependent secreted or membrane anchored endopeptidases, is overexpressed in varieties of diseases including breast cancer. Therefore, noninvasive visualization and quantification of MMP in vivo are of great interest in basic research and clinical application for breast cancer early diagnosis. Herein, we developed a 99mTc labeled membrane type I matrix metalloproteinase (MT1-MMP) specific binding peptide, [99mTc]-(HYNIC-AF7p)(tricine)(TPPTS), for in vivo detection of MDA-MB-231 breast tumor by single photon emission computed tomography (SPECT). [99mTc]-(HYNIC-AF7p)(tricine)(TPPTS) demonstrated nice biostability and high MT1-MMP binding affinity in vitro and in vivo. Tumor-to-muscle ratio was found to reach to the highest (4.17±0.49) at 2 hour after intravenously administration of [99mTc]-(HYNIC-AF7P)(tricine)(TPPTS) into MDA-MB-231 tumor bearing mice. Overall, [99mTc]-(HYNIC-AF7P)(tricine)(TPPTS) demonstrated great potential for MT1-MMP targeted detection in vivo and it would be a promising molecular imaging probe that are probably beneficial to breast cancer early diagnoses.

Phosphoramidate-based peptidomimetic inhibitors of membrane type-1 matrix metalloproteinase

Membrane-type I matrix metalloproteinases (MT1-MMP) is an enzyme critical to the remodeling and homeostasis of extracellular matrix, and when over expressed it contributes to metastasis and cancer cell progression. Because of its role and implication as a biomarker that is upregulated in various cancers, MT1-MMP has become an attractive target for drug discovery. A small pilot library of peptidomimetics containing a phosphoramidate core as a zinc-binding group was synthesized and tested for inhibitory potency against MT1-MMP. From this library, a novel two residue peptidomimetic scaffold was identified that confers potency against MT1-MMP at submicromolar concentrations. The results of this study confirm that for this scaffold, valine is favored as a P1 residue and leucine in the P1' position. Furthermore, steric tolerance was observed for the N-terminus, thus implicating that a second-generation library could be constructed to extend the scaffold to P2 without concomitant loss of affinity within the MT1-MMP catalytic domain.

Development of Radiolabeled Membrane Type-1 Matrix Metalloproteinase Activatable Cell Penetrating Peptide Imaging Probes

Membrane type-1 matrix metalloproteinase (MT1-MMP or MMP-14) plays an important role in adverse cardiac remodelling. Here, we aimed to develop radiolabeled activatable cell penetrating peptides (ACPP) sensitive to MT1-MMP for the detection of elevated MT1-MMP levels in adverse cardiac remodelling. Three ACPP analogs were synthesized and the most potent ACPP analog was selected using MT1-MMP sensitivity and enzyme specificity assays. This ACPP, called ACPP-B, showed high sensitivity towards MT1-MMP, soluble MMP-2, and MT2-MMP, while limited sensitivity was measured for other members of the MMP family. In in vitro cell assays, radiolabeled ACPP-B showed efficient cellular uptake upon activation. A pilot in vivo study showed increased uptake of the radiolabeled probe in regions of infarcted myocardium compared to remote myocardium, warranting further in vivo evaluation.

New strategies for targeting matrix metalloproteinases

The development of matrix metalloproteinase (MMP) inhibitors has often been frustrated by a lack of specificity and subsequent off-target effects. More recently, inhibitor design has considered secondary binding sites (exosites) to improve specificity. Small molecules and peptides have been developed that bind exosites in the catalytic (CAT) domain of MMP-13, the CAT or hemopexin-like (HPX) domain of MT1-MMP, and the collagen binding domain (CBD) of MMP-2 and MMP-9. Antibody-based approaches have resulted in selective inhibitors for MMP-9 and MT1-MMP that target CAT domain exosites. Triple-helical “mini-proteins” have taken advantage of collagen binding exosites, producing a family of novel probes. A variety of non-traditional approaches that incorporate exosite binding into the design process has yielded inhibitors with desirable selectivities within the MMP family.

SORTCERY-A High-Throughput Method to Affinity Rank Peptide Ligands

Uncovering the relationships between peptide and protein sequences and binding properties is critical for successfully predicting, re-designing and inhibiting protein-protein interactions. Systematically collected data that link protein sequence to binding are valuable for elucidating determinants of protein interaction but are rare in the literature because such data are experimentally difficult to generate. Here we describe SORTCERY, a high-throughput method that we have used to rank hundreds of yeast-displayed peptides according to their affinities for a target interaction partner. The procedure involves fluorescence-activated cell sorting of a library, deep sequencing of sorted pools and downstream computational analysis. We have developed theoretical models and statistical tools that assist in planning these stages. We demonstrate SORTCERY's utility by ranking 1026 BH3 (Bcl-2 homology 3) peptides with respect to their affinities for the anti-apoptotic protein Bcl-xL. Our results are in striking agreement with measured affinities for 19 individual peptides with dissociation constants ranging from 0.1 to 60nM. High-resolution ranking can be used to improve our understanding of sequence-function relationships and to support the development of computational models for predicting and designing novel interactions.

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.

Monitoring and Inhibiting MT1-MMP during Cancer Initiation and Progression

Membrane-type 1 matrix metalloproteinase (MT1-MMP) is a zinc-dependent type-I transmembrane metalloproteinase involved in pericellular proteolysis, migration and invasion. Numerous substrates and binding partners have been identified for MT1-MMP, and its role in collagenolysis appears crucial for tumor invasion. However, development of MT1-MMP inhibitors must consider the substantial functions of MT1-MMP in normal physiology and disease prevention. The present review examines the plethora of MT1-MMP activities, how these activities relate to cancer initiation and progression, and how they can be monitored in real time. Examination of MT1-MMP activities and cell surface behaviors can set the stage for the development of unique, selective MT1-MMP inhibitors.

Visualization of protease activity in vivo using an activatable photo-acoustic imaging probe based on CuS nanoparticles

Herein, we for the first time report a novel activatable photoacoustic (PA) imaging nano-probe for in vivo detection of cancer-related matrix metalloproteinases (MMPs). A black hole quencher 3 (BHQ3) which absorbs red light is conjugated to near-infrared (NIR)-absorbing copper sulfide (CuS) nanoparticles via a MMP-cleavable peptide linker. The obtained CuS-peptide-BHQ3 (CPQ) nano-probe exhibits two distinctive absorption peaks at 630 nm and 930 nm. Inside the tumor microenviorment where MMPs present, the MMP-sensitive peptide would be cleaved, releasing BHQ3 from the CuS nanoparticles, the former of which as a small molecule is then rapidly cleared out from the tumor, whereas the latter of which as large nanoparticles would retain inside the tumor for a much longer period of time. As the result, the PA signal at 680 nm which is contributed by BHQ3 would be quickly diminished while that at 930 nm would be largely retained. The PA signal ratio of 680 nm / 930 nm could thus serve as an in vivo indicator of MMPs activity inside the tumor. Our work presents a novel strategy of in vivo sensing of MMPs based on PA imaging, which should offer remarkably improved detection depth compared with traditional optical imaging techniques.

Current microscopic methods for the neural ECM analysis

The extracellular matrix (ECM) occupies the space between both neurons and glial cells and thus provides a microenvironment that regulates multiple aspects of neural activities. Because of the vital role of ECM as a natural environment of cells in vivo, there is a growing interest to develop methodology allowing for the detailed structural and functional analyses of ECM. In this chapter, we provide the detailed overview of current microscopic methods used for ECM analysis and also describe general labeling strategies for ECM visualization. Since ECM remodeling involves the proteolytic cleavage of ECM, we will also describe current experimental approaches to image the proteolytic reorganization and/or degradation of ECM. The special focus of this chapter is set to the application of Förster resonance energy transfer-based approaches to monitor intracellular and extracellular matrix functions with high spatiotemporal resolution.

PET imaging of inflammation biomarkers

Inflammation plays a significant role in many disease processes. Development in molecular imaging in recent years provides new insight into the diagnosis and treatment evaluation of various inflammatory diseases and diseases involving inflammatory process. Positron emission tomography using (18)F-FDG has been successfully applied in clinical oncology and neurology and in the inflammation realm. In addition to glucose metabolism, a variety of targets for inflammation imaging are being discovered and utilized, some of which are considered superior to FDG for imaging inflammation. This review summarizes the potential inflammation imaging targets and corresponding PET tracers, and the applications of PET in major inflammatory diseases and tumor associated inflammation. Also, the current attempt in differentiating inflammation from tumor using PET is also discussed.

Noninvasive monitoring of pulmonary fibrosis by targeting matrix metalloproteinases (MMPs)

While idiopathic pulmonary fibrosis (PF) is a devastating lung disease, the management of PF including effective monitoring of disease progression remains a challenge. Herein, we introduce a novel, fast, and ultrasensitive metalloproteinase (MMP) activatable optical probe, named MMP-P12, to noninvasively monitor PF progression and response to PF treatment. A bleomycin (BLM)-induced mouse PF model was subjected noninvasively to optical imaging at various time points after BLM treatment. The mouse PF model developed fibrosis during 21 days of experimental period, and the progression of PF was well correlated with the stepwise increase of MMP-2 expression as examined by quantitative RT-PCR and Western blot analysis on the 7-, 14-, and 21-day post-BLM administration. On these days, MMP-activated fluorescence images were acquired in vivo and ex vivo. Signal quantification showed time-dependent lung-specific incremental increases in fluorescence signals. As a treatment for PF, secretoglobin 3A2 was daily administered intravenously for five days starting on day seven of BLM administration, which resulted in reduced MMP-2 activity and reduction of PF as previously demonstrated. Importantly, the fluorescence signal that reflected MMP activity also decreased in intensity. In conclusion, MMPs may play an important role in PF development and the MMP-P12 probe could be a promising tool for PF detection, even at an early stage of the disease as well as an indicator of therapy response.

Nanoparticles for Improving Cancer Diagnosis

Despite the progress in developing new therapeutic modalities, cancer remains one of the leading diseases causing human mortality. This is mainly attributed to the inability to diagnose tumors in their early stage. By the time the tumor is confirmed, the cancer may have already metastasized, thereby making therapies challenging or even impossible. It is therefore crucial to develop new or to improve existing diagnostic tools to enable diagnosis of cancer in its early or even pre-syndrome stage. The emergence of nanotechnology has provided such a possibility. Unique physical and physiochemical properties allow nanoparticles to be utilized as tags with excellent sensitivity. When coupled with the appropriate targeting molecules, nanoparticle-based probes can interact with a biological system and sense biological changes on the molecular level with unprecedented accuracy. In the past several years, much progress has been made in applying nanotechnology to clinical imaging and diagnostics, and interdisciplinary efforts have made an impact on clinical cancer management. This article aims to review the progress in this exciting area with emphases on the preparation and engineering techniques that have been developed to assemble "smart" nanoprobes.