Peptide Microarray-Based Metal Enhanced Fluorescence Assay for Multiple Profiling of Matrix Metalloproteinases Activities

Development of a peptide microarray-based metal-enhanced fluorescence assay for ultrasensitive detection of multiple matrix metalloproteinase activities by using a gold nanorod-polymer substrate

Matrix metalloproteinases (MMPs) are attractive biomarkers for cancer diagnosis and treatment, while it is still a challenge to precise analysis of MMP activities owing to their very low abundance in the biological samples, especially at the early stages of tumors. Herein, a peptide microarray-based metal-enhanced fluorescence assay (PMMEFA) is proposed to simultaneously detect MMP-1, -2, -3, -7, -9, and -13 activities. The assay involves immobilization of Förster resonance energy transfer dye pair decorated peptides (FRET-peptides) on a poly(glycidyl methacrylate-co-2-hydroxyethyl methacrylate) coated gold nanorod modified glass slide (GNR@P(GMA-HEMA)). To fabricate the GNR@P(GMA-HEMA) slide, GNRs are self-assembled onto an aminated glass slide, and a polymer brush (P(GMA-HEMA)) is grown through a surface-initiated atom transfer radical polymerization reaction (SI-ATRP). Upon the addition of MMPs, the FRET pairs are broken due to the specific cleavage of FRET-peptides by enzymes, resulting in the recovery of fluorescence signals and further enhancement by the MEF of GNRs. The fluorescence recovery degree provides a direct indicator for MMP activity. The PMMEFA exhibits excellent sensitivity, which enables to detect MMP-1, -2, -3, -7, -9, and -13 activities, with low limits of detection (LODs) of 1.7 fg mL-1, 0.3 fg mL-1, 2.0 fg mL-1, 1.8 fg mL-1, 2.2 fg mL-1 and 14.0 fg mL-1, respectively. To substantiate the practicability of PMMEFA, MMP activities were measured in a range of matrices, encompassing cell culture medium, serum, and tumor tissue homogenate, and MMP activities can be detected only in 0.15 μL serum and 0.025 mg tumor tissue.

Signal-On Mass Spectrometric Biosensing of Multiplex Matrix Metalloproteinases with a Phospholipid-Structured Mass-Encoded Microplate

The detection of matrix metalloproteinases (MMPs) is of great importance for diagnosis and staging of cancer. This work proposed a signal-on mass spectrometric biosensing strategy with a phospholipid-structured mass-encoded microplate for assessment of multiplex MMP activities. The designed substrate and internal standard peptides were subsequently labeled with the reagents of isobaric tags for relative and absolute quantification (iTRAQ), and DSPE-PEG(2000)maleimide was embedded on the surface of a 96-well glass bottom plate to fabricate the phospholipid-structured mass-encoded microplate, which offered a simulated environment of the extracellular space for enzyme reactions between MMPs and the substrates. The strategy achieved multiplex MMP activity assays by dropping the sample in the well for enzyme cleavages, followed by adding trypsin to release the coding regions for ultrahigh performance liquid chromatography-tandem mass spectrometric (UHPLC-MS/MS) analysis. The peak area ratios of released coding regions and their respective internal standard (IS) peptides exhibited satisfied linear ranges of 0.05-50, 0.1-250, and 0.1-100 ng mL^-1 with the detection limits of 0.017, 0.046, and 0.032 ng mL^-1 for MMP-2, MMP-7, and MMP-3, respectively. The proposed strategy demonstrated good practicability in inhibition analysis and detections of multiplex MMP activities in serum samples. It is of great potential for clinical applications and can be expanded for multiplex enzyme assays.

Profiling of Multiple Matrix Metalloproteinases Activities in the Progression of Osteosarcoma by Peptide Microarray-Based Fluorescence Assay on Polymer Brush-Coated Zinc Oxide Nanorod Substrate

Peptide microarray provides the ability to miniaturize, parallelize, and automate high-throughput screening substrate specificities of enzymes, profiling of multiple enzyme activities, discovery of disease biomarkers, and development of drugs. Matrix metalloproteinases (MMPs) are demonstrated as important biomarkers of tumor invasion and metastasis. Herein, a peptide microarray-based fluorescence assay is proposed to profile multiple MMPs (MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, and MMP-13) activities in the culture medium of four human osteosarcoma (OS) cells and in the progression of OS by using the mouse-bearing xenograft OSs including U-2OS and Saos-2 human. This method has excellent selectivity and sensitivity, which enables to detect the activities of cellular secreted MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, and MMP-13 with limit of detection downs to 10 pM, 30 pM, 113 pM, 13 pM, 93 pM, and 12 pM, respectively. Furthermore, it is demonstrated that the activity pattern of MMPs is serum closely relevant to the disease progression and type of tumor.

Peptide Array-Based In Situ Fluorescence Assay for Profiling Multiple Matrix Metalloproteinase Activities

Peptide array-based in situ fluorescence assay is a reliable and efficient technique for high-throughput profiling and localization of enzyme activity. Here, peptide array is fabricated by spotting five specific MMPs (MMP-2, MMP-3, MMP-7, MMP-9, and MMP-14) peptide substrates containing FAM/Dabcyl fluorescent resonance energy transfer (FRET) pair on the surface of cell monolayers or tissue sections. MMP activities are determined in situ by the fluorescence intensity of stained cells/tissues due to the cellular internalization of hydrolyzed peptide fragments with FAM moieties. Identification of MMP expression patterns of cells, highly sensitive determination of MMP activities in cell monolayer (as low as hundreds of cells per square centimeter), and evaluation of inhibition potencies of six compounds toward five MMPs are achieved by this method. Five MMP activities in the localized parts of 32 thyroid tissues are also well profiled without separation or extraction procedures.

Label-free OIRD microarray chips with a nanostructured sensing interface: enhanced sensitivity and mechanism

Oblique-incidence reflectivity difference (OIRD) is a novel optical technique for protein microarray detection with the characteristics of being real-time, label-free, high-throughput and compatible with arbitrary chip substrates. It is necessary yet challenging to improve the sensitivity of the OIRD microarray and gain a clear understanding of the enhancement mechanism for practical applications. In this study, we report a microarray chip specifically designed for OIRD to improve its sensitivity by using an electrochemically etched nanostructured fluorine-doped tin oxide (FTO) slide as the substrate. Compared with chips printed on a conventional glass slide and pristine FTO, the OIRD sensitivity and signal-to-noise ratio of this microarray are significantly improved, reaching a limit of detection (LOD) as low as 50 ng mL^-1 for the streptavidin target in 10% human serum, which is one order of magnitude lower than that of the glass-based chip. On-chip ELISA and theoretical calculation reveal that the enhanced sensitivity is not only because of its higher capture efficiency towards the target, but also benefits from the optical enhancement enabled by its unique nanostructured sensing interface. This work provides a new universal strategy for designing high performance OIRD-based chips via rational interfacial engineering, thus paving the way to a label-free OIRD immunoassay and real-time analysis of biomolecular interactions.

In situ ratiometric SERS imaging of intracellular protease activity for subtype discrimination of human breast cancer

Accurate discrimination between different cells at the molecular level is of fundamental importance for disease diagnosis. Endogenous proteases are such molecular candidates for cancer cell subtype study. But in situ probing their activity in live cells remains challenging for surface-enhanced Raman scattering (SERS). Here, we present a sensitive ratio-type SERS nanoprobe for imaging of matrix metalloproteinase-2 (MMP-2) in different cancer cells subtypes. The nanoprobe contained three components: a plasmon-active gold nanoparticle as the SERS enhancing matrix, Raman dye rhodamine B (Rh B)-labelled substrate peptides as the specific MMP-2 recognizer, and 2-naphthalenethiol (2-NT) as the internal standard. MMP-2-responsive cleavage of peptides from the nanoprobe surface results in decrease or even disappearance of SERS emission of Rh B, which was ratioed over the emission of 2-NT for the quantification of MMP-2 activity. Both in-tube assay and in-cell imaging results show that the MMP-responsive nanoprobe can work and serve to differentiate the normal breast cells from the tumorous ones, to differentiate two breast cancer cell subtypes with a different degree of malignancy. We believe that this SERS nanoprobe could find a wide application in the fields of tumor biology and accurate disease diagnosis.

In Situ Protease Secretion Visualization and Metastatic Lymph Nodes Imaging via a Cell Membrane-Anchored Upconversion Nanoprobe

Matrix metalloproteinase (MMP) secretion is highly associated with tumor invasion and metastasis; therefore, monitoring MMP secretion is important for disease progression study and therapy choosing. Though working well for intracellular MMP imaging, the performance of current MMP detection probes is impaired in secretion monitoring due to the diffusion of MMP in an extracellular environment after secretion and low secreted amount. Here, we design a cell membrane-anchored ratiometric upconversion nanoprobe (UCNPs-Cy3/Pep-QSY7/Ab) for in situ MMP secretion visualization. Anti-EGFR is functionalized on the nanoprobe to provide specific recognition to tumor cells and guarantee fast response to MMP2 in the local place of secretion. MMP-responsive cleavage of Pep-QSY7 results in Cy3 luminescence recovery at 580 nm, which is ratioed over an internal standard of UCNP emission at 654 nm for MMP2 detection. The presented cell membrane-anchored ratiometric upconversion nanoprobe demonstrated that satisfactory results for in situ monitoring of MMP2 secretion from MDA-MB-231 cells and MCF-7 cells, as well as in vivo imaging of metastatic lymph nodes, would provide a universal platform for protease secretion study and contribute to tumor invasiveness assessment.

Biosensors and bioassays for determination of matrix metalloproteinases: state of the art and recent advances

Matrix metalloproteinases (MMPs) are closely associated with various physiological and pathological processes, and have been regarded as potential biomarkers for severe diseases including cancer. Accurate determination of MMPs would advance our understanding of their roles in disease progression, and is of great significance for disease diagnosis, treatment and prognosis. In this review, we present a comprehensive overview of the developed bioassays/biosensors for detection of MMPs, and highlight the recent advancement in nanomaterial-based immunoassays for MMP abundance measurements and nanomaterial-based biosensors for MMP activity determination. Enzyme-linked immunosorbent assay (ELISA)-based immunoassays provide information about total levels of MMPs with high specificity and sensitivity, while target-based biosensors measure the amounts of active MMPs, and allow imaging of MMP activities in vivo. For multiplex and high-throughput analysis of MMPs, microfluidics and microarray-based assays are described. Additionally, we put forward the existing challenges and future prospects from our perspective.

TNRC6C Functions as a Tumor Suppressor and Is Frequently Downregulated in Papillary Thyroid Cancer

Our previous study found that trinucleotide repeat containing adaptor 6C (TNRC6C) may act as a tumor suppressor in papillary thyroid cancer (PTC). In this study, we aimed to confirm the effect of TNRC6C on PTC and investigate the underlying molecular mechanism. The difference of mRNA level of TNRC6C between PTC tissue and noncancerous thyroid tissue and the association of expression level of TNRC6C with clinicopathological features of PTC were analyzed using TCGA data. Immunohistochemical assay was performed to detect the protein expression of TNRC6C in PTC and its adjacent noncancerous tissue. Cell proliferation, migration, invasion, and apoptosis were analyzed after knockdown or overexpression of TNRC6C in BCPAP cells. RNA-sequencing was performed to find the target genes of TNRC6C, and potential targets were validated in BCPAP and TPC1 cells. Our results showed that TNRC6C was downregulated in PTC, and lower expression level of TNRC6C was associated with worse clinicopathological features. Overexpression of TNRC6C significantly inhibited proliferation, migration, and invasion of BCPAP cells and promoted its apoptosis, while knockdown of TNRC6C acted the opposite role. By analyzing RNA-sequencing data and TCGA data, 12 genes (SCD, CRLF1, APCDD1L, CTHRC1, PTPRU, ALDH1A3, VCAN, TNC, ECE1, COL1A1, CAMK2N2, and MMP14) were considered as potential target genes of TNRC6C, and most of them were associated with clinicopathological features of PTC in TCGA. All of them except CAMK2N2 were significantly downregulated after overexpressing TNRC6C. Our study demonstrated that TNRC6C functions as a tumor suppressor in PTC and may serve as a useful therapeutic target and prognostic marker for PTC patients.

Electrochemical impedance spectroscopy for quantization of matrix Metalloproteinase-14 based on peptides inhibiting its homodimerization and heterodimerization

We reported here two novel electrochemical impedance spectroscopy biosensors were developed for the first time for highly sensitive quantification of matrix metalloproteinase-14 (MMP-14) based on binding interaction between hemopexin-like domain (PEX) of MMP-14 (PEX-14) and its inhibitory peptides. Specific inhibitory peptides (IVSC or ISC) inhibiting homodimerization or heterodimerization of MMP-14 was first self assembled on the surface of gold electrode and blocked with 6-mercapto-1-hexanol on a gold electrode surface used as IVSC or ISC modified biosensor, respectively. IVSC modified biosensor can be used for detection of MMP-14 by using the direct IVSC-MMP-14 interaction inhibiting MMP-14 homodimerization as well as ISC modified biosensor for indirect detection of MMP-14 via PEX-14 mediated peptide-MMP-14 binding. The electron transfer resistance (R_et) of biosensor was monitored to measure MMP-14 using Fe(CN)₆^3-/4- as probe. The increase of the R_et of the biosensors are linear with the concentration of MMP-14 in the range from 1 μg L^-1 to 10 μg L^-1 with detection limit of 0.19 μg L^-1 for IVSC modified biosensor and 0.1 ng L^-1 to 50 ng L^-1 with detection limit of 7 ng L^-1 for ISC modified biosensor. This work demonstrates that probing the interaction between peptide inhibitor and PEX of MMPs represents a novel approach to assess MMPs-mediated cancer dissemination.

Towards precision medicine: the role and potential of protein and peptide microarrays

Techniques to comprehensively analyze protein signatures are pivotal to unravel disease mechanisms, develop novel biomarkers and targeted therapies. In this frame, protein and peptide microarrays can play a major role in fuelling precision medicine.

Amperometric Biosensor of Matrix Metalloproteinase-7 Enhanced by Pd-Functionalized Carbon Nanocomposites

Matrix metalloproteinase-7 plays a pivotal role in tumour progression and metastasis as an enzyme that can degrade the cell-matrix composition and cleave peptides between alanine and leucine in various biomolecular activation processes. In this work, a Pd-functionalised carbon nanocomposite was designed as a new impedance enhancer for an amperometric sensor of MMP-7. Pd nanoparticles in the enhancer can catalyse the oxidation of 4-chloro-1-naphthol with H₂O₂ to generate insoluble precipitation in situ, forming high-resistance precipitation on electrodes. In addition, poorly conductive carbon nanospheres of the nanocomposite increased the precipitation resistance, further causing a dramatic increase in resistivity of the enhancer and, subsequently, a significant decrease in current. This can significantly promote the current signal difference between the biosensor treated with and without the target analyte, which is directly related to the sensitivity of the amperometric biosensor. Overall, electrochemical biosensor can sensitively detect MMP-7 in the range of 100 fg mL^-1 to 100 ng mL^-1 with a limit of detection for MMP-7 of 17.38 fg mL^-1.