Detection of circulating tumor-associated antigen depends on the domains recognized by the monoclonal antibodies used: N-terminal trimmed EpCAM-levels are much higher than untrimmed forms

Graphene/MoS2 Nanohybrid for Biosensors

Graphene has been studied a lot in different scientific fields because of its unique properties, including its superior conductivity, plasmonic property, and biocompatibility. More recently, transition metal dicharcogenide (TMD) nanomaterials, beyond graphene, have been widely researched due to their exceptional properties. Among the various TMD nanomaterials, molybdenum disulfide (MoS2) has attracted attention in biological fields due to its excellent biocompatibility and simple steps for synthesis. Accordingly, graphene and MoS2 have been widely studied to be applied in the development of biosensors. Moreover, nanohybrid materials developed by hybridization of graphene and MoS2 have a huge potential for developing various types of outstanding biosensors, like electrochemical-, optical-, or surface-enhanced Raman spectroscopy (SERS)-based biosensors. In this review, we will focus on materials such as graphene and MoS2. Next, their application will be discussed with regard to the development of highly sensitive biosensors based on graphene, MoS2, and nanohybrid materials composed of graphene and MoS2. In conclusion, this review will provide interdisciplinary knowledge about graphene/MoS2 nanohybrids to be applied to the biomedical field, particularly biosensors.

Efficient expression of EpEX in the cytoplasm of Escherichia coli using thioredoxin fusion protein

Recombinant epithelial cell adhesion molecule extracellular domain (EpEX) has a high potential as a candidate for passive and active immunotherapy as well as cancer vaccination. In the present study, EpEX was expressed as a thioredoxin fusion protein in Escherichia coli (E. coli). The effect of different hosts and expression conditions on the expression level of the fusion protein was also evaluated. Moreover, the effect of temperature and isopropyl-β-d-thiogalactopyranoside (IPTG) concentration on protein solubility was assessed. The codon optimized-synthetic gene was cloned into pET32a (+) expression vector and transformed into E. coli BL21 (DE3), Rosetta™ (DE3), and Origami™ (DE3). The protein expression was confirmed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting. Lowering the expression temperature to 16 °C and IPTG concentration to 0.5 mM also dramatically increased the volumetric productivity of the fusion protein. In optimum culture condition, high-level expression of the target fusion protein was detected in Rosetta™ (DE3) and Origami™ (DE3) (207 and 334 μg/mL, respectively), though they were expressed as inclusion bodies. No improvement was observed in the solubility of the fusion protein by reducing the temperature or IPTG concentration even when expressed in a TrxB/gor mutant strain. Results showed that Trx tag combined with other strategies utilized here could be effective to achieve high level of protein production but not effective in solubility improvement. However, new approaches might be necessary to enhance the solubility of EpEX in the E. coli system.

Enzyme-free ultrasensitive fluorescence detection of epithelial cell adhesion molecules based on a toehold-aided DNA recycling amplification strategy

Epithelial cell adhesion molecules (EpCAMs) play a significant role in tumorigenesis and tumor development. EpCAMs are considered to be tumor signaling molecules for cancer diagnosis, prognosis and therapy. Herein, an enzyme-free and highly sensitive fluorescent biosensor, with a combined aptamer-based EpCAM recognition and toehold-aided DNA recycling amplification strategy, was developed for sensitive and specific fluorescence detection of EpCAMs. Due to highly specific binding between EpCAMs and corresponding aptamers, strand a, which is released from the complex of aptamer/strand a in the presence of EpCAMs which is bound to the corresponding aptamer, triggered the toehold-mediated strand displacement process. An amplified fluorescent signal was achieved by recycling strand a for ultrasensitive EpCAM detection with a detection limit as low as 0.1 ng mL-1, which was comparable or superior to that of reported immunoassays and biosensor strategies. In addition, high selectivity towards EpCAMs was exhibited when other proteins were selected as control proteins. Finally, this strategy was successfully used for the ultrasensitive fluorescence detection of EpCAMs in human serum samples with satisfactory results. Importantly, the present strategy may be also expanded for the detection of other targets using the corresponding aptamers.

A fluorescence turn-on biosensor based on graphene quantum dots (GQDs) and molybdenum disulfide (MoS2) nanosheets for epithelial cell adhesion molecule (EpCAM) detection

This paper presents a "turn-on" fluorescence biosensor based on graphene quantum dots (GQDs) and molybdenum disulfide (MoS₂) nanosheets for rapid and sensitive detection of epithelial cell adhesion molecule (EpCAM). PEGylated GQDs were used as donor molecules, which could not only largely increase emission intensity but also prevent non-specific adsorption of PEGylated GQD on MoS₂ surface. The sensing platform was realized by adsorption of PEGylated GQD labelled EpCAM aptamer onto MoS₂ surface via van der Waals force. The fluorescence signal of GQD was then quenched by MoS₂ nanosheets via fluorescence resonance energy transfer (FRET) mechanism. In the presence of EpCAM protein, the stronger specific affinity interaction between aptamer and EpCAM protein could detach GQD labelled EpCAM aptamer from MoS₂ nanosheets, leading to the restoration of fluorescence intensity. By monitoring the change of fluorescence signal, the target EpCAM protein could be detected sensitively and selectively with a linear detection range from 3nM to 54nM and limit of detection (LOD) around 450pM. In addition, this nanobiosensor has been successfully used for EpCAM-expressed breast cancer MCF-7 cell detection.

Detection of soluble EpCAM (sEpCAM) in malignant ascites predicts poor overall survival in patients treated with catumaxomab

EpCAM is an attractive target for cancer therapy and the EpCAM-specific antibody catumaxomab has been used for intraperitoneal treatment of EpCAM-positive cancer patients with malignant ascites. New prognostic markers are necessary to select patients that mostly benefit from catumaxomab. Recent data showed that soluble EpCAM (sEpCAM) is capable to block the effect of catumaxomab in vitro. This exploratory retrospective analysis was performed on archived ascites samples to evaluate the predictive role of sEpCAM in catumaxomab-treated patients. Sixty-six catumaxomab-treated patients with an available archived ascites sample were included in this study and tested for sEpCAM by sandwich ELISA. All probes were sampled before treatment start and all patients received at least one catumaxomab infusion. Overall survival, puncture-free survival and time to next puncture were compared between sEpCAM-positive and -negative patients. We detected sEpCAM in ascites samples of 9 patients (13.6%). These patients showed a significantly shorter overall survival. The prognostic significance of sEpCAM in ascites was particularly strong in patients with ovarian cancer. Puncture-free survival and time to next puncture were not significantly different between sEpCAM-positive and -negative patients. We propose sEpCAM in malignant ascites as a potential predictive marker in cancer patients treated with catumaxomab. Prospective studies with larger patients samples are urgently needed to confirm these findings and studies testing dose-intensified catumaxomab in patients with sEpCAM-positive ascites should be envisaged.

Cysteine-poor region-specific EpCAM monoclonal antibody recognizing native tumor cells with high sensitivity

EpCAM is a ∼40 kDa transmembrane glycoprotein. EpCAM overexpression is a popular trait of almost all carcinomas and is considered as a targeted cancer immunotherapy as well as a practical marker for circulating tumor cells (CTC). Its extracellular part (EpEx) consists of an N-terminal EGF-like (EGF) domain, a TY-like (TY) domain, and an uncharacterized cysteine-poor (CP) region. Most commercially available murine monoclonal antibodies (MAbs) to EpCAM, such as HEA 125 and VU-1D9, bind to the small EGF domain. In a previous study, we introduced iCeap (intact CTC enumeration and analysis procedure), keeping cellular integrity during the whole process. Unlike the CellSearch(®) CTC Test, iCeap enables downstream molecular analysis from detected CTC. Use of two EpCAM MAbs, one for immunomagnetic enrichment of rare CTC from blood samples and the other for labeling, is a concept of iCeap while an ideal MAb pair has not been found. In order to obtain a better MAb that recognizes a part of EpEx as different from EGF domain, we established a mouse hybridoma clone producing a new EpCAM MAb, KIJY2. Fluorophore-conjugated KIJY2 and HEA 125-FITC can concomitantly stain the tumor cell line LNCaP within indistinguishable cellular compartments (i.e., the cell surface). Epitope mapping reveals that KIJY2 binds to the CP region. The epitope for KIJY2 is sensitive to paraformaldehyde fixation, but native cells including MCF-7 (EpCAM high-expressing cell line) and PC-3 (EpCAM low and heterogeneously expressing cell line) are detected by KIJY2. In particular, KIJY2 detects all PC-3 cells regardless of their EpCAM expression levels. Therefore, KIJY2 and an EGF domain-directed MAb are a promising pair to form the EpCAM sandwich in iCeap. We demonstrate that KIJY2 incorporated into iCeap yielded favorable results in spike-in experiments of MCF-7 and PC-3.