Highly sensitive monitoring of telomerase activity in living cells based on rapidly triggered cascade amplification reaction

Paper-based electrochemiluminescence telomerase activity detection using hybridization chain reaction and CRISPR/Cas12a dual signal amplification

Sensitive telomerase activity detection becomes particularly significance since the important value of it in early cancer diagnosis as a potential biomarker. Herein, we developed a paper-based analytical devices (PADs) for telomerase activity detection, using positively charged Au@luminol nanoparticles ((+)Au@luminol NPs) as electrochemiluminescence (ECL) signal probe coupling with hybridization chain reaction (HCR) and CRISPR/Cas12a dual signal amplification. Firstly, the initial strong ECL signal was obtained based on the electrostatic adsorption of (+)Au@luminol NPs onto the surface of HCR double-stranded hybrid aggregates. In the presence of telomerase, the primer was efficiently elongated with telomeric repeats of (TTAGGG)n to release activator DNA and trigger the CRISPR/Cas12a, which can prevent the happen of HCR and the adsorption of (+)Au@luminol NPs through cleaving the capture probe on the electrode surface, such results directly inducing the decrease of the ECL signal that was proportional to telomerase concentration, due to the efficient signal amplification of HCR and CRISPR/Cas12a, a low detection limit of 2.3 cells/mL for telomerase could be detected. Moreover, the sensor realized the effective application for telomerase extracts analysis in human serum samples, making it possess potential application value for telomerase activity assays in cancer diagnostics.

A microfluidic chip incorporating magnetic sorting and invasive separation for isolation, culture and telomerase analysis of circulating tumor cells

Circulating tumor cells (CTCs) are a crucial indicator of cancer metastasis, and are vital for early diagnosis, disease monitoring, and treatment response evaluation. However, their extremely low concentration and the complexities of isolation techniques pose a significant challenge in capturing and analyzing CTCs. In this study, we developed a novel microfluidic system that integrates magnetic capture and invasive screening onto a single microfluidic chip. By attaching positively charged magnetic nanoparticles to negatively charged CTCs, the magnetic separation of CTCs within the chip effectively eliminates interference from blood cells. A total of 2 mL blood sample can be processed within 3 min, achieving an impressive tumor capture efficiency of 84 %. Using the chip, we also successfully achieved long-term culture of CTCs, and identified CTCs with high activity and invasive potential in blood samples from 11 patients with colorectal cancer. Finally, we analyzed telomerase activity in cultured CTCs on the microfluidic chip. Significantly higher invasive potential and telomerase activity were observed in CTCs from the malignant tumor group compared to the benign group (P < 0.01), highlighting their increased aggressiveness. This study offers a novel approach for efficient CTCs isolation, culture, and telomerase analysis, clarifying the crucial role of telomerase in tumor metastasis and providing profound insights for future research on telomerase-targeted tumor metastasis.

Simultaneous imaging of telomerase activity and protein tyrosine kinase 7 in living cells during epithelial-mesenchymal transformation via a near-infrared light-activatable nanoprobe

Exploring the relationship between key regulation molecules (such as telomerase and protein tyrosine kinase 7) during epithelial-mesenchymal transformation of cells is beneficial for studying malignant tumor metastasis. Fluorescence is usually used for real-time monitoring the distribution and expression of regulatory molecules in living cells. However, the recognition function of these classical nanoprobes is "always active" due to the absence of exogenous control, which leads to the amplification of both the background signal and the response signal, making it difficult to distinguish changes in biomolecule expression levels. To improve the fluorescence ratio between tumor and normal cells, we constructed near-infrared light-activatable nanoprobes by engineering the functional units of catalytic hairpin assembly and integrating upconversion luminescence nanoparticles. Under near-infrared light irradiation, the nanoparticles, serving as a near-infrared-to-ultraviolet light transducer, induced the photolysis of the photo-cleavable linkers sealed in hairpins. The recognition function of the nanoprobes can be controlled by near-infrared light, preventing them from recognizing the targets in non-irradiated regions. By employing the nanoprobes, we realized simultaneous imaging of two regulatory molecules in living cells and observed an increase in telomerase activity and a decrease in protein tyrosine kinase 7 expression during drug-induced epithelial-mesenchymal transformation. This work provides a promising method for revealing changes and relationships of regulatory molecules during tumor metastasis.

Rolling Circle Amplification Integrating with Exonuclease-III-Assisted Color Reaction for Sensitive Telomerase Activity Analysis

Telomerase activation can lead to the escape from cell senescence and immortalization, playing a crucial role in the growth and proliferation of cancer cells. Therefore, the detection of telomerase activity is essential for cancer diagnosis and treatment. Herein, we develop a novel ultrasensitive and visually detectable platform. By incorporation of exonuclease-III (Exo-III), this platform achieves dual signal amplification of rolling circle amplification products. Additionally, the colorimetric analysis of 3,3',5,5'-tetramethylbiphenyl (TMB) chromogenic reaction system provides this approach with unique advantages such as simplicity, speediness, and sensitivity. The detection platform exhibits high sensitivity and specificity in actual sample testing, which aligns closely with results obtained using commercial kits. Moreover, it offers ease-of-use through visual determination by the naked eyes. This finding indicates that our proposed sensing method performs satisfactorily in detecting telomerase in real biological samples. Henceforth, we believe that this sensing platform holds great potential for clinical diagnosis and anticancer drug development.

Establishment of highly metastatic sublines and insights into telomerase expression during tumor metastasis using a microfluidic system

Metastasis is an important hallmark of malignant tumors, and telomerase often exhibits high expression in these tumors. Monitoring the real-time dynamics of telomerase will provide valuable insights into its association with tumor metastasis. In this study, we described a microfluidic system for screening highly metastatic sublines based on differential cell invasiveness, investigated telomerase expression in the process of tumor metastasis and explored the genes and signaling pathways involved in tumor metastasis. Cells with different metastasis abilities were efficiently classified into different channels, and the fluorescence imaging visually demonstrates that cells with higher metastasis ability have stronger telomerase activity. In addition, we successfully established the high-metastasis-ability LoVo subline (named as LoVo-H) and low-metastasis-ability LoVo subline (named as LoVo-L) from the human colorectal cancer LoVo cell lines through only one round of selection using the system. The results show that the LoVo-H cells display superior proliferation and invasiveness compared to LoVo-L cells. Furthermore, 6776 differentially expressed genes of LoVo-H compared with LoVo-L were identified by transcriptome sequencing. The genes associated with telomerase activity, cell migration and the epithelial to mesenchymal transition were up-regulated in LoVo-H, and PI3K-Akt signaling pathway, extracellular matrix-receptor interaction and Rap1 signaling pathway were significantly enriched in LoVo-H. This microfluidic system is a highly effective tool for selecting highly metastatic sublines and the LoVo-H subline established through this system presents a promising model for tumor metastasis research. Furthermore, this work preliminarily reveals telomerase expression during tumor metastasis and provides a new strategy for studying tumor metastasis and cancer diagnosis.

Triple-helix molecular-switch-actuated rolling circle amplification and catalytic hairpin assembly multistage signal amplified fluorescent aptasensor for detection of aflatoxin B1

BACKGROUND

Mycotoxins, a class of secondary metabolites produced by molds, are widely distributed in nature and are very common in food contamination. Aflatoxin B1 (AFB1) is a highly stable natural mycotoxin, and many agricultural products are easily contaminated by AFB1, it is important to establish a sensitive and efficient AFB1 detection method for food safety. The fluorescence aptamer sensor has shown satisfactory performance in AFB1 detection, but most of the fluorescence aptasensors are not sensitive enough, so improving the sensitivity of the aptasensor becomes the focus of this work.

RESULTS

Herein, an innovative fluorescent aptasensor for AFB1 detection which is based on catalytic hairpin assembly (CHA) and rolling circle amplification (RCA) driven by triple helix molecular switch (THMS) is proposed. A functional single-strand with an AFB1 aptamer, here called an APF, is first designed to lock onto the signal transduction probe (STP), which separates from THMS when target AFB1 is present. Subsequently, STP initiates the RCA reaction along the circular probe, syntheses macro-molecular mass products through repeated triggering sequences, triggers the CHA reaction to produce a large number of H1-H2 structures, which causes FAM to move away from BHQ-1 and recover its fluorescence signal. The fluorescence signal from FAM at 520 nm was collected as the signal output of aptasensor in this work. With high amplification efficiency of RCA and CHA of the fluorescence sensor, resulting in a low LOD value of 2.95 pg mL-1(S/N = 3).

SIGNIFICANCE

The successful establishment of the sensor designed in this work shows that the cascade amplification reaction is perfectly applied in the fluorescent aptamer sensor, and the signal amplification through the reaction between DNA strands is a simple and efficient method. In addition, it's also important to remember that the aptasensor can detect other targets only by changing the sequence of the aptamer, without redesigning other DNA sequences in the reaction system.

Microfluidic Platforms for Real-Time In Situ Monitoring of Biomarkers for Cellular Processes

Cellular processes are mechanisms carried out at the cellular level that are aimed at guaranteeing the stability of the organism they comprise. The investigation of cellular processes is key to understanding cell fate, understanding pathogenic mechanisms, and developing new therapeutic technologies. Microfluidic platforms are thought to be the most powerful tools among all methodologies for investigating cellular processes because they can integrate almost all types of the existing intracellular and extracellular biomarker-sensing methods and observation approaches for cell behavior, combined with precisely controlled cell culture, manipulation, stimulation, and analysis. Most importantly, microfluidic platforms can realize real-time in situ detection of secreted proteins, exosomes, and other biomarkers produced during cell physiological processes, thereby providing the possibility to draw the whole picture for a cellular process. Owing to their advantages of high throughput, low sample consumption, and precise cell control, microfluidic platforms with real-time in situ monitoring characteristics are widely being used in cell analysis, disease diagnosis, pharmaceutical research, and biological production. This review focuses on the basic concepts, recent progress, and application prospects of microfluidic platforms for real-time in situ monitoring of biomarkers in cellular processes.

Recent advances in optical biosensing and imaging of telomerase activity and relevant signal amplification strategies

Telomerase as a new valuable biomarker for early diagnosis and prognosis evaluation of cancer has attracted much interest in the field of biosensors, cell imaging, and drug screening. In this review, we mainly focus on different optical techniques and various signal amplification strategies for telomerase activity determination. Fluorometric, colorimetry, chemiluminescence, surface-enhanced Raman scattering (SERS), and dual-mode techniques for telomerase sensing and imaging are summarized. Signal amplification strategies include two categories: one is nucleic acid-based amplification, such as rolling circle amplification (RCA), the hybridization chain reaction (HCR), and catalytic hairpin assembly (CHA); the other is nanomaterial-assisted amplification, including metal nanoclusters, quantum dots, transition metal compounds, graphene oxide, and DNA nanomaterials. Challenges and prospects are also discussed to provide new insights for future development of multifunctional strategies and techniques for in situ and in vivo analysis of biomarkers for accurate cancer diagnosis.

Current research status of tumor cell biomarker detection

With the annual increases in the morbidity and mortality rates of tumors, the use of biomarkers for early diagnosis and real-time monitoring of tumor cells is of great importance. Biomarkers used for tumor cell detection in body fluids include circulating tumor cells, nucleic acids, protein markers, and extracellular vesicles. Among them, circulating tumor cells, circulating tumor DNA, and exosomes have high potential for the prediction, diagnosis, and prognosis of tumor diseases due to the large amount of valuable information on tumor characteristics and evolution; in addition, in situ monitoring of telomerase and miRNA in living cells has been the topic of extensive research to understand tumor development in real time. Various techniques, such as enzyme-linked immunosorbent assays, immunoblotting, and mass spectrometry, have been widely used for the detection of these markers. Among them, the detection of tumor cell markers in body fluids based on electrochemical biosensors and fluorescence signal analysis is highly preferred because of its high sensitivity, rapid detection and portable operation. Herein, we summarize recent research progress in the detection of tumor cell biomarkers in body fluids using electrochemical and fluorescence biosensors, outline the current research status of in situ fluorescence monitoring and the analysis of tumor markers in living cells, and discuss the technical challenges for their practical clinical application to provide a reference for the development of new tumor marker detection methods.

Proximity ligation-transcription circuit-powered exponential amplifications for single-molecule monitoring of telomerase in human cells

We develop a new strategy for single-molecule monitoring of telomerase based on proximity ligation-transcription circuit-powered exponential amplifications. This strategy exhibits high sensitivity with a detection limit of 0.1 aM for the synthetic telomerase product TPC4 in vitro and 1 HeLa cell in vivo. Moreover, it can screen potential inhibitors, discriminate telomerase from interferents, and distinguish cancer cells from normal cells.