A PCR-free colorimetric strategy for visualized assay of telomerase activity

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.

Sensitive bioanalytical methods for telomerase activity detection: a cancer biomarker

Telomerase is an enzyme that protects the length of telomeres by adding guanine-rich repetitive sequences. In tumors, gametes, and stem cells, telomerase activity is exerted. Telomerase activity can be a cancer biomarker for therapeutic and diagnosis approaches. So, a number of studies concentrating on the discovery of telomerase activity were reported. Bioanalytical devices, in comparison with other tests, have numerous advantages including low expense, simplicity, and excellent sensitivity and specificity. In this article we reviewed recent studies on the subject of various bioanalytical methods based on different nanomaterials. Optical, electrochemical, and quartz crystal microbalance (QCM) are prominent analytical techniques that are mentioned in this paper.

BODIPY-based metal-organic frameworks as efficient electrochemiluminescence emitters for telomerase detection

A boron dipyrromethene (BODIPY)-based metal-organic framework (MOF) nanoemitter was for the first time designed with enhanced electrochemiluminescence (ECL) intensity due to the suppression of non-radiative dissipation originating from the ordered arrangement of BODIPY molecules in the framework. Thus, an ECL biosensor was developed for telomerase detection with excellent performance in real samples.

A scalable and reproducible preparation for the antitumor protein TLC, a human-derived telomerase inhibitor

Telomerase, which is overexpressed in approximately 90% of liver cancer cells, is an ideal target for anti-liver cancer therapy. LPTS, a putative liver tumor suppressor, is the only human-derived protein that can bind telomerase directly and inhibit the extension of telomere activity. Our previous studies demonstrated that TAT-LPTS-LC (TLC), a recombinant protein fused by the C-terminal 133-328 fragment of LPTS and TAT peptides, could be delivered into cells to inhibit telomerase-positive hepatoma cell growth in vitro and in vivo with very low toxicity. In the present study, E. coli strains which expressed TLC in abundance were screened and cultured in a laboratory bioreactor. A reproducible protein separation process was built, and this process was suitable for industrial amplification. The yields of TLC protein were up to 184 mg in one batch with a purity of approximately 95%. The purified TLC protein had a similar inhibitory effect on telomerase activity in vitro compared with those purified by Ni-affinity chromatography. Furthermore, TLC protein could be delivered into the cell nucleus to increase the doubling time of the cell and suppress cell growth in telomerase-positive liver cancer cell lines. Cell growth inhibition was negatively correlated with telomere length, suggesting that TLC is a highly targeted telomerase-telomere anticancer agent. These results will contribute to future preclinical studies of the TLC protein.

Nucleic acid-driven aggregation-induced emission of Au nanoclusters for visualizing telomerase activity in living cells and in vivo

Visual monitoring of telomerase activity in living cancer cells and in vivo is essential for clinical diagnosis and treatment. However, most detection methods were performed in vitro due to the difficulty of probes entering cells and the interferences from complex biological environments. Herein, we developed a novel probe based on Au nanoclusters (AuNCs) with a nucleic acid-driven aggregation-induced emission (AIE) property for the first time. The probe was applied for detection of telomerase with high sensitivity. Importantly, the probe could achieve telomerase imaging in living cells and in solid tumor tissue in vivo. The study provided a specific connection fashion of metal nanoclusters for AIE generation. It holds great potential for the development of AIE-active metal nanoclusters as a diagnostic tool for disease detection in vitro as well as in vivo.

An all-in-one telomerase assay based on CRISPR-Cas12a trans-cleavage while telomere synthesis

As one of the crucial factors associated with human life span and cancer progression, telomerase is regarded as an emerging biomarker for cancer diagnosis. Therefore, a facile, rapid and sensitive approach for telomerase activity detection with point-of-care (POC) diagnosis potential is in great demands. Herein, an all-in-one telomerase activity detection assay was established based on the telomere synthesis activated CRISPR-Cas12a system. A telomerase extension reaction generated telomere repeats sequences (TTAGGG)_n, which was recognized by a customized CRISPR-guided RNA (crRNA) simultaneously, and finally activated a typical trans-cleavage based CRISPR-Cas12a detection assay. With the inherent sensitivity of CRISPR-Cas12a, this approach achieved a great linear regression ranging from 100 to 2000 HeLa cells and a limitation of detection down to 26 HeLa cells. Moreover, by using the proposed method, telomerase can be detected in one pot under isothermal condition (37 °C) by a simple and fast workflow (one step within 1 h). Due to its excellent performance, this all-in-one method shows great potential in POC detection of the telomerase activity.

Gelatin nanoparticles transport DNA probes for detection and imaging of telomerase and microRNA in living cells

Telomerase and microRNA (miRNA) are biomarkers closely related to tumors. Simultaneous detection of both markers can improve accuracy and reliability of early diagnosis. Based on the mechanism of fluorescence resonance energy transfer (FRET), two fluorescent DNA probes were designed for telomerase and miRNA-21. The probes were wrapped by gelatin through electrostatic interaction to form nanoparticles. After that, we synthesized molecularly imprinted coating of transferrin on the surface of gelatin nanoparticles, which can avoid the immune stress response and macrophage phagocytosis to help gelatin nanoparticles enter into the cells smoothly through endocytosis. Following with the degradation of gelatin in the cells, DNA probes were released to react with telomerase and miRNA-21 and lead to the change of the fluorescence signal. Thereby the simultaneous imaging of telomerase and miRNA-21 were successfully achieved in HeLa cells and HepG2 cells. The proposed strategy shows the simultaneous imaging for different biological markers with DNA probes by preventing them from being hydrolyzed with nucleases before the determination and achieves reliable method for early diagnosis of cancer.

Peroxidase-like activity of acetylcholine-based colorimetric detection of acetylcholinesterase activity and an organophosphorus inhibitor

Colorimetric detection of acetylcholinesterase (AChE) and its inhibitor organophosphates (OPs) is attractive for its convenience, but the addition of exogenous catalyst to produce a chromogenic agent may result in complexity and interference. Herein, we first found that acetylcholine (ATCh) itself mimicked peroxidase's activity, based on which a simple and reliable colorimetric system containing ATCh- 3,3',5,5'-tetramethylbenzidine (TMB)-H₂O₂ was developed for the sensitive and selective assay of AChE activity and its inhibitor OPs. Due to the AChE-catalyzed hydrolysis of acetylcholine, the peroxidase-like activity was affected, which was used for highly sensitive detection of AChE activity with a low limit of detection (LOD) of 0.5 mU mL^-1 and a linear detection range from 2.0 to 14 mU mL^-1. Furthermore, due to the inhibition of OPs on AChE, OPs were also detected with the present ATCh regulated colorimetric system with LOD of 4.0 ng mL^-1 and a linear dynamic range from 10 to 10 000 µg L^-1. This strategy was also demonstrated to be applicable for pesticide detection in real samples. Meanwhile, the sensing platform can also be implemented on test strips for rapid and visual monitoring of OPs. Thus, this extremely simple colorimetric strategy without the addition of other exogenous catalysts holds great promise for on-site pesticide detection and can be further exploited for sensing applications in the environmental and food safety fields.

Ratiometric Fluorescent Biosensor for Visual Discrimination of Cancer Cells with Different Telomerase Expression Levels

Telomerase is inactive in normal somatic cells but highly activated in tumor cells to maintain their indefinite proliferation and immortal phenotype. As a specific marker for the generation and progress of almost all tumors, the detection of telomerase activity by classical PCR techniques has served in the biological research of tumors. However, the detection of in situ telomerase activity in cell extracts to evaluate the malignancy, progress, and metastasis of tumors remains a daunting challenge. Here, a precisely designed FRET-based ratiometric fluorescent oligonucleotide probe has achieved high-fidelity detection of telomerase activity for accurate discrimination of different cancer cells toward advanced diagnosis of tumors. Our method is superior to other methods in its capabilities to quantify telomerase activity in cell extracts and visualize various tumor cell extracts with different telomerase expression levels by the naked eye for clinical diagnosis. In particular, the ratiometric fluorescent probe used in the assay could exclude other experimental factors influence, and further avoid false positive signal generation. The method reported here could provide a reliable, accurate, and convenient way in medical diagnostics and therapeutic response assessment.

Optical nano-biosensing interface via nucleic acid amplification strategy: construction and application

Modern optical detection technology plays a critical role in current clinical detection due to its high sensitivity and accuracy. However, higher requirements such as extremely high detection sensitivity have been put forward due to the clinical needs for the early finding and diagnosing of malignant tumors which are significant for tumor therapy. The technology of isothermal amplification with nucleic acids opens up avenues for meeting this requirement. Recent reports have shown that a nucleic acid amplification-assisted modern optical sensing interface has achieved satisfactory sensitivity and accuracy, high speed and specificity. Compared with isothermal amplification technology designed to work completely in a solution system, solid biosensing interfaces demonstrated better performances in stability and sensitivity due to their ease of separation from the reaction mixture and the better signal transduction on these optical nano-biosensing interfaces. Also the flexibility and designability during the construction of these nano-biosensing interfaces provided a promising research topic for the ultrasensitive detection of cancer diseases. In this review, we describe the construction of the burgeoning number of optical nano-biosensing interfaces assisted by a nucleic acid amplification strategy, and provide insightful views on: (1) approaches to the smart fabrication of an optical nano-biosensing interface, (2) biosensing mechanisms via the nucleic acid amplification method, (3) the newest strategies and future perspectives.