Molecular Recognition of Human Liver Cancer Cells Using DNA Aptamers Generated via Cell-SELEX

Development of Better Aptamers: Structured Library Approaches, Selection Methods, and Chemical Modifications

Systematic evolution of ligands by exponential enrichment (SELEX) has been used to discover thousands of aptamers since its development in 1990. Aptamers are short single-stranded oligonucleotides capable of binding to targets with high specificity and selectivity through structural recognition. While aptamers offer advantages over other molecular recognition elements such as their ease of production, smaller size, extended shelf-life, and lower immunogenicity, they have yet to show significant success in real-world applications. By analyzing the importance of structured library designs, reviewing different SELEX methodologies, and the effects of chemical modifications, we provide a comprehensive overview on the production of aptamers for applications in drug delivery systems, therapeutics, diagnostics, and molecular imaging.

Molecular Targets of Aptamers in Gastrointestinal Cancers: Cancer Detection, Therapeutic Applications, and Associated Mechanisms

Gastrointestinal (GI) cancers are among the most common cancers that impact the global population, with high mortality and low survival rates after breast and lung cancers. Identifying useful molecular targets in GI cancers are crucial for improving diagnosis, prognosis, and treatment outcomes, however, limited by poor targeting and drug delivery system. Aptamers are often utilized in the field of biomarkers identification, targeting, and as a drug/inhibitor delivery cargo. Their natural and chemically modifiable binding capability, high affinity, and specificity are favored over antibodies and potential early diagnostic imaging and drug delivery applications. Studies have demonstrated the use of different aptamers as drug delivery agents and early molecular diagnostic and detection probes for treating cancers. This review aims to first describe aptamers' generation, characteristics, and classifications, also providing insights into their recent applications in the diagnosis and medical imaging, prognosis, and anticancer drug delivery system of GI cancers. Besides, it mainly discussed the relevant molecular targets and associated molecular mechanisms involved, as well as their applications for potential treatments for GI cancers. In addition, the current applications of aptamers in a clinical setting to treat GI cancers are deciphered. In conclusion, aptamers are multifunctional molecules that could be effectively used as an anticancer agent or drug delivery system for treating GI cancers and deserve further investigations for clinical applications.

An Update of Nucleic Acids Aptamers Theranostic Integration with CRISPR/Cas Technology

The clustered regularly interspaced short palindromic repeat (CRISPR)/Cas system is best known for its role in genomic editing. It has also demonstrated great potential in nucleic acid biosensing. However, the specificity limitation in CRISPR/Cas has created a hurdle for its advancement. More recently, nucleic acid aptamers known for their high affinity and specificity properties for their targets have been integrated into CRISPR/Cas systems. This review article gives a brief overview of the aptamer and CRISPR/Cas technology and provides an updated summary and discussion on how the two distinctive nucleic acid technologies are being integrated into modern diagnostic and therapeutic applications

Development of a DNA Aptamer against Multidrug-Resistant Hepatocellular Carcinoma for In Vivo Imaging

Hepatocellular carcinoma (HCC) is a type of cancer that has high rates of recurrence and mortality. One of the most important factors that lead to treatment failure of HCC is the acquisition of multidrug resistance (MDR). Development of specific ligands for multidrug-resistant HCC will provide useful molecular tools for precise diagnosis and targeted theranostics. Herein, a multidrug-resistant HCC cell (HepG2/MDR)-specific aptamer was developed through Cell-SELEX (systematic evolution of ligands by exponential enrichment) technology. With dissociation constants lying in the nanomolar range, the molecularly designed PS-ZL-7c aptamer showed great selectivity to drug-resistant cancer cells. The in vivo imaging results illustrated that the PS-ZL-7c specifically accumulated in the drug-resistant tumors but not in drug-sensitive tumors and normal tissues, indicating that the PS-ZL-7c aptamer possessed excellent potential as a targeting ligand for precise diagnosis and target theranostics of multidrug-resistant HCC.

Identification of a New DNA Aptamer by Tissue-SELEX for Cancer Recognition and Imaging

Cancer has become one of the most common diseases with high mortality in humans. Early and accurate diagnosis of cancer is of great significance to enhance the survival rate of patients. Therefore, effective molecular ligands capable of selectively recognizing cancer are urgently needed. In this work, we identified a new DNA aptamer named SW1 by tissue-based systematic evolution of ligands by exponential enrichment (tissue-SELEX), in which cancerous liver tissue sections were used as the positive control and adjacent normal liver tissue sections were used as the negative control. Taking immobilized liver cancer SMMC-7721 cells as the research object, aptamer SW1 exhibited excellent affinity with a K_d value of 123.62 ± 17.53 nM, and its binding target was preliminarily determined as a non-nucleic acid substance in the nucleus. Moreover, tissue imaging results showed that SW1 explicitly recognized cancerous liver tissues with a high detection rate of 72.7% but displayed a low detection rate to adjacent normal tissues. In addition to liver cancer cells and tissues, aptamer SW1 has been demonstrated to recognize various other types of cancer cells and tissues. Furthermore, SW1-A, an optimized aptamer of SW1, maintained its excellent affinity toward liver cancer cells and tissues. Collectively, these results indicate that SW1 possesses great potential for use as an effective molecular probe for clinical diagnosis of cancer.

Aptamer Generated by Cell-SELEX for Specific Targeting of Human Glioma Cells

The most prevalent primary brain tumors are gliomas, which start in the glial cells. Although there have been significant technological advances in surgery and radio-chemotherapy, the prognosis and survival of patients with malignant gliomas remain poor. For routine diagnosis of glioma, computed tomography and magnetic resonance imaging primarily depend on anatomical changes and fail to detect the cellular changes that occur early in the development of malignant gliomas. Therefore, it is urgent to find effective molecular diagnostic tools to detect early stages of malignant gliomas. Currently, cell-based Systematic Evolution of Ligands by EXponential enrichment (cell-SELEX) technology is one effective tool to obtain DNA or RNA aptamers capable of differentiating the molecular signatures among different types of cell lines. Using cell-SELEX, we generated and characterized an aptamer, termed S6-1b, that can distinguish the molecular differences between glioma cell line SHG44 and human astrocytes. Under the conditions of 4 and 37 °C, respectively, the dissociation constants of aptamer-cell interaction were both measured in the low nanomolar range. The aptamer S6-1b also exhibited excellent selectivity, making it suitable for use in a complex biological environment. Furthermore, the aptamer can effectively target glioma cells for in vivo fluorescence imaging of tumors. The target type of aptamer S6-1b was identified as a cell membrane protein. Our work indicates that aptamer S6-1b has diagnostic and therapeutic potential to specifically deliver imaging or therapeutic agents to malignant gliomas.

Selection and identification of an ssDNA aptamer to NB4 cell

This study was to find the aptamers with high affinity and specificity binding to acute promyelocytic leukemia (APL) NB4 cell line.

These aptamers targeted NB4 cells were selected from a random single‐stranded DNA (ssDNA) library of systematic evolution of ligands by exponential enrichment (CELL‐SELEX). The binding rate of FITC‐ssDNA library and NB4 cells was monitored using flow cytometry and fluorescence microscope. After cloned and sequenced, the structure, specificity, and affinity of these candidate aptamers were further analyzed.

After a total of 19 rounds of selection, the ssDNA library was enriched and the BR (19.9%) of the 16th round was 12 times of the first round (1.6%). Three enriched aptamers were obtained from 21 positive clones of the 16th round, and the predicted secondary structures of these aptamers were mainly stem‐loop. The aptamer CX9 had the highest affinity, and the equilibrium dissociation constant (Kd) was 16.2 nM. The fluorescence intensity of CX9 binding to NB4 cells was stronger than HL60 and K562 cells under fluorescence microscopy.

The study indicates that aptamer CX9 exhibits high affinity and specificity with NB4 cells and lay a foundation for the rapid diagnostic method to detect APL with fluorescence‐labeled aptamer.

Recent advances in understanding oligonucleotide aptamers and their applications as therapeutic agents

The innovative discovery of aptamers was based on target-specific treatment in clinical diagnostics and therapeutics. Aptamers are synthetic, single-stranded oligonucleotides, simply described as chemical antibodies, which can bind to diverse targets with high specificity and affinity. Aptamers are synthesized by the SELEX technique, and possess distinctive properties as small size (10-50 kDa), higher stability, easy manufacture and less immunogenicity. These oligonucleotides are easily degraded by nucleases, so require some important modifications like capping and incorporation of modified nucleotides. RNA aptamers can be modified chemically on 2' positions using -NH3, -F, -deoxy, or -OMe groups to enhance their nuclease resistance. Aptamers have been employed for multiple purposes, as direct drugs or aptamer-drug conjugates targeted against different diseased cells. Different aptamer-conjugated nanovehicles (e.g., micelles, liposomes, silica nano-shells) have been designed to transport diverse anticancer-drugs like doxorubicin and cisplatin in bulk to minimize systemic cytotoxicity. Some drug-loaded nanovehicles (up to 97% loading capacity) and conjugated with specific aptamer resulted in more than 60% tumor inhibition as compared to unconjugated drug-loaded nanovehicles which showed only 31% cancer inhibition. In addition, aptamers have been widely used in basic research, food safety, environmental monitoring, clinical diagnostics and therapeutics. Different FDA-approved RNA and DNA aptamers are now available in the market, used for the treatment of diverse diseases, especially cancer. These aptamers include Macugen, Pegaptanib, etc. Despite a good progress in aptamer use, the present-day chemotherapeutics and drug targeting systems still face great challenges. Here in this review article, we are discussing nucleic acid aptamers, preparation, role in the transportation of different nanoparticle vehicles and their applications as therapeutic agents.

Implementation of High-Throughput Sequencing (HTS) in Aptamer Selection Technology

Aptamers are nucleic acid ligands that bind specifically to a target of interest. Aptamers have gained in popularity due to their high potential for different applications in analysis, diagnostics, and therapeutics. The procedure called systematic evolution of ligands by exponential enrichment (SELEX) is used for aptamer isolation from large nucleic acid combinatorial libraries. The huge number of unique sequences implemented in the in vitro evolution in the SELEX process imposes the necessity of performing extensive sequencing of the selected nucleic acid pools. High-throughput sequencing (HTS) meets this demand of SELEX. Analysis of the data obtained from sequencing of the libraries produced during and after aptamer isolation provides an informative basis for precise aptamer identification and for examining the structure and function of nucleic acid ligands. This review discusses the technical aspects and the potential of the integration of HTS with SELEX.

Selection and Characterization of a Novel DNA Aptamer, Apt-07S Specific to Hepatocellular Carcinoma Cells

Background

The efficacy of traditional therapeutic methods for liver cancer is unsatisfying because of the poor targeting, and inefficient drug delivery system. A recent study has proven that aptamers, developed through cell-SELEX, could specifically recognize cancer cells and show great potential in the development of a delivery system for anticancer drugs.

Purpose

To develop a hepatocellular carcinoma specific aptamer using two kinds of hepatocellular carcinoma cell lines, HepG₂ and SMMC-7721, as double targets and a normal hepatocyte, L02, as a negative control cell.

Methods

Hepatocellular carcinoma specific aptamer was developed via cell-SELEX. The enrichment of the library was monitored by flow cytometric analysis. The specificity, affinity, and distribution of the candidate aptamer were explored. Further study was carried to assess its potential in drug delivery.

Results

The library was enriched after 14 rounds of screening. Candidate aptamer Apt-07S can recognize four kinds of hepatocellular carcinoma cells and show little cell-binding ability to normal cells and four cell lines of different cancer types, revealing a high specificity of Apt-07S. Confocal imaging showed that Apt-07S distributed both on the surface and in the cytoplasm of the two target cells. Moreover, an anti-sense nucleotide to gene Plk1 (ASO-Plk1) was connected at the 3' end of Apt-07S to form an integrated molecule (Apt-07S-ASO-Plk1); the functional analysis indicated that the structure of Apt-07S may help ASO-Plk1 enter the cancer cells.

Conclusion

The study indicates that Apt-07S can specifically target HCC and may have potential in the delivery of anticancer drugs.

Cell-SELEX, an Effective Way to the Discovery of Biomarkers and Unexpected Molecular Events

Cell-SELEX can not only generate aptamers for specific cell isolation/detection, diagnosis, and therapy, but also lead to the discovery of biomarkers and unexpected molecular events. However, most cell-SELEX research is concentrated on aptamer generation and applications. In this progress report, recent research progress with cell-SELEX in terms of the discovery of biomarkers and unexpected molecular events is highlighted. In particular, the key technical challenges for cell-SELEX-based biomarker discovery, namely, the methods for identification and validation of target proteins of aptamers, are discussed in detail. Finally, the prospects of the applications of cell-SELEX in this field now and in the near future are described. It is expected that this report will attract attention to the benefit of cell-SELEX and provide a practical reference for biomedical researchers.

Evolution of Nucleic Acid Aptamers Capable of Specifically Targeting Glioma Stem Cells via Cell-SELEX

Glioma stem cells (GSCs), a particular group of cells from gliomas, are capable of infinite proliferation and differentiation. Recent studies have shown that GSCs may be the root of tumor recurrence, metastasis, and resistance. Early detection and targeted therapy of GSCs may significantly improve the survival rate of glioma patients. Therefore, molecular ligands capable of selectively recognizing GCSs are of great importance. The objective of this study is to generate DNA aptamers for selective identification of the molecular signature of GSCs using cell-based Systematic Evolution of Ligands by EXponential enrichment (cell-SELEX). GSCs were used as the positive selection target, while U87 cells were used in negative cycles for removal of DNA molecules binding to common glioma cell lines. Finally, we successfully identified one aptamer named W5-7 with a K_d value of 4.9 ± 1.4 nM. The sequence of the aptamer was further optimized, and its binding target was identified as a membrane protein. The aptamer W5-7 was stable in cerebral spinal fluid over 36 h and could also effectively detect glioma stem cells in cerebral spinal fluid samples. With its superb targeting properties and functional versatility, W5-7 holds great potential for use as a molecular probe for detecting and isolating GSCs.

Potential use of aptamers for diagnosis and treatment of pancreatic cancer

Pancreatic cancer (PC) is highly malignant with a low 5-year survival rate. PC currently does not have good early diagnostic markers and responses poorly to chemotherapeutic drugs. The search for better biomarkers and developing more effective chemotherapy are important ways to improve the healthcare of PC patients. Aptamers are single-stranded nucleic acids with high binding affinity and specificity to target molecules. Many aptamers against different forms of cancer including PC have been selected for both diagnostic and therapeutic use. Aptamers can work as ligands to distinguish tumour cells from normal cells. Using cells as selection targets, the obtained aptamers have been used to discover new cancer biomarkers after identification of the binding target. Aptamers have been shown to have antagonists effect on cancer cell proliferation, apoptosis, and metastasis. In addition, aptamers have been used as carriers to deliver therapeutic agents to selectively kill PC cells. This review summarises the potential use of aptamers in the diagnosis and treatment of PC.

In Vitro Selection of a DNA Aptamer by Cell-SELEX as a Molecular Probe for Cervical Cancer Recognition and Imaging

Aptamers have become the most promising recognition reagents in terms of early diagnosis and effective treatment of cancers. In this study, using cervical cancer as a model, we have identified a DNA aptamer specifically binding to cervical cancer cells with high affinity using the cell-SELEX (systematic evolution of ligands by exponential enrichment) method, in which a negative selection was carried out using normal epithelial cells as control. The binding abilities of 6 selected truncated aptamers were determined by laser confocal fluorescence microscopy and flow cytometry, while most of them only recognize the target cells and do not bind the control cells, and the aptamer C-9S with 51-mer shows the best binding affinity to Ca Ski cells (target cells) with a dissociation constant value of 19.3 ± 2.9 nM. Moreover, at physiological temperature, C-9S remains its specific recognition capability to Ca Ski cells as well. Meanwhile, C-9S shows a similar binding ability to another cervical cancer cells (HeLa). Therefore, on the basis of its excellent targeting properties and inherent functional versatility of aptamer, C-9S holds great potential to be a molecular probe for early detection, in vivo imaging, and targeted delivery for further researches in cancer.

Comprehensive Regression Model for Dissociation Equilibria of Cell-Specific Aptamers

A comprehensive nonlinear regression model for dissociation equilibria of cell-specific aptamers is proposed by considering the effect of receptor expression level. Benefiting from the global regression of simultaneous equations, the fitted parameters reach a very significant level, indicating the statistical validity of this updated model. According to the fitting results, we found that dissociation constants fitted using the previous model are obviously larger than the updated values, which can be explained by the effect of receptor number on curve fitting. In addition, equivalent receptor density can be estimated using the updated model, which may lead to some new judgments about reported results of cell-SELEX.

Aptamers: novelty tools for cancer biology

Although the term ‘cancer’ was still over two thousand years away of being coined, the first known cases of the disease date back to about 3000BC, in ancient Egypt. Five thousand years later, still lacking a cure, it has become one of the leading causes of death, killing over half a dozen million people yearly. So far, monoclonal antibodies are the most successful immune-therapy tools when it comes to fighting cancer. The number of clinical trials that use them has been increasing steadily during the past few years, especially since the Food and Drug Administration greenlit the use of the first immune-checkpoint blockade antibodies. However, albeit successful, this approach does come with the cost of auto-inflammatory toxicity. Taking this into account, the development of new therapeutic reagents with low toxicity becomes evident, particularly ones acting in tandem with the tools currently at our disposal. Ever since its discovery in the early nineties, aptamer technology has been used for a wide range of diagnostic and therapeutic applications. With similar properties to those of monoclonal antibodies, such as high-specificity of recognition and high-affinity binding, and the advantages of being developed using in vitro selection procedures, aptamers quickly became convenient building blocks for the generation of multifunctional constructs. In this review, we discuss the steps involved in the in vitro selection process that leads to functional aptamers - known as Systematic Evolution of Ligands by Exponential Enrichment - as well as the most recent applications of this technology in diagnostic and treatment of oncological illnesses. Moreover, we also suggest ways to improve such use.

Surface Engineering of Nanoparticles for Targeted Delivery to Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-associated deaths worldwide. There is a lack of efficient therapy for HCC; the only available first-line systemic drug, sorafenib, can merely improve the average survival by two months. Among the efforts to develop an efficient therapy for HCC, nanomedicine has drawn the most attention, owing to its unique features such as high drug-loading capacity, intrinsic anticancer activities, integrated diagnostic and therapeutic functionalities, and easy surface engineering with targeting ligands. Despite its tremendous advantages, no nanomedicine can be effective unless it successfully targets the tumor site, which is a challenging task. In this review, the features of HCC are described, and the physiological hurdles that prevent nanoparticles from targeting HCC are discussed. Then, the surface physicochemical factors of nanoparticles that can influence targeting efficiency are discussed. Finally, a thorough description of the physiological barriers that nanomedicine must conquer before uptake by HCC cells if possible is provided, as well as the surface engineering approaches to nanomedicine to achieve targeted delivery to HCC cells. The physiological hurdles and corresponding solutions summarized in this review provide a general guide for the rational design of HCC targeting nanomedicine systems.

Development of Cell-Specific Aptamers: Recent Advances and Insight into the Selection Procedures

Systematic evolution of ligands by exponential enrichment (SELEX) is an established procedure for developing short single-stranded nucleic acid ligands called aptamers against a target of choice. This approach has also been used for developing aptamers specific to whole cells named Cell-SELEX. Aptamers selected by Cell-SELEX have the potential to act as cell specific therapeutics, cell specific markers or cell specific drug delivery and imaging agents. However, aptamer development is a laborious and time-consuming process which is often challenging due to the requirement of frequent optimization of various steps involved in Cell-SELEX procedures. This review provides an insight into various procedures for selection, aptamer enrichment, regeneration and aptamer-binding analysis, in addition to a very recent update on all aptamers selected by Cell-SELEX procedures.

In vitro selection of DNA aptamers against renal cell carcinoma using living cell-SELEX

Renal cell carcinoma (RCC) is the most common form of kidney cancer with poor prognosis. Early diagnosis of RCC would significantly improve patient prognosis and quality of life. In this work, we developed new aptamer probes for RCC by using cell-SELEX (systematic evolution of ligands by exponential enrichment) only after 12 rounds of selection, in which a clear cell renal cell carcinoma (ccRCC) cell line 786-O was used as target cell, and embryonic kidney cell line 293T as negative control cell. The selected aptamers were subjected to flow cytometry and laser confocal fluorescence microscopy to evaluate their binding affinity and selectivity. The dissociation constant K_d values of four selected aptamers are all in the nanomolar range. Aptamer W786-1 with the best binding affinity and a K_d value of 9.4 ± 2.0nM was further optimized and its truncated sequence W786-1S showed considerable affinity to 786-O cells. The proteinase and temperature treatment experiment indicated that W786-1 could recognize the target 786-O cells through surface proteins, and remain good binding affinity and excellent selectivity under physiological conditions. Therefore, on the basis of its excellent targeting properties and functional versatility, W786-1 holds great potential to be used as a molecular probe for identifying and targeting RCC.

A Cholecystokinin B Receptor-Specific DNA Aptamer for Targeting Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinomas (PDACs) constitutively express the G-protein-coupled cholecystokinin B receptor (CCKBR). In this study, we identified DNA aptamers (APs) that bind to the CCKBR and describe their characterization and targeting efficacy. Using dual SELEX selection against “exposed” CCKBR peptides and CCKBR-expressing PDAC cells, a pool of DNA APs was identified. Further downselection was based on predicted structures and properties, and we selected eight APs for initial characterizations. The APs bound specifically to the CCKBR, and we showed not only that they did not stimulate proliferation of PDAC cell lines but rather inhibited their proliferation. We chose one AP, termed AP1153, for further binding and localization studies. We found that AP1153 did not activate CCKBR signaling pathways, and three-dimensional Confocal microscopy showed that AP1153 was internalized by PDAC cells in a receptor-mediated manner. AP1153 showed a binding affinity of 15 pM. Bioconjugation of AP1153 to the surface of fluorescent NPs greatly facilitated delivery of NPs to PDAC tumors in vivo. The selectivity of this AP-targeted NP delivery system holds promise for enhanced early detection of PDAC lesions as well as improved chemotherapeutic treatments for PDAC patients.

Aptamers in Therapeutics

Aptamers are single strand DNA or RNA molecules, selected by an iterative process known as Systematic Evolution of Ligands by Exponential Enrichment (SELEX). Due to various advantages of aptamers such as high temperature stability, animal free, cost effective production and its high affinity and selectivity for its target make them attractive alternatives to monoclonal antibody for use in diagnostic and therapeutic purposes. Aptamer has been generated against vesicular endothelial growth factor 165 involved in age related macular degeneracy. Macugen was the first FDA approved aptamer based drug that was commercialized. Later other aptamers were also developed against blood clotting proteins, cancer proteins, antibody E, agents involved in diabetes nephropathy, autoantibodies involved in autoimmune disorders, etc. Aptamers have also been developed against viruses and could work with other antiviral agents in treating infections.

Evolution of DNA aptamers for malignant brain tumor gliosarcoma cell recognition and clinical tissue imaging

Gliosarcoma, a variant of glioblastoma multiforme (GBM), is a highly invasive malignant tumor. Unfortunately, this disease still marked by poor prognosis regardless of modern treatments. It is of great significance to discover specific molecular probes targeting gliosarcoma for early cancer diagnosis and therapy. Herein, we have selected a group of DNA aptamers with high affinity and selectivity against gliosarcoma cells K308 using cell-SELEX. All the dissociation constants of these aptamers against gliosarcoma cells were in the nanomolar range and aptamer WQY-9 has the highest affinity and good selectivity among them. Furthermore, truncated aptamer sequence, WQY-9-B, shows similar recognition ability to aptamer WQY-9. In addition, WQY-9-B was found to be able to bind selectively and internalize into cytoplasm of target cancer cell at 37 °C. More importantly, compared to a random sequence, aptamer WQY-9-B showed excellent recognition rate (73.3%) for tissue sections of clinical gliosarcoma samples. These data suggests that aptamer WQY-9-B has excellent potential as an effective molecular probe for gliosarcoma diagnosis.

DNA Aptamers in the Diagnosis and Treatment of Human Diseases

Aptamers have a promising role in the field of life science and have been extensively researched for application as analytical tools, therapeutic agents and as vehicles for targeted drug delivery. Compared with RNA aptamers, DNA aptamers have inherent advantages in stability and facility of generation and synthesis. To better understand the specific potential of DNA aptamers, an overview of the progress in the generation and application of DNA aptamers in human disease diagnosis and therapy are presented in this review. Special attention is given to researches that are relatively close to practical application. DNA aptamers are expected to have great potential in the diagnosis and treatment of human diseases.

Development of a panel of DNA Aptamers with High Affinity for Pancreatic Ductal Adenocarcinoma

Pancreatic cancer costs nearly 40,000 lives in the U.S. each year and has one of the lowest survival rates among cancers. Effective treatment of pancreatic ductal adenocarcinoma is hindered by lack of a reliable biomarker. To address this challenge, aptamers were selected by cell-SELEX (Systematic Evolution of Ligands by EXponential enrichment) targeting human pancreatic ductal adenocarcinoma (PL45). Five promising aptamers presenting low K_d values and good specificity were generated. Among these five aptamers, one was tailored into a nanostructure carrying a high drug payload for specific drug delivery. The results show a viability of almost 80% for negative cells while only 50% of the target cells remained alive after 48 h incubation. These results lead to the conclusion that further research could reveal protein biomarkers specific to pancreatic adenocarcinoma, with probes available for early detection.

Selective Targeting to Glioma with Nucleic Acid Aptamers

Malignant glioma is characterised by a rapid growth rate and high capacity for invasive infiltration to surrounding brain tissue; hence, diagnosis and treatment is difficult and patient survival is poor. Aptamers contribute a promising and unique technology for the in vitro imaging of live cells and tissues, with a potentially bright future in clinical diagnostics and therapeutics for malignant glioma. The binding selectivity, uptake capacity and binding target of two DNA aptamers, SA43 and SA44, were investigated in glioma cells and patient tissues. The binding assay showed that SA43 and SA44 bound with strong affinity (Kd, 21.56 ± 4.60 nM and Kd, 21.11 ± 3.30 nM respectively) to the target U87MG cells. Quantitative analysis by flow cytometry showed that the aptamers were able to actively internalise in U87MG and 1321N1 glioma cells compared to the non-cancerous and non-glioma cell types. Confocal microscopy confirmed staining in the cytoplasm, and co-localisation studies with endoplasmic reticulum, Golgi apparatus and lysosomal markers suggested internalisation and compartmentalisation within the endomembrane system. Both aptamers selectively bound to Ku 70 and Ku 80 DNA repair proteins as determined by aptoprecipitation (AP) followed by mass spectrometry analysis and confirmation by Western blot. In addition, aptohistochemical (AHC) staining on paraffin embedded, formalin fixed patient tissues revealed that the binding selectivity was significantly higher for SA43 aptamer in glioma tissues (grade I, II, III and IV) compared to the non-cancerous tissues, whereas SA44 did not show selectivity towards glioma tissues. The results indicate that SA43 aptamer can differentiate between glioma and non-cancerous cells and tissues and therefore, shows promise for histological diagnosis of glioma.