Enzyme Aptamer Screening Service is a specialized contract research service where providers employ SELEX (Systematic Evolution of Ligands by EXponential Enrichment) to discover aptamers that bind with high specificity and affinity to a target enzyme. These aptamers can be designed not only to bind but also to modulate the enzyme's activity (inhibit or activate), making them powerful tools for therapeutics, diagnostics, and biochemical research. Key Differentiators from Antibody Screening: Functional Screening: A major goal is often to identify inhibitory or activating aptamers. Therefore, the screening process may incorporate activity-based selection or functional assays early on. Target Site Complexity: The target can be the entire enzyme, its active site, an allosteric site, or a specific conformational state (e.g., open vs. closed). Conformational Sensitivity: Enzymes are dynamic. Aptamers can be selected to recognize a specific functional conformation, which is a unique advantage. Typical Screening Workflow: 1. Project Design & Target Preparation: Define Objective: Is the goal pure detection, potent inhibition, allosteric modulation, or capturing a specific enzyme form? Enzyme Quality: Requires a highly pure, functional, and correctly folded enzyme. Activity assays confirm functionality. Selection Strategy: Choice of Toggle SELEX (for broad species cross-reactivity), Capture SELEX, or innovative methods like ExSELEX (for complex biological fluids). 2. The SELEX Process with a Functional Focus: Binding & Stringency: Standard incubation, washing, and elution cycles are performed. Functional Partitioning (Optional…
Aptamers are single-stranded oligonucleotides that fold into defined architectures and bind to targets such as proteins. In binding proteins they often inhibit protein–protein interactions and thereby may elicit therapeutic effects such as antagonism. Aptamers are discovered using SELEX (systematic evolution of ligands by exponential enrichment), a directed in vitro evolution technique in which large libraries of degenerate oligonucleotides are iteratively and alternately partitioned for target binding. They are then amplified enzymatically until functional sequences are identified by the sequencing of cloned individuals. For most therapeutic purposes, aptamers are truncated to reduce synthesis costs, modified at the sugars and capped at their termini to increase nuclease resistance, and conjugated to polyethylene glycol or another entity to reduce renal filtration rates. The first aptamer approved for a therapeutic application was pegaptanib sodium (Macugen; Pfizer/Eyetech), which was approved in 2004 by the US Food and Drug Administration for macular degeneration. Eight other aptamers are currently undergoing clinical evaluation for various haematology, oncology, ocular and inflammatory indications. Aptamers are ultimately chemically synthesized in a readily scalable process in which specific conjugation points are introduced with defined stereochemistry. Unlike some protein therapeutics, aptamers do not elicit antibodies, and because aptamers generally contain sugars modified at their 2′-positions,…
What is an Aptamer? An aptamer is a short, single-stranded oligonucleotide (DNA or RNA) or peptide that binds to a specific target molecule (e.g., proteins, small molecules, cells, viruses) with high affinity and specificity. Often called "chemical antibodies," they offer advantages like stability, low-cost synthesis, and minimal batch-to-batch variation. The Core Process: SELEX The standard method for aptamer selection is SELEX (Systematic Evolution of Ligands by EXponential enrichment). Basic SELEX Workflow: Library Synthesis: Create a vast random-sequence oligonucleotide library (typically 10¹³ - 10¹⁵ unique sequences) flanked by constant primer regions for PCR amplification. Incubation: The library is incubated with the target molecule under controlled conditions (buffer, temperature, time). Partitioning: Bound sequences are separated from unbound ones. This is the most critical step and varies based on target (e.g., filtration, affinity columns, magnetic bead separation). Elution: Bound aptamers are recovered from the target (e.g., by denaturation or competitive elution). Amplification: The recovered pool is amplified by PCR (for DNA) or RT-PCR (for RNA) to create an enriched library for the next round. Iteration: Steps 2-5 are repeated (typically 8-15 rounds) to progressively enrich for sequences with the highest affinity and specificity. Cloning & Sequencing: The final enriched pool is cloned and sequenced to identify individual aptamer candidates. Key Variants of…
Antibody: A large, Y-shaped protein produced naturally by the immune system (B cells) in response to a foreign substance (antigen). It is a biological molecule. Aptamer: A short, single-stranded piece of DNA or RNA (or modified nucleotides) that is artificially engineered in a lab to bind to a specific target. It is a chemical molecule. Key Differences at a Glance Feature Antibody Aptamer Chemical Nature Protein (IgG, etc.) Nucleic Acid (DNA or RNA) Origin Biological (from animals) Chemical (SELEX process in vitro) Size Large (~150 kDa) Small (~10-30 kDa) Production Requires animal immunization or cell culture. Batch-to-batch variability possible. Synthetic, produced by chemical synthesis. Highly reproducible. Targets Primarily immunogenic targets (proteins, pathogens). Limited to targets that elicit an immune response. Extremely broad: ions, small molecules, proteins, cells, viruses, tissues. Can target toxins or non-immunogenic substances. Stability Sensitive to temperature (often requires refrigeration), pH, and proteases. Can denature. Thermally stable, can be renatured after denaturation. Resistant to harsh conditions (pH, organic solvents). Modification Difficult to modify chemically without affecting function. Site-specific conjugation is complex. Easy to chemically modify with reporters, drugs, or linkers at precise locations. Immunogenicity Can itself trigger an immune response (especially non-human antibodies). Generally low immunogenicity, but can be designed to be non-immunogenic. Cost…
1. Therapeutics & Medicine This is one of the most promising areas. Drugs: The first FDA-approved aptamer drug is Pegaptanib (Macugen) for treating age-related macular degeneration. It binds to VEGF, a protein that promotes abnormal blood vessel growth. Targeted Drug Delivery: Aptamers can be attached to drug nanoparticles or toxins, acting as a "homing device" to deliver the payload specifically to cancer cells or diseased tissues, minimizing side effects. Antidotes: "Antidote" or control oligonucleotides can be designed to bind and deactivate an aptamer's function, allowing for precise control of therapeutic activity—something very difficult with antibodies. Antiviral & Antibacterial Agents: They can bind to and neutralize viruses (like HIV, influenza, SARS-CoV-2) or specific bacterial proteins. 2. Diagnostics & Biosensing Aptamers are powerful tools for detecting molecules. Aptamer-based Assays: Used in ELISA-like formats (sometimes called ELASA) to detect biomarkers for diseases (cancer, infections) in blood or other samples. Point-of-Care Tests: Integrated into portable biosensors (aptasensors) for rapid, on-site detection of pathogens, toxins, or hormones. They can use optical, electrochemical, or mass-sensitive methods. Medical Imaging: Labeled with fluorescent dyes or radioisotopes, aptamers can help visualize tumors or diseased tissues during surgery or in scans. 3. Research & Biotechnology Protein Function Studies: Used to inhibit specific proteins in cells or in vitro to study their biological function, similar to using…
Aptamers are single-stranded DNA or RNA oligonucleotides (typically 20-80 bases) that fold into specific 3D structures capable of binding target molecules with high affinity and specificity, earning them the nickname "chemical antibodies." Their unique properties make them promising agents for targeted liver cancer therapy. Why Aptamers Are Suitable for Liver Cancer Targeting Molecular Recognition Capabilities Can be selected against specific liver cancer biomarkers (ASGPR, GPC3, EGFR, etc.) High binding affinity (nM to pM range) Specific discrimination between cancerous and normal hepatocytes Advantages Over Antibodies Smaller size (5-25 kDa) for better tissue penetration Chemical synthesis without batch variation Lower immunogenicity Easier modification and conjugation Higher thermal stability Key Targeting Strategies for Liver Cancer 1. Targeted Drug Delivery Aptamer-drug conjugates: Direct conjugation of chemotherapeutic agents (doxorubicin, sorafenib derivatives) Nano-carrier guidance: Aptamers decorating nanoparticles, liposomes, or micelles containing drugs Targeted prodrug activation: Aptamer-mediated delivery of enzyme prodrug systems 2. Targeted Gene Therapy Delivery of siRNA/miRNA to regulate oncogene expression CRISPR/Cas9 delivery for gene editing Examples: Anti-GPC3 aptamers delivering VEGF siRNA to inhibit angiogenesis 3. Multifunctional Theranostic Applications Combined imaging (fluorescence, PET, MRI) and therapy Aptamer-conjugated agents for image-guided surgery or ablation 4. Immomodulation Targeting immune checkpoint molecules (PD-1/PD-L1) Redirecting immune cells to tumor sites Clinically Relevant Targets…
Why Aptamers are Promising for Liver Cancer Imaging Compared to traditional antibodies, aptamers offer key advantages for in vivo applications: Small Size (5-15 kDa): Enables better tissue penetration and faster blood clearance, leading to higher tumor-to-background ratios. Low Immunogenicity: Reduced risk of allergic reactions or neutralization upon repeated administration. Ease of Chemical Synthesis & Modification: Can be stably produced, and easily conjugated with dyes, radionuclides, or nanoparticles. Rapid Tissue Penetration & Clearance: Ideal for imaging shortly after injection. Engineerable Flexibility: Can be designed as multivalent or bispecific constructs. Key Steps in Developing Aptamers for Liver Cancer Imaging Target Selection: Identifying a molecule highly expressed on liver cancer cells but low on normal hepatocytes is critical. Prime targets include: Glypican-3 (GPC3): A heparan sulfate proteoglycan overexpressed in 70-80% of hepatocellular carcinomas (HCC). Alpha-fetoprotein (AFP): A classic serum biomarker, with membrane-bound forms also present on HCC cells. Epithelial Cell Adhesion Molecule (EpCAM): Expressed on cancer stem cells in HCC and cholangiocarcinoma. Asialoglycoprotein Receptor (ASGPR): Highly expressed on normal hepatocytes but often dysregulated in HCC; useful for "background" subtraction or targeting specific isoforms. Receptor Tyrosine Kinases: Like c-Met or VEGFR2. Aptamer Generation: Typically done via SELEX (Systematic Evolution of Ligands by EXponential enrichment). For liver cancer, Cell-SELEX using live HCC cells vs. normal hepatocytes is preferred, as it identifies aptamers…
Aptamers are emerging as powerful molecular tools for the in vitro detection of liver cancer, offering a promising alternative to traditional antibodies. Here’s a comprehensive breakdown: What are Aptamers? Aptamers are short, single-stranded DNA or RNA oligonucleotides (or peptides) that bind to specific target molecules (proteins, cells, small molecules) with high affinity and specificity. They are selected in vitro through a process called SELEX (Systematic Evolution of Ligands by Exponential Enrichment). Why Aptamers for Liver Cancer Diagnosis? Compared to conventional antibodies, aptamers offer key advantages for diagnostics: High Specificity & Affinity: Can distinguish between healthy and cancerous biomarkers. Small Size: Better tissue penetration and access to epitopes. In Vitro Synthesis: Chemically produced, resulting in low batch-to-batch variation. Stability: Thermally stable and easily modifiable. Non-Immunogenic: Suitable for repeated use in assays. Key Targets for Liver Cancer Detection Aptamers are developed to detect liver cancer (primarily Hepatocellular Carcinoma, HCC) by targeting: Circulating Protein Biomarkers: Alpha-fetoprotein (AFP): The most widely used serum biomarker for HCC, but with limited sensitivity/specificity. AFP-specific aptamers are used in electrochemical, fluorescent, and colorimetric sensors to improve detection limits. Glypican-3 (GPC3): A cell-surface proteoglycan overexpressed in >70% of HCCs. GPC3 aptamers are central to many sensitive detection platforms. Vascular Endothelial Growth Factor (VEGF): Associated with angiogenesis and metastasis. Platelet-Derived Growth Factor (PDGF): Involved in…
The application of aptamers in the targeted diagnosis of liver cancer, particularly Hepatocellular Carcinoma (HCC), represents a cutting-edge frontier in oncology and molecular diagnostics. Aptamers offer a powerful alternative to traditional antibodies, with the potential to revolutionize early detection, imaging, and personalized treatment. Here is a comprehensive breakdown of their applications: 1. What are Aptamers? Aptamers are single-stranded DNA or RNA oligonucleotides (or peptides) that bind to specific target molecules (proteins, cells, small molecules) with high affinity and specificity. They are often termed "chemical antibodies." They are selected in vitro through a process called SELEX (Systematic Evolution of Ligands by EXponential enrichment). Key Advantages Over Antibodies: Small size: Better tissue penetration. Chemical synthesis: Highly reproducible, no batch-to-batch variation. Stability: Thermally stable and can be reversibly denatured. Low immunogenicity: Unlikely to provoke an immune response. Ease of modification: Can be easily labeled with dyes, radioisotopes, or nanoparticles. 2. Core Applications in Liver Cancer Diagnosis A. Detection of Circulating Biomarkers (Liquid Biopsy) This is the most prominent application. Aptamers are used as capture/detection probes in biosensors to identify HCC-specific biomarkers in blood, enabling non-invasive, early diagnosis. Targeting Protein Biomarkers: Alpha-fetoprotein (AFP): The most common clinical serum marker for HCC, but its sensitivity and specificity are suboptimal. AFP-specific aptamers have been developed and integrated into…
Aptamers and monoclonal antibodies (mAbs) are both high-affinity, target-specific biomolecules, but they differ fundamentally. Here’s a detailed comparison. Executive Summary Table Feature Monoclonal Antibodies (mAbs) Aptamers Nature Proteins (IgG) Single-stranded DNA or RNA oligonucleotides Size Large (~150 kDa) Small (~10-30 kDa) Production In vivo: Mammalian cell culture (expensive, slow, batch variability) In vitro: SELEX process (chemical synthesis, fast, reproducible, low cost) Targets Primarily immunogenic proteins (epitopes). Limited to molecules that elicit an immune response. Extremely broad: ions, small molecules, proteins, cells, viruses, tissues. Can target non-immunogenic and toxic substances. Affinity/Specificity High (pM-nM). Can distinguish between post-translational modifications. High (nM-pM). Can distinguish between chiral molecules and single amino acid differences. Stability Sensitive to heat, pH; requires cold chain. Thermally stable, can be renatured after denaturation. RNA aptamers need modification for nuclease resistance. Modifiability Complex genetic engineering for fusion proteins (e.g., ADCs). Site-specific conjugation is challenging. Easy chemical synthesis with precise site-specific modifications (fluorescent dyes, PEGylation, drugs, nanomaterials). Immunogenicity Can trigger human anti-drug antibodies (HADA), especially if chimeric/murine. Generally low immunogenicity, but PEG or certain backbones can sometimes cause immune responses. Tissue Penetration Poor due to large size; limited solid tumor penetration. Excellent due to small size; penetrates tissues, blood-brain barrier, and…