Tissue-SELEX Aptamer Screening Service This refers to a specialized contract research service that uses Systematic Evolution of Ligands by EXponential Enrichment (SELEX) to discover aptamers that specifically bind to molecular targets within a complex tissue environment, rather than purified proteins or isolated cells. Core Concept & Key Differentiator While Cell-SELEX uses whole live cells as targets, Tissue-SELEX advances the complexity by using: Tissue sections (fresh, frozen, or FFPE - Formalin-Fixed Paraffin-Embedded) Tissue homogenates Tissue-specific extracellular matrix (ECM) components The goal is to find aptamers that recognize targets in their native, histological context, preserving post-translational modifications and local microenvironments. This is crucial for developing reagents for histopathology and tissue-specific targeting. Typical Workflow Target Preparation: Provider prepares or client supplies well-characterized tissue sections (often on glass slides). Counter-selection tissues (e.g., healthy vs. diseased, organ A vs. organ B) are critical. SELEX on Tissue: The oligonucleotide library is incubated directly on the tissue section. After washing, bound sequences are eluted, often by laser capture microdissection of bound areas or direct extraction. Amplification & Iteration: Recovered sequences are amplified (PCR) and used for subsequent selection rounds, with increasing stringency. Sequencing & Analysis: High-throughput sequencing (NGS) identifies enriched sequence families. Validation: Top candidates are synthesized and validated via: Tissue Staining: Fluorescently-labeled aptamers used like antibodies in immunohistochemistry (IHC). Specificity: Testing on…
Core Components of a Small Molecule Target Service A comprehensive service follows the early drug discovery workflow: 1. Target Identification & Prioritization Bioinformatics & Omics Analysis: Mining genomic, proteomic, and clinical data to find proteins or pathways dysregulated in a disease. Genetic Screens: Using CRISPR-Cas9 or RNAi to knock out/knock down genes and identify which are essential for disease cell survival. Literature & Database Mining: Systematic review of existing scientific and patent data to propose novel or repurposable targets. 2. Target Validation In Vitro Models: Confirming the target's role in disease using engineered cell lines (overexpression, knockout) and relevant disease models (e.g., cancer cell lines, neuronal cultures). In Vivo Models: Using animal models (e.g., zebrafish, mice) to see if modulating the target (genetically or with a tool compound) has the desired therapeutic effect and is safe. Biochemical Validation: Demonstrating the target protein is expressed, has the expected activity, and is "druggable" (has a pocket where a small molecule can bind). 3. Assay Development & Screening This is a critical service. Providers develop robust tests ("assays") to measure target activity. Types of Assays: Biochemical Assays: Test compound binding/interaction with the purified target protein (e.g., enzymatic activity, protein-protein interaction). Cell-Based Assays: Test compound function in a living cell (e.g., reporter…
What is Live Cell SELEX? Traditional SELEX uses purified target proteins. Live Cell SELEX uses intact, living cells in their native state. This is crucial because: It selects for aptamers that bind to targets in their natural conformation and post-translational modifications (e.g., glycosylation). It inherently selects for cell-specificity (e.g., cancer cell vs. healthy cell) without needing to know the exact molecular target upfront. It can discover aptamers against unknown or membrane-bound targets that are difficult to purify. Core Workflow of a Typical Service A full-service provider will manage the entire pipeline: 1. Project Design & Consultation Target Cell Line Definition: Defining the "positive" cell line (e.g., patient-derived cancer cells, activated immune cells). Counter-Selection Strategy: Choosing the "negative" cell line(s) (e.g., healthy counterpart, isogenic control) to eliminate non-specific binders. Library Design: Recommending or customizing the starting random oligonucleotide library (length, modifications like 2'-F pyrimidines for RNA aptamers for stability). 2. The Selection Phase (The Iterative SELEX Cycles) Incubation: The random library is incubated with the counter-selection cells. Unbound/non-specific sequences are collected. Positive Selection: The pre-cleared library is incubated with the target cells. Cells are washed stringently. Recovery: Cell-bound aptamers are recovered (e.g., by cell lysis, heat elution, or protease treatment). Amplification: Recovered sequences are amplified by PCR (for DNA) or RT-PCR (for…
