Aptamers are short single-stranded DNA or RNA molecules that fold into 3D structures capable of binding targets (proteins, small molecules, cells, or even complex particles) with high specificity and affinity. “Aptamer methods” usually refers to the full pipeline: library design → selection (SELEX) → enrichment monitoring → sequencing & bioinformatics → candidate optimization → biophysical/functional validation → stability engineering. Modern platforms improve speed and hit quality by combining smarter selection pressures with microfluidics and next-generation sequencing. 1) Core Aptamer Selection Method: SELEX (Systematic Evolution of Ligands by EXponential Enrichment) 1.1 Classical SELEX workflow (baseline method) Start with a random oligonucleotide library (often 10^13–10^15 unique sequences) Incubate library with the target Partition bound vs unbound sequences Elute binders Amplify (PCR for DNA; RT-PCR + transcription for RNA) Repeat iterative rounds with increasing stringency until enrichment is achieved Why it works: each round increases the fraction of sequences that can bind under the imposed conditions (buffer, temperature, competitor molecules, etc.). Why it’s hard: classical SELEX can be slow, labor intensive, and prone to amplification bias—hence the rise of “advanced SELEX” platforms. 1.2 “Stringency engineering” (how you make aptamers useful) Selection success often depends less on the target itself…
In early drug discovery, hit identification is the disciplined search for molecules that measurably affect a biological target or disease-relevant system, while lead compound selection is the subsequent decision to elevate the best validated “hits” into lead compounds that are strong enough—scientifically and operationally—to justify an optimization campaign. This “hit-to-lead” logic sits between assay development/high-throughput screening and full lead optimization, and its quality strongly influences downstream success. 1) Core Definitions (so the team argues less) What is a “Hit”? A hit is an initial compound (or series) that shows reproducible activity in a primary screen and survives basic confirmation steps. Hits often begin with modest potency (commonly micromolar range) and uncertain mechanism until validated. What is a “Lead Compound”? A lead compound is a more mature chemical starting point: typically a hit-derived molecule (or series) with improved potency and enough evidence for selectivity, developability, and tractable chemistry to justify systematic optimization toward a clinical candidate. Lead optimization then focuses on balancing potency with ADMET (absorption, distribution, metabolism, excretion, toxicity) and related properties. 2) Why Hit Identification Is Harder Than “Finding Actives” Modern discovery can generate many actives quickly, but the bottleneck is identifying…
