Crossselectivity

Crossselectivity is a term used to describe the degree to which a ligand, substrate, or detection element interacts with multiple targets or pathways rather than a single, exclusive target. It sits between strict selectivity and broad reactivity, capturing the tendency to produce overlapping or off-target interactions. The concept is relevant across disciplines, including pharmacology, enzymology, immunology, and analytical chemistry.

In pharmacology and drug design, crossselectivity informs polypharmacology and off-target effects. A drug with high crossselectivity may modulate several receptors or enzymes, potentially yielding beneficial multitarget therapy or, conversely, adverse side effects. Quantitative measures such as binding affinities, inhibition constants, and potency across a panel of targets are used to assess crossselectivity. A selectivity index or cross-reactivity ratio summarizes how much more (or less) a compound favors the intended target over others.

Examples include a receptor ligand that activates multiple receptor subtypes with varying affinities, or an antibody that binds to related antigens due to shared epitopes. In analytical contexts, crossselectivity describes how a detector or antibody responds to related substances, affecting specificity and accuracy.

Key considerations involve structural similarity among targets, conserved binding motifs, and the trade-off between broader activity and precision. Strategies to manage crossselectivity include structural optimization, targeted screening, and design of selective assays to minimize unwanted interactions. See also selectivity, cross-reactivity, and polypharmacology.