biased agonism
Most receptors can talk through more than one channel at once — a single receptor often triggers several downstream pathways. Biased agonism is when a drug deliberately favours one of those channels over the others, like flipping just one of several switches that a receptor normally turns on together.
Many receptors, especially GPCRs, signal through both G-protein pathways and β-arrestin pathways. A biased agonist stabilizes a receptor conformation that couples preferentially to one route, producing a different mix of downstream signals than the natural, balanced ('unbiased') ligand would. The hope is to keep the therapeutic pathway while muting a pathway tied to side effects.
The concept is appealing but harder to deliver than it first seemed. Measuring bias rigorously is subtle — apparent bias can be an artefact of assay sensitivity or receptor reserve — and the clinical payoff has been mixed. Oliceridine, a μ-opioid agonist biased toward G-protein over β-arrestin signaling, reached the market, but whether such bias reliably separates analgesia from opioid side effects remains debated.
Oliceridine activates the μ-opioid receptor with bias toward G-protein signaling over β-arrestin recruitment, an approach intended to provide analgesia while reducing certain opioid side effects.
A biased agonist preferentially engages one of a receptor's signaling pathways.
Biased agonism is about which pathway is activated, whereas allosteric modulation is about where the drug binds. The two ideas are distinct, though an allosteric ligand can also be biased.