In Vitro
Experiments conducted outside a living organism in laboratory containers — test tubes, petri dishes, or cell culture plates. In vitro studies provide controlled conditions for examining biological mechanisms but do not necessarily predict how a compound will behave in a living system.
Technical Context
Common in vitro assays for peptide compounds include: receptor binding assays (radioligand competition — measuring IC50/Ki for receptor affinity), functional assays (cAMP accumulation, calcium flux, reporter gene — measuring EC50/potency), cell viability assays (MTT/MTS, live/dead staining — assessing cytotoxicity), migration/invasion assays (wound healing scratch assay, transwell migration — relevant to tissue repair peptides), and stability assays (plasma stability, microsomal stability, simulated gastric/intestinal fluid stability). In vitro data provide mechanistic understanding and are essential for early drug discovery, but their predictive value for in vivo behaviour is limited by: absence of systemic PK (absorption, distribution, metabolism, excretion), absence of intact physiological feedback systems, and potential for cell culture artefacts. The translational gap between in vitro and in vivo results is a major challenge in peptide drug development.