Radiopeptide internalisation and externalisation assays: Cell viability and radioligand integrity

Various aspects of radiopeptide receptor-mediated cell internalisation and externalisation assays were assessed, including the integrity of externalised peptides and the effect of varying the pH and incubation time of the acid wash step (to remove surface receptor-bound ligand) on efficacy and cell viability. The observed intact proportion of externalised peptide was 5–10%, and acid wash buffers with pH 2.8 or below were found to be detrimental to cell viability and integrity, particularly following prolonged incubation times.