Radioreceptor assay for formulations of salmon calcitonin

Abstract Receptors on cultured human lymphocytes (IM-9) have been shown to bind salmon calcitonin (sCT) specifically. The aim of the present study was to develop an in vitro assay for sCT based on this binding. The assay should fulfil pharmacopoeial requirements for quantitation of biologicals and should be validated against an established in vivo assay of CT. The binding of 125 I-sCT was studied as a function of time and concentration of unlabelled sCT and other peptides. Also dissociation of bound sCT and degradation of sCT in the incubation medium were studied. From these studies, conditions for a radioreceptor assay for sCT were chosen. Concentrations from 7 × 10 −11 to 2 sx 10 −9 M or from 1 to 30 mIU ml −1 caused a linear reduction of binding of 125 I-sCT. This concentration interval was chosen for a three-dose assay. The results obtained with the radioreceptor assay correlated with results from the established in vivo bioassay but were more precise. Since the in vitro method is also less resource demanding than the in vivo bioassay, it is suggested that the former is suitable as a screening method for potency determinations of sCT preparations.