The preservation of teriparatide's biological activity was assessed in a cell-based assay measuring intracellular cAMP levels. Teriparatide binds to parathyroid hormone 1 receptor (PTH1R), a receptor belonging to the family of G-protein coupled receptors (GPCR) primarily expressed in bone, kidney and cartilage. PTH1R couples to several intracellular signalling pathways transmitting stimuli in response to binding of different ligands (e.g. PTH/teriparatide). Upon teriparatide binding, the PTH1R signals primarily via Gαs resulting in a series of downstream signals including an increase in cAMP levels (see Figure ) . In this assay, cAMP levels in a PTH1R overexpressing HEK293 cell line were measured after exposure to teriparatide and the downstream cell signalling through ERK 1/2 confirmed by Western blotting (see Supporting Information Section S3). The cells were exposed to identical concentrations of the native (unprocessed) teriparatide as well as to teriparatide released from a liposomal formulation (DSPC-10), as determined by HPLC analysis. Figure shows cAMP levels measured in HEK-PTH1R cells after a 30-minute exposure to 0.14 ng/mL teriparatide samples. The native peptide and teriparatide released from the formulation showed no significant difference (Student's t-test, p> 0.05) in cAMP levels (0.024 µM and 0.032 µM respectively), thus demonstrating that the functionality of teriparatide is retained.