Effect of etelcalcetide on parathyroid hormone secretion by primary hyperparathyroidism patient-derived primary parathyroid cells

Introduction Etelcalcetide (Parsabiv ® , AMG 416/ONO-5163) is a novel allosteric modulator for the calcium-sensing receptor approved for hemodialysis patients with secondary hyperparathyroidism of uremia. Etelcalcetide reduced parathyroid hormone levels in hemodialysis patients with secondary hyperparathyroidism of uremia in clinical studies. However, its direct effect on parathyroid hormone secretion in human parathyroid cells remains unknown. This study aimed to determine if etelcalcetide suppresses parathyroid hormone secretion by human parathyroid cells in vitro . Materials and methods We prepared primary cell cultures from human parathyroid tissue and determined calcium-sensing receptor expression levels by immunohistochemistry. Pathyroid tumors were removed from fourteen patients with primary hyperparathyrodism. Parathyroid tissue was dispersed with collagenase, resuspended in culture medium, incubated for 2 h with etelcalcetide and Ca 2+ , and the medium was then collected. Final etelcalcetide concentrations in the medium were 0.005–50 µmol/L. Levels of human parathyroid hormone in the medium were determined by enzyme-linked immunosorbent assay. Results In eight of the fourteen parathyroid cell cultures, extracellular Ca 2+ reduced parathyroid hormone levels. In four of the eight parathyroid cell cultures which responded extracellular Ca 2+ , etelcalcetide reduced hormone secretion with the 50% effective concentrations of 0.57, 20.8, 0.42, and 0.57 µmol/L. Expression levels of the calcium-sensing receptor were significantly lower in primary hyperparathyroidism patient-derived parathyroid tissues compared with controls. Conclusion This is the first report that etelcalcetide directly reduced parathyroid hormone secretion from the primary cultured human parathyroid cells from patients with primary hyperparathyroidism. To verify this conclusion, further studies are needed using secondary hyperparathyroidism patient-derived parathyroid cells.