Pathways and kinetics of deslorelin degradation in an airway epithelial cell line (Calu-1)

The objective of this study is to investigate the pathways and kinetics of degradation of deslorelin, pGlu1-His2-Trp3-Ser4-Tyr5-D-Trp6-Leu7-Arg8-ProNHEt9 (Des1-9), in a human airway epithelial cell line (Calu-1).

The degradation of deslorelin in membrane and cytosolic fractions of Calu-1 cells was studied at 37 degrees C up to 24 h. The degradation products were separated using HPLC and identified by amino acid analysis, sequencing, and mass spectrometry. The rate constants for deslorelin degradation and the formation of degradation products were determined by fitting the concentration vs. time data to pharmacokinetic models using WinNonlin. The effect of enzyme inhibitors, captopril, phosphoramidon, and disodium EDTA on deslorelin degradation was also assessed.

Des1-3, Des4-9, and Des5-9 were the deslorelin fragments detected in the membrane fraction. Apart from these degradation products. Des5-7 was also detected in the cytosolic fraction. The deslorelin degradation was 8.5 times faster in the cytosolic fraction compared to the membrane fraction. The disappearance of deslorelin and the kinetics of degradation products could be explained by simple 2 compartment iv bolus model and 1 compartment absorption model, respectively. EDTA and captopril decreased deslorelin degradation in the membrane and cytosolic fractions.

Deslorelin is initially cleaved at the 3-4 bond in the membrane and cytosolic fractions, possibly by a metalloendopeptidase and/or angiotensin converting enzyme, with the degradation being more rapid in the cytosol.