On the structural preservation of recombinant human growth hormone in a dried film of a synthetic biodegradable polymer

In this work we describe the structural investigation of the model protein recombinant human growth hormone (rhGH) under conditions relevant to polyme ric sustained-delivery depots, including the dried protein entrapped in a f ilm of poly(DL-lactic-co-glycolic)acid. At each step of the procedure, dehy dration of rhGH by lyophilization, suspension in methylene chloride, and dr ying from that suspension, the structure of rhGH was probed noninvasively u sing Fourier transform infrared (FTIR) spectroscopy. We found that the stru cture of rhGH was significantly changed by the dehydration process as indic ated by a marked drop in the alpha-helix content and increase in the beta-s heet content. Subsequent suspension of this powder in methylene chloride, d rying from that suspension, and drying from a methylene chloride/PLGA solut ion introduced only minor additional structural changes when using appropri ate conditions. This result is likely due to the limited molecular mobility of proteins in nonprotein-dissolving organic solvents. Finally, when rhGH was co-lyophilized with the lyoprotectant trehalose, which preserves the se condary structure, the rhGH entrapped in the PLGA matrix also had a nativel ike secondary structure.