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 polymeric sustained-delivery depots, including the dried protein entrapped in a film of poly(DL-lactic-co-glycolic)acid. At each step of the procedure, dehydration of rhGH by lyophilization, suspension in methylene chloride, and drying from that suspension, the structure of rhGH was probed noninvasively using Fourier transform infrared (FTIR) spectroscopy. We found that the structure of rhGH was significantly changed by the dehydration process as indicated by a marked drop in the alpha-helix content and increase in the beta-sheet content. Subsequent suspension of this powder in methylene chloride, drying from that suspension, and drying from a methylene chloride/PLGA solution introduced only minor additional structural changes when using appropriate 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 secondary structure, the rhGH entrapped in the PLGA matrix also had a nativelike secondary structure.