How does the pharmaceutical peptide octreotide respond to changes in relative humidity and temperature?

Octreotide is an eight-amino-acid peptide that mimics the activity of somatostatin, a natural hormone in the body. It is used in the management and treatment of diseases such as acromegaly and neuroendocrine tumors. The stability of octreotide under varying environmental conditions, such as relative humidity (rH) and temperature, is crucial for its pharmaceutical applications. Previous studies have shown that environmental factors can significantly impact the crystallinity and stability of peptides. This study investigates the structural evolution of octreotide under controlled rH and temperature conditions using X-ray Powder Diffraction (XRPD).

The study found that octreotide exhibits significant stability across a wide range of relative humidity (from 95% to 30%) and temperature (from 294.15K to 318.15K) conditions. The orthorhombic crystal symmetry of octreotide (space group P212121) is maintained throughout the experiments, with no phase transitions observed. However, the unit-cell parameters of octreotide undergo reversible changes upon dehydration and rehydration, with the a and c axes increasing and the b axis decreasing during dehydration. Temperature variation has a less pronounced effect on the unit-cell dimensions compared to rH changes. The findings highlight the robustness of octreotide's crystalline structure and its potential for use in stable pharmaceutical formulations.