Pharmaceutical Stability of Romiplostim: In-use Functional Study Using Microscale Thermophoresis New Strategy and...

Functional stability is crucial for therapeutic proteins at all stages of their lifecycle. Romiplostim (Nplate®) is world-wide used for treating immune thrombocytopenia purpura. Limited in-use stability data on the proper romiplostim handling is publicly available. This study aimed to evaluate romiplostin in-use functional stability focusing on the interaction with its therapeutic target (TPO-R) and to improve the existing functional assessment strategies by developing a new one using microscale thermophoresis (MST).

Reconstituted romiplostim (Nplate®) samples were analysed. MST and ELISA functional methods were developed and optimized ad hoc to assess romiplostim functional stability. Far-UV-Circular-Dichroism and Intrinsic-Tryptophan-Fluorescence-Spectroscopy were used to ensure MST results by confirming the conformational stability of labelled TPO-R. In-use stability was assessed by subjecting romiplostim to conditions related to hospital handling, e.g. agitation and exposure to natural light; also, freezing and artificial light irradiation were checked as forced degraded condition.

MST and ELISA were described and validated by their figures of merit. Regarding romiplostim functional stability, both approaches yielded similar stability profiles, but MST detected subtle functional declines that were not revealed by ELISA. Furthermore, MST revealed insights into romiplostim binding stoichiometry, suggesting 1:2 interaction at high concentrations.

Regarding functionality, romiplostim was particularly sensitive to light exposure, with less sensitivity to agitation and freezing. These findings also demonstrate that MST serves as new orthogonal strategy to ELISA for assessing functionality, even providing additional data on binding dynamics and stoichiometry. This new MST strategy is applicable for any type of functional study of therapeutic proteins.