Microfluidic formulation, cryoprotection and long-term stability of paclitaxel-loaded π electron-stabilized polymeric micelles

Controlled manufacturing and long-term stability are key challenges in the development and translation of nanomedicines. This is exemplified by the mRNA-nanoparticle vaccines against COVID-19, which require (ultra-)cold temperatures for storage and shipment. Various cryogenic protocols have been explored to prolong nanomedicine shelf-life. However, freezing typically induces high mechanical stress on nanoparticles, resulting in aggregation or destabilization, thereby limiting their performance and application. Hence, evaluating the impact of freezing and storing on nanoparticle properties already early-on during preclinical development is crucial. In the present study, we used prototypic π electron-stabilized polymeric micelles based on mPEG-b-p(HPMAm-Bz) block copolymers to macro- and microscopically study the effect of different cryoprotective excipients on nanoformulation properties like size and size distribution, as well as on freezing-induced aggregation phenomena via in-situ freezing microscopy. We show that sucrose, unlike trehalose, efficiently cryoprotected paclitaxel-loaded micelles, and we exemplify the impact of formulation composition for efficient cryoprotection. We finally establish microfluidic mixing to formulate paclitaxel-loaded micelles with sucrose as a cryoprotective excipient in a single production step and demonstrate their stability for 6 months at -20 °C. The pharmaceutical properties and preclinical performance (in terms of tolerability and tumor growth inhibition in a patient-derived triple-negative breast cancer xenograft mouse model) of paclitaxel-loaded micelles were successfully cryopreserved. Together, our efforts promote future pharmaceutical development and translation of π electron-stabilized polymeric micelles, and they illustrate the importance of considering manufacturing and storage stability issues early-on during nanomedicine development.