Silicon-Based Linkers for Tunable Acid-Sensitive Drug Release from Polymeric Nanoparticles

Active Pharmaceutical Ingredients (APIs) may benefit from a carrier to improve their pharmacokinetic and pharmacodynamic properties. Core-crosslinked polymeric micelles (CCPMs) are carriers for hydrophobic small molecule APIs. In CCPMs, APIs are generally covalently coupled to the core of the micelles by use of a linker, which can be tailored to adjust the release rate of the API. Acid triggered release is promising because of local acidic environment in the tissue of interest, and expected uptake via endocytosis. In the present study, silyl-based linkers were synthesized, and attached to gemcitabine as model API to investigate the tunability of release by introduction of different substituents. Attachment was achieved via an Si ether bond, with the linker coupled to the primary alcohol functionality on gemcitabine. By varying the substituents on the silyl atom, we could vary the release half-life (t_1/2) of native gemcitabine from <1 hour->96 hours at pH 5.0 at 37 °C, compared to a t_1/2 of 24->240 hours at pH 7.4 at 37 °C, respectively. The steric hinderance caused by substituents contributed to an increase of t_1/2 at pH 5.0, as the largest substituents resulted in the slowest release. Extension to other APIs and other carriers is clearly possible.