Designing Highly Stable Poly(sarcosine)-based Telodendrimer Micelles with High Drug Content Exemplified with Fulvestrant

Polymeric micelles have been extensively used as nanocarriers for the delivery of chemotherapeutic agents aiming to improve their efficacy in cancer treatment. However, poor loading capacity, premature drug release, non-uniformity and reproducibility still remain the major challenges. To create a stable polymeric micelle with high drug loading, a telodendrimer micelle was developed as a nanocarrier for fulvestrant, as an example of a drug that has extremely poor water solubility (sub nanomolar range). Telodendrimers were prepared by synthesis of a hydrophilic linear poly(sarcosine) and growing a lysine dendron from the chain terminal amine by a divergent synthesis. At the periphery of the dendritic block, 4, 8, and 16 fulvestrant molecules were conjugated to the lysine dendron creating a hydrophobic block. Having drug as part of the carrier not only reduces the usage of the inert carrier materials but also prevent the drugs from leakage and premature release by diffusion. The self-assembled telodendrimer micelles demonstrated good colloidal stability (CMC < 2 µM) in buffer and were uniform in size. In addition, these telodendrimer micelles could solubilize additional fulvestrant yielding an excellent overall drug loading capacity of up to 77 wt.% total drug load (summation of conjugated and encapsulated). Importantly, the size of the micelles could be tuned between 25-150 nm by controlling (i) the ratio between hydrophilic and hydrophobic blocks and (ii) the amount of encapsulated fulvestrant. The versatility of these telodendrimer-based micelle systems to both conjugate and encapsulate drug with high efficiency and stability, in addition to possessing other tuneable properties makes it a promising drug delivery system for a range of active pharmaceutical ingredients and therapeutic targets.