Complete Regression of Xenograft Tumors upon Targeted Delivery of Paclitaxel via Π–Π Stacking Stabilized Polymeric Micelles

Abstract

Treatment of cancer patients with taxane-based chemotherapeutics, such as paclitaxel (PTX), is complicated by their narrow therapeutic index. Polymeric micelles are attractive nanocarriers for tumor-targeted delivery of PTX, as they can be tailored to encapsulate large amounts of hydrophobic drugs and achiv prolonged circulation kinetics. As a result, PTX deposition in tumors is increased, while drug exposure to healthy tissues is reduced. However, many PTX-loaded micelle formulations suffer from low stability and fast drug release in the circulation, limiting their suitability for systemic drug targeting. To overcome these limitations, we have developed PTX-loaded micelles which are stable without chemical cross-linking and covalent drug attachment. These micelles are characterized by excellent loading capacity and strong drug retention, attributed to π–π stacking interaction between PTX and the aromatic groups of the polymer chains in the micellar core. The micelles are based on methoxy poly(ethylene glycol)-b-(N-(2-benzoyloxypropyl)methacrylamide) (mPEG-b-p(HPMAm-Bz)) block copolymers, which improved the pharmacokinetics and the biodistribution of PTX, and substantially increased PTX tumor accumulation (by more than 2000%; as compared to Taxol or control micellar formulations). Improved biodistribution and tumor accumulation were confirmed by hybrid μCT-FMT imaging using near-infrared labeled micelles and payload. The PTX-loaded micelles were well tolerated at different doses, while they induced complete tumor regression in two different xenograft models (i.e., A431 and MDA-MB-468). Our findings consequently indicate that π–π stacking-stabilized polymeric micelles are promising carriers to improve the delivery of highly hydrophobic drugs to tumors and to increase their therapeutic index.