Light-responsive Biodegradable Polymeric Micelle Nanocarriers For Efficient Intracellular Drug Delivery And Cancer Therapy

This thesis focuses on the study of two light responsive biodegradable polymeric micelle systems based on coumarin for doxorubicin (DOX) encapsulation and light controlled intracellular drug release to realize highly efficient cancer therapy. In chapter2, light-responsive and tumor-targeting polymeric micelles were developed based on hyaluronic acid-g-(7-N, N-diethylamino-4-hydroxymethylcoumarin)(HA-g-CM) graft copolymers for MCF-7tumor cell targeting light controlled DOX release. Graft copolymer HA-g-CM4and HA-g-CM9with different CM contents were synthesized, which could self assemble into polymeric micelles in phosphate buffer (PB,10mM, pH7.4) with HA as shell and CM as hydrophobic core. The micelles of HA-g-CM4and HA-g-CM9had average sizes of147.2and164.5nm (PDI0.17), critical micelle concentration (CMC) of9.1and15.8mg/L, respectively. Hydrophobic anticancer drug DOX could be loaded inside the HA-g-CM micelles with loading efficiencies respectively of71.5%and83.3%. Notably, while being stable during storage, the micelles were subject to change upon light irradiation, e.g. UV (110mW/cm2) and NIR (2W/cm2). After light irradiation, the micelle sizes and PDI increased, and scattering intensity decreased with the prolonging of the incubation time, which was ascribed to the light-induced cleavage and the release of the urethane bonds that connected coumarin and hyaluronic acid. In vitro release studies demonstrated the clear light-responsiveness of DOX and cumarin release from the micelles upon light shining. After irradiation the DOX loaded micelles with UV (110mW/cm2) for5min or NIR (785nm,2W/cm2) for60min, ca.74.9%and51.7%of DOX was released to PB in the subsequent48h from micelles of HA-g-CM4and HA-g-CM9, respectively. This is in great contrast to the low DOX leakage (ca.16.7%) without light treatment under otherwise the same conditions. It is noticed that the micelles were much more sensitive to the UV light than NIR. Moreover, MTT assays displayed that ca.57%MCF-7cells, whose surfaces overexpress CD44receptors, died after treated with DOX loaded micelles for4hr followed by NIR irradiation for60min and subsequent72h incubation. In contrast, only35%MCF-7cells died without NIR illumination, signifying that the DOX release and cell death was caused by NIR illumination. While U-87MG cells with low CD44receptor expression and MCF-7cells pretreated with free HA both after NIR irradiation induced merely25%cell death, confirming that the micelles can target MCF-7tumor cells via receptor-ligand mediated endocytosis. Furthermore, MTT studies demonstrated that HA-g-CM micelles and polymer HA-g-lys12, as well as the degradation product HA-g-lys12+CM were nontoxic to both MCF-7and U-87MG cells (with cell viability of82-105%) at tested concentration up to1mg/mL after24h incubation. In addition, fluorescence microscopy observation displayed that the DOX loaded HA-g-CM micelles could enter the MCF-7cells specifically via the receptor-ligand interaction mediated endocytosis, and the NIR irradiation could induce significant intracellular DOX release.In chapter3, light-responsive shell sheddable biodegradable polymeric micelles based on poly(ethylene glycol) and poly(caprolactone) connected with a coumarin derivative (PEG-CM-PCL) were designed for the loading of anticancer drug, NIR-triggered intracellular drug release and efficient endosomal escape. To this end, a bifuncational coumarin4-hydroxymethyl-7-amino-ethoxylcoumarin (CM), which was used as light sensitive linker was successfully synthesized, In the meantime, the PEG hydroxyl groups was activated by p-nitrophenyl chloroformate to give PEG-4NC. PCL-NH2was synthesized via ring-opening polymerization of CL followed by amine functionality. In the future, we are going to proceed by coupling CM with PEG-4NC to get PEG-CM, then linking to PCL-NH2to obtain PEG-CM-PCL. Such polymer could self assemble into micelles in aqueous solution with DOX loading capacity. Thus obtained micelles could quickly shed the PEG shell upon light irradiation due to the cleavage of the coumarin linker, yielding nanoparticles covered with amine groups, which facilitate the endosomal escape and releasing DOX in the cytosol.