Amphiphilic Diblock Terpolymer PMAgala-b-P(MAA-co-MAChol)s with Attached Galactose and Cholesterol Grafts and Their Intracellular pH-Responsive Doxorubicin Delivery
In this work, a series of diblock terpolymer poly(6-O-methacryloyl-d-galactopyranose)-b-poly(methacrylic acid-co-6-cholesteryloxy hexyl methacrylate) amphiphiles bearing attached galactose and cholesterol grafts denoted as the PMAgala-b-P(MAA-co-MAChol)s were designed and prepared, and these terpolymer amphiphiles were further exploited as a platform for intracellular doxorubicin (DOX) delivery. First, employing a sequential RAFT strategy with preliminarily synthesized poly(6-O-methacryloyl-1,2:3,4-di-O-isopropylidene-d-galactopyranose) (PMAIpGP) macro-RAFT initiator and a successive trifluoroacetic acid (TFA)-mediated deprotection, a series of amphiphilic diblock terpolymer PMAgala-b-P(MAA-co-MAChol)s were prepared, and were further characterized by NMR, Fourier transform infrared spectrometer (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and a dynamic contact angle testing instrument (DCAT). In aqueous media, spontaneous micellization of the synthesized diblock terpolymer amphiphiles were continuously examined by critical micellization concentration assay, dynamic light scattering (DLS), and transmission electron microscopy (TEM), and the efficacies of DOX loading by these copolymer micelles were investigated along with the complexed nanoparticle stability. Furthermore, in vitro DOX release of the drug-loaded terpolymer micelles were studied at 37 °C in buffer under various pH conditions, and cell toxicities of as-synthesized diblock amphiphiles were examined by MTT assay. Finally, with H1299 cells, intracellular DOX delivery and localization by the block amphiphile vectors were investigated by invert fluorescence microscopy. As a result, it was revealed that the random copolymerization of MAA and MAChol comonomers in the second block limited the formation of cholesterol liquid-crystal phase and enhanced DOX loading efficiency and complex nanoparticle stability, that ionic interactions between the DOX and MAA comonomer could be exploited to trigger efficient DOX release under acidic condition, and that the diblock terpolymer micellular vector could alter the DOX trafficking in cells. Hence, these suggest the pH-sensitive PMAgala-b-P(MAA-co-MAChol)s might be further exploited as a smart nanoplatform toward efficient antitumor drug delivery.
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