Precise Ratiometric Co-loading And Co-delivery Of Paclitaxel And Curcumin By Gold Nanorods For Multidrug Resistant Tumor

Combination chemotherapy refers to the treatment by using several anticancer drugs at the same time,and it plays an increasingly important role in the treatment of multidrug-resistant cancer nowadays.It has many advantages,such as reducing the occurrence of multidrug resistance,improving therapeutic effect and minimizing side effects.Even among the same drug combination,different ratios may cause three different kinds of effects:synergistic,additive and antagonistic effects.Rational combination chemotherapy is supposed to improve therapeutic effects and reduce adverse effects.Thus it is crucial to screen the optimal ratio of drug combination to produce the strongest synergistic effect.Free drug cocktails are commonly used in clinical treatment,however due to their diverse physicochemical properties and distinct pharmacokinetics,drug combinations may not reach tumor cells at predetermined optimal ratio.Nano-drug co-delivery systems provide admirable solutions to address this problem as they enable different drugs to be co-delivered synchronously and efficiently into tumor cells at predetermined ratio.In this paper,biotin-PEG modified gold nanorod?Biotin-PEG-GNR,BPGNR?was used as drug carrier to prepare nano-drug delivery system which co-loaded and co-delivered anticancer drug paclitaxel?PTX?and P-gp inhibitor curcumin?CUR?.The anti-multidrug resistant tumor effect was preliminary assessed and the mechanisms of action of it were discussed.Firstly,CTAB-capped gold nanorods were prepared by the seed-growth method and then CTAB on the surface was replaced by biotin-PEG to obtain BPGNR.Transmission electron microscope?TEM?images showed that BPGNR had homogeneous morphology and good monodispersity.In vitro cytotoxicities experiments indicated that BPGNR had good biocompatibility.Evaluation of near-infrared?NIR?photothermal effects showed that the photothermal effects of BPGNR were excellent,and they had obviously positive correlation with concentrations of BPGNR and power densities of NIR laser.Secondly,the hydroxyl groups of PTX and CUR were utilized to react with the carboxyl groups of lipoic acid?LA?by esterification to obtain PTX-LA and CUR-LA.The obtained products were purified by column chromatography and their molecular structures were confirmed by NMR and MS.Thirdly,PTX-LA and CUR-LA of certain ratio?corresponding PTX/CUR mass ratio of 1:1?were conjugated onto the surface of BPGNR via the robust Au-S bond and the co-delivery system PTX/CUR@BPGNR was constructed.TEM images showed that they had homogeneous morphology and good monodispersity,and changed little after drug loading.The zeta potential of PTX/CUR@BPGNR was-3.97mV and PTX/CUR@BPGNR have a maximum absorption at the wavelength of 808 nm.The encapsulation efficiencies?EEs?of PTX-LA and CUR-LA were 85.3%?85.0%,respectively.The corresponding drug loading capacities?DLCs?of PTX and CUR were 5.32%and 5.21%,respectively.The mass ratio of the two drugs was approximately 1:1,which accorded with the primary feed ratio,this phenomenon indicated that the prepared BPGNR could precisely ratiometric co-load PTX and CUR.In vitro drug release experiments demonstrated the following:?1?PTX/CUR@BPGNR released little drug in blood circulation as well as extracellular environment and exhibited high stability;?2?drugs released rapidly under intracellular abundant glutathione and esterase;?3?drug released even faster after NIR irradiation was given.Most important of all,the release rates of PTX and CUR were almost the same in all tested release media.These characteristics can reduce the leakage and premature release of PTX and CUR before entering into tumor cells,and drugs can be co-released in tumor cells thus the strongest synergistic effects can be achieved.Finally,in vitro antitumor activity and mechanisms of action of PTX/CUR@BPGNR were investigated.The data of combination index indicated that PTX/CUR@BPGNR with the mass ratio of PTX and CUR at 1:1 exhibited the best synergy while free drug mixture with the mass ratio of PTX and CUR at 1:0.75 displayed the strongest synergism.PTX/CUR@BPGNR exhibited excellent anti-multidrug resistant tumor(the corresponding IC₅₀ value of PTX in PTX/CUR@BPGNR was 1/11of that of free PTX).Experiments for the mechanisms of action indicated that PTX/CUR@BPGNR?mass ratio of PTX and CUR at 1:1?remarkably induced MCF-7/ADR cell apoptosis,further experiments showed that it significantly inhibited P-gp expression in MCF-7/ADR cells,arrested cell cycle at G2/M phase and generated reactive oxygen species to promote cell apoptosis.Intracellular experiments indicated that PTX and CUR released nearly simultaneously inside MCF-7/ADR cells,which means they released at predetermined ratio.