Stimuli-responsive Polymeric Micelles Based On Rigid Building Units And Their Controllable Drug Release Properties

Chemotherapy is currently the main method for clinical cancer therapy.However,most of the hydrophobic anticancer drugs in chemotherapy have several shortcomings,such as low solubility in water,poor targeting,serious side effects,etc.To solve these problems,nano drug delivery systems have been developed and paid extensive attentions by the researches.Among them,polymeric micelles as drug carriers show wide prospect because of their controllable particle sizes,adjustable structure and properties(thermodynamic stability,drug loading capacity,and drug release behavior).While several challenges and bottlenecks lie in the road to good chemotherapy efficiency for polymeric micelles,including insufficient thermodynamic stability,low drug loading capacity and uncontrollable drug release,etc.With the wide studies of the physical environments of cancer cells,it is realistic to solve the problems mentioned above through the construction of stimuli-responsive polymeric micelles based on the differences of environment between the normal tissues and cancer cells.In our works,a series of self-assembled polymeric micelles with good stability,high drug loading capacity and well stimuli-responsiveness were prepared based on the rigid adamantane building unit.The relationship between structure and properties of polymeric micelles was investigated in detail.To prevent the uncontrollable drug release of polymeric micelles in the human tissues or bloodstream,according to the well-defined pH gradients between the normal tissues(pH 7.4)and cancer cells(pH 5.0),a linear pH-responsive polymer Ad-P(LA-co-GA)-b-PDEAEMA-mPEG was synthesized via ring opening polymerization(ROP),atom transfer radical polymerization(ATRP)and copper-catalyzed azide-alkyne cycloaddition(CuAAC)reaction.P(LA-co-GA)and PDEAEMA were designed as the hydrophobic core and pH responsive block,respectively,which plays an important role in solubilization and encapsulation for the anticancer drugs.Hydrophilic mPEG was designed as the hydrophilic shell to maintain the stability of polymeric micelles during biological circulation.The self-assembled polymeric micelles and drug-loaded micelles were prepared via dialysis method.The loading capacity of linear polymeric micelles for anticancer drugs(DOX,PTX,OXA)and the controllable drug release behaviors of drug-loaded micelles were studied.The results showed that the loading capacity of polymeric micelles for DOX(loading content was 21.5%)was higher than that for PTX and OXA.Moreover,the linear DOX-loaded micelles displayed controllable drug release behaviors reflected by 18.5%of DOX release in the environment of normal tissue(pH 7.4)and higher cumulative drug release(77.6%of DOX)in the environment of cancer cells(pH 5.0)within 80 h.Furthermore,the linear DOX-loaded micelles exhibited low cytotoxicity to normal tissues(NIH-3T3 cells),indicative of the mitigation of the side effects of anticancer drugs.To improve the stability and drug loading capacity of pH-responsive polymeric micelles,the four-arm star-shaped polymer Ad-[P(LA-co-GA)-b-PDEAEMA-mPEG]4 and its self-assembled polymeric micelles were prepared based on the rigid adamantane building unit.Compared with the linear polymers,star-shaped polymers owned lower critical micelle concentration(CMC)and hydraulic radius which is beneficial to the self-assembly of star-shaped polymers to form more stable polymeric micelles.In addition,the rigid adamantane served as building core of polymers could provide better support for the multi-arm of star-shaped polymers and larger free volume for the hydrophobic core of the polymeric micelles.The stability and drug loading capacity of the star-shaped polymeric micelles were studied.These four-arm star-shaped polymers displayed low CMC values with 0.003 1?0.0061 mg/mL,and their self-assembled polymeric micelles showed almost unchanged particle size before and after incubation for 7 days,indicative of high stability of the polymeric micelles with star-shaped topology.Additionally,as-prepared four-arm star-shaped polymeric micelles exhibited good loading capacity for anticancer drugs,such as DOX,PTX,OXA,and almost them,the loading capacity for DOX was the highest(loading content was 24.8%).Therefore,these polymeric micelles with four-arm star-shaped topology owned better stability and loading capacity for anticancer drugs,in comparison to the polymeric micelles with linear topology and most of the reported star-shaped polymeric micelles with non-rigid polymeric core.Meanwhile,the four-arm star-shaped polymeric micelles with longer PDEAEMA block length exhibited higher stability and drug loading capacity.Aiming to improve the environmental stimuli-responsiveness and the controllable release behavior of polymeric micelles for anticancer drugs,pH-reduction dual-stimuli-responsive four-arm star-shaped polymer Ad-[P(LA-co-GA)-b-PDEAEMA-SS-mPEG]4 was synthesized via ROP,ATRP,CuAAC and esterification reaction,according to the characteristic acidic(pH 5.0)and reducing(10 mM glutataione,GSH)environment of cancer cells.Its self-assembled polymeric micelles and DOX-loaded micelles(loading content was 21.1%)were prepared by dialysis method.The in vitro drug release experiment showed that only 22.6%of DOX was released from DOX-loaded micelles in the environment of normal tissue,while the cumulative DOX release was increased to 89.5%in the environment of cancer cells(pH 5.0+10 mM GSH)and was higher than that of pH or reduction-responsive drug-loaded micelles.The self-assembled polymeric mixed micelles and DOX-loaded mixed micelles of the pH-responsive polymer 4sAd-P(LA-co-GA)-b-PDEAEMA12 and reduction-responsive polymer Ad-P(LA-co-GA)-SS-mPEG were prepared by dialysis method.The stability and DOX loading capacity of polymeric mixed micelles were studied.And the controllable DOX release behavior,anticancer efficacy as well as the cellular uptake of DOX-loaded mixed micelles were further investigated.In the case of the mixing ratio of 50 mg:50 mg,the self-assembled polymeric mixed micelles displayed the highest stability(CMC=0.0016 mg/mL)and DOX loading capacity(loading content was 26.7%and encapsulation efficiency was 73.2%).Typically,the remarkable stability and DOX loading capacity of the polymeric mixed micelles mentioned above were better than that of pH-reduction dual-stimuli-responsive polymeric micelles Ad-[P(LA-co-GA)-b-PDEAEMA-SS-mPEG]4.In the environment of normal tissue,the accumulative DOX release of the DOX-loaded mixed micelles was only 14.1%.Taking advantage of the pH and reduction dual-responsiveness,DOX-loaded mixed micelles showed a distinct DOX release behavior in the environment of cancer cells(pH 5.0+10 mM GSH),reflected by the high accumulative DOX release of 94.7%within 80 h.Moreover,confocal laser scanning microscope(CLSM)results showed that the DOX-loaded mixed micelles could be endocytosed by cancer cells,thereby inhibiting the proliferation of cancer cells(MCF-7 cells)of which cell viability was 22.8%after 48 h cultivation.In conclusion,a series of stimuli-responsive polymeric micelles and their drug-loaded micelles were prepared to encapsulate and release hydrophobic anticancer drugs.The four-arm star-shaped polymers and their self-assembled polymeric micelles were prepared based on the high rigidity adamantane building unit,to improve the stability and drug loading capacity of the polymeric micelles.Based on the difference of the environment between normal tissues and cancer cells,pH-reduction dual-responsive polymeric micelles and mixed micelles were prepared,respectively,to improve the drug release properties of drug-loaded micelles in cancer cells.This work could provide reference for the design of micellar structure,the regulation of performance and application of polymeric micelles for controllable drug delivery.